Chapter 14Environmental Health and Toxicology

This chapter will help you

• Identify major environmental health hazards and explain the goals of environmental health• Describe the types, abundance, distribution, and movement of toxic

substances in the environment• Discuss the study of hazards and their effects, including case histories,

epidemiology, animal testing, and dose-response analysis• Evaluate risk assessment and risk management• Compare philosophical approaches to risk• Describe regulatory policy in the United States and internationally

Poison in a Bottle:Is Bisphenol A Safe?

• The chemical bisphenol A (BPA for short) has been associated with everything from neurological effects to miscarriages, yet it’s in hundreds of products we use every day, and there’s a better than 9 in 10 chance that it is coursing throughyour body right now.• With so many sues, bisphenol A, and

organic compound with the chemicalformula C15H16O2, has become one of the world’s most produced chemicals; each year w make 1 pound of BPA for each person on the planet, and over 6 pounds per person in the United States!

BPA continued…

• Bisphenol A leaches out of its many products and into our food, water, air, and bodies.

• Fully 93% of Americans carry detectable concentrations in their urine, according to the latest National Health and Nutritional Examination Survey conducted by the Centers for Disease Control and Prevention (CDC).

BPA continued…

• Over 200 studies with rats, mice, and other animals have shown many apparent effect of BPA, including a wide range of reproductive abnormalities.• Scientists say this is because BPA mimics the female sex hormone

estrogen; that is, it is structurally similar to estrogen and can induce some of its effects in animals.

Chemical structures and uses of common endocrine disruptors. DES, bisphenol-a and genistein are classified as estrogen agonists while both of the phthalates are androgen antagonists. DDT is classified as both an estrogen agonist and an androgen antagonist.

BPA continued…

• In reaction to the burgeoning research, a growing number of researchers, doctors, and consumer advocates are calling on governments to regulate Bisphenol A and for manufacturers to stop using it.• In 2008, Canada became the first nation to

declare bisphenol A toxic. It banned the sale, import, and advertising of baby products using BPA.

BPA continued…

• In the face of mounting press coverage and public concern, many companies are choosing to voluntarily remove BPA from their products.

Environmental HealthThe study and practice of environmental health assesses environmental

factors that influence human health and quality of life.

We face four types of environmental hazards

• Physical hazards arise from processes that occur naturally in our environment and pose risks to human life or health. • Examples include ultraviolet (UV) radiation from sunlight, or discrete events

such as earthquakes, volcanic eruptions, fires, floods, blizzards, landslides, hurricanes, and droughts.

• Chemical hazards include many of the synthetic chemicals that our society produces, such as disinfectants and pesticides, and also include chemicals produced naturally by organisms.

• Biological hazards result from ecological interactions among organisms. • When we become sick from a virus, bacterial infection, or other pathogen, we

are suffering parasitism by other species that are simply fulfilling their ecological roles, and this is what we call infectious disease.

• Hazards that result from our place of residence, our socioeconomic status, our occupation, or our behavioral choices can be thought of as cultural hazards or lifestyle hazards. • Choosing to smoke, poor diet, and living in proximity to toxic waste are all

cultural hazards.

Many environmental health hazards exist indoors

• Cigarette smoke and radon are leading indoor hazards and are the top two causes of lung cancer in developed nations.• Another indoor hazard is asbestos causing a condition called

asbestosis.• Lead poisoning is another indoor health hazard. When ingested, lead,

a heavy metal, can cause damage to the brain, liver, kidney, and stomach; learning problems and behavioral abnormalities; anemia; hearing loss; and even death.

• A recently recognized hazard is a group of chemicals known as polybrominated diphenyl ethers (PBDEs). These chemicals appear to be endocrine disruptors, affecting thyroid hormones in animals, and have been banned in Europe.

Disease is a major focus of environmental health

• Many major killers, such as cancer, heart disease, and respiratory disorders, have genetic bases but are also influenced by environmental factors.• Malnutrition can foster a wide variety of illnesses, as can poverty,

poor hygiene, lifestyle choices, and lack of exercise.• Over half the world’s deaths result from non-infections diseases, such

as cancer and hear disease, while 1 death in 11 is due to injuries.

• In developed nations like the United States, lifestyle trends are altering the prevalence of non-infections disease in ways both good and bad. • Although infectious disease accounts for fewer deaths than non-

infectious disease, it robs society of more years of human life because it tends to strike people at all ages, including the very young.

Infectious disease interacts with social and environmental influences• Many diseases are spreading because we are so mobile in our modern

era of globalization.• The changes we cause to our environment can also cause diseases to

spread.• To predict and prevent infections disease, environmental health

experts assess the complicated relationships among technology, land use, and ecology.

Health workers are fighting disease in many ways

• Perhaps the best way to reduce disease is to improve the basic living conditions of the world’s poor. Other than providing them food security, this means ensuring their access to safe drinking water and imporving sanitation by minimizing exposure to human waste, garbage3, and wastewater.• Another important pursuit is to expand access to health care. In

developing nations, this includes opening clinics, immunizing children against diseases, providing prenatal and postnatal care for mothers and babies, and making generic and inexpensive pharmaceuticals available.

• Education campaigns play a vital role in rich and poor nations alike.• Such efforts are being spearheaded internationally by the United

Nations, the World Health Organization, the U.S. Agency for International Development, and by non-governmental organizations and funding agencies.

Toxicology is the study of poisonous substances

• Toxicology is the science that examines the effects of poisonous substances on humans and other organisms.• Toxicologist assess and compare substances to determine their

toxicity, the degree of harm a chemical substance can inflict.

• A toxic substance, or poison, is called a toxicant, but any chemical substance may exert negative impacts if we ingest or expose ourselves to enough of it.• These trends have driven the rise of environmental toxicology, which

deals specifically with toxic substances that come from or are discharged into the environment.

Risks must be balanced against rewards

Toxic Substances in the Environment

Our environment contains countless natural substances that may pose health risks. These include toxins, toxic chemicals manufactured in the tissues of living organisms, and many synthetic (artificial, or human-made) chemicals.

Synthetic chemicals are all around us

• Thousands of synthetic chemicals have been manufactured and many have found their way into soil, air, and water.

Synthetic chemicals are in all of our bodies

• And a result of exposure, every one of us carries traces of numerous industrial chemicals in our bodies.• Not all synthetic chemicals pose health risks, and relatively few are

known with certainty to be toxic. However, very few have been thoroughly tested.

Silent Spring began the public debate over synthetic chemicals

• Rachel Carson was a naturalist, author, and government scientist.• Using Scientific studies, medical case histories, and other data, she

showed that DDT and artificial pesticides in general were hazardous to people, wild life, and the environment.• Carson’s book was a bestseller and generated significant social

changes in views and actions toward the environment.• The United States does not use DDT, but manufactures and exports it

to countries that still use it, especially for mosquito control. Certain species of mosquitoes are vectors for malaria, which is considered to be a greater risk than the toxic effects of the pesticide.

Toxicants come in different types

• Carcinogens are substances or types of radiation that cause cancer• Mutagens are chemicals that cause mutations in the DNA of

organisms.• Chemicals that cause harm to the unborn are called teratogens.• Neurotoxins assault the nervous system• Allergens over activate the immune system, causing an immune

response when one is not necessary.• Endocrine disruptors are toxicants that interfere with the endocrine

system.

Toxicants may concentrate in water

• Water runoff often carries low amounts of toxicants from large areas of land and concentrates them in small volumes of surface water.• Many chemicals are soluble in water, and thus are very accessible to

organisms. This is why aquatic animals such as fish, frogs, and stream invertebrates are especially good indicators of pollution.

Airborne substances can travel widely

• Because many chemical substances can be transported by air, chemicals can exert impacts far from the site of their origin and use. Airborne transport of pesticides is sometimes termed pesticide drift.• Earth’s polar regions are particularly contaminated, because patterns

of global atmospheric circulation tend to move airborne chemicals toward the poles. Thus, although we manufacture and apply synthetic substances mainly in temperate and tropical regions, contaminates are strikingly concentrated in the tissues of Arctic polar bears, Antarctic penguins, and people living in Greenland.

Some toxicants persist

• DDT and PCBs have long persistence times, while Bt toxin has a very short persistence time.• Toxicants remain in the environment because they are designed to

persist. Some plastics, for example, were developed because they resist breakdown.• Some toxicants have breakdown products that are just as toxic as the

original chemical, or more so. For example, DDT breaks down into DDE, a highly persistent and toxic compound.

Toxic substances may accumulate and move up the food chain

• Fat-soluble toxicants such as DDT and DDE are absorbed and stored in fatty tissues and may build up in animals in a process called bioaccumulation.• Toxic substances that bioaccumulate in the tissues of one organism

may then be transferred to other organisms in the food chain, in a process called biomagnification.• Polar bears in arctic Norway are suffering from PCB contamination

because of biomagnification, resulting in high cub mortality, and persistence of toxins across generations.

Not all toxicants are synthetic, and not all synthetic chemicals are toxic• Toxic substances exist naturally in the environment around us and in

the foods we eat.• Scientists have actively debated just how much risk is posed by

natural toxicants.

Studying Effects of Hazards

Wildlife studies integrate work in the field and the lab

• Scientists study the impacts of environmental hazards on wild animals to help conserve animal populations and also to understand potential risks to people.• Often wildlife toxicologists work in the field to take measurements,

document patterns, and generate hypothesis, and then head to the laboratory to run controlled manipulative experiments to test ehir hypotheses.

Human studies rely on case histories, epidemiology, and animal

testing• In studies of human health, we gain much knowledge by studying sickened

individuals directly. This process of observation and analysis of individual patients is known as a case history approach.• Epidemiological studies involve large-scale comparisons among groups of

people, usually contrasting a group known to have been exposed to some toxicant with a group that has not.• The advantages of epidemiological studies are their realism and ability to

enable relatively accurate predictions about risk. Drawbacks include the length of time it takes to obtain results and the inability to address future effects of new hazards.• Manipulative experiments are needed to truly nail down causation. However,

this is not possible with human subjects, so other animals are substituted.

Dose-response analysis is a mainstay of toxicology

• The standard method of testing lab animals in toxicology is called dose-response analysis.• The dose is the amount of toxicant the test animal receives, and the response is the type or magnitude

of negative effects the animal exhibits as a result. The response is generally quantified by measuring the proportion of animals exhibiting negative effects.

• Once a dose-response curve is plotted, scientists can calculate a convenient shorthand gauge of a substance’s toxicity- the amount of toxicant it takes to kill half the population of study animals used (LD50)

• Nonlethal health effects are determined by the level of toxicant at which 50% of the population is affected (ED50).

• Common sense suggests that the greater the dose, the stronger the response will be. However, sometimes responses occur only above a certain dose, called the threshold dose.

• Sometimes responses decrease with dosage. Some dose-response curves are U-shaped, J-shaped, or shaped like an inverted U; these curves appear to apply to endocrine disruptors.

• Knowing the shape of the dose-response curve is important for predicting effects. For some toxicants, such as endocrine disruptors

Endocrine disruption poses challenges for toxicology

• Because so many novel synthetic chemicals exist in very low concentrations over wide areas, many scientists suspect that we may have underestimated the dangers of compounds that exert impacts at low concentrations.

• The idea that synthetic chemicals might be altering the hormones of animals was not widely appreciated until the 1996 publication of the book Our Stolen Future, by Theo Colburn, Dianne Dumanoski, and J.P. Myers.

• Today, thousands of studies have linked hundreds of substance to effects on reproduction, development, immune function, brain and nervous system function, and other hormone-driven processes in animals. Many studies also suggest impacts on people.

• Much of the research into hormone disruption has brought about strident debate, partly because a great deal of scientific uncertainty is inherent in any young and developing field, and that negative findings about chemicals pose an economic threat to the manufacturers of those chemicals.

Individuals vary considerably in their

response to hazards

The type of exposure can affect the response

• The toxicity of many substances varies according to whether the exposure is in high amounts for short periods of time –acute exposure- or in lower amounts over long periods of time-chronic exposure.• Acute exposure is easier to recognize but chronic exposure is more

common, and is more difficult to detect and diagnose.

Mixes may be more than the sum of their parts

• Traditionally, environmental health has tackled the effects of single hazards one at a time, and single-substance tests have revieved priority. This is changing, but scientists will never be able to test all possible combinations.

Risk Assessment and Risk Management

We express risk in terms of probability

• Risk can be measured in terms of probability, a quantitative description of the likelihood of a certain outcome, The probability that some harmful outcome (for instance, injury, death, environmental damage, or economic loss) will result from a given action, event, or substance expresses the risk posed by that phenomenon.

Our perception of risk may not match reality

Risk assessment analyzes risk quantitatively

• The quantitative measurement of risk and the comparison of risks involved in different activities or substances together are termed risk assessment.• Assessing risk for a chemical substance entails several steps:• The first steps involve the scientific study of toxicity we examined above-

determining whether a substance has toxic effects and, through dose-response analysis, measuring how effects vary with the degree of exposure.• Subsequent steps involve assessing the individual’s or population’s likely

extent of exposure to the substance, including the frequency of contact, the concentrations likely encountered, and the length of encounter.

Risk management combines science and other social factors

• Accurate risk assessment is a vital step toward effective risk management, which consists of decisions and strategies to minimize risk.• In most developed nations, risk management is handled largely by

federal agencies.

Philosophical and Policy Approaches

Two approaches exist for determining safety

• One approach is to assume that substances are harmless until shown to be harmful- the innocent-until-proven-guilty approach.• This approach encouraged

technological innovation but may put some dangerous substances into wide use.

• The other approach, called the precautionary principle, is to assume hat substances are harmful until shown to be harmless. • This enables us to identify

toxicants before they are released into the environment, but may also impede technological and economic advances.

Philosophical approaches are reflected in policy

• Most nations follow a blend of the two approaches.• At present, European nations follow the precautionary principle.• The U.S. largely follows the innocent-until-proven-guilty approach.• In the U.S., the tracking and regulation of synthetic chemicals is

shared among several federal agencies.

EPA regulation is only partly effective

• The EPA also regulates diverse chemicals under the Toxic Substances Control Act (TSCA).• Many public health and environmental advocates view TSCA as being too

weak.• The registration process involves risk assessment and risk management.• Because the registration process takes economic considerations into account,

critics say it allows hazardous chemicals to be approved if the economic benefits are judged to outweigh the hazards.

Toxicants are regulated internationally

• In 2007, the European Union’s REACH (registration, evaluation, authorization and restriction of chemicals) program went into effect. The burden of proof for chemical safety shifted from governments to industry. REACH will also test previously authorized chemicals for toxicity; 1,500 chemicals should become restricted.• These new regulations are expected to cost as much as $7 billion, but

the benefits to public health are estimated to be $67 billion.• In 2004, an international treaty, the Stockholm Convention, was ratified

by over 140 nations. The convention aims first to end the use and release of 12 persistent organic pollutants (POPs) called the “dirty dozen”. It appears to be on its way to ratification.

Conclusion

• International agreements such as the Stockholm Convention represent a hopeful sign that governments will act to protect the world’s people, wildlife, and ecosystems from harm by toxic chemicals and other environmental hazards.• A society’s philosophical approach to risk management will determine

what policy decisions it makes.