Background:
Since the dawn of civilizations, farming and establishing settlements have been a keystone piece to improving the quality of life for populations. With permanent homesteads, groups were able to establish an agricultural system; growing crops and domesticating livestock. With these new systems in place, a constant supply of food and shelter helped revolutionize civilization. Nature would in turn adapt and use these new systems to their advantage as well. Insects and invasive vegetation were now subjected to a higher density of nutrient resources in these communities, insects also had access to structures and environments conducive for harborage and proliferation. For centuries, control measures have been taken to protect crops and homes alike from unwanted pests. The first known use of pesticides occurred by the Sumerians about 4,500 years ago when they used Sulphur based compounds to ward off insects and mites. The Chinese followed approximately a thousand years later, obtaining arsenic and mercury-based compounds to eliminate lice in their communities1.
Up until the 1940s, all methods of controlling pests were of natural derivation such as sulfuric acid, chemicals from plants like Chrysanthemums, or from animals. Once innovations occurred in the early to mid-20th century, homeowners and farmers alike were exposed to a slew of new synthetic compounds such as DDT, 2,4-D, and parathion, which provided a broad spectrum of target pests. In the 1970s and 80s, the world’s top-selling herbicide, glyphosate, was introduced to the public1. These discoveries helped drive food prices down, as many farmers were able to achieve a higher percent yield from harvests. The new compounds also aided in ridding homes of pests and driving in a new industry of pest control.
The USEPA reported an estimated 678 million pounds of herbicides and 64 million pounds of insecticides were used in the US in 20122. Glyphosate and atrazine were both the most used pesticides and herbicides in the agricultural sector, ranking #1 and #2 respectively. The organophosphate, chlorpyrifos, was the #1 most used insecticide, and the 14th most used pesticide overall in agriculture2. In the private sector, 2,4-D and glyphosate were the most used herbicides. For insecticides used in the private sector, bifenthrin was the most widely used product when controlling pests on homes. It ranked overall as the tenth most used pesticide in the private sector in the US in 20122. Another largely used variety of insecticides are fumigants. These toxic gases are used to control smaller insects that often infest stored products such as wheat, corn, flour, and spices. In the private sector, sulfuryl fluoride was the most used in 20122.
These scientific innovations have improved the quality of life and increased the number of jobs in the pest control industry. The USEPA places restrictions on many of the chemicals used in applications, requiring applicators to take a course, then a written test to obtain a license to purchase and apply the pesticides. In 2012, the USEPA recorded 23,413 exterminating and pest control firms in the US, with 425,086 licensed Commercial Certified Applicators2. In New York state, the Department of Environmental Conservation is responsible for exams, recording, and enforcement of regulations on pesticides. In terms of regulation, states can be stricter than the USEPA regarding restricting substances or laws regarding applicators; they cannot have legislation that is looser than federal legislation, however.
With this large volume of chemicals being applied into the ecosystem, combined with a high number of applicators and consumers who use their services, a vast number of individuals and wildlife are exposed to these chemicals. In this term paper, I will evaluate the risks and hazards associated with the use of these chemicals. As a pest control business owner and certified commercial applicator, I will be focusing on a product used in the highest volume for my specific company, Platinum Pest Control. This product is Talstar P (Bifenthrin 7.9%)
Talstar P (Bifenthrin):
Talstar P is a broad-spectrum insecticide frequently used by pest control companies for preventative maintenance applications. It is approved for use in both the United States as well as Europe6. In New York, this is a restricted use pesticide, requiring a commercial applicators license to purchase. This product is approved for use against a variety of species of wasps, ants, spiders, and most crawling or flying insects. When applied, a residual of bifenthrin is left on the treated surface for up-to 3 months3. The highest rate of application by law is a 0.06% mixture (1 fl oz. per 1 gallon)3. Upon contact or ingestion when cleaning themselves, insects will die. Bifenthrin and other pyrethroids of the same chemical family interfere with the sodium channels. This class I pyrethroid holds open sodium channels and causes an overload of Na+, thus overwhelming the central and peripheral nervous systems, causing the demise of target pests4. Bifenthrin, specifically Talstar P, is attractive to pest control companies due to its low cost) and effectiveness across species. In the Talstar P formulation, there is 97% 1R-cis isomers and 3% 1S-cis isomers. The 1R-cis isomers are the ones toxic to insects and spiders while the 1S-cis isomers three to four times more toxic to humans4.
Generally, for large surface treatments, a gas-powered sprayer is used to apply the formulation of Talstar P and water with minimal effort; a backpack sprayer can also be used. According to the label, the required personal protective equipment (PPE) is a shirt, pants, shoes and waterproof gloves when applying. While mixing, however, gloves, eye protection, long sleeves, pants, and shoes are required. This is due to the concentrated form not being diluted yet.
Environmental Fate and Impact:
Bifenthrin seldom contaminates groundwater due to its high soil sorption coefficient (1.31 x 105 – 3.02 x 105). Once in the soil, bifenthrin will bind to soil and is rendered immobile, making it difficult to reach groundwater. This also means that degradation in the soil is slow; depending on the soil type, bifenthrin can possess an aerobic half-life of 97 to 250 days4. In some field dissipation studies the soil half-life of 122 to 345 days4. The water solubility is extremely low at <1 ug/L, thus long-term mixture with water is not an issue. The issue, however, lies within the sediments found in water bodies. In a study in California, bifenthrin was detected in 95-100% of sediment samples taken, with a maximum concentration of 122 ug/kg and 542 ug/kg in the dry and wet seasons respectively4. This predicament can be an extreme issue for toxicity in fish, covered in the next section. Air and vegetation contamination are low priorities due to the nature of the bifenthrin molecule. The low vapor pressure and Henry’s constant of bifenthrin give it a low potential for volatilization. On apples, bifenthrin was not metabolized by the fruit after 21 days of the last of three applications4, foliage and other vegetation do not uptake the pesticide and no translocation within the plant occurs4.
Toxicity to Mammals:
Due to lower ion channel sensitivity, larger body size and higher body temperature, mammals are far less prone to bifenthrin toxicity4. In mammals, the main instance of toxicity is observed via the oral route. When mice were fed an undiluted dose of bifenthrin, an LD50 of 43 mg/kg was established, in rats a range of 53.4 mg/kg to 210.4 mg/kg for LD50 was observed4. Dermal toxicity in rats and rabbits was found to occur at over 2000 mg/kg. According to the USEPA IRIS, the acute reference dose (RfD) was calculated as 0.328 mg/kg/day for humans after incorporating modifying factors and a chronic RfD of 0.013 mg/kg/day5. A NOAEL of 5 mg/kg/day (100 ppm) was established after a study of feeding rats technical-grade bifenthrin (88.4% purity) for 90 days at doses of 0, 12, 50, 100 or 200 ppm. Tremors occurred in all rats in the study at 200 ppm4. When studying the effects of the chemical on dogs, a NOAEL was established at 2.5 mg/kg/day after tremors were observed in animals fed 5 mg/kg/day4.
Bifenthrin has been classified as a Category C, possible human carcinogen by the US EPA. In studies with mice, bifenthrin increased the rates in the growth of urinary bladder tumors, adenoma and adenocarcinoma of the liver (in males). In female mice, some subjects saw an increase in bronchioalveolar adenoma and adenocarcinomas of the lung4.
Conclusion:
Bifenthrin is overall a cheap and effective insecticide. Pest control technicians across the globe utilize this compound to provide a service to customers, as well as make a living themselves. With the right training, knowledge, and execution, bifenthrin can effectively eliminate pests in a residential and commercial setting. The risks associated with this chemical are highest for aquatic wildlife, and technicians who use the chemical on a daily basis. Mostly, the risk is minimized via dilutions made before applications. Accidental spills of the concentrate are most worrisome and if they occur near bodies of water, could be devastating to ecosystems. Risks to the general public are minimized when proper application techniques are employed.
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