Diquat
Diquat is a contact herbicide that has been utilized in the United States since the 1950s, primarily for agricultural and aquatic weed management. It is mainly imported, with about one million pounds brought into the country annually. Diquat serves two primary functions: as a desiccant to prepare crops for harvest, particularly in potatoes and legumes, and as a means to control aquatic weeds, provided that endangered species are not affected. Although it is biodegradable, diquat can adhere to soil and sediment, where it may remain stable for extended periods.
The herbicide is known for its potential toxicity, especially when ingested or inhaled, and exposure primarily occurs in occupational settings among agricultural workers. Chronic exposure can lead to health issues such as cataracts and damage to the central nervous system and kidneys. Given its nonselective nature, the application of diquat is closely regulated by the Environmental Protection Agency (EPA). The long-term effects of diquat usage are not fully understood, partly due to reduced funding for related research. As such, while it plays a significant role in managing weed overgrowth, its environmental and health implications warrant careful consideration.
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Diquat
DEFINITION: Contact herbicide
As is the case for many herbicides, diquat has the potential to contaminate supplies of drinking water if it is released into wastewater and subsequently absorbed into soil.
The diquat, which has been used in the United States since the 1950s, is potentially toxic if swallowed or inhaled. It is not produced in the United States, but nearly one million pounds of the compound are imported each year. Approximately two-thirds of this amount is utilized as desiccant or defoliant, with another one-third used for aquatic weed control. Diquat is readily adsorbed into clay particles in the soil, sediment in water, and the surfaces of weeds. While it is biodegradable, if it is adsorbed into plant life and subject to photodegradation by sunlight, when bound to sediment diquat remains stable for weeks or even months. Ultimately, however, the herbicide undergoes degradation through the action of soil flora.
The extensive overgrowth of weeds affecting both crops and waterways has created significant problems in management. Regulations pertaining to use of herbicides remain under the auspices of the Environmental Protection Agency (EPA) and its various offices. Cutbacks in funding, however, have hampered research into the short- and long-term effects of using herbicides in the control of weed problems; therefore, the long-term effects of diquat are unclear.
Since diquat is a nonselective herbicide, its use is limited. It is used as a growth regulator in suppressing the flowering of sugarcane and to control aquatic weeds in the absence of endangered plant species. However, the most important use of diquat is in the desiccation of potato haulm or seed crops such as clover and alfalfa. Such practices are generally carried out to prepare crops for harvest. Application of diquat results in loss of moisture from the leaf, usually killing the plant. Desiccation may also be utilized in prevention of seed loss resulting from scattering of seed upon opening of the pod. The application of diquat prior to harvest of crops such as alfalfa greatly reduces seed loss.
The primary metabolic effect of diquat seems to be its ability to divert electrons activated during photosynthesis into the production of toxic compounds such as hydrogen peroxide. Peroxide production in turn results in membrane damage to those parts of the plant in contact with the herbicide. Human to diquat is primarily occupational, with agricultural workers who use the chemical at highest risk. Most actual poisonings have been intentional, with diquat used as a means of suicide. Nevertheless, though diquat is not as toxic as some herbicides, the level of its is mainly a function of degree. Exposure to significant levels of the chemical may cause damage to the central nervous system and kidneys, while cataract formation is the most common effect of chronic exposure.
Bibliography
Basilicata, Pascale, et al. "Diquat Poisoning: Care Management and Medico-Legal Implications." Toxics, vol. 10, no. 4, Apr. 2022, p. 166, doi.org/10.3390%2Ftoxics10040166. Accessed 16 July 2024.
Manahan, Stanley E.“Water Pollution.” In Fundamentals of Environmental Chemistry. 2d ed. CRC Press, 2001.
Udeh, Patrick J. “Organic Contaminants in Drinking Water.” In A Guide to Healthy Drinking Water: All You Need to Know About the Water You Drink. iUniverse, 2004.
Yanguang, Ren, Feng Gui, and Lin Wang. "Imaging Findings and Toxiological Mechanisms of Nervous System Injury Caused by Diquat." Molecular Neurobiology, 15 Apr. 2024, doi.org/10.3390%2Ftoxics10040166. Accessed 16 July 2024.