Effect of soil contaminant extraction method in determining toxicity usingthe Microtox (R) assay

This project examined the influence of different extraction methods on the measured toxicity of contaminated soils collected from manufactured gas pla nt (MGP) sites differing in soil composition and contaminant concentration. Aged soils from a number of MGP sites were extracted using a saline soluti on, supercritical fluid extraction (SFE), and Soxhlet extraction. Toxicity was assessed using two forms of Microtox(R) tests: acute aqueous tests on s aline and SFE soil extracts and solid-phase tests (SPTs) an soil particles, Microtox SPTs were performed on soils before and after SFE to determine re sulting toxicity reduction. Three hypotheses were tested: (1) Toxicity of s oil extracts is related to contaminant concentrations of the extracts, (2) measured toxicity significantly decreases with less vigorous methods of ext raction, and (3) supercritical fluid extractability correlates with measure d toxicity. The EC50s for SPTs performed before and after SFE were not diff erent for same soils but were significantly greater after extraction for ot her soils tested. The most significant toxicity reductions were observed fo r sails exhibiting the highest toxicity in both preextraction SPTs and acut e aqueous tests. Acute Microtox tests performed on SFE extracts showed sign ificantly lower EC50s than those reported from saline-based extraction proc edures. Toxicity of the soils measured by Microtox SPTs was strongly correl ated with both SFE efficiency and measures of contaminant aging. Data from this project provide evidence of sequestration and reduced availability of polycyclic aromatic hydrocarbons (PAHs) from soils extracted via physiologi cally based procedures compared to vigorous physical extraction protocols.