PANNA: Disrupting the Balance: Ecological Impacts of Pesticides in California (Executive summary)

Thirty-seven years after Rachel Carson's eloquent warning to the world about the devastating effect pesticides have on birds and beneficial insects, pesticides continue to be a pervasive and insidious threat to California's ecosystems. A massive chemical assault on our environment is launched each year by California's residents, farmers, and official agencies, as we apply hundreds of millions of pounds of pesticide active ingredients in our homes and gardens, on crops and roadsides and in forests. This poisonous barrage aggravates other pressures on ecosystems, such as expanding suburban development and dammed rivers, threatening the survival of many birds, fish, insects, and small aquatic organisms that form the basis of the food web.

Pesticides affect all members of an ecosystem, from the smallest invertebrate to birds and humans. In California, the annual application of more than 100,000,000 pounds of the most toxic pesticides in both urban and agricultural settings is responsible for the deaths of many birds, fish, and the smaller aquatic animals that fish depend on for food. More generally, pesticides reduce species diversity in the animal kingdom and contribute to population declines in animals and plants by destroying habitat, reducing food supplies, and impairing reproduction. This report provides basic information about pesticides and how they are transported through the environment, documents the specific impacts of pesticides on California birds, fish, and their food supply, and presents a brief overview of viable, least-toxic pest control methods.

Pesticides Are Still Killing Birds, Both Directly and Indirectly

More than 25 years after DDT was banned, pesticides are still killing birds and impairing their reproduction. An estimated 672 million birds are exposed to pesticides every year in the United States from agricultural pesticide use alone. An estimated ten percent, or 67 million of these birds die. The loss of even a few individuals from rare, endangered, or threatened species--for example, burrowing owls, Aleutian Canada geese, or raptors like the bald eagle, Swainson's hawk, and the peregrine falcon--pushes the entire species that much closer to extinction. Research and observation have documented that:

• The insecticides diazinon and carbofuran are responsible for most documented bird kills in California. Diazinon is heavily used on almonds and stonefruits, in structural pest control and landscaping, and in unreported home pest control applications. Carbofuran is used primarily on alfalfa, grapes, and rice.
• Organochlorine pesticides (like DDT) continue to impair avian reproduction, years after most organochlorine pesticide use was discontinued. Because synthetic pyrethroids--commonly used in structural pest control and on cotton, alfalfa, and leafy vegetables--have a mode of action similar to the organochlorines, they are likely to have similar effects.
• Birds exposed to sublethal doses of pesticides are afflicted with chronic symptoms that affect their behavior, reproduction, and nervous system. Weight loss, increased susceptibility to predation, decreased disease resistance, lack of interest in mating and defending territory, and abandonment of nestlings have all been observed as side-effects of pesticide exposures.
• Most bird kills caused by pesticides go undocumented, with reported kills representing only a small fraction of actual bird mortality due to pesticides.
• Toxic pesticides are still being sprayed in national wildlife refuges in California, even though the National Wildlife Refuge Improvement Act of 1997 mandates protection of wildlife and the environment as the highest priority use for these areas.

Pesticides Threaten Fish and Their Food Supply

In an ecosystem that is already stressed from too many dams, diversion of water to farms and cities, and invasion of exotic species, the influx of toxic pesticides into California streams, sloughs, rivers, and bays is particularly damaging to many aquatic species. Several well-documented facts emerge from recent studies on pesticides and aquatic organisms in California.

• Multiple pesticides are commonly found in California waters and sediments, frequently at concentrations that exceed lethal levels for many species of zooplankton, small organisms eaten by fish. Because of both high use and significant water solubility, the insecticides diazinon and chlorpyrifos and the herbicides simazine, diuron, and EPTC are found most commonly.
• Toxic pulses of pesticides are a routine occurrence in California rivers, as stormwater and irrigation runoff carry pesticides from urban and agricultural areas into surface waters. These pulses are a violation of the Clean Water Act and the Basin Plans set forth by the Regional Water Quality Control Boards because they create lethal conditions for many consecutive days for the small organisms fish eat. The pesticides most commonly found in toxic concentrations in these pulses are diazinon and chlorpyrifos from sprays to dormant almond and stonefruit orchards, as well as from urban applications to buildings and in landscape maintenance.
• Most fish species and many species of zooplankton in the San Francisco Bay-Delta have experienced dramatic population declines in the last several decades. Multiple factors contribute to these declines, including toxic contaminants in waterways, dams, diversions, exotic species, and reduction in food sources. Pesticides known to kill aquatic animals and plants, impair their reproduction, and reduce food sources for fish are thought to be one of the major stressors affecting the aquatic organisms in the Bay-Delta ecosystem.

Pesticides Disrupt the Natural Balance Between Pest and Predator Insects

Broad-spectrum pesticides such as the organophosphorus, carbamate, and organochlorine insecticides destroy both pest and beneficial organisms indiscriminately, upsetting the balance between pest and predator insects. Many people believe that more insecticides mean fewer pests and higher crop yields. However, even though use of insecticides increased 10-fold from 1945 to 1989, crop losses from insects nearly doubled in the same time period, from 7% to 13%. In addition, the number of insect pests that are resistant to pesticides increased dramatically over the same time period. With fewer and fewer "effective" pesticides left in their arsenals, many growers are increasing the quantities of chemicals they apply to their crops. Others, however, are moving to non-toxic methods of pest control that focus on biological controls to solve their pest problems. Research and experience have shown that:

• Beneficial organisms serve many valuable functions in an agricultural ecosystem, including pollination, soil aeration, nutrient cycling, and pest control.
• Application of insecticides indiscriminately kills pests and beneficial organisms. Pest populations often recover rapidly because of their larger numbers and ability to develop resistance, but beneficial insects do not, resulting in a resurgence of the target pest as well as secondary pests that reproduce rapidly with no predators to check their numbers.
• Resistance and resurgence often lead to escalation of pesticide applications, resulting in pests with even greater resistance to pesticides. The resulting "pesticide treadmill" has created resistance to broad-spectrum insecticides in more than 500 pest species nationwide.

Restoring the Balance: Alternatives to Pesticides Are Available

Pesticides destroy the delicate balance between species that characterizes a functioning ecosystem. Fortunately, there are alternatives to dumping massive quantities of toxic chemicals on our crops, forests, and roadsides, and in our homes and gardens. Every crop in California that is commonly grown with intensive pesticide use is also being grown organically at other farms in the state. Least-toxic methods of pest control are available, and a growing number of California farmers are utilizing them. They include the following strategies:

• "Cultural" pest control methods such as crop rotation, reduction of habitat for pest species, provision of habitat for beneficial insects, and timing of plantings are effective in controlling many pests in agricultural settings. In urban settings, strategies such as pest exclusion by sealing cracks and other openings, as well as reduction of the pests' food supply are effective.
• A number of least-toxic methods for controlling pests are available. In agricultural settings, these include mulching, hand weeding, mating disruption, release of beneficial insects, and judicious application of low-toxicity pesticides such as oils, soaps, biopesticides, and sulfur. In urban settings, insect pests can be controlled with exclusion strategies and low-toxicity baits, and weeds can be controlled by mulching or hand-weeding.

Recommendations

Fish, birds, and wildlife that live in direct contact with environments subject to pesticide exposure are sentinel species that may be predictive of our own fate. With pesticides now found routinely in drinking water, on food, and in the air, we are all taking part in an experiment in pesticide exposure on a global scale, but without the benefit of an unexposed control group for comparison. We will probably not be able to quantify the exact risk of these exposures, or their interaction with other environmental factors affecting human health. Because we can't know for certain the consequences of expanding pesticide use, the rational and most protective course of action is to take a precautionary approach--phasing out use of the most dangerous pesticides, reducing our reliance on toxic chemicals for pest control, and promoting ecologically based pest management.