Monkeys as guard dogs against lead

U. WASHINGTON—Because Asian monkeys share the same ecological niche as humans, researchers believe they might play a significant role in determining exposure to lead.

In parts of South and Southeast Asia, macaques and people are synanthropic, which means they drink from identical water sources, breathe the same air, share food sources, and play on the same ground.

“Macaques are similar to humans anatomically, physiologically, and behaviorally,” says Lisa Jones-Engel, a senior research scientist at the National Primate Research Center at the University of Washington.

“They are also similar in their response to toxic exposures,” says Gregory Engel, a physician at Swedish Cherry Hill Family Medicine in Seattle and a research scientist at the UW National Primate Research Center.

When macaques live in environments polluted by motor vehicles, openly disposed garbage, and industrial waste, they can come into contact with toxic substances such as lead, just as their human neighbors might.

The researchers’ study was published in the American Journal of Physical Anthropology.

Lead toxicity, the authors note, remains a significant public health problem around the world. Intense exposure to lead can damage the nervous, circulatory, and reproductive systems, as well as the kidneys and liver.

Further, exposure during childhood may cause more subtle effects, such as decreased intelligence.

According to Jones-Engel, the researchers believe that young macaques, in particular, would be good sentinels for human exposure to lead.

“Young macaques share a propensity for curiosity and have a penchant for picking up objects and inserting them into their mouths, just as young children do,” Jones-Engel notes.

“A juvenile macaque has all the curiosity and energy of a toddler, and then some.”

She and her team tested urban macaques as a potential early indicator that their human neighbors, especially children, are being exposed to lead and other toxic metals.

They took hair samples from three groups of free-ranging macaques at the Swoyambu temple overlooking Kathmandu, Nepal. The macaques patrolling the site have abundant contact with people and with human-made environments.

The temple is located in a densely populated urban area with poor infrastructure that leaves point sources like discarded lead batteries, flaking leaded paint, and lead contaminated soil, a by-product of decades of leaded fuel, in the environment.
Hair lead levels differed among the three groups of macaques, and were much higher in younger macaques.

The researchers’ data did not support the idea that these lead levels were from basic differences in the animals’ diet, and instead suggested that, in this population of macaques, behavioral or physiological factors among young macaques might play a significant role in determining exposure to lead and subsequent tissue concentration.

“While using animal sentinels is not a new phenomenon, we argue that not all animal species are relevant models for human toxicant exposures, but young macaques that share the same ecological niche with humans may be one of the best animal sentinels we have,” Engel explains.

The researchers note, “All of these factors contribute to making synanthropic macaques—those  that share the environment with humans—potentially valuable as sentinels for toxic exposures and predictors of physiologic responses in humans.”

The research team concludes: “Chemical analysis of hair is a promising, non-invasive technique for determining exposure to toxic elements in free-ranging, non-human primates.

“Further multidisciplinary research is needed to establish whether it can be used to predict lead levels in humans who live in the same areas.”

The study was funded by grants from the Defense Advanced Research Projects Agency and the National Institutes of Health.

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