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Chemical pollutant impacts can be categorized as neurotoxins, carcinogens, teratogens, allergens, or endocrine disruptors

47-4 What are the impacts of chemical pollutants?

Chemicals can have many different effects on organisms, and some of the most harmful are common in our environment; TABLE 47.1 lists those of current concern. They can be grouped into five categories: neurotoxins, carcinogens, teratogens, allergens, and endocrine disruptors.

TABLE 47.1 Some chemicals of major concern

Chemical Sources Type Effects

Lead Paint, gasoline Neurotoxin Impaired learning, nervous

system disorders, death

Mercury Coal burning, fish consumption Neurotoxin Damaged brain, kidneys,

liver, and immune system

Arsenic Mining, groundwater Carcinogen Cancer

Asbestos Building materials Carcinogen Impaired breathing, lung cancer

Polychlorinated biphenyls (PCBs) Industry Carcinogen Cancer, impaired learning, liver damage

Radon Soil, water Carcinogen Lung cancer

Vinyl chloride Industry, water from vinyl chloride pipes Carcinogen Cancer

Alcohol Alcoholic beverages Teratogen Reduced fetal

growth, brain and nervous

system damage

Atrazine Herbicide Endocrine disruptor Feminization of males,

low sperm counts

DDT Insecticide Endocrine disruptor Feminization of males,

thin eggshells of birds

Phthalates Plastics, cosmetics Endocrine disruptor Feminization of males

Neurotoxins

Neurotoxins are chemicals that disrupt the nervous systems of animals. Many insecticides, for example, are neurotoxins that interfere with an insect’s ability to control its nerve transmissions. Insects and other invertebrates are highly sensitive to neurotoxin insecticides. These animals can become completely paralyzed, cannot obtain oxygen, and quickly die. Other important neurotoxins include lead and mercury, which are heavy metals that can damage the human kidneys, brain, and nervous system.

Neurotoxin

A chemical that disrupts the nervous systems of animals.

Carcinogens

Carcinogens are chemicals that cause cancer. Carcinogens cause cell damage and lead to uncontrolled growth of these cells either by interfering with the normal metabolic processes of the cell or by damaging the genetic material of the cell. Carcinogens that cause damage to the genetic material of a cell are called mutagens (although not all mutagens are carcinogens). Some of the most well-known carcinogens include asbestos, radon, formaldehyde, and the chemicals found in tobacco. Asbestos was once commonly used as a fireproof insulation material, radon is a naturally occurring gas that can enter through building foundations, and formaldehyde has been used in a wide range of preservatives including in many building materials.

Carcinogen

A chemical that causes cancer.

Mutagen

A type of carcinogen that causes damage to the genetic material of a cell.

Teratogens

Teratogens are chemicals that interfere with the normal development of embryos or fetuses. One of the most infamous teratogens was the drug thalidomide, prescribed to pregnant women during the late 1950s and early 1960s to combat morning sickness. Sadly, tens of thousands of these mothers around the world gave birth to children with defects before the drug was taken off the market in 1961. One of the most common modern teratogens is alcohol. Excessive alcohol consumption reduces the growth of the fetus and damages the brain and nervous system of the fetus, a condition known as fetal alcohol syndrome. This is why physicians recommend that women not consume alcoholic beverages while they are pregnant.

Teratogen

A chemical that interferes with the normal development of embryos or fetuses.

AP® Exam Tip

You should be able to identify specific examples of chemical toxins, their source, and their human health impacts.

Allergens

Allergens are chemicals that cause allergic reactions. Although allergens are not pathogens, allergens are capable of causing an abnormally strong response from the immune system. In some cases, this response can cause breathing difficulties and even death. Typically, a given allergen only causes allergic reactions in a small fraction of people. Some common chemicals that cause allergic reactions include the chemicals naturally found in peanuts and milk, and several drugs including penicillin and codeine.

Allergen

A chemical that causes allergic reactions.

Endocrine Disruptors

Endocrine disruptors are chemicals that interfere with the normal functioning of hormones in an animal’s body. Hormones are normally manufactured in the endocrine system and released into the bloodstream in very low concentrations. As the hormones move through the body, they bind to specific cells. Binding stimulates the cell to respond in a way that regulates the functioning of the body including growth, metabolism, and the development of reproductive organs. As FIGURE 47.9 shows, an endocrine disruptor can bind to receptive cells and cause the cell to respond in ways that are not beneficial to the organism.

Endocrine disruptor

A chemical that interferes with the normal functioning of hormones in an animal’s body.

FIGURE 47.9 Endocrine disruption. In normal endocrine processes, hormones bind with receptors on cells to regulate the functioning of the body including growth, metabolism, and the development of reproductive organs. Hormone-disrupting chemicals mimic the hormones in the body and also bind to receptive cells and cause the cell to respond in ways that are not beneficial to the organism.

One high-profile example of endocrine disruptors in our environment is the group of reproductive hormones that can be found in the wastewater, which is the water produced by livestock operations and human activities, including human sewage from toilets and gray water from bathing and washing clothes and dishes. In waterways exposed to hormones through wastewater, scientists are increasingly finding that male fish, reptiles, and amphibians are becoming feminized; males possess testes that have low sperm counts and, in some cases, testes that produce both eggs and sperm. Males normally convert the female hormone estrogen into the male chemical testosterone. Reproductive hormones in wastewater can interfere with the production of testosterone, which causes males to have higher concentrations of estrogen and lower concentrations of testosterone in their bodies.

Wastewater

The water produced by livestock operations and human activities, including human sewage from toilets and gray water from bathing and washing clothes and dishes.

In the Chesapeake Bay, the U.S. Fish and Wildlife Service announced that estrogen from sewage in the water was the most likely reason that 23 percent of male largemouth bass and 82 percent of male smallmouth bass developed into hermaphrodites; their male sex organs grow eggs, a function that normally only occurs in the sex organs of female fish. This impact not only concerns fish, but also is a concern for humans who share many similarities in their reproductive systems and may consume water contaminated with estrogens.

In addition to real animal hormones, some pesticides can mimic animal hormones and also serve as endocrine disruptors. Such discoveries raise serious concerns about whether endocrine disruptors might affect the normal functioning of human hormones. These effects include developmental disorders, low sperm counts in men, and an increased risk of breast cancer in women.