Pesticides - History

Minerals and Metals

One of the first pesticides was sulfur, used by the Chinese in around 1000 BC to control bacteria and mold (fungus). Sulfur is still widely used today. For example, it is used in fungides to control diseases on both agricultural and ornamental plants, and in the wine industry, sulfur is used to control unwanted bacterial growth in empty wine barrels and is commonly added to wine to kill unwanted yeast. The Chinese also pioneered the use of arsenic-containing compounds to control insects. Arsenic has a long history of use both as an insecticide and herbicide, and also as a medicine. Arsenic trioxide was used as a weed killer (herbicide) in the late 1800s, and lead arsenate, containing both lead and arsenic, was used as an insecticide, particularly in orchards, prior to the development of synthetic pesticides following WWII. Some of the first concerns about pesticide safety were raised over lead arsenate residue on fruit and in orchards, and to this day, some orchard soils remain contaminated with lead and arsenic. Arsenic in the form of chromated copper arsenate (CCA) is used today as a wood preservative (to keep wood in contact with soil or moisture from rotting).

Plant-based Pesticides

Plants have provided several other important nonsynthetic pesticides. In the late 1600s nicotine, an extract from tobacco leaves, was recognized as a potent insecticide and is now in limited use as a pesticide. Another group of nonsynthetic insecticides is pyrethrums, which are harvested and refined from chrysanthemums. The Strychnine tree, Nux vomica, contains strychnine used to kill rodents. Finally, rotenone, an insecticide and fish poison, is extracted from the root of Derris elliptica, a climbing plant from Southeast Asia. Plant extracts are useful for controlling pests, but they are often difficult to purify and produce in large quantities. Consequently, the modern use of plant-based pesticides didn't significantly increase until advances were made in synthetic chemistry and pest biology.

Synthetic Pesticides

Synthetic chemistry advanced rapidly in the 1930s and by the early 40s, a range of new pesticides had been developed, including organochlorine insecticides like DDT. In 1937 the first organophosphate compounds were synthesized by a group of German chemists. These very potent compounds were kept secret during World War II and were originally developed as potential chemical warfare agents. After the war, these organophosphate compounds were re-purposed as insecticides, and many organophosphate insecticides continue to be used today.

Herbicides were developed after WWII in order to increase food production and create possible warfare agents. In 1946, the first commercially available chlorine-based herbicides were marketed to kill broadleaf plants. This class of compounds includes 2,4-D (2,4-Dichlorophenoxyacetic acid) and 2,4,5-T (2,4,5-Trichlorophenoxyacetic acid), synthetic auxins (plant hormones) that disrupt plant growth. These herbicides have been extensively utilized in agriculture and to clear roadsides and rights of way. 2,4,5-T was used extensively during the Vietnam War to defoliate jungle plants. During the manufacturing process, 2,4,5-T was often contaminated with the persistent and very toxic dioxin, TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin). Dioxins, like other chlorinated compounds including DDT, bioaccumulate in body fat and persist in the environment for many years (the soil half-life is 10 to 12 years). Dioxins are classified as carcinogens and are also known to affect the reproductive and immune systems.

The U.S. EPA cancelled the use of 2,4,5-T because of the dioxin contamination, but 2,4-D is still one of the most widely used herbicides.

(Photo: A UH-1D helicopter from the 336th Aviation Company sprays a defoliation agent on a dense jungle area in the Mekong Delta. 26 July 1969/National Archives photograph.)

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