Health risk assessment and benchmark of lead pollution in agricultural soils in East Yunnan, China

Heavy metal contamination of agricultural soil has posed risks and potential dangers to human and livestock, due mainly to most heavy metals are toxic in nature that can cause serious health illness, even at very low concentration. Excessive heavy metals, such as lead, enter the ecological system from the agricultural runoff and industrial discharges to agricultural products of food chain. Since both high geological background and mining activities simultaneously determine the agricultural soils in eastern Yunnan, the lead pollution in agricultural soil has drawn much widespread attention recently. In this study, a simultaneous sampling and analysis test was performed on agricultural soils and products in 6 cities (prefectures) in eastern Yunnan, China, aiming to characterize the lead accumulation in agricultural land. A health risk assessment model was used to evaluate the health risks that caused by lead in the agricultural soils in eastern Yunnan to residents. A species-sensitive distribution model (Log-logistic) was used to construct the species sensitivity distribution curve (SSD) of different crop varieties, and to reverse benchmark values of soil lead safety, according to the protection of 95% and 5% of crop categories. The result showed that: 1) The average content of lead in agricultural soils from various cities (prefectures) in eastern Yunnan was from more to less in the order of Honghe Prefecture , Qujing city, Zhaotong city, Wenshan prefecture, Yuxi city,Kunming city. The average lead content of Zhaotong city, Qujing city, Wenshan prefecture, and Honghe prefecture exceeded the screening value of lead pollution risk released by National Standards of China. 2) The total point exceeding rate of agricultural products in the 6 cities (prefectures) of eastern Yunnan was 11.9%, where the various types of crops showed the different ability of absorbing and enriching lead. Specifically, peas and peanuts from beans had higher lead accumulation capacity, followed by lettuce from rhizome, rape from leafy vegetables, and wheat from cereals. 3) The health risk assessment showed that there was no significant non-carcinogenic risk and carcinogenic risk to the residents. The non-carcinogenic risk of lead to children was higher than that of adults in various regions of eastern Yunnan, where the non-carcinogenic health risk index of various exposure routes was ranked from much to less in the order of hand-oral intake, skin exposure, breathing inhalation. 4) In the species sensitivity distribution model (Log-logistic), the benchmark values of soil lead health risk were inversely deduced for agricultural products in eastern Yunnan. When rhizomes, nightshades, planting beans, cereals crops were planted, the critical value of Pb were13.0, 19.7, 35.1, 11.3, 18.1 mg/kg, respectively; and the alarm value of Pb were 269.5, 481.3, 500.7, 367.5, 560.3 mg/kg, respectively. It can provide scientific basis for establishing more accurate local standard and realizing the safe utilization of lead-contaminated soil in agricultural soil in eastern Yunnan and similar regions.