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

MERCURY 411
5. POTENTIAL FOR HUMAN EXPOSURE
concentrations of mercury over lakes in Wisconsin averaged 2.0 ng/m 3 (Wiener et al. 1990) and ranged
from 6.3 ng/m 3 to 16.0 ng/m 3 above the water surface of the mercury-contaminated Wabigoon River in
Ontario (Schroeder and Fanaki 1988). Mean vapor concentrations of mercury in air over a forested
watershed (Walker Branch Watershed) in Tennessee were 5.5 ng/m 3 in 1988–1989, while particle-
associated aerosol mercury concentrations were determined to be 0.03 ng/m 3 , or approximately 0.5% of the
total atmospheric mercury (Lindberg et al. 1991). Lindberg et al. (1994) measured mercury vapor at
concentrations of 2–6 ng/m 3 and particulate mercury at 0.002–0.06 ng/m 3 at Walker Branch Watershed,
Tennessee, from August 1991 to April 1992. Particulate mercury concentrations are greater in precipitation
than in ambient air. In the St. Louis River estuary, mercury levels in precipitation averaged 22 ng/L (ppt),
although ambient air levels averaged 3 ng/m 3 (Glass et al. 1990).
Total gaseous mercury was measured (1992–1993) as part of the Florida Atmospheric Mercury Study
(FAMS) (Gill et al. 1995). Average total gaseous mercury concentrations for 3- to 6-day integrated samples
ranged from 1.43 to 3.11 ng/m3 (mean, 1.64 ng/m3 ). In the same study, Dvonch et al. (1995) reported that
the mean concentrations of total gaseous mercury measured at two inland Florida sites were significantly
higher (3.3 and 2.8 ng/m3 ) than measurements at an Atlantic coastal site (1.8 ng/m3 ). The mean
concentrations of particle phase mercury collected at the inland sites (51 and 49 pg/m3 ) were 50% higher
than those at the coastal site (34 pg/m3 ). The mean mercury concentration in rain samples was 44 ng/L
(ppt) (range, 14–130 ng/L). Guentzel et al. (1995) also reported results of the FAMS from 1992 to 1994.
These authors found that the summer time wet season in south Florida accounted for 80–90% of the annual
rainfall mercury deposition. Depositional rates in south Florida are 30 to almost 50% higher than those in
central Florida. Particle phase measurements ranged from 2 to 18 pg/m 3 at all sites. Measurement of
monomethylmercury in precipitation ranged from 2.5 µm) at concentrations
similar to vapor phase mercury. Particulate phase mercury levels in rural areas of the Great Lakes and
Vermont ranged from 1 to 86 pg/m3 , whereas particulate mercury levels in urban and industrial areas were
in the range of 15–1,200 pg/m3 . Sweet and Vermette (1993) sampled airborne inhalable particulate matter
in urban areas (southeast Chicago and East St. Louis) and at a rural site. Mean particulate phase mercury
concentrations in particles (2.5 µm) at the rural site were 0.3 ng/m3 (range,