butoxide, or PBO as it is most often called, is a pesticide synergist. A
synergist is another chemical that is added to a pesticide product, in
addition to the active and inert ingredients, to increase the potency of
the active ingredient. While the increased potency make the pesticides
more deadly to their targets, synergists may also compromise the
detoxifying mechanisms of non-target species, including humans. A typical
pesticide product contains 5-20 times more synergist than active
ingredient. Many products from repellants and pediculicides (lice killers)
to foggers and garden sprays contain synergists. Formulations of
permethrin, resmethrin and sumithrin, including ScourgeTM and
along the for mosquito control to combat the West Nile Virus, commonly
contain the synergist PBO. Prethroids, pyrethrins, rotenone and carbamates
are the pesticides most often formulated in combination with PBO (Gosselin
et al., 1984).
affects humans by inhibiting important liver enzymes responsible for
breakdown of some toxins, including the active ingredients of pesticides.
Specifically, it has been shown to inhibit hepatic microsomal oxidase
enzymes in laboratory rodents and interfere in humans. Because these
enzymes act to detoxify many drugs and other chemicals, a heavy exposure
to an insecticidal synergist may make a person temporarily vulnerable to a
variety of toxic insults that would normally be easily tolerated (Gosselin
et al., 1984). In addition to the symptoms induced by the active
ingredients, signs of PBO poisoning include anorexia, vomiting, diarrhea,
intestinal inflammation, pulmonary hemorrhage and perhaps mild central
nervous system depression. Repeated contact may cause slight skin
irritation. Chronic toxicity studies have shown increased liver weights,
even at the lowest doses, 30 mg/kg/day. Animal studies have shown
hepatocellular carcinomas, even treatments as low as 1.2% (Takahashi et
al., 1994). EPA considers PBO to be a class C possible human carcinogen.
in the Environment
is moderately toxic to most amphibians, crustaceans, fish and other
aquatic organisms. However, study published by the U.S. Fish and Wildlife
Service found piperonyl butoxide to be very highly toxic to bluegills and
aquatic sowbugs (Johnson, 1980). Very little is known about the
persistence of PBO in the environment.
R.E. 1984. Clinical Toxicology of Commercial Products. Williams and
Wilkins. Baltimore, MD.
and M.T.Finley Handbook of Acute Toxicity of Chemicals to Fish and
Resource Publication 137, Fish Wildlife Service, U.S.D.I., Washington,
Takahashi, O., et al., 1994. “Chronic toxicity studies of piperonyl butoxide in F344 rats: induction of hepatocellular carcinoma.” Fund. Appl. Toxicol. 22:293-303.