M6S1: Enviromental Toxicities Flashcards
What are environmental toxicities
-chemical that is released in environment and can produce adverse health effects on living organisms
Acute verse chronic toxicities
Acute toxicity -> associated with a single exposure to a chemical and often (but not necessarily) a large dose of the chemical. For ex. Chemical spill
Chronic toxicity -> associated with repeated exposure to a small dose of a chemical over a long period of time. For ex. Eating contaminated food
Toxic effects of aflatoxin B1
-acute and chronic toxic effects can present differently and not just as exaggerated effect that is dependent on dose (ex. Liver failure vs liver cancer)
-common food contaminant in Southeast Asia and central Africa specifically, in corn, peanuts and groundnuts
-can result in liver necrosis, liver failure, and death, while chronic toxicity of aflatoxin B1 can cause liver cancer
Common environmental toxicant 3 sources
- Air pollution
- Tobacco smoke
- Pesticides
- Air pollution
-human contribution has long and complicated history
-2 main categories: particulate matter and gaseous air pollutants
-can be attributed to both natural and anthropogenic sources (resulting from human influence)
History of air pollution
1273
First anti-pollution law was established by Edward 1, king of England. He made it illegal to burn coal while parliament was in session. Punishment was decapitation
Early 1900s
First automobiles were manufactured during early 1900s. Within a few decades, number of vehicles went from zero to millions. Gasoline internal combustion engines became, and still are major source
1952
“Killer smog” in London, England was responsible for an estimated 4000 deaths, where main cause of death were bronchitis, pneumonia and other respiratory illnesses. Event demonstrated lethality of air pollution and lead to clean air act
1956
-clean air act introduced a number of measures to reduce air pollution. One measure was shift source of home-heating towards cleaner coals, electricity and gas, thereby reducing amount of smoke pollution released from household fireplaces
Major air pollutants
Particulate matter
-refers to mixture of tiny particles composed of non-gaseous pollutants (ex. Biological materials). Particulate matter can be solids or liquid droplets
Gaseous air pollutants
-carbon monoxide, carbon dioxide, nitrogen oxides, sulfur oxides, hydrogen sulfide, ozone
Sources of air pollutants
Natural air pollutants
Ex. Volcanoes, forest and prairie fires, dust storms
Anthropogenic air pollutants
-man-made
1. Heating and power
-combustion of fossil fuels releases carbon dioxide, carbon monoxide, sulfur oxides, nitrogen oxides
Coal largest contributor to human-made increase of carbon dioxide in air
2.Automobiles
-exhaust releases smoke, lead particles, carbon monoxide and nitrogen oxides
-in late 20th century, government regulations forced decrease fo emissions, particularly with use of low-lead or unleashed gasoline
-recent emission testing and green vehicles (hybrids, electrical) help reduce these emisssions
3. Industrial processes
-release a wide variety of pollutants
-types of pollutants depend on manufacturing processes
-ex. Acids (sulfur acid and acetic acid)< solvents (ex. Ethanol), Chlorine and ammonia gas, metals (copper, lead, and zinc from smelters)
Human health and air pollutants
-predominant health effect associated with air pollution is chemical irritation of respiratory tract
-certain subpopulations particularly susceptible to air pollution, including very young children, older adults and people with cardiorespiratory diseases like asthma
-in most cases, health problems due to combined action of particulates and sulfur oxides, but no single pollutant seems to be responsible
- Tobacco smoke
Environmental tobacco smoke, or secondhand smoke, is the combination of mainstream smoke (exhaled smoke) and sidestream smoke (smoke from burning end of cigarette)
Research on secondhand smoke exposure
-2022 international agency for research on cancer concluded can cause lung cancer
(Also sudden infant death syndrome, respiratory infections, ear infections, asthma attacks, heart disease, stroke)
-carries same risks as directly smoking
-bylaws in place to restrict smoking locations
3.pesticides
-unique among environmental pollutions because unlike others
-used to intentionally kill organisms
-insecticides and herbicides two major classes
Insecticides
-chemicals used to kill insects or make insects unable to reproduce or develop normally
-number of different types of insecticides are used
2 types:
Organochloride insecticides
-work by increasing sensitivity of neurons, resulting in increased CNS stimulation that manifests as tremors, convulsions, eventually death
-residue in humans, animals and environment can present long-term problems so largely phased out
Ex. DDT (dichlorodiphenyltrichloroethane)
-originally introduced in 1945 to control malaria-containing mosquitoes
-effective and widely used intel 1970s when stopped because:
Insects developing resistance, bird and fish populations decreasing, soil and water concentrations of DDT increasing, levels of DDT in food increasing
Organophosphorus insectides
-first synthesized during WW2, used as potential warfare agents (ex. Nerve gas)
Since then, selective organophsophorus insecticides have developed (ex. Malathion) that require metabolic activation to work. Occurs rapidly in insects
-agents relatively unstable ad break down in environment therefore considered to have small impact on environment, overall
Toxicitiy:
-very toxic to humans
-absorbed through skin and leading cause of poisoning in agricultural sector
Mechanism of action:
-irreversibility inhibit acetylcholinesterase
Remember acetylcholinesterase (AchE) responsible for breaking down acetylcholine in synaptic cleft
Effects:
If AchE inhibited, then acetylcholine no longer broken down, leading to increase in acetylcholine in nervous tissue
-results in increased acetylcholine-mediated neuronal firing throughout body, resulting in decreased heart rate, severe difficulty breathing, fecal and urinary incontinence, blurred vision. Death can occur due to respiratory failure
*refer to goodnotes
Herbicides
-second class of pesticides
-chemicals capable of killing or injuring plants
Two types to learn about:
Agent orange
-mixture common in Vietnam war as defoliant to make easier to spot targets hidden by tree cover
-acts by mimicking plant growth hormones, causing uncontrolled, unsustainable growth, leading to plant death
-major concern that has chemical called TCDD (2,3,7,8-tetrachlorodibenzodioxin) that introduced during manufacturing of agent orange
Action: bind to receptor known as Aral-hydrocarbon receptor, which involved in expression of many genes required for normal cellular functioning
-manifests as chloracne (severe form of acne), impairment of liver and CNS function. Increased occurrence of cancers and may cause birth defects and stillbirths
-TCDD poisoning happened in Ukrainian president victor yushchenko in 2004
Paraquat
-one of most common used herbicides but highly toxic if ingested
-causes cellular damage
-when ingested causes immediate burns to mouth and stomach
-regardless of route of entry, primary target of paraquat toxicity is lungs, where cellular damage results in development of fibrous tissue that inhibits ability to breathe
-ingestion of as little as 2 teaspoons can cause death due to lung damage
*refer to goodnotes
Toxic effects of specific chemicals 3 most common that can be exposed to include
- Lead
- Mercury
- Bisphenol A
Lead
-ubiquitous, natural-occurring element found in environment and in many different chemical compounds
2 main toxic compounds: lead oxide and tetraethyl lead
