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Title: Evaluation of occupational and environmental exposure to mercury among dental amalgam and chlor-alkali workers in Pakistan and among small-scale gold miners in Cambodia, Burkina Faso, Chile and Sudan
Author: Elgazali, Abdelkarem Abdullah Saad
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2013
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Mercury is a well-known toxic element which can be taken up into the human body in different forms, causing particular harm to the nervous system. Despite this fact, it is still used widely in industrial processes, with chlor-alkali electrolysis one of the most extensive pollution sources of mercury. Though most industries today use mercury-free processes, some chlor-alkali factories still use the mercury process, especially in less developed countries. In addition, small-scale gold mining activity remains the largest global mercury consumer and continues to increase the use of mercury given the upward trend in the price of gold. The aim of this study is to investigate the level of mercury exposure to workers in chlor-alkali factories and a dental hospital in Pakistan. In addition, it is to investigate the level of mercury exposure to miners in small-scale gold mining areas (AGM) in Cambodia, Burkina Faso and Chile. Both investigations were undertaken within the United Nations Environment Programme (management of mercury waste). Within this study, the investigation of mercury exposure to miners was conducted in four small-scale gold mining areas in Sudan. A simple analytical digestion and extraction method for total mercury (T-Hg) analysis in biological and environmental samples with fast sample preparation procedure using CV-AFS and ICP-MS was developed. In addition, for SSIDMS-GC-ICP-MS analysis, the alkaline microwave assisted extract method and acid leaching assisted extract method for Me-Hg analysis in biological samples (hair samples) were developed. These developed analytical methods were used to evaluate the levels of occupational and environmental exposure in the selected areas with Hg hot spots. For Pakistan, to establish chlor-alkali workers' Hg exposure, hair and nail samples of 23 individuals were investigated for total mercury. Within this cohort, 15 individuals had hair total mercury levels above 100 μg g-1, thus exceeding the WHO regarded "safe limit" of 2 μg g-1 in hair Hg by a factor of 50. Several samples showed hair T-Hg levels above 1000 μg g-1, suggesting extreme exposure to Hg. These levels must be regarded as extremely toxic, assuming that these Hg levels in hair correspond to Hg ingestion. In the process of chlor-alkali electrolysis, volatile mercury compounds are formed, including Hg0 and other volatile mercury compounds. These volatile species can adsorb on surfaces, and it is suggested that besides uptake by inhalation, Hg compounds may be adsorbed on keratinous hair and nail material. The investigation of single hairs with synchrotron techniques showed that most of the mercury is found on the outside of the hair, but certain amounts were also metabolised. Adsorption experiments with Hg0 and HgCl2 were conducted to assess the sorption characteristics of these volatile Hg compounds. The results showed that both mercury species' vapour pressures are related to the adsorption of volatile mercury compounds. HgCl2 has a higher vapour pressure and is about two orders of magnitude higher in adsorption than Hg0, suggesting that the chlor- alkali workers have been exposed to HgCl2 in the chlor-alkali plant. Finally, mercury speciation was performed on the ICL chlor-alkali hair samples which showed that almost all mercury was in inorganic form. The source of Me-Hg in the hair seems to be dietary, as no correlation between inorganic and Me-Hg in the hair could be found. The highest value for Me-Hg is around 5.0 μg g-1, which is in the range of concentration found in communities with a high fish diet. Finally, the high mercury result suggests that the mercury (Hg) in the hair samples from workers in the ICL chlor-alkali is from external adsorption rather than from inhalation and was subsequently incorporated into the hair. Nevertheless, in the second chlor-alkali factory in Pakistan (SCL chlor-alkali factory), the average total mercury concentrations in hair and nails are low and almost at control level. However, in this factory, mercury cell technique was phased out a few years ago. This factory now uses membrane cell instead of mercury cell technology. For the dental hospital sector in Pakistan, inorganic mercury concentrations were 6 times higher than Me-Hg concentration in hair samples i.e. Me-Hg and In-Hg in hair accounted for, on average 14.13 % and 85.87 % of T-Hg respectively for these dental workers. However, the high mercury levels in hair could be due to exposure to amalgam. For AGM areas, the T- Hg concentration (μg g-1) in hair samples from AGM miners in Burkina Faso (mean, 3.80 μg g-1) were compared with Cambodian AGM miners and Sudan AGM miners (mean 5.78 and 5.04 μg g-1 respectively). This mean value was significantly lower than that found in the hair of miners in the Cambodia and Sudan AGM areas. This indicates that the AGM miners in these countries are exposed to mercury vapour during the AGM processes. Otherwise, the AGM workers in Cambodia are also exposed to considerable amounts of methylmercury (Me-Hg) through seafood consumption that is a more toxic Hg form. However, the long-term implications for water bodies such as River Nile and Red Sea ecosystems, fish as food and irrigation water use (e.g. for rice paddies) may be disastrous. Therefore, further investigation of Hg analysis in hair and soils should be conducted in these areas to analyse the risk of Hg contamination.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Mercury ; Industrial safety