Introduction to Endocrine Disrupting Chemicals

These environmental sources of DDTs accumulate in animals and are amplified
up the food chain. In fact, intake of DDTs by Inuit people is comparable to that of
people living in regions using DDT to control malaria (72).
Several aspects of climate change predictions indicate that exposure to DDTs
will increase over the next decades, although the processes are complex. Climate
change is expected to increase the incidence of malaria, potentially leading to
increased demand for and use of DDT (73). Melting glaciers contributed 46% of
the DDTs entering the Canadian Archipelago, and over 60% of the DDTs entering
Canadian subalpine lakes; melting sea ice and permafrost provide further DDT
(74, 75). Climate change also increases partitioning of POPs from water and soil to
the atmosphere and higher wind speeds increase airborne transport, so deposition
in the Arctic is likely to increase again. Because DDTs accumulate at the top of the
food chain to levels that are thousands of times higher than at the bottom, and
hundreds of thousands fold higher than in the water, it is likely that DDTs released
from melting glaciers will increase concentrations of DDTs in people who eat from
the Arctic food chain. Additionally, exposure to EDCs has been demonstrated to
affect the thyroid hormone system, which due to its role in maintenance of body
temperature would likely affect the ability of Arctic wildlife to adapt to climate
change (76).
Science on why DDT is an EDC
DDT was one of the first recognized EDCs, with a broad range of effects on
reproduction and hormonal systems. It was used indiscriminately as a pesticide
for decades, until attention was called to its devastation of entire ecosystems by
Rachel Carson in her landmark book, Silent Spring. Laboratory animal studies
and human observations consistently show associations between DDTs and negative
health consequences, making DDTs one of the most widely accepted classes
of EDCs. In animals and cell lines, DDTs modify the thyroid, estrogen, androgen,
renin-angiotensin, insulin, and neuroendocrine systems. These pathways are involved
in normal functioning of reproductive, cardiovascular, and metabolic processes,
among others. Some effects of DDTs are as estrogen mimics, and DDTs also
interfere with androgen (testosterone) pathways in the body (77). In mammals (including
humans), gonads of females (ovaries) and males (testes) make estrogens
and androgens, albeit at different levels. Females have higher estrogens and lower
androgens, and males have higher androgens and lower estrogens. By disrupting
the body’s major normal sex hormones individually, and by causing changes in
the ratios of sex hormones, DDTs are associated with a plethora of reproductive
problems. Numerous studies indicate that high exposure to DDTs reduces male,
and possibly female, fertility, including in humans (67). For instance, men living
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