DEVELOPMENT AND EVALUATION OF TRIGGERS FOR SEDIMENT TOXICITY TESTING OF PESTICIDES WITH BENTHIC MACROINVERTEBRATES

Concerns regarding the potential of pesticides that partition into sed iments to affect benthic organisms have led to the development of sedi ment toxicity test methods. However, not all pesticides have the poten tial to accumulate in sediments or affect benthic organisms. Thus, a s cientific rationale for identifying appropriate compounds (triggering) for regulatory sediment toxicity testing is required. Here we propose that testing should only be required for compounds that are relativel y adsorptive and persistent in sediment, and also have the potential f or toxicity to invertebrates. Trigger endpoints and values are propose d and include soil aerobic degradation rate (time for 50% degradation to occur greater than or equal to 30 d), soil adsorption coefficients (organic carbon partition coefficient greater than or equal to 1000), and Daphnia acute and chronic toxicity (48-h median effective concentr ation < 1 mg/L or 21-d no-observed-effect concentration < 0.1 mg/L). T hese data are available internationally for the majority of pesticides . Where appropriate, these preliminary triggers can be augmented by ad ditional data (e.g., water-sediment degradation studies, toxicity data on benthic species) to make more sophisticated triggering cases or ri sk assessments. An evaluation of the proposed triggers was performed b y reviewing regulatory data from standardized studies on 140 pesticide s. A total of 22% of the compounds triggered sediment toxicity testing , of which the majority were insecticides and fungicides. For insectic ides, fungicides, and herbicides 44, 27, and 6% of compounds within th e group met the triggers, respectively. Those compounds that triggered testing are probably representative of the classes of pesticides that might be expected to raise concerns for sediment toxicity.