Persistent organic pollutants (POPs) associated with a platinum mine in the Limpopo Province, South Africa
South Africa ratified the Stockholm Convention (SC), which became legally binding on 17 May 2004. This Convention targets 12 particularly toxic persistent organic pollutants (POPs) for virtual elimination. The Convention also requires parties to reduce the release of organochlorine pesticides and the intentionally- and unintentionally-produced POPs such as dioxins, furans and polychlorinated biphenyls (PCBs) (referred to as dioxin-like chemicals). Dioxins are a heterogeneous mixture of chlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) congeners. These substances were never intentionally produced but are produced as by-products of industrial processes (such as metallurgical processes and bleaching of paper pulp). They can also be formed during natural processes such as volcanic eruptions and forest fires. The largest contributor to releases of PCDD/Fs in the environment is incomplete combustion from waste incinerators leading to the unintentional production of these compounds. Polychlorinated biphenyls (PCBs) are used in transformers and capacitors, but can also be formed unintentionally during industrial and thermal processes. Dioxin-like chemicals (PCDD/Fs and/or PCBs) are classified as persistent because of the following characteristics: lipophilicity and hydrophobicity; resistance to photolytic, chemical and biological degradation and they are able to travel long distances. As South Africa is a semiarid region, POPs will be less prone to travel here because these substances favour colder regions with high soil organic matter. Fish, predatory birds, mammals (including humans) absorb high concentrations of POPs through the process of bio-concentration, leading to bio-accumulation of these substances in the fatty tissue. PCDD/Fs occur as unwanted trace contaminants in air, water, land, in residues and products (such as consumer goods e.g. paper and textiles). The distribution of these chemicals into various matrices is problematic since they cause damage to the environment and human health. These chemicals pose a threat to human health when found in high concentrations that may lead to acute hepatoxicity and dermal toxicity (chloracne). Long-term exposure to low concentrations of these substances might lead to chronic effects such as reproductive problems and carcinogenicity. Since ferrous and non-ferrous metal production is a source of dioxin-like chemicals, a platinum mine in the Limpopo Province, South Africa, was selected for this investigation. The aim of the study was to determine if there are dioxin-like chemicals associated with platinum mining and processing, and if the H4IIE reporter gene bio-assay could be used to semi-quantify and assess the potencies of the complex environmental and process samples by determining their Toxic Equivalency Quotients (TEQ). The implications of the sources to the formation of dioxin-like chemicals regarding the SC were investigated and recommendations were made to improve this study. Samples were collected from tailings dams, woodchips, a dumpsite and slag from the smelter at Union Section. Samples were extracted with the Soxhlet apparatus using hexane as solvent. The percentage total organic carbon (%TOC) was determined for each sample to normalise the data. The method used was the Walkley-Black method. In determining the TEQ of each sample, the H4IIE luc cell line was used. The cells of the H4IIE luc line are genetically modified rat hepatoma cells stably transfected with a luciferase firefly gene. The luciferase gene is activated by the presence of dioxin-like compounds and the concentration of the enzyme is measured as relative light units (RLUs). The amount of RLUs is directly proportional to the dioxin load in the extract. This method is rapid, cost and time-effective in determining the TEQ when compared to chemical analysis. The TEQ2o-valuesin the various samples, as determined with the H4IIE luc cell line, ranged from 0.007 ngTEQ/kg to 54.06 ngTEQ/kg. Thermal processes at the smelter, sorption of hydrophobic organic compounds (HOCs) to soil and tailings, and external sources such as anthropogenic activities contributed to high TEQ2o-values. Climatic conditions, wind, precipitation, and solubility of HOCs into surfactants lead to low TEQ20. The smelter at Union Section had a very high TEQ20of 44.62 ngTEQ/kg compared to Impala Platinum mine (5.15 ngTEQ/kg). This implies that workers at Union Section are possibly exposed to low and high concentrations of dioxin-like chemicals. Long-term exposure to these compounds could lead to bio-accumulation in the fatty tissue of the mine workers, leading to chronic effects such as reproductive problems and cancer. The air emission of the furnace at the smelter was 0.03 gTEQ/annum and the release of the PCDD/Fs into the slag was 0.60 gTEQ/annum. By effectively managing the smelter it is possible to reduce the TEQ. The TEQ of each sample increased due to normalising the data. The normalised TEQ20 ranged from 0.94 ng TEQ/kg to 42497.48 ngTEQ/kg. Dioxin-like chemicals are present on a platinum mine, but at varying quantities and the effects of these compounds might be detrimental to the environment and the workers at the platinum mine. Further analyses of the health impacts associated with the platinum mine are needed. The H4IIE reporter gene bio-assay could be used to effectively determine the TEQ of each sample. Although this investigation has identified the formation and presence of dioxin-like chemicals at certain stages of mining and processing, not all of the processes were investigated. Some of these processes have the potential to add, and even destroy, these chemicals, affecting potential human exposure and amounts released to the environment. This, however, requires further investigation. The financial assistance of the National Research Foundation (NRF) towards this research is hereby acknowledged. Opinions expressed and conclusions arrived at, are those of the author and are not necessarily to be attributed to the NRF.
- ETD@PUK