Industrialization led to an increase in chemicals in the environment. The soil absorbs these chemicals and holds them for years until treated. The action of bacteria, fungi, and algae utilize the pollutants and generate energy. The bioremediation contains a diverse treatment process, but the effectiveness of the bioremediation increases by the enzymatic action. Laccase, a copper-containing enzyme, is versatile and oxidizes complex organic compounds without generating reactive oxygen species (ROS). This process is carried by laccase-mediated systems (LCMs) controlled by low redox potential. The presence of redox mediators oxidizes the chemical compounds at the higher rate, making laccase degradation of the pollutants effectively. The chapter provides a glimpse of soil bioremediation by bacteria and fungi as individual species and symbiotic species, the production of laccase enzyme by bacteria and fungi, methods adopted to enhance the enzyme activity, and degradation of pollutants in soil.
TopIntroduction – Soil Pollution
The environmental transition that impacts its physical, chemical, and biological features is referred to as pollution. The foreign substances in the environment sourced from different sites – household, industry, mining, automobile wastes, and radioactive wastes – cause undesirable environmental changes. Soil, mentioned as “Universal Sink” contains all types of pollutants (Doran et al., 1996; Havugimana et al., 2018). The contamination affects the structure of the soil and is rendered unhealthy or abandoned if it crosses its threshold. Based on the nature of the pollutants, they are biodegradable and non-biodegradable. The heavy metals are considered biodegradable and persistent in soil. In turn, the biodegradable pollutants produce intermediates or products of toxic nature, increasing the soil toxicity (Sims & Cupples, 1999; Havugimana et al., 2018). The Persistent Organic Pollutants (POPs), plastics, heavy metals and xenobiotics have inert characteristics making degradation difficult. The POPs generate from sources such as industries, automobiles, waste incineration. The Stockholm Convention comprising 152 countries reported 12 highly toxic POPs and called them a “Dirty Dozen”. It contains - dieldrin, aldrin, dioxins, chlordane, furans, mirex, DDT, endrin, heptachlor, hexachlorobenzene, PCBs, and toxaphene - (UNEP 2009). During 2017, the list was extended further by the addition of 16 more POPs - α-hexachlorocyclohexane, chlordecone, β-hexachlorocyclohexane, decabromo diphenyl ether, hexabromobiphenyl, hexabromodiphenyl ether/heptabromodiphenyl ether, hexachlorobutadiene, hexabromocyclododecane, lindane, pentachlorobenzene, perfluorooctane sulfonic acid, pentachlorophenol and its salts and esters, perfluorooctane sulfonyl fluoride, polychlorinated naphthalenes, short-chain chlorinated paraffin, endosulfan and its related isomers, tetrabromodiphenyl ether, and pentabromodiphenyl ether (Bull et al., 2014, Araki et al., 2014; Jarosiewicz et al., 2017). The ingestion of polluted soil by the animals enters the food chain, reaching the higher trophic levels leading to the accumulation of POPs. The diverse source of pollutants (Figure 1) has impeccable effects on plants, animals and humans.
The agrochemical pollution in the soil contributes as large as synthetic fertilizers made of hydrocarbon. The applied pesticide passes through the soil horizons and gets absorbed by the soil particles. Thus, it remains in the soil for a prolonged period causing ill effects in living organisms. Based on the living systems' level of adsorption, the pesticides are classified into three categories (Mirsal 2008);
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Contact pesticides – pesticides are remaining on the surface of the plants/soil.
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Quasi Systemic pesticides – pesticides transported to the leaves cuticle and epidermis of the animals.
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Systemic pesticides – pesticides in the internal systems of plants and animals.