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This scoping study presents an investigation of the total and bioaccessible mercury concentrations in road dust (RD) from three international urban sites, where a one-off sampling campaign was conducted at each. This was done to address the hypothesis that the matrix in which mercury is found influences its ability to become accessible to the body once inhaled. For that purpose, the samples were analysed for total and pulmonary bioaccessible mercury and the data compared to the chemical structure of individual particles by SEM. The results obtained from this study suggest that a high mercury content does not necessarily equate to high bioaccessibility, a phenomenon which could be ascribed to the chemical character of the individual particles. It was found that the Manchester samples contained more pulmonary soluble mercury species (as determined by elemental associations of Hg and Cl) in comparison to the other two samples, Curitiba, Brazil, and Johannesburg, South Africa. This finding ultimately underlines the necessity to conduct a site-specific in-depth analysis of RD, to determine the concentration, chemical structure and molecular speciation of the materials within the complex matrix of RD. Therefore, rather than simply assuming that higher bulk concentrations equate to more significant potential human health concerns, the leaching potential of the metal/element in its specific form (for example as a mineral) should be ascertained. The importance of individual particle behaviour in the determination of human health risk is therefore highlighted.

-Mercury concentrations (Hg TOT ) were analysed in total and size fractions in urban dust. The results showed that Hg TOT ranged from 270 to 1350 µg kg -1 for PM 25 particle size fraction. The distribution was as follows: Hg Industrial > Hg CBD > Hg Residential . The Hg TOT showed a positive correlation with percent volume of the PM 25 size fraction. This indicated that as the particles size decreased, the Hg TOT increased. The dust was mainly characterized by high concentration levels of quartz (74.3 to 97.6 wt. %). The tailings dumps showed similar levels of quartz (65 to 81 wt. %), which indicated that tailings are the major anthropogenic sources of mercury in the dust. Both, the tailings dumps and the dust samples showed well defined crystalline structures of the quartz coated with trace elements.

Abstract. The growing global concern over the release of mercury to the environment has prompted specific inventories that quantify mercury emissions from various sources. Investigations of atmospheric mercury have been mostly done on gaseous species. Although, to assess human expose to mercury, especially in urban areas, the inhalable dust should be included in a study. The Witwatersrand Basin in South Africa is one of the most important gold mining regions in the world. Mercury (Hg), which occurs in gold-bearing ores, was also used for gold recoveries in previous centuries (19 th and early 20 th century) and presently in illegal artisanal mining.The consequences of these mining activities were the release of Hg to the environment, mainly due to AMD from tailings dumps which are presently reprocessed. The city of Johannesburg is a multimillion population exposed strongly to industrial pollution. The aim of this study was to determine the magnitude of mercury pollution in this urban area and assess its bioavailability. The gaseous samples were collected by trapping mercury on various gold traps. Dust samples were collected from a ground and on inhalation levels (1-2 m above a ground). They were later separated into different fractions by micro sieving. Bioavailability of mercury in inhalable dust (25 µm) was tested by leaching collected samples with artificial lung fluid (ALF, pH 4.5), Gray's solution (pH 7.4) and water. The leaching conditions were selected to mimic lungs environment (incubator at 30 0 C, time 24 hrs, rotation of samples 150 rpm). Total concentrations of mercury in dust fractions were also determined after microwave digestion. The results showed extremely high concentration levels of mercury in air and dust in industrial areas. Especially high levels were found around presently reprocessed old gold tailings dumps, up to 900 000 µgl -1 . The levels dropped significantly in CBD area but still showing elevated concentrations up to 10 µgl -1 . They depend strongly on prevailing wind directions, dry and wet seasons, and day time. Leaching experiments showed that the Gray's solution extracts more mercury from the dust followed by ALF and much lower by water. This suggests that most of the mercury inhaled with dust will be extracted in the deep interstitial parts of the lungs. In the upper region of lungs extraction will occur to a lesser extent.