Salinity effects on the bioavailability of aqueous metals for the estuarine killifish Fundulus heteroclitus.

Estuarine organisms experience varying salinity conditions on a daily and seasonal basis, and these fluctuations could influence the amount of metal accumulated from the aqueous phase. The present study experimentally assessed the role of salinity (0, 2, 6, 12, and 25 ppt) on the uptake of As, Cd, Cr, inorganic Hg [Hg(II)], and methylmercury (MeHg) into the euryhaline killifish (Fundulus heteroclitus) from the aqueous phase using gamma-emitting radioisotopes. Patterns of metal uptake as a function of salinity varied by metal. Chromium showed no relationship with salinity; Cd, which was most affected by salinity, showed an inverse relationship; and As, Hg(II), and MeHg uptake increased as salinity increased from 0 ppt to 25 ppt. Arsenic (salinities ≤ 6 ppt) and Cr were regulated by the fish, whereas Cd, Hg(II), and MeHg were not. Cadmium, Hg(II), and MeHg are chloro-complexed, increasing bioavailability for Hg(II) and MeHg, and reducing bioavailability for Cd. Concentration factors (CFs) were >1 at all salinities for Cd, Hg(II), and MeHg, indicating that the fish were more enriched in the metal than the surrounding water, whereas As and Cr CFs were <1 at all salinities. Uptake rate constants (k(u)s) were highest for MeHg (0.79-2.29 L g(-1) d(-1)), followed by Hg(II), Cd, Cr, and lowest for As (0.0004-0.0008 L g(-1) d(-1)). Tissue distribution of each metal was determined by dissections. Data for Cd showed that as salinity increased, the concentration of this metal increased in the viscera, whereas it decreased in the head and gills, suggesting that drinking to osmoregulate may account for a portion of Cd uptake from the aqueous phase in marine fish.