Effects of Physical Chemistry and Bioturbation by Estuarine Macrofauna on the Transport of Hydrophobic Organic Contaminants in the Benthos

Abstract

Effects of macrobenthos on hydrophobic organic contaminant (HOC) transport during two seasons characterized by high (summer) and low (winter) bioturbation were studied in the laboratory. HOC burial and loss from microcosms were followed in the presence and absence of macrofauna after the introduction of particle-associated polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) to the sediment−water interface. During summer, HOC burial depths and modeled diffusive losses (DL) increased with compound relative effective diffusivity ( ), consistent with enhanced fluid transport rates due to macrofauna. Although more than 50% of HOC loss was independent of macrofauna, macrofauna-mediated processes had significant effects on the long-term (56 d) removal of the hydrophobic compounds TCB and BaP. A possible mechanism for this effect is direct particle resuspension by macrofauna, which has been shown to enhance loss of materials from our experimental systems. During winter, macrofauna had little effect on HOC burial but may have enhanced HOC retention. Thus, effects of macrofauna-mediated processes depend on HOC physico-chemistry as well as the temporal phasing and duration of contaminant−biota interac tions. Bioturbation has important implications for contaminant fate because macrofauna significantly alter the distributions of HOCs near the sediment−water interface.