92 CHAPTER 4 Risk Analysis and Environmental Health Hazards
For example, soy-based foods such as bean curd and soymilk
contain natural estrogens.
Congress amended the Food Quality Protection Act and the
Safe Drinking Water Act in 1996 to require the Environmental
Protection Agency to develop a plan and establish priorities
to test thousands of chemicals for their potential to disrupt
endocrine systems. Chemicals testing positive are tested
further to determine what specific damage, if any, they cause to
reproduction and other biological functions. These tests, which
may take decades to complete, should reveal the level of human
and animal exposure to endocrine disrupters and the effects of
this exposure.Endocrine Disrupters
Mounting evidence suggests that dozens of widely used
industrial and agricultural chemicals are endocrine disrupters,
which interfere with the normal actions of the endocrine
system (the body’s hormones) in humans and animals. These
chemicals include chlorine-containing industrial compounds
known as PCBs and dioxins, the heavy metals lead and
mercury, pesticides such as DDT, and certain plastics and
plastic additives.
Hormones are chemical messengers that organisms
produce to regulate their growth, reproduction, and other
important biological functions. Some endocrine disrupters
mimic estrogens, a class of female sex hormones. Other
endocrine disrupters mimic androgens (male hormones
such as testosterone) or thyroid hormones. Like hormones,
endocrine disrupters are active at very low concentrations
and therefore may cause significant health effects at relatively
low doses.
Many endocrine disrupters appear to alter the
reproductive development of various animal species. A
chemical spill in 1980 contaminated Lake Apopka, Florida’s
third largest lake, with DDT and other agricultural chemicals
that have known estrogenic properties. In the years following
the spill, male alligators had low levels of testosterone and
elevated levels of estrogen. The mortality rate for eggs in
this lake was extremely high, which reduced the alligator
population for many years (see photo). Fortunately, a 2006
study indicates that Lake Apopka’s alligator population is
recovering.
Humans may also be at risk from endocrine disrupters.
The number of reproductive disorders, infertility cases, and
hormonally related cancers (such as testicular cancer and
breast cancer) appears to be increasing. However, we cannot
make definite connections between environmental endocrine
disrupters and human health problems at this time because
of the limited number of human studies. Complicating such
assessments is the fact that humans are also exposed to
natural, hormone-mimicking substances in the plants we eat.
Steve Cooper/Science Source Images
Lake Apopka alligators
A young American alligator hatches from eggs that University
of Florida researchers took from Lake Apopka, Florida. Many
of the young alligators that hatch have abnormalities in their
reproductive systems. This young alligator may not leave any
offspring.CASE STUDY ✓✓THE PLANNER
- What is the precautionary principle? What
are two criticisms of the precautionary
principle?
environmental, and social changes. Given the certainty
that changes are occurring, but high uncertainty about
the extent, severity, and timing of the effects, many sci-
entists and policy makers argue that reducing emissions
quickly is necessary to avoid future losses and suffering.