Unit 3 Environmental Chemistry- Topic 2

A Growing Concern

Role of Pesticides in Agriculture

• Insecticides, herbicides, and water are utilized to enhance food production.

• Agriculture allows for selective nurturing of plants, providing humans an advantage in food sourcing.

• Competing species, such as pests and weeds, are controlled to maximize plant harvest.

• Pesticides, including insecticides, herbicides, and fungicides, are commonly used to manage pest populations.

• Chemical pesticides like DDT and dieldrin kill insects but raise environmental concerns.

Human Intervention in Ecosystems

• Spraying crops with pesticides targets specific pest species, but can lead to unintended ecological effects.

• Tools like citronella candles repel insects without killing them, offering alternative pest control.

• The effectiveness of these methods raises questions about sustainable agricultural practices regarding pests and diseases.

Issues Associated with DDT

Historical Context of DDT

• DDT, discovered by Paul Hermann Müller, was initially hailed for its efficacy in treating insect-borne diseases like typhus during WWII.

• Müller received the Nobel Prize in 1948 for DDT's effectiveness against various arthropods.

• DDT was later considered for malaria control, impacting over 120 million people yearly.

Environmental Impact of DDT

• The application of dieldrin in Borneo eradicated mosquitoes but led to ecological imbalance, affecting lizards and cat populations, which caused a rodent population spike.

• The resultant plague prompted intervention to reintroduce cats.

DDT and Food Chains

• DDT is a persistent pesticide that accumulates in organisms and poses risks as it moves up the food chain (biomagnification).

• Seabirds show significant levels of DDT due to their position at the top of marine food webs, leading to reproductive issues.

DDT's Biological Impact

DDT's Toxicity and Regulations

• Rachel Carson's book "Silent Spring" raised awareness about pesticide dangers, resulting in reduced use of DDT after 1969 in Canada.

• Evidence linked DDT to declining populations of birds of prey, as it thinly-shelled their eggs.

• Biological magnification illustrates how toxins can concentrate in top predators, harming their reproductive viability.

Current Status of Pesticide Use

• Despite its dangers, DDT continues to be utilized in some tropical areas due to its effectiveness against pests, impacting global ecosystems.

• Contaminated food sources can transfer these pesticides to humans.

Pesticide Resistance and Alternatives

Challenges with Pesticides

• There is an increasing number of pest species that have developed resistance to existing pesticides.

• Alternatives are being researched, but DDT remains unmatched in efficacy and cost-effectiveness, especially in less developed nations.

Organic Agriculture

Principles and Growth

• Canada's organic agricultural sector is among the top producers of organic grains and oilseeds, with guidelines ensuring minimal environmental harm.

• Approved organic pesticides often derive from natural sources and are subject to stricter regulations.

Sustainable Practices

• Natural pest control methods focus on maintaining soil health and biodiversity, promoting environmentally friendly farming practices.

• Organic farming practices emphasize the reduction or elimination of harmful pesticides and chemicals.

Social Perspectives on DDT

Public Response and Misconceptions

• A ban on DDT has ignited concern over public health, particularly regarding malaria re-emergence after the pesticide's restriction.

• While DDT is recognized for its dangers, the immediacy of public health needs drives debate over its continued use in certain regions.

Review Questions

1. Define what constitutes a pest and describe the role of pesticides.

2. Discuss the historical use of DDT and its implications.

3. Evaluate the distinction between toxic substances and poisons.

4. Explain organic farming and its benefits versus conventional farming, considering cost and practicality.