Chapter 8: Environmental Health and Toxicology

By Anna Blum and Maggie Ellis

Environmental Health

• Environmental Health-focused on factors that cause disease, including elements of the natural, social, cultural, and technological world in which we live

• Ever since Silent Spring, focus on discharge, movement, fate, and effects of synthetic chemical toxins

• Risks come from:– Toxins – Radiation – Infectious Agents – Trauma – Pollution

The Global Disease Burden is Changing

• Disease burden calculated in terms of DALYs• Chronic conditions now affect poor as well as

affluent because people live longer• Causes: By 2020

– Heart disease to be leading cause of global disease– Global cancer rates will increase by 50%– Psychiatric and neurological conditions will increase

from 10% to 15% (Depression expected to be the second largest cause of all years lived with disability worldwide)

– Chronic obstructive lung diseases expected to increase

Things That Kill You (part 1)

• Heart disease number one killer, kills women more than men

• Suicide is the fourth largest cause of female deaths

• Smoking predicted to be single biggest cause of death worldwide

Infectious Diseases Are Scary

• Communicable diseases responsible for about 1/3 of all disease-related mortality

• 11 million children under 5 die annually due to infectious diseases

• Most of these deaths could be eliminated through better nutrition, clean water, improved sanitation, and inexpensive inoculations

More Infectious Diseases• Malaria- 515 million cases each year, 1 million

people die• Spreading as climate changes expands

mosquito habitats• Emergent diseases-those not previously known

or have been absent for at least 20 years– SARS– Avian Flu– H1N1– Ebola– West Nile Virus– AIDS/HIV

Case Study: Chronic Wasting Disease

• Chronic Wasting Disease—deer and elk populations in North America– Caused by strange prion protein– One of a family of irreversible,

degenerative neurological diseases known as transmissible spongiform encephalopathies (TSE) including mad cow

– Canadian government spending $65 million to fight CWD

– Cattle imported from Canada found to have TSE in 2004

– Worry about it spreading to humans, as of yet no one in the US has died

Causes of Emergent Disease• Environmental change stresses

biological systems– Cut down forests– Drain wetlands– Invasive species introduced by

humans– Increased human incursion into

wilderness– Increased consumption of wild

species allows diseases to jump barriers---3/4 of all emerging diseases are zoonotic, or shared by animals and humans

– Climate change allows animals to expand their range

Increasing Resistance to Antibiotics and

Pesticides is• Partially through natural selection and ability to evolve rapidly– Mutated bacteria that are resistant live and multiply via natural

selection

• Partially through human tendency to use control measures aimlessly– DDT spread everywhere, so that some were only minimally

exposed—encouraged natural selection and the survival of resistant

Antibiotics, Farming, and Disease• More than half of the antibiotics

used in the US each year are fed to livestock

• These antibiotics and hormones are excreted in urine and feces

• Spread on land or water where they evolve into supervirulent pathogens

• At least half of the 100 million antibiotic doses prescribed to humans each year are unnecessary or wrong—improper disposal or use can lead to illness

Toxicology• Study of toxins (poisons) and

their effects on living systems

• Damage or kill living organisms because they react with cellular components to disrupt metabolic functions

• Toxins harmful even in dilute concentrations

Ecotoxicology• All toxins hazardous, but not all

hazardous materials are toxic– Some materials are hazardous

because they are flammable, explosive, etc.

• Environmental Toxicology=ecotoxicology, deals with the interactions, transformation, fate, and effects of natural and synthetic chemicals in the biosphere, including individual organisms, populations, and whole ecosystems

How Do Toxins Affect Us?

• Allergens & Antigens• Immune system depressants• Endocrine disrupters• Sick building syndrome

– poor indoor air quality may cost USA $60 billion in sick days and reduced productivity

Teratogens • Chemicals or other factors that

specifically cause abnormalities during embryonic growth and development

• Example: Fetal alcohol syndrome- a cluster of symptoms including craniofacial abnormalities, developmental delays, behavioral problems, and mental defects that last throughout a child’s life

• Even on drink during pregnancy puts a child at risk

• By some estimates, between 300,000 and 600,000 children born every year in the US are exposed in the womb to unsafe levels of mercury

• Effects include reduced intelligence, ADD, and behavioral problems, costing $8.7 billion annually

Carcinogens• Substances that cause cancer• According to the American Cancer

Society, ½ males and 1/3 females will have some sort of cancer in their lifetime

• Debate over environment vs. lifestyle• According to the EPA, 200 million US

residents live in combined lifetime cancer risk form environmental carcinogens exceeds 1 in 100,000 or ten times the acceptable risk

Diet Affects Health• Strong correlation between cardiovascular disease and the

amount of salt and animal fat in one’s diet• Fruits, vegetables, whole grains, complex carbs, and dietary

fiber have a positive affect• Vitamins A,C, and E, substances produced in cruciferous

vegetables, and selenium seem to have anticancer effects• Every year in the US 300,000 deaths are linked to obesity• 1/3 of US children may become diabetic unless people start

eating less and exercising more, increased risk (1/2) for Black and Hispanic children

Case Study: Poisoning Bhopal• December 3rd, 1984

• Bhopal, central India, • Noxious gas methylisocyanate (MIC), a

component of pesticide Temik, made at the Union Carbide plant in Bhopal.

• Water had gotten into tank and it exploded, sending MIC throughout the city

• 15,000 died instantly; 800,000 suffered medical problems

• More than 20 years after the catastrophe, no one punished and most of the $470 million paid by Union Carbide has yet to be distributed

Solubility• Solubility is important in determining how, when,

and where a toxic material will move to the site of action

• Water soluble compounds move widely and rapidly and have ready access to most cells

• Oil or fat soluble compounds generally need a carrier to move but can easily penetrate cells– more likely to accumulate and be stored in lipid

deposits for years

Exposure & Susceptibility

• Airborne toxins generally cause more ill health

• Toxins also enter through food, water, skin contact

• Largest exposure for toxins

are found in industrial settings

• Condition of being & timing

of exposure influence toxicidty

Bioaccumulation & Biomagnification

• Cells have mechanisms for bioaccumulation– allows them to accumulate

nutrients and essential materials but also leaves the risk of absorbing bad toxins

• Bioaccumulation• Biomagnification: When the

toxic burden of a large number of organisms at a lower trophic level is accumulated and concentrated by a predator in a higher tropic level

Persistence• Some chemical compounds are unstable

and degrade rapidly so their concentrations decline quickly after release

• Others are more persistent and last for a few centuries– cause more problems and unexpected effects

Things That Kill You (part 2)

• PBDEs are in textiles, upholstery, and plastic. They effect behavioral & nervous system development

• PFOs and PFOA/C8s are found in nonstick, water-proof, stain-resistant products and everywhere. Literally. – cause liver damage, cancer, reproductive and developmental

problems in rats; kill pet birds

• Phthalates are found in cosmetics, deodorants, and many plastics– cause kidney and liver damage,

cancer in rats; endocrine hormone

disrupters that cause reproductive

abnormalities and decreased

fertility/quality of sperm

Things That Kill You (part 3)

• Perchlorate is a waterborne containment left over from propellants and rocket fuels; it pollutes water used to water crops. – Disrupts adult metabolism and childhood developments

• BPA is in polycarbonate plastic.– Causes abnormal chromosome numbers, aneuploidy

(the leading cause of mental retardations and miscarriages)

• Atrazine is a widely used herbicide– Causes birth defects, abnormal development

Interactions!• Antagonistic reactions

interfere with the effects or stimulate the breakdown of other chemicals

• Additive reactions occur together in exposure

• Synergism: An interaction in which one substance exacerbates the effects of another

Degradation & Excretion

• Enzymes process waster products and environmental poisons to reduce their toxicity– can make chemicals more dangerous by breakdown

ones that should not be broken down– Factors that affect post reproduction stages usually

don't effect reproductive success or exert selective pressure

• Excretion reduces the effects of

waste products and environmental toxins by

eliminating them from the body

Repair

• Our skin and organ linings have high cellular reproduction rates to replace injured cells– Chance that cells will lose normal

growth controls and create a tumor and irritants will be turned into carcinogens

Why Lab Animals Die• Because we test toxins on them!

• Expensive, time-consuming, painful to animals– takes hundreds of animals, years of work, thousands

of dollars for one text– however, most accurate and reliable data– more human toxicity tests are being developed

• Problems– differences in sensitivity in members of a population– unrelated species can react very differently to same

toxin

Acute versus Chronic

• Acute effects

• Chronic effects

• Usually difficult to detect

the specific health risks

because of other factors

• Different toxicity levels for everything

• Just because they are detectable doesn't mean you'll die

Risky Business• Risk: The possibility of

something undesirable will happen as a result of exposure to a hazard

• Risk assessment: The scientific process of estimating the threat hazards pose to health – Includes risk identification,

dose response assessment, exposure appraisal risk characterization

Why We Do Stupid Things (part 1)

• People downplay certain risks and emphasize others that suit their agenda

• Tolerate risks that we choose and

object those we don't• Have difficulty understanding and

believing probabilities• Personal experiences can be misleading

• Exaggerated view of our ability to control fate• Media gives a biased perspective of things

• Irrational fear or mistrust of new technology

Why We Do Stupid Things (part 2)• Most people will tolerate a higher

probability of an event if the harm caused by it is low

• If we enjoy or find an activity profitable, we will ignore the risks

• Perception of risks based on whether they are known or unknown, we are in control of the outcome or not, and how bad the results can be

Things That Keep You Alive• It is difficult to separate the effects of different hazards

and evaluate their risks accurately• When setting standards for environmental toxins,

consider:– combined effect of exposure to many different areas of

damage– different sensitivities of members of the population– effects of chronic and acute exposure– how does it affect our overall environment?