Boric acid (borax and boron-containing salts) is a
low-toxicity mineral with insecticidal, fungicidal, and herbicidal
properties. It does not evaporate or volatilize into the air or pose the
considerable health concerns associated with synthetic pesticides; however
it can still pose health hazards and should be used with care. As with any
pesticide, keep boric acid pesticide products out of reach of children and
only use it in locations where it will not come in contact with people or
animals, such as in cracks and crevices, behind counters, and in
baseboards. While boric acid is somewhat slower acting than the synthetic
pesticides, like chlorpyrifos, diazinon, or pyrethrins, it is highly
effective over a long period of time.
and Mode of Action
Registered in 1983 for control of cockroaches, ants, grain
weevils and several beetles, it has also been used as an herbicide along
rights-of-way and as a fungicide for citrus, and as a wood
preservative/fire retardant, and even as an insect repellent in
insulation. As an insecticide, boric acid acts as a stomach poison for
ants, cockroaches, silverfish and termites, and as abrasive to the insects
exoskeleton. As an herbicide, boric acid causes desiccation or interrupts
photosynthesis in plants.
Boric acid may be used either in a bait formulation
containing a feed attractant or as a dry powder. The powder may be
injected into cracks and crevices, where it forms a fine layer of dust.
Insects travel through the boric acid, which adheres to their legs. When
the insects groom themselves, they then ingest the poison, which causes
death three to ten days later of starvation and dehydration. As long as
the material is not allowed to become wet, its continuous presence ensures
that hatching insects, which sprays commonly spare, are exposed and die.
Many insecticidal formulations can be effective for more than a year.
While exposure to boric acid has been linked to adverse
health effects, experts agree that careful application offers a safe and
effective alternative without the indoor air problems associated with
sprays. Boron is a naturally-occurring element in the earth’s crust and
background levels even circulate in the human bloodstream. Boric acid’s
exposure risks are minimal because of its method of application.
However, while boric acid has become one of the chemicals of
choice for many urban pest control programs, it can be toxic. EPA
considers boric acid as a moderately acutely toxic due to acute effects
including oral and dermal toxicity, and eye and skin irritation. EPA’s
reregistration document states that a subchronic borax feeding study using
dogs resulted in blood and metabolism disorders as well as effects to the
testes, endocrine system, brain weight, and size ratios among various
organs and glands. In chronic oncogenicity studies using mice, rats and
beagle dogs, boric acid and borax were found not to be carcinogenic;
however, testicular effects and decreases in body weight resulted at high
dose levels. EPA has classified boric acid as a “Group E” carcinogen,
indicating that it shows “evidence of noncarcinogenicity” for humans.
In reproductive and developmental toxicity studies using rats, mice and
rabbits, maternal liver and kidney effects and decreased weight gain as
well as decreased fetal body weights were observed. In two studies, at the
highest dose levels, no litters were produced. Prenatal mortality occurred
at the highest dose levels in the rabbit study. Boric acid does not cause
mutagenicity (U.S. EPA 1993).
Applicators and others in treatment
areas may be exposed to boric acid and its sodium salts during or after
application. However, there is no reasonable expectation that these
pesticide uses may constitute a hazard or risk to people involved in, or
near to, handling or application activities. Proper care and adhering to
label directions and precautions should reduce exposure and any associated
risk (U.S. EPA 1993).
Boric acid is practically nontoxic
to birds, fish, aquatic invertebrates, and relatively nontoxic to
beneficial insects. It’s noncrop herbicidal use may harm endangered or
threatened plants, and therefore EPA is requiring three phytotoxicity
studies to assess these risks (U.S. EPA 1993).
An EPA assessment of a boric acid pilot pest control program
conducted at the U.S. Army’s Aberdeen Proving Ground in Maryland found
that boric acid was both more economical and more effective than monthly
spray treatment. At least one study has shown that
the combination of heat, 110 degree F for two hours with boric acid, will
increase the speed at which the German cockroach is killed. For more information on leat-toxic pest control, see here.
S.M. & F.M. Sullivan.
1982. Reproductive Hazards of Industrial Chemicals: An Evaluation of
Animal & Human Data. Academic Press, New York, NY. pp. 130-135.
Bianchini, R.J. 1987. “The use of
borate-treated wood in structures.” Presentation by U.S. Borax at Forest
Products Research Society Conference on Wood Protection Techniques and the
Use of Treated Wood in Construction. Memphis, TN. October 28-30.
“Borate prospects are seen as
promising.” Chemical Marketing
Reporter. November 16, 1987.
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Pest control insulation.” Energy
Design Update 4 (11):13-14.
W. and S. Daar. 1987. “Boric acid: New formulations and application
equipment.” The IPM Practioner 9(6-7):3-4. Bio-Integral Resource Center. Berkeley, CA.
E. and S. Wason. 1986. “Boric acid toxicity.” Pediatric Clinics of North America
R. 1972. “The ecological significance of boron.” U.S. Borax Research
Corp. Anaheim, CA.
EPA. 1993. “Boric acid.” R.E.D.
Facts. EPA-738-F-93-006. Office of
Pesticide Programs. Washington, DC.
EPA. 1985. “Guidance for the reregistration of pesticide products
containing boric acid and boron containing salts as the active
ingredient.” Office of Pesticide Programs. Washington, DC.
and R. Fisher. 1972. “Toxicological studies on borax and boric acid.” Toxicology of Applied Pharmacology 23:351-364.