Joy J. Leaner

Global Mercury Emissions to the Atmosphere from Natural and Anthropogenic Sources

This chapter provides an up-to-date overview of global mercury emissions from natural and anthropogenic sources at country and regional/continental scale. The information reported in Chapters 2–8 is the basis of the assessment reported in this chapter, however, emissions data related to sources and regions not reported in chapters 2–8 have been derived, to the extent possible, from the most recent peer-reviewed literature and from official technical reports. Natural sources, which include the contribution from oceans and other surface waters, rocks, top soils and vegetation, volcanoes and other geothermal activities and biomass burning are estimated to release annually about 5207 Mg of mercury, part of which represent previously deposited anthropogenic and natural mercury from the atmosphere to ecosystem-receptors due to historic releases and part is a new contribution from natural reservoirs. Current anthropogenic sources, which include a large number of industrial point sources are estimated to release about 2917 Mg of mercury on an annual basis, the major contribution is from fossil fuel-fired power plants (1422 Mg yr-1), artisanal small scale gold mining (400 Mg yr-1), waste disposal (187 Mg yr-1), non-ferrous metals manufacturing (310 Mg yr-1) and cement production (236 Mg yr-1). Our current estimate of global emissions suggest that summing up the contribution from natural and anthropogenic sources nearly 8124 Mg of mercury is released annually to the global atmosphere. The evaluation of global emissions presented in this report differs from previous published assessments because in the past, emissions from several sources, i.e., forest fires and coal-bed fires have not been accounted for, and also because of improved knowledge of some anthropogenic and natural sources (i.e., emissions from oceans, vegetation) as suggested by the most up-to-date literature.

Mercury emissions from point sources in South Africa

As a first step towards assessing Hg levels in a systematic approach in South Africa, representatives from the South African government, academia, research councils and key industries recently initiated a South African Mercury Assessment (SAMA) Programme (Leaner et al., 2006). The SAMA Programme has undertaken some limited Hg inventory development and monitoring studies in South Africa. The preliminary results of those studies and that of Hg monitoring undertaken at Cape Points Global Atmospheric Watch Station (Baker et al., 2002), are discussed in this paper.

A review of mercury pollution in South Africa: Current status

The present paper is a review on the status of mercury (Hg) as a pollutant in South African aquatic ecosystems. Spatial patterns of Hg distribution and bioaccumulation in water resources were investigated by collecting and analyzing multimedia samples for physiochemical and Hg-species determination from 62 sampling sites. The data presented showed a wide range in concentrations, which was expected given the array of environmental parameters, water chemistry and sources of Hg. Generally, higher Hg concentrations were measured in environmental compartments impacted by the major anthropogenic Hg sources which, in South Africa, are largely represented by emissions from coal-fired power stations (i.e. Olifants and Upper Vaal WMAs) and artisanal gold mining (i.e., Inkomati WMA). Ancillary water quality parameters (e.g. pH, temperature, DOC, EC and nutrients) were measured and regressed with the measured Hg concentrations to determine which environmental parameters most influenced regional Hg concentrations. The TotHg sed and DOC concentrations were identified as important factors controlling TotHg aq , while TotHgsed were correlated to TotHg aq . This result is indicative of the combined effects of sediment settling and resuspension in the aquatic environment. In contrast, MeHg aq was not correlated to DOC. MeHginvert were correlated to MeHg sed , while MeHg fish were correlated to MeHg aq and water quality variables (chlorides - Cl− and electrical conductivity - EC). A steady progress has been made in Hg research in South Africa. However, despite the substantial knowledge about Hg toxicity, there are still considerable knowledge gaps on the fate and transport of Hg. Hence, further environmental and human health studies are proposed.

Determination of inorganic mercury using a polyaniline and polyaniline-methylene blue coated screen-printed carbon electrode

Inorganic mercury ions (Hg2+) in laboratory prepared solutions were determined with a screen-printed carbon electrode (SPCE) coated with a polyaniline-methylene blue (PANI-MB) polymer layer. The structure and properties of the PANI-MB polymer layer were compared to that of normal polyaniline (PANI) in order to elucidate the structure of the PANI-MB layer. The electrically-conducting polymers were prepared by electrochemical polymerisation of monomer solutions of aniline, and mixed solutions of aniline with methylene blue onto respective screen-printed carbon electrodes (SPCEs). Scanning Electron Microscopy (SEM) analyses of the SPCE polymer coated electrodes have shown that nanostructured materials have formed with the diameters of the PANI nanoclusters and PANI-MB nanorods at approximately 200 nm. Anodic stripping voltammetry (ASV) was used to evaluate a solution composed of 1 × 10−6 M Hg2+, in the presence of the SPCE/PANI-MB polymer sensor electrode. The Hg2+ ions were determined as follows: (i) pre-concentration and reduction on the modified electrode surface and (ii) subsequent stripping from the electrode surface during the positive potential sweep. The experimental conditions optimised for Hg2+ determination included the supporting electrolyte concentration and the accumulation time. The results obtained have shown that the SPCE/PANI-MB polymer sensor electrode operates optimally at a pH 2, with the supporting electrolyte concentration at 0.5 M HCl. A linear calibration curve was found to be in the range of 1 × 10−8 M to 1 × 10−5 M Hg2+ after 120 s of pre-concentration. The detection limit was calculated and found to be 54.27 ± 3.28 µg L−1 of Hg2+. The results have also shown that a conducting polymer modified SPCE sensor electrode can be used as an alternative transducer for the voltammetric stripping and analysis of inorganic Hg2+ ions.

Mercury concentrations in water resources potentially impacted by coal-fired power stations and artisanal gold mining in Mpumalanga, South Africa.

Total mercury (TotHg) and methylmercury (MeHg) concentrations were determined in various environmental compartments collected from water resources of three Water Management Areas (WMAs) – viz. Olifants, Upper Vaal and Inkomati WMAs, potentially impacted by major anthropogenic mercury (Hg) sources (i.e coal-fired power stations and artisanal gold mining activities). Aqueous TotHg concentrations were found to be elevated above the global average (5.0 ng/L) in 38% of all aqueous samples, while aqueous MeHg concentrations ranged from below the detection limit (0.02 ng/L) to 2.73 ± 0.10 ng/L. Total Hg concentrations in surface sediment (0–4 cm) ranged from 0.75 ± 0.01 to 358.23 ± 76.83 ng/g wet weight (ww). Methylmercury accounted for, on average, 24% of TotHg concentrations in sediment. Methylmercury concentrations were not correlated with TotHg concentrations or organic content in sediment. The concentration of MeHg in invertebrates and fish were highest in the Inkomati WMA and, furthermore, measured just below the US EPA guideline for MeHg in fish.