Efficiency of uptake of hexachlorobenzene from water by the tellinid clam, Macoma nasuta

Abstract

A study was undertaken to determine the efficiency with which a marine deposit-feeding clam ( Macoma nasuta) extracted hexachlorobenzene (HCB) from water (EPW). An exposure chamber (clambox) was designed that separated the inhalant and exhalant siphons, allowing the collection of ventilated water. Seawater dosed with 14C-labeled HCB was pumped into the inhalant chamber of the clambox. Clams were exposed to three temperatures (12, 17, 22°C) to vary weight-specific ventilation volume ( Vg). Loss of HCB from the exhalant chamber precluded determination of EPW from the difference in HCB concentrations between the inhalant and exhalant chambers. Instead, gross EPW was calculated by dividing the HCB tissue residues by the amount of HCB to which the clam was exposed (water ventilated × the HCB concentration). Gross EPW averaged 82%. Correcting for non-gill uptake (surface sorption of HCB), gill EPW averaged 64–66%, and did not decrease with increasing Vg. In M. nasuta, Vg varied less than two-fold, which may explain the lack of a ventilation effect on EPW. HCB tissue residues were linearly related ( R 2 = 0.93) to gill exposure. The linear relationship between tissue residues and exposure supports a bioenergetics-based bioaccumulation model and indicates that factors that increase Vg, such as low oxygen concentrations, would result in more rapid uptake and a greater body burden.