Week 6 Flashcards
pesticides
Any substance or mixture of substances used for preventing, destroying, repelling, or mitigating any pest.
The term pest means any harmful, destructive, or troublesome animals, plants, or micro-organisms
pesticides are designed to kill living things
For most environmental toxicants, toxicity is an unwanted characteristic
- asbestos has useful properties, but it unfortunately also causes cancers and asbestosis. We would prefer it if asbestos did not affect living things
pesticides are hazardous and intentionally added to our environment
Many toxicants are released as an unwanted byproduct of another activity
For example, we burn fuels to power vehicles and industries, and air pollutions is an unwanted byproduct that we would prefer not to release
ways to categorise pesticides
by target:
- insecticides -> insects
- herbicides -> weeds
- rodenticides -> rodents
By chemical group:
- organochlorines
- organophosphate
- neonicotinoids
Why are pesticides used, and what problems do they solve?
- Used to prevent, destroy, repel, or mitigate pests, which can be harmful animals, plants, or microorganisms.
- They are used primarily in agriculture to protect crops from weeds, insects, and diseases.
- Pesticides control vectors of diseases such as mosquitoes (malaria, yellow fever), ticks (Lyme disease), and rodents (contamination of food).
pesticide classifications
Ia - extremely hazardous
Ib - highly hazardous
II - moderatley hazardous
III - slightly hazardous
U - unlikely to present acute hazard
based on acute toxicities
the more hazardous pesticides would generally be restricted and used in agricultural settings by certified applicators
herbicides
- used to kill weeds and aid the growth of preferred species
–> weeds compete with other plants for water, soil nutrients, etc.
Commonly used herbicides: - atrazine
- 2, 4-D
- glyphosate (“round up”)
Ways to categorise:
- contact vs. systemic
- mode of action
- selective vs. non-selective (“broad spectrum”)
–> genetically modified crops, e.g., “round up ready”
insecticides
- kill insects
- most important group of pesticides for acute toxicity in humans
–> most insecticides currently in use are neurotoxic
Types of insecticide:
- organochlorines
- organophosphate
- carbamates
- pyrethroids
- neonicotinoids
organochlorine insecticides
- low volatility, chemically stable, slow degradation
–> persistent in the environment
The properties that made these chemicals such effective insecticides also Brough about their demise because of their persistence, bioconcentration and biomagnification in food chains, and the acquisition of biologically active body burdens at higher trophic levels - rarely used in wealthy countries; still used in some low and middle income countries
DDT - dichlorodiphenyltrichloroethane
DDT is a synthetic pesticide once widely used to insects that carry diseases and to protect crops
- DDT is an organochlorine pesticide.
- first widely used as an insecticide in WW2 (typhus and malaria)
Key Facts:
- Highly effective but persistent in the environment.
- Banned - due to human health and environmental concerns.
- Human health risks: hormone disruption, cancer concerns.
- Still used in some countries for malaria control under WHO guidelines.
organochlorine insecticides: DDT
- persistent in the environment and in humans
–> biodegradation half life in soil: 2-5 years
–> soluble in fat –> bioaccumulation
Acute effects: - irritability, dizziness, hyper-susceptibility to external stimuli (light, touch, sound)
- little dermal toxicity, not readily absorbed through skin
Chronic effects: - endocrine disruption, reproductive effects
- breast cancer
Rachel Carson
- MA in zoology from John Hopkins in 1932
- Raised awareness about pesticide harm to humans, wildlife, and ecosystems.
- Helped spark the modern environmental movement.
- Led to the ban of DDT in many countries.
persistent pollutants (forever chemicals)
Stockholm Convention
- global treaty ratified by ~ 150 countries, intended to protect humans and the environment from the impacts of persistent organic pollutants (POPs)
- came into effect in 2004, initially focused on 12 pollutants of concern (the dirty dozen)
- amendments in 2009 and 2011 added additional pollutants (now 28 in total)
organophosphate (OP) insecticides
- largely replaced the organochlorine insecticides
- responsible for most pesticide poisonings and deaths
- mild poisoning: fatigue, headache, dizziness, nausea, vomiting, abdominal pain, cramping, chest tightness
- moderate poisoning: inability to walk, weakness, CNS effects including confusion, insomnia, slurred speech
- severe poisoning: respiratory depression, convulsions, loss of consciousness, coma, death
organophosphate insecticides
- motor neurons stimulate muscles by releasing the neurotransmitter acetylcholine (ACh)
- ACh immeditaley eliminated by acetylcholinesterase (AChE)
- inhibition of AChE leads to accumulation of ACh at neuromuscular junction
–> muscle twitching
–> paralysis of respiratory muscles
carbamates insecticides
- similar biological mechanism to organophosphate insecticides
- but less acutely toxic than organophosphate insecticides
–> lower affinity for acetylcholinesterase (effects are reverible unlike OP)
–> poisonings much less common (death is rare)
pyrethroids insecticides
- synthetic versions of naturally occurring chemicals pyrethrins
- less acutely toxic than organophosphate insecticides
–> allergens; rare fatalities associated with severe allergic reactions
What are neonicotinoids, and what concerns are associated with their use?
- New class of insecticides chemically similar to nicotine.
- They are systemic insecticides, meaning they are taken up through the roots of plants and can be found throughout the plant tissues.
Concerns: their persistence in the environment (half-lives in soil can be quite long), potential harm to beneficial insects like bees, and possible impacts on human health.
pesticide exposure
- Dietary ingestion
- residues on food - Inhalation
- some communities (“spray drift”) - Dermal
- some communities (“spray drift”)
organic vs conventional foods
- strong evidence of lower concentrations of pesticides residues on organically grown foods
- mixed evidence of nutritional content; some evidence of:
–> higher contents of phenolic compounds in organic fruit and vegetables
–> higher content of Omega-3 fatty acids in organic dairy products - less antibiotic use in organic agriculture
- growing evidence of health benefits
–> confounding may be an issue
pesticides and health - acute effects
- most often associated with organophosphate
Global annual estimates: - approx 3-5 million unintentional poisonings
–> 20,000 deaths
–> majority of poisonings, and vast majority of deaths, in low and middle income countries
–> inadequate training
–> lack of personal protective equipment (PPE)
–> weak regulations - 2 million intentional poisonings
–> ~150,000 pesticides suicide deaths annually
2 reasons that pesticides are used for
- To increase crop yields (amount of a crop harvested per unit of land)
- To prevent vector-borne diseases
List the 5 main chemical classes of insecticides.
- Organochlorines
- Organophosphate
- Carbamates
- Pyrethroids
- Neonicotinoids
Why were organochlorine insecticides largely phased out in favour of organophosphates?
Organophosphates do not persist in environment as long as organochlorines.
Discuss the advantages and disadvantages of environmental persistence in the context of pesticides.
Advantages:
- Makes insecticides more effective as they can ward off insects for longer periods of time
Disadvantages:
- Causes bioaccumulation in the food chain thus increasing burdens at higher trophic levels
What chemical class of poisonings accounts for the majority of pesticide poisonings?
Organophosphates (b/c organochlorine is banned)
Identify the important routes of pesticide exposure
- Dermal - occupational exposures
- Dietary ingestion - residues on food (general pop)
- Inhalation - occupational exposures and communities adjacent to farms
List some of the health effects caused (or suspected to be caused) by chronic exposure to pesticides.
- (Un)intentional poisonings
- Cancer
- Nervous system effects
- Reproductive health effects
- Developmental growth challenges
In which chemical class is DDT?
DDT belongs to the organochlorine class of chemicals.
How do organochlorine and organophosphate insecticides compare in terms of their environmental persistence?
Organochlorine:
- highly persistent in the environment and has a slow degradation.
- tend to have more chronic effects onto humans.
Organophosphate:
- less persistent in the environment as they degrade faster.
- more acutely toxic effects onto humans and have replaced most of the organochlorine insecticides.
What is “regrettable substitution”?
Regrettable substitution is when a chemical that is deemed hazardous is replaced with another chemical, however this new chemical turns out to be just as hazardous or even worse the original chemical.
what is pesticides suicide?
When people intentionally consume toxic pesticides to take their own lives. This is a major issue in rural farming areas, where pesticides are easily accessible
- common in Asia
Integrated Pest Management
A comprehensive approach to pest control that uses reduces amount of pests to tolerable levels while maintaining a quality environment
- physical control
- mechanical control (traps, screens)
- monitoring
- control (biological, chemical)
What are the benefits of organic food compared to conventionally grown food?
- Organic food production prohibits the use of synthetic pesticides.
- Studies show that organic foods have lower concentrations of pesticide residues compared to conventionally grown foods.
- There’s mixed evidence regarding nutritional content, but some studies suggest that organic fruits and vegetables may have higher levels of phenolic compounds, and organic dairy products may have higher levels of Omega-3 fatty acids.
- Organic agriculture also uses less antibiotics.
What are organochlorine pesticides, and why were they restricted?
- Organochlorine insecticides, such as DDT, are chemically stable compounds with low volatility and slow degradation.
- This persistence in the environment led to bioaccumulation and biomagnification in food chains, posing risks to wildlife and potentially human health.
- Due to these environmental and ecological concerns, as well as possible human health impacts like endocrine disruption and reproductive effects, the use of organochlorines like DDT was heavily restricted in high-income countries starting in the 1970s.
What is glyphosate and why has it been in the news in recent years?
- AKA roundup, glyphosate is the most commonly used herbicide around the world.
- The WHO labelled it a probably carcinogen and its faced multiple lawsuits for causing cancer in users and not warning of the health effects and proper PPE use.
