Development of species sensitivity distributions and estimation of HC(5) of organochlorine pesticides with five statistical approaches.

Eighteen organochlorine pesticides (OCPs) were studied to develop species sensitivity distributions (SSDs) and calculate hazardous concentration thresholds for 5% of species (HC5), using both parametric (log-normal and log-logistic) and nonparametric bootstrap methods. In order to avoid picking repetitive values in each resample when performing bootstrap, and to determine the influence of fluctuation of toxicity data of single species on the SSDs and HC5, a modified bootstrap method was introduced, which can generate unrepetitive sampling data other than original elements in datasets. This method can enlarge a dataset without any assumption of a special distribution. Combined with parametric methods, modified bootstrap was also used to develop SSDs and determine HC5. The HC5 estimated by five approaches coincide well with each other with good positive correlation. Even if there is intra-species variation in a certain range of toxicity data; SSDs and HC5 are not very sensitive to the local fluctuation of toxicity of single species. The studied OCPs were classified according to their estimated HC5. A lower HC5 indicates higher ecological toxicity potentials. Endrin, DDTs and Endosulfan are OCPs with very high ecological toxicity potential. alpha-HCH has the lowest ecological toxicity potential in the studied OCPs. For OCPs with high ecological potential, more attention should be paid to their ecological risk.