Chapter 14 Topics: Environmental health and environmental hazards Toxic substances in the environment Hazards and their effects Risk assessment and risk management Philosophical and policy approaches to risk

Environmental health Environmental health assesses natural and human-caused environmental factors that influence human health and quality of life

Types of environmental hazards There are four types of environmental hazards Physical Chemical Biological Cultural

Physical hazards Occur naturally in our environment Earthquakes, volcanoes, fires, floods, droughts, exposure to UV light, temperature extremes We increase our risk by deforesting slopes (landslides), channelizing rivers (flooding), etc.

Chemical hazards Synthetic chemicals Natural chemicals Pharmaceuticals Disinfectants Pesticides Solvents Natural chemicals Venom Plant poisons

Biological hazards Result from ecological interactions Infectious disease = viruses, bacteria, and other pathogens parasitize humans Vectors = organisms that transfers pathogens to a host

Cultural hazards Result from our lifestyles Where we live, our socioeconomic status, our occupation, our behavioral choices Smoking, drug use, diet and nutrition, crime, mode of transportation

Some hazards are indoors Radon = a highly toxic, radioactive gas Colorless, odorless, and difficult to detect Can build up in basements Asbestos = a fibrous mineral Used for insulation, sound-deadening, and resistance to fire Asbestosis = scarred lungs that cease to function

Other indoor hazards Lead poisoning = caused by ingestion of lead Damages the brain, liver, kidney, and stomach Causes learning problems, behavior abnormalities, and death Exposure from lead paint or from drinking water that flows through lead pipes Polybrominated diphenyl ethers (PBDEs) a fire- retardant chemical Used in computers, plastics, and furniture Mimics hormones Also affects brain and nervous system development May cause cancer

Disease – a major focus Despite our technology, disease kills most of us Disease has a genetic and environmental basis Cancer, heart disease, respiratory disorders Poverty and poor hygiene foster illnesses

Infectious disease Infectious diseases kill 15 million people/year Half of all deaths in developing countries Public health efforts are having an effect But some diseases (AIDS) are still spreading And others develop resistance to antibiotics

Disease, society, the environment Lifestyles in developed nations increase the rate of non-infectious disease (diabetes, cardiovascular) Our mobility spreads diseases West Nile Virus spread from Africa to all of the lower 48 U.S. states in 5 years New diseases are emerging H5N1 avian flu, H1N1 swine flu Climate change will expand the range of diseases

The best first step The best way to reduce disease? Improve the basic living conditions of the poor Food security, sanitation, clean drinking water

Other public health actions Expanded access to health care Health clinics, immunizations Pre- and postnatal care Education campaigns work in rich and poor nations Public service and governments give advice Packaging and ads advise us on smoking, etc. Sex and reproductive health education slows population growth and spread of HIV/AIDS

Toxicology Toxicology = the study of the effects of poisonous substances on humans and other organisms Toxicity = the degree of harm a toxicant can inflict “The dose makes the poison” = toxicity depends on the combined effect of the chemical and its quantity Toxicant = any toxic substance (poison) Environmental toxicology = deals with toxic substances that come from or are discharged into the environment

Toxic substances in the environment The environment contains natural chemicals that may pose health risks Toxins = toxic chemicals made in tissues of living organisms But synthetic chemicals are also in our environment Every human carries traces of industrial chemicals in their bodies

They are all around us In 2002 study, 80% of U.S. streams contained trace amounts of 82 contaminants In 2006 study, 42 volatile organic compounds (VOCs) in 92% of aquifers tested Pesticides are present in streams and groundwater at levels high enough to be harmful to aquatic and human life

Perspective Rachel Carson’s Silent Spring (1962) showed DDT’s risks to people, wildlife, and ecosystems Prior to that, untested pesticides were sprayed over public areas with assumption they would do no harm But here is a tradeoff between the risks and rewards of most hazards Synthetic chemicals have helped to give us our high standard of living

Types of toxicants Carcinogens = cause cancer – can be hard to identify (long time between exposure and onset) Mutagens = cause DNA mutations Teratogens = cause birth defects in embryos Neurotoxins = assault the nervous system Allergens = over-activate the immune system Endocrine disruptors = affect the endocrine (hormone) system

Endocrine disruptors Hormones Endocrine disruptors Normally present at very low concentrations Stimulate growth, development, and sexual maturity Endocrine disruptors Block natural hormones from performing their function Mimic hormones, misdirecting the body’s response Bisphenol A (BPA) binds to estrogen receptors Phthalates, used to soften plastics and enhance fragrances, are a widely used endocrine disruptor

Toxicants move in water Runoff carries toxins from land to surface water Chemicals in the soil can leach into groundwater, contaminating drinking water Chemicals enter organisms through drinking or absorption Aquatic organisms (fish, frogs, etc.) are good pollution indicators

Toxicants move in the air As simple as pesticide drift where sprayed pesticides are carried downwind into adjacent fields As complex as the long- distance transport of chemicals to polar regions where synthetic chemicals are found in the middle of wilderness areas

Environmental fate of toxicants Persistence Some degrade quickly and become harmless Others remain unaltered and persist for decades Rates of degradation depend on the substance, temperature, moisture, and sun exposure Breakdown products Simpler chemicals formed when toxicants degrade May be more or less harmful than the original substance DDT degrades into DDE, which is also highly persistent and toxic

Fate of toxicants in organisms Toxicants in the body can be excreted, degraded, or stored Bioaccumulation = toxicants build up in animal tissues Biomagnification = concentrations of toxicants become magnified up the food chain

Studying toxic effects Wildlife studies integrate field and lab work Museum collections provide data from times before synthetic chemicals were used Measurements from animals in the wild can be compared to controlled experiments in the lab

Human studies Case history approach = studies individual patients Autopsies tell us about lethal doses Don’t tell about rare, new, or low-concentration toxins Don’t tell about probability and risk Epidemiological studies = large-scale comparisons between exposed and unexposed groups Studies can last for years Yield accurate predictions about risk Measure an association between a health hazard and an effect – but not necessarily the cause of the effect

Laboratory studies Manipulative experiments show causation Animals are used as test subjects Mammals share evolutionary history Substances that harm rats and mice probably harm us Some people object to animal tests New techniques may replace some live- animal testing

Dose-response Dose-response analysis = measures the strength of the effect a toxicant produces or the number of animals affected at different doses Dose = the amount of substance the test animal receives Response = the type or magnitude of negative effects

Dose-response curves Dose-response curve = the dose plotted against the response LD50/ED50= the amount of toxicant required to kill 50% of the subjects Threshold dose = the level where observable responses begin to occur

Unusual dose-response curves Sometimes a response decreases as a dose increases, creating an inverted J- or U-shape dose- response curve Counterintuitive curves occur with endocrine disruptors because the hormone system is geared to respond to very low levels

Variation in response Different people respond differently to toxicants Sensitivity is affected by Genetics Surrounding environmental conditions General health conditions Sex, age, and weight Exposure route (inhalation, ingestion, dermal contact) Fetuses, infants, and young children are more sensitive

Variation in exposure The type of exposure affects the response Acute exposure = high exposure for short periods Easy to recognize Discrete events: ingestion, oil spills, nuclear accident, etc. Chronic exposure = low exposure for long periods More common but harder to detect and diagnose Affects organs gradually: lung cancer, liver damage Cause and effect may not be easily apparent

Nature is messy In the real world, toxicants do not exist in isolation Difficult to determine the impact of mixed hazards They may act in ways that cannot be predicted from the effects of each in isolation Mixed toxicants can sum, cancel out, or multiply each other’s effects Synergistic effects = interactive impacts that are greater than the sum of their constituent effects

Evaluating hazards from toxicants Given all the variables connecting a toxicant to an actual health effect, a probability-based approach must be used to quantify such hazards Risk = the probability that some harmful outcome will result from a given action, event, or substance Everything we do involves some risk We try to minimize risk but perception is not reality We feel more at risk when we do not control a situation

Risk Assessment The quantitative determination of risk Risk assessment has several steps: Scientific study of the toxicity effects of substances Development of “exposure scenarios” for a population’s exposure to the substances in question (frequency, duration, concentrations, exposure routes) Calculation of risks posed by combining toxicity and exposure information

Risk management Risk management = decisions/policies to minimize risk Several Federal agencies manage environmental risk U.S. EPA, the Centers for Disease Control (CDC), the Food and Drug Administration (FDA) Scientific assessments are considered with economic, social, and political needs and values Comparing costs and benefits is hard Benefits are economic and easy to calculate Health risks (costs) are hard-to-measure probabilities of a few people suffering and lots of people not

Risk management visualized

Philosophies of risk management Innocent-until-proven-guilty: assumes a substance is harmless until it is shown to be harmful Helps technological innovation and economic advancement But it allows dangerous substances to be used Precautionary principle: assumes a substance is harmful until it is shown to be harmless Identifies troublesome toxicants before being released May impede the pace of technology and economic advance

Philosophy affects policy Different nations use different policies Europe use the precautionary principle The U.S. uses innocent- until-proven-guilty Who should have to prove a product is safe: the manufacturers or government/citizens?

Major U.S. laws - TSCA The Toxic Substances Control Act (TSCA, 1976) charges EPA with monitoring chemicals made in or imported into the U.S. Many health advocates think the TSCA is too weak 83,000 chemicals are “grandfathered” Catch-22 – to get detailed meaningful testing, toxicity must already be proven Only 10% of have been thoroughly tested for toxicity Only 2% tested for carcinogenicity, mutagenicity, etc. Almost none have been tested for endocrine, nervous, or immune system damage

Major U.S. laws - FIFRA The Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA, 1974) charges EPA with “registering” new pesticides Manufacturers provide toxicity & safety information EPA examines ingredients, use, etc. to determine risks to people, other organisms, water, or air It approves, denies, or sets limits on the chemical’s sale and use, and approves language used on the label Hazardous chemicals are approved if economic benefits outweigh hazards