Nickel (metal)

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Nickel,  ₂₈Ni

Nickel
Appearance	lustrous, metallic, and silver with a gold tinge
Standard atomic weight Ar, std(Ni)	58.6934(4)
Nickel in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson – ↑ Ni ↓ Pd cobalt ← nickel → copper
Atomic number (Z)	28
Group	group 10
Period	period 4
Block	d-block
Element category	transition metal
Electron configuration	[Ar] 3d8 4s2 or [Ar] 3d9 4s1
Electrons per shell	2, 8, 16, 2 or 2, 8, 17, 1
Physical properties
Phase at STP	solid
Melting point	1728 K ​(1455 °C, ​2651 °F)
Boiling point	3003 K ​(2730 °C, ​4946 °F)
Density (near r.t.)	8.908 g/cm3
when liquid (at m.p.)	7.81 g/cm3
Heat of fusion	17.48 kJ/mol
Heat of vaporization	379 kJ/mol
Molar heat capacity	26.07 J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 1783 1950 2154 2410 2741 3184
Atomic properties
Oxidation states	−2, −1, +1, +2, +3, +4 (a mildly basic oxide)
Electronegativity	Pauling scale: 1.91
Ionization energies	1st: 737.1 kJ/mol 2nd: 1753.0 kJ/mol 3rd: 3395 kJ/mol (more)
Atomic radius	empirical: 124 pm
Covalent radius	124±4 pm
Van der Waals radius	163 pm
Spectral lines of nickel
Other properties
Natural occurrence	primordial
Crystal structure	​face-centered cubic (fcc)
Speed of sound thin rod	4900 m/s (at r.t.)
Thermal expansion	13.4 µm/(m·K) (at 25 °C)
Thermal conductivity	90.9 W/(m·K)
Electrical resistivity	69.3 nΩ·m (at 20 °C)
Magnetic ordering	ferromagnetic
Young's modulus	200 GPa
Shear modulus	76 GPa
Bulk modulus	180 GPa
Poisson ratio	0.31
Mohs hardness	4.0
Vickers hardness	638 MPa
Brinell hardness	667–1600 MPa
CAS Number	7440-02-0
History
Discovery and first isolation	Axel Fredrik Cronstedt (1751)
Main isotopes of nickel
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct 58Ni 68.077% stable 59Ni trace 7.6×104 y ε 59Co 60Ni 26.223% stable 61Ni 1.140% stable 62Ni 3.635% stable 63Ni syn 100 y β− 63Cu 64Ni 0.926% stable

Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile. Pure nickel, powdered to maximize the reactive surface area, shows a significant chemical activity, but larger pieces are slow to react with air under standard conditions because an oxide layer forms on the surface and prevents further corrosion (passivation). Even so, pure native nickel is found in Earth's crust only in tiny amounts, usually in ultramafic rocks, and in the interiors of larger nickel–iron meteorites that were not exposed to oxygen when outside Earth's atmosphere.

Meteoric nickel is found in combination with iron, a reflection of the origin of those elements as major end products of supernova nucleosynthesis. An iron–nickel mixture is thought to compose Earth's inner core.
 
Use of nickel (as a natural meteoric nickel–iron alloy) has been traced as far back as 3500 BCE. Nickel was first isolated and classified as a chemical element in 1751 by Axel Fredrik Cronstedt, who initially mistook the ore for a copper mineral, in the cobalt mines of Los, Hälsingland, Sweden. The element's name comes from a mischievous sprite of German miner mythology, Nickel (similar to Old Nick), who personified the fact that copper-nickel ores resisted refinement into copper. An economically important source of nickel is the iron ore limonite, which often contains 1–2% nickel. Nickel's other important ore minerals include pentlandite and a mixture of Ni-rich natural silicates known as garnierite. Major production sites include the Sudbury region in Canada (which is thought to be of meteoric origin), New Caledonia in the Pacific, and Norilsk in Russia.

Nickel is slowly oxidized by air at room temperature and is considered corrosion-resistant. Historically, it has been used for plating iron and brass, coating chemistry equipment, and manufacturing certain alloys that retain a high silvery polish, such as German silver. About 9% of world nickel production is still used for corrosion-resistant nickel plating. Nickel-plated objects sometimes provoke nickel allergy. Nickel has been widely used in coins, though its rising price has led to some replacement with cheaper metals in recent years.

Nickel is one of four elements (the others are iron, cobalt, and gadolinium) that are ferromagnetic at approximately room temperature. Alnico permanent magnets based partly on nickel are of intermediate strength between iron-based permanent magnets and rare-earth magnets. The metal is valuable in modern times chiefly in alloys; about 68% of world production is used in stainless steel. A further 10% is used for nickel-based and copper-based alloys, 7% for alloy steels, 3% in foundries, 9% in plating and 4% in other applications, including the fast-growing battery sector. As a compound, nickel has a number of niche chemical manufacturing uses, such as a catalyst for hydrogenation, cathodes for batteries, pigments and metal surface treatments. Nickel is an essential nutrient for some microorganisms and plants that have enzymes with nickel as an active site.

Properties

Atomic and physical properties

Electron micrograph of a Ni nanocrystal inside a single wall carbon nanotube; scale bar 5 nm.

 

Nickel is a silvery-white metal with a slight golden tinge that takes a high polish. It is one of only four elements that are magnetic at or near room temperature, the others being iron, cobalt and gadolinium. Its Curie temperature is 355 °C (671 °F), meaning that bulk nickel is non-magnetic above this temperature. The unit cell of nickel is a face-centered cube with the lattice parameter of 0.352 nm, giving an atomic radius of 0.124 nm. This crystal structure is stable to pressures of at least 70 GPa. Nickel belongs to the transition metals. It is hard, malleable and ductile, and has a relatively high for transition metals electrical and thermal conductivity. The high compressive strength of 34 GPa, predicted for ideal crystals, is never obtained in the real bulk material due to the formation and movement of dislocations; however, it has been reached in Ni nanoparticles.

Electron configuration dispute

The nickel atom has two electron configurations, [Ar] 3d⁸ 4s² and [Ar] 3d⁹ 4s¹, which are very close in energy – the symbol [Ar] refers to the argon-like core structure. There is some disagreement on which configuration has the lowest energy. Chemistry textbooks quote the electron configuration of nickel as [Ar] 4s² 3d⁸, which can also be written [Ar] 3d⁸ 4s². This configuration agrees with the Madelung energy ordering rule, which predicts that 4s is filled before 3d. It is supported by the experimental fact that the lowest energy state of the nickel atom is a 3d⁸ 4s² energy level, specifically the 3d⁸(³F) 4s^{2 3}F, J = 4 level.

However, each of these two configurations splits into several energy levels due to fine structure, and the two sets of energy levels overlap. The average energy of states with configuration [Ar] 3d⁹ 4s¹ is actually lower than the average energy of states with configuration [Ar] 3d⁸ 4s². For this reason, the research literature on atomic calculations quotes the ground state configuration of nickel as [Ar] 3d⁹ 4s¹.

Isotopes

The isotopes of nickel range in atomic weight from 48 u (⁴⁸Ni) to 78 u (⁷⁸Ni). 

Naturally occurring nickel is composed of five stable isotopes; ⁵⁸Ni, ⁶⁰Ni, ⁶¹Ni, ⁶²Ni and ⁶⁴Ni, with ⁵⁸Ni being the most abundant (68.077% natural abundance). Isotopes heavier than ⁶²Ni cannot be formed by nuclear fusion without losing energy. 

Nickel-62 has the highest mean nuclear binding energy per nucleon of any nuclide, at 8.7946 MeV/nucleon. Its binding energy is greater than both ⁵⁶Fe and ⁵⁸Fe, more abundant elements often incorrectly cited as having the most tightly-bound nuclides. Although this would seem to predict nickel-62 as the most abundant heavy element in the universe, the relatively high rate of photodisintegration of nickel in stellar interiors causes iron to be by far the most abundant.

Stable isotope nickel-60 is the daughter product of the extinct radionuclide ⁶⁰Fe, which decays with a half-life of 2.6 million years. Because ⁶⁰Fe has such a long half-life, its persistence in materials in the solar system may generate observable variations in the isotopic composition of ⁶⁰Ni. Therefore, the abundance of ⁶⁰Ni present in extraterrestrial material may provide insight into the origin of the solar system and its early history. 

Some 18 nickel radioisotopes have been characterised, the most stable being ⁵⁹Ni with a half-life of 76,000 years, ⁶³Ni with 100 years, and ⁵⁶Ni with 6 days. All of the remaining radioactive isotopes have half-lives that are less than 60 hours and the majority of these have half-lives that are less than 30 seconds. This element also has one meta state.

Radioactive nickel-56 is produced by the silicon burning process and later set free in large quantities during type Ia supernovae. The shape of the light curve of these supernovae at intermediate to late-times corresponds to the decay via electron capture of nickel-56 to cobalt-56 and ultimately to iron-56. Nickel-59 is a long-lived cosmogenic radionuclide with a half-life of 76,000 years. ⁵⁹Ni has found many applications in isotope geology. ⁵⁹Ni has been used to date the terrestrial age of meteorites and to determine abundances of extraterrestrial dust in ice and sediment. Nickel-78's half-life was recently measured at 110 milliseconds, and is believed an important isotope in supernova nucleosynthesis of elements heavier than iron. The nuclide ⁴⁸Ni, discovered in 1999, is the most proton-rich heavy element isotope known. With 28 protons and 20 neutrons ⁴⁸Ni is "double magic", as is ⁷⁸Ni with 28 protons and 50 neutrons. Both are therefore unusually stable for nuclides with so large a proton-neutron imbalance.

Occurrence

Widmanstätten pattern showing the two forms of nickel-iron, kamacite and taenite, in an octahedrite meteorite

 

On Earth, nickel occurs most often in combination with sulfur and iron in pentlandite, with sulfur in millerite, with arsenic in the mineral nickeline, and with arsenic and sulfur in nickel galena. Nickel is commonly found in iron meteorites as the alloys kamacite and taenite. 

The bulk of the nickel is mined from two types of ore deposits. The first is laterite, where the principal ore mineral mixtures are nickeliferous limonite, (Fe,Ni)O(OH), and garnierite (a mixture of various hydrous nickel and nickel-rich silicates). The second is magmatic sulfide deposits, where the principal ore mineral is pentlandite: (Ni,Fe)
₉S
₈. 

Australia and New Caledonia have the biggest estimate reserves, at 45% of world's total.

Identified land-based resources throughout the world averaging 1% nickel or greater comprise at least 130 million tons of nickel (about the double of known reserves). About 60% is in laterites and 40% in sulfide deposits.

On geophysical evidence, most of the nickel on Earth is believed to be in the Earth's outer and inner cores. Kamacite and taenite are naturally occurring alloys of iron and nickel. For kamacite, the alloy is usually in the proportion of 90:10 to 95:5, although impurities (such as cobalt or carbon) may be present, while for taenite the nickel content is between 20% and 65%. Kamacite and taenite are also found in nickel iron meteorites.

Compounds

Tetracarbonyl nickel

 

The most common oxidation state of nickel is +2, but compounds of Ni⁰, Ni⁺, and Ni³⁺ are well known, and the exotic oxidation states Ni²⁻, Ni¹⁻, and Ni⁴⁺ have been produced and studied.

Nickel(0)

Nickel tetracarbonyl (Ni(CO)
₄), discovered by Ludwig Mond, is a volatile, highly toxic liquid at room temperature. On heating, the complex decomposes back to nickel and carbon monoxide:

Ni(CO)
₄ ⇌ Ni + 4 CO

This behavior is exploited in the Mond process for purifying nickel, as described above. The related nickel(0) complex bis(cyclooctadiene)nickel(0) is a useful catalyst in organonickel chemistry because the cyclooctadiene (or cod) ligands are easily displaced.

Nickel(I)

Nickel(I) complexes are uncommon, but one example is the tetrahedral complex NiBr(PPh₃)₃. Many nickel(I) complexes feature Ni-Ni bonding, such as the dark red diamagnetic K
₄[Ni
₂(CN)
₆] prepared by reduction of K
₂[Ni
₂(CN)
₆] with sodium amalgam. This compound is oxidised in water, liberating H
₂.

It is thought that the nickel(I) oxidation state is important to nickel-containing enzymes, such as [NiFe]-hydrogenase, which catalyzes the reversible reduction of protons to H
₂.

Nickel(II)

Color of various Ni(II) complexes in aqueous solution. From left to right, [Ni(NH
₃)
₆]²⁺, [Ni(C₂H₄(NH₂)₂)]²⁺, [NiCl
₄]²⁻, [Ni(H
₂O)
₆]²⁺

 

Crystals of hydrated nickel sulfate.

Nickel(II) forms compounds with all common anions, including sulfide, sulfate, carbonate, hydroxide, carboxylates, and halides. Nickel(II) sulfate is produced in large quantities by dissolving nickel metal or oxides in sulfuric acid, forming both a hexa- and heptahydrates useful for electroplating nickel. Common salts of nickel, such as the chloride, nitrate, and sulfate, dissolve in water to give green solutions of the metal aquo complex [Ni(H
₂O)
₆]²⁺. 

The four halides form nickel compounds, which are solids with molecules that feature octahedral Ni centres. Nickel(II) chloride is most common, and its behavior is illustrative of the other halides. Nickel(II) chloride is produced by dissolving nickel or its oxide in hydrochloric acid. It is usually encountered as the green hexahydrate, the formula of which is usually written NiCl₂•6H₂O. When dissolved in water, this salt forms the metal aquo complex [Ni(H
₂O)
₆]²⁺. Dehydration of NiCl₂•6H₂O gives the yellow anhydrous NiCl
₂. 

Some tetracoordinate nickel(II) complexes, e.g. bis(triphenylphosphine)nickel chloride, exist both in tetrahedral and square planar geometries. The tetrahedral complexes are paramagnetic, whereas the square planar complexes are diamagnetic. In having properties of magnetic equilibrium and formation of octahedral complexes, they contrast with the divalent complexes of the heavier group 10 metals, palladium(II) and platinum(II), which form only square-planar geometry.

Nickelocene is known; it has an electron count of 20, making it relatively unstable. 

Nickel(III) antimonide

Nickel(III) and (IV)

Numerous Ni(III) compounds are known, with the first such examples being Nickel(III) trihalophosphines (Ni_III(PPh₃)X₃). Further, Ni(III) forms simple salts with fluoride or oxide ions. Ni(III) can be stabilized by σ-donor ligands such as thiols and phosphines.

Ni(IV) is present in the mixed oxide BaNiO
₃, while Ni(III) is present in nickel oxide hydroxide, which is used as the cathode in many rechargeable batteries, including nickel-cadmium, nickel-iron, nickel hydrogen, and nickel-metal hydride, and used by certain manufacturers in Li-ion batteries. Ni(IV) remains a rare oxidation state of nickel and very few compounds are known to date.

History

Because the ores of nickel are easily mistaken for ores of silver, understanding of this metal and its use dates to relatively recent times. However, the unintentional use of nickel is ancient, and can be traced back as far as 3500 BCE. Bronzes from what is now Syria have been found to contain as much as 2% nickel. Some ancient Chinese manuscripts suggest that "white copper" (cupronickel, known as baitong) was used there between 1700 and 1400 BCE. This Paktong white copper was exported to Britain as early as the 17th century, but the nickel content of this alloy was not discovered until 1822. Coins of nickel-copper alloy were minted by the Bactrian kings Agathocles, Euthydemus II and Pantaleon in the 2nd Century BCE, possibly out of the Chinese cupronickel.

nickeline/niccolite

 

In medieval Germany, a red mineral was found in the Erzgebirge (Ore Mountains) that resembled copper ore. However, when miners were unable to extract any copper from it, they blamed a mischievous sprite of German mythology, Nickel (similar to Old Nick), for besetting the copper. They called this ore Kupfernickel from the German Kupfer for copper. This ore is now known to be nickeline, a nickel arsenide. In 1751, Baron Axel Fredrik Cronstedt tried to extract copper from kupfernickel at a cobalt mine in the Swedish village of Los, and instead produced a white metal that he named after the spirit that had given its name to the mineral, nickel. In modern German, Kupfernickel or Kupfer-Nickel designates the alloy cupronickel.

Originally, the only source for nickel was the rare Kupfernickel. Beginning in 1824, nickel was obtained as a byproduct of cobalt blue production. The first large-scale smelting of nickel began in Norway in 1848 from nickel-rich pyrrhotite. The introduction of nickel in steel production in 1889 increased the demand for nickel, and the nickel deposits of New Caledonia, discovered in 1865, provided most of the world's supply between 1875 and 1915. The discovery of the large deposits in the Sudbury Basin, Canada in 1883, in Norilsk-Talnakh, Russia in 1920, and in the Merensky Reef, South Africa in 1924, made large-scale production of nickel possible.

Coinage

Dutch coins made of pure nickel

 

Aside from the aforementioned Bactrian coins, nickel was not a component of coins until the mid-19th century.

Canada

99.9% nickel five-cent coins were struck in Canada (the world's largest nickel producer at the time) during non-war years from 1922–1981; the metal content made these coins magnetic. During the wartime period 1942–45, most or all nickel was removed from Canadian and U.S. coins to save it for manufacturing armor. Canada used 99.9% nickel from 1968 in its higher-value coins until 2000.

Switzerland

Coins of nearly pure nickel were first used in 1881 in Switzerland.

United Kingdom

Birmingham forged nickel coins in about 1833 for trading in Malaya.

United States

In the United States, the term "nickel" or "nick" originally applied to the copper-nickel Flying Eagle cent, which replaced copper with 12% nickel 1857–58, then the Indian Head cent of the same alloy from 1859–1864. Still later, in 1865, the term designated the three-cent nickel, with nickel increased to 25%. In 1866, the five-cent shield nickel (25% nickel, 75% copper) appropriated the designation. Along with the alloy proportion, this term has been used to the present in the United States.

Current use

In the 21st century, the high price of nickel has led to some replacement of the metal in coins around the world. Coins still made with nickel alloys include one- and two-euro coins, 5¢, 10¢, 25¢ and 50¢ U.S. coins, and 20p, 50p, £1 and £2 UK coins. Nickel-alloy in 5p and 10p UK coins was replaced with nickel-plated steel began in 2012, causing allergy problems for some people and public controversy.

World production

Time trend of nickel production

 

Nickel ores grade evolution in some leading nickel producing countries.

 

More thant 2 million tonnes of nickel per year are mined worldwide, with Indonesia (560 t), The Philippines (340 t), Russia (210 t), New Caledonia (210 t), Australia (170 t) and Canada (160 t) being the largest producers as of 2019. The largest deposits of nickel in non-Russian Europe are located in Finland and Greece. Identified land-based resources averaging 1% nickel or greater contain at least 130 million tons of nickel. Approximately 60% is in laterites and 40% is in sulfide deposits. In addition, extensive deep-sea resources of nickel are in manganese crusts and nodules covering large areas of the ocean floor, particularly in the Pacific Ocean.

The one locality in the United States where nickel has been profitably mined is Riddle, Oregon, where several square miles of nickel-bearing garnierite surface deposits are located. The mine closed in 1987. The Eagle mine project is a new nickel mine in Michigan's upper peninsula. Construction was completed in 2013, and operations began in the third quarter of 2014. In the first full year of operation, Eagle Mine produced 18,000 tonnes.

Extraction and purification

Evolution of the annual nickel extraction, according to ores.

 

Nickel is obtained through extractive metallurgy: it is extracted from the ore by conventional roasting and reduction processes that yield a metal of greater than 75% purity. In many stainless steel applications, 75% pure nickel can be used without further purification, depending on the impurities.

Traditionally, most sulfide ores have been processed using pyrometallurgical techniques to produce a matte for further refining. Recent advances in hydrometallurgical techniques resulted in significantly purer metallic nickel product. Most sulfide deposits have traditionally been processed by concentration through a froth flotation process followed by pyrometallurgical extraction. In hydrometallurgical processes, nickel sulfide ores are concentrated with flotation (differential flotation if Ni/Fe ratio is too low) and then smelted. The nickel matte is further processed with the Sherritt-Gordon process. First, copper is removed by adding hydrogen sulfide, leaving a concentrate of cobalt and nickel. Then, solvent extraction is used to separate the cobalt and nickel, with the final nickel content greater than 99%. 

Electrolytically refined nickel nodule, with green, crystallized nickel-electrolyte salts visible in the pores.

Electrorefining

A second common refining process is leaching the metal matte into a nickel salt solution, followed by the electro-winning of the nickel from solution by plating it onto a cathode as electrolytic nickel.

Mond process

Highly purified nickel spheres made by the Mond process.

The purest metal is obtained from nickel oxide by the Mond process, which achieves a purity of greater than 99.99%. The process was patented by Ludwig Mond and has been in industrial use since before the beginning of the 20th century. In this process, nickel is reacted with carbon monoxide in the presence of a sulfur catalyst at around 40–80 °C to form nickel carbonyl. Iron gives iron pentacarbonyl, too, but this reaction is slow. If necessary, the nickel may be separated by distillation. Dicobalt octacarbonyl is also formed in nickel distillation as a by-product, but it decomposes to tetracobalt dodecacarbonyl at the reaction temperature to give a non-volatile solid.

Nickel is obtained from nickel carbonyl by one of two processes. It may be passed through a large chamber at high temperatures in which tens of thousands of nickel spheres, called pellets, are constantly stirred. The carbonyl decomposes and deposits pure nickel onto the nickel spheres. In the alternate process, nickel carbonyl is decomposed in a smaller chamber at 230 °C to create a fine nickel powder. The byproduct carbon monoxide is recirculated and reused. The highly pure nickel product is known as "carbonyl nickel".

Metal value

The market price of nickel surged throughout 2006 and the early months of 2007; as of April 5, 2007, the metal was trading at US$52,300/tonne or $1.47/oz. The price subsequently fell dramatically, and as of September 2017, the metal was trading at $11,000/tonne, or $0.31/oz.

The US nickel coin contains 0.04 ounces (1.1 g) of nickel, which at the April 2007 price was worth 6.5 cents, along with 3.75 grams of copper worth about 3 cents, with a total metal value of more than 9 cents. Since the face value of a nickel is 5 cents, this made it an attractive target for melting by people wanting to sell the metals at a profit. However, the United States Mint, in anticipation of this practice, implemented new interim rules on December 14, 2006, subject to public comment for 30 days, which criminalized the melting and export of cents and nickels. Violators can be punished with a fine of up to $10,000 and/or imprisoned for a maximum of five years. 

As of September 19, 2013, the melt value of a U.S. nickel (copper and nickel included) is $0.045, which is 90% of the face value.

Applications

Nickel foam (top) and its internal structure (bottom)

 

The global production of nickel is presently used as follows: 68% in stainless steel; 10% in nonferrous alloys; 9% in electroplating; 7% in alloy steel; 3% in foundries; and 4% other uses (including batteries).

Nickel is used in many specific and recognizable industrial and consumer products, including stainless steel, alnico magnets, coinage, rechargeable batteries, electric guitar strings, microphone capsules, plating on plumbing fixtures, and special alloys such as permalloy, elinvar, and invar. It is used for plating and as a green tint in glass. Nickel is preeminently an alloy metal, and its chief use is in nickel steels and nickel cast irons, in which it typically increases the tensile strength, toughness, and elastic limit. It is widely used in many other alloys, including nickel brasses and bronzes and alloys with copper, chromium, aluminium, lead, cobalt, silver, and gold (Inconel, Incoloy, Monel, Nimonic).

A "horseshoe magnet" made of alnico nickel alloy.

 

Because it is resistant to corrosion, nickel was occasionally used as a substitute for decorative silver. Nickel was also occasionally used in some countries after 1859 as a cheap coinage metal (see above), but in the later years of the 20th century was replaced by cheaper stainless steel (i.e., iron) alloys, except in the United States and Canada. 

Nickel is an excellent alloying agent for certain precious metals and is used in the fire assay as a collector of platinum group elements (PGE). As such, nickel is capable of fully collecting all six PGE elements from ores, and of partially collecting gold. High-throughput nickel mines may also engage in PGE recovery (primarily platinum and palladium); examples are Norilsk in Russia and the Sudbury Basin in Canada. 

Nickel foam or nickel mesh is used in gas diffusion electrodes for alkaline fuel cells.

Nickel and its alloys are frequently used as catalysts for hydrogenation reactions. Raney nickel, a finely divided nickel-aluminium alloy, is one common form, though related catalysts are also used, including Raney-type catalysts. 

Nickel is a naturally magnetostrictive material, meaning that, in the presence of a magnetic field, the material undergoes a small change in length. The magnetostriction of nickel is on the order of 50 ppm and is negative, indicating that it contracts. 

Nickel is used as a binder in the cemented tungsten carbide or hardmetal industry and used in proportions of 6% to 12% by weight. Nickel makes the tungsten carbide magnetic and adds corrosion-resistance to the cemented parts, although the hardness is less than those with a cobalt binder.

⁶³Ni, with its half-life of 100.1 years, is useful in krytron devices as a beta particle (high-speed electron) emitter to make ionization by the keep-alive electrode more reliable.

Around 27% of all nickel production is destined for engineering, 10% for building and construction, 14% for tubular products, 20% for metal goods, 14% for transport, 11% for electronic goods, and 5% for other uses.

Biological role

Although not recognized until the 1970s, nickel is known to play an important role in the biology of some plants, eubacteria, archaebacteria, and fungi. Nickel enzymes such as urease are considered virulence factors in some organisms. Urease catalyzes the hydrolysis of urea to form ammonia and carbamate. The NiFe hydrogenases can catalyze the oxidation of H
₂ to form protons and electrons, and can also catalyze the reverse reaction, the reduction of protons to form hydrogen gas. A nickel-tetrapyrrole coenzyme, cofactor F430, is present in methyl coenzyme M reductase, which can catalyze the formation of methane, or the reverse reaction, in methanogenic archaea. One of the carbon monoxide dehydrogenase enzymes consists of an Fe-Ni-S cluster. Other nickel-bearing enzymes include a rare bacterial class of superoxide dismutase and glyoxalase I enzymes in bacteria and several parasitic eukaryotic trypanosomal parasites (in higher organisms, including yeast and mammals, this enzyme contains divalent Zn²⁺).

Dietary nickel may affect human health through infections by nickel-dependent bacteria, but it is also possible that nickel is an essential nutrient for bacteria residing in the large intestine, in effect functioning as a prebiotic. The U.S. Institute of Medicine has not confirmed that nickel is an essential nutrient for humans, so neither a Recommended Dietary Allowance (RDA) nor an Adequate Intake have been established. The Tolerable Upper Intake Level of dietary nickel is 1000 µg/day as soluble nickel salts. Dietary intake is estimated at 70 to 100 µg/day, with less than 10% absorbed. What is absorbed is excreted in urine. Relatively large amounts of nickel – comparable to the estimated average ingestion above – leach into food cooked in stainless steel. For example, the amount of nickel leached after 10 cooking cycles into one serving of tomato sauce averages 88 µg.

Nickel released from Siberian Traps volcanic eruptions is suspected of assisting the growth of Methanosarcina, a genus of euryarchaeote archaea that produced methane during the Permian–Triassic extinction event, the biggest extinction event on record.

Toxicity

Nickel

Hazards
GHS pictograms
GHS signal word	Danger
GHS hazard statements	H317, H351, H372, H412
GHS precautionary statements	P273, P280, P314, P333+313
NFPA 704	0 2 0

The major source of nickel exposure is oral consumption, as nickel is essential to plants. Nickel is found naturally in both food and water, and may be increased by human pollution. For example, nickel-plated faucets may contaminate water and soil; mining and smelting may dump nickel into waste-water; nickel–steel alloy cookware and nickel-pigmented dishes may release nickel into food. The atmosphere may be polluted by nickel ore refining and fossil fuel combustion. Humans may absorb nickel directly from tobacco smoke and skin contact with jewelry, shampoos, detergents, and coins. A less-common form of chronic exposure is through hemodialysis as traces of nickel ions may be absorbed into the plasma from the chelating action of albumin. 

The average daily exposure does not pose a threat to human health. Most of the nickel absorbed every day by humans is removed by the kidneys and passed out of the body through urine or is eliminated through the gastrointestinal tract without being absorbed. Nickel is not a cumulative poison, but larger doses or chronic inhalation exposure may be toxic, even carcinogenic, and constitute an occupational hazard.

Nickel compounds are classified as human carcinogens based on increased respiratory cancer risks observed in epidemiological studies of sulfidic ore refinery workers. This is supported by the positive results of the NTP bioassays with Ni sub-sulfide and Ni oxide in rats and mice. The human and animal data consistently indicate a lack of carcinogenicity via the oral route of exposure and limit the carcinogenicity of nickel compounds to respiratory tumours after inhalation. Nickel metal is classified as a suspect carcinogen; there is consistency between the absence of increased respiratory cancer risks in workers predominantly exposed to metallic nickel and the lack of respiratory tumours in a rat lifetime inhalation carcinogenicity study with nickel metal powder. In the rodent inhalation studies with various nickel compounds and nickel metal, increased lung inflammations with and without bronchial lymph node hyperplasia or fibrosis were observed. In rat studies, oral ingestion of water-soluble nickel salts can trigger perinatal mortality effects in pregnant animals. Whether these effects are relevant to humans is unclear as epidemiological studies of highly exposed female workers have not shown adverse developmental toxicity effects.

People can be exposed to nickel in the workplace by inhalation, ingestion, and contact with skin or eye. The Occupational Safety and Health Administration (OSHA) has set the legal limit (permissible exposure limit) for the workplace at 1 mg/m³ per 8-hour workday, excluding nickel carbonyl. The National Institute for Occupational Safety and Health (NIOSH) specifies the recommended exposure limit (REL) of 0.015 mg/m³ per 8-hour workday. At 10 mg/m³, nickel is immediately dangerous to life and health. Nickel carbonyl [Ni(CO)
₄] is an extremely toxic gas. The toxicity of metal carbonyls is a function of both the toxicity of the metal and the off-gassing of carbon monoxide from the carbonyl functional groups; nickel carbonyl is also explosive in air.

Sensitized individuals may show a skin contact allergy to nickel known as a contact dermatitis. Highly sensitized individuals may also react to foods with high nickel content. Sensitivity to nickel may also be present in patients with pompholyx. Nickel is the top confirmed contact allergen worldwide, partly due to its use in jewelry for pierced ears. Nickel allergies affecting pierced ears are often marked by itchy, red skin. Many earrings are now made without nickel or low-release nickel to address this problem. The amount allowed in products that contact human skin is now regulated by the European Union. In 2002, researchers found that the nickel released by 1 and 2 Euro coins was far in excess of those standards. This is believed to be the result of a galvanic reaction. Nickel was voted Allergen of the Year in 2008 by the American Contact Dermatitis Society. In August 2015, the American Academy of Dermatology adopted a position statement on the safety of nickel: "Estimates suggest that contact dermatitis, which includes nickel sensitization, accounts for approximately $1.918 billion and affects nearly 72.29 million people."

Reports show that both the nickel-induced activation of hypoxia-inducible factor (HIF-1) and the up-regulation of hypoxia-inducible genes are caused by depletion of intracellular ascorbate. The addition of ascorbate to the culture medium increased the intracellular ascorbate level and reversed both the metal-induced stabilization of HIF-1- and HIF-1α-dependent gene expression.

Exercise prescription

From Wikipedia, the free encyclopedia

Exercise prescription commonly refers to the specific plan of fitness-related activities that are designed for a specified purpose, which is often developed by a fitness or rehabilitation specialist for the client or patient. Due to the specific and unique needs and interests of the client/patient, the goal of exercise prescription should be focused on motivation and customization, thus making achieving goals more likely to become successful. The prescription of exercise came about because of the major impact that exercise can have on our health and the many benefits it brings to our body. Exercise benefits our mind, body and emotional state. It can also benefit our social life as well. Exercising daily can help to prevent various illnesses, which is another reason why physicians prescribe exercise to their patients. Many people don't get the adequate amount of exercise or don't exercise at all which leads to them contracting harmful ailments.

Patient referral

In the United Kingdom there is a scheme called "Exercise on prescription" in which doctors are able to prescribe exercise to those with conditions that benefit from it, such as asthma, depression, or obesity. The initiative particularly aimed to lower the rate of heart disease. National standards for such initiatives from doctors were established by the Department of Health in 2001. Exercise on prescription aims to prevent deterioration of conditions, and views exercise as a preventative health measure. Fitness classes or a course at the local gym are available on prescription at a reduced rate to people who might benefit from them. It aims to make it easier for people to follow their doctors' advice about taking more exercise or losing weight. Such preventative measures hope to lead to savings for the National Health Service.

Researchers in New Zealand have also discussed the benefits of exercise referral by medical practitioners there. In New Zealand it is known as a green prescription, while in the United States a similar initiative is known as Exercise is Medicine. A green prescription is a referral given by a doctor or nurse to a patient, with exercise and lifestyle goals written on them. The term, used by health practitioners in New Zealand draws parallel to the usual prescriptions given to patients for medications, and emphasises the importance of exercise in improving their condition, and not relying on drugs. The green prescription is written after discussing the issues and goals in the consultation. Studies have shown that an increase in exercise, better sense of well-being, and a decrease in blood pressure results from using the method. A decreased risk of coronary heart disease has not been shown. This was shown in two studies, one by Swinburn (1998), that surveyed patients in Auckland and Dunedin. The other was Elley (2003) and was done in 42 practices in the same region of New Zealand.

General practitioners like the idea as it formalises what they are telling the patient about how their lifestyle changes are necessary (Swinburn 1997).

Research in Australia has suggested that an exercise prescription program would be very beneficial and many ICU physiotherapists are already performing this practice, however there is no national standards to govern how this practice is administered so there is great variety in the ways this is administered therefore more research is needed.

Mental and Emotional Benefits

Exercise is a great stress relief whether you go for a jog or hit the gym. Both physical and mental stress are reduced by daily exercise. Working out can also make you feel happier and more joyful due to the fact that endorphins are released which create feelings of jubilation. The release of endorphins can alleviate symptoms of depression and anxiety. Even just exercising for 30 minutes a few times a week can enhance overall mood. Self-confidence and self-worth can also be enhanced with exercise by promoting self-love and taking care of ones health. Exercising outdoors can also increase self-love even more by getting much needed vitamin d, getting fresh air, and enjoying the beautiful outdoor scenery. People start to gain a more positive mood and outlook on life through working out and become more emotionally stable. They become more emotionally stable because they are less consumed by responsibilities and commitments while enjoying their physical activity. 

As humans age and get older, their brain cells start to shrink and people start to lose many important brain functions. Exercise can't cure decline in functions of the brain but it can prevent degenerations of cognitive processes that usually occur after age 45. Studies have also demonstrated that cardiovascular exercise can improve brain performance and enhance levels of a brain-derived protein that assist with decision-making, higher thinking, and learning. Regular physical activity can also sharpen memory, assist in controlling addiction, and increase levels of relaxation. Memory is sharpened because there is an increase in production of cells in the hippocampus, which is responsible for memory and learning. For example, a study demonstrated how running sprints improved vocabulary retention among healthy adults. Some people can become addicted to the chemical dopamine and the substances that produce it such as drugs and alcohol. Physical activity can help addicts recover by distracting them from their addictions and make them think less about their cravings. Physical activity restarts the circadian rhythm and allows addicts to fall asleep at the right time and stay up all night. While working a few hours before bedtime raises body temperature, then few hours later the body temperature cools down and signals to the body that its time to relax and fall asleep which initiates better relaxation and fulfilling sleep.

Physical Benefits

Physical activity is a widely known as one of the main ways of losing weight along with a health diet. Certain studies have shown that inactivity played a major role in obesity and weight gain. Frequent exercise increases metabolic rate, which leads to burning more calories and weight loss. Combination of aerobic exercise with strength training can boost fat loss and muscle mass maintenance. Through regular exercise, strong muscles and bones can be developed. It is essential to build bone density when you're younger in order to prevent muscle mass loss and to build and maintain bone density and muscle strength. For some people suffering from severe fatigue such as chronic fatigue syndrome or other illnesses would benefit from regular exercise by increased energy levels. For instance, "a study found that six weeks of regular exercise reduced feelings of fatigue for 36 healthy people who had reported constant fatigue" (Healthline). 

Frequent physical activity decreases chances of getting a chronic disease and decreases belly fat. Frequent physical activity has also been proven to enhance insulin sensitivity, cardiovascular fitness and body composition, while lowering blood pressure and blood fat levels. Exercise boosts the overall health of your skin by reducing oxidative stress in the body. Oxidative stress in the body is when there is an imbalance between free radicals and antioxidants in the body. When the antioxidants are not strong enough to counteract the damaging free radicals then oxidative stress occurs. Moderate exercise increases levels of antioxidants and produces more blood flow, which protects skin and hinders signs of aging. Chronic pain may be controlled and reduced by frequent exercise as well. Physical activity may also increase pain tolerance which will lessen pain interpretation.

For specific diseases

Osteoarthritis

Studies show that exercise prescription aids in both preventing and minimizing the effects of joint disorders such as osteoarthritis. Evidence shows that in addition to the general physiological, psychological and functional benefits gained from exercise, greater quadriceps strength has a mitigating effect on knee joint pain.

Depression

A large body of research indicates that exercise prescription has beneficial effects for patients suffering depression. One study shows a significant improvement for a randomized group of women with major depressive disorder engaging in a twice-weekly resistance training program compared to a control group. The reasons for this marked change is thought to have biochemical, physiological and psychosocial aspects.

Peripheral arterial disease (PAD)

Blockage or closing of the arteries of the lower limbs impairs blood flow to the legs and results in significant reduction in physical capacity. Alternate exercise prescriptions to walking are considered. Aerobic exercises such as arm-cranking or cycling are recommended. Risk factors for disease progression should also be taken into account when aiming to improve waling ability. Functional capacity should be determined prior to commencement of prescribe exercise programs.

Diabetes mellitus

The number of individuals diagnosed with diabetes mellitus are rapidly increasing and a lot of evidence suggests this is due to an insufficiently active lifestyle. Benefits of exercise include stress reduction, reduced risk of heart disease, lowers blood pressure, helps control weight and aids insulin in improving management of diabetes. Exercise that is not too strenuous is recommended. Such activities may include walking, swimming, gardening, cycling or golfing. Incidental activities are encouraged, such as using the stairs instead of an escalator/lift or walking short distances instead of driving. Dr Gebel, who works at James Cook University's Centre for Chronic Disease Prevention conducted a study reporting increased health benefits through incorporation of more vigorous exercise. He stated that this could include 'vigorous gardening', not necessarily meaning going to the gym. Diabetes Australia suggest 30 minutes of exercise daily as a suitable target, which can be divided into three 10-minute sessions throughout the day. Exercise programs however should be tailored and delivered by individuals with appropriate qualifications.

Cancer

According to the Center for Disease Control and Prevention, regular exercise may lower your risk of various cancers. Studies have found that working out can reduce risk of recurrence or death by as much as 50% in people with colorectal cancer. Physical activity may also decrease the risk of recurrence for breast cancer patients, by regulating hormone levels. Exercise also has the ability to reduce side effects of cancer treatments such as nausea and fatigue.

Heart Disease

Frequent physical activity lowers blood pressure, helps maintain a healthy body weight, and reduces cholesterol levels which all lower the chance of getting heart disease.

Sleep Apnea

Sleep apnea is a blockage in the upper airway of the throat that prevents proper breathing. Normally, the brain would immediately wake you up to continue normal breathing patterns. People identified as obese have a higher chance of contracting this disease, exercise can help to prevent this disease by lowering weight before problems arise.

Obesity

Obesity is a complex health condition where a person is excessively overweight. People who exercise regularly and eat a healthy diet are much less likely to become obese and experience the health complications it can bring. Any physical activity that you can enjoy week after week will assist in losing weight along with a change in diet.

Dementia

Several studies have shown that aerobic exercise in middle-aged and older adults have reported improvements in thinking and memory, reduced chances of dementia. A study done on 2,000 men in Wales over 35 years were examined on five behaviors (regular exercise, not smoking, moderate alcohol intake, healthy body weight, and healthy diet), exercise had the greatest effect in lowering the risk of dementia(Alzheimer's Society). In another study of 716 people with an average age of 82 years old, people who were in the bottom 10 percent were more than twice as likely to develop Alzheimer's disease than those in the top 10 percent. Aerobic exercise has also been proven to affect the brains of older people. For example, in a modest-size trial, one year of aerobic exercise resulted in a small increase in the size of the hippocampus, which was equal to reversing one to two years of age-related shrinkage (Alzheimer's Society).

Exercise recommendations

According to Exercise and Sport Science Australia, a minimum amount of 210 minutes of moderate intensity exercise or 125 minutes of vigorous intensity exercise should be performed per week. Exercise should include both aerobic and resistance training. For greater health benefits, exercise should be performed regularly with no more than a two-day gap between training sessions.

Elderly

Research has found that having a well planned exercise routine can greatly benefit the elderly. It an reduce the risks of coronary heart disease, diabetes mellitus and insulin resilience, hypertension and obesity as well as vast improvements in bone density and muscle mass.

Exercise program development

Exercise prescription is designed to modulate acute exercise programming variables to create the adaptations desired by the individual or sport. With aerobic exercise prescription, the type of exercise, duration of exercise, frequency, and duration is adjusted. For resistance exercise prescription, the type of exercise, total session volume, rest period, frequency, and intensity are determined. Prescription of stretching and other activities is also commonly seen. Exercise prescription can be divided into 5 components:

• Type of exercise or activity (eg, walking, swimming, cycling)
• Specific workloads (eg, watts, walking speed)
• Duration and frequency of the activity or exercise session
• Intensity guidelines – Target heart rate (THR) range and estimated rate of perceived exertion (RPE)
• Precautions regarding certain orthopedic (or other) concerns or related comments

Steps to a Healthier You

1. Before beginning any exercise program it is best to assess your fitness level. This can be done by:

• Checking your pulse rate before and immediately after walking 1 mile
• Seeing how long it takes to walk a mile
• Count how many half situps, standard pushups, and modified pushups you can do at a time
• Measuring your waist circumference
• Measuring body mass index

2. After assessing your fitness level then create a fitness program.

• Think about what your fitness goals are: ensure clear fitness goals are declared so that you stay motivated and can determine progress
• Design a balanced routine: According to the Department of Health and Human Services, "it is recommended that you get at least 150 minutes of moderate aerobic activity or 75 minutes of vigorous aerobic activity a week, or a combination of moderate and vigorous".
• Begin slowly and progress slowly: if your just starting to exercise then start slowly and gingerly. If you have any pre-existing health conditions or injuries then meet with a doctor before beginning to exercise.
• Incorporate activity into daily routine: Schedule time to workout like any appointment and have it written down on a calendar or a planner.
• Incorporate different types of activities: Participating in the same activity over and over again again can get boring. To prevent boredom, try different types of activities such as walking, biking, swimming, and strength training.
• Have adequate amount of recovery time: Set time in between workout sessions that allow the body to rest and recuperate.
• Write goals and plans on paper: having plans written may help people stick to their goals

3. Get started

• Start slowly and progress gradually: Give enough time to warm up and cool down. Try to start working out for at least 30 minutes then build up to 60 minutes.
• Break a session up: If you don't have time for a full 30 minute or 60 minute session then break it up throughout the day. You can do one 15 minute session in the morning and one 15 minute session in the night.
• Creativity: Include fun activities that also add to your workout regimen such as scuba diving with friends or going for a hike with family.
• Listen to your body: If you're feeling any kind of pain, dizziness, or nausea then take a break and don't over do it. If you're not feeling well and have the flu then take a few days off and give your body the proper time to rest.

Overcoming Psychological Barriers

Low Self Motivation

If it is hard to motivate yourself to go to the gym or to just workout period, then it may be best to find a workout buddy or buddies. Joining fitness groups or classes would be beneficial as well to help motivate you and push you to your highest potential. Working out with a group or a friend can also make it a more enjoyable experience.

Fear of injury

If you have been injured in the past and are afraid of being re-injured then participate in a low-impact activity such as using the elliptical. The fear of re-injury is not a good enough reason to stop exercising which will prolong and benefit your life in the long run.

Poor Self Image

Millions of people have low self-esteem and poor self image. Going to the gym for the first time may be intimidating for some because they are surrounded by people who they feel are fitness experts and that are looking down on them and criticizing them. However, they were all beginners too and there's a high chance that they are not watching you and are focusing on their own workout. Going with a friend for the first time may help or meeting with a therapist may help as well.

Lack of Confidence

For many beginners, the gym equipment may seem daunting but there are fitness coaches available at the gym that can assist with any confusions. Along with fitness coaches, there are online fitness resources as well that will explain all the different fitness techniques to be successful in the gym and on your new fitness journey.

Self-Management Skills

To overcome this obstacle of not being able to manage yourself then you should set specific goals for your self.

• Set reachable goals
• Be specific
• Have mini goals
• Write down all goals and when you want to meet them by
• Identify what your motives are for working out
• Reward yourself after achieving each goal

Some people love working out while others completely despise it. If your are someone that finds it hard to enjoy exercise then try more creative activities such as rock climbing or playing a game of basketball or soccer. Another fun way of getting your cardio in is dancing instead of just running on the treadmill.

4 Types of Exercise

Endurance

Endurance/aerobic activities enhance breathing and heart rate. They keep your heart, lungs, and circulatory system healthy. Endurance exercises include:

• Jogging
• Working in the yard
• Dancing

Strength

Strength exercises make muscles stronger, protect bone and muscle mass, keeps extra weight off, develop better body mechanisms, and more calories burned. These exercises can help you to become stronger and make doing everyday activities easier. Strength exercises include:

• Weight lifting
• Working out with a resistance band
• Exercising using your own body weight

Balance

Balance exercises aid in preventing falls which is common among older adults. Balance exercises include:

• Standing on one foot
• Heel-to-toe walk
• Tai Chi

Flexibility

Flexibility exercises stretch your muscles and helps the body to stay agile.You experience less pain, fewer injuries, and improved posture and balance. Being more limber gives more freedom of movement for other types of activities and everyday activities. Flexibility exercises include:

• Yoga
• Calf stretch
• Shoulder and upper arm stretch

Amphibian 'apocalypse' caused by most destructive pathogen ever

The first-ever global tally of the disease's toll reveals that it caused declines in at least 501 frog and salamander species.

PUBLISHED March 28, 2019 by Michael Greshko

Original link:  https://www.nationalgeographic.com/animals/2019/03/amphibian-apocalypse-frogs-salamanders-worst-chytrid-fungus/?cmpid=org=ngp::mc=social::src=facebook::cmp=editorial::add=fb20190328animals-chytridfungus::rid=&sf210088124=1&fbclid=IwAR2ND4sCQ0wgA_57M3IbjqfQL1JYN799tCdmiY72XoA26HKBbYwu4XVZZ70

For decades, a silent killer has slaughtered frogs and salamanders around the world by eating their skins alive. Now, a global team of 41 scientists has announced that the pathogen—which humans unwittingly spread around the world—has damaged global biodiversity more than any other disease ever recorded.

The new study, published in Science on Thursday, is the first comprehensive tally of the damage done by the chytrid fungi Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal). In all, the fungi have driven the declines of at least 501 amphibian species, or about one out of every 16 known to science.

Of the chytrid-stricken species, 90 have gone extinct or are presumed extinct in the wild. Another 124 species have declined in number by more than 90 percent. All but one of the 501 declines was caused by Bd.

“We’ve known that's chytrid's really bad, but we didn't know how bad it was, and it's much worse than the previous early estimates,” says study leader Ben Scheele, an ecologist at Australian National University. “Our new results put it on the same scale, in terms of damage to biodiversity, as rats, cats, and [other] invasive species.”

Scheele has seen the fungus's carnage firsthand. At one of his field sites in Australia, an extended El Niño fueled mass frog breeding and dispersal—letting Bd spread as never before. Before the fungus, populations of the alpine tree frog were so abundant there, he had to watch his step when he went out at night. Now, the species is nearly impossible to find.

Saddened and shocked, Scheele resolved to put numbers to the decline. Four years—and innumerable email conversations—later, Scheele's team has finally combined all known reports of chytrid declines into a single consistent database, revealing Bd and Bsal's record-breaking toll.

“Chytrid fungus is the most destructive pathogen ever described by science—that's a pretty shocking realization,” adds Wendy Palen, a biologist at Simon Fraser University in British Columbia who wrote about the study for Science. 

The bulk of amphibian die-offs occurred in the 1980s—when the disease began to circulate around the globe—with a second uptick in mortality in South America in the mid-2000s. Many the affected frogs live in Central and South America, though outbreaks also occur across Europe, North America, Australia, and Africa. There are no known declines from Asia, where the fungus has co-existed for millions of years.

What's more, the study's counts are conservative. Earlier die-offs from the 1950s and 1960s in Europe and North America aren't included for lack of evidence. And the 501 species tallied are just the ones that scientists know about. Researchers keep identifying new species of frogs—even after they've been nearly wiped out in the wild.

The study's authors hope that the new research will act as a call to arms against the pandemic.

“I can totally understand why some people might see this issue as too little, too late, but I strongly disagree with that, because saying that does not truly take into consideration how much worse it can still get,” says study co-author Jonathan Kolby, a National Geographic Explorer and policy specialist at the U.S. Fish and Wildlife Service.

That's why researchers are urging governments around the world to buy amphibians time by curbing the trade of wild amphibians, protecting amphibian habitats, combating invasive species that threaten amphibians, and supporting captive-breeding programs.

Origins of a killer

There are hundreds of species of chytrid fungi, and most of them are unobtrusive decomposers. But Bd is an oddball: It has a fanatical taste for the proteins in amphibian skin. In the early 20th century, human activity—such as trade and war—accidentally spread the fungus around the world.

Along the way, it evolved, spawning a highly virulent strain that's primarily responsible for the pandemic.

Some amphibians can tolerate Bd, but in many others, it degrades the animals' permeable skin, which they use to breathe and regulate their water levels. Runaway infections trigger a death spiral that ends in cardiac arrest.

Not only is Bd lethal, it's also devastatingly effective at spreading. While most pathogens target specific hosts, Bd can infect at least 695 species to varying degrees. It also doesn't kill its victims quickly, which increases the odds that the fungus will spread. Species it doesn't kill, such as the American bullfrog, can act as reservoirs.

In addition, the fungus can spread by touch or by water; Bd spores can swim a short distance. And if conditions are right, the fungus can live outside of its host for weeks to months—maybe even years—at a time. “In some respects, it’s the perfect pandemic recipe,” says biologist Dan Greenberg, a Ph.D. student at Simon Fraser University. “If it were a human pathogen, it'd be in a zombie film.”

As National Geographic has previously reported, Bd snuck up on researchers much like a fictional zombie plague. Scientists first started noticing frog die-offs in the 1970s, but researchers didn't realize these “enigmatic declines” were a global phenomenon until the 1990s. Researchers described Bd in 1997; within a decade, it was the top suspect in the killings.

Study co-author Karen Lips, an ecologist at the University of Maryland, watched as the fungus spread through sites she had been monitoring for more than 15 years. From 2004 to 2008, one of her sites in Panama lost more than two fifths of its amphibian species to Bd. “You get to know this system, and it’s all completely wiped out,” she says. “It’s just horrible to see that degree of change.”

Similar scenes played out in the French Pyrenees, where midwife toads keel over by the hundreds on mountain lake shores. “Early in the outbreak, midwife toads would be calling at full volume—it’s a beautiful chorus. Once the disease has swept through, you don't hear any calling,” adds study co-author Mat Fisher, an epidemiologist at Imperial College London. “The world becomes very quiet.”

Holding the line

Researchers say that we can't reverse the damage that Bd has already done. The fungus is already worldwide, and purging it from the environment is impossible. While topical fungicides can heal Bd-stricken amphibians in the wild, they can't be applied on a global scale.

In the face of this reality, the study's authors say our best bet is to greatly curtail the global trade of wild amphibians, or at the very least improve screening procedures. The pet and meat trades probably play a major role in continuing the pathogen's spread. A 2018 study confirmed that all major strains of Bd, including the one most responsible for the global pandemic, are present in pet-shop animals.

Despite its impact, the fungus hasn't attracted the same attention as wildlife diseases such as white-nose syndrome, a fungal disease that infects bats.

“If you look at the number of species impacted, [white-nose syndrome] is so incredibly dwarfed by the number of amphibians—and then you look at the levels of effort and funding and attention,” says Kolby. “Why aren’t we giving that much attention to the frogs?”

U.S. officials are monitoring the situation, but because Bd is already widespread in the United States, there's only so much they can do. But researchers have pointed out that Bd consists of many different lineages. One 2011 study suggested that BdGPL, the deadliest strain of all, emerged when separate Bd strains hybridized.

“If we stop trying to emphasize the importance of biosecurity, disease control, and disease surveillance at the government level, it's hard to think that we're not going to have another hybrid event,” says Kolby. “That would start everything all over again: a new strain, with new virulence. That's what I find scary.”

The U.S. has room to take a more proactive approach to Bsal, which has ravaged salamanders in Europe but hasn't yet been detected in the U.S., a global haven for salamander biodiversity. In 2015, U.S. government agencies formed a task force expressly focused on Bsal. In 2016, U.S. officials moved to ban the import of 201 salamander species.

The U.S. is hardly alone in the fight against Bd; officials around the world are working to curb the fungus. Scientists have set up regional networks to track the fungi's spread, and the World Organization for Animal Health (OIE)—the non-human equivalent of the World Health Organization—has issued recommendations for how to trade amphibian products while minimizing the risk of spreading Bd. In 2015, the OIE and CITES, the treaty that oversees the global wildlife trade, signed an agreement to work more closely together.

Even now, some species stand a chance of evolving resistance to Bd and Bsal. Of the 292 chytrid-stricken species that have survived, 60 show some signs of recovery.

To buy critical time, Scheele says, the world needs to lessen the other threats amphibians face, from habitat loss to invasive species. In addition, captive-breeding efforts such as the Amphibian Ark could act as genetic lifeboats.

But Palen notes that the basic remedies have been known for decades: “It's pretty sobering that we haven’t been able to do those sorts of obvious things,” she says. “Maybe this is a real wake-up call.”