Toxicology: Chemical Risks

Ch 17 APES

CHEMICAL HAZARDSA toxic chemical can cause temporary or permanent

harm or death.Mutagens

chemicals or forms of radiation that cause or increase the frequency of mutations in DNA. Type of carcinogen

Carcinogens chemicals or types of radiation that can cause or promote

cancer.Teratogens

chemicals that cause harm or birth defects to a fetus or embryo.

AllergensChemicals that cause allergic reactions. Can cause

abnormally high response of the immune system

Mutagens

Ionizing RadiationGamma, X and UVRadioactive decay

PAH – polycyclic aromatic hydrocarbons

Benzo[a]pyrene

If affect sperm/egg can be passed down to children

Cystic Fibrosis, Down Syndrome, Sickle Cell

Carcinogen Asbestos (synergistic with smoking tobacco)

Acrylamide (used as a polymer; plastics)

Dioxins (herbicides & paper bleaching)

BPA (bisphenol-A), PCB BPA found in plastics PCB used to manufacture electronics (banned in 1979)

Many chemicals in cigarette smoke

Viruses- HPV

Key factors in cancer risk: #1 Smoking (30%) #2 Diet (30%) #3 Industrial Chemicals (30%)

Occupational (15), Environmental (10) #4 Genetic (10%)

Teratogen

PCB’s (polychlorinated biphenyl )

Herbicides

Thalidimide

Acutane (acne medicine)

Heavy MetalsArsenic, lead, cadmium,

mercury

Alcohol

Endocrine DisruptersChemicals that interfere with the normal

functions of hormones.Found in drinking water from sewage, farming,

& pesticides that mimic animal hormones Growth hormones in cattle etc., human birth

control pillsMany male fish, amphibians, and reptiles

becoming feminized:Low sperm countTestes that produce both egg and sperm

Examples: DDT, Atrazine (herbicide)

Effects of Chemicals on the Immune, Nervous, and Endocrine Systems

Endocrine Disruptorsp235Reduced penis size, female shellfish with male organs,

decreased fertility rates, decreased sperm counts and endometirosis, early puberty

Figure 18-9Figure 18-9

CHEMICAL HAZARDSA hazardous chemical can harm humans or other

animals because it: Is flammable Is explosiveAn irritant Interferes with oxygen uptake Induce allergic reactions.

Effects of Chemicals Immune, Nervous, and Endocrine Systems

Chronic vs. Acute

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

against disease and harmful substances. Synthetic Pesticides, PCB

Nervous system: brain, spinal cord, and peripheral nerves. DDT, Heavy Metals – Pb, Hg, Cd

Endocrine system: complex network of glands that release minute amounts of hormones into the bloodstream. DDT, BPA, PCB, Dioxin, Pthalates, diethylstilbestrol (DES)

Industrial Disasters

Bhopal, India – The world’s worst industrial accident occurred in 1984 at a pesticide plant in

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.

Minamata, Japan – methylmercury, caused Minimata Disease

Love Canal – Industrial Waste near town and site turned school. NIAGARA FALLS, N.Y

ToxicityMeasurement of how harmful a substance is

Chemical or ionizing radiation

Depends on DoseExposureAgeGenetic Make-up of IndividualDetoxification SystemSolubilityPersistenceBioaccumulationBiomagnificationChemical Interactions

Dose-Response StudiesExpose organism to different amounts of a

chemical and observe a variety of responses to:Mortality (most common; i.e. LD-50)Changes in behaviorChanges in reproduction

Measured as a concentration of a chemical in air, water or food.

Also measured as a dose – the amount of chemical absorbed/consumed by an organism

Because of their short duration (1-4 days) called acute studies.

Dose-Response StudiesCount how many die after exposure to

each concentrationData usually exhibits an S-shaped curve

Lowest dose no mortalityThreshold – dose at which effect can be

detectedLD50 – measurement useful in comparing

harmful effects of different chemicalsImportant in assessing the toxicity of new

chemicals to determine if the new chemical is more or less lethal

LD50 can be different among species and rats and mice are usually used to test LD50 in humans. Extrapolate to account for mass differences.

Testing StandardsChemicals are regulated by EPA as of 1976

Manufacturer of chemical must demonstrate that chemical will not cause adverse effects.

Devised a system of testing a bird, mammal, fish & invert.

Using LD50 values:Safe concentrations for animals are determined by

taking the LD50 value/10For humans LD50 values determined for rats/mice

are divided by 1000 to ensure an extra level of caution (very conservative).

Toxicity - Dose

LD50

Median lethal doseThe amount of

chemical in 1 dose that kills 50% of animals within a 14 day period

Poison - LD50 of 50mg/kg of body weight

Toxicity - Dose

“The dose makes the poison” Paracelsus, 1540Supertoxic (dioxin, nerve gas and botulism

toxin)Extremely toxic (nicotine)Very toxic (mercury salts, codeine)Toxic (lead salts, caffeine, DDT)Moderately Toxic (methyl alcohol, aspirin)Slightly Toxic (ethyl alcohol, soap)Essentially nontoxic (water)

Toxicity - ExposureMethods of Exposure

Ingestion InhalationThrough Skin

How often and for how long?

Acute vs. Chronic

TOXICOLOGY: ExposureEstimating human

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

Figure 18-11Figure 18-11

Persistence

Bioacculumlation and Biomagnification Lipid soluble POP – persistent organic pollutantsPCB, Dioxin, DDTHeavy Metals – methyl mercury, tetraethyl

leadAlgal Blooms – “red tide” makes mussels

toxic.

DDT and Bioaccumulation(absorbed or stored in organs) and Biomagnification (through a food chain)

Fig. 11-4p. 231

TOXICOLOGY: genetic make-upTypical

variations in sensitivity to a toxic chemical within a population, mostly because of genetic variation.

Figure 18-10Figure 18-10

Other Studies

Chronic Studies:Toxicology studies conducted over a long period of

time.Goal is to examine the long-term effects of

chemicals on survival and impacts on reproduction

Retrospective vs. Prospective Studies:Epidemiology – understanding the causes of

disease in humans & wildlifeRetrospective Studies – monitor people who have

been exposed to a chemical in the past. Ex: Bhopal, India – still monitoring people who were exposed.

Prospective Studies – monitor people who might be exposed to chemicals.