Influence of humic acid on the uptake of aqueous metals by the killifish Fundulus heteroclitus

The role of humic acids, over a concentration range of 0 to 20mgL^-1, was investigated in the uptake of three metals (Cd, Cr, and Hg-as both inorganic Hg [Hg(II)] and methylmercury [MeHg]) and a metalloid (As) from the aqueous phase by the killifish (Fundulus heteroclitus). Cadmium uptake showed no relationship with humic acid concentration, whereas Cr, Hg(II), and MeHg uptake showed an inverse relationship, and As uptake increased with increasing humic acid concentration. Concentration factors were >1 for Cd, Hg(II), and MeHg at all humic acid concentrations, indicating killifish were more enriched in the metal than the experimental media, whereas As and Cr generally had concentration factors <1 at the end of a 72-h exposure. The uptake of As and Cr reached steady state within the 72-h exposure, whereas uptake of Cd, Hg(II), and MeHg did not. Uptake rate constants (k_us;mlg^-1d^-1) were highest for MeHg (91-3,936), followed by Hg(II), Cd, and Cr, and lowest for As (0.17-0.29). Dissection data revealed that the gills generally had the highest concentration of all metals under all humic acid treatments. The present study concludes that changes in humic acid concentration can influence the accumulation of aqueous metals in killifish and should be considered when modeling metal bioaccumulation.