Toxicity in Flea & Tick Control Products


 A female flea can lay around 25 eggs a day, which hatch into larvae in 2-12 days. In optimal conditions larvae develop into pupae in 8 -24 days but can take up to 200 days. Pupal development takes up to a year in unfavourable conditions but normally lasts 1-2 weeks. Ideal conditions are hot, rainy summers. Dryness is fatal to larvae because they cannot close their spiracles (breathing holes) to retain moisture(1). Fleas develop throughout the year and at different rates, so in the summer season infestations are likely to take hold.

Chemical control

 Pesticides used to control fleas include collars, sprays, spot-ons, shampoos and powders.

The main active ingredients are listed in table 1.

Table 1. Concerns about flea treatments used in UK (10, 11)

amitraz (amidine) - suspected endocrine disruptor

carbaryl (CA) - suspected endocrine disruptor; human carcinogen; cholinesterase,inhibitor; toxic to bees

coumaphos (OP) - cholinesterase inhibitor; toxic to fish

cythioate (OP) - cholinesterase inhibitor

diazinon (OP) - suspected endocrine disruptor; cholinesterase inhibitor; mild eye and skin irritant; toxic to birds; highly toxic to bees

dichlorvos (OP) - suspected endocrine disruptor; cholinesterase inhibitor; mild eye and skin irritant; moderately toxic to birds; toxic to bees and fish

fenitrothion (OP) - suspected endocrine disruptor; cholinesterase inhibitor; toxic to bees

fenthion (OP) - cholinesterase inhibitor; toxic to bees

fipronil (phenyl pyrazole) - mild eye irritant

flumethrin (SP)

imidacloprid - toxic to bees; moderately toxic to birds

iodofenphos (OP) - cholinesterase inhibitor

lufenuron (benzoylurea)

permethrin (SP) - suspected endocrine disruptor; mild skin and eye irritant; skin sensitizer; toxic to aquatic invertebrates and bees; highly toxic to fish

phenothrin (SP) - suspected endocrine disruptor; toxic to fish and bees

phosmet (OP) - cholinesterase inhibitor; mild skin and eye irritant; embryotoxic; teratogenic; harmful to birds and animals; toxic to fish and bees

piperonyl butoxide(synergist)

propoxur (CA) - cholinesterase inhibitor; very toxic orally; mild eye irritant; foetotoxic; highly toxic to bees; phytotoxic to some species

pyrethrin/pyrethrum(botanical) - mild skin and eye irritant; highly toxic to fish; toxic to bees

s-methoprene - formulations can be skin sensitizers

CA = carbamates; OP = organophosphates; SP = synthetic pyrethroid. Inerts used include: disodium edetate, polyoxy-ethylene lanoline, sulphamlamide and sodium polyborate on which there is little information available in the public domain. 

 Concern about the harmful effects of pesticides in flea products were heightened with press reports of veterans complaining of Gulf War Syndrome after being exposed to a combination of chemicals, including OPs during the Gulf War. OPs and carbamates are nerve poisons which kill by inhibiting the nerve enzyme cholinesterase thereby disrupting the nervous system. In February 1997, Droplix, an anti flea treatment which contains the OP diazinon, was linked with dozens of pet deaths in Britain (see PN35 pp6-7). Table 2 is a summary of incidents reported to the Appraisal Panel for Human Suspected Adverse Reactions to Veterinary Medicines in the UK(2).

Table 2. Incidents of suspected adverse reactions to veterinary products

amitraz in three separate incidents (1992-95) small children aged 2 & 3 reported to have lost consciousness after accidentally swallowing a small amount of shampoo product, in one case with bradycardia followed by hypothermia and laboured breathing. 6 other incidents include symptoms of nausea, abdominal pain, severe eye irritation, flatulent dyspepsia, and headache and vomiting

diazinon three cat owners (1994-1996) reported a variety of symptoms from diarrhoea, headache, internal trembling, nervousness, facial burning, nausea and loss of appetite, stinging eyes and breathlessness

dichlorvos & fenitrothion (1991-1995) 11 separate incidents reported, symptoms included: nausea, diarrhoea aching limbs, dizziness, rashes, flu-like symptoms, chest pain, respiratory problems, abdominal pain and vomiting, depression, anxiety and lethargy

fenthion symptoms from 9 reported cases (1994-96) include nausea, sore throat and coughing, breathlessness, sore eyes, aches and pains, burning and itching, swollen lips and eyes, and in 2 cases development of lobar pneumonia days later

permethrin after treating dog one owner had an asthmatic attack (1992), another had an itching and nettle rash on body and arms (1994)

phosmet 8 incidents (1994-1996) symptoms included burning sensation in mouth, headaches, blurred vision, dizziness, nausea, difficulty in breathing and burning sensation in chest

propoxur 2 incidents reported (1995), one with rash on hands and arms, the other with nausea, chest tightness, shortness of breath and blurred vision

pyrethrins + piperonyl butoxide pet owner reported coughing up blood for 3 days after using small animal spray product (1994). Also used paint stripper the previous day. 2 cases of itchy rashes (1994)
skin rashes were also reported in incidents concerning pyrethrum powder (1993), tetrachlorvinphos(1991), piperonyl 

butoxide + pyrethrum extract (1991)

 The US Journal of Pesticides Reform 1997(3) cited research papers relating to pesticide exposure and childhood illness: In Denvor, Colorado, research has found that home pesticides may be associated with some childhood cancers(4), one study in Los Angeles found a significant increased risk of leukaemia in children whose parents used pesticides in the home and garden(5), and in Missouri childhood brain cancer was associated with use of pesticides to control household pests; flea collars on pets were identified as a risk factor(6).

 The National Office of Animal Health (NOAH) and the British Pest Control Association (BPCA) both take the view that a product is safe, if used according to the label's instructions.

  However in 1993 the BPCA asked: "What insecticide formulation is approved for amateur use, applied directly to the body, touched by unprotected hands, provides a source of long-term insecticide contamination of skin surface including those of children? Think twice before recommending their use."(7)

 Safer chemical products that contain insect growth regulators (IGRs) act by preventing development during one of the four stages of the flea life cycle. In 1996 Your Cat readers voted Program the 'Best Flea Treatment' for cats. It is available for both cats and dogs and the active ingredient, lufenuron acts by preventing the hatching of any eggs once the flea has bitten its host. However the US Food and Drugs Administration observed the following adverse effects in cats and dogs: vomiting, depression, lethargy, diarrhoea, loss of appetite and itchy, scratchy skin(8).

Article reprinted with permission from
Pesticide Action Network
Pesticide Action Network (PAN) is a network of over 600 participating nongovernmental organizations, institutions and individuals in over 90 countries working to replace the use of hazardous pesticides with ecologically sound alternatives. Its projects and campaigns are coordinated by five autonomous Regional Centers.