Bioavailability of heavy metals in surface sediment of Anzali International Wetland, Iran

Abstract

The study aimed to determine the metal concentration, mobility, bioavailability, ecological risk, and toxicity in the surface sediment of Anzali International Wetland. Pb, As, Cd, Cr, Ni, Zn, and Fe Concentrations in 33 samples are reported here. A five-step sequential extraction technique was used to determine the chemical forms of metals. To assess ecological risk (Er), Risk Index (RI), Toxic Unit (TU), the sum of Toxic Units (ΣTUs), Toxic Risk Index (TRI), and modified Hazard Quotients (mHQ) were calculated. Mean concentrations of heavy metals (mean ± S.D.) were Zn (95.46±20.71) > Cr (19.79±2.79) > Ni (18.49±5.23) > Pb (13.97±3.20) > As (6.45±1.87) > Cd (0.90±0.34). Cd exhibited the highest mobility and bioavailability, while Cr, Pb, Zn, Ni, and As, were found mainly in residual fractions, which are non-bioavailable and pose a little ecological risk. Cd showed the highest levels in the reducible and organic phases; Cr, Pb, Zn, and Ni had the lowest ones. Ecological risk assessment suggested that Cd had “moderate” to “considerable” risk potential at some sampling sites. Risk index indicated that Anzali sediment had “low” to “moderate” risk potential (150 < RI < 300). Based on values of RI, ∑TUs, and mHQ we conclude that sediment of Anzali Wetland has low to moderate risk potential and low toxicity.