Pollution Characteristics and Risk Assessment of Heavy Metals in Dujiangyan Irrigation District, China

Dujiangyan Irrigation District is the largest irrigation district in China. To understand heavy metal pollution and its potential hazards, the contents and distribution of typical heavy metals in rivers, soils and plant samples from 19 sites were studied and their ecological risks and health risks were evaluated. The results showed that the concentrations of nine heavy metals in the river water did not exceed the safe values (GB 3838-2002). They showed a trend of the highest in the middle reaches followed by the upstream and downstream areas, and the concentration in the dry season (winter) was higher than that in the wet season (summer). The average values of heavy metals in the soil were 0.3–3.08 times the background values in Chengdu. The highest average enrichment factor was Cd (7.52). The Nemerow pollution index indicated that the quality of the river water was at a clean level. However, the heavy metals in the soil at sites B1 and B3 were at a heavy pollution level. The potential ecological hazard index also showed that Cd in the soils of the study area at sites B1 and B3 was very highly hazardous and 26% of the sample area was at a highly hazardous level. The cumulative carcinogenic health risks due to total heavy metals exceeded the safety limits for both children and adults. Furthermore, the risks were higher in children than in adults. This study provides theoretical support for dealing with heavy metal pollution in the irrigation district.