Stimulatory and toxic effects of acid, pentachlorophenol or zinc on the mineralization of acetate in acid and calcerous soils and subsoil

Abstract

The effect of pollutants on the mineralization of 1 mug/L [14C acetate was studies in bottles with 10 g fresh soil and 10 ml groundwater. The chalk containing sandy surface soil was most sensitive for pentachlorophenol (PCP) giving 10% inhibiyion of the initial mineralization rate (IC10) at 12 mg PCP/kg. Moreover a marked stimulation of the 14CO2 production from acetate was shown to occur at concentrations above 0.1 mg PCP/kg soil. The chalk containing subsurface soil was most sensitive for the addiction of zinc giving an IC10 value of 39 mg Zn/kg, which included the background concentration of 12 mg Zn/kg. Addition of 100 mmol HCl/kg to the chalk containing surface soil gave an rapid drop in the pH of the soil slurry to pH-2.3, which rose to pH=5 in 3 minutes. The IC10 of the acid addition was 4 mmol HCl/kg in this soil. The chalk containing alkaline soil and subsoil neutralized added HCl rapidly and showed a strong sorption of zinc. Nevertheless these soils showed a much higher sensitivity for the addition of acid or zinc and were also more sensitive for pentachlorophenol. Hence the different sensitivity for pollutants was mainly caused by differences between the microbial communities of these soils. Already at natural background levels of acid and zinc effects on sensitive microbial communities living in soils with low levels or zinc or acid can occur. Therefore these low background levels should not be increased till average natural background levels.<br>