Dogs are ingesting, inhaling and otherwise being exposed to garden and lawn chemicals that have been associated with bladder cancer, according to a new study.
The paper, which will appear in the July issue of Science of the Total Environment, also found that wind could carry the chemicals to untreated properties. The researchers also found that dogs, once contaminated by the chemicals, can transfer them to their owners.
The chemicals are common herbicides containing the following: 2,4-dichlorophenoxyacetic acid (2,4-D), 4-chloro-2- methylphenoxypropionic acid (MCPP) and/or dicamba.
"The routes of exposure that have been documented in experimental settings include ingestion, inhalation and transdermal exposures," lead author Deborah Knapp of Purdue University's Department of Veterinary Clinical Sciences, told Discovery News.
"In the case of dogs," she added, "they could directly ingest the chemicals from the plant, or they could lick their paws or fur and ingest chemicals that have been picked up on their feet, legs or body."
Scottish terriers, West Highland white terriers, Shetland sheepdogs, beagles and wire hair fox terriers are all at particular risk, the researchers suggest, because these breeds have a high genetic propensity for bladder cancer.
Knapp and her colleagues first conducted an experimental grass plot study that involved spraying various defined patches with the chemicals under different conditions. These included spraying the herbicides on plots that were green, dry brown, wet or recently mowed. The researchers next measured how much of the chemicals remained on the grass up to 72 hours post treatment.
Co-author Angus Murphy, also from Purdue, explained that dead or dying plant material does not readily absorb the chemicals, "so the herbicide can remain longer on the surface of the plant."
He continued, "If an excessive amount of herbicide is applied, then the capacity of the target plant to take up the compound may be overwhelmed."
In a second experiment, the researchers analyzed urine samples of dogs from households that either used herbicides or didn't. The majority of dogs from homes that used the chemicals were found to have these same herbicides in their urine. Some dogs from untreated homes also had the chemicals in their urine.
Knapp explained that wind could cause the herbicides to travel up to 50 feet away from the application site. Neighbors who use the chemicals might therefore impact other individuals in the area.
"There are industry guidelines for restricting lawn chemical application based on wind speed, although homeowners may not be aware of these," Knapp said.
Once contaminated, dogs can pass the chemicals on to their owners and to others. The study only looked at dogs, but the researchers suspect that cats and other pets could also be affected.
"Dogs can pick up the chemicals on their paws and their fur," Knapp said. "They can then track the chemicals inside the house, leaving chemicals on the floor or furniture. In addition, if the dog has chemicals on its fur, the pet owner could come in contact with the chemicals when they pet or hold the dog."
John Reif, a professor emeritus of epidemiology at the Colorado School of Public Health, told Discovery News, "The paper presents important information since exposure to 2,-4-D, a widely used broad leaf herbicide, has been associated with increased risk of cancer in pet dogs and humans."
Reif added, "This study has potentially important implications for human health since it demonstrates widespread exposure to pet dogs. The likelihood that children, who share the local environment with their pets, are similarly exposed to these chemicals is high and thus additional studies should be conducted to evaluate this possibility."
The researchers suggest that if owners still must use herbicides, they should follow manufacturer guidelines, allow gardens and lawns to dry before allowing pets out, wash their dog's feet each time the dog comes inside, and consider treating the back yard one week before the front (or vice versa) so that pets will have an area of less potential chemical exposure available to them.