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Exponent's human health risk assessment work has been conducted
at a variety of sites, including mining and smelter sites,
pesticide and chemical manufacturing facilities, petroleum
facilities and sites, wood treating facilities and pulp mills,
other industrial facilities and sites, and defense installations
and weapons complex sites. Through these projects, we have
gained extensive experience in evaluating general, chemical,
and site-specific risk assessment issues involving a variety
of contaminants, including metals, polycyclic aromatic hydrocarbons
(PAHs), chlorinated solvents and pesticides, dioxins, and
polychlorinated biphenyls (PCBs).
 Development
of Cleanup Levels at Smelter Sites At a former zinc smelter
site in Bartlesville, Oklahoma, Exponent scientists developed
and supported negotiations for cleanup levels for cadmium
in soil that were among the highest at any site in the United
States (100 mg/kg for residential areas), but that were amply
protective of public health. The cleanup levels were supported
by studies of bioavailability, indoor dust concentrations,
and interactions of cadmium and zinc. At a former copper smelter
site in Anaconda, Montana, we provided technical direction
for a comprehensive research program that led to health-protective
arsenic cleanup levels of 250 mg/kg, 500 mg/kg, and 1,000
mg/kg for residential, industrial, and recreational land use
areas, respectively. Development of these cleanup levels was
just one component of a decade's worth of integrated risk
assessment support for a group of interrelated mining and
smelting sites in Montana.
 Bioaccumulation
Assessment at Pesticide and Chemical Manufacturing Facilities
Chlorinated organic pesticides, PCBs, and mercury have been
key substances of concern at many sites because of their persistence
and tendency to bioaccumulate in the food chain. Exponent's
assessment of these substances has taken into account their
relatively widespread occurrence in the environment and in
food supplies, even in the absence of known sources. For example,
at Onondaga Lake in New York, PCBs and methylmercury found
in fish caught from the lake were the primary contributors
to human health risks. However, a detailed review of fishes
collected from other surface waters in the state indicated
that risks associated with these chemicals were similar to
or lower in Onondaga Lake than in other New York State waters.
 Technical
Support at Petroleum Hydrocarbon Sites Exponent staff
have applied their technical expertise at numerous petroleum
hydrocarbon sites. This experience includes developing risk-based
cleanup approaches, conducting site-specific investigations,
and assisting in the development of risk-based regulatory
policies. We have successfully negotiated risk-based cleanups
at refineries, former and operating bulk fuel terminals, and
other petroleum hydrocarbon sites. At such sites, Exponent
has advocated using a site-specific approach to establish
cleanup requirements. In many cases, we have combined realistic
assessments of likely exposures with evaluations of the individual
toxic constituents of total petroleum hydrocarbons (TPH),
rather than relying solely on TPH measurements as an indicator
of site contamination. Based on consideration of realistic
scenarios of human exposure and chemical migration, Exponent
can often demonstrate that substantially higher cleanup goals
are more appropriate than the originally proposed cleanup
targets.
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