1. Toxicology

2. Toxicology studies poisonous substances
Toxicology = the study of the effects of poisonous substances on humans and other organisms
Toxicity = the degree of harm a toxicant can inflict
Toxicant = any toxic substance (poison)
“The dose makes the poison” = toxicity depends on the combined effect of the chemical and its quantity
Environmental toxicology = deals with toxic substances that come from or are discharged into the environment
Studies health effects on humans, other animals, and ecosystems
The Toxic Substances Control Act regulates Industrial chemicals

3. Four types of environmental hazards

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

5. Toxicants come in different types
Carcinogens = cause cancer
Hard to identify because of the long time between exposure and onset of cancer
Mutagens = cause DNA mutations
Can cause cancer
Teratogens = cause birth defects in embryos
Neurotoxins = assault the nervous system
Allergens = over activate the immune system
Endocrine disruptors = affect the endocrine (hormone) system

6. Individuals vary in their responses to hazards
Different people respond differently to hazards
Affected by genetics, surroundings, etc.
People in poor health are more sensitive
Sensitivity also varies with sex, age, and weight
Fetuses, infants, and young children are more sensitive
The Environmental Protection Agency (EPA) sets standards for responses based on adult responses
Often, standards are not low enough to protect babies

7. Some toxicants persist
Toxins can degrade quickly and become harmless
Or they may remain unaltered and persist for decades
Rates of degradation depend on the substance, temperature, moisture, and sun exposure
Breakdown products = simpler products that toxicants degrade into
May be more or less harmful than the original substance
DDT degrades into DDE, which is also highly persistent and toxic
PCB contamination a continuing problem because PCBs are non-biodegradable and persist in the environment

8. Routes of chemical transport
Transport of airborne toxicants, a specific problem in agricultural environments, is called pesticide drift.
All pesticides in the U.S. are registered through the EPA.
FIFRA (Federal Insecticide, Fungicide, and Rodenticide Act) and its later amendments were charge the EPA with registering new pesticides and regulating their sale, use, and labeling

9. Endocrine disruptors mimic hormones
Hormones stimulate growth, development, sexual maturity
Synthetic chemicals
Block hormones
Mimic hormones
The book Our Stolen Future (1996) was important because it focused on the impacts of endocrine-disrupting chemicals on humans.

10. Silent Spring began the debate over chemicals
In the 1960s, untested pesticides were sprayed over public areas, with assumption they would do no harm
Rachel Carson’s Silent Spring (1962) showed DDT’s risks to people, wildlife, and ecosystems
Chemical companies challenged the book
Discrediting Carson’s personal reputation
DDT was banned in the U.S. in 1973
But is still made in the U.S. and exported

11. Toxicants can accumulate and biomagnify
Toxicants in the body can be excreted, degraded, or stored
Fat-soluble toxicants are stored in fatty tissues
Bioaccumulation = toxicants build up in animal tissues
Biomagnification = concentrations of toxicants become magnified
Near extinction of peregrine falcons and bald eagles

12. Indoor environmental health hazards
Radon = a highly toxic, radioactive gas that is colorless and undetectable
It can build up in basements
Asbestos = a mineral that insulates, muffles sounds, and resists fire
Asbestosis = scarred lungs that cease to function

13. Lead poisoning
Lead poisoning = caused by lead, a heavy metal
Damages the brain, liver, kidney, and stomach
Causes learning problems, behavior abnormalities, and death
Exposure is from drinking water that flows through lead pipes or from lead paint
Education led to declines in poisoning, but China still used it in toy paint until recently

14. Much of the lead problem is in some older homes
Text in Arial black
28 point size – if possible
Nothing smaller than 24 point
7% of the homes in St. Lawrence County are considered to be putting their residents at risk with significant exposure to lead.

15. Synthetic chemicals are in all of us
Every one of us carries traces of hundreds of industrial chemicals in our bodies
Including toxic persistent organic pollutants restricted by international treaties
Babies are born “pre-polluted” – 232 chemicals were in umbilical cords of babies tested
Not all synthetic chemicals pose health risks
But very few of the 100,000 chemicals on the market have been tested
Of the chemicals that fall under the protection of the EPA 10% have been tested for toxicity and 2% have been tested for endocrine, nervous, or immune system damage.

16. The Dose Makes a Difference
“Too much of anything may be bad for you.” Consider the effects of one glass of beer vs. 20 glasses of beer – alcohol poisoning

17. Dose-response analysis
Dose-response analysis = measures the effect a toxicant produces or the number of animals affected
At different doses
Dose = amount of substance the test animal receives
Response = the type or magnitude of negative effects
Dose-response curve = the dose plotted against the response

18. The dose of toxicant which is deadly to 50% of the population
LD50
The dose of toxicant which is deadly to 50% of the population
Toxicologist often measure the toxicity of a substance in terms of the dose (or amount) of the substance that it takes to kill an organism (such as a lab mouse). the term LD50 (or lethal dose 50) refers to the dose of a toxicant that will kill 50% of the population – or half of the mice, in the case of this graphic.
LD50 is not the lethal dose for all individuals; some may be killed by much less, while others survive doses far higher than the LD50.

19. Dose response curves
LD50/ED50= the amount of toxicant required to kill (affect) 50% of the subjects
A high number indicates low toxicity
Threshold dose = the level where certain responses occur
Organs can metabolize or excrete low doses of a toxicant
Scientists extrapolate downward from animal studies to estimate the effect on humans

20. QUESTION: Interpreting Graphs and Data
If the “low” dose = 5 units of a chemical, the “medium” dose = 10 units, and the “high” dose = 15 units, how much of the chemical is required to kill 50% of the study population?
About 5 units
About 10 units
About 15 units
You can’t tell from the graph.
Answer: b

21. We express risk in terms of probability
Exposure to health threats doesn’t automatically produce an effect
Rather, it causes some probability (likelihood) of harm
A substance’s threat depends on its identity and strength
Chance and frequency of an encounter
An organism’s exposure and sensitivity to the threat
Risk = the probability that some harmful outcome will result from a given action, event, or substance
Probability = describes the likelihood of a certain outcome

22. What is the probability of a Risk?
0 = No Risk
1 = Risk
Closer to 0 the better
= 1 in 1 million chance

23. Toxicology Practice
1.The Toxic Substances Control Act regulates ________. 2. Pesticides in the United States are registered through the ________. 3. Transport of airborne toxicants, a specific problem in agricultural environments, is called pesticide ________. 4. The book Our Stolen Future was important because it ________. 5. Why is PCB contamination a continuing problem? 6. What was the result of FIFRA (Federal Insecticide, Fungicide, and Rodenticide Act)?

24. Toxicology Practice
7.Aquatic animals such as fish and frogs are especially good indicators of pollution because ________. 8. Of the chemicals that fall under the EPA ________% have been tested for toxicity and ________ have been tested for endocrine, nervous, or immune system damage. 9. The goal of the Stockholm Convention is to ________. 10. The Yaqui Valley, Mexico, study showed that ________ 11. Properties of toxicants likely to build up in animals through bioaccumulation are ________.

25. Toxicology Practice
12. Acute toxicity test are run to develop a _____________________ curve, which shows the effects of various doses of a toxic agent on a group of test organisms, 
13. LD50 means ___________________________.
14. Effects produced from a long-term, low level exposure are called _____.
15. What is meant by “persistence”?
16. The mathematical probability that some harmful outcome will result from a given action, event, or substance.