Environmental Health And Toxicology

CASE STUDY

ENVIRONMENTAL HEALTH The study and practice of environmental health assess environmental factors that influence human health and quality of life

3 Categories of human health risk Physical Biological Chemical

Leading Causes of Death - Global

Leading Health Risks - Global Low Income Countries High Income Countries

Environmental Risks: Physical Occur naturally in the environment Earthquakes Fires Floods and droughts UV from the sun

Environmental Risks : Cultural Result from where we live, socioeconomic status, occupation or behavioral choice Choosing to smoke, poor diet, living in proximity to toxic waste are all cultural hazards Not necessarily a choice

Environmental Risks: Chemical Include synthetic chemicals such as pesticides and disinfectants Include chemicals produced naturally by organisms

Environmental Risks: Chemical Neurotoxins - chemicals that disrupt the nervous system (Hg, Pb) Carcinogens - chemicals that cause cancer Teratogens - chemicals that interfere with the normal development of embryos or fetuses (thalidomide)

Environmental Risks: Chemical Allergens - chemicals that cause allergic reactions Endocrine disruptors - chemicals that interfere with the normal functioning of hormones in an animal’s body (herbicides, nitrates, BPA) Mutagens are chemicals that cause mutations in the DNA of organisms

Environmental Risks: Biological A disease is any impaired function of the body with characteristic symptoms Caused by virus, bacterium, fungus or other pathogen If illness can be spread to other humans, then it is an infectious disease (e.g., malaria, cholera, flu)

Environmental Risks: Biological Chronic diseases slowly impair the functioning of the body – Heart disease Acute diseases rapidly impair the functioning of the body – Ebola

Risk Factors for Disease Many major killers (cancer, heart disease, etc.)have genetic bases but are also influenced by environmental factors Malnutrition can foster a wide variety of illnesses, Poverty, poor hygiene, lifestyle choices, and lack of exercise also contribute

Risk Factors for Disease Infectious disease involves a pathogen or an infection may occur through a vector In order to predict and prevent infectious disease, experts deal with the interrelationships among technology, land use, and ecology

Risk Factors for Disease Increased human mobility has made diseases a potential global epidemic. Diseases like tuberculosis and malaria are becoming more drug resistant Through habitat alteration and climate change, tropical diseases are moving further from the equator

Risk Factors for Disease An epidemic occurs when a pathogen causes a rapid increase in disease A pandemic occurs when an epidemic covers a large geographic region (continent)

Historically Important Diseases Plague (bubonic plague, black death) caused by a bacterium carried by fleas Malaria caused by a protist carried by mosquito Tuberculosis is caused by a bacterium spread by person-to-person airborne

Emergent Diseases HIV/AIDS (virus) Ebola Hemorrhagic Fever (virus) Mad Cow Disease (prion) Bird Flu (H1N1 virus) made the ‘jump’ from bird to human West Nile Virus also sourced from birds

Genetic Resistance to Antibiotics Is Increasing Methicillin-resistant Staphylococcus aureus (MRSA) Tuberculosis Influenza or flu virus - #1 Killer HIV - #2 Killer Hepatitis B virus (HBV) - #3 Killer

Environmental Health Hazards Exist Indoors Indoor environmental health threats include radon, lead poisoning, and asbestos A recently recognized hazard is a group of chemicals known as polybrominated diphenyl ethers (PBDEs). These chemicals appear to affect thyroid hormones in animals, (banned in Europe)

Toxicology Studies the effects of poisonous substances on humans and other organisms A toxicant, or toxic agent, must be compared to other substances to determine the toxicity, or the degree of harm that it can inflict

Toxicology With toxins, “the dose makes the poison” means that the quantity received is an important factor in the damage done Environmental toxicology deals specifically with toxic substances that come from or are discharged into the environment, and includes the study of health effects on humans, other animals, and ecosystems

TOXIC AGENTS IN THE ENVIRONMENT

Synthetic Chemicals Thousands of synthetic chemicals have been manufactured and many have found their way into soil, air, and water. Every one of us carries traces of numerous industrial chemicals in our bodies Very few of these chemicals have been tested for harmful effects

Silent Spring Began the public debate over pesticide use Rachel Carson was a naturalist, author, and government scientist She showed that DDT and artificial pesticides in general were hazardous to people, wildlife, and the environment

Silent Spring The book was a bestseller and generated significant social changes in views and actions toward the environment The United States manufactures and exports DDT to countries that still use it, especially for mosquito control

Endocrine Disruptors First presented in 1996 in the book Our Stolen Future Endocrine effects have been most widely found in animals World-wide drops in sperm count (humans) may be attributed to this phenomenon

Endocrine Disruptors Endocrine response is sensitive to minute quantities Debate generated – herbicide mfr’s stand to lose a LOT of $ Bisphenol-A (a plastic) is an estrogen mimic Atrazine has also been linked

Toxins and Water Water runoff carries toxins from large land areas & concentrates them in small volumes of surface waters (remember watersheds?) Many chemicals are soluble in water, thus accessible to organisms; therefore… Fish, frogs, stream invertebrates are good indicators

Persistence DDT and PCBs have long persistence times, Bt toxin is short-lived Breakdown products may be just as toxic or more toxic than parent compound Many toxins are designed to persist

Synergy Synergistic interactions- when two risks come together and cause more harm that one would. For example, the health impact of a carcinogen such as asbestos can be much higher if an individual also smokes tobacco

Toxicants and the Food Chain Fat-soluble toxicants (DDT 7 DDE) are absorbed and stored in fatty tissue Build-up of toxicants in animal tissue is bioaccumulation Toxicants that bioaccumulate can be transferred to other organisms in the food chain, a process called biomagnification

Not All Toxicants Are Synthetic Toxicants also exist naturally in the environment Products of microbes, fungi, etc. are examples Debate over risk

STUDYING EFFECTS OF HAZARDS

Wildlife v. Human Studies Wildlife studies use observations in the field and lab Human studies rely on case histories, epidemiology, and animal testing Epidemiological studies involve large-scale comparisons among groups of people

Wildlife v. Human Studies Advantages of epidemiological studies: realism and ability to enable accurate predictions Drawbacks include length of time it takes to obtain results and inability to address possible effects of new products Manipulative experiments are then needed (animals tested)

Dose-Response Analysis Standard method of testing lab animals Dose is the amount of toxicant received Response is the type or magnitude of negative effects; generally quantified Once a dose-response curve is plotted, scientist calculate the toxicity (LD 50 ) LD 50 is the amount of toxicant it takes to kill half the population of study animals

Dose-Response Analysis ED 50 is the level of toxicant at which 50% of the population to display harmful effects Sometimes responses occur only above a certain dose (threshold dose) Sometimes responses decrease with increase in dose (endocrine disruptors)

Dose-Response Analysis Knowing the shape of the dose-response curve is important for predicting effects For some toxicants, (endocrine disruptors) the U-shaped curve indicates impact at low concentrations Individuals vary considerably in response to hazards

Type of Exposure Acute exposure – high exposure for short duration Chronic exposure – low exposure over long duration Acute exposure is easier to recognize Chronic is more common but difficult to detect and diagnose

Type of Exposure Interactive impacts may result when toxicants are mixed Synergistic effects: effects are more than the sum of the parts Traditionally, environmental health has tackled effects of single hazards

RISK ASSESSMENT & MANAGEMENT

Risk Expressed in terms of probability Exposure causes some probability of harm; a statistical chance that damage will result Probability depends on the toxin, strength, frequency and duration of exposure, sensitivity

Risk Risk assessment analyzes risk quantitatively It involves the scientific study of toxicity and likely extent of exposure Often performed by scientists associated with the industries Risk management combines science and social factors Usually handled by federal agencies; considered in light of economic, social, political needs and values

PHILOSOPHY AND POLICY

Determining Safety Innocent-until-proven-guilty approach: assume substances are harmless until shown to be harmful Assume substances are harmful until shown to be harmless

Policy Reflects Philosophy Most nations blend the two approaches European nations follow precautionary principle In US – largely innocent-until-proven-guilty approach Tracking and regulation of synthetic chemicals is shared among federal agencies

Policy Reflects Philosophy EPA regulates under the Toxic Substances Control Act (TSCA) – 1 st law to require screening before entering marketplace – Many view TSCA as being too weak – Manufacturers should be made to bear the burden of proof for the safety of their products

EPA Regulates Pesticides Registration process involves risk assessment and management Process allows hazardous chemicals to be approved if they offer enough economic benefit

Toxicants are Regulated Internationally Stockholm Convention (2004) ratified by 140 nations – 1 st aim – end the use of the “dirty dozen” EU’s REACH (registration, evaluation, authorization and restriction of chemicals) – burden of proof for chemical safety shifted from gov’t to industry Cost = $5 billion, benefits to public health estimated to be $67 billion