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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.