SEDIMENT-PHASE AND AQUEOUS-PHASE FENVALERATE EFFECTS ON MEIOBENTHOS -IMPLICATIONS FOR SEDIMENT QUALITY CRITERIA DEVELOPMENT

Estuarine sediments sequester heavy metals and non-ionic pollutants at concentrations manyfold greater than those in the water column. Sedim ent-associated pollutants probably have a greater impact on the wholly sediment-dependent meiobenthos than any other invertebrate group. In this study we compared acute effects of a highly lipophilic synthetic pyrethroid pesticide, fenvalerate (i.e. FV, log K(ow) = 6.20), on surv ival of a sediment-cultured meiobenthic copepod, Amphiascus tenuiremis , exposed to aqueous and sediment-associated FV phases. Empirical resu lts were compared to predictions generated by the equilibrium partitio ning approach to sediment quality criteria. Additionally, sediment-ass ociated FV effects on a generic group of marine nematodes and one othe r species of field-collected benthic copepod, Paronychocamptus wilsoni , were tested. For sediment-associated FV, nematodes showed the highes t acute sensitivity (96-h LC5, = 26.1 < 33.2 < 40.5 mug-FV g-1 carbon) , followed by the field-collected copepod. Paronychocamptus wilsoni (9 6-h LC50: 61.9 < 73.9 < 91.7), and cultured copepod Amphiascus tenuire mis (96-h LC25: 56.2 < 84.2 < 147.4). In a major departure from equili brium partitioning theory (EqPT) predictions, A. tenuiremis exposed to aqueous FV concentrations 7300 x higher than EqPT porewater values (i .e. 0.017 to 0.068 mug-FV liter-1) exhibited only 1-27% higher mean mo rtalities than in sediment-associated FV exposures. Based on EqPT, the high sediment-carbon (3.8%) particulate phase probably reduced porewa ter FV concentrations. However, the particulate phase in this study ap peared a more important FV exposure route to the sediment-ingesting A. tenuiremis than porewater or even direct aqueous exposures.