Rachel Carson's Silent Spring warned us of the threats to life attending widespread use of chemical pesticides. As a result of her effort the EPA was founded in 1970 and DDT was banned in 1972.

Nevertheless, we did not curtail our domestic reliance on toxic chemicals for pest control. The yearly amount of pesticide sold in our country is now more than double the amount marketed in 1962 when Silent Spring was published.

Pesticide residues in our food and in the environment reflect years of chemical production and use.

We face the continuing problems of the toxic by-products of manufacturing, runoff from outdoor applications, ground water contamination, and finally disposal of unused material as hazardous waste.

Pesticides are used in virtually all public buildings, golf courses, schools, restaurants, hotels, hospitals and private homes as well as in agriculture and forestry.

Rachel Carson described the detrimental effects of pesticides on animals including robins, caddis fly larvae, quail, salmon, and cats. Silent Spring shows clearly how deeply caring and fiercely protective Rachel Carson was of wildlife. Her concern extended to pet animals as well.

A cat owner, she was enchanted by these companions. She once commented: "I have always found that a cat has a truly great capacity for friendship. He asks only that we respect his personal rights and individuality; in return he gives his devotion, understanding and companionship. Cats are extremely sensitive to the joys and sorrows of their human friends; they share our interests" (The House of Life).

Much of Miss Carson's writing took place in the company of cats. She would, no doubt, encourage sharing information on pets, as sentinels of pesticide effects on health and the ecosystem.

For thousands of years the company of animals, domestic and wild, has alleviated our isolation, loneliness and physical hardship. They also could help us monitor the environment; giving early warnings of environmental contamination.

Information from pet-owning households should be incorporated into research projects and even the census of the human population.

Collecting information on the medical histories and behavior of our pets does not require deliberate experimentation on animals.

The 1991 report from scientists of the National Research Council recommended that the government and other institutions develop pet animal population surveys and structured investigations of their diseases and exposure to toxics to monitor human and environmental health.

As pet owners we spend time observing our pet's behavior. This type of information gathering, different from the formal investigations, is open to anyone and is part of being a responsible pet owner.

In addition, each of us should become aware of the identity and toxic nature of various pesticides which may be applied in or around our home.

Based on their own observations, an owner may conclude that a pesticide has caused an adverse effect to their pet.

This should be reported to Rachel Carson Council, or to others collecting such information.

After consulting toxicologists and relevant literature sources, the Council will report available information back to the pet owner.

Most people of course do not keep pets in order to monitor the environment. Nevertheless, studying companion animals is invaluable for several reasons.

In the first place, we share our living space with our animals; the pet dog or cat actually lives even closer to the toddler than to the adult human air space.

Secondly, animals may be more sensitive and easily poisoned by conditions which seem safe to people.

Thirdly, most animal diseases progress at a more rapid rate than the same condition in humans, so they can be studied more rapidly and the results extrapolated to humans.

And finally, a majority of pets (70%) are seen by veterinarians, so that medical histories are available for analysis.

Unfortunately, this type of research has not been sufficiently supported by generous grants from public or private sources.

Deliberately exposing an organism which is sensitive to an adverse environmental effect and observing the creature for evidence of toxicity is the principle behind miners' use of canaries to detect dangerous levels of methane. We do not condone this exploitation of vulnerable animals.

However, information generated in the normal course of care-giving for pets and wildlife needs to be collected and used for environmental monitoring.

A cat was described by Malcom Gladwell as "a whiskered canary in a coal mine" (in "Cats Nipped by a Mystery Malady" Washington Post 7/12/92).

Cats do not have efficient ways of metabolizing and removing complex synthetic chemicals from their bodies.

Unlike dogs, cats seem to protect themselves from poisoning by virtue of their discriminating eating habits: their well known finickiness.

But they endlessly groom themselves and any chemical which contacts their fur or their feet is carefully removed and swallowed.

Various veterinary institutions have files containing thousands of reports of animals having been poisoned, some fatally, following pesticide exposure.

This information has never been fully integrated with other data on animals and their animal diseases in government and private hands to complete the circle and provide a total pesticide profile.

The "dancing" cats of Minimata, Japan

A dramatic environmental tragedy resulted in crippling nervous conditions and birth defects, affecting an entire generation from a Japanese fishing village. In the mid-1950s a disturbing event surfaced. Citizens noticed that many of the town's cats behaved strangely. For no apparent reason they exhibited frenzied behavior, throwing themselves against stone walls, prancing or staggering as though intoxicated, and frequently hurling themselves into Minamata Bay, where many drowned. What may have been faintly amusing at first rapidly produced much concern by the more thoughtful people of Minamata. This abnormal behavior in local cats was the first sign of trouble, but failed to avert disaster. Years later, a careful toxicological survey disclosed that the fish and shellfish of the Minamata Bay were heavily contaminated with methyl mercury, as were the internal organs of the frenzied cats and the local fish-eating citizens. Thus far, 1,760 victims have been identified but a local university places the victims at over 10,000.

Bearing this tragedy in mind, we should never dismiss 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, muscle tremors, chest tightness, urgency to urinate or rarely, death.

In contrast to the usual reactions, a cat owner and his cat both displayed 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 family dog received the same treatment at the same time, but he did not become more aggressive.

When pesticide applications were stopped, both owner and cat resumed their normal, agreeable demeanor.

An association between the use of this type of pesticide, cholinesterase inhibitors or anticholinesterases, and aggression has been reported.

"Irritability, paranoia and physical assaults have been sporadically reported following anticholinesterase exposure in man" (Psychosomatics, 7-86 (27) #7: 535-536).

Aggression and killing among cats brought about by similar anticholinesterase products have been blocked by antidotes for these chemicals.

Three reports of unprovoked aggression including two homicides, followed exposure to similar chemicals (Journal of Neuropsychiatry, 1992 (4) #2: 189-194).

Increases in the level of aggression in the general population following aerial applications of organophosphate and carbamate insecticides have not been adequately monitored by EPA.

Needless to say, 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 high levels of thyroid hormone in the blood.

Cats which were regularly treated with flea powders and sprays, and were also exposed to lawn pesticides, have been found more likely to have hyperthyroidism.

A higher level of canned cat food in the diet was also an increased risk factor (Preventive Veterinary Medicine, 1988(6): 295-309).

Thyroid enlargement has been seen in Great Lakes fish and in rodents fed on these fish. This has been attributed to pesticides and other contaminants in the lake water (Advances in Modern Toxicology, 1992(XXl): 129-145).

President George Bush, his wife Barbara, and First Dog Millie were also found to have enlarged thyroids.

It is not clear what if any similarities exist among the thyroid conditions in the salmon, rodent, cat, dog, and former First Family, 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 the same cancers in humans, they can be studied more rapidly and the results extrapolated to humans.

Cancer is one of the leading causes 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 in dogs has been found.

The risk of bladder cancer was increased further in dogs living in proximity to areas sprayed regularly with insecticides for mosquitoes.

An increased rate of bladder cancer in humans has recently been reported (Journal of Toxicology 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 to have increased cancer risks from contact with 2, 4-D (Journal of the National Cancer Institute, 1991(83) #17: 1226-1231).

This herbicide was a component of Agent Orange, and is the active ingredient in many herbicide products on 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 in her lifetime.

Research published in the article, "Blood Levels of Organochlorine Residues and Risk of Breast Cancer," by Dr. Mary Wolf et al. reported a statistically significant association between higher levels of DDE in the blood and increased risk of malignant breast cancer (Journal of the National Cancer Institute, 1993(85) #8: 648-652).

DDT and its metabolites such as DDE are known for their estrogen-like actions.

When dog years are expressed as human equivalents, there are similarities in the epidemiology of breast cancer in humans and dogs.

Further study of canine mammary cancer is needed.

Chlorpyrifos Toxicity in an Aviary

In a home where pet birds had been bred and raised for six years, the organophosphate insecticide chlorpyrifos was introduced for roach control.

After five applications, fledglings began to die off, then egg production ceased, and finally the adults deteriorated and died.

The owner, no doubt, realized that this tragedy meant he was also in danger; this was part of the basis of settlement of his lawsuit against the exterminating company.

The report concludes: "The case was settled to cover the cost of the 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 in this case.

Chlorpyrifos is still registered and widely used for structural pests indoors and for insects on ornamental plants, lawns, on food and 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. Birdwatching and gardening are two of the largest leisure time activities in the U.S. and many homeowners include bird feeders in their yards.

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 careful analysis of animal disease and pesticide exposure has detected significant associations.

Much more such work could and should be done. The medical and environmental communities need to join forces in investigating pesticide-related illness.

As Rachel Carson wrote in Silent Spring: "Today we are concerned with a different kind of hazard that lurks in our environment--a hazard 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 us of pesticide related health and environmental problems.

For those people wary of pesticide use and wishing for alternative methods, Rachel Carson Council has prepared information on non-toxic roach, ant and flea control in the home as well as weed, insect and fungus control for the lawn and the garden.

Rachel Carson Council, Inc.
PO Box 10779, Silver Spring, Maryland 20914
Phone: (301) 593-7507