Water is a vital resource which if goes unprotected can become a permanent destination for pesticides. As a precious component of our environment, protecting water should be a high priority when applying pesticides. Protection of this liquid treasure must be a foremost concern for all applicators. As an applicator, it is your responsibility to prevent pesticides from entering water by understanding the characteristics of soils and pesticides, and by properly storing, mixing and applying them.
When considering water sources the two that come to mind naturally are ground and surface water. Groundwater is water that is located within soils below the earth’s surface moving slowly through rock and soil particles. Groundwater can also be found in limestone areas where it can flow through large underground canals or caverns. Groundwater is capable of providing large amounts of water known as an aquifer. Aquifers provide us with drinking, washing and irrigation water by providing water to a well. Surface water can be characterized as natural water that has not penetrated much below the surface of the ground and is typically collected by ponds, streams, lakes, canals or ditches.
Pesticides can find their way into either aquifers or surface bodies, through the process of leaching or runoff, and if they do there is a potential for contamination of the water people use every day for living.
To be a better applicator it is important to understand how pesticides move into water sources along with knowing a few of their basic chemical and physical properties. By understanding these concepts you as an applicator will have made a vital decision to take a role in preventing water contamination. Let’s get started!!
Leaching: Leaching is the movement of water through the soil profile and can occur downward, upward or sideways. As water infiltrates it removes soluble materials which can carry pesticides to the water table. If the water table is close to the surface, there is a greater likelihood of contamination.
Runoff: Runoff is the movement of water over a sloping surface and can carry pesticides dissolved in water or bound to the soil. If heavy rainfall or overhead irrigation occurs shortly after an application, runoff can be encouraged, leading to pesticides being moved off site. Heavy rainfall or irrigation can also wash off pesticide residues adding to stormwater runoff.
Adsorption: Adsorption occurs when a positively charged pesticide molecule binds tightly to a negatively charged one. When a pesticide binds itself tightly to soil particles it is less likely to move from the spray site. The amount that a pesticide is adsorbed to the soil varies with the type of pesticide, soil, moisture, soil pH, and soil texture.
A pesticide that is held strongly on the surface of soil particles by adsorption is less likely to leach. However if the pesticide is strongly attached to the soil particle, and runoff is a concern the applicator must try to provide for barriers to prevent soil from finding its way into waterbodies.
Solubility: When a pesticide is soluble it will become dissolved with water that is moved throughout or over the soil. Pesticides that are highly soluble in water will dissolve easily and are more likely to move with either surface or soil water.
Persistence: Persistence is the ability for a pesticide to remain present in the soil and is often expressed in terms of half-life. Half-life is the length of time for one-half of the original quantity to break down. Pesticides are typically broken down into three categories based on their half-lives, non-persistent with a half-life of less than thirty days, moderately persistent with a half-live of 30 to 100 days, and persistent with a half-live of greater than 100 days. Persistence can be desirable for long term control. However if a pesticide is rapidly broken down, it is less prone to leaching or runoff because it remains in the soil for short periods of time.