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Monday, December 27, 2021

Indirect land use change impacts of biofuels

The indirect land use change impacts of biofuels, also known as ILUC or iLUC (pronounced as i-luck), relates to the unintended consequence of releasing more carbon emissions due to land-use changes around the world induced by the expansion of croplands for ethanol or biodiesel production in response to the increased global demand for biofuels.

As farmers worldwide respond to higher crop prices in order to maintain the global food supply-and-demand balance, pristine lands are cleared to replace the food crops that were diverted elsewhere to biofuels' production. Because natural lands, such as rainforests and grasslands, store carbon in their soil and biomass as plants grow each year, clearance of wilderness for new farms translates to a net increase in greenhouse gas emissions. Due to this off-site change in the carbon stock of the soil and the biomass, indirect land use change has consequences in the greenhouse gas (GHG) balance of a biofuel.

Other authors have also argued that indirect land use changes produce other significant social and environmental impacts, affecting biodiversity, water quality, food prices and supply, land tenure, worker migration, and community and cultural stability.

History

The estimates of carbon intensity for a given biofuel depend on the assumptions regarding several variables. As of 2008, multiple full life cycle studies had found that corn ethanol, cellulosic ethanol and Brazilian sugarcane ethanol produce lower greenhouse gas emissions than gasoline. None of these studies, however, considered the effects of indirect land-use changes, and though land use impacts were acknowledged, estimation was considered too complex and difficult to model. A controversial paper published in February 2008 in Sciencexpress by a team led by Searchinger from Princeton University concluded that such effects offset the (positive) direct effects of both corn and cellulosic ethanol and that Brazilian sugarcane performed better, but still resulted in a small carbon debt.

After the Searchinger team paper, estimation of carbon emissions from ILUC, together with the food vs. fuel debate, became one of the most contentious issues relating to biofuels, debated in the popular media, scientific journals, op-eds and public letters from the scientific community, and the ethanol industry, both American and Brazilian. This controversy intensified in April 2009 when the California Air Resources Board (CARB) set rules that included ILUC impacts to establish the California Low-Carbon Fuel Standard that entered into force in 2011.

In May 2009 U.S. Environmental Protection Agency (EPA) released a notice of proposed rulemaking for implementation of the 2007 modification of the Renewable Fuel Standard (RFS). EPA's proposed regulations also included ILUC, causing additional controversy among ethanol producers. EPA's February 3, 2010 final rule incorporated ILUC based on modelling that was significantly improved over the initial estimates.

The UK Renewable Transport Fuel Obligation program requires the Renewable Fuels Agency (RFA) to report potential indirect impacts of biofuel production, including indirect land use change or changes to food and other commodity prices. A July 2008 RFA study, known as the Gallager Review, found several risks and uncertainties, and that the "quantification of GHG emissions from indirect land-use change requires subjective assumptions and contains considerable uncertainty", and required further examination to properly incorporate indirect effects into calculation methodologies. A similarly cautious approach was followed by the European Union. In December 2008 the European Parliament adopted more stringent sustainability criteria for biofuels and directed the European Commission to develop a methodology to factor in GHG emissions from indirect land use change.

Studies and controversy

UK figures for the carbon intensity of bioethanol and fossil fuels. Graph assumes all bioethanols are burnt in country of origin and prior cropland was used to grow feedstock. No ILUC effects were included.

Before 2008, several full life cycle ("Well to Wheels" or WTW) studies had found that corn ethanol reduced transport-related greenhouse gas emissions. In 2007 a University of California, Berkeley team led by Farrel evaluated six previous studies, concluding that corn ethanol reduced GHG emissions by only 13 percent. However, 20 to 30 percent reduction for corn ethanol, and 85 to 85 percent for cellulosic ethanol, both figures estimated by Wang from Argonne National Laboratory, are more commonly cited. Wang reviewed 22 studies conducted between 1979 and 2005, and ran simulations with Argonne's GREET model. These studies accounted for direct land use changes. Several studies of Brazilian sugarcane ethanol showed that sugarcane as feedstock reduces GHG by 86 to 90 percent given no significant land use change. Estimates of carbon intensity depend on crop productivity, agricultural practices, power sources for ethanol distilleries and the energy efficiency of the distillery. None of these studies considered ILUC, due to estimation difficulties. Preliminary estimates by Delucchi from the University of California, Davis, suggested that carbon released by new lands converted to agricultural use was a large percentage of life-cycle emissions.

Searchinger and Fargione studies

In 2008 Timothy Searchinger, a lawyer from Environmental Defense Fund, concluded that ILUC affects the life cycle assessment and that instead of saving, both corn and cellulosic ethanol increased carbon emissions as compared to gasoline by 93 and 50 percent respectively. Ethanol from Brazilian sugarcane performed better, recovering initial carbon emissions in 4 years, while U.S. corn ethanol required 167 years and cellulosic ethanol required a 52 years payback period. The study limited the analysis a 30-year period, assuming that land conversion emits 25 percent of the carbon stored in soils and all carbon in plants cleared for cultivation. Brazil, China, and India were considered among the overseas locations where land use change would occur as a result of diverting U.S. corn cropland, and it was assumed that new cropland in each of these regions correspond to different types of forest, savanna or grassland based on the historical proportion of each converted to cultivation in these countries during the 1990s.

Summary of Searchinger et al.
comparison of corn ethanol and gasoline GHG emissions
with and without land use change
(Grams of CO2 released per megajoule of energy in fuel)
Fuel type
(U.S.)
Carbon
intensity
Reduction
GHG
Carbon
intensity
+ ILUC
Reduction
GHG
Gasoline
92
-
92
-
Corn ethanol
74
-20%
177
+93%
Cellulosic ethanol
28
-70%
138
+50%
Notes: Calculated using default assumptions for 2015 scenario for ethanol in E85.
Gasoline is a combination of conventional and reformulated gasoline.

Fargione and his team published a separate paper in the same issue of Science claiming that clearing lands to produce biofuel feedstock created a carbon deficit. This deficit applies to both direct and indirect land use changes. The study examined six conversion scenarios: Brazilian Amazon to soybean biodiesel, Brazilian Cerrado to soybean biodiesel, Brazilian Cerrado to sugarcane ethanol, Indonesian or Malaysian lowland tropical rainforest to palm biodiesel, Indonesian or Malaysian peatland tropical rainforest to palm biodiesel, and U.S. Central grassland to corn ethanol. The carbon debt was defined as the amount of CO2 released during the first 50 years of this process of land conversion. For the two most common ethanol feedstocks, the study found that sugarcane ethanol produced on natural cerrado lands would take about 17 years to repay its carbon debt, while corn ethanol produced on U.S. central grasslands would result in a repayment time of about 93 years. The worst-case scenario is converting Indonesian or Malaysian tropical peatland rainforest to palm biodiesel production, which would require about 420 years to repay.

Criticism and controversy

The Searchinger and Fargione studies created controversy in both the popular media and in scientific journals. Robert Zubrin observed that Searchinger's "indirect analysis" approach is pseudo-scientific and can be used to "prove anything".

Wang and Haq from Argonne National Laboratory are claiming: the assumptions were outdated; they ignored the potential of increased efficiency; and no evidence showed that "U.S. corn ethanol production has so far caused indirect land use in other countries." They concluded that Searchinger demonstrated that ILUC "is much more difficult to model than direct land use changes". In his response Searchinger rebutted each technical objection and asserted that "... any calculation that ignores these emissions, however challenging it is to predict them with certainty, is too incomplete to provide a basis for policy decisions."

Another criticism, by Kline and Dale from Oak Ridge National Laboratory, held that Searchinger et al. and Fargione et al. "... do not provide adequate support for their claim that bioufuels cause high emissions due to land-use change", as their conclusions depends on a misleading assumption because more comprehensive field research found that these land use changes "... are driven by interactions among cultural, technological, biophysical, economic, and demographic forces within a spatial and temporal context rather than by a single crop market". Fargione et al. responded in part that although many factors contributed to land clearing, this "observation does not diminish the fact that biofuels also contribute to land clearing if they are produced on existing cropland or on newly cleared lands". Searching disagreed with all of Kline and Dale arguments.

The U.S. biofuel industry also reacted, claiming that the "Searchinger study is clearly a 'worst case scenario' analysis ..." and that this study "relies on a long series of highly subjective assumptions ..." Searchinger rebutted each claim, concluding that NFA's criticisms were invalid. He noted that even if some of his assumptions are high estimates, the study also made many conservative assumptions.

Slash and burn forest removal in Brazil
 
Cattle ranching in Brazil

Brazil

In February 2010, Lapola estimated that planned expansion of Brazilian sugarcane and soybean biofuel plantations through 2020 would replace rangeland, with small direct land-use impact on carbon emissions. However, the expansion of the rangeland frontier into Amazonian forests, driven by cattle ranching, would indirectly offset the savings. "Sugarcane ethanol and soybean biodiesel each contribute to nearly half of the projected indirect deforestation of 121,970 km2 by 2020, creating a carbon debt that would take about 250 years to be repaid..."

The research also found that oil palm would cause the least land-use changes and associated carbon debt. The analysis also modeled livestock density increases and found that "a higher increase of 0.13 head per hectare in the average livestock density throughout the country could avoid the indirect land-use changes caused by biofuels (even with soybean as the biodiesel feedstock), while still fulfilling all food and bioenergy demands." The authors conclude that intensification of cattle ranching and concentration on oil palm are required to achieve effective carbon savings, recommending closer collaboration between the biofuel and cattle-ranching sectors.

The main Brazilian ethanol industry organization (UNICA) commented that such studies missed the continuing intensification of cattle production already underway.

A study by Arima et al. published in May 2011 used spatial regression modeling to provide the first statistical assessment of ILUC for the Brazilian Amazon due to soy production. Previously, the indirect impacts of soy crops were only anecdotal or analyzed through demand models at a global scale, while the study took a regional approach. The analysis showed a strong signal linking the expansion of soybean fields in settled agricultural areas at the southern and eastern rims of the Amazon basin to pasture encroachments for cattle production on the forest frontier. The results demonstrate the need to include ILUC in measuring the carbon footprint of soy crops, whether produced for biofuels or other end-uses.

The Arima study is based on 761 municipalities located in the Legal Amazon of Brazil, and found that between 2003 and 2008, soybean areas expanded by 39,100 km² in the basin's agricultural areas, mainly in Mato Grosso. The model showed that a 10% (3,910 km²) reduction of soy in old pasture areas would have led to a reduction in deforestation of up to 40% (26,039 km²) in heavily forested municipalities of the Brazilian Amazon. The analysis showed that the displacement of cattle production due to agricultural expansion drives land use change in municipalities located hundreds of kilometers away, and that the Amazonian ILUC is not only measurable but its impact is significant.

Implementation

United States

California LCFS

California carbon intensity values
for gasoline, diesel and fuels that substitute them (grams of CO2 equivalent released per MJ of energy produced)
Fuel type Carbon
intensity
Carbon
intensity
+ land-use
changes
Intensity
change
respect to
2011 LCFS
Midwest corn ethanol
75.10
105.10
+10%
California gasoline
95.86
95.86
+0.2%
CARB LCFS 2011 for gasoline
-
95.61
-
California diesel (ULSD)
94.71
94.71
+0.2%
CARB LCFS 2011 for diesel
-
94.47
-
California ethanol
50.70
80.70
-16%
Brazilian sugarcane ethanol
27.40
73.40
-23%
Biodiesel (B100) Midwest soybeans(1)
26.93
68.93
-27%
Renewable diesel Midwest soybeans(1)
28.80
68.93
-27%
Cellulosic ethanol (farmed trees)(1)
2.40
20.40
-79%
Compressed natural gas (bio-methane)
11.26
11.26
-88%
Note: the complete lifecycle analysis for these fuels and others evaluated are available
at CARB's website (see Lifecycle Analysis). (1) Preliminary values of fuels not included
in the 2009 LCFS ruling and subject to refining.

On April 23, 2009, California Air Resources Board (CARB) approved the specific rules and carbon intensity reference values for the California Low-Carbon Fuel Standard (LCFS) that take effect January 1, 2011. CARB's rulemaking included ILUC. For some biofuels, CARB identified land use changes as a significant source of additional GHG emissions. It established one standard for gasoline and alternative fuels, and a second for diesel fuel and its replacements.

Controversy

The public consultation process before the ruling, and the ruling itself were controversial, yielding 229 comments. ILUC was one of the most contentious issues. On June 24, 2008, 27 scientists and researchers submitted a letter saying, "As researchers and scientists in the field of biomass to biofuel conversion, we are convinced that there simply is not enough hard empirical data to base any sound policy regulation in regards to the indirect impacts of renewable biofuels production. The field is relative new, especially when compared to the vast knowledge base present in fossil fuel production, and the limited analyses are driven by assumptions that sometimes lack robust empirical validation." The New Fuels Alliance, representing more than two-dozen biofuel companies, researchers and investors, questioned the Board intention to include indirect land use change effects into account, wrote "While it is likely true that zero is not the right number for the indirect effects of any product in the real world, enforcing indirect effects in a piecemeal way could have very serious consequences for the LCFS.... The argument that zero is not the right number does not justify enforcing a different wrong number, or penalizing one fuel for one category of indirect effects while giving another fuel pathway a free pass."

On the other side, more than 170 scientists and economists urged that CARB, "include indirect land use change in the lifecycle analyses of heat-trapping emissions from biofuels and other transportation fuels. This policy will encourage development of sustainable, low-carbon fuels that avoid conflict with food and minimize harmful environmental impacts.... There are uncertainties inherent in estimating the magnitude of indirect land use emissions from biofuels, but assigning a value of zero is clearly not supported by the science."

Industry representatives complained that the final rule overstated the environmental effects of corn ethanol, and also criticized the inclusion of ILUC as an unfair penalty to domestic corn ethanol because deforestation in the developing world was being tied to U.S. ethanol production. The 2011 limit for LCFS means that Mid-west corn ethanol failed, unless current carbon intensity was reduced. Oil industry representatives complained that the standard left oil refiners with few options, such as Brazilian sugarcane ethanol, with its accompanying tariff. CARB officials and environmentalists counter that time and economic incentives will allow produces to adapt.

UNICA welcomed the ruling, while urging CARB to better reflect Brazilian practices, lowering their estimates of Brazilian emissions.

The only Board member who voted against the ruling explained that he had a "hard time accepting the fact that we're going to ignore the comments of 125 scientists", referring to the letter submitted by a group of scientists questioning the ILUC penalty. "They said the model was not good enough ... to use at this time as a component part of such an historic new standard." CARB advanced the expected date for an expert working group to report on ILUC with refined estimates from January 2012 to January 2011.

On December 2009 the Renewable Fuels Association (RFA) and Growth Energy, two U.S. ethanol lobbying groups, filed a lawsuit challenging LCFS' constitutionality. The two organizations argued that LCFS violated both the Supremacy Clause and the Commerce Clause, jeopardizing the nationwide ethanol market.

EPA Renewable Fuel Standard

U.S. Environmental Protection Agency
Draft life cycle GHG emissions reduction results
for different time horizon and discount rate approaches
(includes indirect land use change effects)
Fuel Pathway 100 years +
2% discount
rate
30 years +
0% discount
rate
Corn ethanol (natural gas dry mill)(1)
-16%
+5%
Corn ethanol (Best case NG DM)(2)
-39%
-18%
Corn ethanol (coal dry mill)
+13%
+34%
Corn ethanol (biomass dry mill)
-39%
-18%
Corn ethanol (biomass dry mill with
combined heat and power)
-47%
-26%
Soybean-based biodiesel
-22%
+4%
Waste grease biodiesel
-80%
-80%
Sugarcane ethanol
-44%
-26%
Cellulosic ethanol from switchgrass
-128%
-124%
Cellulosic ethanol from corn stover
-115%
-116%
Notes: (1) Dry mill (DM) plants grind the entire kernel and generally produce
only one primary co-product: distillers grains with solubles (DGS).
(2) Best case plants produce wet distillers grains co-product.

The Energy Independence and Security Act of 2007 (EISA) established new renewable fuel categories and eligibility requirements, setting mandatory lifecycle emissions limits. EISA explicitly mandated EPA to include "direct emissions and significant indirect emissions such as significant emissions from land use changes."

EISA required a 20% reduction in lifecycle GHG emissions for any fuel produced at facilities that commenced construction after December 19, 2007 to be classified as a "renewable fuel"; a 50% reduction for fuels to be classified as "biomass-based diesel" or "advanced biofuel", and a 60% reduction to be classified as "cellulosic biofuel". EISA provided limited flexibility to adjust these thresholds downward by up to 10 percent, and EPA proposed this adjustment for the advanced biofuels category. Existing plants were grandfathered in.

On May 5, 2009, EPA released a notice of proposed rulemaking for implementation of the 2007 modification of the Renewable Fuel Standard, known as RFS2. The draft of the regulations was released for public comment during a 60-day period, a public hearing was held on June 9, 2009, and also a workshop was conducted on June 10–11, 2009.

EPA's draft analysis stated that ILUC can produce significant near-term GHG emissions due to land conversion, but that biofuels can pay these back over subsequent years. EPA highlighted two scenarios, varying the time horizon and the discount rate for valuing emissions. The first assumed a 30-year time period uses a 0 percent discount rate (valuing emissions equally regardless of timing). The second scenario used a 100-year time period and a 2% discount rate.

On the same day that EPA published its notice of proposed rulemaking, President Obama signed a Presidential Directive seeking to advance biofuels research and commercialization. The Directive established the Biofuels Interagency Working Group, to develop policy ideas for increasing investment in next-generation fuels and for reducing their environmental footprint.

Maize is the main feedstock for the production of ethanol fuel in the U.S.
 
Sugarcane is the main feedstock for the production of ethanol fuel in Brazil.

The inclusion of ILUC in the proposed ruling provoked complaints from ethanol and biodiesel producers. Several environmental organizations welcomed the inclusion of ILUC but criticized the consideration of a 100-year payback scenario, arguing that it underestimated land conversion effects. American corn growers, biodiesel producers, ethanol producers and Brazilian sugarcane ethanol producers complained about EPA's methodology, while the oil industry requested an implementation delay.

On June 26, 2009, the House of Representatives approved the American Clean Energy and Security Act 219 to 212, mandating EPA to exclude ILUC for a 5-year period, vis a vis RFS2. During this period, more research is to be conducted to develop more reliable models and methodologies for estimating ILUC, and Congress will review this issue before allowing EPA to rule on this matter. The bill failed in the U.S. Senate.

On February 3, 2010, EPA issued its final RFS2 rule for 2010 and beyond. The rule incorporated direct and significant indirect emissions including ILUC. EPA incorporated comments and data from new studies. Using a 30-year time horizon and a 0% discount rate, EPA concluded that multiple biofuels would meet this standard.

EPA's analysis accepted both ethanol produced from corn starch and biobutanol from corn starch as "renewable fuels". Ethanol produced from sugarcane became an "advanced fuel". Both diesel produced from algal oils and biodiesel from soy oil and diesel from waste oils, fats, and greases fell in the "biomass-based diesel" category. Cellulosic ethanol and cellulosic diesel met the "cellulosic biofuel" standard.

The table summarizes the mean GHG emissions estimated by EPA modelling and the range of variations considering that the main source of uncertainty in the life cycle analysis is the GHG emissions related to international land use change.

U.S. Environmental Protection Agency
Life cycle Year 2022 GHG emissions reduction results for RFS2 final rule
(includes direct and indirect land use change effects and a 30-year payback period at a 0% discount rate)
Renewable fuel Pathway
(for U.S. consumption)
Mean
GHG emission
reduction(1)
GHG emission
reduction
95% confidence
interval(2)
Assumptions/comments
Corn ethanol
21%
7–32%
New or expanded natural gas fired dry mill plant, 37% wet and 63% dry DGS it produces, and employing corn oil fractionation technology.
Corn biobutanol
31%
20–40%
Natural gas fired dry mill plant, 37% wet and 63% dry DGS it produces, and employing corn oil fractionation technology.
Sugarcane ethanol(3)
61%
52–71%
Ethanol is produced and dehydrated in Brazil prior to being imported into the U.S. and the residue is not collected. GHG emissions from ocean tankers hauling ethanol from Brazil to the U.S. are included.
Cellulosic ethanol from switchgrass
110%
102–117%
Ethanol produced using the biochemical process.
Cellulosic ethanol from corn stover
129%
No ILUC
Ethanol produced using the biochemical process. Ethanol produced from agricultural residues does not have any international land use emissions.
Biodiesel from soybean
57%
22–85%
Plant using natural gas.
Waste grease biodiesel
86%
No ILUC
Waste grease feedstock does not have any agricultural or land use emissions.
Notes: (1) Percent reduction in lifecycle GHG emissions compared to the average lifecycle GHG for gasoline or diesel sold or distributed as transportation fuel in 2005.
(2) Confidence range accounts for uncertainty in the types of land use change assumptions and the magnitude of resulting GHG emissions.
(3) A new Brazil module was develop to model the impact of increased production of Brazilian sugarcane ethanol for use in the U.S. market and the international impacts of Brazilian sugarcane ethanol production. The Brazil module also accounts for the domestic competition between crop and pasture land uses, and allows for livestock intensification (heads of cattle per unit area of land).
Reactions

UNICA welcomed the ruling, in particular, for the more precise lifecycle emissions estimate and hoped that classification the advanced biofuel designation would help eliminate the tariff.

The U.S. Renewable Fuels Association (RFA) also welcomed the ruling, as ethanol producers "require stable federal policy that provides them the market assurances they need to commercialize new technologies", restating their ILUC objection.

RFA also complained that corn-based ethanol scored only a 21% reduction, noting that without ILUC, corn ethanol achieves a 52% GHG reduction. RFA also objected that Brazilian sugarcane ethanol "benefited disproportionally" because EPA's revisions lowered the initially equal ILUC estimates by half for corn and 93% for sugarcane.

Several Midwestern lawmakers commented that they continued to oppose EPA's consideration of the "dicey science" of indirect land use that "punishes domestic fuels". House Agriculture Chairman Collin Peterson said, "... to think that we can credibly measure the impact of international indirect land use is completely unrealistic, and I will continue to push for legislation that prevents unreliable methods and unfair standards from burdening the biofuels industry."

EPA Administrator Lisa P. Jackson commented that the agency "did not back down from considering land use in its final rules, but the agency took new information into account that led to a more favorable calculation for ethanol". She cited new science and better data on crop yield and productivity, more information on co-products that could be produced from advanced biofuels and expanded land-use data for 160 countries, instead of the 40 considered in the proposed rule.

Europe

As of 2010, European Union and United Kingdom regulators had recognized the need to take ILUC into account, but had not determined the most appropriate methodology.

UK Renewable Transport Fuel Obligation

The UK Renewable Transport Fuel Obligation (RTFO) program requires fuel suppliers to report direct impacts, and asked the Renewable Fuels Agency (RFA) to report potential indirect impacts, including ILUC and commodity price changes. The RFA's July 2008 "Gallager Review", mentioned several risks regarding biofuels and required feedstock production to avoid agricultural land that would otherwise be used for food production, despite concluding that "quantification of GHG emissions from indirect land-use change requires subjective assumptions and contains considerable uncertainty". Some environmental groups argued that emissions from ILUC were not being taken into account and could be creating more emissions.

European Union

On December 17, 2008, the European Parliament approved the Renewable Energy Sources Directive (COM(2008)19) and amendments to the Fuel Quality Directive (Directive 2009/30), which included sustainability criteria for biofuels and mandated consideration of ILUC. The Directive established a 10% biofuel target. A separate Fuel Quality Directive set the EU's Low Carbon Fuel Standard, requiring a 6% reduction in GHG intensity of EU transport fuels by 2020. The legislation ordered the European Commission to develop a methodology to factor in GHG emissions from ILUC by December 31, 2010, based on the best available scientific evidence.

In the meantime, the European Parliament defined lands that were ineligible for producing biofuel feedstocks for the purpose of the Directives. This category included wetlands and continuously forested areas with canopy cover of more than 30 percent or cover between 10 and 30 percent given evidence that its existing carbon stock was low enough to justify conversion.

The Commission subsequently published terms of reference for three ILUC modeling exercises: one using a General Equilibrium model; one using a Partial Equilibrium model and one comparing other global modeling exercises. It also consulted on a limited range of high-level options for addressing ILUC to which 17 countries and 59 organizations responded. The United Nations Special Rapporteur on the Right to Food and several environmental organizations complained that the 2008 safeguards were inadequate. UNICA called for regulators to establish an empirical and "globally accepted methodology" to consider ILUC, with the participation of researchers and scientists from biofuel crop-producing countries.

In 2010 some NGOs accused the European Commission of lacking transparency given its reluctance to release documents relating to the ILUC work. In March 2010 the Partial and General Equilibrium Modelling results were made available, with the disclaimer that the EC had not adopted the views contained in the materials. These indicate that a 1.25% increase in EU biofuel consumption would require around 5,000,000 hectares (12,000,000 acres) of land globally.

The scenarios for varied from 5.6–8.6% of road transport fuels. The study found that ILUC effects offset part of the emission benefits, and that above the 5.6% threshold, ILUC emissions increase rapidly increase. For the expected scenario of 5.6% by 2020, the study estimated that biodiesel production increases would be mostly domestic, while bioethanol production would take place mainly in Brazil, regardless of EU duties. The analysis concluded that eliminating trade barriers would further reduce emissions, because the EU would import more from Brazil. Under this scenario, "direct emission savings from biofuels are estimated at 18 Mt CO
2
, additional emissions from ILUC at 5.3 Mt CO
2
(mostly in Brazil), resulting in a global net balance of nearly 13 Mt CO
2
savings in a 20 years horizon". The study also found that ILUC emissions were much greater for biodiesel from vegetable oil and estimated that in 2020 even at the 5.6% level were over half the greenhouse gas emissions from diesel.

As part of the announcement, the Commission stated that it would publish a report on ILUC by the end of 2010.

Certification system

On June 10, 2010, the EC announced its decision to set up certification schemes for biofuels, including imports as part of the Renewable Energy Directive. The Commission encouraged E.U. nations, industry and NGOs to set up voluntary certification schemes. EC figures for 2007 showed that 26% of biodiesel and 31% of bioethanol used in the E.U. was imported, mainly from Brazil and the United States.

Reactions

UNICA welcomed the EU efforts to "engage independent experts in its assessments" but requested that improvements because "... the report currently contains a certain number of inaccuracies, so once these are corrected, we anticipate even higher benefits resulting from the use of Brazilian sugarcane ethanol." UNICA highlighted the fact that the report assumed land expansion that "does not take into consideration the agro-ecological zoning for sugarcane in Brazil, which prevents cane from expanding into any type of native vegetation."

Critics said the 10% figure was reduced to 5.6% of transport fuels partly by exaggerating the contribution of electric vehicles (EV) in 2020, as the study assumed EVs would represent 20% of new car sales, two and six times the car industry's own estimate. They also claimed the study "exaggerates to around 45 percent the contribution of bioethanol—the greenest of all biofuels—and consequently downplays the worst impacts of biodiesel."

Environmental groups found that the measures "are too weak to halt a dramatic increase in deforestation". According to Greenpeace, "indirect land-use change impacts of biofuel production still are not properly addressed", which for them was the most dangerous problem of biofuels.

Industry representatives welcomed the certification system and some dismissed concerns regarding the lack of land use criteria. UNICA and other industry groups wanted the gaps in the rules filled to provide a clear operating framework.

The negotiations between the European Parliament and the Council of European Ministers continue. A deal is not foreseen before 2014.

Environmental impact of electricity generation

From Wikipedia, the free encyclopedia

Electric power systems consist of generation plants of different energy sources, transmission networks, and distribution lines. Each of these components can have environmental impacts at multiple stages of their development and use including in their construction, during the generation of electricity, and in their decommissioning and disposal. These impacts can be split into operational impacts (fuel sourcing, global atmospheric and localized pollution) and construction impacts (manufacturing, installation, decommissioning, and disposal). The United States Environmental Protection Agency clearly states that all forms of electricity generation have some form of environmental impact. The European Environment Agency view is the same. This page looks exclusively at the operational environmental impact of electricity generation. The page is organized by energy source and includes impacts such as water usage, emissions, local pollution, and wildlife displacement.

More detailed information on electricity generation impacts for specific technologies and on other environmental impacts of electric power systems in general can be found under the Category:Environmental impact of the energy industry.

Water usage

Water usage is one of the main environmental impacts of electricity generation. All thermal cycles (coal, natural gas, nuclear, geothermal, and biomass) use water as a cooling fluid to drive the thermodynamic cycles that allow electricity to be extracted from heat energy. Other energy sources such as wind and solar use water for cleaning equipment, while hydroelectricity has water usage from evaporation from the reservoirs. The amount of water usage is often of great concern for electricity generating systems as populations increase and droughts become a concern. In addition, changes in water resources may impact the reliability of electricity generation. The power sector in the United States withdraws more water than any other sector and is heavily dependent on available water resources. According to the U.S. Geological Survey, in 2005, thermo-electric power generation water withdrawals accounted for 41 percent of all freshwater withdrawals or 760 million m3 (201 billion US gal) per day. Nearly all of the water withdrawn for thermoelectric power was surface water used for once-through cooling at power plants. Withdrawals for irrigation and public supply in 2005 were 37% and 13% of all freshwater withdrawals respectively. Likely future trends in water consumption are covered here.

Discussions of water usage of electricity generation distinguish between water withdrawal and water consumption. According to the USGS, "withdrawal" is defined as the amount of water removed from the ground or diverted from a water source for use, while "consumption" refers to the amount of water that is evaporated, transpired, incorporated into products or crops, or otherwise removed from the immediate water environment. Both water withdrawal and consumption are important environmental impacts to evaluate.

General numbers for fresh water usage of different power sources are shown below.

  Water Consumption (gal/MW-h)
Power source Low case Medium/average case High case
Nuclear power 100 (once-through cooling) 270 once-through, 650 (tower and pond) 845 (cooling tower)
Coal 58  500 1,100 (cooling tower, generic combustion)
Natural gas 100 (once-through cycle) 800 (steam-cycle, cooling towers) 1,170 (steam-cycle with cooling towers)
Hydroelectricity 1,430 4,491 18,000
Solar thermal 53 (dry cooling) 800 1,060 (Trough)
Geothermal 1,800
4,000
Biomass 300
480
Solar photovoltaic 0 26 33
Wind power 0 0 1

Steam-cycle plants (nuclear, coal, NG, solar thermal) require a great deal of water for cooling, to remove the heat at the steam condensers. The amount of water needed relative to plant output will be reduced with increasing boiler temperatures. Coal- and gas-fired boilers can produce high steam temperatures and so are more efficient, and require less cooling water relative to output. Nuclear boilers are limited in steam temperature by material constraints, and solar thermal is limited by concentration of the energy source.

Thermal cycle plants near the ocean have the option of using seawater. Such a site will not have cooling towers and will be much less limited by environmental concerns of the discharge temperature since dumping heat will have very little effect on water temperatures. This will also not deplete the water available for other uses. Nuclear power in Japan for instance, uses no cooling towers at all because all plants are located on the coast. If dry cooling systems are used, significant water from the water table will not be used. Other, more novel, cooling solutions exist, such as sewage cooling at the Palo Verde Nuclear Generating Station.

Hydroelectricity's main cause of water usage is both evaporation and seepage into the water table.

Fossil fuels

Most electricity today is generated by burning fossil fuels and producing steam which is then used to drive a steam turbine that, in turn, drives an electrical generator.

Such systems allow electricity to be generated where it is needed, since fossil fuels can readily be transported. They also take advantage of a large infrastructure designed to support consumer automobiles. The world's supply of fossil fuels is large, but finite. Exhaustion of low-cost fossil fuels will have significant consequences for energy sources as well as for the manufacture of plastics and many other things. Various estimates have been calculated for exactly when it will be exhausted (see Peak oil). New sources of fossil fuels keep being discovered, although the rate of discovery is slowing while the difficulty of extraction simultaneously increases.

More serious are concerns about the emissions that result from fossil fuel burning. Fossil fuels constitute a significant repository of carbon buried deep underground. Burning them results in the conversion of this carbon to carbon dioxide, which is then released into the atmosphere. The estimated CO2 emission from the world's electrical power industry is 10 billion tonnes yearly. This results in an increase in the Earth's levels of atmospheric carbon dioxide, which enhances the greenhouse effect and contributes to global warming. The linkage between increased carbon dioxide and global warming is well accepted, though fossil-fuel producers vigorously contest these findings.

Depending on the particular fossil fuel and the method of burning, other emissions may be produced as well. Ozone, sulfur dioxide, NO2 and other gases are often released, as well as particulate matter. Sulfur and nitrogen oxides contribute to smog and acid rain. In the past, plant owners addressed this problem by building very tall flue-gas stacks, so that the pollutants would be diluted in the atmosphere. While this helps reduce local contamination, it does not help at all with global issues.

Fossil fuels, particularly coal, also contain dilute radioactive material, and burning them in very large quantities releases this material into the environment, leading to low levels of local and global radioactive contamination, the levels of which are, ironically, higher than a nuclear power station as their radioactive contaminants are controlled and stored.

Coal also contains traces of toxic heavy elements such as mercury, arsenic and others. Mercury vaporized in a power plant's boiler may stay suspended in the atmosphere and circulate around the world. While a substantial inventory of mercury exists in the environment, as other man-made emissions of mercury become better controlled, power plant emissions become a significant fraction of the remaining emissions. Power plant emissions of mercury in the United States are thought to be about 50 tons per year in 2003, and several hundred tons per year in China. Power plant designers can fit equipment to power stations to reduce emissions.

According to Environment Canada:

"The electricity sector is unique among industrial sectors in its very large contribution to emissions associated with nearly all air issues. Electricity generation produces a large share of Canadian nitrogen oxides and sulfur dioxide emissions, which contribute to smog and acid rain and the formation of fine particulate matter. It is the largest uncontrolled industrial source of mercury emissions in Canada. Fossil fuel-fired electric power plants also emit carbon dioxide, which may contribute to climate change. In addition, the sector has significant impacts on water and habitat and species. In particular, hydro dams and transmission lines have significant effects on water and biodiversity."

Coal mining practices in the United States have also included strip mining and removing mountain tops. Mill tailings are left out bare and have been leached into local rivers and resulted in most or all of the rivers in coal producing areas to run red year round with sulfuric acid that kills all life in the rivers.

The efficiency of some of these systems can be improved by co-generation and geothermal (combined heat and power) methods. Process steam can be extracted from steam turbines. Waste heat produced by thermal generating stations can be used for space heating of nearby buildings. By combining electric power production and heating, less fuel is consumed, thereby reducing the environmental effects compared with separate heat and power systems.

Switching from fuels to electricity

Electric cars burn no petroleum, thereby shifting any environmental impact from the car user to the electric utility. In South Africa an electric car, will be powered by coal generated electricity and harm the environment. In Norway an electric car will be powered by hydroelectricity and be harmless. Electric cars by themselves are neither beneficial or harmful, it depends how a region generates electricity.

Homeowners can get 90% efficiency using natural gas to heat their home. Heat pumps are very efficient and burn no natural gas, shifting the environmental impacts from homeowners to electric utilities. Switching from natural gas to electricity in Alberta Canada burns natural gas and coal at about a 40% efficiency to supply the heat pump. In Quebec Canada where electric resistance heating is common, the heat pump will use 70% less hydroelectricity. Heat pumps may be beneficial for the environment or not, it depends how a region generates electricity.

Nuclear power

The Onagawa Nuclear Power Plant – a plant that cools by direct use of ocean water, not requiring a cooling tower
 

Nuclear power plants do not burn fossil fuels and so do not directly emit carbon dioxide; because of the high energy yield of nuclear fuels, the carbon dioxide emitted during mining, enrichment, fabrication and transport of fuel is small when compared with the carbon dioxide emitted by fossil fuels of similar energy yield. These plants still produce other environment damaging wastes though.

A large nuclear power plant may reject waste heat to a natural body of water; this can result in undesirable increase of the water temperature with adverse effect on aquatic life.

Emission of radioactivity from a nuclear plant is controlled by regulations. Abnormal operation may result in release of radioactive material on scales ranging from minor to severe, although these scenarios are very rare.

Mining of uranium ore can disrupt the environment around the mine. Disposal of spent fuel is controversial, with many proposed long-term storage schemes under intense review and criticism. Diversion of fresh or spent fuel to weapons production presents a risk of nuclear proliferation. Finally, the structure of the reactor itself becomes radioactive and will require decades of storage before it can be economically dismantled and in turn disposed of as waste.

Renewable energy

Renewable power technologies can have significant environmental benefits. Unlike coal and natural gas, they can generate electricity and fuels without releasing significant quantities of CO2 and other greenhouse gases that contribute to climate change, however the greenhouse gas savings from a number of biofuels have been found to be much less than originally anticipated, as discussed in the article Indirect land use change impacts of biofuels.

Both solar and wind have been criticized from an aesthetic point of view. However, methods and opportunities exist to deploy these renewable technologies efficiently and unobtrusively: fixed solar collectors can double as noise barriers along highways, and extensive roadway, parking lot, and roof-top area is currently available; amorphous photovoltaic cells can also be used to tint windows and produce energy. Advocates of renewable energy also argue that current infrastructure is less aesthetically pleasing than alternatives, but sited further from the view of most critics.

Hydroelectricity

The major advantage of conventional hydroelectric dams with reservoirs is their ability to store potential power for later electrical production. The combination of a natural supply of energy and production on demand has made hydro power the largest source of renewable energy by far. Other advantages include longer life than fuel-fired generation, low operating costs, and the provision of facilities for water sports. Some dams also operate as pumped-storage plants balancing supply and demand in the generation system. Overall, hydroelectric power can be less expensive than electricity generated from fossil fuels or nuclear energy, and areas with abundant hydroelectric power attract industry.

However, in addition to the advantages above, there are several disadvantages to dams that create large reservoirs. These may include: dislocation of people living where the reservoirs are planned, release of significant amounts of carbon dioxide at construction and flooding of the reservoir, disruption of aquatic ecosystems and bird life, adverse impacts on the river environment, potential risks of sabotage and terrorism, and in rare cases catastrophic failure of the dam wall.

Some dams only generate power and serve no other purpose, but in many places large reservoirs are needed for flood control and/or irrigation, adding a hydroelectric portion is a common way to pay for a new reservoir. Flood control protects life/property and irrigation supports increased agriculture. Without power turbines, the downstream river environment would improve in several ways, however dam and reservoir concerns would remain unchanged.

Small hydro and run-of-the-river are two low impact alternatives to hydroelectric reservoirs, although they may produce intermittent power due to a lack of stored water.

Tidal

Tidal turbines

Land constrictions such as straits or inlets can create high velocities at specific sites, which can be captured with the use of turbines. These turbines can be horizontal, vertical, open, or ducted and are typically placed near the bottom of the water column.

The main environmental concern with tidal energy is associated with blade strike and entanglement of marine organisms as high speed water increases the risk of organisms being pushed near or through these devices. As with all offshore renewable energies, there is also a concern about how the creation of EMF and acoustic outputs may affect marine organisms. Because these devices are in the water, the acoustic output can be greater than those created with offshore wind energy. Depending on the frequency and amplitude of sound generated by the tidal energy devices, this acoustic output can have varying effects on marine mammals (particularly those who echo-locate to communicate and navigate in the marine environment such as dolphins and whales). Tidal energy removal can also cause environmental concerns such as degrading far-field water quality and disrupting sediment processes. Depending on the size of the project, these effects can range from small traces of sediment build up near the tidal device to severely affecting nearshore ecosystems and processes.

Tidal barrage

Tidal barrages are dams built across the entrance to a bay or estuary that captures potential tidal energy with turbines similar to a conventional hydrokinetic dam. Energy is collected while the height difference on either side of the dam is greatest, at low or high tide. A minimum height fluctuation of 5 meters is required to justify the construction, so only 40 locations worldwide have been identified as feasible.

Installing a barrage may change the shoreline within the bay or estuary, affecting a large ecosystem that depends on tidal flats. Inhibiting the flow of water in and out of the bay, there may also be less flushing of the bay or estuary, causing additional turbidity (suspended solids) and less saltwater, which may result in the death of fish that act as a vital food source to birds and mammals. Migrating fish may also be unable to access breeding streams, and may attempt to pass through the turbines. The same acoustic concerns apply to tidal barrages. Decreasing shipping accessibility can become a socio-economic issue, though locks can be added to allow slow passage. However, the barrage may improve the local economy by increasing land access as a bridge. Calmer waters may also allow better recreation in the bay or estuary.

Biomass

Electrical power can be generated by burning anything which will combust. Some electrical power is generated by burning crops which are grown specifically for the purpose. Usually this is done by fermenting plant matter to produce ethanol, which is then burned. This may also be done by allowing organic matter to decay, producing biogas, which is then burned. Also, when burned, wood is a form of biomass fuel.

Burning biomass produces many of the same emissions as burning fossil fuels. However, growing biomass captures carbon dioxide out of the air, so that the net contribution to global atmospheric carbon dioxide levels is small.

The process of growing biomass is subject to the same environmental concerns as any kind of agriculture. It uses a large amount of land, and fertilizers and pesticides may be necessary for cost-effective growth. Biomass that is produced as a by-product of agriculture shows some promise, but most such biomass is currently being used, for plowing back into the soil as fertilizer if nothing else.

Wind power

Onshore wind

Wind power harnesses mechanical energy from the constant flow of air over the surface of the earth. Wind power stations generally consist of wind farms, fields of wind turbines in locations with relatively high winds. A primary publicity issue regarding wind turbines are their older predecessors, such as the Altamont Pass Wind Farm in California. These older, smaller, wind turbines are rather noisy and densely located, making them very unattractive to the local population. The downwind side of the turbine does disrupt local low-level winds. Modern large wind turbines have mitigated these concerns, and have become a commercially important energy source. Many homeowners in areas with high winds and expensive electricity set up small wind turbines to reduce their electric bills.

A modern wind farm, when installed on agricultural land, has one of the lowest environmental impacts of all energy sources:

  • It occupies less land area per kilowatt-hour (kWh) of electricity generated than any other renewable energy conversion system, and is compatible with grazing and crops.
  • It generates the energy used in its construction within just months of operation.
  • Greenhouse gas emissions and air pollution produced by its construction are small and declining. There are no emissions or pollution produced by its operation.
  • Modern wind turbines rotate so slowly (in terms of revolutions per minute) that they are rarely a hazard to birds.

Landscape and heritage issues may be a significant issue for certain wind farms. However, when appropriate planning procedures are followed, the heritage and landscape risks should be minimal. Some people may still object to wind farms, perhaps on the grounds of aesthetics, but there is still the supportive opinions of the broader community and the need to address the threats posed by climate change.

Offshore wind

Offshore wind is similar to terrestrial wind technologies, as a large windmill-like turbine located in a fresh or saltwater environment. Wind causes the blades to rotate, which is then turned into electricity and connected to the grid with cables. The advantages of offshore wind are that winds are stronger and more consistent, allowing turbines of much larger size to be erected by vessels. The disadvantages are the difficulties of placing a structure in a dynamic ocean environment.

The turbines are often scaled-up versions of existing land technologies. However, the foundations are unique to offshore wind and are listed below:

Monopile foundation

Monopile foundations are used in shallow depth applications (0–30 m) and consist of a pile being driven to varying depths into the seabed (10–40 m) depending on the soil conditions. The pile-driving construction process is an environmental concern as the noise produced is incredibly loud and propagates far in the water, even after mitigation strategies such as bubble shields, slow start, and acoustic cladding. The footprint is relatively small, but may still cause scouring or artificial reefs. Transmission lines also produce an electromagnetic field that may be harmful to some marine organisms.

Tripod fixed bottom

Tripod fixed bottom foundations are used in transitional depth applications (20–80 m) and consist of three legs connecting to a central shaft that supports the turbine base. Each leg has a pile driven into the seabed, though less depth is necessary because of the wide foundation. The environmental effects are a combination of those for monopile and gravity foundations.

Gravity foundation

Gravity foundations are used in shallow depth applications (0–30 m) and consist of a large and heavy base constructed of steel or concrete to rest on the seabed. The footprint is relatively large and may cause scouring, artificial reefs, or physical destruction of habitat upon introduction. Transmission lines also produce an electromagnetic field that may be harmful to some marine organisms.

Gravity tripod

Gravity tripod foundations are used in transitional depth applications (10–40 m) and consist of two heavy concrete structures connected by three legs, one structure sitting on the seabed while the other is above the water. As of 2013, no offshore windfarms are currently using this foundation. The environmental concerns are identical to those of gravity foundations, though the scouring effect may be less significant depending on the design.

Floating structure

Floating structure foundations are used in deep depth applications (40–900 m) and consist of a balanced floating structure moored to the seabed with fixed cables. The floating structure may be stabilized using buoyancy, the mooring lines, or a ballast. The mooring lines may cause minor scouring or a potential for collision. Transmission lines also produce an electromagnetic field that may be harmful to some marine organisms.

Ecological Impact of Wind Energy

One large environmental concern of wind turbines is the impact on wildlife. Wind turbines and their associated infrastructure – notably power lines and towers – are among the fastest-growing threats to birds and bats in the United States and Canada. Bird and bat deaths often occur when the animals collide with the turbine blades. They are also harmed by collisions and electrocutions with transmission lines. Even though siting of wind energy plants are thoroughly reviewed before construction, they can be a cause of habitat loss.

There is also concern of how wind energy impacts weather and climate change. Although wind energy could have the least amount of contribution to climate change, compared to other electricity generators, it still has some room for improvement. Wind turbines can impact the weather of its close vicinity, affecting temperature and rainfall. There are also studies suggesting that large scale wind farms could increase local temperatures if built on land, while reducing local temperature if built on water. Using wind turbines to meet 10 percent of global energy demand in 2100 could cause local temperatures to rise by one degree Celsius in the regions on land where the wind farms are installed, while decreasing by one degree Celsius in regions where wind farms are installed over water. This effect is a change in redistribution of heat due to changed wind patterns, not a general increase of global temperature. The study is a simulation based on increased friction and the writer recommends further research to investigate if the effect actually exist.

Geothermal power

Geothermal energy is the heat of the Earth, which can be tapped into to produce electricity in power plants. Warm water produced from geothermal sources can be used for industry, agriculture, bathing and cleansing. Where underground steam sources can be tapped, the steam is used to run a steam turbine. Geothermal steam sources have a finite life as underground water is depleted. Arrangements that circulate surface water through rock formations to produce hot water or steam are, on a human-relevant time scale, renewable.

While a geothermal power plant does not burn any fuel, it will still have emissions due to substances other than steam which come up from the geothermal wells. These may include hydrogen sulfide, and carbon dioxide. Some geothermal steam sources entrain non-soluble minerals that must be removed from the steam before it is used for generation; this material must be properly disposed. Any (closed cycle) steam power plant requires cooling water for condensers; diversion of cooling water from natural sources, and its increased temperature when returned to streams or lakes, may have a significant impact on local ecosystems.

Removal of ground water and accelerated cooling of rock formations can cause earth tremors. Enhanced geothermal systems (EGS) fracture underground rock to produce more steam; such projects can cause earthquakes. Certain geothermal projects (such as one near Basel, Switzerland in 2006) have been suspended or canceled owing to objectionable seismicity induced by geothermal recovery. However, risks associated with "hydrofracturing induced seismicity are low compared to that of natural earthquakes, and can be reduced by careful management and monitoring" and "should not be regarded as an impediment to further development of the Hot Rock geothermal energy resource".

Solar power

Between 2010 and 2020 the installation cost per kilowatt of solar photovoltaic power dropped by 85 % and is since among the cheapest alternatives for new power generation in many regions. Also without any financial support, it undercuts the cost of the cheapest new coal alternatives. Photovoltaic power is more cost efficient, as one might expect, in areas where sunlight is abundant.

Solar photovoltaic power works by converting the sun's radiation into direct current (DC) power by use of photovoltaic cells. This power can then be converted into the more common AC power and fed to the power grid.

Its negative impact on the environment lies in the creation of the solar cells which are made primarily of silica (from sand) and the extraction of silicon from silica may require the use of fossil fuels, although newer manufacturing processes have eliminated CO2 production. Solar power carries an upfront cost to the environment via production, but offers clean energy throughout the lifespan of the solar cell.

Large scale electricity generation using photovoltaic power requires a large amount of land, due to the low power density of photovoltaic power. Land use can be reduced by installing on buildings and other built up areas, though this reduces efficiency.

Concentrated solar power

Also known as solar thermal, this technology uses various types of mirrors to concentrate sunlight and produce heat. This heat is used to generate electricity in a standard Rankine cycle turbine. Like most thermoelectric power generation, this consumes water. This can be a problem, as solar powerplants are most commonly located in a desert environment due to the need for sunlight and large amounts of land. Many concentrated solar systems also use exotic fluids to absorb and collect heat while remaining at low pressure. These fluids could be dangerous if spilled.

Negawatt power

Negawatt power refers to investment to reduce electricity consumption rather than investing to increase supply capacity. In this way investing in Negawatts can be considered as an alternative to a new power station and the costs and environmental concerns can be compared.

Negawatt investment alternatives to reduce consumption by improving efficiency include:

  • Providing customers with energy efficient lamps – low environmental impact
  • Improved thermal insulation and airtightness for buildings – low environmental impact
  • Replacing older industrial plant – low environmental impact. Can have a positive impact due to reduced emissions.

Negawatt investment alternatives to reduce peak electrical load by time shifting demand include:

Note that time shifting does not reduce total energy consumed or system efficiency; however, it can be used to avoid the need to build a new power station to cope with a peak load.

Banana equivalent dose

From Wikipedia, the free encyclopedia
 
A banana contains naturally occurring radioactive material in the form of potassium-40.

Banana equivalent dose (BED) is an informal measurement of ionizing radiation exposure, intended as a general educational example to compare a dose of radioactivity to the dose one is exposed to by eating one average-sized banana. Bananas contain naturally occurring radioactive isotopes, particularly potassium-40 (40K), one of several naturally occurring isotopes of potassium. One BED is often correlated to 10−7 sievert (0.1 μSv); however, in practice, this dose is not cumulative, as the potassium in foods is excreted in urine to maintain homeostasis. The BED is only meant as an educational exercise and is not a formally adopted dose measurement.

History

The origins of the concept are uncertain, but one early mention can be found on the RadSafe nuclear safety mailing list in 1995, where Gary Mansfield of the Lawrence Livermore National Laboratory mentions that he has found the "banana equivalent dose" to be "very useful in attempting to explain infinitesimal doses (and corresponding infinitesimal risks) to members of the public". A value of 9.82×10−8 sieverts or about 0.1 microsieverts (10 μrem) was suggested for a 150-gram (5.3 oz) banana.

Usage

The banana equivalent dose is an informal measurement, so any equivalences are necessarily approximate, but it has been found useful by some as a way to inform the public about relative radiation risks.

Approximate doses of radiation in sieverts, ranging from trivial to lethal. The BED is the third from the top in the blue section (from Randall Munroe, 2011)

The radiation exposure from consuming a banana is approximately 1% of the average daily exposure to radiation, which is 100 banana equivalent doses (BED). The maximum permitted radiation leakage for a nuclear power plant is equivalent to 2,500 BED (250 μSv) per year, while a chest CT scan delivers 70,000 BED (7 mSv). An acute lethal dose of radiation is approximately 35,000,000 BED (3.5 Sv, 350 rem). A person living 16 kilometres (10 mi) from the Three Mile Island nuclear reactor received an average of 800 BED of exposure to radiation during the 1979 Three Mile Island accident.

Dose calculation

Source of radioactivity

The major natural source of radioactivity in plant tissue is potassium: 0.0117% of the naturally occurring potassium is the unstable isotope potassium-40. This isotope decays with a half-life of about 1.25 billion years (4×1016 seconds), and therefore the radioactivity of natural potassium is about 31 becquerel/gram (Bq/g), meaning that, in one gram of the element, about 31 atoms will decay every second. Plants naturally contain radioactive carbon-14 (14C), but in a banana containing 15 grams of carbon this would give off only about 3 to 5 low-energy beta rays per second. Since a typical banana contains about half a gram of potassium, it will have an activity of roughly 15 Bq. Although the amount in a single banana is small in environmental and medical terms, the radioactivity from a truckload of bananas is capable of causing a false alarm when passed through a Radiation Portal Monitor used to detect possible smuggling of nuclear material at U.S. ports.

The dose uptake from ingested material is defined as committed dose, and in the case of the overall effect on the human body of the radioactive content of a banana, it will be the "committed effective dose". This is typically given as the net dose over a period of 50 years resulting from the intake of radioactive material.

According to the US Environmental Protection Agency (EPA), isotopically pure potassium-40 will give a committed dose equivalent of 5.02 nSv over 50 years per becquerel ingested by an average adult. Using this factor, one banana equivalent dose comes out as about 5.02 nSv/Bq × 31 Bq/g × 0.5 g ≈ 78 nSv = 0.078 μSv. In informal publications, one often sees this estimate rounded up to 0.1 μSv. The International Commission on Radiological Protection estimates a coefficient of 6.2 nSv/Bq for the ingestion of potassium-40, with this datum the calculated BED would be 0.096 μSv, closer to the standard value of 0.1 μSv.

Criticism

Several sources point out that the banana equivalent dose is a flawed concept because consuming a banana does not increase one's exposure to radioactive potassium.

The committed dose in the human body due to bananas is not cumulative because the amount of potassium (and therefore of 40K) in the human body is fairly constant due to homeostasis, so that any excess absorbed from food is quickly compensated by the elimination of an equal amount.

It follows that the additional radiation exposure due to eating a banana lasts only for a few hours after ingestion, i.e. the time it takes for the normal potassium content of the body to be restored by the kidneys. The EPA conversion factor, on the other hand, is based on the mean time needed for the isotopic mix of potassium isotopes in the body to return to the natural ratio after being disturbed by the ingestion of pure 40K, which was assumed by EPA to be 30 days. If the assumed time of residence in the body is reduced by a factor of ten, for example, the estimated equivalent absorbed dose due to the banana will be reduced in the same proportion.

These amounts may be compared to the exposure due to the normal potassium content of the human body of 2.5 grams per kilogram, or 175 grams in a 70 kg adult. This potassium will naturally generate 175 g × 31 Bq/g ≈ 5400 Bq of radioactive decays, constantly through the person's adult lifetime.

Radiation from other household consumables

Other foods rich in potassium (and therefore in 40K) include potatoes, kidney beans, sunflower seeds, and nuts.

Brazil nuts in particular (in addition to being rich in 40K) may also contain significant amounts of radium, which have been measured at up to 444 Bq/kg (12 nCi/kg).

Tobacco contains traces of thorium, polonium and uranium.

 

Right to property

From Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Right_to_property The right to property , or the right to own property ...