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Lecture 9

EESA10 Lecture 9 Notes.docx

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University of Toronto Scarborough
Environmental Science
Jovan Stefanovic

Lecture 9: Toxicology Toxicology • Definition: – Study of poisons – “the science which studies toxic substances or poisons, that are substances which cause alteration or perturbation in the function of an organisms leading to harmful effects (Truhaut, 1974) -substances that cause harm and lead to adverse effects Toxicology: assessing chemical hazards (1) • How harmful a substance is depends on: – Chemical properties of the substance • Electronegativity • Polarity • Oxidation state • Molecular weight • Dissociation • Solubility – Water soluble toxins (inorganic chemicals) – Fat soluble toxins: they easily enter cells, that is why they bioaccumulate Toxicology: assessing chemical hazards (2) • Persistence of chemical • Bioaccumulation – the accumulation of a toxic substance, in various tissues of a living organism • Biomagnification – the process by which the concentration of toxic substances increases in teach successive link in the food chain • Chemical interaction – Antagonistic: One chemical reduces the toxicity of another chemical. (E.g. Vitamins A and E might reduces carcinogenic effects of chemicals – Synergistic: two different chemicals that are taken up by the same individual at the same time. Their toxicity is even higher than if they were taken up at different times (E.g. being exposed to asbestos and smoking increases lung cancer by 100 fold). • Multiple chemicals – food additives, pesticides, air pollution • Receptor – an individual exposed to a contaminant • Dose – concentration of exposure • Response – adverse effects (illness, % of deaths per million, etc.) Toxicology: Receptor 1. Receptor – organism receiving exposure or dose • Frequency of exposure • Age • General health • Genetic makeup Toxicology: Dose 2. Dose – the amount of substance a person has been exposed to • Ingested (often greatest source of chemical exposure, 85%) • Inhaled (air pollution, particles and volatiles, 10%) • Absorbed through the skin (dermal contact) (industrial, 5%) • Debate about actual amount that receptor site “sees” vs. amount taken in – 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 Toxicology: Response 3. Response –symptoms that can be measured as a result of negative effects of chemicals • Nonspecific: there is no specific tissue that is affected – Burning – destruction of cells caused by exposure to high concentration of strong acids or bases – Narcosis – depression in sensory activity(vision, balance, speech), reversible, caused by alcohols, ethers, benzene • Specific – Damage to excretory organs – Damage to respiratory organs – Damage to reproductive function – Mutagenesis – Carcinogenesis • Acute toxicity– rapid death • Chronic toxicity Paracelsus’ Principle “ The dose makes the poison” • Every chemical is harmful at some level of exposure -even water, if you drink 3 litres of water at once, it could cause serious effects -100 cups of coffee can cause death -100 pills of asparin -any substance can be considered as a poison • How much exposure causes a harmful response???? Measuring manifestations • Endpoint – toxicological manifestation that is related to toxicant • 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 for determining toxicity – Laboratory experiments on animals (mice and rates) Lethal dose (LD50) is the dose of the chemical received at once, that will cause mortality of 50% of the experimented animals, in a period of 14 days. – Case reports: accidents, homicides, and suicides due to poisoning, what symptoms are noticed and what possible complications – Epidemiological studies: controlled group and another group that is exposed to the chemical; both compared. Both groups are similar in age and lifestyle. – Computer simulations – Tissue cultures of cells and bacteria: these studys can sometimes be hard to relate the results to reality, but these studies do help us to go into the right direction • Dose-Response – Acute toxicity tests are used – Graded response as a function of dose – In population B has to have a certain dose because it causes health effects, but one molecule of A will have cause a response. Non-threshold chemical – any dose (theoretically 1 molecule) of chemical will cause a response Threshold chemical – dose will increase, but no response. At one point there was a response. Risk Assessment Risk and Risk Assessment • Risk - possibility of suffering harm from a hazard or getting a disease etc. • Possibility & probability 1 out of 250 of everyday smokers get cancer Risk Paradigm Contaminants, Receptors, Exposure pathways (all not overlapping) = no risk Contaminants, Receptors, Exposure pathways (all overlapping one another) = risk What are Risk Assessment and Risk Management? Phase 1 – Assessment – Document Review, Interviews, Site Inspection, Contact Authorities Phase 2 – Characterization – Intrusive Sampling, Investigation, Physical Testing Phase 3 – Remediation/Management – Contaminant Destruction or Removal, Risk Assessment Phase 4 – Verification – Verification Sampling to Confirm Estimate, Management Plan • Risk assessment – scientific process in estimating how much harm a particular hazard can cause. It is usually done with a big group of scientists that are from very different areas (E.g. Biologists, Hydrologists, mathematicians, etc) “…technical, scientific assessment of the nature and magnitude of risks” (from MOE Guidance document) Benefits of Risk Assessment (extracted from Natural Research Council 1994) • When agent suspected of causing diseases or testing new chemical • Help rank contribution to overall risk • Help identify risk that are easily reduced or eliminated • Help clarified what is known and not known about situation • Can provide quantitative information for decision making Applications of risk assessments • Health Canada – regulations for foods and drags • Canada Council of Ministers of the Environment – National Contaminated Sites Program – Canada-Wide Environmental Standards (CWES) • Ontario Ministry of Environment – Site-spec
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