revised final - Agency for Toxic Substances and Disease Registry ...

MERCURY 413
5. POTENTIAL FOR HUMAN EXPOSURE
particulate mercury levels were 0.00003 µg/m 3 at the control site, compared with mean concentrations at
the on-site stations ranging from 0.00006 to 0.00024 µg/m 3 (Turner and Bogle 1993).
Mercury has been identified in air samples collected at 25 sites of the 714 NPL hazardous waste sites
where it has been detected in some environmental media (HazDat 1998).
5.4.2 Water
Concentrations of mercury in rainwater and fresh snow are generally below 200 ng/L (ppt) (EPA 1984b).
Fitzgerald et al. (1991) measured total mercury in rainwater from May through August 1989 at Little
Rock Lake, Wisconsin. The total mercury concentrations ranged from 3.2 to 15.2 ng/L (ppt). Mercury
concentrations in precipitation collected in Minnesota during 1988 and 1989 averaged 18 ng/L (ppt) for
an average annual mercury deposition of 15 µg/m 2 (Glass et al. 1991). Antarctic surface snow contained
a mean mercury concentration of less than 1 pg/g (ppt) (Dick et al. 1990). In Ontario, Canada, mercury
present in precipitation at an average concentration of 10 ng/L (ppt) accounted for more than half of the
mercury inputs to surface waters compared with inputs from stream runoff, suggesting that atmospheric
deposition is a significant source of mercury in surface waters (Mierle 1990). Lindberg et al. (1994)
measured total mercury in rain collected at Walker Branch Watershed, Tennessee from August 1991 to
April 1992. Rain concentrations of total mercury ranged from 7.57 ng/L (ppt) in February 1992 to
17.4 ng/L (ppt) in April 1992. Burke et al. (1995) reported that the average concentration of mercury in
precipitation samples measured over Lake Champlain was 8.3 ng/L (ppt) for the sampling year, and the
average amount of mercury deposited per precipitation event was 0.069 µg/m 2 . The highest
concentrations of mercury in precipitation samples occurred during spring and summer months. Guentzel
et al. (1995) reported results of the Florida Atmospheric Monitoring Study from 1992 to 1994. These
authors found that the summer time wet season in south Florida accounted for 80 to 90% of the annual
rainfall mercury deposition. Depositional rates in south Florida are 30–50% higher than those in central
Florida. Measurement of monomethylmercury in precipitation samples ranged from