Primates living in Uganda have 97 chemical pollutants in their digestive tract, some of which are linked to hormonal changes in females and young primates.
Chemical pollutants have reached every corner of our planet, making exposure to these often-harmful substances in air, food and water all but unavoidable for both humans and wildlife. To find out how these are impacting wild primates, researchers used a minimally invasive sampling method: collecting droppings.
Over two months in 2017, Tessa Steiniche at Indiana University and her colleagues collected a total of 71 faecal samples from chimpanzees (Pan troglodytes), olive baboons (Papio anubis), red colobus (Piliocolobus tephrosceles) and red-tailed monkeys (Cercopithecus ascanius) in Uganda’s Kibale National Park.
The researchers tested the faeces using chemical analyses and found 97 pollutants, most of which are known to disrupt how hormones function in mammals. Pesticides and flame retardants, both present in the samples, are examples of such pollutants.
The team also tested hormone levels. Across all species, females that had a higher concentration of pesticides in their faeces were more likely to have higher levels of cortisol – a stress hormone that helps regulate metabolism and the immune system. The researchers found a similar pattern in young primates, where greater concentrations of flame retardants in faeces were associated with higher cortisol and decreased levels of the reproductive hormone oestradiol.
“Our results showing effects in juveniles are especially concerning,” says Steiniche, because early exposure to these chemicals during development can have life-long effects. She says the team will need to monitor the primates over the long term to see how these toxins impact their growth and reproduction.
This is a wake-up call to those that view national parks as places free from human influence. “I think we still tend to have an idealised image of wild primates living in beautiful, undisturbed habitats, but the unfortunate reality is that even protected areas are not buffered from the impacts of pollution,” says Steiniche.