Environmental Science

Unit 4 - Risk, Toxicology, & Human Health

(STE 7th ed. Chapter 11)

Where are we going?

- Types of hazards- Toxicology- Chemical hazards- Biological hazards- Risk Analysis

estimating risk, major risks, issues

Types of Hazards

• Risk is a measure of the possibility of experiencing a hazard that can cause harm

– expressed as a probability; 1 in 200, 1 in 1000 etc.e.g. risk of death from flying in US 1 in 7,000,000

– risk assessment involves estimation of the probability of harm to human health, society, or the environment that may result from exposure to specific hazards

– risk management involves the decision to reduce a risk and the costs associated

Types of Hazards

Identify the (i) Risk, (ii) Hazard and (iii) Risk Management

Types of Hazards Risk as a Probability

NYT Jan 29th 1995

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NOVAHow Risky is Flying?

NOVA: Deadliest Plane Crash

NOVAHow Risky is Flying?

NOVA: Deadliest Plane Crash

Types of Hazards Major Hazards

• cultural hazards

• chemical hazards

• physical hazardsnoise, fire, tornadoes, hurricanes, earthquakes, volcanic eruptions, floods, & ionizing radiation;

• biological hazardspathogens, pollen & other allergens, & animals such as bees & poisonous snakes

unsafe working conditions, smoking, poor diet, drugs, drinking, driving, flying, criminal assault, poverty;

harmful chemicals in air, water, soil, & food;

Causes of DeathAnnual Deaths

WHO estimates 80 x 106 deaths 1950-2000

3 x more than all wars of 20th century

US deaths in 2003

3 x 400 passenger jets crashing every day

+ many more

MovieThe Realities of Risk (13 of 29 mins)

View the following movie:http://vega.org.uk/video/programme/5(part of the series http://www.open2.net/nextbigthing/

Questions:

(i) What is risk bootstrapping?

(ii) Why does the scientist think it was ‘daft’ to ban the pesticide ‘alar’?

Case Study: A Black Day in Bhopal, India

• The world’s worst industrial accident:1984 pesticide plant, Bhopal India.

– An explosion at Union Carbide pesticide plant in an underground storage tank released a large quantity of highly toxic methyl isocyanate (MIC) gas.

– 15,000-22,000 people died

– Indian officials claim that simple upgrades could have prevented the tragedy.

Toxicology

• study of the adverse effects of chemicals on health

– toxicity: measure of how harmful a substance is; depends on:

– dose: amount of a potentially harmful substance ingested, inhaled, or absorbed through the skin;

– response: resulting type & amount of damage to health may be acute or chronic

Also: frequency of exposure, age, effectiveness of detox systems, genetics

Toxicology

The dose makes the poisonAny chemical be it natural or synthetic can be harmful

Should we be concerned?…traces of synthetic chemicals in our environment

• Lack of data

• Effects difficult to determine

• Life expectancy has increased

• Lower levels and new contaminants are being detected due to new technology

Poor diet + pollution = brain damage

Which is major factor?

Misconception

• Misconception that all natural chemicals are safe and all sythentics are bad

e.g. fruit seeds and pips form cyanide in the stomach, green potatoes, naturally occuring pesticides, mould/fungi on food

ToxicologyToxicity of Chemicals

• Animal testing, case and epidemiological reports

• generally defined by LD50 – amount in a dose that kills 50 %

of population in 14 days

• poison: legally defined as a chemical that has an LD50 of 50 milligrams or less per kilogram of body weight

Toxicity Rating LD50

Average Lethal Dose Examples

super toxic < 0.01 less than 1 drop nerve gases, botulism, mushroom toxins, dioxin

extremely toxic < 5 less than 7 drops

potassium cyanide, heroin, atropine, parathion, nicotine

very toxic 5–50 7 drops to 1 tsp mercury salts, morphine, codeine

toxic 50–500 1 teaspoon to 1 ounce

lead salts, DDT, sodium hydroxide, fluoride, sulfuric acid, caffeine, carbon tetrachloride

moderately toxic

500– 5,000

1 ounce to 1 pint

methyl alcohol, ether, pehobarbital, amphetamines, kerosine, aspirin

slightly toxic 5,000– 15,000

1 pint to 1 quart ethyl alcohol, lysol, soaps

Table 17–1

ToxicologyResponses

• Acute toxicity:

– Sudden and severe exposure

– Rapid onset of symptoms

• Chronic toxicity:

– Continuous, long-term exposure

– Relatively low dose

– Cancer, birth defects, neurological damage

Same chemical may show both effects

e.g. skin irritation vs. cancer

ToxicologyDose-Response

• Acute toxicity tests

• design:

– Controls (no dose) & treatments (low to high dose)

– test organism (usually rats or mice)

– replicates (usually 60–200 animals total)

– period (often 14 days)

High doses are used to reduce no. subjects and increase speed of test

- Extrapolated down to low doses

2-5 years, $200,000-$2 million

Dose–Response Curves

Any dosage is harmful

(Assumed in most cases)

Lower limit to harmful dose

Question

If a dose of 0.1 μg is sufficient to kill a mouse, what mass would be fatal to you?

What average level of substance would have to be present in drinking water for you to receive a fatal dose in one week?

Ratio mass human : mouse = 200 : 1

Mass that would kill you = 200 x 0.1 μg = 20 μg

2 L water d-1 x 7 d w-1 = 14L

For fatal dose 20 μg / 14 L = 1 μg L-1 = 1 ppb

Toxicology

• Complications

– Different physiology

– Synergestic effects – difficult and expensive to test for 1, no. tests multiply when consider more than 1

• Because of complexity in determining toxicity allowed exposure levels are set 100-1000 x below harmful levels

Toxicology

Estimating human exposure to chemicals and their effects is very difficult because of the many and often poorly understood variables involved.

Toxicology

• Children are more susceptible to the effects of toxic substances because:– Children breathe more air, drink more water, and eat more

food per unit of body weight than adults.– They are exposed to toxins when they put their fingers or

other objects in their mouths.– Children usually have less well-developed immune systems

and detoxification processes than adults

Toxicology

• The U.S. Environmental Protection Agency proposed that regulators should assume children have 10 times the exposure risk of adults to cancer-causing chemicals

• Some health scientists contend that regulators should assume a risk 100 times that of adults

Background

• Birth defects due to exposure to synthetic chemicals

• Toxicity to mammals and birds• Carcinogenic effects• Xenoestrogenic effects

•Gt. Lakes cormorant with crossed bill

ES&T Article

Chemical Hazards

Toxic chemicals(kill)

Hazardous chemicals(harm)

Temporary or Permanent harm or death:

• mutagens: cause random mutations (changes in the DNA)e.g. nitrous acid, UV, γ, α radiation

• teratogens: cause birth defects e.g., alcohol, PCBs, steroid hormones, heavy metals

• neurotoxins: damage nervous systeme.g., DDT, alcohol, heavy metals

• carcinogens: cause cancer- over 100 types

e.g. benzene, dioxin, radionuclides, asbestos

Chemical HazardsToxic Chemicals

http://en.wikipedia.org/wiki/International_Agency_for_Research_on_Cancer

Hazardous Chemicals

cause harm in various ways

• flammable or explosive (e.g., gasoline);

• irritating or damaging to skin or lungs (e.g., strong acids or alkalis)

• interfering with or preventing oxygen uptake & distribution (e.g., carbon monoxide, CO);

• inducing allergic reactions of the immune system (allergens)

Dioxin IncidentsTimes Beach, Missouri

NYT 121682

Dioxin IncidentsTimes Beach, Missouri

Shown in History Channel Modern Marvels #20

1972-76dirt roads were sprayed with waste oil containing super concentrated dioxin from Agent Orange manufacture

1992 - Town was demolished

1997 - 265,000 tons of soil was incinerated on site

Now Route 66 State Park

Long-term exposure to some chemicals at low doses may disrupt the body’s:• Immune system: specialized cells and tissues that

protect the body against disease and harmful substances.• Nervous system: brain, spinal cord, and peripheral

nerves.• Endocrine system: complex network of glands that

release minute amounts of hormones into the bloodstream.

Effects at Low Doses

Hormone Disrupters

• hormones: molecules that act as messengers to regulate various bodily processes, including reproduction, growth, & development (endocrine system)

• hormone disrupters: interfere with hormone function

• so far 51 chemicals shown to act as hormone disrupters on wildlife, laboratory animals, & humans

- e.g., dioxins, certain PCBs, various chemicals in plastics, some pesticides, lead & mercury

• 1997 study shows that sperm count of men in U.S. & Europe has declined 50%

Hormone Disrupters

Molecules of certain synthetic chemicals have shapes similar to those of natural hormones and can adversely affect the endocrine system

Biomagnification

A chemical whose concentration increases along a food chain is said to be biomagnified

•DDT concentration in Lake Ontario Trout

Biomagnification results from a

sequence of bioaccumulation steps

Biomagnification

when a chemical becomes concentrated in specific organs or tissues

e.g., DDT, dioxin, PCBs accumulates in fatty tissues

Known as persistent organic pollution (POP)

contributing factors:• organic chemical (like dissolves like)• high persistence• not easily broken down or excreted

Health EffectsEffects in Utero

• Exposure to low levels results in impaired intellectual development

NYT, September 12th 1998

Health EffectsDioxins, Furans and PCBs in Food

•95% of human exposure to•dioxins and furans is from•the presence of these•compounds from food•Fresh water fish has the•highest level of PCBs

•Schecter et al., 1997 NYT July 2nd 2003

Why do we know so little?

• Under existing laws, most chemicals are considered innocent until proven guilty, and estimating their toxicity is difficult, uncertain, and expensive.– Federal and state governments do not regulate about 99.5%

of the commercially used chemicals in the U.S.– Only 10% of 80,000 chemicals have been tested for toxicity– Chemicals are considered innnocent until proven guilty

Pollution Prevention“better safe than sorry”

• Some scientists and health officials say that preliminary but not conclusive evidence that a chemical causes significant harm should spur preventive action (precautionary principle)

• Manufacturers contend that wide-spread application of the precautionary principle would make it too expensive to introduce new chemicals and technologies

Pollution and Cancer

• Bruce Ames believes that the focus on man-made chemicals as causes of cancer is a distraction from the real threats of smoking and diet

• Media:http://www.bruceames.org/bnamedia.html

Environmental Testing

• Experiments with test animals are used to determine how carcinogenic a compound is, take many years

• The simple Ames test can be used fairly rapidly to distinguish compounds likely to be human carcinogens

Biological Hazards

nontransmissible diseases

• cardiovascular disorders, cancers, emphysema, & malnutrition;

transmissible (infectious) diseases

• caused by bacteria, viruses, protozoa, or parasites

• colds, flus, hepatitis, sexually transmitted diseases, malaria

• many transmissible diseases spreading over broad geographic areas

- Lyme disease (bacteria)

- Giardia (protozoa)

Biological Hazards

Infectious disease pathways

Transmissible Diseases

WHO estimates that each year the world’s seven deadliest infections kill 13.6 million people – most of them the poor in developing countries

Case Study: Growing Germ Resistance to Antibiotics

• Rabidly producing infectious bacteria ‘superbugs’ (e.g. MRSA) are becoming genetically resistant to widely used antibiotics due to:

– Genetic resistance: Antibiotic resistance is a consequence of evolution via natural selection

– Overuse of antibiotics:

(i) A 2000 study found that half of the antibiotics used to treat humans were prescribed unnecessarily

(ii) over 70% of all antibiotics used in US given to animals in the absence of disease

Case Study: The Growing Global Threat from Tuberculosis

• The highly infectious tuberculosis (TB) kills 1.7 million people per year and could kill 25 million people 2020.

• Recent increases in TB are due to:– Lack of TB screening and control programs especially in developing

countries due to expenses– Genetic resistance to the most effective antibiotics

Viral Diseases

• Flu, HIV, and hepatitis B viruses infect and kill many more people each year then highly publicized West Nile and SARS viruses– The influenza virus is the biggest killer virus worldwide– Pigs, chickens, ducks, and geese are the major reservoirs of flu. As

they move from one species to another, they can mutate and exchange genetic material with other viruses

• HIV is the second biggest killer virus worldwide. Five major priorities to slow the spread of the disease are:– Quickly reduce the number of new infections to prevent further

spread– Concentrate on groups in a society that are likely to spread the

disease– Provide free HIV testing and pressure people to get tested.– Implement educational programs– Provide free or low-cost drugs to slow disease progress

Case Study: Malaria – Death by MosquitoMalaria kills about 2 million

people per year and has probably killed more than all of the wars ever fought

Case Study: Malaria – Death by Mosquito

• Spraying insides of homes with low concentrations of the pesticide DDT greatly reduces the number of malaria cases.– Under international treaty enacted in 2002, DDT is being

phased out in developing countries

http://www.doc3d.com/malaria/malaria_WMV.html

http://www.learner.org/channel/courses/biology/units/infect/images.html

Bioterrorism

• Possible targets: air, water, and food

• Inexpensive

• Fairly easy to produce biological agents

• Recombinant DNA techniques

Risk Analysis

Scientists have developed ways to evaluate and compare risks, decide how much risk is acceptable, and find affordable ways to reduce it.

Risk AssessmentTo perform risk assessment it is important to know:• Hazard evaluation information (acute, cancer ???)• Quantitative dose-response information• An estimate of the potential human exposure to the chemical

The highest dose at which no observable effects level is called NOEL

(expressed in terms of mg kg-1 body weight day-1)

To determine the threshold level for the most sensitive members of the human population, EPA uses Toxicity reference dose or RfD.

(RfD is also referred as Acceptable Daily Intake or ADI)

RfD (or ADI) = NOEL/100 (divide by safety factor of 100)

If NOEL for a chemical is 0.01 mg/kg/day, the ADI or RfD for a 80 kg man

would be (0.01 mg/kg/day /100) x 80 kg = 0.008 mg

• Estimating risks from using many technologies is difficult due to unpredictability of human behavior, chance, and sabotage.

• Reliability of a system is multiplicative:– If a nuclear power plant is 95% reliable and human

reliability is 75%, then the overall reliability is (0.95 X 0.75 = 0.71) 71%.

RISK ANALYSIS

• Annual deaths in the U.S. from tobacco use and other causes in 2003

RISK ANALYSIS

• Number of deaths per year in the world from various causes. Parentheses show deaths in terms of the number of fully loaded 400-passenger jumbo jets crashing every day of the year with no survivors.

Perceiving Risk

• Most individuals evaluate the relative risk they face based on:– Degree of control– Fear of unknown– Whether we voluntarily take the risk– Whether risk is catastrophic– Unfair distribution of risk

• Sometimes misleading information, denial, and irrational fears can cloud judgment

RISK ANALYSIS

• Comparisons of risks people face expressed in terms of shorter average life span.

Becoming Better at Risk Analysis

• We can carefully evaluate or tune out of the barrage of bad news covered in the media, compare risks, and concentrate on reducing personal risks over which we have some control