1. Toxicology

2. Toxicology Toxicology is the science that examines
Fig. 11-3
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Toxicology
Toxicology is the
science that examines
the effects of poisonous
substances on humans and other organisms
Any chemical substance may cause negative effects if ingested in great enough quantities
A toxicant in a minute enough quantity may pose no health risks

3. Synthetic chemicals in the environment
Synthetic chemicals are made by humans and there are thousands in our soil, water, and air
80% of US streams contain at least 82 chemicals
Not all synthetic chemicals pose health risks, and most are only found in minute amounts

4. Silent Spring In 1962, Rachel Carson published the novel Silent Spring
This novel brought the perils of DDT and other pesticides into public consciousness
It was written at a time when chemicals were prayed over residential neighborhoods on the assumption that they could do no harm to people
The book helped to generate significant social change, and resulted in the subsequent ban of DDT in the US in 1973
DDT is still used in many countries

5. Types of Toxicants
Carcinogens—chemicals or types of radiation that cause cancer
Ex) the chemicals in cigarette smoke
Mutagens—chemicals that cause mutations in the DNA of organisms
Teratogens—affect the development of human embryos
Ex) thalidomide: was used as a sleeping pill but turned out to cause birth defects in single doses

6. Practice Question!
___________ cause birth defects while the human embryo is growing and developing during pregnancy
Mutagens
Carcinogens
Teratogens
Biogens
Hanta viruses

7. Types of Toxicants
Allergens—overactivate the immune system and cause an immune response when not necessary
Neurotoxins—assault the nervous system
Ex) mercury, lead, and some chemical weapons
Endocrine disruptors—interfere with the endocrine system (makes hormones)

8. Endocrine Disruptors
Hormones stimulate growth, development, and sexual maturity, as well as regulating brain function, appetite, sexual drive, etc
Some toxicants disrupt an animal’s system by blocking the hormones or accelerating their breakdown
Others mimic the hormone and block receptors

10. Endocrine Disruptors
Ex) some chemicals cause feminization of male animals by mimicking estrogen
Many people think this is occurring in humans due to chemicals found in our water and in plastic products

11. Toxicants in surface water and groundwater
Runoff often carries toxicants from large areas of land
Many chemicals leach down into groundwater and contaminate drinking water supplies

12. Airborne Toxicants
Pesticide drift occurs when pesticides are transported through the air and may cause effects far from the site of direct chemical use

13. Toxicants may accumulate in the food chain
Some toxicants are not easily broken down in the body and build up in the body
Some substances are stored in fat or muscle tissue
Bioaccumulation refers to the process where toxicants build up in an organisms

14. Toxicants may accumulate in the food chain
Biomagnification occurs when the concentration of toxicants increases each step up the food chain
Ex) the most famous example of this occurred with DDT into birds; this caused many species of birds in the US to decline

15. Practice Question
In order for biomagnification to occur, a pollutant must be
Concentrated by producers
Soluble in water
Long-lived
1) I only
2) I and III only
3) I and II only
4) II and III only
5) I, II, and III

16. Germ Resistance to Antibiotics
Bacteria’s high reproductive rate allows these organisms to become genetically resistant to an increasing number of antibiotics
The overuse of pesticides and antibiotics has fostered this resistance
Every major disease-causing bacteria now has at least one strain that resist common antibiotics

17. Case study on pesticides: Bhopal, India
On December 3, 1984 the world’s worst industrial accident occurred at a Union Carbide pesticide plant
An underground storage tank exploded and released a large quantity of toxic gas used to produce pesticides
600,000 people were exposed and at least 22,000 died
The company was found to be at fault

18. Case Study: DDT
DDT (dichloro-diphenyl-trichloroethane) was discovered in 1874
In 1939 it was developed as an insecticide
In 1948 the inventor won a Nobel Prize
DDT is a broad-spectrum insecticide, meaning that it is toxic to many species

19. Case Study: DDT
DDT is extremely effective in killing mosquitoes and stemming the spread of malaria

20. Case Study: DDT
DDT has a long persistence time and thus will stay in the environment for extended periods (up to 15 years)—it will be biomagnified
In birds, DDT decreases the reproductive rate by causing eggshell thinning and embryo deaths
In aquatic animals, DDT is highly toxic
In humans, DDT is a probable human carcinogen, damages the liver, temporarily damages the nervous system, and damages reproductive system
Currently, DDT cannot be used in the US, but it can be manufactured and sold to other companies

21. Types of exposure affect responses
Acute exposure occurs when a person experiences high exposure for short periods of time
Chronic exposure occurs with lower exposure over long periods of time
This is harder to recognize as the effects show up gradually
Ex) alcohol abuse can cause liver damage, pesticide residues on food can build up in your body

22. Synergistic effects of toxicants
Synergistic effects are the interactive impacts that occur when toxicants are mixed together
These may be more than or different than the simple sum of their separate effects
Ex) wild wood frogs will suffer deformities in their limbs due to parasitic infection
The infections are exacerbated when the frogs are exposed to pesticides that weaken their immune responses

23. Regulating toxicants
The Food and Drug Administration (FDA) regulates foods, food additives, cosmetics, and drugs and medical devices
Formed under the Food, Drug, and Cosmetic Act of 1938
The Environmental Protection Agency (EPA) regulates pesticides under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) of 1947
They also regulate chemicals not covered by other laws, under the 1976 Toxic Substances Control Act (TSCA)
The Occupational Safety and Health Administration (OSHA) regulates workplace hazards

24. More details on the EPA
The FIFRA was intended not to protect public health and the environment but to assure consumers that products actually worked as their manufacturers claimed
Later amendments changed the focus to protecting health and charged the EPA with registering each new pesticide
TSCA directed the EPA to monitor around chemicals and requires screening of substances