There have been case controlled studies of the risk of canine malignant lymphoma (a cancer of the lymph system), 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.
Lawn Checmicals and Dogs
A study (May 2001) from Italy suggests that canine malignant lymphoma is very slightly associated with residence in urban industrial areas, and with the use of paints or solvents by the owner. That said more detailed studies need to be performed before and firm conclusions can be reached.
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 prevent possible overexposure. Large, short-term exposures can cause illness such as vomiting, nervous system signs, and diarrhea.