What are endocrine disruptors, and why can small amounts of exposure produce big effects in an individual?
Why You Should Care
Every person lives, eats, and makes a unique combination of risk choices. Every person is also a unique genetic combination, which means that while they may look like other humans, their metabolism will respond in slightly different ways. Synergistic combinations of risks lead to literally billions of possible outcomes.
One example of this is endocrine disruptors, chemicals that mimic hormones’ effect within our cells. These hormones regulate our DNA and control our development, growth, and life span. Adding in more hormones can obviously change our bodies in unpredictable ways.
Since we cannot predict the effect of exposure for each individual person, regulators use risk assessment to generalize risk for the majority of the population (assuming specific levels of exposure, genetic risks, and synergistic effects). This is very difficult to do well, so in the interests of minimizing risks in an increasingly complex environment, some scientists have proposed replacing risk assessment with the precautionary principle. This could be summarized as "if we don’t know its exact risks, then we shouldn’t use it until we do."
Test Your Vocabulary
Choose the correct term for each of the following definitions:
Term
Definition
A molecule released by the body that directs cellular activity and produces changes in how the body functions.
A molecule that interferes with the endocrine system, typically by mimicking a hormone or preventing a hormone from having an effect.
A structure on or inside a cell that binds a hormone, thus allowing the hormone to affect the cell.
A rule of thumb that calls for leaving a safety margin when the data about a particular substance’s potential for harm are uncertain and where the substance may cause unexpected or unpredictable effects.
Weighing the risks and benefits of a particular action in order to decide how to proceed.
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Question Sequence
1.
Exposure to DDT appears to slow down development and sexual maturity in humans. In this case, DDT is acting as a(n):
A.
B.
C.
D.
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2.
Once studies demonstrated that DDT had some effect on humans, regulatory agencies began looking at safe levels of exposure to DDT. This was part of the ______ for DDT.
A.
B.
C.
D.
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3.
Imagine that DDT had not yet been released or used and scientists were weighing whether or not to use it. A group of researchers declares, “DDT should not be used until its overall effects are well understood.” This viewpoint is called:
A.
B.
C.
D.
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4.
Today, we know that DDT’s effects are much more widespread than we first believed when DDT usage was banned in 1972. How did the risk assessment of DDT change from when it was first used in the 1930s until its ban in the 1970s?
Risk assessment is an imperfect science because it is always limited by the data that are available, and in the 1930s, the data on DDT indicated that there were few dangers from its widespread use. It was not until DDT was actually used and began bioaccumulating and biomagnifying that the larger dangers became apparent. Also, toxicological research advanced greatly, and DDT’s effects would have been discovered if it were put through a more modern toxicology research study.
Short-Answer Questions
Polychlorinated biphenyls (PCBs) are synthetic chemicals that were used widely in the twentieth century as very persistent industrial coolants: Their production was banned in 1977. Research has shown that PCBs cause endocrine disruption of the liver and thyroid of children at very low levels (leading to obesity and adult-onset diabetes). PCBs are chemicals that both bioaccumulate and biomagnify.
1. In the late 1990s, the Environmental Protection Agency (EPA) proposed cleaning up rivers near historic PCB-production factories in New York and Connecticut.
A) These rivers were too polluted to eat fish from, so what basis would the EPA use to justify these multibillion-dollar cleanups?
B) How would PCB molecules affect fish in those rivers? How about birds that prey on those fish?
C) How would the EPA describe the risk assessment for a sport fisherman on a PCB-polluted river? Would assessment be different for his wife or daughter?
2. Imagine that the EPA decided that risk assessment was too complex to be useful and decided instead to adopt the precautionary principle for PCB regulation.
A) What would the EPA have needed to know when PCBs were first developed?
B) Does the precautionary principle help regulate PCBs today (decades after its production was banned)? Why or why not?
1. A) From an anthropocentric environmental ethic, the bioaccumulation and biomagnifications of the PCB would allow the chemical to move up the food chain and ultimately leave the river, and possibly enter human food chains along the river.
From an ecosystem point of view (biocentric or ecocentric), the EPA could use the Clean Water Act to protect non-human species' exposure to PCBs. However, the high cost of these cleanups would create controversy, as the EPA justified their cleanup using anything other than an anthropocentric point of view.
B) The fish should show endocrine disruption of development of the liver and thyroid. The PCB molecules bioaccumulate and biomagnify, so fish that are predators of other fish (higher on the food chain) would show higher concentrations and greater effects. Birds that prey on those fish should show greater concentrations from biomagnifications and even greater effects than the fish did.
C) The fisherman has a higher risk because he is exposed to the PCB-contaminated water, at least more exposed than people who are not going in the water or touching fish from that water. The assessment would also be based on how often he fished in the water, PCB levels in the waters in which he fished, and whether he illegally ate the fish that he caught. For his wife and daughter, the risk assessment would be simpler: Did they accompany him while fishing? Did they eat the fish he caught? Their access to the water is more limited, so their risk assessment should be lower.
2. A) The EPA would need to have completed as thorough a study of the possible interactions as science would allow. The result of that research would have to leave significant gaps in knowledge. For instance, if PCBs were known to bioaccumulate and cause cancer in animals (which in vitro and in vivo studies would show), then detailed research on those effects may take decades for complications to arise in humans. That should be enough to invoke the precautionary principle.
B) The precautionary principle doesn’t help to regulate current use since it is banned, but it might help to give a stronger emphasis to the cleanup.
