Dust from Zambian smelters: mineralogy and contaminant bioaccessibility

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.     

Heavy metal recovery from the fine fraction of solid waste incineration bottom ash by wet density separation

Journal of Material Cycles and Waste Management - This work is aimed at exploring the recovery of heavy metals from the fine fraction of solid waste incineration bottom ash. For this study,...     

Cannabis sativa L. and Brassica juncea L. grown on arsenic-contaminated industrial soil: potentiality and limitation for phytoremediation

Environmental Science and Pollution Research - Phytoremediation represents a natural method to remove contaminants from soil. The goal of this study was to investigate the potential of...     

DOM-Flocculation: A suitable approach for separating free and DOM-bound herbicides?

Dissolved organic matter (DOM) in soil solution is considered to interact with herbicides enhancing their mobility and promoting subsequent leaching. Batch experiments were conducted to test if free and DOM-bound herbicides can be separated by a DOM-flocculation technique with Cu as a coagulant. DOM was extracted from the H and A horizons of two soils (Terric Histosol, Cumuli-Calcaric Cambisol) and from the O horizon of a forest soil (Humic Cambisol). DOM-solutions (100 mL) were fortified with the herbicides terbuthylazine and pendimethalin (100 μg active ingredient each) and equilibrated for 14 hours. After DOM-flocculation with Cu (addition of 0,5 mM CuCl₂) herbicide recovery was determined in the supernatant solutions and in the precipitate of Humic Cambisol-DOM, respectively. Recovery of the herbicides from pure water was 85–99% and was not influenced by the addition of Cu. At low pH (4,8–5,3) DOM-flocculation of different DOM-extracts was insufficient and varied in a range of 18 – 90%. Herbicide recovery from DOM-solutions decreased moderately for terbuthylazine (60–90%) and strongly for pendimethalin (5 – 30%). In general, the addition of Cu caused no further reduction of herbicide recovery from supernatant solutions, except for Humic Cambisol-DOM. The effects of Cu-addition were most evident for pendimethalin (strongly reduced concentration in the supernatant solutions) and were considered to be caused by a flocculation of DOM-bound moieties. Flocculation of Humic Cambisol-DOM increased from 18 – 24% at pH 5 to > 95% at pH 8. However, at this pH the formation of Cu(OH)₂ as a sorbing subcomponent of the flocculated matter lead to an overestimation of DOM-bound pendimethalin. Calculating this side effect 6% of pendimethalin added was DOM-bound. Only traces of terbuthylazine (< 1%) were found in the solid matter of flocculated Humic Cambisol-DOM. To sum up, the new approach to separate freely dissolved herbicides from DOM-bound moieties not fully corresponded to our expectations. DOM-flocculation was found to depend strongly on pH-environment influencing not only DOM-herbicide interactions but also the clear separation of DOM-bound herbicides from herbicides in solutions.