(Reprinted from the Endangered Species Bulletin * Vol. XXI No. 2)

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Pesticide Impacts

By Linda Lyon

 

Environmental contaminants from such sources as hazardous waste sites, mines, urban runoff, and oil spills pose significant threats to endangered and threatened species. The Fish and Wildlife Service's (FWS) Environmental Contaminants Program works with other FWS programs, as well as other Federal and State agencies and the private sector, to prevent losses of endangered species and other organisms from pollutants. This article, the first in a series describing the effects of environmental contaminants on endangered species, discusses some of the threats associated with pesticides.

Now that the pesticide DDT has been banned in the United States, it no longer poses a hazard to our endangered species. True or false? To the surprise of many, the correct answer is false. Although it is true that DDT can no longer be used legally in the U.S., many of our wildlife species are still being affected by this chemical. DDT and its breakdown products can persist in the environment for decades. Also, there are stocks of DDT remaining in private hands, and container leakage or usage from these stocks can release DDT into the environment. Old production and disposal sites provide further sources of DDT. In addition, residues of DDT and other pesticides can be transported to the U.S. through air currents. These compounds, many of which are still widely used in Central and South America, can be picked up during the winter by migratory species.

In addition to the lingering effects of certain banned pesticides, endangered species potentially can be affected by some of the thousands of pesticide products currently registered for use in the U.S. (see sidebar on pesticide consultation). The combined domestic application of these pesticides totals about 2 billion pounds of active ingredients annually. Although many of these pesticides are designed to kill organisms, pesticides actually have a much broader range of intended effects. According to the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), a pesticide is "... any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any pest, and any substance or mixture of substances intended for use as a plant regulator, defoliant, desiccant."

Pesticides are used in myriad settings, including farms, rangeland, forests, rights-of-way, industrial sites, and homes. The types of pesticides available are as varied as the organisms for which they are intended. Among the most common pesticides are insecticides and herbicides, which are also the categories to which listed species are most likely to be exposed. However, effects may also result from rodenticides, fungicides, and avicides (compounds used to control birds).

Pesticides are used for many beneficial purposes. When a pesticide is highly selective for a specific pest, it generally does not pose notable hazards to endangered species. However, many widely used pesticides are not particularly specific for the "target" organism. Such pesticides can cause unintended and unwanted effects to "non-target" resources. Endangered species can be exposed to pesticides by many routes, with the simplest form being direct contact. Animals can ingest pesticides indirectly through contaminated foods such as leafy material, seeds, and prey (including insects and other animals), or by water contamination through precipitation and irrigation. For example, birds, mammals, amphibians, and invertebrates may use contaminated puddles in a farm field for drinking, bathing, or breeding. Aquatic organisms can be exposed to pesticides entering water bodies through runoff and groundwater infiltration. Measurable amounts of pesticides have even been detected in rainwater.

Under FIFRA, pesticides may be used only in accordance with product labels that accompany or are affixed to the product from the point of manufacture. The labels may contain public health and safety warnings or other environmental limitations on the manner in which the pesticides can be applied. When pesticides are used according to the product label and in a specialized manner, such as spot treatment of weeds with herbicides, exposure of non-target organisms may be avoided. However, there are many pesticides that are not specific in their toxicity or exposure potential, and these compounds can pose threats to endangered species and other non-target organisms. Many poisonings of listed species are unintentional and related to normal agricultural uses of pesticides.

Indirect effects of pesticides can also have significant implications to endangered species. For example, herbicide drift can harm plants and consequently damage the habitat upon which an endangered animal depends. A given pesticide can be relatively non-toxic to an endangered species, but may be lethal to its prey or food plants. Similarly, an insecticide can indirectly harm an endangered plant that may depend upon a specific insect pollinator.

There are few cases showing a singular link between a given pesticide and the status of a particular endangered species. However, because these compounds are designed to be toxic and are widely present in the environment, a strong program of research, education, interagency consultation, and careful management of pesticide use is vital for the conservation of many endangered and threatened species.

Linda Lyon is a biologist with the FWS Division of Environmental Contaminants in Washington, D.C.

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Sidebar: The relatively low population sizes of many threatened and endangered species often precludes using them for studies to assess the effects of pesticides and other pollutants. In some cases, FWS biologists use surrogate species for study. For example, in North Carolina, a non-endangered mussel, the eastern elliptio (Elliptio complanata), serves as a surrogate species for research into pesticide effects on the endangered Tar spinymussel (E. steinstansana). This work grew out of the 1990 investigation of a Tar spinymussel die-off that was linked to agricultural insecticides.

  • Land managers sometimes use pesticides to protect endangered species. For example, careful use of selected herbicides can control the rampant spread of exotic weeds that degrade natural habitats. In these situations, the herbicides may be applied with hand-held equipment to direct the chemical onto the target plant. Such pesticide use often is done in conjunction with other Integrated Pest Management (IPM) methods, such as biological controls. Biological control includes techniques such as selected grazing or releasing insect herbivores that are specific for the exotic plant. IPM also can include cultural techniques such as managing soil fertility to favor native plants and select against exotic invaders.
  • FWS works with other government agencies and the private sector to mitigate the effects of pesticides on endangered species. In eastern Wyoming, a task force with members from FWS, the Environmental Protection Agency, State and municipal agencies, environmental organizations, and the ranching community collaborated on a successful plan that allowed for mosquito control while protecting the Wyoming toad (Bufo hemiophrys baxteri). In southern Texas, the Cameron County Wildlife-Agriculture Coexistence Committee works to protect endangered species such as the aplomado falcon (Falco femoralis septentrionalis) from pesticides in the agricultural lands surrounding Laguna Atascosa National Wildlife Refuge. (See Bulletin Vol. XX, No.4.) In North Dakota, FWS and the State's Department of Agriculture have a formal agreement addressing the protection of endangered species from pesticide threats..