A wood-decay or xylophagous fungus is any species of

fungus A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

that digests moist

wood Wood is a structural tissue/material found as xylem in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulosic fibers that are strong in tension and embedded in a matrix of lignin t ...

, causing it to rot. Some species of wood-decay fungi attack dead wood, such as ''

Serpula lacrymans ''Serpula lacrymans'' is a species of fungi known for causing dry rot. It is a basidiomycete in the order Boletales. It has the ability to rapidly colonise sites through unique and highly specialised mycelium which also leads to greater degrada ...

'', and some, such as ''

Armillaria ''Armillaria'' is a genus of fungi that includes the '' A. mellea'' species ('honey fungus') that live on trees and woody shrubs. It includes about 10 species formerly categorized summarily as ''A. mellea''. ''Armillaria'' sp. are long-live ...

'' (honey fungus), are

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

and colonize living trees. Excessive moisture above the fibre saturation point in wood is required for fungal colonization and proliferation. In nature, this process causes the breakdown of complex molecules and leads to the return of nutrients to the soil. Wood-decay fungi consume wood in various ways; for example, some attack the

carbohydrate A carbohydrate () is a biomolecule composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The typical hydrogen-to-oxygen atomic ratio is 2:1, analogous to that of water, and is represented by the empirical formula (where ''m'' and ''n'' ...

s in wood, and some others decay

lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidit ...

. The rate of decay of wooden materials in various climates can be estimated by empirical models.Viitanen, T. et al. (2010). Towards modelling of decay risk of wooden materials. European Journal of Wood and Wood Products 68:303-313. Wood-decay fungi can be classified according to the type of decay that they cause. The best-known types are brown rot, soft rot, and white rot. Each produce different enzymes, can degrade different plant materials, and can colonise different environmental niches.Vane, C. H., et al. (2005). "Decay of cultivated apricot wood (''Prunus armeniaca'') by the ascomycete ''Hypocrea sulphurea'', using solid state 13C NMR and off-line TMAH thermochemolysis with GC–MS." International Biodeterioration & Biodegradation 55(3): 175-185. Brown rot and soft rot both digest a tree's

cellulose Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important s ...

and

hemicellulose A hemicellulose (also known as polyose) is one of a number of heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all embryophyte, terrestrial plant cell walls. Cellulose is crystalline, strong, an ...

but not its lignin; white rot digests lignin as well. The residual products of decomposition from fungal action have variable pH, solubility and redox potentials. Over time this residue becomes incorporated in the soil and sediment so can have a noticeable effect on the environment of that area. Wood decay fungi are considered key species in the forest ecosystems because the process of decomposing dead wood creates new habitats for other species, helps in the nutrient recycling, participate in the energy transportation and transformation and provides food to other species. They are also used as indicator species for conservation projects. Wood decay fungi are dependent on wood. Due to forestry, cutting trees and removal of decaying wood, many species are classified as threatened.

Brown rot

Cubical rot checked quercus bialowieza 1 beentree

Brown-rot fungi break down

and

that form the wood structure. Cellulose is broken down by

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...

(H₂O₂) that is produced during the breakdown of hemicellulose. Because hydrogen peroxide is a small

molecule A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...

, it can diffuse rapidly through the wood, leading to a decay that is not confined to the direct surroundings of the fungal

hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one o ...

e. As a result of this type of decay, the wood shrinks, shows a brown discoloration, and cracks into roughly cubical pieces, a phenomenon termed cubical fracture. The fungi of certain types remove cellulose compounds from wood, and hence the wood turns brown. Brown rot in a dry, crumbly condition is sometimes incorrectly referred to as ''dry rot'' in general. The term ''brown rot'' replaced the general use of the term ''dry rot'', as wood must be damp to decay, although it may become dry later.

Dry rot Dry rot is wood decay caused by one of several species of fungi that digest parts of wood which give it strength and stiffness. It was previously used to describe any decay of cured wood in ships and buildings by a fungus which resulted in a ...

is a generic name for certain species of brown-rot fungi. Brown-rot fungi of particular economic importance include ''

'' (true dry rot), ''

Fibroporia vaillantii ''Fibroporia vaillantii'', also known as mine fungus, white pore fungus, ''Antrodia vaillantii'', ''Polyporus vaillantii'', and various other namesConiophora puteana'' (cellar fungus), which may attack timber in buildings. Other brown-rot fungi include the sulfur shelf, ''

Phaeolus schweinitzii ''Phaeolus schweinitzii'', commonly known as velvet-top fungus, dyer's polypore, dyer's mazegill, or pine dye polypore, is a fungal plant pathogen. Taxonomy ''P. schweinitzii'' is named after Lewis David de Schweinitz, a Pennsylvania-born Mo ...

'', and ''

Fomitopsis pinicola ''Fomitopsis pinicola'', is a stem decay fungus common on softwood and hardwood trees. Its conk (fruit body) is known as the red-belted conk or red-belted bracket. The species is common throughout temperate Europe and Asia. It is a decay fungu ...

''. Brown-rot fungal decay is characterised by extensive demethylation of lignins whereas white-rot tends to produce low yields of molecules with demethylated functional groups.Vane, C. H., et al. (2001). "The effect of fungal decay (''Agaricus bisporus'') on wheat straw lignin using pyrolysis–GC–MS in the presence of tetramethylammonium hydroxide (TMAH)." Journal of Analytical and Applied Pyrolysis 60(1): 69-78. There are very few brown rot fungi in

tropical climate Tropical climate is the first of the five major climate groups in the Köppen climate classification identified with the letter A. Tropical climates are defined by a monthly average temperature of or higher in the coolest month, featuring hot te ...

s or in southern

temperate In geography, the temperate climates of Earth occur in the middle latitudes (approximately 23.5° to 66.5° N/S of the Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ran ...

zones. Most brown rot fungi have a geographical range north of the

Tropic of Cancer The Tropic of Cancer, also known as the Northern Tropic, is the Earth's northernmost circle of latitude where the Sun can be seen directly overhead. This occurs on the June solstice, when the Northern Hemisphere is tilted toward the Sun ...

(23.5° latitude), and most of these are found north of the 35° latitude, corresponding to a roughly

boreal Boreal, northern, of the north. Derived from the name of the god of the north wind from Ancient Greek civilisation, Boreas (god), Boreas. It may also refer to: Climatology and geography *Boreal (age), the first climatic phase of the Blytt-Sernand ...

distribution. Those brown rot fungi between latitudes 23.5° and 35° are typically found at high elevations in pine forest regions, or in

coniferous forest Conifers () are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All e ...

regions such as the

Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in great-circle distance, straight-line distance from the northernmost part of Western Can ...

or the

Himalayas The Himalayas, or Himalaya ( ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the Earth's highest peaks, including the highest, Mount Everest. More than list of h ...

Soft rot

Soft-rot fungi secrete

cellulase Cellulase (; systematic name 4-β-D-glucan 4-glucanohydrolase) is any of several enzymes produced chiefly by fungi, bacteria, and protozoans that catalyze cellulolysis, the decomposition of cellulose and of some related polysaccharides: : Endo ...

from their hyphae, an enzyme that breaks down cellulose in wood. This leads to the formation of microscopic cavities inside the wood and, sometimes, to a discoloration and cracking-pattern, similar to brown rot. Soft-rot fungi need

fixed nitrogen Nitrogen fixation is a chemical process by which molecular dinitrogen () is converted into ammonia (). It occurs both biologically and abiologically in chemical industries. Biological nitrogen fixation or ''diazotrophy'' is catalyzed by enz ...

in order to synthesize enzymes, which they obtain either from the wood or from the environment. Examples of soft-rot-causing fungi are ''

Chaetomium ''Chaetomium'' is a genus of fungi in the Chaetomiaceae family. It is a dematiaceous (dark-walled) Mold (fungus), mold normally found in soil, air, cellulose and plant debris. According to the ''Dictionary of the Fungi'' (10th edition, 2008), th ...

'', '' Ceratocystis'', and '' Kretzschmaria deusta''. Soft-rot fungi are able to colonise conditions that are normally too hot, cold or wet for brown- or white-rot to inhabit. They can also decompose woods containing high levels of protective from the compounds that are resistant to biological attack; the

bark Bark may refer to: Common meanings * Bark (botany), an outer layer of a woody plant such as a tree or stick * Bark (sound), a vocalization of some animals (which is commonly the dog) Arts and entertainment * ''Bark'' (Jefferson Airplane album), ...

of many woody plants contains a high concentration of

tannin Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and Precipitation (chemistry), precipitate proteins and various other organic compounds including amino acids and alkaloids. The term ''tannin'' is widel ...

s, which are difficult for fungi to decompose, as well as

suberin Suberin is a lipophilic, complex polyester biopolymer found in plants. It is composed of long-chain fatty acids (called suberin acids) and glycerol. Suberin is interconnected with cutin and lignin and forms a protective barrier in the epidermal ...

, which may act as a microbial barrier.Vane, C. H., et al. (2006). "Bark decay by the white-rot fungus Lentinula edodes: Polysaccharide loss, lignin resistance and the unmasking of suberin." International Biodeterioration & Biodegradation 57(1): 14-23. The bark acts as a form of protection for the more vulnerable interior of the plant. Soft-rot fungi are, apparently, not able to decompose matter as effectively as white-rot fungi, as they are less aggressive decomposers.

White rot

White-rot fungi are a type of fungi comprising

agaricomycetes The Agaricomycetes are a class of fungi in the division Basidiomycota. The taxon is roughly identical to that defined for the Homobasidiomycetes (alternatively called holobasidiomycetes) by Hibbett & Thorn, with the inclusion of Auriculariales ...

basidiomycetes Basidiomycota () is one of two large division (mycology), divisions that, together with the Ascomycota, constitute the subkingdom Dikarya (often referred to as the "higher fungi") within the kingdom Fungi. Members are known as basidiomycetes. Mor ...

, and some

ascomycetes Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The de ...

that are capable of decomposing many tree species. It is now recognized that

saprotrophic Saprotrophic nutrition or lysotrophic nutrition is a process of chemoheterotrophic extracellular digestion involved in the processing of decayed (dead or waste) organic matter. It occurs in saprotrophs, and is most often associated with fungi ...

interactions have profound effects on forest biomes. White-rot fungi are characterized by their ability to break down the lignin, cellulose, and hemicellulose of wood. As a result of this ability, white-rot fungi are considered a vital component of the

carbon cycle The carbon cycle is a part of the biogeochemical cycle where carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of Earth. Other major biogeochemical cycles include the nitrogen cycle and the water cycl ...

, because of their ability to access carbon pools that would otherwise remain inaccessible. The name “white rot” derives from the white color and rotting texture of the remaining crystalline cellulose from wood degraded by these fungi.Martinez, D., Larrondo, L. F., Putnam, N., Gelpke, M. D. S., Huang, K., Chapman, J., Helfenbein, K. G., Ramaiya, P., Detter, J. C., Larimer, F., Coutinho, P. M., Henrissat, B., Berka, R., Cullen, D., & Rokhsar, D. (2004). Genome sequence of the lignocellulose degrading fungus Phanerochaete chrysosporium strain RP78. Nature Biotechnology, 22(6), 695–700. Most knowledge of white-rot fungi comes from ''Coriolus versicolor'' and ''Phanerochaete chrysosporium''. White-rot fungi show strong participation in

interspecific competition Interspecific competition, in ecology, is a form of competition in which individuals of ''different'' species compete for the same resources in an ecosystem (e.g. food or living space). This can be contrasted with mutualism, a type of symbiosis. ...

, culminating in the evolution of lignin

catabolism Catabolism () is the set of metabolic pathways that breaks down molecules into smaller units that are either oxidized to release energy or used in other anabolic reactions. Catabolism breaks down large molecules (such as polysaccharides, lipid ...

specificity. The current and future applications of white-rot fungi as a potential component of

mycoremediation Mycoremediation (from ancient Greek (), meaning "fungus", and the suffix , in Latin meaning 'restoring balance') is a form of bioremediation in which fungi-based remediation methods are used to decontaminate the environment. Fungi have been pro ...

merit greater study of these saprotrophs.

Biochemistry

Compared to other saprotrophs, white-rot fungi possess the specialized ability to cleave lignin into smaller, more processable molecules. Lignin is a biopolymer which combines with cellulose to form the lignocellulose complex, an important complex that confers strength and durability to plant cell walls. Lignin is a macromolecule formed from the combination of many phenolic aromatic groups via

oxidative coupling Oxidative coupling in chemistry is a coupling reaction of two molecular entities through an oxidative process. Usually oxidative couplings are catalysed by a transition metal complex like in classical cross-coupling reactions, although the under ...

. Because of its high stability, lignin is incapable of being broken down through simple decomposition. As a result, white-rot fungi employ a series of enzymes that break lignin down into smaller aromatic rings. The relative abundance of

phenylpropane Propylbenzene may refer to: * ''n''-Propylbenzene, the straight chain isomer (IUPAC name propylbenzene) * Cumene Cumene (isopropylbenzene) is an organic compound that contains a benzene ring with an isopropyl substituent. It is a constituent ...

alkyl

side chain In organic chemistry and biochemistry, a side chain is a substituent, chemical group that is attached to a core part of the molecule called the "main chain" or backbone chain, backbone. The side chain is a hydrocarbon branching element of a mo ...

s of lignin characteristically decreases when decayed by white-rot fungi. Since lignin is the specialized food source of white-rot fungi, understanding the two different catabolic pathways is important.

Lignin metabolism through peroxidases

The first way white-rot fungi can break down lignin involves a high-redox-potential catalyzed

peroxidase Peroxidases or peroxide reductases ( EC numberbr>1.11.1.x are a large group of enzymes which play a role in various biological processes. They are named after the fact that they commonly break up peroxides, and should not be confused with other ...

attack on the heme pocket, thus reducing the stability of lignin. The process starts with creation of extracellular hydrogen peroxide (H₂O₂), a process completed via glyoxal oxidase (GLX). Extracellular hydrogen peroxide may be responsible for creation of hydroxyl radical (·OH) via the

Fenton reaction Fenton's reagent is a solution of hydrogen peroxide (H2O2) and an iron catalyst (typically iron(II) sulfate, FeSO4). It is used to oxidize contaminants or waste water as part of an advanced oxidation process. Fenton's reagent can be used to destr ...

: Fe²⁺ + H₂O₂ → Fe³⁺ + ·OH + OH⁻ The peroxidases used to oxidize lignin are lignin peroxidase (LiP), manganese peroxidase (MnP), and versatile peroxidase (VP). These peroxidases are commonly referred to as fungal class II peroxidases (PODs). Research suggests there may be another group of POD enzymes: basal peroxidases, including novel peroxidase (NoP). The NoP of ''Postia placenta'' is characterized by its inability to bind Mn²⁺ and its low redox potential. PODs developed in the common ancestor of white-rot, brown-rot and mycorrhizal fungi but these enzyme families have undergone

secondary loss In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

or contraction in the latter two groups. LiPs are oxidioreductases specific to lignin degradation. VPs are a class of peroxidase that combines elements of both LiPs and MnPs. LiPs and VPs are specific to heme product architecture allowing direct oxidation of benzene groups regardless of linkages. Direct oxidation of benzene groups results in the creation of an unstable radical aromatic. However, the hydrogen peroxide, bound to the heme group on the heme pocket, is unable to access the bulky lignin due to steric hindrance. As a result, LiP and VP enzymes create a

tryptophan Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α-carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromat ...

radical on their protein surface which allows long-range electron transfer from the aromatic substrate to the activated cofactor.

Lignin metabolism through laccase

Illustration of the cellulose composition

The second mechanism for breaking down lignin involves

laccase Laccases () are multicopper oxidases found in plants, fungi, and bacteria. Laccases oxidize a variety of phenolic substrates, performing one-electron oxidations, leading to crosslinking. For example, laccases play a role in the formation of li ...

, a low-redox-potential oxidase incapable of direct attack. Laccase can be used both in breaking and forming lignin. It cleaves lignin by reducing oxygen, creating a free radical which allows a hydroxyl radical (·OH) to attack the ring and deposit an alcohol group (OH). Deprotonation follows, resulting in the breaking of C-C (aryl-alphaC) bond into two aromatic rings. These products enter the fungal hyphae to be further broken down via catabolic processes. After the lignin complex is broken down, other saprotrophs can enter and begin degrading the newly created products. The final products of these transformations are carbon dioxide and water. While it is known that brown-rot fungi can also target lignin, they are only capable of modifying and are not capable of completely recycling it with a few exceptions. The ability to degrade lignin, previously supposed to only occur in white-rot fungi which have PODs, was found in ''Botryobasidium botryosum'' and ''Jappia argillacea'', two brown-rot fungi, lacking PODs. While the general pathway is currently unknown, research supports the existence of a continuum of features that separate the two fungal types rather than distinct categories.

Cellulose metabolism

While white-rot fungi specialized in catabolizing lignin, they are also capable of metabolizing other common organic forms of carbon like cellulose. Cellulose is also a laborious molecule to cleave. First, cellobiohydrolases, found in all white-rot fungi, hydrolyze the 1,4-beta-D-glycosidic bonds partially degrading cellulose. GH61 enzymes initiate a copper-dependent oxidative (LPMO) attack on crystalline cellulose. LPMOs boost degradation by activating oxygen using a copper-containing

histidine Histidine (symbol His or H) is an essential amino acid that is used in the biosynthesis of proteins. It contains an Amine, α-amino group (which is in the protonated –NH3+ form under Physiological condition, biological conditions), a carboxylic ...

brace that increases glycoside hydrolase activity, effectively lowering the activation cost of the reaction, making cleavage much cheaper, and therefore, more profitable for the fungi. Products from the cleavage are glucose and cellobiose. Another method involves endoglucanases hydrolyzing cellulose at random points before cellobiohydrolases cleave the chains, resulting in cellobiose. At the end of both processes, Beta-glucosidases further catabolize cellobiose into glucose.

Hemicellulose metabolism

Another main food source of white-rot fungi is

, a heteropolymer like cellulose that is not exclusively catabolized by white-rot fungi. The prevalent hemicellulose found in soft wood trees is Galactoglucomannan, a molecule made up of b-1,4-linked D-mannopyranose and D-glucopyranose units. Endo-1,4-b-D-mannanase breaks the prior linkages along the main chain of galactoglucomannan. Recent studies have found that LPMOs, previously only thought to be used in cellulose cleavage, were also found to be important in the catabolism of hemicellulose in conjunction with glycoside hydrolase enzymes (GHs). The availability of non white-rot fungi to catabolize cellulose and hemicellulose results in the creation of interspecific competition for access to these resources. Understanding the methods white-rot fungi use to dominate a resource and prevent competition will prove an important facet to understanding white-rot fungi.

Ecology

White rot competitive ability

Since white-rot fungi aren't the only saprotrophs capable of accessing cellulose and hemicellulose, competition ensues. Researchers attempted to estimate the effect of competition on white rot fungi. They reported that in sterile environments with no microbiota competitors present, white-rot fungi had good growth, but in soil with natural microbiota present, white-rot growth was variable. Even though white-rot fungi have a very specialized process for acquiring carbon, they are still vulnerable to competitors. Researchers clarified that white-rot fungi survival is dependent on its ability to defend lignocellulose substrate against attack by soil microbiota and its ability to establish itself within the soil bulk. These findings suggest that white-rot fungi and soil microbiota remain largely antagonistic in interactions, with only the highly competitive ''

Pleurotus ''Pleurotus'' is a genus of gilled mushrooms which includes one of the most widely eaten mushrooms, '' P. ostreatus''. Species of ''Pleurotus'' may be called oyster, abalone, or tree mushrooms, and are some of the most commonly cultivated ...

'' species capable of establishing themselves with only negligible negative impact due to soil microbiota. Less competitive white-rot fungi either failed to establish or produced lower enzyme concentrations associated with respiration. Successful interactions are characterized by which microbe arrives first and establishes a foothold.Lang, E., Eller, G., & Zadrazil, F. (1997). Lignocellulose Decomposition and Production of Ligninolytic Enzymes during Interaction of White Rot Fungi with Soil Microorganisms. Microbial Ecology, 34(1), 1–10. Brown-rot fungi and white-rot fungi have similar interspecific mycelial interactions. When white-rot fungal species occupied the same host distinct districts formed known as ‘decay columns’. Interactions were classified as interspecific competition. There were two important results when competition occurs: ‘deadlock’, when neither species could dominate the other; and ‘replacement’ when once species achieved complete colonization and replaced the other. A different study noted a third option: ‘reciprocal replacement’ when fungi successfully captured some territory and simultaneously lost other territory.

Mutualism Mutualism may refer to: * Mutualism (biology), positive interactions between species * Mutualism (economic theory), associated with Pierre-Joseph Proudhon * Mutualism (movement), social movement promoting mutual organizations * Mutualism model o ...

between two white-rot fungi was noted to be very rare. Findings suggested the important distinction between primary competition, that is competition to colonize unoccupied territory and antagonistic capture and defense of territory. Many competitive interactions were ‘intransitive’, meaning interactions involved more than two fungal species each often deploying a different antagonistic mechanism that gave it an advantage over one species but a disadvantage over others. Research further highlighted the importance of environmental factors including temperature, water potential, and invertebrate interactions in influencing competition. Findings suggested that competition increased decay, due to competition being expensive and saprotrophs needing to access more resources to fund it. Similarly, decay rates increased in smaller environments where natural resources were limited and competition intense. Even though brown-rot fungi lack the ability to decompose lignin, a relatively energetically expensive molecule, brown-rot fungi were slightly more competitive than white-rot fungi since they could still access the relatively cheaper cellulose and hemicellulose and devote more energy to competition and less to extracting nutrients. Further evidence for white-rot fungi possessing long-term advantages was found in a study that determined that a longer time was required for white-rot fungal invasion of wood chips than for foliage litters. The data they collected on white-rot mass loss was sigmoid-shaped. This finding suggests that while white-rot fungi are not as competitive at decomposing carbon from common sources as other decomposers within the first year, but they proved to be more competitive after one year due to their specialized ability to access carbon from lignin. Competition is not just limited between fungi. The presence of white rot fungi, in this case ''Hypholoma fasciculare'' and ''Resinicium bicolor'', on sterilized

beech Beech (genus ''Fagus'') is a genus of deciduous trees in the family Fagaceae, native to subtropical (accessory forest element) and temperate (as dominant element of Mesophyte, mesophytic forests) Eurasia and North America. There are 14 accepted ...

wood blocks resulted in a lower number of wood-inhabiting bacteria, even though lignin is not a food source of these bacteria. This finding points to an antagonistic relationship between white-rot fungi and bacteria that both compete for cellulose and hemicellulose, as well as the existence of

bactericidal A bactericide or bacteriocide, sometimes abbreviated Bcidal, is a substance which kills bacteria. Bactericides are disinfectants, antiseptics, or antibiotics. However, material surfaces can also have bactericidal properties based solely on their p ...

and

bacteriostatic A bacteriostatic agent or bacteriostat, abbreviated Bstatic, is a biological or chemical agent that stops bacteria from reproducing, while not necessarily killing them otherwise. Depending on their application, bacteriostatic antibiotics, disinfec ...

weapons utilized by white-rot fungi against competitor bacteria. Though the mechanism is unknown, researchers suggested that white-rot fungi may utilize lignin decomposing enzymes, hydroxyl radicals, and aryl alcohols to create a toxic environment. Further environmental manipulation involved the release of PODs to lower the pH and create a more acidic habitat. The resulting conclusion is that peroxides not only make lignin accessible, but create a more accessible environment for white-rot fungi to compete in. Even with a specialized catabolic mechanism, competition remains a highly selective force on white-rot evolution.

Evolution

Insight on the evolutionary development of white-rot fungi comes from the evolution of lignin catabolism. Lignin is a precursor to the development of coal. During the

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

(360-300 mya) and

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

(300-250 mya) there was a very high carbon accumulation. However, near the end of the Permian there was a sharp decline in carbon accumulation. White-rot fungi and their ability to cleave lignin evolved at the end of the Permian period. Researchers attempted to reconstruct the evolution of saprotrophic capabilities. Results suggested that white-rot saprotrophs were the common ancestors of brown-rot fungi and ectomycorrhiza (ECM), but that in the latter two groups genes coding for PODs were lost. To gain insight on the evolution of lignolytic peroxidases, researchers resurrected ancestral lignolytic peroxidases from the

Polyporales The Polyporales are an order (biology), order of about 1,800 species of fungi in the division (mycology), division Basidiomycota. The order includes some (but not all) polypores as well as many corticioid fungi and a few agarics (mainly in the ge ...

, a basidiomycete order that emerged 150 mya, and analyzed the lineage from that ancestor to the modern ''P. chrysosporium''. One of the major findings was that ancestral versatile peroxidase (AVP) was not capable of functioning efficiently at low pH, a characteristic associated with modern LiPs. Findings also suggested that AVP possessed a much wider substrate specificity, the loss of which being an evolutionary cost of developing further specificity. Early peroxidases were unable to directly degrade lignin and relied on metal cations to separate phenol groups. Only later would peroxidases acquire the ability use a tryptophanyl radical, interacting with a bulky polymer at the surface of the peroxidase, to attack non-phenolic lignin. These findings highlight the importance of taking plant evolution into account when analyzing the evolution of white-rot fungus. Researchers note that plant cell walls have been steadily increasing and show evidence of convergent evolution. White-rot PODs also demonstrated convergent evolution. As plant cell walls have become more efficient, so have the peroxidases that destroy them. Researchers attempted to further understand the evolutionary development of white-rot fungi by using bioinformatics. They analyzed sixty-two genomes of Agaricomycetes of white-rot, brown-rot, ECM and other nutritional modes. Given that both white-rot and brown-rot share the ability to cleave cellulose and hemicellulose, they suggest that PODs developed after cellulolytic enzymes and that white-rot mechanisms were an elaboration based on the already existing saprotrophic model, not just on the utilization of PODs. Understanding the evolutionary development of white-rot fungi provides insight onto a variety of potential uses.

Current and future applications

White-rot fungi have historically been valued as food, but in recent years exploration of their enzymatic capabilities has revealed white-rot fungi’s potential in depollution. White-rot fungi have long since been staples of human diet and remain an important source of nutrition for people around the world. White-rot fungi are commercially grown as a source of food – for example the

shiitake mushroom The shiitake (; ''Chinese/black mushroom'' or ''Lentinula edodes'') is a macrofungus native to East Asia, which is cultivated and consumed around the globe. Taxonomy The fungus was first described scientifically as '' Agaricus edodes'' by ...

, which in 2003 constituted approximately 25% of total mushroom production.Vane, C. H. (2003). "Monitoring Decay of Black Gum Wood (''Nyssa sylvatica'') During Growth of the Shiitake Mushroom (''Lentinula edodes'') Using Diffuse Reflectance Infrared Spectroscopy." Applied Spectroscopy 57(5): 514–517. Due to white-rot fungi’s important ability to degrade lignin, they have been increasingly explored as potential sources in mycoremediation applications, applications focused on removing organic pollutants from the environment. All three enzyme types of lignin decomposition (LiPs, MnP, and Laccase) have been explored. White-rot fungi have been determined to degrade chlorinated aromatic hydrocarbons ( CAHs),

DDT Dichlorodiphenyltrichloroethane, commonly known as DDT, is a colorless, tasteless, and almost odorless crystalline chemical compound, an organochloride. Originally developed as an insecticide, it became infamous for its environmental impacts. ...

lindane Lindane, also known as ''gamma''-hexachlorocyclohexane (γ-HCH), gammaxene, Gammallin and benzene hexachloride (BHC), is an organochlorine chemical and an isomer of hexachlorocyclohexane that has been used both as an agricultural insecticide an ...

polycyclic aromatic hydrocarbon A Polycyclic aromatic hydrocarbon (PAH) is any member of a class of organic compounds that is composed of multiple fused aromatic rings. Most are produced by the incomplete combustion of organic matter— by engine exhaust fumes, tobacco, incine ...

polychlorinated biphenyl Polychlorinated biphenyls (PCBs) are organochlorine compounds with the formula Carbon, C12Hydrogen, H10−''x''Chloride, Cl''x''; they were once widely used in the manufacture of carbonless copy paper, as heat transfer fluids, and as dielectri ...

s, PCP, polychlorinated dibenzo(p)dioxins, and

azo dye Azo dyes are organic compounds bearing the functional group R−N=N−R′, in which R and R′ are usually aryl and substituted aryl groups. They are a commercially important family of azo compounds, i.e. compounds containing the C−N=N−C l ...

s when studied in ''

Phanerochaete chrysosporium ''Phanerochaete'' is a genus of crust fungi in the family Phanerochaetaceae. Taxonomy The genus was circumscription (taxonomy), circumscribed by Finnish mycologist Petter Karsten in 1889. Marinus Anton Donk redefined the limits of the genus in t ...

'', ''

Trametes versicolor ''Trametes versicolor''also known as ''Coriolus versicolor'' and ''Polyporus versicolor''is a common polypore mushroom found throughout the world. Owing to its shape being similar to that of a wild turkey's tail feathers, ''T. versicolor ...

'', '' Bjerkandere adusta'', and ''

Pleurotus ostreatus ''Pleurotus ostreatus'' (commonly known the oyster mushroom, grey oyster mushroom, oyster fungus, hiratake, or pearl oyster mushroom). Found in temperate and subtropical forests around the world, it is a popular edible mushroom. Name Both th ...

''. Noted limitations of white-rot fungi as pollutant cleaners is due to difficulty establishing the fungi in non-natural conditions. Other applications include

biosorption Biosorption is a physiochemical process that occurs naturally in certain biomass which allows it to passively concentrate and bind contaminants onto its cellular structure. Biosorption can be defined as the ability of biological materials to accumu ...

, a process where biomass is utilized to remove solute wastes preventing pollution. Researchers studied the effect white-rot fungi could have on absorbing heavy metal ions via

alginic acid Alginic acid, also called algin, is a naturally occurring, edible polysaccharide found in brown algae. It is hydrophilic and forms a viscous gum when hydrated. When the alginic acid binds with sodium and calcium ions, the resulting salts are kn ...

, a linear polysaccharide composed of 1,4-linked beta-D-mannuronic and alpha-L-guluronic acid. The findings from the study indicated that '' Fungalia trogii'' was capable of biosorption of Hg²⁺, Cd²⁺, and Zn²⁺ in low pH environments. The potential establishment of white-rot fungi as a stable mycoremediator remains an important future discovery. White-rot fungi remain an important source of great unrealized potential.

Induced fungal decay

A special way of giving grown wood an unusual structure is to infect it with a

fungus by storing it in a humid environment (''fungal decay''). The fungus penetrates the layers of the wood and changes the nature of the

cells Cell most often refers to: * Cell (biology), the functional basic unit of life * Cellphone, a phone connected to a cellular network * Clandestine cell, a penetration-resistant form of a secret or outlawed organization * Electrochemical cell, a d ...

. This process creates individual patterns and shades of colour. The wood treated in this way is then excellently suited for the production of all kinds of design objects. In order to stabilise the wood structure weakened by the fungus,

resin A resin is a solid or highly viscous liquid that can be converted into a polymer. Resins may be biological or synthetic in origin, but are typically harvested from plants. Resins are mixtures of organic compounds, predominantly terpenes. Commo ...

s or plastics are usually introduced into the material by special

vacuum A vacuum (: vacuums or vacua) is space devoid of matter. The word is derived from the Latin adjective (neuter ) meaning "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressur ...

processes. This also kills the residual fungus after the desired pattern has been achieved, thus preserving the wood from being further consumed by the fungus. A special icing process applied to

wood leads to results similar to those obtained with fungal decay. After the wood has been soaked, it is iced and then dried. The result is a very light wood with an almost black

grain A grain is a small, hard, dry fruit (caryopsis) – with or without an attached husk, hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and ...

. This result, which also occurs very rarely in nature, is called ''ice-beech''.

Natural durability

Natural durability is the inherent capability of wood to tolerate and resist fungal decay and

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

attacks, such as

woodboring beetle The term woodboring beetle encompasses many species and families of beetles whose larval or adult forms eat and destroy wood (i.e., are xylophagous). In the woodworking industry, larval stages of some are sometimes referred to as woodworms. The ...

s and

termite Termites are a group of detritivore, detritophagous Eusociality, eusocial cockroaches which consume a variety of Detritus, decaying plant material, generally in the form of wood, Plant litter, leaf litter, and Humus, soil humus. They are dist ...

s, and

marine organisms Marine life, sea life or ocean life is the collective ecological communities that encompass all aquatic animals, plants, algae, fungi, protists, single-celled microorganisms and associated viruses living in the saline water of marine habita ...

. This protective feature is attributable to specific biological compounds, called ''extractives'' that are toxic to wood-destroying organisms. Along with the tree’s growth, the

sapwood Wood is a structural tissue/material found as xylem in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulosic fibers that are strong in tension and embedded in a matrix of lignin that ...

converts into

heartwood Wood is a structural tissue/material found as xylem in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulosic fibers that are strong in tension and embedded in a matrix of lignin t ...

and this brings physical and chemical changes to the wood. As a result, the permeability decreases while the natural durability increases. Thus, the extractives responsible for natural durability are mainly present in the heartwood, although they may also be contained in small amounts in the sapwood. Different chemicals have been isolated from the heartwood of naturally rot-resistant trees and have shown to be protectants, including

polyphenol Polyphenols () are a large family of naturally occurring phenols. They are abundant in plants and structurally diverse. Polyphenols include phenolic acids, flavonoids, tannic acid, and ellagitannin, some of which have been used historically as ...

lignans The lignans are a large group of low molecular weight polyphenols found in plants, particularly seeds, whole grains, and vegetables. The name derives from the Latin word for "wood". Lignans are precursors to phytoestrogens. They may play a role ...

(e.g.

gmelinol Gmelinol is a lignan. (+)-Gmelinol can be isolated from the heartwood of ''Gmelina arborea ''Gmelina arborea'', (in English beechwood, gmelina, goomar teak, Kashmir tree, Malay beechwood, white teak, yamane ), locally known as gamhar, is a fast ...

plicatic acid Plicatic acid is a carboxylic acid from the resin acid group. It is naturally found in ''Thuja'' and cypress resin, and the main irritant and contact allergen present in thuja wood; in contrast to pine, where the primary irritant is abietic aci ...

flavonoid Flavonoids (or bioflavonoids; from the Latin word ''flavus'', meaning yellow, their color in nature) are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans. Chemically, flavonoids ...

s (e.g.

mesquitol Mesquitol is a flavan-3-ol, a type of flavonoid. '' Prosopis juliflora'', an invasive New World mesquite now found in Kenya, has unusually high levels of (−)-mesquitol in its heartwood. Mesquitol, with its pyrogallol-type A-ring, is more suscep ...

tropolone Tropolone is an organic compound with the chemical formula . It is a pale yellow solid that is soluble in organic solvents. The compound has been of interest to research chemists because of its unusual electronic structure and its role as a liga ...

s (e.g.

hinokitiol Hinokitiol (β-thujaplicin) is a natural monoterpenoid found in the wood of trees in the family Cupressaceae. It is a tropolone derivative and one of the thujaplicins. Hinokitiol is used in oral and skin care products, and is a food additive us ...

and other

thujaplicin Thujaplicin (isopropyl cycloheptatrienolone) is any of three isomeric tropolone-related natural products that have been isolated from the softwoods of the trees of ''Cupressaceae'' family. These compounds are known for their antibacterial, antifu ...

s),

sesquiterpenoids Sesquiterpenes are a class of terpenes that consist of three isoprene units and often have the molecular formula C15H24. Like monoterpenes, sesquiterpenes may be cyclic or contain rings, including many combinations. Biochemical modifications such ...

(e.g. α-cadinol). The natural durability varies between tree species, geographic regions, environmental conditions, growth stage, and increases with the age. Thereby, some trees are more resistant to fungal diseases and insects and their

timber Lumber is wood that has been processed into uniform and useful sizes (dimensional lumber), including beams and planks or boards. Lumber is mainly used for construction framing, as well as finishing (floors, wall panels, window frames). ...

lasts longer than other trees. Notably, the timber of these trees remain durable for a long-time period, even around a century, thereby they have been used as a reliable building material for centuries. Since the young trees do not produce enough protecting chemicals, some trees grow with a hollow, rotten trunk at an early age. However, the stands of old-growth trees are more naturally durable than second-growth stands. Tree species that have significant natural durability include '' Lagarostrobos franklinii'' (Huon pine), ''

Intsia bijuga ''Intsia bijuga'', commonly known as Borneo teak, ipil, merbau, Johnstone River teak, and kwila, amongst many other names, is a species of tree in the flowering plant family Fabaceae, native to coastal areas from east Africa, through India and ...

'' (ipil), some ''

Eucalyptus ''Eucalyptus'' () is a genus of more than 700 species of flowering plants in the family Myrtaceae. Most species of ''Eucalyptus'' are trees, often Mallee (habit), mallees, and a few are shrubs. Along with several other genera in the tribe Eucalyp ...

'' species (

ironbark Ironbark is a common name of a number of species in three taxonomic groups within the genus ''Eucalyptus'' that have dark, deeply furrowed bark. Instead of being shed annually as in many of the other species of ''Eucalyptus'', the dead bark accum ...

), ''

Podocarpus totara ''Podocarpus totara'' (), commonly known as the , is a species of podocarp tree endemic to New Zealand. It grows throughout the North Island, South Island and rarely on Stewart Island / Rakiura in lowland, montane and lower subalpine forest at ...

'' (totara), ''

Vitex lucens ''Vitex lucens'', commonly known as pūriri, is an evergreen tree endemic to New Zealand. History Pūriri was first collected (by Europeans) at Tolaga Bay by Joseph Banks, Banks and Daniel Solander, Solander during Cook's first visit in 1769. ...

'' (puriri), ''

Agathis australis ''Agathis australis'', commonly known as kauri, is a species of coniferous tree in the family Araucariaceae, found north of 38°S in the northern regions of New Zealand's North Island. It is the largest (by volume) but not tallest species ...

'' (kauri), and trees of the

Cupressaceae Cupressaceae or the cypress family is a family of conifers. The family includes 27–30 genera (17 monotypic), which include the junipers and redwoods, with about 130–140 species in total. They are monoecious, subdioecious or (rarely) dioecio ...

family, such as ''

Chamaecyparis obtusa ''Chamaecyparis obtusa'' (Japanese cypress, hinoki cypress or hinoki; or , ) is a species of cypress native to central Japan in East Asia, and widely cultivated in the temperate climate, temperate northern hemisphere for its high-quality timber ...

'' (Hinoki cypress), ''

Thuja plicata ''Thuja plicata'' is a large evergreen coniferous tree in the family Cupressaceae, native to the Pacific Northwest of North America. Its common name is western redcedar in the U.S. or western red cedar in the UK, and it is also called pacific re ...

'' (Western red cedar), ''

Thujopsis dolabrata ''Thujopsis'' () is a genus of conifers in the cypress family (Cupressaceae), the sole member of which is ''Thujopsis dolabrata''. It is endemic to Japan, where it is known as ''asunaro'' (). It is similar to the closely related genus ''Thuja'' ...

'' (Hinoki asunaro), ''

Juniperus cedrus ''Juniperus cedrus'', the Canary Islands juniper, is a species of juniper, native to the western Canary Islands (Tenerife, La Palma, Gran Canaria, Gomera) and Madeira (''J. cedrus'' Webb & Berthel. subsp. ''maderensis'' (Menezes) Rivas Mart ''et ...

'' (Canary Islands juniper), ''

Cedrus atlantica ''Cedrus atlantica'', the Atlas cedar, is a species of tree in the pine family Pinaceae, native to the Rif and Atlas Mountains of Morocco ( Middle Atlas, High Atlas), and to the Tell Atlas in Algeria.Gaussen, H. (1964). Genre ''Cedrus''. Les F ...

'' (Atlas cedar), ''

Chamaecyparis taiwanensis ''Chamaecyparis taiwanensis'' (Taiwan cypress; ) is a species of cypress, native to the mountains of Taiwan, where it grows at altitudes of 1300–2800 m.Rushforth, K. (1987). ''Conifers''. Helm . Description It is a slow-growing coniferous tree ...

'' (Taiwan cypress), among others. According to th
EN 350:2016 standards
by the

APA – The Engineered Wood Association APA – The Engineered Wood Association is a nonprofit trade association of the United States and Canadian engineered wood Engineered wood, also called mass timber, composite wood, man-made wood, or manufactured board, includes a range of der ...

, the durability of wood and wood-based products to fungal decay can be classified into five categories: very durable (DC1); durable (DC2); moderately durable (DC3); slightly durable (DC4); and not durable (DC5). The durability to insect attacks can be categorized as durable (DC D); moderately durable (DC M); and not durable (DC S). Generally, the heartwood of durable tree species is considered as very durable, whereas the sapwood of all tree species is considered as not durable and is the most vulnerable.

Wood preservation

A wide selection of timber preservation has been developed to give the wood an improved durability and to protect it from decay. The wood can be treated according to the purpose (biological protection, e.g. fungi, insects, marine organisms) and the environment (interior, exterior, above ground, in ground, in water) of its use. Timber preservatives include

chromated copper arsenate Chromated copper arsenate (CCA) is a wood preservative containing compounds of chromium, copper, and arsenic, in various proportions. It is used to impregnate timber and other wood products, especially those intended for outdoor use, in order to pr ...

(CCA),

alkaline copper quaternary Alkaline copper quaternary, usually abbreviated ACQ, is a type of water-based wood preservative product containing a soluble copper#Coordination chemistry, copper(II) complex and quaternary ammonium alkyl- or aryl-substituted compounds ("quats"). ...

(ACQ), copper azole (CuAz),

borates A borate is any of a range of boron oxyanions, anions containing boron and oxygen, such as orthoborate , metaborate , or tetraborate ; or any salt (chemistry), salt of such anions, such as sodium metaborate, and borax . The name also refers to es ...

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

and

potassium silicate Potassium silicate is the name for a family of inorganic compounds. The most common potassium silicate has the formula K2SiO3, samples of which contain varying amounts of water. These are white solids or colorless solutions.Gerard Lagaly, Werner ...

, oil-based preservatives, such as

creosote Creosote is a category of carbonaceous chemicals formed by the distillation of various tars and pyrolysis of plant-derived material, such as wood, or fossil fuel. They are typically used as preservatives or antiseptics. Some creosote types w ...

and

pentachlorophenol Pentachlorophenol (PCP) is an organochlorine compound used as a pesticide and a disinfectant. First produced in the 1930s, it is marketed under many trade names. It can be found as pure PCP, or as the sodium salt of PCP, the latter of which disso ...

, light organic solvent preservatives (LOSP),

propiconazole Propiconazole is a triazole fungicide, also known as a DMI, or demethylation inhibiting fungicide due to its binding with and inhibiting the Lanosterol 14 alpha-demethylase, 14-alpha demethylase enzyme from demethylating a precursor to ergosterol. ...

tebuconazole Tebuconazole is a triazole fungicide used agriculturally to treat plant pathogenic fungi. Environmental hazards Though the U.S. Food and Drug Administration considers this fungicide to be safe for humans, it may still pose a risk. It is listed as ...

imidacloprid Imidacloprid is a systemic insecticide belonging to a class of chemicals called the neonicotinoids which act on the central nervous system of insects. The chemical works by interfering with the transmission of stimuli in the insect nervous system. ...

epoxy Epoxy is the family of basic components or Curing (chemistry), cured end products of epoxy Resin, resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide fun ...

resins, wood acetylation, natural or biological preservation, such as treatment with heat (

thermally modified wood Thermally modified wood is engineered wood that has been modified by a controlled pyrolysis process of wood being heated to temperatures above in an oxygen free atmosphere. This process changes to the chemical structures of wood's cell wall co ...

mud Mud (, or Middle Dutch) is loam, silt or clay mixed with water. Mud is usually formed after rainfall or near water sources. Ancient mud deposits hardened over geological time to form sedimentary rock such as shale or mudstone (generally cal ...

tung oil Tung oil or China wood oil is a drying oil obtained by pressing the seed from the nut of the tung tree (''Vernicia fordii''). Tung oil hardens upon exposure to air (through polymerization), and the resulting coating is transparent and has a d ...

, impregnation using biopolymers from agricultural waste ( biological modified timber), covering wood with copper sheathes, etc. Treatment of timber with natural extractives derived from rot-resistant trees, such as

tannins Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids. The term ''tannin'' is widely applied to any large po ...

, and tree extracts, is another promising environmentally-friendly wood preservation method. The more permeable is the wood, the easier is it to treat. According to th
EN 350:2016 standards
the treatability of woods can be categorized in four levels: (1) easy to treat; (2) moderately easy to treat; (3) difficult to treat; and (4) extremely difficult to treat.

Safety

Over the years a lot of concerns have arisen regarding the

arsenic Arsenic is a chemical element; it has Symbol (chemistry), symbol As and atomic number 33. It is a metalloid and one of the pnictogens, and therefore shares many properties with its group 15 neighbors phosphorus and antimony. Arsenic is not ...

and

chromium Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal. Chromium ...

contents of CCA. In 1986, the U.S.

Environmental Protection Agency Environmental Protection Agency may refer to the following government organizations: * Environmental Protection Agency (Queensland), Australia * Environmental Protection Agency (Ghana) * Environmental Protection Agency (Ireland) * Environmenta ...

(EPA) recognized arsenic as a human carcinogen. Water contamination with arsenic and its compounds is a serious public health issue, and their release to the environment and

soil pollution Soil contamination, soil pollution, or land pollution as a part of land degradation is caused by the presence of xenobiotic (human-made) chemicals or other alteration in the natural soil environment. It is typically caused by industrial activit ...

is another environmental problem. Different regulatory interventions have been undertaken worldwide to restrict their use in the wood industry, especially in timber for residential use. By the end of 2003, the U.S EPA and the wood industry agreed to discontinue the use of CCA in treating timber for residential use. Its use is also prohibited in

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

, and the

European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are Geography of the European Union, located primarily in Europe. The u ...