Ecology, Environment and Health Lecture 14: Solvents & Pesticides (PDF)

Ecology, Environment and Health 1950-331 Lecture 14 Chemical Stressors: Solvents & Pesticides 27 October 2024 1 This Lecture Will Help You To: Identify and describe sources and uses of solvents and pestici...

Ecology, Environment and Health 1950-331 Lecture 14 Chemical Stressors: Solvents & Pesticides 27 October 2024 1 This Lecture Will Help You To: Identify and describe sources and uses of solvents and pesticides Describe the movement of solvents in the environment Identify the general mechanisms of toxicities of solvents and pesticides List and describe the major classes of pesticides and their health effects 2 Solvents 13 What is a Solvent? In the case of occupational toxicology: Liquid Organic compound Dissolves other organic compounds Lipophilic Usually volatile 4 Products – Mostly Solvents Products – Partly Solvents Glues Gasoline Adhesives Diesel Fuel Oil based paints Charcoal lighter fluid Furniture polishes Lantern fuel Floor polishes and Grease waxes Lubricating oils Spot removers Degreasing agents Metal and wood Paint stripers cleaners White out Paint thinner Computer disk Turpentine cleaner Nail polish remover Varnishes and shellacs Wood and concrete stains 15 Chemical Classes of Solvents Aliphatic hydrocarbons: Gasoline Cyclic hydrocarbons: Cyclohexane Aromatic hydrocarbons: Benzene, toluene Ketones: Cyclohexanone, acetone Aldehydes: Acetaldehyde Alcohols: Ethanol, methanol Ethers: Glycol ethers Esters: Ethyl acetate 6 Toxicokinetics of Solvents Rapid absorption Inhalation route (volatile solvents, by diffusion) Transdermal route Ingestion (uncommon) Distribution Depends on tissue lipid content and vascularity Adipose and lipid-rich tissues are depots for storage 7 Toxicokinetics of Solvents Metabolism Generally hepatic, by mixed function oxidase (MFO) system Bioactivation to toxic metabolites for some compounds Excretion Urine, conjugated products Expired air, volatile solvents 8 Common Features in Toxicity of Solvents Local dermal effects due to extraction of lipid from dermis CNS depressant effect Neurotoxicity Hepatotoxic effects Nephrotoxicity Variable cancer risk 9 Peripheral Neurotoxicity (PN) and Solvents Distal axonal neuropathy Specific solvents known or suspected to cause PN: n-hexane, methyl-n-butyl ketone (MnBK), carbon disulfide (known) Styrene, tetrachlorethylene (suspected) Generally presents first in lower extremities 10 General Toxicology of Halogenated Aliphatic Solvents May be significant water disinfection byproducts Severe hepatotoxicity (CCl4, CHCl3) Nephrotoxicity Cardiac arrhythmias Carcinogenicity: Alkanes: polyhalides, chlorides Alkenes: monohalides, chlorides 11 Pesticides 12 What are Pests? Pests are not limited to organisms that transmit disease, and could be any living thing that negatively affects human interests. Some of the characteristics of pests include: A loss of resources such as agricultural crops, food and property damage, and damage to lawns and gardens Agents of disease Sources of annoyance and discomfort Examples of impacts of pests: Weeds compete for agricultural space Fresh mussels clog intake pipes Rabbits decimate field crops Wasps that sting Moths that eat clothes Roaches and flies that carry disease organisms into food 13 Insects, fungi, or viruses that attack crops or people Pesticides A short video of a pesticide story: http://www.youtube.com/watch?v=DSndZ9Xi640 Pesticide Food Poisoning from Contaminated Watermelons in California, 1985 https://nap.nationalacademies.org/read/4795/chapter/45 14 Definition – US EPA “…a pesticide is any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any pest.” “…a pest is any harmful, destructive, or troublesome animal, plant or microorganism.” 15 Pesticide Benefits Allow agricultural producers to improve the quality, quantity, and diversity of our food supply Used in timber, turf, horticulture, aquatic, and structural pest control industries Homeowners and home gardeners often use pesticides in their homes, yards, and on pets 16 What Happens After Application? When pesticides are applied, the goal is that they will remain in the target area long enough to control a specific pest and then degrade into harmless compounds Once applied, many pesticides are mobile in the environment (air, soil, water) This movement can be beneficial (moving pesticide to target area, such as roots) but can also reduce the effect on the target pest and injure nontarget plants and animals 17 Properties of Pesticides Vapor Pressure (volatility) – pesticides with a low VP are more likely to change to a gas and escape into the atmosphere Sorption – attraction to soil surfaces, pesticides with higher sorption values have reduced leaching 18 Properties of Pesticides Water Solubility/dissolvability - more soluble pesticides have lower sorption and are more mobile in the environment as they are leached or moved with runoff Persistence – the amount of time a pesticide remains in the environment, measured by half-life. Pesticides with longer half-lives pose a greater threat to the environment 19 Pathways of Environmental Transfer of Pesticides 20 Problems Bioaccumulate – example DDT, PCB 35,000 or more commercial products that use pesticides Many pesticides are neurotoxic (affect the nervous system) Many kill desirable insects or plants Contaminate streams and lakes 21 Absorption Ingestion Inhalation (lung) Skin (dermal) 22 Home & Occupational Exposure Home: Accidental ingestion Lawn and garden use Insect control Food supply Water supply Occupational: Farms & farm worker Pesticide applicator Manufacture Mixing & handling Landscapers Many more… 23 Other Exposures Dietary exposure Pesticide residues on crops Community exposure Airborne drift from commercial application Contaminated drinking water Leaching from soils to ground water 24 Insecticides Insecticides (kill insects) Organochlorines Organophosphates Carbamates Synthetic Pyrethroids 25 Mechanism of Action 26 Organochlorines Examples DDT, methoxychlor, aldrin, dieldrin, endrin, heptachlor, kepone, lindane, chlordane Toxicity Acute toxicity variable, CNS – convulsions, coma Environmental characteristics Highly persistent in environment Fat soluble Bioaccumulation Biomagnification Mostly banned in US and Europe 27 Organophosphates Examples Malathion, parathion, guthion, diazinon, TPN, TOCP, nerve gases – tabun, sarin, soman, VX Toxicity Acute toxicity highly variable – Parathion, TPN, sarin very toxic, malathion much less Environmental characteristics Rapidly degrade in outdoor environment (last longer in doors) Do not bioaccumulate 28 Organophosphates (contd) Mechanism of toxicity Inhibition of acetylcholinesterase (AchE) in nerve tissue Symptoms Over-stimulation of parasympathetic nervous system - salivation, constricted pupils, diarrhea, sweating, muscle twitching, CNS disturbances – coma and death Treatment Reverse AchE inhibition effects – use Atropine to block Ach receptors or AchE inhibiton with 2-PAM 29 Organophosphates (contd) Other Toxic Effects Delayed peripheral neuropathy (TOCP) Not a carcinogen or teratogen Possible long term neurological consequences from repeated exposures 30 Carbamates Examples Sevin (carbaryl), Baygon (propoxur), Temik (aldicarb) Toxicity Aldicarb very toxic, others less toxic Mechanism and signs of toxicity Similar to organophosphates Environmental characteristics Not persistent in environment 31  How to get rid of pesticides residues from vegetables http://www.youtube.com/watch?v=lRe4jJF Umrs 132 Summary - Important Concepts to Focus On For Solvents: Uses/applications Toxicokinetics: what makes them accumulate in tissues Exposure routes: inhalation …why…. Major health effects For pesticides: How their properties affect environmental persistence and exposure (slides 17-19) Sources of exposure (slides 23-24) Toxicity of organophosphates: main health effect and its mechanism 33 Assignment for Tuesday: Midterm Review Lectures 1 - 8 34