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Lecture 9

ENVS4012 notes Lecture 9

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University of Guelph
Environmental Sciences
ENVS 4012

Lecture 9 Toxicology:  Definition: o Study of poisons o “the science which studies toxic substances or poisons, that are substance which cause alteration or perturbation in the function of an organisms leading to harmful effects” (Truhaut, 1974).  How harmful a substance is depends on the chemical characteristics of the substances: o Some characteristics to consider are:  Electronegativity  Polarity  Oxidation State  Molecular Weight  Dissociation  Solubility  water soluble toxins (hard to enter human cells) and fat soluble toxins (can easily enter the human cell and bioaccumulate).  Assessing Chemical Hazards o Persistence of the chemical: do they break down or remain in the same chemical configuration (e.g. DDT). o Bioaccumulation o Biomagnification o Chemical interaction  Antagonistic effects: two different chemicals taken up by the same given individuals and behave antagonistic towards each other; however, they are very toxic if taken up separately. One chemical reduces the toxicity of the other if mixed or existing together. For example, Vitamins A and E may decrease chemical toxins that may induce cancer  Synergistic effects: one chemical enhances the toxicity of the other chemical present. For example, exposure to asbestos can lead to lung cancer by 20-fold. However, smoking in the presence of asbestos increases the risk of lung cancer by 400-fold. o Multiple chemicals – food additives, pesticides, air pollution—complicates the risk of getting harmed and diseased even more o When studying toxicology, it is important to determine three things:  Who the receptor is  Any organism that receives exposures to toxins.  To study the receptor, we must understand the frequency of the exposure that person has undergone  Age is important (i.e. a child, elder are more vulnerable)  General health  Genetic makeup  What dose they received  Amount of chemical a person takes up  Ingested (greatest source of exposure-95%)  Inhalation (air pollutants, particles, and volatiles -10%)  Absorbed through the skin (industrial -5%)  There is a debate between how much chemical is taken up into the body and how much the receptor really receives. o Individual takes up a higher concentration of the chemical than the receptor (proteins) receive. Why? They can be metabolized before reaching the targets. o There are three types of doses  Acute dose – refers to single dose, usually high  Chronic dose – repeated or continuous low dose over time  Long term –low dose over a life time (many professional doses are long term, approx. 45 years).  What is the receptor’s response (e.g. illness)  Nonspecific: attack any tissue (general), the whole system is affected o Burning: destruction of cells caused by exposure to high concentration of strong acids or bases o Narcosis: depression in sensory activity, reversible, caused by alcohols, ethers, benzene  Specific o Damage to excretory organs o Damage to respiratory organs o Damage to reproductive function o Mutagenesis o Carcinogenesis  Acute toxicity – leads to rapid death  Chronic toxicity – delayed response; you are poisoned today and you die on your birthday next year  Is every chemical poisonous? o Yes it can be at certain levels of exposure o Even water. If you drink 3L or more at once, it may lead to dangerous health effects (e.g. the lady who died drinking water non-stop to win a Wii and her bladder busted). o Any substance is poisonous, but the question is how often or how much of a given substance is considered poisonous  Measuring Manifestations o It is hard to define a start and endpoint of measuring toxicity o Endpoint – toxicological manifestation is impossible to measure so we have to wait for… o …Measurement Endpoint – physiological manifestation  Can be readily measured  More easily measured than endpoint  Use of “biomarkers” e.g. changes in hormone levels, protein markers, enzyme induction  Methods of determining toxicity o We conduct laboratory experiments on animals (e.g. mice and rats and snitches) to find the Lethal dose (L50): amount of chemical received at a single dose that will cause the mortality of 50% of experimental animals after a period of 14 days. o Case reports: family physician makes a report of the last 5 years of the cases of poisoning and its characteristics o Epidemiological studies o Computer simulations o Tissue cultures of cells and bacteria o It is difficult to compare studies on animals and bacterium to human cases  Dose-Response Curves o Curve displays how the response will change in relation to dose increments o Used for acute toxins o The green line represents non-threshold chemicals: carcinogenic – one molecule causes a response o Threshold chemical are non-carcinogenic RISK ASSESSMENT  Risk and Risk Assessment o Risk – possibility of suffering harm from a hazard. It contains the possibility and probability suffering harm from hazards. o Risk assessment: scientific processes in estimating how much harm a particular hazard can cause (e.g. if someone is smoking, they have a
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