Comparison of Aqueous and Solid-Phase Uptake for Hexachlorobenzene in the Tellinid Clam Macoma Nasuta (Conrad): A Mass Balance Approach

Abstract

The uptake of sediment-associated hexachlorobenzene (HCB) by the deposit-feeding clam Mucoma nusuta (Conrad) was determined using a clam ventilation chamber. Clams were exposed to [ ''C]HCB-dosed sediment, and the 14C amounts were measured in inhalant and exhalant waters, fecal pellets and soft tissues. The volume of water the clam ventilated and the amount of fecal pellets produced were measured. The contributions of 10 possible uptake routes to HCB tissue residues were estimated using a bioenergetic-based bioaccumulation model. Mass balance results indicate that uptake of HCB by the gut from ingested solids was the single most important route, accounting for 63 to 84% of HCB tissue residues. The next largest route was uptake from interstitial water ventilated across the gills, which accounted for 11 to 12% of tissue residues. Uptake of HCB from overlying water was minimal. These results indicate that sediment-bound HCB is bioavailable to benthic deposit feeders such as Mucoma and supports the contention that ingested sediment is an important uptake route for highly lipophilic pollutants.

Toxicokinetics in aquatic systems: Model comparisons and use in hazard assessment

“…There are fewer data to evaluate the accuracy of kinetic models with sediment contaminants. In a short-term laboratory experiment with Mucoma exposed to sediment-associated hexachlorobenzene, the mass balance derived from a BE model was very close to the observed tissue residues (92-114%) [75]. When using independently derived values for k, and k,, an RC model predicted BAFs by Macomu within 90% (range 69-165%) of observed BAF for a range of PCB congeners, although the kinetics were less successful in predicting the time to steady state [ 1101.…”

“…Application of the BE model to sediment-ingesting invertebrates includes 10 potential uptake routes, even when considering sediment as a single food source [75]. In most cases, however, modeling interstitial and overlying water fluxes and the ingested sediment as the food source should be adequate.…”

“…In the simplest case, sorption can be incorporated as a constant (i.e., simple partitioning phenomenon) [75]. The where S = toxicant sorption onto body surface (micrograms per gram).…”

“…These potential sources are readily accommodated in kinetic models, except there are no references for multiple sources using the CV model in aquatic studies. These additional sources generally involve the diet of the organism, whether it is sediment detrital material [31,39,44,75,78,79,112,113] or prey for fish [24,46,47,66,106,. The extent of the dietary route depends on the feeding rate [79,113]; assimilation efficiency, which can vary with feeding rate [78]; and concentration in the food [66].…”

Toxicological benchmarks for screening contaminants of potential concern for effects on sediment-associated biota: 1996 revision

“…In contrast to this, marine burrowing species frequently ingest sediment (Adams 1987). For the clam Macoma nasuta, uptake of highly lipophilic pollutants occurred primarily by ingestion of solids (63 to 84%), followed by ventilation of interstitial water across the gills (1 1 to 12%) (Boese et al 1990). This may be because Macoma nasuta predominantly ventilates overlying water, not interstitial water.…”