Pesticides in the Atmosphere

U.S. Geological Survey, Fact Sheet FS-152-95

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Pesticides Found in the Atmosphere

Most pesticides that have been studied in the atmosphere have been detected, and many pesticides from several different chemical groups have been detected at more than half the sites sampled nationwide (see Figure 3). Results for different groups and individual pesticides reflect a range of influencing factors.

Figure 3. Detection frequencies for those pesticides that have been analyzed in air and rain at 10 or more sites in the United States.

Because of their widespread use during the 1960's and 1970's, and their resistance to environmental degradation, organochlorine insecticides have been detected in the atmosphere of every state where measurements were made (see Figure 4). The most heavily used organochlorine insecticides during this time period were toxaphene, DDT, and aldrin. Because of reduced effectiveness and regulatory restrictions, their total use in agriculture declined steadily from 63 percent of insecticide use in 1966 to less than 5 percent in 1988. The most frequently detected organochlorine insecticides have been DDT, alpha-HCH, gamma-HCH (lindane), heptachlor, and dieldrin (see Figure 3). Toxaphene and aldrin were detected less frequently than other organochlorine compounds, despite their high use, partially because of their chemical properties. Toxaphene is a complex mixture of over 200 different compounds that is difficult to sample and analyze. Since toxaphene use was banned in 1982, the analytical "fingerprint" of environmental samples often differs considerably from the analytical standards due to changes over time in its chemical nature. Also, the analytical limit of detection is much higher than for other organochlorine insecticides. Aldrin, on the other hand, degrades rapidly into dieldrin in the environment, which is much more chemically stable. This is why dieldrin was detected more frequently than aldrin even though it was used in much less quantities.

Organophosphorus insecticides also have been used heavily for decades and account for 65 percent of insecticide use today. Generally, they are not as long-lived in the environment as the organochlorine insecticides, but have nevertheless been detected in the air and rain of many states (see Figure 4), even though they are not often included as target analytes. The organophosphorus insecticides detected most often in air, rain, and fog were diazinon, methyl parathion, parathion, malathion, chlorpyrifos, and methidathion. Diazinon, methyl parathion, parathion, and malathion have been among the most widely used insecticides in each of the last three decades, although parathion, malathion, and diazinon use is declining.

Figure 4. The number of pesticides detected in air, rain, snow, and fog in each state for each of the four major pesticide categories.

The use of triazine herbicides has increased from 24 million pounds in 1966 to nearly 104 million pounds in 1988, accounting for about 23 percent of national herbicide use. Studies that searched for these compounds in the atmosphere did not begin until the late 1970's, when atrazine was detected in Maryland precipitation. Since then, atrazine and other triazine herbicides have been detected in rain in many midwestern and northeastern states, sometimes at high levels.

The acetanilide herbicides, which include alachlor and metolachlor, comprised about 26 percent of total herbicide use in 1988, up from only 5 percent in 1966, and now have use comparable to the triazines. These herbicides are frequently used in conjunction with triazine herbicides. Although they are not as long-lived in the environment as the triazines, they have been detected at equivalent and even higher concentrations in rain.

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