Toxaphene is a synthetic insecticide once widely used in agriculture. Introduced in 1947, it became one of the most heavily applied pesticides in the United States, particularly during the 1970s after DDT was banned. Concerns about its environmental impact and potential health effects led to its discontinuation. This chemical is now banned globally due to risks associated with its environmental presence.
Historical Use as a Pesticide
Toxaphene’s use peaked from the late 1960s through the early 1980s, becoming the most heavily applied pesticide in the United States during the early to mid-1970s. Over 34 million pounds were used annually between 1966 and 1976. Its primary target was the boll weevil on cotton crops, especially in the southern United States from Texas to Georgia, accounting for approximately 85% of its total usage.
Beyond cotton, toxaphene was also applied to other field crops, including corn, small grains, fruits, vegetables, and soybeans. About 7% of its use controlled insect pests like lice, flies, ticks, and mange mites on livestock and poultry. It was also used to eliminate undesirable fish species in lakes and streams.
Environmental Persistence and Contamination
Toxaphene’s persistence in the environment is a major concern. It does not readily break down in soil or water, with a half-life in soil ranging from 1 to 14 years. This slow degradation means the chemical remains present in various environmental media decades after its ban. It resists breakdown by microbial organisms, hydrolysis, or photolysis in water.
The compound also bioaccumulates, building up in the fatty tissues of organisms. As smaller organisms are consumed by larger ones, toxaphene concentrations increase up the food chain, a process known as biomagnification. This leads to elevated levels in predatory fish, marine mammals like beluga whales and seals, and birds, posing risks to wildlife and human consumers.
Toxaphene’s moderate volatility allows for long-range atmospheric transport, enabling it to evaporate from treated areas and travel vast distances through the air. This explains its presence in remote regions, such as the Arctic, far from where it was originally applied. Once transported, it can deposit onto land or water bodies, leading to widespread contamination globally.
Human Health Risks
Exposure to toxaphene, primarily through contaminated food, poses several human health risks. Fish and shellfish are notable sources, as toxaphene accumulates in their fatty tissues. Regular consumption of large quantities of contaminated seafood can lead to higher exposure.
High levels of toxaphene can directly affect the central nervous system, leading to symptoms such as tremors and convulsions. Ingestion of large amounts has resulted in temporary liver and kidney damage, and in severe cases, death. Animal studies indicate that chronic exposure can cause broader impacts on the liver, kidneys, spleen, adrenal and thyroid glands, and the immune system.
Toxaphene is also recognized as an endocrine disruptor, interfering with hormonal systems due to its estrogenic activity. It has been classified as a probable human carcinogen by the U.S. Environmental Protection Agency (EPA), based on animal studies where it caused liver cancer in mice and possibly thyroid cancer in rats. The International Agency for Research on Cancer (IARC) also considers toxaphene possibly carcinogenic to humans.
Regulatory Status and Global Ban
In response to evidence of its dangers, the U.S. Environmental Protection Agency (EPA) acted against toxaphene. Most uses were cancelled in the United States in 1982, with exceptions for livestock and certain crops in Puerto Rico and the U.S. Virgin Islands. By 1990, all remaining uses of toxaphene in the United States were banned.
The international community also recognized the threat posed by toxaphene. In 2001, it was included as one of the original 12 “dirty dozen” chemicals under the Stockholm Convention on Persistent Organic Pollutants (POPs). This global treaty aims to eliminate or restrict the production and use of persistent organic pollutants worldwide due to their long-range transport, bioaccumulation, and toxicity. Toxaphene is listed in Annex A of the Convention, requiring parties to eliminate its production and use.