The effect of salinity on binding of Cd, Cr, Cu and Zn to dissolved organic matter

Salinity can affect binding of metals to humic acid and thus affect bioavailability, however, the effects are poorly understood. The fraction of Cu, Zn, Cd and Cr (at 100 μg/L) complexed with Suwannee River Humic Acid (SRHA) was measured at salinities of 0, 1, 3, 10, and 15 psu using 1000 Dalton ultrafiltration membranes. In distilled water, 10 mg SRHA/L bound at least 40% of each metal. Except for Cu, metal binding decreased to less than 20% at salinities between 1 and 15 psu. Copper binding decreased to 27% at 3 psu, but increased to approximately 60% bound at 15 psu. Copper complexation with natural dissolved organics from a local estuary was also measured and ranged from 25 to 100%.