Distribution, migration and potential risk of heavy metals in the Shima River catchment area, South China

Abstract

The distribution, migration and potential risk of heavy metals in water and soil environments, related to city water supply, were investigated. Heavy metal concentrations in waters from the Shima River water ranged from not detected (n.d.) to 749 μg L⁻¹ for Mn, n.d. to 151 μg L⁻¹ for Ni, 7.00 to 494 μg L⁻¹ for Zn, n.d. to 93.0 μg L⁻¹ for Cu and n.d. to 9860 μg L⁻¹ for Fe. The highest concentration of heavy metals was found at an upstream site in February as a result of industrial effluent discharge. Groundwater (GW1–GW5) and soil (S1–S8) samples along the riverbank showed similar levels of contamination due to a close hydraulic relationship and frequent exchange of water, probably resulting in migration of heavy metals from river water to the aquifer and accumulation at the interface. The mean concentrations of heavy metals in soil profiles were in the ranges of 2.50–19.0 mg kg⁻¹ for As, 2.80–11.2 mg kg⁻¹ for Cd, 20.3–165 mg kg⁻¹ for Cr, 14.5–298 mg kg⁻¹ for Cu, 11.4–102 mg kg⁻¹ for Ni, 7.00–95.0 mg kg⁻¹ for Pb, 40.4–465 mg kg⁻¹ for Zn, 8.80 × 10³–21.8 × 10³ mg kg⁻¹ for Fe, and 62.2–430 mg kg⁻¹ for Mn, showing severe soil pollution by Cd. LUMISTox testing and the potential ecological risk index (RI) were used to assess the potential for adverse ecological effects caused by heavy metals in water and soil media. River water samples posed slight acute toxicity to Vibrio fischeri with luminescence inhibition rates (LIRs) ranging from 24.6% to 38.4% in February. Elevated Zn and Cu concentrations significantly contributed to the toxicity. However, groundwater did not exhibit any toxicity to Vibrio fischeri. The severity of the potential ecological risk for individual metals (E_rⁱ) decreased in the order of Cd > Cu > Ni > As > Pb > Zn > Cr. RI values indicated that all soil samples in the study area posed a high level of ecological risk. Cd contributed significantly (95.5–98.9%) to potential ecological risk in soils.