ENSC 201 Lecture 9 - Pesticides

What are the key characteristics of Persistent Organic Pollutants (POPs) like DDT?

POPs are Persistent, Bioaccumulative, and Toxic (PBT), meaning they persist in the environment, accumulate in organisms, and are harmful at high concentrations.

What is the main challenge with modern pesticides in terms of environmental impact?

Modern pesticides must not be persistent (P) and should minimize bioaccumulation (B), while still maintaining enough toxicity (T) to be effective.

How are organophosphate pesticides categorized?

• Type A: Controlled release (e.g., pest strips, flea collars), intermediate toxicity (LOD50 25 mg/kg).

• Type B: Highly toxic (LOD50 3 mg/kg), many phased out in high-income countries.

• Type C: Widely used (e.g., mosquito spraying), low toxicity (LOD50 885 mg/kg), concerns about long-term health effects.

What is the main issue with organophosphate pesticides?

Organophosphate pesticides inhibit acetylcholinesterase, which can lead to neurotoxicity in both target and non-target organisms, including humans.

How are modern pesticides made more selective for target organisms?

Modern pesticides aim to be non-persistent, and they focus on being more selective by having high acute toxicity to target organisms and low toxicity to non-target organisms

What are pyrethrins, and how do they work as insecticides?

Pyrethrins are plant-based insecticides isolated from chrysanthemum, also known as mum flowers, with low toxicity to humans. They act by inhibiting sodium channels, causing paralysis in insects.

What is the role of Piperonyl Butoxide (PBO) in pyrethrin-based pesticides?

PBO is a synergist that inhibits metabolizing enzymes in insects, allowing pyrethrin to be more effective. It also affects human metabolism, but mammals metabolize it more efficiently.

What is the benefit of using natural pyrethrins in products like Raid Essentials?

Natural pyrethrins are less stable than synthetic versions but are marketed as organic and environmentally friendly due to their lower toxicity to humans.

What is a key challenge with pesticide persistence?

Persistence in pesticides like Atrazine can lead to long-term environmental contamination, such as groundwater contamination, especially in aquatic ecosystems.

How do herbicides like Atrazine affect plants and animals?

• interfere with photosystem II
  - used to control weeds among less sensitive plants (e.g. corn)

what are herbicides ?

easier than other pesticides to make non-toxic to vertebrates/mammals/humans

What are the key characteristics of atrazine in terms of persistence and environmental impact?

• Moderately water-soluble with a log KOW of 2.7, meaning it does not bioconcentrate.

• Persistent in soil and water, raising concerns for aqueous ecosystems (guideline of 2 ppb).

• Can end up in groundwater; detected in groundwater across France and the U.K.

• Banned in Europe and the U.K., but still used in North America after a 2007 review.

• Given its persistence and European experience, Ontario's groundwater resources may eventually face atrazine contamination.

What are the key properties of 2,4-D and 2,4,5-T as herbicides?

Selective herbicides that target broadleaf dicotyledon plants (weeds) while leaving monocots (like grasses) unaffected.

Mimic auxin, a plant hormone, causing uncontrolled growth in dicot plants.

what the environmental impact of 2,4-D and 2,4,5-T as herbicides

Low environmental impact:

• Soluble (570 mg/L) and log KOW < 1.

• Non-persistent in soil and water (degrades in <30 days).

• Low toxicity to humans (LD50 > 500 mg/kg).

• Some concern for persistence in clays and other types of soil.

Why was 2,4,5-T banned, and what is the current status of 2,4-D?

2,4,5-T was banned due to the dioxin byproducts produced during its manufacture

2,4-D is still in wide use and is considered fairly safe for environmental use when properly managed.

What are the health concerns related to chronic exposure to 2,4-D?

• Chronic exposure (mainly among occupational users like farmers) is linked to non-Hodgkin's lymphoma and other chronic diseases.

• IARC has classified it as a carcinogen.

How are restrictions on 2,4-D affecting its use in various jurisdictions?

Cosmetic pesticide use of 2,4-D has been banned in many areas (including most Canadian provinces, such as Ontario) to minimize direct exposure, especially to vulnerable groups

Commercial/agricultural use is still permitted, but users are required to have training and wear PPE (Personal Protective Equipment) to reduce exposure risks.

How does glyphosate work as a herbicide?

Glyphosate inhibits the shikimic acid synthesis pathway, which is a precursor for essential aromatic amino acids in plants, effectively targeting all plants.

What are the key properties of glyphosate in terms of environmental impact?

• Water soluble and non-persistent, with a log KOW < 1 (no bioconcentration).

• Does not migrate to groundwater and is degraded into harmless products.

• Low toxicity to humans (LD50 > 4000 mg/kg).

How is glyphosate beneficial for farming?

Glyphosate is considered environmentally friendly as it enables no-till farming, which can reduce soil erosion and improve soil health.

What are the current restrictions on glyphosate usage?

Cosmetic use of glyphosate has been banned to minimize direct exposure to users, even though it is still widely used in agriculture.

Why has glyphosate become a controversial herbicide?

• Persistence concerns in some compartments (e.g., clays, anaerobic sediments, macrophytes with low metabolism).

• Health concerns for direct exposure, with IARC labeling it as "probably carcinogenic" in 2015.

What are the health concerns regarding glyphosate?

• Direct exposure to glyphosate, even with controlled use, is of concern.

• The IARC classified glyphosate as "probably carcinogenic" in 2015.

How is glyphosate linked to genetically modified organisms (GMOs)?

• Glyphosate is used in the production of "Roundup Ready" GMOs, which are resistant to the herbicide.

• This practice has been criticized for its impact on biodiversity, sustainability, and food security.

What is Monsanto's involvement with glyphosate?

• Monsanto marketed glyphosate as Roundup herbicide.

• The company was criticized for its practices related to GMOs and glyphosate use.

• In 2018, Bayer purchased Monsanto, phased out its name, but continues to sell glyphosate products.

What are neonicotinoids used for and what is their toxicity level?

• Used to protect seeds and crops from a range of insect pests, including sucking and chewing insects, soil insects, and fleas on domestic animals.

• Low toxicity to humans, birds, and other animals.

• LD50 is between 50-500 mg/kg.

How persistent are neonicotinoids in the environment, and when were they developed?

• Not persistent in the environment, breaks down in water and sunlight.

• Can be persistent in soil where applied, but not mobile.

• Developed in the 1980s, with widespread use starting around 2000 as other pesticides were restricted.

Which neonicotinoid is now the most used pesticide globally, and why?

• midacloprid is now the most used pesticide globally (by mass).

• It is widely used due to its effectiveness in pest control.

What is the controversy surrounding neonicotinoids and bees?

• Neonicotinoids have been linked to the collapse of bee colonies, which is a concern for agriculture due to bees' role in pollination.

• The evidence is complex, and while industry resistance remains, neonicotinoid use is now restricted in many jurisdictions, starting in the EU, now also in Canada and other countries.

What is unique about the restrictions on neonicotinoids?

• Neonicotinoids are an example of a pesticide restricted due to environmental impact, rather than human health concerns.

• Activism played a significant role in bringing attention to the issue and restrictions were eventually imposed.