Degradation and impact of phthalate plasticizers on soil microbial communities

To assess the impact of phthalates on soil microorganisms and to supplement the environmental risk assessment for these xenobiotics, soil was treated with diethyl phthalate (DEP) or di (2-ethyl hexyl) phthalate (DEHP) at 0.1 to 100 mg/g. Bioavailability and membrane disruption were proposed as the characteristics responsible for the observed fate and toxicity of both compounds. Diethyl phthalate was biodegraded rapidly in soil with a half-life (t(50)deg) of 0.75 d at 20 degrees C, and was not expected to persist in the environment. The DEHP, although biodegradable in aqueous solution (t(50)deg < 15 d at 20 degrees C), was recalcitrant in soil, because of poor bioavailability (only 10% degraded by 70 d at 20 degrees C) and was predicted to account for the majority of phthalate contamination in the environment. Addition of DEP or DEHP to soil at a concentration similar to that detected in nonindustrial environments (0.1 mg/g) had no impact on the structural diversity (bacterial numbers, fatty acid methyl ester analysis) or functional diversity (BIOLOG) of the microbial community. At concentrations representative of a phthalate spill, DEP (>1 mg/g) reduced numbers of both total culturable bacteria (by 47%) and pseudomonads (by 62%) within 1 d. This was due to disruption of membrane fluidity by the lipophilic phthalate, a mechanism not previously attributed to phthalates. However, DEHP had no effect on the microbial community or membrane fluidity, even at 100 mg/g, and was predicted to have no impact on microbial communities in the environment.