Large quantities of mercury (Hg) have been placed in municipal landfills from a wide array of sources, including fluorescent lights, batteries, electrical switches, thermometers, and general waste. Despite its known volatility, persistence, and toxicity in the environment, the fate of this Hg has not been widely studied. Using automated flux chambers and atmospheric sampling, we quantified the primary pathways of Hg vapor releases to the atmosphere at two municipal landfill operations in south Florida for eight days in April 1997. These pathways included landfill gas (LFG) releases from passive and active vent systems, passive emissions from landfill surface covers of different ages (including CH 4 "hot spots"), and emissions from daily activities at a working face (WF). Hg vapor was released to the atmosphere at readily detectable rates from all sources measured. Emission rates ranged from ~1 to 20 ng m -2 hr -1 over aged surface covers (generally comparable to background soils), from ~6 to 2400 ng/hr from LFG vents and flares, and from ~5 to 60 mg/hr at the WF. In general the fluxes increased from older to newer landfills, from fresh to aged cover, and from passive to active venting systems. Limited data suggest that methyl-and other organo-mercury compounds may also be emitted from these sites, suggesting an important area for future research. We estimate that atmospheric Hg releases from municipal landfill operations in the state of Florida are on the order of 10 kg/yr, or <1% of the estimated total anthropogenic Hg releases to air in this region.

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L-shell x-ray production cross sections by 0.25 -2.5-MeV 2He ions in 28Ni, »Cu, »Ge, 33AS, 37Rb 3/Sr 3QY, 40Zr, and~Pd axe reported. The data are compared to the first-Born approximation and the ECPSSR theory that accounts for the projectile energy loss (E) and Coulomb deflection (C) as vvell as the perturbed-stationary-state (PSS) and relativistic (R) effects in the treatment of the target I.-sheH electron. Surprisingly, the first Born approximation appears to converge to the data while the ECPSSR predictions underestimate them in the low-velocity limit. This is explained as the result of improper use of single-hole fluorescence yields. A heuristic formula is proposed to account for multiple ionizations in terms of a classical probability for these phenomena and, after it is applied, the ECPSSR theory of I.-shell ionization is found to be in good agreement~ith the data.

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