Mountain-Prairie Region





Vol I, No. 3


3. Pesticides and Wildlife -- A Perilous Mix

As earth's population grows so does the demand for food, and the use of pesticides has become essential in meeting this demand. Improved agricultural yields, reduced energy costs for producers and lowered costs of food for consumers are attributed to the controlled use of pesticides. In the United States alone more than one billion pounds of pesticides are used annually, resulting in $6 billion in retail sales for pesticides per year.


Pesticide use skyrocketed after World War II. At the same time, significant numbers of wildlife deaths began appearing. And by 1962, with the publication of author Rachel Carson's book Silent Spring, there was a realization that pesticides could be disastrous if used improperly.

While the U.S. Environmental Protection Agency oversees pesticide registration and use, it's the responsibility of the U.S. Fish and Wildlife Service (USFWS) to monitor impacts of pesticides on wildlife and provide input about how to avoid such impacts.

DDT -- an organochlorine compound -- is one of the most infamous pesticides, banned in the United States in the 1970s. The dramatic decline of bald eagles, peregrine falcons and brown pelicans was traced to DDT, which caused egg shell thinning and an inability for eggs to survive full-term. DDT's ability to spread through the food chain was especially insidious because the chemical was able to biomagnify.

Biomagnification is a process by which some organisms accumulate chemical residues in higher concentrations that those found in the organism they consume. After application as a pesticide, DDT was found in waterways in low concentrations; but DDT had biomagnified 10 million times by the time it had reached the top of the food chain -- the birds.

Because of the problems from using organochlorine pesticides, new pesticides have been developed. These chemicals aren't as persistent in the food chain as organochlorines, but some are more immediately toxic to wildlife. Others are extremely toxic to certain non-target species like bees, fish and aquatic invertebrates.

The toxicity of pesticides to wildlife depends on several factors, including the persistence and degree of toxicity of the chemicals. Factors such as dose, time and duration of application play important roles in a pesticide's toxicity. Wildlife, for example, are more susceptible to pesticide effects during nesting, nursing of young or during times of low food availability.

A pesticide's degree of toxicity also depends on how it is exposed to wildlife. Primary exposure includes eating, drinking, preening feathers, skin contact or breathing of vapors. Secondary exposure occurs from scavenging on contaminated food, such as exposed carcasses, or feeding upon insects. If pesticide levels are high enough, wildlife often die suddenly.

Not as readily observed in wildlife are the sublethal, or non-fatal, consequences of ingesting pesticides. Behavior changes, weight loss, impaired or unsuccessful reproduction, high offspring mortality or deformed embryos are results of sublethal exposure to pesticides. Affected wildlife become easy prey for predators, while many loose their ability to adapt to environmental changes.

Pesticides can reduce insects that may be important food sources for young birds and fish, and habitat is similarly reduced when vegetation is destroyed -- a critical factor for small wildlife populations already stressed by insufficient habitat. New research continues to find other sublethal effects linked to pesticides, which could affect threatened and endangered species as well as humans.

The use of pesticides should be limited and confined to those that are less toxic and persistent in the environment. Directions for use should always be carefully followed, with care taken not to kill other organisms. When beneficial organisms are inadvertently destroyed by pesticides, pest species often flourish.

The use of pesticides and enjoyment of wildlife are integral parts of society. Most pesticide use can be compatible with wildlife if applications are correctly selected and integrated with other pest control measures. Many wildlife species, such as the bald eagles, have made a strong recovery because of steps taken through pesticide research, banning pesticides like DDT that cause serious effects, and educating people about the correct use of pesticides.

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