LIFE-STAGE-SPECIFIC TOXICITY OF SEDIMENT-ASSOCIATED CHLORPYRIFOS TO AMARINE, INFAUNAL COPEPOD

The life-stage-specific acute toxicity of sediment-associated chlorpyr ifos to the marine, infaunal copepod, Amphiascus tenuiremis, was asses sed. Chlorpyrifos is a common-use, high K-ow, organophosphate pesticid e. Duplicate 96-h tests were conducted with each major life stage of t he copepod (adult, copepodite, and nauplius) exposed to sediments spik ed with chlorpyrifos. Calculated median lethal concentrations (LC50s) were 66, 74, and 40 mu g chlorpyrifos per kilogram sediment for the ad ult, copepodite, and nauplius stages, respectively. Analysis of covari ance and logistical regression analysis on the mortality data revealed significant (alpha = 0.05) sensitivity differences for the life stage s. The nauplius stage was significantly more sensitive than either the adult or copepodite stages. However, the copepodite stage showed no s ignificant sensitivity difference versus the adult stage. The lowest-o bserved-effect concentrations (LOECs) also showed these relationships, with the naupliar LOEC being almost three times lower than that of ei ther the adult or copepodite stages. A predicted sediment quality crit erion (SQC) based on the equilibrium partitioning theory (EqPT) for ch lorpyrifos was calculated to be 38 mu g chlorpyrifos per kilogram sedi ment. This calculated criterion, supposedly protective of most sedimen t-dwelling invertebrates, was only 2 mu g/kg lower than the LC50 for t he nauplius life stage and far above the LOEC. An EqPT-derived SQC for chlorpyrifos clearly would not be protective of this meiobenthic cope pod.