Fipronil is a broad-spectrum insecticide that belongs to the phenylpyrazole chemical family. Fipronil disrupts the insect central nervous system by blocking GABA-gated chloride channels and glutamate-gated chloride (GluCl) channels. This causes hyperexcitation of contaminated insects' nerves and muscles. Fipronil's specificity towards insects is believed to be due to its greater affinity to the GABA receptor in insects relative to mammals and its effect on GluCl channels, which do not exist in mammals.
Because of its effectiveness on a large number of pests, Fipronil is used as the active ingredient in flea control products for pets and home roach traps as well as field pest control for corn, golf courses, and commercial turf. Its widespread use makes its specific effects the subject of considerable attention. This includes ongoing observations on possible off-target harm to humans or ecosystems as well as the monitoring of resistance development.
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Effects
Toxicity
Fipronil is classed as a WHO Class II moderately hazardous pesticide, and has a rat acute oral LD50 of 97 mg/kg.
It has moderate acute toxicity by the oral and inhalation routes in rats. Dermal absorption in rats is less than 1% after 24 h and toxicity is considered to be low. It has been found to be very toxic to rabbits.
The photodegradate MB46513 or desulfinylfipronil, appears to have a higher acute toxicity to mammals than fipronil itself by a factor of about 10.
Symptoms of acute toxicity via ingestion includes sweating, nausea, vomiting, headache, abdominal pain, dizziness, agitation, weakness, and tonic-clonic seizures. Clinical signs of exposure to fipronil are generally reversible and resolve spontaneously. As of 2011, no data were available regarding the chronic effects of fipronil on humans. The U.S. EPA has classified fipronil as a group C (possible human) carcinogen based on an increase in thyroid follicular cell tumors in both sexes of the rat. However, as of 2011, no human data are available regarding the carcinogenic effects of fipronil.
Two Frontline TopSpot products were determined by the New York State Department of Environmental Conservation to pose no significant exposure risks to workers applying the product. However, concerns were raised about human exposure to Frontline spray treatment in 1996, leading to a denial of registration for the spray product. Commercial pet groomers and veterinarians were considered to be at risk from chronic exposure via inhalation and dermal absorption during the application of the spray, assuming they may have to treat up to 20 large dogs per day. Fipronil is not volatile, so the likelihood of humans being exposed to this compound in the air is low.
In contrast to neonicotinoids such as acetamiprid, clothianidin, imidacloprid, and thiamethoxam, which are absorbed through the skin to some extent, fipronil is not absorbed substantially through the skin.
Ecological toxicity
Fipronil is highly toxic for crustaceans, insects and zooplankton, as well as bees, termites, rabbits, the fringe-toed lizard, and certain groups of gallinaceous birds. It appears to reduce the longevity and fecundity of female braconid parasitoids. It is also highly toxic to many fish, though its toxicity varies with species. Conversely, the substance is relatively innocuous to passerines, wildfowl, and earthworms.
Its half-life in soil is four months to one year, but much less on soil surface because it is more sensitive to light (photolysis) than water (hydrolysis).
Few studies of effects on wildlife have been conducted, but studies of the nontarget impact from emergency applications of fipronil as barrier sprays for locust control in Madagascar showed adverse impacts of fipronil on termites, which appear to be very severe and long-lived. Also, adverse effects in were indicated in the short term on several other invertebrate groups, one species of lizard (Trachylepis elegans), and several species of birds (including the Madagascar bee-eater).
Nontarget effects on some insects (predatory and detritivorous beetles, some parasitic wasps and bees) were also found in field trials of fipronil for desert locust control in Mauritania, and very low doses (0.6-2.0 g a.i./ha) used against grasshoppers in Niger caused impacts on nontarget insects comparable to those found with other insecticides used in grasshopper control. The implications of this for other wildlife and ecology of the habitat remain unknown, but appear unlikely to be severe. Unfortunately, this lack of severity was not observed in bee species in South America. Fipronil is also used in Brazil and studies on the stingless bee Scaptotrigona postica have shown adverse reactions to the pesticide, including seizures, paralysis, and death with a lethal dose of .54 ng a.i./bee and a lethal concentration of .24 ng a.i./?l diet. These values are highly toxic in Scaptotrigona postica and bees in general. Toxic baiting with fipronil has been shown to be effective in locally eliminating German wasps. All colonies within foraging range were completely eliminated within one week.
In May 2003, the French Directorate-General of Food at the Ministry of Agriculture determined that a case of mass bee mortality observed in southern France was related to acute fipronil toxicity. Toxicity was linked to defective seed treatment, which generated dust. In February 2003, the ministry decided to temporarily suspend the sale of BASF crop protection products containing fipronil in France. The seed treatment involved has since been banned. Fipronil was used in a broad spraying to control locusts in Madagascar in a program that began in 1997.
Notable results from wildlife studies include:
- Fipronil is highly toxic to fish and aquatic invertebrates. Its tendency to bind to sediments and its low water solubility may reduce the potential hazard to aquatic wildlife.
- Fipronil is toxic to bees and should not be applied to vegetation when bees are foraging.
- Based on ecological effects, fipronil is highly toxic to upland game birds on an acute oral basis and very highly toxic on a subacute dietary basis, but is practically nontoxic to waterfowl on both acute and subacute bases.
- Chronic (avian reproduction) studies show no effects at the highest levels tested in mallards (NOEC) = 1000 ppm) or quail (NOEC = 10 ppm). The metabolite MB 46136 is more toxic to the parent than avian species tested (very highly toxic to upland game birds and moderately toxic to waterfowl on an acute oral basis).
- Fipronil is very highly toxic to bluegill sunfish and highly toxic to rainbow trout on an acute basis.
- An early-lifestage toxicity study in rainbow trout found that fipronil affects larval growth with a NOEC of 0.0066 ppm and an LOEC of 0.015 ppm. The metabolite MB 46136 is more toxic than the parent to freshwater fish (6.3 times more toxic to rainbow trout and 3.3 times more toxic to bluegill sunfish). Based on an acute daphnia study using fipronil and three supplemental studies using its metabolites, fipronil is characterized as highly toxic to aquatic invertebrates.
- An invertebrate lifecycle daphnia study showed that fipronil affects length in daphnids at concentrations greater than 9.8 ppb.
- A lifecycle study in mysids shows fipronil affects reproduction, survival, and growth of mysids at concentrations less than 5 ppt.
- Acute studies of estuarine animals using oysters, mysids, and sheepshead minnows show that fipronil is highly acutely toxic to oysters and sheepshead minnows, and very highly toxic to mysids. Metabolites MB 46136 and MB 45950 are more toxic than the parent to freshwater invertebrates (MB 46136 is 6.6 times more toxic and MB 45950 is 1.9 times more toxic to freshwater invertebrates).
Colony collapse disorder
Fipronil is one of the main chemical causes blamed for the spread of colony collapse disorder among bees. It has been found by the Minutes-Association for Technical Coordination Fund in France that even at very low nonlethal doses for bees, the pesticide still impairs their ability to locate their hive, resulting in large numbers of forager bees lost with every pollen-finding expedition. A 2013 report by the European Food Safety Authority identified fipronil as "a high acute risk to honeybees when used as a seed treatment for maize and on July 16, 2013 the EU voted to ban the use of fipronil on corn and sunflowers within the EU. The ban took effect at the end of 2013."
Pharmacodynamics
Fipronil acts by binding to allosteric sites of GABAA receptors and GluCl receptors (of insects) as an antagonist (a form of noncompetitive inhibition). This prevents the opening of chloride ion channels normally encouraged by GABA, reducing the chloride ions' ability to lower a neuron's membrane potential. This results in an overabundance of neurons reaching action potential and likewise CNS toxicity via overstimulation.
In animals and humans, fipronil poisoning is characterized by vomiting, agitation, and seizures, and can usually be managed through supportive care and early treatment of seizures, generally with benzodiazepine use.
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Discovery and use
Fipronil was discovered and developed by Rhône-Poulenc between 1985 and 1987, and placed on the market in 1993 under the US Patent No. US 5,232,940 B2. Between 1987 and 1996, fipronil was evaluated on more than 250 insect pests on 60 crops worldwide, and crop protection accounted for about 39% of total fipronil production in 1997. Since 2003, BASF holds the patent rights for producing and selling fipronil-based products in many countries.
Fipronil is or has been used in:
- Under the trade name Regent, it is used against major lepidopteran (moth, butterfly, etc.) and orthopteran (grasshopper, locust, etc.) pests on a wide range of field and horticultural crops and against coleopteran (beetle) larvae in soils. In 1999, 400,000 hectares were treated with Regent. It became the leading imported product in the area of rice insecticides, the second-biggest crop protection market after cotton in China.
- Under the trade names Goliath and Nexa, it is employed for cockroach and ant control, including in the US. It is also used against pests of field corn, golf courses, and commercial lawn care under the trade name Chipco Choice.
- It has been used under the trade name Adonis for locust control in Madagascar and Kazakhstan.
- Marketed under the names Termidor, Ultrathor, and Taurus in Africa and Australia, fipronil effectively controls termite pests, and was shown to be effective in field trials in these countries.
- Termidor has been approved for use against the Rasberry crazy ant in the Houston, Texas, area, under a special "crisis exemption" from the Texas Department of Agriculture and the Environmental Protection Agency. The chemical is only approved for use in Texas counties experiencing "confirmed infestations" of the newly discovered ant species. Use of Termidor is restricted to certified pest control operators in the following states: Alaska, Connecticut, Nebraska, South Carolina, Massachusetts, Indiana, New York, and Washington State.
- In Australia, it is marketed under numerous trade names, including Combat Ant-Rid, Radiate and Termidor, and as generic fipronil
- In the UK, provisional approval for five years has been granted for fipronil use as a public hygiene insecticide.
- Fipronil is the main active ingredient of Frontline TopSpot, Fiproguard, Flevox, and PetArmor (used along with S-methoprene in the 'Plus' versions of these products); these treatments are used in fighting tick and flea infestations in dogs and cats.
- In New Zealand, fipronil was used in trials to control wasps (Vespula spp.), which are a threat to indigenous biodiversity. It is now being used by the Department of Conservation to attempt local eradication of wasps, and is available to the public in an award-winning protein-based bait designed to avoid attracting honey bees.
2017 Fipronil egg contamination
In July/August 2017 millions of chicken eggs were blocked from sale or withdrawn from the market in the Netherlands, Belgium, Germany and France after high levels of fipronil were discovered by the Dutch food and product safety board. About 180 Dutch farms were temporarily shut down. In early August, Aldi reported removing all eggs for sale in their German stores as a precaution. Fipronil contaminated eggs may have been sold for a long time prior to the discovery of high levels. Authorities in the Netherlands had already noted that eggs were contaminated with fipronil in November 2016 but failed to communicate the findings.
Because the use of fipronil is illegal in the production of food for human consumption in Europe, a criminal investigation has been initiated.
Early investigation led to two companies: ChickFriend, a provider of pest control services in the Netherlands suspected of knowingly using and selling DEGA-16 mixed with fipronil to hundreds of chicken farmers and Poultry Vision in Belgium accused of selling DEGA-16 mixed with fipronil to ChickFriend. DEGA-16 is a cleaning and sanitising natural product, that is approved to clean chicken stables. The Dutch owners of ChickFriend were arrested during a large scale operation conducted by Dutch law enforcement agencies on the 10th of August. First results of an investigation by Belgian police led to the discovery of 6 cubic meters of fipronil that Poultry Vision had imported from a chemical manufacturing company in Romania.
As a result of the alleged cover-up by the Dutch authorities, the Dutch Safety Board announced on the 8th of August that an official investigation has been initiated.
Source of the article : Wikipedia
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