Toxicology Toxicology Fig 11 3 p 230 Toxicology

Toxicology

Toxicology Fig. 11 -3 p. 230 • 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

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

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

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

Practice Question! ______ cause birth defects while the human embryo is growing and developing during pregnancy 1) Mutagens 2) Carcinogens 3) Teratogens 4) Biogens 5) Hanta viruses

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)

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

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

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

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

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

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

Practice Question In order for biomagnification to occur, a pollutant must be I. Concentrated by producers II. Soluble in water III. 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

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

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

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

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

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

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

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

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

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 75000 chemicals and requires screening of substances