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. Sediment-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 survival of a sediment-cultured meiobenthic copepod, Amphiascus tenuiremis, exposed to aqueous and sediment-associated FV phases. Empirical results were compared to predictions generated by the equilibrium partitioning approach to sediment quality criteria. Additionally, sediment-associated FV effects on a generic group of marine nematodes and one other species of field-collected benthic copepod, Paronychocamptus wilsoni, were tested. For sediment-associated FV, nematodes showed the highest acute sensitivity (96-h LC5, = 26.1 < 33.2 < 40.5 mug-FV g-1 carbon), followed by the field-collected copepod. Paronychocamptus wilsoni (96-h LC50: 61.9 < 73.9 < 91.7), and cultured copepod Amphiascus tenuiremis (96-h LC25: 56.2 < 84.2 < 147.4). In a major departure from equilibrium 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 mortalities than in sediment-associated FV exposures. Based on EqPT, the high sediment-carbon (3.8%) particulate phase probably reduced porewater FV concentrations. However, the particulate phase in this study appeared a more important FV exposure route to the sediment-ingesting A. tenuiremis than porewater or even direct aqueous exposures.