An investigation of the kinetic processes influencing mercury emissions from sand and soil samples of varying thickness.

Mercury flux from HgCl2-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 ofvariability in the emissions profile of all sand samples (R = 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 (R2 = 0.66-0.91); however, thicker samples did not show a consistent fit to first- or second-order kinetic models (1 degree R2 = 0.00-0.46; 2 degree R2 = 0.00-0.54). The data suggest that mercury emissions from soil samples may follow a multicomponent model for which more