Soil ecotoxicity of polycyclic aromatic hydrocarbons in relation to soil sorption, lipophilicity, and water solubility

A data set was generated aiming to predict the toxicity of PAHs to soil organisms. Toxicity data include the effects of 16 PAHs on the survival and reproduction of the soil-dwelling springtail Folsomia fimetaria. The results show that only PAHs with reported log K-ow values less than or equal to 5.2 (i.e., naphthalene, acenaphthene, acenaphthylene, anthracene, phenanthrene, fluorene, pyrene, and fluoranthene) significantly affected the survival or reproduction of the test organisms. Threshold values for the toxicity of the individual PAHs could be expressed as pore-water concentrations by the use of reported organic carbon-normalized soil-pore-water partitioning coefficients (K-oc values). For the PAHs with a log K-ow +/- 5.2, toxicity significantly increased with increasing lipophilicity of the substances (r(2) = 0.67; p 0.012; n = 8), suggesting a narcotic mode of toxic action for most substances. However, the position of anthracene in the regression plot indicated a more specific mode of toxic action than narcosis, and removing this data point yielded the following regression equation: log EC10 (mumol/L) = -0.97 log K-ow + 4.0 (r(2) = 0.80; p = 0.006; n 7). Using this quantitative structure-activity relationship (QSAR) to calculate threshold values for the toxicity of the remaining nontoxic substances (benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, dibenz[a,h]anthracene, benzo[a]pyrene, perylene, and indeno[1,2,3-cd]pyrene), the absence of toxicity could in most cases, be explained by a limited water solubility, indicating that these substances do act by narcosis as the mode of toxic action and that their toxicity is governed by concentrations in the pore-water. The results provide important input to future model predictions of the ecological risk posed by PAH contaminated sites.