CONTENTS AND RISK ASSESSMENT OF HEAVY METALS IN SURFACE WATER IN THE MAIN CANAL OF MIDDLE ROUTE OF THE SOUTH-TO-NORTH WATER DIVERSION PROJECT

The concentrations of 18 heavy metals were detected in surface water from 11 sampling sites along the Main Canal of Middle Route of the South-to-North Water Diversion Project from May, 2018 to June, 2020, and the health risk assessment model recommended by USEPA and Species sensitivity distributions (SSD) method were used to estimate the human health hazard risk levels and ecological risk levels, respectively. The results showed that all the heavy metals were frequently detected, and the average concentrations ranked as Fe>Sr>Ba>Zn>Ti>Ni>Mn>Cu>V>Cr>As>U>Rb>Se>Pb>Bi>Co>Cd, with concentrations of all heavy metals not exceeding the class I water standard of Quality Standard for Surface Water (GB 3838—2002) and the limit of Standard for Drinking Water Quality (GB 5749—2006). The health risk assessment showed that the mean values of the total health risk of adults and children caused by 8 common heavy metals (Cr, Cd, As, Cu, Pb, Zn, Ni and Mn) were at 10^–8 range in surface water from the Main Canal of Middle Route of the South-to-North Water Diversion Project. Based on the SSD curves of 8 heavy metals (AS, Ni, Pb, Cr, Zn, Se, Cd and Cu), the hazardous concentrations for 5% of species (HC5) and the potential affected fractions (PAF) were calculated. The results demonstrated that the percentage of the whole aquatic organisms affected by the investigated heavy metals were below 5% in surface water of the Main Canal of Middle Route of the South-to-North Water Diversion Project, but Cu and Zn affect 8.54% and 16.77% of the algal population, respectively, and Cr affect 6.44% of the crustacean population. Overall, our results indicated that the current contents of heavy metals remain low in surface water of the Main Canal of Middle Route of the South-to-North Water Diversion Project, posing no potential health risks to humans, and that several heavy metals may pose potential risks to the population status of algal and crustaceans, which needs further investigations.