These compounds can result from chemical synthesis, coal mining, and petroleum processing. Organic pesticides show less dramatic effects on soil microbiology than do other classes of toxic organics, probably because the former are screened to avoid such effects. Some alleviation and enhanced degradation of n-alkanes occurred through fertilization with urea and phosphate. Addition of oil-degrading bacteria showed little promise. Revegetation lessened the effect of oil shale, apparently because bacteria are insulated in the rhizospheres of the range plants employed.
Toxic metals can be abundant in some sewage sludges.
Microbes can mobilize and increase the toxicity of cadmium, perhaps by producing water-soluble ligands or otherwise changing soil properties. Effects of Mining Operations on Soil Biology Acidification can occur when excavation of ores containing iron sulfides leads to oxidative production of sulfates. Discharge waters from mine spoils may have pH values of 1-2, and can cause severe problems off site. Waters draining from coal mines and associated spoils can be high in Zn, Cu, Ni, or Mn, all potentially toxic. Reclamation of strip-mined sites does not arrest such discharges immediately.