Environmental Engineering Reference
In-Depth Information
table 12.4
Guidance and Risk Levels for Methylmercury Determined by Different Agencies
Agency and measure
Year
Value
Basis
USEPA, long-term
oral RfD
1985
1995 IRIS
2001 IRIS
0.3
g/kg/day
Effects on adults in Iraq
Developmental effects in Iraq
Studies in New Zealand and Faroe Islands
0.1
g/kg/day
0.1
g/kg/day
a
ATSDR MRL (oral)
1994 Toxicological profi le
1997 Draft profi le
1999 Toxicological profi le
0.1
g/kg/day
Seychelles study
Seychelles study
Seychelles study
0.5
g/kg/day
0.3
g/kg/day
USFDA ADI
1984
0.4
g/kg/day
Corresponds to 1 ppm action level
UN FAO/WHO
1993
3.3
g/kg/wk
Based on studies in Iraq with no fetal consideration
JECFA
Reaffi rmed 1999
1.6
g/kg/wk
b
JECFA (1999)
Guidance value
Revised 2003
0.23
g/kg/day
JECFA (2003)
PTWI
Seychelles and Faroes
note:
Some agencies do not distinguish between total mercury and methylmercury or assume that all mercury is methylmercury (the typical
conversion is 90%).
a.
Method recommended by NRC (2000a). There is no separate provision for adults.
b.
Accepted and used by the European Food Safety Authority (2004). JECFA (2006) notes that the 1.6 value is to protect the fetus and probably
children and that adults may tolerate twice the PTWI.
ADI
acceptable daily intake; MRL
minimal risk level; PTWI
provisional tolerable weekly intake; RfD
reference dose.
Faroes and Seychelles data (JECFA, 2003), but subsequently
acknowledged that adults could tolerate twice that level,
while data for children under 17 was uncertain (JECFA,
2004, 2006) (see Table 12.4).
The Seychelles are tropical islands in the Indian Ocean.
The study has been conducted mainly by the University
of Rochester. The islands' residents, largely Muslim, con-
sume fi sh daily and the Seychelles Child Development
Study, which began at the same time as the Faroes study,
has not found evidence of harm from prenatal exposure
to methylmercury at the levels encountered in that popu-
lation. Fish from the surrounding reefs and ocean are a
major source of protein. This study is generally consid-
ered “negative,” although there has been evidence of a
late effect on children whose mothers had high mercury
levels in hair (Davidson et al., 2006), although in many
studies, the causal relationships are unclear (Myers et al.,
2009).
The Faroe Islands in the North Atlantic are inhabited
mainly by people of Scandinavian background. Oceanic
fi sh are a major source of protein, and some families also
capture Pilot Whales periodically, which are a major source
of both methylmercury and polychlorinated biphenyls.
A prospective study of mother-child pairs was initiated
in 1990; there was evidence of impaired neurobehav-
ioral functions in children at the age of 7 years, who had
higher in utero exposure to mercury, particularly during
the third trimester (Grandjean et al., 1998). The EPA's reas-
sessment lowered the RfD to 0.1 µg/kg/day based on the
positive Faroes study, although its reasoning has been
criticized (e.g. Davidson et al., 2004). The literature review,
risk-estimation procedures, and rationale are detailed in
the USEPA's IRIS database (USEPA, 2001c).
Both the Faroe and Seychelles studies involved popu-
lations with very high fi sh consumption, and extensive
efforts have been devoted to contrasting the studies and
reconciling the apparent differences. Probable confound-
ers include ethnic differences, the high levels of polychlo-
rinated biphenyls ingested intermittently in the Faroe
Islands after Pilot Whale hunts, the higher levels of fresh
fruit consumption in the Seychelles, and differences in
measurement techniques.
An Example of a Formal Human Risk Assessment
In response to the need for coordinated risk communica-
tion by the Department of Energy and the States of South
Carolina and Georgia, we undertook a risk assessment
for people consuming fi sh from the Savannah River. We
assumed that the people who actually fi shed the river were
most likely to consume large amounts of fi sh, and we took
a dual approach. We captured fi sh from the river, includ-
ing species sought and favored by sportsmen, and analyzed
their edible tissues, and we interviewed fi shers to determine
how much fi sh they ate. Our risk assessment included radio-
nuclides as well as mercury, but only the latter is reported
here (Table 12.5). We have conducted similar risk assess-
ments in New Jersey, around the Oak Ridge nuclear facility,
and in the Aleutians near Amchitka Island, where there were
three underground nuclear tests in the 1965-1971 period
(Campbell et al., 2002; Burger and Campbell, 2004; Burger
et al., 2005, 2007b; Burger and Gochfeld, 2007).
