Chemical pesticides and synthetic fertilizers stand out as two of the major developments of the 20th century, but their damaging effects are just now beginning to be understood by science. The first public outcry against pesticide overuse was in Rachel Carson’s "The Silent Spring," written in the 1950s. In it, she warned of the loss of wildlife and potential health damage that would likely occur from chemical poisoning of the soil, water and air.
Pesticides are absorbed into the soil through leaching. A Cornell University Extension paper on soil pollution and pesticides defines leaching as a process “whereby pollutants are flushed through the soil by rain or irrigation water as it moves downward.” Some of the pesticide sticks to soil particles and some mixes with the soil water between particles. Sandy soils are more permeable, where leaching is a more serious problem.
Pesticides in the Soil
Pesticides that are absorbed by the soil are transferred to vegetables and fruits through their root structures. They are also eaten by animals, insects, worms and billions of tiny microorganisms that inhabit the soil. Some pesticides degrade through contact with sunlight; some are broken down by soil microorganisms. The U.S. Environmental Protection Agency advises that soil amended with compost can help transmute pesticides and return it to natural functioning.
Estimating Pesticide Problems
Pesticide products have varying half-lives, which is the amount of time it takes for it to degrade in the soil. Estimating potential pesticide damage is difficult because of the complexity of local individual soil conditions. Cornell University says that a “quantitative prediction of pesticide loss via runoff and leaching requires complex computer models which utilize suite-specific soil, crop, and climatological information.”
Large-scale sustainable agriculture businesses use several methods to avoid the use of pesticides that leach into soil and cause health problems. Integrated pest management involves the use of biological controls, cultural practices such as companion planting and pest monitoring. The University of California at Davis has an Integrated Pest Management program designed to help farmers “expand the use of computer-based crop disease forecasting with the goal of reducing unnecessary pesticide use.”
Home Garden Solutions
Home gardeners may want to avoid using pesticides because they pose a serious health threat, especially to children. The EPA has identified these potential problems as birth defects, nerve damage and cancer. Alternatives to pesticide use are organic pest-control sprays, companion planting to deter harmful insects and biological controls such as ladybugs and praying mantis.