Bentazone
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Bentazon (Bentazone, Basagran, Herbatox, Leader, Laddock) is a chemical manufactured by BASF Chemicals for use in
herbicide Herbicides (, ), also commonly known as weed killers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page f ...
s. It is categorized under the thiadiazine group of chemicals. Sodium bentazon is available commercially and appears slightly brown in colour.


Usage

Bentazon is a selective herbicide as it only damages plants unable to metabolize the chemical. It is considered safe for use on
alfalfa Alfalfa () (''Medicago sativa''), also called lucerne, is a perennial plant, perennial flowering plant in the legume family Fabaceae. It is cultivated as an important forage crop in many countries around the world. It is used for grazing, hay, ...
, beans (with the exception of garbanzo beans ),
maize Maize (; ''Zea mays''), also known as corn in North American English, is a tall stout grass that produces cereal grain. It was domesticated by indigenous peoples in southern Mexico about 9,000 years ago from wild teosinte. Native American ...
,
peanut The peanut (''Arachis hypogaea''), also known as the groundnut, goober (US), goober pea, pindar (US) or monkey nut (UK), is a legume crop grown mainly for its edible seeds. It is widely grown in the tropics and subtropics by small and large ...
s,
pea Pea (''pisum'' in Latin) is a pulse or fodder crop, but the word often refers to the seed or sometimes the pod of this flowering plant species. Peas are eaten as a vegetable. Carl Linnaeus gave the species the scientific name ''Pisum sativum' ...
s (with the exception of blackeyed peas ), pepper,
peppermint Peppermint (''Mentha'' × ''piperita'') is a Hybrid (biology), hybrid species of Mentha, mint, a cross between Mentha aquatica, watermint and spearmint. Indigenous to Europe and the Middle East, the plant is now widely spread and cultivated in m ...
,
rice Rice is a cereal grain and in its Domestication, domesticated form is the staple food of over half of the world's population, particularly in Asia and Africa. Rice is the seed of the grass species ''Oryza sativa'' (Asian rice)—or, much l ...
,
sorghum ''Sorghum bicolor'', commonly called sorghum () and also known as great millet, broomcorn, guinea corn, durra, imphee, jowar, or milo, is a species in the Poaceae, grass genus ''Sorghum (genus), Sorghum'' cultivated for its grain. The grain i ...
,
soybeans The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean. Soy is a staple crop, the world's most grown legume, and an important animal feed. Soy is a key source of f ...
and
spearmint Spearmint (''Mentha spicata''), also known as garden mint, common mint, lamb mint and mackerel mint, is native to Europe and southern temperate Asia, extending from Ireland in the west to southern China in the east. It is naturalized in many othe ...
; as well as lawns and
turf Sod is the upper layer of turf that is harvested for transplanting. Turf consists of a variable thickness of a soil medium that supports a community of turfgrasses. In British and Australian English, sod is more commonly known as ''turf'', ...
. Bentazon is usually applied aerially or through contact spraying on food crops to control the spread of weeds occurring amongst food crops. Herbicides containing bentazon should be kept away from high heat as it will release toxic
sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...
and
nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...
fumes. Bentazon is currently registered for use in the United States in accordance with requirements set forth by the
United States Environmental Protection Agency The Environmental Protection Agency (EPA) is an independent agency of the United States government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it began operation on De ...
. However, as of September 2010, the herbicides Basagran M60, Basagran DF, Basagran AG, Prompt 5L and Laddock 5L are currently under review for pending requests for voluntary registration cancellation.


Water and ground contamination

In general, bentazon is quickly metabolized and degraded by both plants and animals. However, soil leaching and runoff is a major concern in terms of water contamination. In 1995 the Environmental Protection Agency (EPA) stated that levels of bentazon in both ground water and surface water "exceed levels of concern". Despite the establishment of a 20 parts per billion Health Advisory Level there is no requirement to measure for bentazon in water supplies as the
Safe Drinking Water Act The Safe Drinking Water Act (SDWA) is the primary federal law in the United States intended to ensure safe drinking water for the public. Pursuant to the act, the Environmental Protection Agency (EPA) is required to set standards for drinking wa ...
does not regulate bentazon. The United States EPA found bentazon in 64 out of 200 wells in California - the highest number of detections in their 1995 study. This prompted the
State of California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
to review existing
toxicology Toxicology is a scientific discipline, overlapping with biology, chemistry, pharmacology, and medicine, that involves the study of the adverse effects of chemical substances on living organisms and the practice of diagnosing and treating ex ...
studies and establish a "Public Health Goal" that limits bentazon in drinking water to 200 parts per billion. The EPA requires ground water and environmental hazard advisory labels on all commercially available herbicides containing bentazon. Both statements warn against application and/or disposal of bentazon directly into water, or in areas where soil leaching is common.


Food contamination

A number of limits have been placed on bentazon to reduce the possibility of toxic effects on humans. Tolerance levels vary depending on the use of the food/animal product. The following tolerance levels for bentazon have been established in the United States: * 0.02 ppm for milk. * 0.05 ppm (parts per million) for meat and animal byproducts (poultry, eggs, cattle, hogs, sheep and goats). * 0.05 ppm for dried beans (excluding soybeans), corn (fresh and grain), bohemian chili peppers, peanuts, rice, soybeans, and sorghum used for fodder and grain. * 0.5 ppm for succulent beans and peas. * 0.3 ppm for peanut hulls. * 1 ppm for mint and dried peas. * 3 ppm for rice (straw), corn for fodder and forage, and peanuts used in hay and forage. * 8 ppm for pea vine hays (dried), and soybeans used for foraging or hay. It is recommended that food and feed supplies be stored away from herbicides containing bentazon. Aerial spraying should be conducted in a manner that prevents spray drift towards water sources and food crops susceptible to bentazon.


Toxicity to nonhuman species

A 1994 study concluded that bentazon is non-toxic to
honeybees A honey bee (also spelled honeybee) is a eusocial flying insect within the genus ''Apis'' of the bee clade, all native to mainland Afro-Eurasia. After bees spread naturally throughout Africa and Eurasia, humans became responsible for the cur ...
, and is not harmful to beetles. Studies have found that bentazon is toxic to
rainbow trout The rainbow trout (''Oncorhynchus mykiss'') is a species of trout native to cold-water tributary, tributaries of the Pacific Ocean in North America and Asia. The steelhead (sometimes called steelhead trout) is an Fish migration#Classification, ...
and
bluegill sunfish The bluegill (''Lepomis macrochirus''), sometimes referred to as "bream", "brim", "sunny", or, in Texas, "copper nose", is a species of North American freshwater fish, native to and commonly found in streams, rivers, lakes, ponds and wetlands ea ...
at 190 ppm and 616 ppm, respectively. Bentazon is considered toxic to birds as it affects their reproductive capacities. Among mammals, bentazon is found to be moderately toxic when ingested or absorbed through the skin. Lethal doses ( LD50, the dose required to kill half the population being studied) for bentazon have been established for: * Cats: 500 mg/kg * Rats: 1100 mg/kg to 2063 mg/kg * Mice: 400 mg/kg * Rabbits: 750 mg/kg Dogs in a study being fed 13.1 mg of bentazon a day developed diarrhoea, anemia and dehydration. In another study using dogs, prostate inflammation was also observed along with previously noted health effects In experiments conducted on hamsters, mice and rats, bentazon was not found to cause gene mutations to damage to DNA and chromosomes.


Toxicity to humans

Bentazon has been classified by the EPA as a "Group E" chemical, because it is believed to be non-carcinogenic to humans (as based on testing conducted on animals). However, there are no studies or experiments that can determine toxic and/or carcinogenic effects of bentazon on humans. Workers applying the herbicide would be most exposed to bentazon, and so have been advised to wear protective clothing (goggles, gloves and aprons) at all times when handling the chemical. Bentazon causes allergy-like symptoms as it irritates the eyes, skin and respiratory tract. Ingesting bentazon causes
nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. It can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the throat. Over 30 d ...
,
diarrhoea Diarrhea (American English), also spelled diarrhoea or diarrhœa (British English), is the condition of having at least three loose, liquid, or watery bowel movements in a day. It often lasts for a few days and can result in dehydration d ...
, trembling, vomiting and difficulty breathing. Workers handling bentazon must wash their hands before eating, drinking, smoking, and using the bathroom to minimize contact with skin. The effects of bentazon ingestion has been observed in humans who chose the herbicide to commit suicide. Ingestion of bentazon was observed to cause fevers,
renal failure Kidney failure, also known as renal failure or end-stage renal disease (ESRD), is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney fa ...
(kidney failure), accelerated heart rate (
tachycardia Tachycardia, also called tachyarrhythmia, is a heart rate that exceeds the normal resting rate. In general, a resting heart rate over 100 beats per minute is accepted as tachycardia in adults. Heart rates above the resting rate may be normal ...
), shortness of breath (
dyspnea Shortness of breath (SOB), known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing discomfort that ...
) and
hyperthermia Hyperthermia, also known as overheating, is a condition in which an individual's body temperature is elevated beyond normal due to failed thermoregulation. The person's body produces or absorbs more heat than it dissipates. When extreme te ...
. Ingestion of 88 grams of bentazon caused death in an adult.


References

{{Reflist Herbicides Benzothiadiazines Isopropyl compounds Sultams Group 6 herbicides