Health risk assessment for human exposure by direct ingestion of Pb, Cd, Zn bearing dust in the former miners' village of Jebel Ressas (NE Tunisia)

Mining activity in Jebel Ressas (1880-1956) generated important quantities of wastes. The former miners' village is expanding very close to the waste dumps which are highly concentrated in Pb, Zn and Cd. Under the semi-arid Mediterranean climate, wind erosion triggers the transport of contaminated dust towards the village. A health risk may exist for inhabitants related to their exposure to contaminated dust via ingestion, inhalation and dermal contact. This study is dedicated to the evaluation of the health risk after direct ingestion of dusts. Seven samples of dusts were collected in living places over the village. Anomalous metal concentrations in dusts range respectively from 0.16 wt% to 1.14 wt% of Pb, 0.35 wt% to 2.49 wt% of Zn and 14 to 109 mg/kg of Cd. SEM-EDS analysis of the dust particles shows that calcite is dominant and that metalliferous minerals are mainly Pb and Zn carbonates and Zn silicates. Iron oxy-hydroxides exist in small proportions and Pb and Zn sulfides are scarce. Modeling the quantity of dissolved metals in a simulated gastric fluid was performed taking into account the dust mineralogy and the daily ingested quantities of dust, ranging from 100 mg for adults to 200 mg for children. The ratio of dissolved metals to initially ingested ones defines the bioaccessibility factor. It gives the fraction of metals able to reach the blood through the intestinal wall. Modeling the dissolution of two dust samples, the most and the less concentrated ones in metals, was performed considering a gastric fluid with two extreme pH values (0.93 and 5.0). All dust minerals totally dissolve except cerussite for the most concentrated sample in a gastric fluid of pH 5. Therefore, the bioaccessibility factor of Zn and Cd is equal to 1, that of Pb ranges between 0.27 and 1. Then, an estimation of the occurrence of risk was calculated from the ratio of the daily exposure dose by direct ingestion and the reference dose. The risk occurs with a ratio above 1. The global risk of ingestion of three metals is high for the children, especially for Pb with a ratio reaching 39. The risk for adults appears for Pb with a ratio of 4.6 in the case of ingestion of most concentrated dusts. However, the integration of the other routes of exposure in the calculation of the risk must be taken into account for a thorough estimation.