Life-stage-specific toxicity of sediment-associated chlorpyrifos to a marine, infaunal copepod

The life-stage-specific acute toxicity of sediment-associated chlorpyrifos to the marine, infaunal copepod, Amphiascus tenuiremis, was assessed. Chlorpyrifos is a common-use, high K(ow), organophosphate pesticide. Duplicate 96-h tests were conducted with each major life stage of the copepod (adult, copepodite, and nauplius) exposed to sediments spiked with chlorpyrifos. Calculated median lethal concentrations (LC50s) were 66, 74, and 40 μg chlorpyrifos per kilogram sediment for the adult, copepodite, and nauplius stages, respectively. Analysis of covariance and logistical regression analysis on the mortality data revealed significant (α = 0.05) sensitivity differences for the life stages. The nauplius stage was significantly more sensitive than either the adult or copepodite stages. However, the copepodite stage showed no significant sensitivity difference versus the adult stage. The lowest-observed-effect concentrations (LOECs) also showed these relationships, with the naupliar LOEC being almost three times lower than that of either the adult or copepodite stages. A predicted sediment quality criterion (SQC) based on the equilibrium partitioning theory (EqPT) for chlorpyrifos was calculated to be 38 μg chlorpyrifos per kilogram sediment. This calculated criterion, supposedly protective of most sediment- dwelling invertebrates, was only 2 μg/kg lower than the LC50 for the nauplius life stage and far above the LOEC. An EqPT-derived SQC for chlorpyrifos clearly would not be protective of this meiobenthic copepod.