Appendix D Food Codes for NHANES - OEHHA

SRP Review Draft Version 2 June, 2012
Table I.9. Methylmercury BAFs for Lentic/Lotic a Ecosystems from U.S. EPA and
California Data
Agency Environment/Comments Mean Trophic Level
3 4
U.S. EPA Lentic Only Geometric 1.1 x 10 6 5.7 x 10 6
U.S. EPA Lentic Only Arithmetic 1.5 x 10 6 6.2 x 10 6
California Lentic Alternative Geometric NP NP
California Lentic Alternative Arithmetic NP NP
U.S. EPA Lotic Only Geometric 5.7 x 10 5 1.2 x 10 6
U.S. EPA Lotic Only Arithmetic 1.3 x 10 6 3.9 x 10 6
California Lotic Alternative Geometric 6.8 x 10 5 1.1 x 10 6
California Lotic Alternative Arithmetic 1.4 x 10 6 3.5 x 10 6
U.S. EPA Lentic/Lotic Combined Arithmetic 1.4 x 10 6 5.0 x 10 6
a Lentic environments are characterized by still (not flowing) water, as in lakes and reservoirs.
Lotic environments are characterized by flowing water, as in streams and rivers.
In California, using a MeHg BAF developed by U.S. EPA is complicated by the large
number of Hg point sources originating from legacy mining activities, a situation
somewhat unique to California. Atmospheric deposition of Hg into water bodies may be
overshadowed by the existing Hg already present due to legacy mining. In addition,
very little published data exist for California lentic ecosystems in order to determine if
total Hg concentrations are good predictors of MeHg concentration. The BAFs and
translators developed by U.S. EPA were based primarily on atmospheric deposition of
Hg into water bodies. Hg speciation in water and fish may be quite different depending
on whether the Hg originated from mining or atmospheric deposition.
Nevertheless, OEHHA (2006) found that the national values predicted California fish
MeHg concentrations very well except for some water bodies where Hg concentrations
in water were statistically higher. Hg concentrations (≥0.2 ng/L) in these water bodies
were found to be more than one standard derivation from the mean for other data used
in these tests. We concluded that the national default values for BAFs and translators
may not work well for all water bodies in California. However, based on the limited
comparisons possible, BAFs and translators based on the California data and
international studies (U.S. EPA database) were found to be similar.
In partial support, Kelly et al. (1995) observed that total Hg concentration was not a
good predictor of MeHg concentration in stream water or in lakes in general, but it
appeared to be a good predictor for lakes within individual geographic areas. In lotic
ecosystems, Southworth et al. (2004) concluded that it is not valid to assume that the
fraction of total waterborne Hg comprised by MeHg would remain constant while total
Hg varies at high total Hg concentrations (roughly >50 ng/L) typical of systems affected
by point-source or legacy contamination. However, at total Hg concentrations less than
10 ng/L, the %MeHg varies little. They postulated that such a relationship results from
saturation of the ecosystems capacity to methylate inorganic Hg at high total Hg
concentrations.
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