An Investigation of the Kinetic Processes Influencing Mercury Emissions from Sand and Soil Samples of Varying Thickness

Abstract

Mercury flux from HgCl 2 –treated sand and untreated soil samples of varying thickness (0.5–15 mm) were measured in dark and light under a Teflon dynamic flux chamber. Mean emissions over a 5.5‐d sampling period showed an increase with depth for sand samples between 0.5 and 2 mm, but increasing depth above 2 mm had no effect. First‐order kinetic models showed strong goodness of fit to the data and explained a high degree of variability in the emissions profile of all sand samples ( R 2 = 0.70–0.98). Soil samples showed an initial emissions peak that was not correlated with depth, suggesting a very shallow process at work. However, longer‐term “baseline” emissions, measured as mean emissions between Days 4.5 and 5.5, did show a relationship with depth. First‐order kinetic models showed good fit for soil samples up to 4 mm thick ( R 2 = 0.66–0.91); however, thicker samples did not show a consistent fit to first‐ or second‐order kinetic models (1° R 2 = 0.00–0.46; 2° R 2 = 0.00–0.54). The data suggest that mercury emissions from soil samples may follow a multicomponent model for which more than one component is affected by incident radiation.