Understanding how pesticides move in the environment is crucial. While drift is a direct result of spray applications, pesticides can also move after the initial application. This movement, influenced by pesticide properties, affects their final destination and activity. It’s beneficial for applicators to comprehend this process to mitigate the downstream impact on different environments and ecosystems. Post-application, pesticides continue to move through various mediums. Applicators must understand these mediums to control unintended movement away from target plants.
Pesticide movement away from the target plants can occur through several mediums:
1. Through air via spray drift (Pesticides Drift from Spray Applications)
2. On or in animals and/or objects:
If pesticide movement were confined to the target plants being sprayed and the immediate environment, there would be no need to consider their further environmental impact. However, this is not the case. Pesticide drift occurs in all spray applications, as previously discussed. A significant concern is the movement of pesticides onto or into animals and objects. After spraying, the immediate concern is the potential for pesticides to contact animals, including humans, or objects used by applicators. Pesticides can transfer from spray droplets or treated plants to animals or objects primarily through two processes: adsorption or absorption.
Adsorption is the process by which pesticides adhere to the surface of an object or animal. Pesticide residue can be transferred from application sites via personal protective equipment, work clothing, containers, and other tools to different environments, including homes. Further movement of pesticides can occur from contaminated objects, affecting the sense organs of animals and potentially causing severe acute or chronic impacts. Since sense organs have varying sensitivity to foreign chemicals like pesticides, it is crucial to exercise caution when spraying pesticides to minimize this type of movement.
Absorption is the process where pesticide molecules move from the surface of an object or animal into its interior. Once pesticide residue is adsorbed onto an animal, it can then be absorbed. For instance, human skin, which has an oily coating, is more prone to absorbing oil-soluble pesticides than water-soluble herbicides. Consequently, pesticide formulations that are emulsifiable concentrates are more easily absorbed through the skin compared to other formulations because they typically contain oil-soluble active ingredients.
3. Through water
When examining pesticide movement through water, we generally categorize it into two types: surface water and groundwater.
Surface water Surface water refers to the visible water on the earth’s surface, including springs, streams, rivers, lakes, seas, and oceans. Pesticides primarily enter surface water through runoff and erosion, except when directly applied to aquatic weeds. Runoff occurs when pesticides dissolved or suspended in water move across soil surfaces to reach surface water. Erosion involves the movement of soil particles due to rain or irrigation, carrying pesticides from application sites with them. Factors influencing the likelihood of runoff and erosion include soil characteristics, the slope of the application site, the volume and rate of water used, temperature and rainfall, and the proximity of the application site to surface water.
Ground Water is water that accumulates or flows beneath the earth’s surface, filling the porous spaces in soil, sediments, and rocks. Leaching refers to the process by which pesticides move through the soil to reach groundwater. Water-soluble pesticides are more likely to leach and can eventually contaminate artesian wells, man-made wells, and aquifers. The movement of pesticides through ground water is directly connected to the type and dept of soil involved.
4. Through Soil
The movement of pesticides to groundwater occurs through the soil. Therefore, it is crucial to understand how soil properties influence a pesticide’s potential to leach. Soil texture and structure determine the soil type, which can be categorized as clay, silt, sand, or loam. A key concern is whether pesticides will reach groundwater sources, making the depth of the soil to the groundwater an important factor. Shallow water tables are more susceptible to pesticide contamination. Sandy soils, with their larger particle sizes, allow pesticides to move more easily through them, while clay soils offer less space for pesticides to travel far distances.
It is important to employ management practices to contain pesticides in target sites as best as possible to minimize their environmental impact. The principal route of exposure from the movement of pesticides through objects or animals is contact with the skin. Using appropriate personal protective equipment (PPE) is essential to minimize absorption but not adsorption. Therefore, proper hygiene in handling contaminated PPE and objects is crucial to minimize the movement of pesticides. Additionally, consider the vulnerability of the site to determine if pesticides can be applied, considering potential runoff, erosion, or leaching. Evaluate the locations of water sources to determine their proximity to the application site. Finally, consider weather and irrigation when determining what pesticide to spray.
