Dust from Zambian smelters: mineralogy and contaminant bioaccessibility

Abstract

Metal smelting is often responsible for local contamination of environmental compartments. Dust materials escaping from the smelting facilities not only settle in the soil, but can also have direct effects on populations living close to these operations (by ingestion or inhalation). In this particular study, we investigate dusts from Cu-Co metal smelters in the Zambian Copperbelt, using a combination of mineralogical techniques (XRD, SEM/EDS, and TEM/EDS), in order to understand the solid speciation of the contaminants, as well as their bioaccessibility using in vitro tests in simulated gastric and lung fluids to assess the exposure risk for humans. The leaching of metals was mainly dependent on the contaminant mineralogy. Based on our results, a potential risk can be recognized, particularly from ingestion of the dust, with bioaccessible fractions ranging from 21 to 89% of the total contaminant concentrations. In contrast, relatively low bioaccessible fractions were observed for simulated lung fluid extracts, with values ranging from 0.01% (Pb) up to 16.5% (Co) of total contaminant concentrations. Daily intakes via oral exposure, calculated for an adult (70 kg, ingestion rate 50 mg dust per day), slightly exceeded the tolerable daily intake limits for Co (1.66× for fly ash and 1.19× for slag dust) and occasionally also for Pb (1.49×, fly ash) and As (1.64×, electrostatic precipitator dust). Cobalt has been suggested as the most important pollutant, and the direct pathways of the population's exposures to dust particles in the industrial parts of the Zambian Copperbelt should be further studied in interdisciplinary investigations.

The role of organic colloids in the sequestration and mobilization of copper in smelter-impacted soils

“…The top-down approach would involve the formation of CuS x phases through the breakdown of larger (micrometer-size) particles most likely emitted by the smelter. For example, Lanteigne et al, 36,57 Knight and Henderson 47 and Ettler et al 58 showed that micrometer-size CuS x phases are common in smelter-emitted particulate matter (PM) in the surcial soils of Sudbury, Rouyn-Noranda and Namibia, respectively, however, numerous observations point against this top-down approach:…”

Contaminant Binding and Bioaccessibility in the Dust From the Ni‐Cu Mining/Smelting District of Selebi‐Phikwe (Botswana)

“…However, it is assumed that larger inhaled particles (2.5–10 μm) are cleared from the airways by the mucociliary escalator, swallowed, and transported into the gastrointestinal tract so that only particles <2.5 μm can access the deep lung (e.g., Kastury et al., 2017 ; Meza‐Figueroa et al., 2020 ; Morman & Plumlee, 2013 and references therein). It is also known that the release of contaminants in a simulated lung fluid (SLF) is substantially lower compared to the highly acidic SGF, especially because of the near‐neutral pH of the SLF (see, e.g., Ettler et al., 2014 ; Plumlee & Morman, 2011 ; Thomas et al., 2018 ). For this reason, we decided to perform oral bioaccessibility tests only, which correspond to the “worst‐case scenario.” The bioaccessibility extractions were carried out according to the experimental protocol called SBRC‐G (gastric phase extraction using the Solubility Bioaccessibility Research Consortium assay) adopted by US EPA ( 2007 , 2017 ).…”

“…Whereas many bioaccessibility studies have been conducted in developed parts of the world, similar investigations are still relatively rare in the sub‐Saharan Africa, where direct exposure to (contaminated) dust is expected to be significantly higher than in high‐income countries. The high risks of metal(loid) contaminant intake through dust ingestion and inhalation have been demonstrated in pioneering biomonitoring and bioaccessibility studies from the ore mining and processing areas of DR Congo (Banza et al., 2009 ; Cheyns et al., 2014 ), Namibia (Ettler et al., 2019 ; Kříbek et al., 2014 ; Mapani et al., 2010 ; Nejeschlebová et al., 2015 ), Zambia (Ettler et al., 2012 , 2014 , 2020 ; Kříbek et al., 2019 ; Yabe et al., 2018 ) and Uganda (Mwesigye et al., 2016 ).…”

A novel two-step sequential bioaccessibility test for potentially toxic elements in inhaled particulate matter transported into the gastrointestinal tract by mucociliary clearance

“…[23] In addition, PM 10 collected on different types of filters (quartz fibre filters [24, 25], Teflon filters [26] and cellulose nitrate filters [27]) have been analysed. A key study [3] proposed a novel in vitro simulated epithelial lung fluid that contained high molecular mass proteins, antioxidants and a surfactant, in addition to inorganic components, and so more closely simulated conditions in the real human respiratory system.…”