Challenges of the 21st Century - Science For Environmental Protection: The Road Ahead - page 20

posures and reducing or preventing associated health effects can be more challeng-
ing.
Although new chemicals continue to be created and enter the environment,
many of the problems they cause are not new. Cancer was among the dominant
health concerns through the early decades of EPA. Carcinogenic pollutants—
including asbestos, arsenic, benzene, hexavalent chromium, dioxin, and vinyl
chloride—were a major focus of interest in human health effects because of both
public concerns and expanded toxicologic and epidemiologic findings. Identify-
ing and controlling carcinogens was a dominant driver of EPA science, from
analytic chemistry through toxicity testing and risk assessment. While cancer
will continue to be an EPA and societal priority, other health outcomes are likely
to receive increasing attention given growing epidemiologic and toxicologic
evidence. Many of these health effects are chronic and subtle, and there is still
much to be learned. For example, hormonally active chemicals have long been
researched, but the importance of their potential health effects continues to be
elucidated. A new class of hormonally active substances receiving increased
attention are obesogens, which target lipid metabolism and may interfere with
natural hormone signaling (Kirchner et al. 2010).
Another challenge related to exposure to chemicals or other stressors is
characterizing susceptibility to adverse health effects. Susceptibility can vary
greatly in a population as a function of factors that are not often systematically
evaluated. Young children may be at greater risk for neurologic and endocrine
effects, and the elderly may be more susceptible to immune effects, cardiovascu-
lar effects, or infection. Race or socioeconomic status may increase the risk of
cumulative environmental effects that result from living disproportionally closer
to pollution sources (Bullard 2000). Poverty, stress, and lack of access to medi-
cal care decrease human resilience and the ability to adapt; disadvantaged com-
munities are at increased risk when faced with increased exposure. Genetic fac-
tors also influence susceptibility and underscore the importance of gene-
environment interaction in determining health outcomes.
Transgenerational effects and sensitive populations are also of great con-
cern for public health. Exposure to chemicals and other stressors during gesta-
tion can affect the mother, the fetus, and even the germ cells of the fetus and
lead to effects on the third generation (Holloway et al. 2007). Some research
indicates that chemical exposure in the womb can trigger epigenetic changes
much later in life. Adipose-tissue development, food intake, and lipid metabo-
lism may be altered as a result of exposure to organotins, perfluorooctanoic acid,
diisobutyl phthalate, bisphenol A, and other xenobiotic chemicals found in the
environment (Grun and Blumberg 2006). The epidemic of obesity, diabetes, and
metabolic syndrome in the United States and elsewhere indicates that research is
needed to determine whether there is a causal link to the chemicals described
above at concentrations measured in the environment. If environmental expo-
sures caused even a tiny fraction of the almost 130% increase in obesity in the
United States over the last 40 years (Wang and Beydoun 2007), they constitute
an important emerging challenge for EPA science and regulation.