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

MERCURY 310
2. HEALTH EFFECTS
Concerning interactions with other chemicals, there is an ongoing debate about the value of fish in the diet
versus the risk from increased exposure to methylmercury that may be in the fish. One recent study reported
a beneficial effect from increased fish consumption even though mercury body burdens were increased to
some extent (Davidson et al. 1998). One possible factor in the fish that could improve health is omega 3­
fatty acid. Children and adults both benefit from a healthy diet, but there may more emphasis on the benefits
to growing children. Other interactions for mercury include the effect of various substances on its
gastrointestinal absorption (e.g., iron, zinc) or possibly protective effects from prevention or repair of
mercury related oxidative damage (e.g., interactions with selenium as an antioxidant). No information was
identified that specifically addresses differences in these interactions for children compared to adults.
The methods used to reduce peak absorption and to reduce body burdens in exposed adults (i.e., chelation
therapy) are also used for exposures in children.
No information was identified on parental exposures affecting children in areas of parental germ cells or
germ line mutations. The topic of exposure pathways for mercury via nursing or pregnant women who have
been exposed is of main concern and has been addressed earlier in this section.
2.7 BIOMARKERS OF EXPOSURE AND EFFECT
Biomarkers are broadly defined as indicators signaling events in biological systems or samples. They have
been classified as markers of exposure, markers of effect, and markers of susceptibility (NAS/NRC 1989).
A biomarker of exposure is a xenobiotic substance or its metabolite(s), or the product of an interaction
between a xenobiotic agent and some target molecule(s) or cell(s), that is measured within a compartment
of an organism (NAS/NRC 1989). The preferred biomarkers of exposure are generally the substance itself
or substance-specific metabolites in readily obtainable body fluid(s) or excreta. However, several factors
can confound the use and interpretation of biomarkers of exposure. The body burden of a substance may
be the result of exposures from more than one source. The substance being measured may be a metabolite
of another xenobiotic substance (e.g., high urinary levels of phenol can result from exposure to several
different aromatic compounds). Depending on the properties of the substance (e.g., biological half-life) and
environmental conditions (e.g., duration and route of exposure), the substance and all of its metabolites
may have left the body by the time samples can be taken. It may be difficult to identify individuals exposed