Pesticides and Environmental Impact

• The document discusses pesticides and their environmental impact and fate.

Pesticides: Environmental Issues

• The document aims to help the reader understand the meaning of "environment" in relation to pesticides, define pesticide residues, enumerate factors affecting pesticide breakdown, explain terms describing pesticide impact, describe factors influencing pesticide concentration, distinguish between point and non-point sources of contamination, describe direct and indirect effects on biota, and recognize harm to non-target organisms.

Introduction

• Pesticide movement in the environment is complex, involving transformation between liquid, solid, and gas forms.
• The environmental fate varies for each pesticide.
• DDT residue findings highlighted the issue of pesticides being detected far from where they were applied.
• DDT presence is linked to tumors and eggshell thinning.
• Released pesticides either break down (due to various factors) or remain unchanged, with persistent pesticides potentially leading to increased residue levels and health concerns.

Environmental Fate of Pesticides

• The environmental fate of pesticides depends on how and where it enters the environment, its movement, and its persistence.
• Application method influences the fate of the pesticide.
• The environment consists of physical, chemical, and biotic factors influencing an organism's form and survival.
• These factors include air, soil, water, plants, animals, and structures.
• Pesticide residue is what remains on/in food crops after pesticide application.
• Safe residue levels are regulated.
• Regulations prevent harvesting crops or livestock products too soon after treatment.
• Exposure is common through food consumption or contact with treated areas.
• Application method affects pesticide distribution.
• Distribution is affected by the method, quantity, timing, frequency, and weather conditions during application.
• Other factors include land's nature, plant cover density, soil conditions, and proximity to water.
• Greenhouse applications differ from outdoor applications.

Pesticides Move and Degrade After Application

• Pesticide degradation and movement occur simultaneously.
• Movement occurs via wind, water, or other objects, both within and outside the application site (off-site movement).
• Pesticides can break down into less toxic molecules, but some degrade into more toxic ones.
• Spray drift involves airborne pesticide droplets.
• This can be reduced by following requirements in aerial spraying such as using buffer zones, controlling droplet size, wind speed, application volume, and using aerial application.
• Pesticides transfer off-site through harvesting treated crops or livestock, vertical movement in soil to groundwater, runoff to water bodies, and wind currents to the atmosphere.

Pesticides Break Down in Many Ways

• Chemical breakdown occurs via oxidation or hydrolysis.
• Photodegradation: Sunlight breaks down pesticides.
• Microbial breakdown: Microorganisms "eat" pesticides.
• Soil moisture, temperature, pH, aeration, fertility, and adsorption influence microbial breakdown.
• Breakdown occurs inside plants and animals via similar pathways.

Pesticides Breakdown at Different Rates

• Breakdown rate depends on the pesticide's chemical structure.
• Some parts of the molecule are easily broken down by sunlight, microbes, or metabolism.
• Some molecules are persistent.
• Persistence can lead to use as termiticides.
• Pesticide persistence is measured by half-life, which is the time for half the pesticide to breakdown, and will vary based on the environmental conditions.
• Persistence depends on breakdown speed, influenced by chemical reactions with water, soil, UV light, microbial action, and soil particle adsorption.
• Breakdown speed is influenced by how quickly the pesticide reacts to the environment.
• Soil and water conditions also play a role.
• Plant surface characteristics, like trichomes and ridges, also affect pesticide persistence.
• Pesticides can be categorized by half-life into: non-persistent (less than 30 days), moderately persistent (30-100 days), and persistent (greater than 100 days).

Pesticide Breakdown or Degradation

• Mineralization is the complete breakdown into smaller molecules.
• Eventually, pesticides break down into carbon dioxide, water, and minerals.
• Breakdown products are incorporated into soil organic matter and taken up by plants/animals.

Pesticides Get Into the Atmosphere Through Volatilization

• When pesticides move from plant surfaces, soil, and water into the air.
• The pesticide changes from liquid or solid to a gas or vapor.
• Increased air temperature increases volatilization.
• Volatilization is reduced if the pesticide sticks tightly to the surface or is highly soluble in water.

Pesticides Can Also Get Into Ground and Surface Water

• Pesticides can be washed off into nearby bodies of surface water or percolate through the soil to lower layers and groundwater.
• Injected termiticides can move through the soil to reach groundwater.
• Leaching is the vertical movement of pesticides that reaches the underground water.
• Leaching from the soil surface means less exposure to sunlight and bacteria, which means slower the degradation.
• Pesticide residues used in rice have been detected in waters from pump water areas near rice paddies.
• Movement in soil depends on the type of soil: less movement in clay soils and those with high organic matter content.
• Faster in sandy soil thus leaching of residues becomes a concern when the groundwater is contaminated.
• Water soluble herbicides can move to contaminate groundwater.
• Most pesticides that are not highly soluble in water stick strongly to soil, and do not leach easily.
• Movement through soil can also be horizontal from runoff, rain, or irrigation.
• This may lead to contamination of nearby water bodies, like in rice production.
• Pesticide residues can wash away through waterways and reach rivers, which can cause fish kills.
• Dilution reduces concentration, but residues enter the food chain.

Residues in Bodies of Water

• Pesticides in soil or silt carried in run-off can end up in bodies of water.
• The pesticide in the soil is released to the water and is absorbed by fish, plankton and algae.
• Contaminants pass the food chain: Plankton and algae with residues are eaten by small fish and large fish eat small fish.
• Birds eat fish and humans then eat birds as well as fish.

Residues in all Components

• Residues found in the components may eventually be consumed by man.
• Pesticides that remain in the fatty tissues of some animals can lead to increasing residue levels, known as biomagnification.
• Biomagnification is the process by which a compound increases its concentration in the tissues of organisms as it travels up the food chain.
• Chemical characteristics that cause concern are persistence, high solubility in water, and low adsorption in soil.
• The existence of environmental contamination and/or human exposure to pesticide residues in food and water can be traced back to the characteristics listed above.

Plant Uptake Affects Pesticide Movement

• Pesticide residues degrade over time by entering aquatic plants, such as kangkong and duckweed, through their roots.
• Contaminated plants cannot move into the atmosphere, ground, or surface water after being taken up by plants.
• However, harvested or eaten contaminated plants may move residues off-site.

Pesticides Applied Indoors Breakdown Slowly

• Lack of sunlight, wind, or rain contribute to a slow breakdown.
• Less pesticides become vapor by not being exposed to the heat of the sun.

Special Environmental Considerations

• Ground water protection
• Contamination of the ground water could lead to contamination of drinking water sources
• Pesticides in groundwater degrade very slowly as there are not many microorganisms and no sunlight, sandy soil allows pesticides to leach quickly into the groundwater aquifer.
• Measure pesticides accurately and do not over apply
• Do not mix or load near water or drains.
• Avoid spills, and triple rinse used containers; place the rinse water into the spray tank.
• Protection of non-target organisms:
• Pesticide drift should be reduced to slow down transfer of pesticides.
• These organisms which are not pests include beneficials like pollinators (bees), predators (capture and eat other organisms), parasitoids (insects whose larvae feed or live in other host insects), fish, wildlife, endangered and threatened species.

Summary

• Identifying and minimizing concerning situations is possible.
• Significant knowledge gaps exist regarding pesticide movement and fate, leading to minimizing the unnecessary release of pesticides.
• Fewer pesticides released leads to a safer environment.