Microbial enzyme activity and biomass relationships in soil ecotoxicology

Abstract

AbstractMultispecies toxicity testing is emerging as a useful tool in ecotoxicological assessments. Understanding the relationship between soil microbial biomass levels and microbial enzyme activities (MEA) is basic to clarifying ecotoxicity effects and bioremediation potential in soil systems.Saturated subsurface soils were exposed to fluctuating concentrations of a mixture of 1‐choromethyl‐2‐methyl naphthalene, phenothiazine and 2,4,2′4′‐tetrachlorobiphenyl. An enzyme suite composed of dehydrogenase, amylase, esterase, alkaline phosphatase, and protease was monitored, along with simultaneous biomass estimates using total plate counts for facultative aerobes and anaerobes, acridine orange direct counts (AODC) for total bacteria, and endogenous protein. Results indicate that quantitative biomass levels (AODC) remained relatively constant. Mean log10 values of AODC biomass reached a plateau between 6.45 (±0.15) and 7.06 (±0.10) with coefficients of variation <3.0. AODC adjusted to biovolume carbon estimates indicated that bacterial organic carbon could represent 0.03 and 0.35% of the mean measured levels of total organic carbon depending on the number of cells and the volume of each cell in μm3. Multivariate statistical analyses identified significant correlations among some MEA, biomass measurements, and chemical pollutants. The general implications of these results to ecosystem function and bioremediation potential are discussed.