HUMAN HEALTH AND ENVIRONMENT lec 9 Toxicology and Risk Assessment

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Department
Environmental Science
Course
EESA10H3
Professor
Jovan Stefanovic
Semester
Winter

Description
HUMAN HEALTH AND ENVIRONMENT – Lecture 9: Toxicology and Risk Assessment ***majority of questions on final exam and hardest questions on final exam will come from this lecture Toxicology -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)  Assessing chemical hazards -how harmful a substance depends on: -checmical properties of the substance -electronegativity -polarity -oxidation state -molecular weight -dissociation -solubility -water soluble toxins (mostly inorganic)  unable to penetrate cell wall  stay between cells and this what they effect -fat soluble toxins (mostly organic toxins)  able to penetrate cell wall and enter the cell and harms within the cells -persistence of a chemical  easy/slow breakdown of chemicals in body/environment -i.e. DDT  desirable to be persistent to kill insects but not desirable to be persistent in the environment and human body -bioaccumulation  build up of the chemical over time in tissues and organs -biomagnification  build up of chemicals in the food chain over time (animals at the bottom of the food chain have lower amounts of chemicals and animals higher in the food chain have higher amounts of chemicals -chemical interaction  interaction between chemicals can reduce or increase toxicity -antagonisticpresence of one chemical reduces the toxicity of another i.e. vitamins E and A can slightly reduce carcinogenic effects of some chemicals -synergistic  presence of one chemical increases the toxicity of another i.e. if an individuals who is exposed to asbestos and is a smoker increases their risk of cancer 400 folds -receptor -dose -response  Receptor -who’s receiving exposure or dose  humans, animals plants -frequency of exposure  how often -age  age is also directly related to general health -general health -genetic makeup  consequences to exposure will differ among indivudals  Dose -the amount of substance a person has: -ingested (often the greatest source of chemical exposure 85%0) -inhaled (air pollution, particles and volatiles, 10%) -absorbed through the skin (industrial 5%) -debate about actual amount that receptor sites “sees” vs. amount take in  we excrete and breakdown the chemicals -acute dose  refers to single dose, usually high -chronic dose  repeated or continuous low dose over time i.e. radiation -long term  low dose over a life time  Response -symptoms and illness that someone can observe and record as a result of exposure  two groups: specific and nonspecific -nonspecific  whole body/system has been affected  no particular organ is affected, whole system is -b urning – destruction of cells caused by exposure to high concentration of strong acids or bases -narcosis – depression in sensory activity, 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  expressed in percent mortality -chronic toxicity -Paracelsus’ principle  “the dose makes the poison.” -every chemical can be toxic, it’s just the question of what amount -i.e. water  about 3 L of water can have very serious health consequences -how much exposure causes a harmful response? -affects differently for different individuals Measuring manifestations -endpoint  physiological manifestation  first one that can be readily measured -use of “biomarkers” i.e. changes in hormone level, protein markers, enzyme induction Methods for determining toxicity -laboratory experiments on animals (mice and rates) -it is important to calculate the lethal dose (50 ) of a chemical and the dose response curve -dose response is the graded response as a function of dose  how does response change in dose increases/decreases -the lethal dose can be determined from the dose response -you can find out the lethal dose of a chemical rom case reports (accidental poisoning, attempted suicide), epidemiological studies, computer simulations, tissue cultures of cells and bacteria (testing on animals) -dose response uses acute toxicity tests (on animals)  high dose over a short period of time)Figure 1. 100 50- Doae 100 75 50 o 25 Threshold level I LD50 Low High Logarithm of dose (mg/kg of body weight) A Non-threshold chemical B Threshold chemical 100 Toxicant A 75 Toxicant B 50 I LD50 for A o 25 VI LD50 for B LILLLLLLLLLLLLL High Low Logarithm of dose (mg/kg of body weight Figure 1. 100 50- Doae 100 75 50 o 25 Threshold level I LD50 Low High Logarithm of dose (mg/kg of body weight) A Non-threshold chemical B Threshold chemical 100 Toxicant A 75 Toxicant B 50 I LD50 for A o 25 VI LD50 for B LILLLLLLLLLLLLL High Low Logarithm of dose (mg/kg of body weightDose Response Curve -green is non-threshold chemicals  does not have a threshold  mortality happens immediately with application of first dose -no safe dose -red is threshold chemicals  increasing the dose does not result in death (UP TO SOME POINT) after which, there will be deaths of the animals which will increase significantly until all the animals are dead (100% mortality) -there can be a safe dose amountContaminants Receptors Contaminant Receptors Ris No Risk Exposure Exposure pathways pathways PHASE PHASE PHASE PHASE Assessment Characterization Remediation/ Verification Management Document Review Intrusive sampling Contaminant Verification Sampling Destruction or to Confirm Estimates Interviews Investigation Removal Management Plan Site Inspection Physical Testing Risk Assessment Contact Authorities technical, scientific assessment of the nature and magnitude of risks" Risk assessment scientific process in estimating how much harm a (from MOE Guidance document) particular hazard can cause Contaminants Receptors Contaminant Receptors Ris No Risk Exposure Exposure pathways pathways PHASE PHASE PHASE PHASE Assessment Characterization Remediation/ Verification Management Document Review Intrusive sampling Contaminant Verification Sampling Destruction or to Confirm Estimates Interviews Investigation Removal Management Plan Site Inspection Physical Testing Risk Assessment Contact Authorities technical, scientific assessment of the nature and magnitude of risks" Risk assessment scientific process in estimating how much harm a (from MOE Guidance document) particular hazard can cause-LD 50 single dose that will cause death in 50% of animals within 14 days -toxicant A and B have different levels of LD 50 -LD 50lows us to compare the toxicity of chemicals  it is the standard -Toxicant A and B cause 50% mortality  response is the same but what is changing is the dose
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