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Investigation of the Accuracy of
Monomethyl Mercury Measurements in Rainwater in the
Presence of Increased Inorganic Mercury
Kate McPeek*, Lucas Hawkins
Corresponding author - Frontier Geosciences,
414 Pontius Avenue North, Seattle WA 98109
Eric Prestbo
Tekran Canada R&D Facility, 330 Nantucket Blvd., Toronto, ON M1P2P4, Canada.
| Measurements of mercury in rainwater are an important
tool used to assess deposition rates into watersheds and other sensitive
environments. Monomethyl mercury (MMHg) is of special concern due to its
known toxicity to living organisms. For eight years MMHg has been measured
at many National Atmospheric Deposition Program/Mercury Deposition Network
(NADP/MDN) sites. This study investigates standard NADP/MDN sampling protocol
for potential enrichment of wet MMHg deposition. For this experiment,
inorganic mercury (Hg2+) was added to rain collectors prior to deployment
to test for a positive MMHg bias. Each collection event consisted of three
samples spiked with 10 ng of Hg2+ and three control samples containing
no Hg2+ spike. All samples were analyzed for total and monomethyl mercury
via cold vapor atomic fluorescence spectrometry (CVAFS). A total of five
weeklong sampling events resulting in 30 samples were collected in Seattle,
WA from May 2006 to November 2006. The outside temperature during collection
events ranged from 40-70°F. Results were evaluated using three statistical
tests: paired t-test (mean delta=0.008ng/L, p=0.4579), linear regression
(slope=1.0843), and linear regression with intercept forced through zero
(slope=0.960). Preliminary results indicate that there is not enrichment
of MMHg.
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