Screening of native low mercury accumulation crops in a mercury-polluted mining region: Agricultural planning to manage mercury risk in farming communities

Abstract

Historical mercury (Hg) mining in the Wanshan Hg mining area in southwest China and other regions worldwide has contaminated soils and left a legacy of health risks for communities consuming crop products harvested from these soils. Agricultural planning strategy is urgently needed in these regions for reducing human exposure to Hg pollution through selecting native low-Hg-accumulating crops for future planting in contaminated farmlands. For this purpose, 43 existing crops grown on the farmlands across the Wanshan Hg mining areas (with a total of 4566 ha farmlands) were screened for identifying their Hg concentrations and accumulation capacities. A total of 679 sets of samples were collected, and Hg concentrations were in the range of 2.4–1075 μg kg−1 in the edible sections of the studied crops, and 0.6–789.6 mg kg−1 in the corresponding soils. Four types of the investigated crops had Hg concentrations in their edible sections, which were lower than the Chinese governmental reference values (10–20 μg kg−1 in fresh weight). These four crops include radish (2.03–10.71 μg kg−1, n = 13), strawberry (2.80–10.43 μg kg−1, n = 15), corn (1.23–21.32 μg kg−1, n = 28) and potato (0.84–13.39 μg kg−1, n = 41). The four crops were planted again in the second year at two contaminated farmlands with soil Hg concentrations of 105 ± 5.2 mg kg−1 in Aozhai village and 23 ± 3.3 mg kg−1 in Wawu village, and consistent results with those from the field survey were obtained, i.e., the four crops had the Hg concentrations lower than the Chinese governmental reference values. Based on these findings, a land-use strategy was proposed for the farmlands with different soil Hg concentrations in the Wanshan Hg mining area for properly planting the four screened low-Hg-accumulating crops. Implementing this strategy would reduce Hg accumulation in the edible sections of agricultural products by up to 92% while increasing the economic output by 3.6 times as compared to the current cropping practice in the region. Thus, the agricultural planning strategy developed in the present study has large potential in reducing human dietary Hg exposure while preserving local horticulture.