Development and evaluation of triggers for sediment toxicity testing of pesticides with benthic macroinvertebrates

Concerns regarding the potential of pesticides that partition into sediments to affect benthic organisms have led to the development of sediment toxicity test methods. However, not all pesticides have the potential to accumulate in sediments or affect benthic organisms. Thus, a scientific 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 relatively adsorptive and persistent in sediment, and also have the potential for toxicity to invertebrates. Trigger endpoints and values are proposed and include soil aerobic degradation rate (time for 50% degradation to occur ≤ 30 d), soil adsorption coefficients (organic carbon partition coefficient ≤ 1000), and Daphnia acute and chronic toxicity (48-h median effective concentration < 1 mg/L or 21-d no-observed-effect concentration < 0.1 mg/L). These data are available internationally for the majority of pesticides. Where appropriate, these preliminary triggers can be augmented by additional data (e.g., water- sediment degradation studies, toxicity data on benthic species) to make more sophisticated triggering eases or risk assessments. An evaluation of the proposed triggers was performed by reviewing regulatory data from standardized studies on 140 pesticides. A total of 22% of the compounds triggered sediment toxicity testing, of which the majority were insecticides and fungicides. For insecticides, fungicides, and herbicides 44, 27, and 6% of compounds within the 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.