Lead from mining and mineral processing activities to the community via the air-dust pathway: An example from Mount Isa city using human health risk assessment approach

Abstract

This study followed the Australian human health risk assessment procedure from enHealth and utilised an innovative approach of integrated methodologies to study the impacts of lead on the Mount Isa community. The aim of this study was to identify the significant sources of lead via the air-dust pathway at Mount Isa and to estimate the potential impact of the air-dust pathway on human health by using a human health risk assessment approach. The two research questions derived from aims were related to the “issue identification” “hazard assessment” “exposure assessment” and “risk characterisation” of the risk assessment procedure. The first research question considered if lead-containing particulates were dispersed from mining operations via air-dust pathway to the community using a statistically representative set of houses in the Mount Isa City (n=67) to examine the spatial distribution of chemical and physical characteristics, including heavy metal and metalloid total concentrations, lead isotopic feature of the potential sources associated with historical mining and mineral processing activities. High resolution lead isotope ratios for natural outcrops, mine site samples, community samples indicated that roof gutter dust, fallout dust, soil PM10, and outdoor air particulates, floor, interior window sill, window trough, veranda wipe and indoor carpet dust showed close feature to lead isotopic characteristics of the mine site lead ore samples (mean 208Pb/204Pb of 35.8751 ± 0.0018 (SE) and mean 16.1302 ± 0.0006 (SE) of 206Pb/204Pb) from a lead mineralised origin (Urquhart Shale). The Mann-Whitney U Test of lead isotope ratios indicated that carpet dust was not significantly different (p > 0.05) from soil PM10, floor wipes, window sill wipes, and veranda wipes, whereas city fallout dust was not significantly different from haul road dust (p = 0.23) from the mine site, Urquhart Shale lead-bearing outcrops (p = 0.26), and window trough wipes (p = 0.48). The test also showed that Urquhart Shale outcrops were not significantly different (p > 0.05) from the mine site haul road dust (p = 0.89) and surface tailings (p = 0.36) and dust from the city residential area roof gutter dust (p = 0.06) and window trough wipes (p = 0.37) for lead isotopic ratios. The second research question of evaluating the significant lead exposure route was answered by considering if lead-containing particulates at Mount Isa were a significant lead exposure source via inhalation and ingestion routes in the community regarding human health exposure assessment. Total concentrations of lead in soil, air particulates, house wipes were compared with Australian and international health risk guidelines. Lead speciation by synchrotron-based X-ray absorption spectroscopy using X-ray absorption near edge structure (XANES) technique and bioaccessibility of lead in samples using the physiologically-based extraction test (PBET) to give a prediction of bioavailability were also analysed to conduct the hazard assessment. Lead species in samples from Mount Isa city were generally dominated by PbS, Pb-goethite, PbSO4, and other lead containing minerals based on quantitative XANES analysis using linear combination fitting against model compounds. Bioaccessibility data for lead indicated that the mean levels of 41% for all mine dust sample and 20% for dust samples from the community. Lead absorption via ingestion route was identified as more significant than inhalation route at Mount Isa City based on ingested amounts of lead in dust compared with inhaled material. The final approach of the risk assessment procedure in this study was to estimate the health risk to young children living in Mount Isa by predicting the blood lead level with the US EPA Integrated Exposure Uptake Biokinetic Model (IEUBK). The predicted blood lead results for children based on exposure at the statistically representative set of houses in Mount Isa city showed that one house exceeded the Australian NHMRC recommended blood lead level of 10 µg/dL. The significant contribution of soil and dust to lead exposure were obvious, with the median contribution of 19% and 51% respectively. The dominant role of ingestion pathway over inhalation pathway at semi-arid Mount Isa area was identified. This work developed an integrated methodology to assess the human health risk of lead mining and mineral processing activities on the surrounding community in semi-arid environment of Mount Isa following sustainable mining development practices. The characterisation of the human health risk in the study area was finally addressed. The study emphasised the importance of minimising the blood lead levels in children living in Mount Isa whenever possible even though their blood lead concentrations were predicted to be lower than 10 µg/dL. It is clearly from IEUBK model that the increasing blood lead is associated with ingestion of soil and dust. This highlighted the need for mitigation steps to minimise lead exposure of children from soil and dust ingestion at houses in Mount Isa.