Pesticides of Potential Ecological Concern in Sediment from South Florida Canals: An Ecological Risk Prioritization for Aquatic Arthropods

Abstract

A two-tier ecological risk assessment was conducted for pesticides monitored in sediment at 36 sampling sites in south Florida freshwater canals from 1990–2002. For tier 1, we identified the chemicals of potential ecological concern (COPECs) as DDT, DDD, DDE, chlordane and endosulfan based on their exceedence of sediment quality standards at 20 sites. For 12 sites with data on the fraction of organic carbon in sediments, whole sediment concentrations of COPECs were converted to pore water concentrations based on equilibrium partitioning. In tier 2, a probabilistic risk assessment compared distributions of pore water exposure concentrations of COPECs with effects distributions of freshwater arthropod response data from laboratory toxicity tests. Arthropod effects distributions included benthic and non-benthic arthropod species for chlordane (n = 9), DDD (n = 12), DDE (n = 5), DDT (n = 48), and endosulfan (n = 26). The overlap of predicted pore water concentrations and arthropod effects distributions was used as a measure of risk. DDE was the most frequently detected COPEC in sediment at the 12 sites. Chlordane was present at only one site. The mean 90th centile concentration for pore water exposure was highest for endosulfan and lowest for DDT. The estimated acute 10th centile concentration for effects was highest for chlordane and lowest for DDD. The probability of pore water exposures of COPECs exceeding the estimated 10th centile concentrations for species sensitivity distributions of arthropod acute toxicity data was between 0 and 1%. The estimated NOEC 10th centile concentration from arthropod chronic toxicity distributions was exceeded by the estimated 90th centile concentration for pore water distributions at three sites. Endosulfan had the highest potential chronic risk at S-178 in the C-111 canal system, based on the probability of pore water exposure concentrations exceeding the arthropod estimated chronic NOEC 10th centile at 41%. The COPEC with the next highest probability of exceeding the chronic NOEC 10th centile was DDD at 17.7% and 19.8% in the Everglades Agricultural Area (at S-2 and S-6). DDT had minimal potential chronic risk. Uncertainties in exposure and effects analysis and risk characterization are discussed.