In Vitro Bioaccessibility of Lead in Artisanal Mining Contaminated Soils and Sediments from the Anka Area, NW Nigeria

Abstract

The gastric bioaccessibility of Pb was investigated in soils and sediments from five villages in the Anka area of north-western Nigeria which has been adversely affected by artisanal mining of gold from lead-rich ores. In vitro bioaccessibility experiments were used to determine the extractability of Pb in order to evaluate the human health risk, especially to children below the age of five. The concentration of Pb in the simulated gastric fluids ranges from ~ 198 to 41740 µg.g⁻¹ (mean, 9732 µg.g⁻¹), with corresponding human bioaccessible fraction between ~ 29 and 100% (mean, ~ 60%). Chemical daily intake (CDI, µg/Kg/Day) values of between 111 and 41587 are generally very high compared to the tolerable daily intake (TDI) of ~ 3.6 µg Pb/Kg/Day. The high bioaccessibility is a result of high total concentration of Pb and the presence of highly soluble carbonate and oxide minerals in the ores. These results point to the very adverse health effects likely to result from incidental hand-to-mouth ingestion of soils by children in the affected villages. The results further show that the low pH of gastric juices enhances the extraction of Pb. Given the likelihood of sub-nutrition in the affected communities, characterized by skipping of meals, which can result in lowering of the pH over extended periods, the risk of Pb poisoning is further increased. This study was based on a hand-to-mouth ingestion scenario alone, but as other exposure routes, such as eating improperly washed vegetables and inhalation of dust are possible, the risk might even be higher. This, along with the fate of extracted Pb in the intestinal environment may need to be evaluated in order to fully quantify the bioavailability of Pb in the area.