pesticides containing fipronil, a phenylpyrazole insecticide, are
Frontline®, Frontline® Topspot™, Combat®, and MaxForce® (NPTN 1997).
Concerns about human exposure to Frontline spray treatment were raised in
1996, leading to a denial of registration for the spray product (PAN
Mode of Action
is a disruptor of the insect central nervous system via the GABA channel,
acting with contact and stomach action. It blocks the GABA-gated chloride
channels of neurons in the central nervous system, resulting in neural
excitation and death of the insect (NPTN 1997).
It is used against cockroaches, ants, fleas, ticks, and mites (PAN
technical form of fipronil has the signal word "Warning,"
implying moderate toxicity, while all formulated or end-use products in
the U.S. carry the signal word "Caution," indicating low
toxicity. Signs of toxicity in rats include anuria (no urination),
increased excitability, seizures, and reduced feed consumption. It may
cause mild irritation of the eyes and slight skin irritation, but is not a
skin sensitizer (NPTN 1997). It has a rat acute LD50 of 97
mg/kg, and has moderate acute toxicity by oral and inhalation routes in
rats. It is of moderate dermal toxicity to rabbits, and is less toxic to
mammals than to fish, some birds, and invertebrates.
is neurotoxic in both rats and dogs.
Severe skin reactions to Frontline Topspot for Cats and Topspot for
Dogs have occurred, with skin irritation and hair loss at the site of
application. Organs affected by chronic exposure may include the liver,
thyroid and kidney. Reproductive toxicity occurred at the higher doses
tested, with clinical signs including reduced fertility, decreased litter
size, decreased body weights in litters, and fetus mortality. There is no
evidence of fipronil causing birth defects, but it may cause a delay in
development at high doses (NPTN 1997).
is carcinogenic to rats at doses of 300 ppm, causing thyroid cancer
related to disruption in the thyroid-pituitary status, and is classified
as a Group C (Possible Human) Carcinogen based on the rat carcinogenicity
study (PAN 2000).
is highly toxic to fish and aquatic invertebrates, highly toxic to bees,
and highly toxic to upland game birds, but is almost non-toxic to
waterfowl and other bird species. Fipronil is excreted in rats via the
feces (45-75%) and urine (5-25%) (NPTN 1997).
photodegradate of fipronil, MB46513, is about 10 times more acutely toxic
to mammals than fipronil itself. The metabolite MB 461 is more highly
toxic to birds, and the metabolites MB 46136 and MB 45950 are more highly
toxic to freshwater invertebrates than fipronil itself (PAN 2000).
half-life of fipronil was found to range from 122-128 days in oxygenated
sandy loam soil, 0.7 to 1.7 months on soil surfaces, and 3 to 7.3 months
when incorporated in soil. It has low soil mobility and little potential
for groundwater contamination. In water and sediment that lack oxygen,
fipronil degrades more slowly, with a half-life of 116-130 days. Its
half-life in basic solutions is 28 days, and it remains stable to
breakdown by water at a mildly acidic to neutral pH. When exposed to
sunlight, fipronil has a half-life of 3.6 hours in water and 34 days in
loamy soil (NPTN 1997). The half-life on vegetation is 3-7 months. Studies
showed that there is potential for bioaccumulation of the photodegradate
MB 46513 in fatty tissues (PAN 2000).
Pesticide Telecommunication Network (NPTN). 1997. Fipronil Technical
Fact Sheet. December. Oregon State University. Corvallis, OR.
Pesticide Action Network – UK (PAN). 2000. Active Ingredient Fact Sheet: Fipronil. June. Pesticide News 48:20-22. London, England.