Health Risk Assessment and Environmental Benchmark of Heavy Metals in Cultivated Land in Mountainous Area of Northwest Guizhou Province

Abstract

An extensive investigation of heavy metal (Cd, Hg, As, Pb, and Cr) levels in 137 pairs of soil-maize/rice samples was conducted in cultivated land from a typical karst mountain area in the Northwest of Guizhou Province. A health risk assessment model was used to assess the health risks of those areas, and the environmental benchmarks of heavy metals in soils were evaluated using the species sensitivity distribution (SSD) model. The results showed that the soils of maize and rice were polluted by heavy metals. Cd was the primary pollutant, with an exceeding rate ranging from 87% to 445%. The contaminated level of maize fields was higher than those of rice fields. In contrast, only 3.51% and 13.4% of Cd content in maize kernels and rice grains exceeded the national threshold, and the Cd heavy metal accumulation ability of rice was higher than that of maize. The carcinogenic and non-carcinogenic risks of heavy metals for adults and children in the study area were at a low level. The carcinogenic risk of rice consumption was slightly higher than that of maize, and the health risk to children was higher than that to adults. The results derived from the SSD method showed that the 95% and 5% hazardous concentrations (HC5 and HC95) of maize fields were 0.67 for Cd, 771.99 for As, 40.85 for Pb and 609.88 for Cr mg·kg-1, and HC95were 48.47 for Cd, 159.67 for As, 1735.68 for Pb and 1671.74 for Cr mg·kg-1, respectively. The HC5 values of rice fields were 2.42 for Cd, 8.88 for As, 41.41 for Pb and 27.84 for Cr mg·kg-1, and the HC95 values were 48.47 for Cd, 159.67 for As, 1735.68 for Pb and 1671.74 for Cr mg·kg-1, respectively. The HC5 values of Cd, As, and Cr in maize fields and Cd in rice fields were significantly higher than the soil risk screening values in the current standard, and the HC95 values of the two fields were higher than the soil risk intervened values. The results indicated that the current standard would be too strict to evaluate the actual pollution level of soil heavy metals in this area.