PETS AS SENTINELS
OF PESTICIDE TOXICITY
The "dancing cats" of Minimata
A dramatic environmental tragedy resulted in crippling nervous conditions and birth defects, affecting an entire generation froma Japanese fishing village. Abnormal behavior, resembling frenzied dancing, in local cats was the first sign of trouble, but failedto avert disaster. With the benefit of hindsight, we understand that the "dancing cats" of Minimata were warning the villagersthat fish from the bay had been contaminated with toxic levels of methyl mercury. Bearing this tragedy in mind, we should neverdismiss out of hand animal epidemics since they might indicate environmental deterioration.
Aggression and Anticholinesterases
Signs associated with acute toxicity of carbamate insecticides in mammals are excessive saliva and tear production, muscletremors, chest tightness, urgency to urinate or rarely, death. In contrast to the usual reactions, a cat owner and his cat bothdisplayed objectionable, uncharacteristic aggressiveness after the owner treated the cat with carbaryl, a carbamate insecticide.The owner himself was exposed to the chemical, although he wore gloves and a mask when applying the powder. The familydog received the same treatment at the same time, but he did not become more aggressive. When pesticide applications werestopped, both owner and cat resumed their normal, agreeable demeanor. There has been an association between the use of thistype of pesticide, cholinesterase inhibitors or anticholinesterases, and aggression. "Irritability, paranoia and physical assaultshave been sporadically reported following anticholinesterase exposure in man" (Psychosomatics, 7-86;V.27,#7:535-536).Aggression and killing among cats brought about by similar anticholinesterase products have been blocked by antidotes forthese chemicals. Three reports of unprovoked aggression including two homicides, followed exposure to similar chemicals(Journal of Neuropsychiatry, 1992;V.4,#2:189-194). Increases in the level of aggression in the general population followingaerial applications of organophosphate and carbamate insecticides have not been adequately monitored by EPA. Needless tosay, any release of aggression-causing agents into the environment should be very carefully considered.
Insecticides and Feline Hyperthyroidism
Since the early 1980s, increasing numbers of cats have been found with hyperthyroidism, enlarged thyroid glands and highlevels of thyroid hormone in the blood. Cats which were regularly treated with flea powders and sprays, and were alsoexposed to lawn pesticides, have been found more likely to have hyperthyroidism. A higher level of canned cat food in the dietwas also an increased risk factor (Preventive Veterinary Medicine, 1988;6:295-309). Thyroid enlargement has been seen inGreat Lakes fish and in rodents fed on these fish. This has been attributed to pesticides and other contaminants in the lakewater (Advances in Modern Toxicology, 1992;V.XXl:129-145). President George Bush was also found to have an enlargedthyroid. It is not clear what if any similarities exist among the thyroid conditions in the salmon, rodent, cat, and former President,but further research is needed.
The majority of cancers are caused by environmental factors. Since most animal cancers progress at a more rapid rate than thesame cancers in humans, they can be studied more rapidly and the results extrapolated to humans. Cancer is one of the leadingcauses of death in dogs and cats today. Compared to humans, dogs develop tumors twice as frequently.
Insecticides Associated With Bladder Cancer in Dogs
A statistically significant association between exposure to topical flea and tick dips, and the occurrence of bladder cancer indogs has been found. The risk of bladder cancer was increased further in dogs living in proximity to areas sprayed regularlywith insecticides for mosquitoes. An increased rate of bladder cancer in humans has recently been reported (Journal ofToxicology and Environmental Health, 1989;28:407-414).
2,4-D and Increased Cancer Risk
Lymphosarcoma, a cancer in dogs, has been associated with exposure to the herbicide 2,4-D. People also have been found tohave increased cancer risks from contact with 2,4-D (Journal of the National Cancer Institute,1991;V.83,#17;1226-1231). This herbicide was a component of Agent Orange, and is the active ingredient in many productson the market.
DDT and Breast Cancer
Breast cancer is a disease of increasing concern. In the U.S. one woman in eight is now said to be at risk for developing it. Therecent publication, "Blood Levels of Organochlorine Residues and Risk of Breast Cancer," by Dr. Mary Wolf et al. reported astatistically significant association between higher levels of DDE in the blood and increased risk of malignant breast cancer(Journal of the National Cancer Institute, 1993;V.85,#8:648-652). DDT and its metabolites such as DDE are known fortheir estrogen-like actions. When dog years are expressed as human equivalents, there are similarities in the epidemiology ofbreast cancer in humans and dogs. Further study of canine breast cancer should occur.
Chlorpyrifos Toxicity in an Aviary
In a home where pet birds had been bred and raised for six years, the organophosphate insecticide chlorpyrifos was introducedfor roach control. After five applications, fledglings began to die off, then egg production ceased, and finally the adultsdeteriorated and died. The owner, no doubt, realized that this tragedy meant he was also in danger; this was part of the basis ofsettlement of his lawsuit against the exterminating company. The report concludes: "The case was settled to cover the cost ofthe birds and for creating a health hazard for the occupant of the house" (Proceedings, Association of Avian Veterinarians,1990:112-114). The warning of the environmental sentinels was heeded.
Chlorpyrifos is still registered and widely used for structural pests indoors and for insects on ornamental plants, lawns, on foodand fiber crops and for mosquito control outdoors.
Wild Birds at Risk From Pesticides
Although we cannot claim them as pets, we have close ties to wild birds. More vulnerable than mammals to pesticide toxicity,they have suffered massive die-offs and population reductions as the result of agricultural and horticultural chemical pesticideuse. Fledglings, more sensitive to this toxicosis than mature birds, can be poisoned in their nests or through the insects receivedfrom parent birds.
Chemical pesticides have been associated with increased aggression in cats and people, enlarged thyroid glands in cats, bladder cancer and lymphosarcoma in dogs, breast cancer in people and fatalities in birds
Minimal effort has been expended in studying pet animal populations for long-term chemical pesticide toxicity, but carefulanalysis of animal disease and pesticide exposure has detected significant associations. Much more such work could and shouldbe done. The medical and environmental communities need to join forces in investigating pesticide-related illness. As RachelCarson wrote in Silent Spring: "Today we are concerned with a different kind of hazard that lurks in our environment--ahazard we ourselves have introduced into our world as our modern way of life has evolved."
Dogs, cats and birds have been our companions for centuries. Their behavior, diseases and even their deaths have warned usof pesticide related health and environmental problems. For those people wary of pesticide use and wishing for alternativemethods, Rachel Carson Council has prepared information on non-toxic roach, ant and flea control in the home as well asweed, insect and fungus control for the lawn and the garden.
Written by: Rachel Carson
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