Soils reductive metabolism

Pentachlorophenol applied to beech forest soils every 2 months for 2 years at the rate of 1.0 g/m2 markedly reduced populations of soil organisms. At 5.0 g/m2, it drastically reduced most of the soil animal species and also the microflora (Zietz et al. 1987). Reduction of the soil metabolism by PCP retards decomposition and affects the overall nutrient balance of forest ecosystems (Zietz et al. 1987). Pentachlorophenol is more toxic to earthworms in soils with comparatively low levels of organic materials. The LC50 (14-day) value for Lumbricus rubellus was 1094 mg PCP/kg DW soils with 6.1% organic matter, and 883 mg/kg DW soils with 3.7% organic matter (Van Gestel and Ma 1988). The earthworm Eisenia fetida andrei is more sensitive than Lumbricus rubellus ... 

The nature of the radioactivity in the water, soil and fish from the carbon-14 DDT experiment was examined by thin-layer chromatography as shown in Figure 5. The radioactivity in the water was very polar in nature and did not migrate appreciably from the origin. About 78% of the radioactivity in the soil was extracted with methanol. The major metabolite in the extractable fraction was DDD which represented 33% of the total radioactivity. The reductive dechlorination of DDT to DDD is a known pathway under anaerobic conditions and has been shown to be due to microbial metabolism (5). Since carbon-14 DDT was incor-... 

This requires a biomass which can be metabolized. The process usually involves enzymatic transfer of electrons by micro-organisms from the decomposing biomass (represented in the above equation as CH2O) to the Fe " in Fe " oxides. As seen from eq.16.3, reduction consumes protons and is, therefore, favoured, the lower the pH (see also Chap. 12). It usually takes place when all pores are filled with water (see reviews by Fischer, 1988 and Van Breemen, 1988). Biotic reduction of Fe oxides is now recognized as an important process in the oxidation (metabolism) of organic pollutants in soils by dissimilatory, iron-reducing bacteria. 

The observed ozone-induced growth reductions of roots could result from (a) a direct toxic effect of ozone on the root, (b) an ozone modification of the foliage metabolism which alters the quantity and/or quality of metabolites translocated to the roots, or (c) an alteration in soil chemistry. 

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