Environmental quality standards for a deltamethrin sea louse treatment in marine finfish aquaculture based on survival time analyses and species sensitivity distributions

This paper describes the use of time to event and Species Sensitivity Distribution (SSD) analyses to derive environmental quality standards (EQS) for the synthetic pyrethroid deltamethrin when used to treat lice in marine finfish aquaculture. Long-term EQS are of limited applicability for parasiticides used in coastal aquaculture because initially high concentrations are rapidly dissipated and diluted. Short-term EQS related to likely exposure duration are a more useful management tool. Accelerated Life Testing was used to analyse high-quality, time-specific survival data (LC10 values) for saltwater fish and crustacean species for which observations on survival over several time periods were available. These data were then plotted as SSDs, allowing the estimation of time-specific median HC5 values, protective of 95% of organisms in saltwater assemblages if the test data are representative of species in the field. These analyses show that after 3 h, the HC5 of LC10 values for deltamethrin in saltwater is 9.3 ng L(-1), declining to 1.4 ng L(-1) after 48 h of continuous exposure. Such values are consistent with data on effect concentrations from other lines of evidence, including mesocosm and field studies, and can be used as time-specific EQS when monitoring discharges from aquaculture facilities immediately after the treatment of fish with deltamethrin.