A method linking the toxic effects at community-level with contaminant concentrations

In this study, we developed a method to quantify and link the toxic effects in community-level ecosystems with concentrations of petroleum hydrocarbons. The densities of Platymonas helgolandica var. tsingtaoensis, Isochrysis galbana, and Brachionus plicatilis in single-species tests and customized ecosystems were examined in response to a concentration gradient of petroleum hydrocarbons ranging from 0 to 8.0mgL(-1). A three-population ecological model with interspecies competition-grazing relationships was used to characterize population sizes with concentrations of petroleum hydrocarbons. A threshold concentration of the simplified plankton ecosystem of 0.376mgL(-1) for petroleum hydrocarbons was calculated from the proposed model, which was higher than the no-effect concentration of 0.056mgL(-1) derived from the single-species toxicity tests and the predicted no-effect concentration of 0.076mgL(-1) calculated from the species sensitivity distribution. This finding indicates that interspecies competition and grazing reduced the toxic effect of petroleum hydrocarbons at the community level. The sensitivity analysis for model parameters demonstrates that plankton population biomasses are highly sensitive to filtration rates. Antagonism between interspecies interactions and petroleum hydrocarbon toxicity was attributed to the reduced filtration rate and zooplankton grazing pressure. The proposed method is a simple means to address the concern regarding the impacts of ecological interactions on ecological risk assessments of pollutants.