Atmospheric mercury emissions from polluted gold mining areas (Venezuela)

摘要

Soil, waste rock and mud from mercury-gold amalgamation mining areas of El Callao (Venezuela) are highly enriched in Hg (0.5-500 μg g~(-1)) relative to natural background concentrations ( < 0.1 μg g~(-1)). Mercury fluxes to the atmosphere from twelve polluted sites of this area were measured in situ (6 a.m. to 8 p.m.) using a Plexiglas flux chamber connected to a portable mercury analyzer (model RA-915+; Lumex, St. Petersburg, Russia). Mercury fluxes ranged between 0.65 and 420.1 μg m~(-2) h~(-1), and the average flux range during the diurnal hours was 9.1-239.2 μg m~(-2) h~(-1). These flux values are five orders of magnitude higher than both reported world background Hg fluxes (1-69 ng m~(-2) h~(-1)) and the regional values, which are in the range 2-10 ng m~(-2) h~(-1). The flux results obtained in this study are, however, similar to those measured at Hg polluted sites such as chloro-alkali plants or polymetallic ore mining districts ( > 100,000 ng m~(-2) h~(-1)). The results from this study also show that Hg emissions from the soil are influenced by solar radiation, soil temperature and soil Hg concentration. Our data suggest that solar radiation may be the dominant factor affecting Hg° emission since the major species of mercury in polluted soil is Hg° (85-97% of total Hg). The simple release of Hg° vapor is probably the dominant process occurring with incident light in the field. The apparent activation energy for mercury emission indicates that the volatilization of mercury mainly occurred as a result of the vaporization of elemental mercury in soil. The degree of Hg emission differed significantly among the soil sites studied, which may be due to variations in soil texture, organic matter content and soil compaction.