Lawn Chemicals and Your Dog

This question is an important one, and is a part of a bigger question about the possible potential impact of long-term, low level exposure to agriculture and lawn chemicals (pesticides, herbicides, fungicides) and other industrial chemicals (paints, oils, solvents etc.) on many species.

There have been case controlled studies of the risk of malignant lymphoma (a cancer of the lymph system) of the dog, and exposure to 2, 4-dichlorophenoxyacetic acid (2,4-D) herbicides. Though some early studies found a link, other more recent analyses do not confirm the connection. It is clear only that dogs on recently sprayed lawns do pick up the chemical because they excrete 2,4-D in their urine.

Other pesticides have also come under scrutiny in studies as well.

Those households engaging commercial spraying companies, and those applying pesticides frequently have a weak association (that requires further study) of increased non-Hodgkin's lymphoma, a human cancer that closely parallels canine lymphoma in cell type.

A very recent study (May 2001) from Italy suggests that malignant lymphoma in the dog is very slightly associated with residence in urban industrial areas, and with the use of paints or solvents by the owner.

If you find this a bit confusing, be aware that a very solid scientific study design needs to be applied to a large population of dogs undergoing the same chemical exposure exactly (type of chemical, dosage, length of time etc.) before firm conclusions can be reached. We also do not jump to conclusions when we look at evidence in other species—if it has effect X in species Y, we do not assume it has the same effect X in species Z. Species vary considerably in how they process toxic compounds and in their susceptibility to tissue damage such as cancers. We also commonly have a situation where the dog has been exposed to more than one chemical in the same time span, or concurrently, owners have been treating the dog with flea control products or administering pharmaceuticals for medical problems that will confound or complicate environmental exposure assessment.

In order to draw a conclusion of cause and effect, one needs to have a large sample with consistent exposure data over time. As you can imagine, a study such as this is not easy to implement. Confounding factors can influence the outcome of many designs, so some study designs are considered much more useful than others. For a number of reasons, there are still differences of expert opinion about the impact of chronic exposure to these chemical compounds, but important research continues.

Until more information is available, it would be prudent as a rule of thumb for pet owners to reduce or eliminate the use of chemicals on lawns where pets run and roll around if they cannot be restricted from accessing the lawn following chemical applications during the time the product label suggests there be no access to the lawn. Packages and inserts of sprays and granules provide detailed application and toxicity information, and commercial lawn sprayers and the homeowner should follow product recommendations to the letter to prevent possible overexposure. Large, short-term exposures can cause illness such as vomiting, nervous system signs, and diarrhea.

Reprinted with permission from www.animalhealthcare.ca