Establishing a method to assess comprehensive effect of gradient variation human health risk to metal speciation in groundwater

Highlights: • A new method to assess variation health risk of metal species was proposed. • The approach is based on pH and metal total concentration variation. • An application of the method for Ni species in groundwater was studied. • Only in pH 6.5–8.5, HI_Ni would increase with the increase of total-Ni. • Only at alkaline condition, HI_Ni would decrease with the increase of pH. A method was proposed to evaluate comprehensive effects of pHs and total metal concentration (TMC) variation for metal speciation human health risk in groundwater. The method used for the health assessment considered comprehensive and mutative effects caused by oral ingestion of groundwater based on human health risk assessment model and MINTEQ simulation. The results demonstrated that the dissolution rate of Ni²⁺ was affected by pH and Ni total concentration (total-Ni). With the increase of pH, the Ni²⁺ dissolved rate was smaller in the higher total-Ni at same pH. Ni²⁺ was dominant components contributed to health risk in groundwater. With the increase of pH in various total-Ni, HI_Ni keep constant at first, and then decreased gradually. The HI_Ni values of Ni speciation above acceptable level only in high total-Ni with alkaline conditions. The obtained results to verify that metals speciation were determined in health risk, and variation factors (pH and metal total concentration) played important role in risk estimation. These results provide basic information of heavy metal pollution control as well as remediation management.