Bioavailability of sediment-bound and algal metals to killifish Fundulus heteroclitus

We used a radiotracer technique to experimentally assess whether As(V), Cd, Cr(III), Hg(II), and methylmercury (MeHg) bound to sediment from 3 contaminated field sites (Baltimore Harbor, Elizabeth River, and Mare Island) and the green alga Dunaliella tertiolecta are bioavailable to killifish Fundulus heteroclitus. Algae are a component of the killifish diet in salt marshes, and although killifish do not actively consume sediment, some is accidentally ingested due to attachment to benthic prey. For both sediment and algae, the assimilation efficiencies (AE) of ingested metals were highest for MeHg, followed by Hg(II), As, and Cd, and lowest for Cr. Following sediment intubations, AE values ranged from 0.01-0.03% (Cr) to 10-14% (MeHg), and ranged from 0.7% (Cr) to 82% (MeHg) following algal intubation. Following sediment intubations, loss rate constants (k_ef) were similar for As, Cd, and Hg(II) and lowest for MeHg, whereas following algal intubation, the k_ef values were highest for As, followed by Cr, Hg(II), and Cd, and lowest for MeHg. At the end of depuration, tissue distribution data showed that Cd and Hg(II) remained primarily associated with the viscera, whereas As and MeHg were distributed throughout the body. Calculated trophic transfer factors (TTF) showed that only MeHg bound to algae, and Elizabeth River sediment is expected to biomagnify at this trophic step (TTF > 1). Metals can accumulate to high concentrations in sediment in industrialized coastal areas, but the present study indicates that the risk of exposure for killifish from ingesting contaminated sediment is minimal.