Depressed Microbial Activity

Healthy bacterial populations are essential for soil fertility. Heavy metals, pesticides, and petroleum chemicals are toxic to soil microorganisms. Illustrative examples of the impacts of these toxins follow. 

Elevated copper and zinc concentrations in soil adversely affect microbial biomass, activity, and composition of microbial communities in soil adjacent to copper smelters and copper-tailings dumps. 3,4 Nitrogen fixation was adversely impacted when heavy metal-contaminated sewage sludge was added to soils. 5  

The herbicide Paraquat was found to cause mutations in nitrogen-fixing soil bacteria and also reduce chlorophyll content of algae. 6,7 DDT and its metabolites DDE and DDD are widespread soil pollutants that alter the species composition of soil algae and nitrogen-fixing bacteria and entirely eliminate some species of these. 8 The pesticides hexaconazole, carbo-furan, and ethion are toxic to soil microflora and result in the reduction of soil bacteria countsJ9  

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However, the microbial activity is depressed during long and severe wintertime, and this leads to an accumulation of semi-mineralizable plant residues on the soil surface. With the increasing duration of cold season from south to north, the mass of these half-destroyed remains enlarges from 15 ton/ha of dry organic matter in Broad-Leaved Sub-Boreal Forest ecosystems to 80-85 ton/ha in Northern Taiga Forest ecosystems. 

Kraft mill that had used elemental chlorine historically Microbial community and diatom species in lake sediments sampled from 2-8 cm depths Drop in the ATP content, depressed butyrate-esterase activity indicating toxicity to microorganisms, and reduction in diatom species richness Mika et al., 1999 [31]... 

The mechanism of action for diesel fuels is not well characterized due to the complexity of its petroleum hydrocarbon mixture. The presence of additives that improve fuel combustion or prevent microbial growth may contribute to toxicity. Based on research conducted with individual components of diesel fuels, the primary mechanism of action for central nervous system (CNS) depression from diesel fuel is the reversible, physical interaction of the aromatic and aliphatic hydrocarbons with cell membranes. Renal toxicity is possibly attributed to oxidative metabolites of some of the aromatic constituents. Eye and skin injury are attributable to direct irritant action and the high lipid solubility that may dissolve protective skin oils and allow penetration into the skin tissue. The dermal carcinogenesis observed in rodents subjected to chronic dermal exposure to diesel may be attributed to the genotoxic activity of PAHs and the promoting activity of repeated dermal injury. 

Ciprofloxacin interferes with microbial DNA synthesis. Hydrocortisone depresses formation, release, and activity... 

Soil organisms are exposed to changing environmental conditions (Voroney, 2006). Extremes are marked by stimulation, depression, or death. Domsch, Jagnow, and Anderson (1983) have considered the following naturally occurring stress situations on soil microbial populations and their activities. Some of them can occur in soil treated by electrokinetic technology ... 

The substance that enhances the activity of the lactoferrin is the IgA normally present in human milk, though IgA by itself has no antimicrobial activity whatever. It has been proposed that whereas lactoferrin (the active factor of milk) sequesters the iron and makes it unavailable to most microorganisms, the igA acts to depress the production or elaboration of microbial siderophores,... 

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