Piperonyl butoxide (PBO) is an organic compound derived from benzodioxole. It is a colorless oil, although commercial samples can appear as a yellow or even brown liquid. It is used as an adjuvant component of pesticide formulations for synergy. That is, despite having no pesticidal activity of its own, it enhances the potency of certain pesticides such as carbamates, pyrethrins, pyrethroids, and rotenone. It is a semisynthetic derivative of safrole and is produced from the condensation of the sodium salt of 2-(2-butoxyethoxy) ethanol and the chloromethyl derivative of hydrogenated safrole (dihydrosafrole); or through 1,2-Methylenedioxybenzene.
History PBO was developed in the late 1930s and early 1940s to enhance the performance of the naturally derived insecticide pyrethrum. Pyrethrum is a type of potent insecticide that kills mosquitoes and other disease-carrying vectors, thereby providing public health benefits, such as preventing malaria. Although exhibiting little intrinsic insecticidal activity of its own, PBO increases the effectiveness of pyrethrins, thus it is called a synergist. PBO was first patented in 1947 in the US by Herman Wachs. There are three known manufacturers of PBO in the world, Endura, Tagros and Catasynth (Anthea) who manufacture PBO through the MDB route.
Uses PBO was first registered in the United States in the 1950s. PBO is mainly used in combination with insecticides, such as natural pyrethrins or synthetic pyrethroids, in ratios (PBO: pyrethrins) ranging from 3:1 to 20:1. Appearing in over 1,500 United States EPA-registered products, PBO is one of the most commonly registered synergists as measured by the number of formulas in which it is present. It is approved for pre- and postharvest application to a wide variety of crops and commodities, including grain, fruits and vegetables. The application rates are low; the highest single rate is 0.5 lbs PBO/acre. It is used extensively as an ingredient with insecticides to control insect pests in and around the home, in food-handling establishments such as restaurants, and for human and veterinary applications against ectoparasites (head lice, ticks, fleas). A wide variety of water-based PBO-containing products such as crack and crevice sprays, total release foggers, and flying insect sprays are produced for and sold to consumers for home use. PBO has an important public health role as a synergist used in pyrethrins and pyrethroid formulations used for mosquito control (e.g. space sprays, surface sprays and bed nets). Because of its limited, if any, insecticidal properties, PBO is never used alone.
Mechanism of action PBO acts as an insecticide synergist by inhibiting the natural defense mechanisms of the insect, the most important of which is the mixed-function oxidase system, (MFOs) also known as the cytochrome P-450 system. The MFO system is the primary route of detoxification in insects, and causes the oxidative breakdown of insecticides such as pyrethrins and the synthetic pyrethroids – thus when PBO is added, higher insecticide levels remain in the insect to exercise their lethal effect. An important consequence of this property is that, by enhancing the activity of a given insecticide, less may be used to achieve the same result. PBO does not appear to have a significant effect on the MFO system in humans. PBO is found to be an efficacious, low-potency, neutral antagonist of G-protein-coupled CB1 receptors. Other synergists for pyrethroid insecticides include Sesamex and "Sulfoxide" (not to be confused with the functional group).
Regulatory PBO is regulated in the United States and some other countries as a pesticide, even though PBO does not have this property. The United States Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), the law that gives United States EPA its authority to regulate pesticides, includes certain synergists in its definition of a "pesticide" and is thus subject to the same approval and registration as products that kill pests, like the insecticides with which PBO is formulated. Pesticide registration is the process through which United States EPA examines the ingredients of a pesticide, where and how the pesticide is used (e.g., whole room fogger, crack-and-crevice, etc.), and the specific use pattern (amount and frequency of its use). United States EPA also evaluates the pesticide to ensure that it will not have unreasonable adverse effects on humans, the environment and non-target species. The United States EPA must register pesticides before they may be sold or distributed in the United States. Registration is required for the pesticide itself, as well as for all products containing it. The World Health Organization recognizes the public health value of PBO when used in conjunction with the synthetic pyrethroids deltamethrin or permethrin used in mosquito nets.
Hazard assessment Numerous toxicology studies have been conducted over the past 40 years on PBO examining the full range of potential toxic effects. These studies were conducted in accord with regulatory requirements put forth by the United States EPA or other international agencies. Many were conducted following United States EPA Good Laboratory Practices (GLPs), a system of processes and controls to ensure the consistency, integrity, quality, and reproducibility of laboratory studies conducted in support of pesticides registration. The following types of studies have been conducted in support of PBO registration:
Acute toxicity studies Acute toxicity studies are designed to identify potential hazards from acute exposures. The studies usually employ a single or a few high doses over a short time period. The data are used for the development of appropriate precautionary statements for pesticide product labels. Acute studies identify:
Dermal toxicity Eye irritation Inhalation toxicity Oral toxicity Skin irritation Skin sensitization PBO has a low acute toxicity by oral, inhalation, and dermal routes in adults. It is minimally irritating to the eyes and skin. It is a not a skin sensitizer.
Dermal absorption The available data indicate that less than 3% of the amount on the skin (forearm) is absorbed over an 8-hour period. Other studies with a pediculicide formulation indicate that about 2% crossed the skin and about 8% crossed the scalp.
Endocrine disruption
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