In order to reveal the transfer factor and perform health risk assessments of heavy metals in soil-crop systems in the high incidence area of nasopharyngeal carcinoma (NPC) in Guangdong province of China, the farmland system of Sihui City in the high incidence area of NPC was selected as the research object, and rice, lettuce, and corresponding soil samples were collected. As, Cu, Hg, Mn, Ni, Pb, and Cd in the soil and crop samples were analyzed. Based on the contents and chemical forms of seven heavy metals, the environmental pollution, bioavailability, and transfer factors of heavy metals in the soil-crop system were assessed using statistical analyses, pollution index evaluations, and transfer factor methods, and the health risks of adults and children in the study area were assessed using the health risk assessment model recommended by the U.S. Environmental Protection Agency. The results showed that the farmland soil in the study area was basically clean (P=0.43); Cd and Mn mainly existed in a bioavailable state, Hg mainly existed in a potentially available state, and As Cu, Ni, and Pb mainly existed in a residual state. The lettuce was safe (P=0.48), while the pollution index of rice (P=7.66) was higher than that of lettuce, and the main polluting element was Pb (PI=10.25). The results of soil pollution assessments are not completely consistent with those of crop pollution assessments, so they should be combined with the bioavailability of heavy metals and crop effects for correlation analyses. Cd and Cu are more easily absorbed by lettuce, while Cd, Cu, and As are more easily enriched by rice. Special attention should be paid to Cd and Cu pollution in farmland soils, and As pollution should be of focus in paddy fields. In the study area, the non-carcinogenic risk index (HI) value of edible lettuce for adults and children was less than 1 and the average value of the total carcinogenic risk index (Risk) of edible lettuce was less than 1×10-4. Therefore, the health risk of edible local lettuce was within the acceptable range. The average HI index of rice for adults and children was more than 1 and the main non-carcinogenic factor was Pb; the risk index of rice was more than 1×10-4, and the main carcinogenic factor was As. Rice consumption in the study area will cause certain health risks, and the threat to adults is greater than that to children. Therefore, As in rice may be related to the high incidence of NPC in Sihui City. It is suggested that the remediation of heavy metals in farmland soils be strengthened or that residents be forbidden to plant or eat local rice and other crops with greater health risks.
Keywords: health risk assessment; heavy metals; high incidence area of nasopharyngeal carcinoma; soil crop system; transfer factor.