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A system, based on annular gold-coated denuders, was optimized
and used in the atmospheric sampling of mercury in urban and rural sites of
the Alta Floresta, a region in the Brazilian Amazon. Results showed that vapour
phase mercury (Hgv) is dominant in samples collected
in both sites. However, particulate mercury (Hg) may sometimes be
significant at the urban site, with values representing up to 77% of
the total Hg collected during sampling, but may also be insignificant at the
same site, depending on the gold commercialization activity and, probably,
on the meteorological conditions during the sampling period. The presence
of mercury in both the vapour and particulate phases in the atmosphere of
the urban site can explain the high mercury concentrations found in urban
dust reported for some cities in the Amazon, and also the relatively high
Hg concentrations found in soils adjacent to the urban centre of Alta Floresta.
It appears that the urban dust of “garimpo” areas in the Amazon
can act as an efficient adsorber of Hgv emitted by gold dealer
operations during the purification process. Mercury emissions from gold dealer
shops in the Amazon have been considered as a human health risk through the
inhalation of Hg vapour. However, although true for indoor sites, the significant
contribution of particulate phase Hg shown in this study in outdoor urban
sites calls for a re-evaluation of the risk assessment estimates performed
up to now in urban centres in the Amazon.
An annular Au-coated denuder system for the atmospheric sampling of Hg was optimized by evaluating the effects of temperature, r.h. and air flow rate. The desorbed Hg was determined by cold vapour AAS. It was necessary to decontaminate the denuders before use, due to high blank values; repeated use made them more efficient. Air flow rates above 3 l/min resulted in a rapid fall in Hg retention. Retained masses were high and constant at r.h. 45-70% but decreased above this value. Field measurements were made at rural and urban sites, and the levels of vapour phase and particulate Hg are discussed.
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Journal of Environmental Monitoring
- Information Point
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