Researchers at the University of California-Davis (UC-Davis) recently investigated levels of methylmercury in a small sampling of commercial dog foods and found reassuring results, the university said in an announcement.
Of the 24 diets tested, only three were positive for low concentrations of total mercury, and only one of those contained detectable methylmercury.
The study was published in Topics in Companion Animal Medicine.
"The concentrations detected are unlikely to pose a risk to healthy adult dogs," said lead author Rae Sires, a nutrition resident at the UC-Davis Veterinary Medical Teaching Hospital. "These results should be reassuring to dog owners."
Excess mercury exposure is a health hazard for people and animals. Depending on the method of exposure — such as skin contact, ingestion or inhalation — it can lead to respiratory and gastrointestinal disease, kidney injury, fetal development issues and neurologic problems.
While previous studies have measured total mercury in commercial pet foods, additional testing for methylmercury had not been done, the researchers said.
"That is the form where we worry about bio-accumulation, or the ability to become more concentrated in animal tissues as it moves through the food chain," Sires said. "We know there is some level of total mercury in commercial dog foods based on recent studies, but we didn't yet know whether it is cause for concern."
Because methylmercury is known for its presence in aquatic species, Sires said the researchers evaluated diets containing fish — mostly salmon — and control samples, which didn't have fish-based ingredients.
In the research abstract, the researchers said salmon is becoming a more common ingredient in pet foods as manufacturers seek to include unconventional proteins and omega-3 fatty acids in their product formulations.
Of the three samples testing positive for total mercury, Sires said two of those were from non-fish-containing diets, suggesting that common sources of mercury in pet foods may not originate from seafood. That said, the single positive sample that included fish was the one found to contain methylmercury.
Sires acknowledged that this study included a relatively small sample size and said it should be viewed as a jumping-off point for further research that could be expanded to cover more samples and to be completed over a longer period of time and seasons.
"We need more data to determine where the total mercury detected in dog foods is coming from, but our study doesn't support avoiding fish or salmon-based diets," Sires said.