Sediment- and aqueous-phase fenvalerate effects on meiobenthos: implications for sediment quality criteria development

Abstract

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 LC 50 = 26·1 < 33·2 < 40·5 μg-FV g −1 carbon), followed by the field-collected copepod. Paronychocamptus wilsoni (96-h LC 50: 61·9 < 73·9 < 91·7), and cultured copepod Amphiascus tenuiremis (96-h LC 25: 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 μg-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.