Common environmental household contaminants diethylhexyl phthalate (DEHP) and polychlorinated biphenyl 153 (PCB153) interfere with sperm function in both humans and dogs, according to a recent study published in Nature.
DEHP is a ubiquitous plasticizer that leaches into food and liquids. It is found in clothes, wires, toys, carpets, flooring, and upholstery. PCBs are lipophilic and present in fatty foods. Of note, although PCBs have been globally banned, they continue to persist in the environment. Exposure to these chemicals largely occurs via diet and serves as risk factors for reproductive health. In addition to being found in human food sources, these chemicals are often present in dry and wet dog food.
“A temporal decline in human and dog sperm quality is thought to reflect a common environmental [e]tiology,” wrote the authors, led by Rebecca N. Sumner, PhD, School of Veterinary Medicine & Science, University of Nottingham, Sutton Bonington, United Kingdom. “This may reflect direct effects of seminal chemicals on sperm function and quality.”
The researchers acquired semen samples from 9 human donors and 11 stud dogs, which were then incubated with PCB153 and DEHP in an in vitro setting.
Exposure to DEHP, PCB153, or both increased DNA fragmentation and decreased motility in sperm— markers of ejaculate quality. The magnitude of dose-related effects varied based on the concentrations of these chemicals. Progressive sperm motility was negatively associated with DNA fragmentation in both human and dog sperm.
The researchers suggested that the dog is the sentinel species for human exposure, based on their results. Pet dogs are exposed to the same household pollutants that result in DNA damage as humans. This finding means that dogs could make good experimental models for exposure, especially because their diets can be modified.
Sperm counts have experienced a 50% global reduction in quality between 1938 and 2011. This trend has also been noted in dogs.
Decreasing sperm function and quality has been associated with exposure to anthropogenic chemicals, of which many can disrupt endocrine activity. In many studies, experts have demonstrated that such environmental chemicals are present in the semen of a wide range of species, including humans.
The researchers note that “testing the effects of individual chemicals on sperm functional parameters does not represent ‘real-life’ exposure to a mixture of chemicals, many of which exhibit synergistic, antagonistic or additive effects.”
Dr. Sumner reflected on the importance of the findings: “We know that when human sperm motility is poor, DNA fragmentation is increased, and that human male infertility is linked to increased levels of DNA damage in sperm.”
“We now believe this is the same in pet dogs because they live in the same domestic environment and are exposed to the same household contaminants. This means that dogs may be an effective model for future research into the effects of pollutants on declining fertility, particularly because external influences such as diet are more easily controlled than in humans,” she added.
In the current study, the investigators obtained semen samples from dogs and humans living in the same region of the United Kingdom. Looking forward, the researchers predict that detrimental effects to semen could depend on specific location, with chemicals present in the environment varying by region.