Pesticides in the Environment
Pesticide Contamination Overview
Pesticides are very useful when managing weeds, damaging insects, and animal pests. However, once pesticides move from the targeted area or pest, it then becomes a pollutant to the environment. The environment contains all the soil, water, air, and living things, along with the physical, chemical, and biological properties of each. The most common pesticide pollutants occur within soil and water systems. Contaminated soil prevents life from flourishing, and tainted water poisons animals and humans alike. Bodily effects of pesticide poisoning will be covered in a future article. Pollution factors and methods of prevention are vital when preventing the damaging effects of pesticide pollution.
Applications of pesticides cannot be used without directly or indirectly effecting one or more non-target components within the environment. There are many things that happen to pesticides within the environment, and care must be taken to reduce side effects as much as possible.
Where Do Pesticides Go?
One of the main question asked when relating to pesticide use is 'Where do pesticides go within the environment after they are used?". Pesticides move to non-target areas and can even transform into a different form when exposed to the elements of nature.
There are several examples of what happens to pesticides after they are applied...
- Pesticides can turn into a gas (volatilize) on treated surfaces such as asphalt and concrete. The volatile pesticides then dissipate into the atmosphere.
- Applications of pesticides can be rinsed off hard surfaces and enter the soil. Pesticides have several fates once they have entered the soil.
- Plant residues contaminated with pesticides can enter the soil.
- Pesticide solutions that are sprayed can be transported away from application sites via wind, which is referred to as "drift."
- Runoff and erosion can carry pesticides to non-target areas and water systems.
- Pesticides can leach through the soil and into water tables.
- Animals can ingest pests that were targeted with pesticides. Poisoning can occur within a predator animal if enough targeted prey are consumed.
How Pesticides Travel
There are several factors that determine the movement of pesticides within and outside a target area. Understanding such factors will determine risks and effectiveness of applications.
- Adsorption - This determines how well pesticides attach to soil particles. Pesticides that adsorb strongly to soil particles have a lesser chance of leaving the target area via surface water, run-off, and leaching. Although, adsorption does not stop erosion from carrying pesticides away from the target area and into waters systems.
- Solubility - This determines how well pesticides dissolve in water. Highly soluble pesticides have a greater chance of movement away from target areas compared to pesticides with low solubility.
- Drift - Drift occurs when pesticide solutions are sprayed during a windy day. Wind can carry tiny droplets of pesticides away from the target site, sometimes up to a few miles away.
- Degradation Rate - The rate of degradation of a pesticide is the amount of time the pesticide takes to break down within the environment. Degradation can be physical, chemical, and biological. Biological degradation is caused by bacteria, fungi, and other microorganisms. Most pesticide degradation occurs within the soil.
- Persistence - This is the amount of time a pesticide remains active within the environment. This may be desirable or undesirable depending on the situation. Long-term control of a pest will require a persistent pesticide that is residual over time. A lingering persistence will also allow the pesticide to move from the target area, which is undesirable and a pollutant.
- Bioaccumulation - Predatory animals that consume pests that are exposed and targeted by a pesticide will accumulate pesticides within their tissues, usually in fatty tissue. Harmful levels can be reached if enough exposed prey are consumed. This can also occur in humans who consume the meat of an animal who has been consuming poisoned prey.
- Biomagnificaton - The food chain allows biomagnification to occur. Pesticides that accumulate can become concentrated as they move through the food chain. Fish that consume plants that have absorbed pesticide runoff will accumulate pesticide toxins. The fish can then be eaten by a bigger fish, which in turn can be consumed by other predatory fish, birds, and humans. The toxicity can persist throughout several levels of the food chain.
Pesticides in Groundwater
Sources of Groundwater Pesticide Pollution
Groundwater contamination usually occurs from a spill or mishap that has allowed large amounts of pesticides to reach the water table. Other sources of ground water pesticide pollution can occur from rainfall and snowmelt moving over an area where pesticides have been applied. Often times it is difficult to determine the source of pollution, and even more difficult to determine how long ago the pesticide contamination began.
Preventing Groundwater Pesticide Contamination
Groundwater is water that is contained within cracks and pores of rocks and between sand grains and mineral particles underground. Groundwater is drawn to the surface via wells, and many people worldwide obtain water through wells.
Spilled pesticides can be carried and leached down into the groundwater. It is very hard to do anything to reverse the pollution once pesticides seep into the water table and mix with groundwater. Containing the source of pesticide pollution is all that can be done to reduce the impact of pesticide pollution within groundwater.
The best solution to pesticide contamination within groundwater is to prevent spills and contamination. Containing a spill is the next best solution if contamination has already occurred via a spill or mishap.
Pesticides in Surface Water
Streams, rivers, lakes, and wetlands are all susceptible to pesticide contamination. Pesticides can reach surface waters via storm drains, runoff, and contaminated groundwater. Mixing, using, and handling pesticides properly prevents surface water contamination.
Applying pesticides near surface waters greatly increases the risk of contamination and should only be used when absolutely necessary, mainly when all other eradication methods have failed. Pesticides that strongly adsorb to soil particles are susceptible to runoff and erosion, which can flow into surface waters.
Contamination of surface waters disrupt the ecosystem and little can be done once contamination has occurred. Flora and fauna suffer irreversible effects such as death and even genetic mutation of future generations.
Pesticides in Soil
Pesticides and Soil Types
Pesticide pollution within soil depends heavily on the composition of the soil. Soils high in organic matter, medium-to-fine in texture, and with adequate drainage can capture pesticides well. The captured pesticides are then eventually broken down by microbial activity. Sandy and rocky soils allow pesticides to seep deep into the soil with little resistance. Soils that experience a heavy spill or mishap can essentially become sterile and prevent any life, including microorganisms, from growing.
Pesticide Filtering Within Soil
Soils that are deep with a large distance between the surface and water table can capture and filter pesticides. Rocky and sandy soils allow pesticides to move downward into the water table with little resistance and filtering. Rain and snow melt saturate soils and increase the ability for pesticides to reach groundwater. High water tables increase the chance of contamination as well.
Prevention of Environmental Pesticide Contamination
Spills and reckless handling are the main reasons for soil and water contamination. Proper transit, storage, mixing, and disposal of pesticides must be followed precisely to prevent disastrous mistakes. A few guidelines can prevent such disasters from occurring.
- Secure pesticide containers in the back of a vehicle during transport.
- Store pesticides over a floor that is impermeable.
- Check containers frequently for damage. Replace damaged containers immediately.
- Store bulk and highly concentrated pesticides in a secondary container, within the main container.
- Mix and load pesticides over an area with an impermeable floor or pad.
- Never spray pesticide solutions on a windy day.
- Protect the water supply when mixing by using an "air gap" (do not place garden hose down into mixing container) and a one-way valve to prevent back-flow.
- Dispose of pesticide waste correctly. Contact local authorities and landfill operators for information regarding the disposal of waste and empty pesticide containers. Do not simply throw pesticide waste in the trash!
- Never mix or apply pesticides near wells, cisterns, surface waters, saturated soil, or high water tables.
- Follow directions on the pesticide container! Do not use more than directed!