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

MERCURY 355
2. HEALTH EFFECTS
mercury. Additional work studying the effectiveness of prophylactic administration of vitamin E (or other
antioxidants) and of proper diet are needed. Improved chelation and drug therapies for treating acute and
chronic mercury poisonings are greatly needed.
Children’s Susceptibility. The systemic health effects from different forms of mercury and exposure
routes have been fairly well characterized (EPA 1997; Sue 1994; WHO 1990). There is generally
sufficient information on the symptoms to resolve the form and route of exposure when children are
exposed to high levels of mercury. There is less information to assist the physician or public health official
in recognizing the symptoms that might arise from lower level exposure to multiple forms of mercury (e.g.,
dental amalgam and fish) and multiple pathways (inhalation and ingestion). Whether concurrent exposures
would result in a different presentation of symptoms would be important information in determining the
best therapeutic treatment. Some health effects categories are not well defined (e.g., immune responses).
Earlier identification of immunotoxicity is of concern for children because of the progressive nature of
hypersensitization to environmental pollutants, and the burden that a compromised immune system can
place on a person’s long-term health.
There are not presently adequate measures for neurologic development. Delayed developmental effects
are of grave concern for children exposed to mercury; methods for early determination and detection of
progressively worsening changes in a child’s behavioral or cognitive function are needed. For the
measures to be truly useful they should in some way be integrated into a more directed exposure
assessment and body burden analysis and to resolve the contribution from other influences on cognitive
abilities and behaviors. Other data needs related to developmental effects are discusses above under
Developmental Toxicity.
Pharmacokinetics are different for children, and more data are needed to improve chelation therapies for
both acute high-level poisoning and for chronic low-level exposures. This is perhaps the area that deserves
the most attention because accidental poisonings continue to occur and there are virtually no therapies to
ameliorate the inevitable progression of mercury intoxication. Since environmental levels of mercury are
also continuing to rise, and levels in food will concurrently rise, strategies to boost the body’s ability to
eliminate absorbed mercury are going to become increasingly important (i.e., the alternative is to change
dietary patterns, i.e., eat less fish, and the risk/benefits of doing that are already being hotly debated).
There appears to be adequate information on the metabolism of mercury, and there are no special
metabolites or metabolic pathways that are unique to children and require further evaluation.