- Bats play a crucial role in tropical regions as pollinators, seed dispersers and agricultural pest controllers. But they are exposed to a wide range of threats, pollution among them.
- Two recent papers show how natural landscape transformation and degradation, due to pasture and crop monoculture creation and mining in Brazil’s Atlantic Forest, can increase bioaccumulation of toxins and heavy metals in bat populations, leading to potential health impacts.
- Over time, this toxic accumulation could increase the likelihood of local bat extinctions and the loss of vital ecosystem services. The toxic contamination of these landscapes also poses a concern for human health, researchers say.
- These findings are likely applicable to bats living in other highly disturbed tropical habitats around the world, researchers say.
Bats play a key role in maintaining the health of forest ecosystems as pollinators, seed dispersers and insect pest controllers. But according to new research, bats and the ecosystem services they offer are under threat in Brazil’s heavily fragmented Atlantic Forest biome, where natural lands have been largely converted for agriculture and mining, degradation that is increasing wildlife exposure to toxic heavy metals.
Scientists at Brazil’s Santa Cruz State University plucked hair samples from bats in the state of Bahia across a patchwork of landscapes — including cattle pasture, eucalyptus and coffee monocultures and cacao agroforest — then tested them for three metals: lead, manganese and copper.
“We found that bats living in areas where the landscape is dominated by intensive agriculture or grasslands have higher levels of toxic metals, particularly lead and manganese,” says Julián Barillaro, the study leader and a conservation ecology researcher at Santa Cruz State University. This, he says, is likely due to use of agrochemicals and leaded fuel. Reduced natural habitat also likely increased exposure.
Other factors, such as bat species and sex, didn’t affect bioaccumulation, leading the authors to believe that the bats came into direct contact with these heavy metals by resting on contaminated leaves or trees and then grooming. The exposure levels within different monocultures requires further study, Barrilaro says, as some bat species are highly mobile and could be moving from crop to crop.
By comparison, the researchers found that bats in cacao agroforestry areas with higher natural forest cover had lower levels of contamination, though some bats had elevated levels of copper, possibly due to the use of fungicides.
This finding, Barillaro says, is important, as it suggests that organic cacao farming, which replaces agrochemicals with less environmentally harmful crop management methods, could be a win-win for farmers and biodiversity. “We are demonstrating that a landscape with more agroforest is more bat-friendly than a monoculture landscape,” Barillaro says.
“These findings are very important for bat conservation, as well as for other wildlife, because they demonstrate that monocultures with extensive use of contaminants can affect animals through direct contact, not only with fruits but also with water,” says Ana Luiza Destro, a postdoctoral researcher in the Department of Biochemistry and Molecular Biology at the Federal University of Viçosa, Brazil, who wasn’t involved in the research.
A diversity of pollution
In another study published earlier this year, Destro and colleagues found that fruit bats exposed to toxic pollutants emanating from iron ore and bauxite mining in the Atlantic Forest suffer direct health impacts. Bats in these highly disturbed areas accumulate metals, including aluminum, iron and barium, and show evidence of liver, kidney, brain and muscle damage or inflammation, which researchers trace back to these contaminants. Bats from iron ore mining areas had higher levels of contamination.
“This impact, in addition to contamination from the increase of metals in the environment, is also closely linked to the loss of habitat and food for animals. This, in turn, affects animal health, potentially amplifying the harmful effects of contaminants,” Destro says. Agricultural monocultures also limit habitat and food availability, likely resulting in a similar effect.
Barillaro says the physiological damage found in the mining study supports concerns raised in his group’s paper: “Together, these studies highlight the significant threats faced by bats from human activities and the urgent need for policies that address not only direct pollution, but also habitat degradation and sustainable landscape management.”
Though it’s challenging to link these findings to wider ecosystem and human health impacts, both researchers say that in all likelihood if the environment is polluted with toxins, it is a potential risk for other species and people.
“If the environment is contaminated, if animals are contaminated, it will inevitably reach humans,” Destro says. “Whether through the food chain, the ingestion of contaminated water or even through inhalation.”
“This study shows that there are a lot of heavy metals in [these disturbed places], and that can affect human health, principally the people that work directly in the crops,” Barillaro agrees. That exposure can be further heightened if workers lack adequate personal protective equipment. Lead is of special concern for both bats and humans as it is particularly harmful and linked to a range of serious health impacts.
Wider implications
The findings of both studies point to risks for bat populations and the ecosystem services they provide to people. Bats not only play a key role in forest regeneration by pollinating plants or widely spreading seeds, but they also are crucial as pest controllers. Research suggests that bats, along with birds, play an important role in cacao crop yields.
Faced with other pressures such as the loss of habitat and access to food, pollution could increase the risk of local extinctions. And there could be other consequences: Research in the U.S. published earlier this year linked widespread bat declines and increased agricultural insecticide use to higher human infant mortality in affected areas.
In the Atlantic Forest, the role of bats may be particularly important, as the beleaguered biome has faced severe deforestation for decades, placing wildlife and tree species at risk. Without healthy bat populations, the resilience of remaining forest patches may be impacted and regeneration could take a hit, the researchers say. “If the health of these animals is threatened, the forests and their ability to regenerate will also be increasingly jeopardized,” Destro says.
Protecting remaining forest, adopting sustainable agriculture such as cacao agroforestry, prioritizing rainforest regeneration and minimizing agrochemical use are all key steps to aid bat populations, Barillaro says. More sustainable approaches to mining and measures to reduce tailing pollution are also needed.
Though both studies focused on the highly fragmented Atlantic Forest, it’s likely the pattern of toxic bioaccumulation found there is similar in other tropical regions degraded by agriculture and mining around the globe, Barillaro adds. “This is probably happening with bats and other wildlife, where landscape transformation, degradation and monoculture occur, because in those areas [animals] are potentially more exposed to contaminants.”
Banner image: A pale spear-nosed bat covered in pollen. Another recent study linked metal contamination and health impacts on bats to iron and bauxite mining in the Atlantic Forest. Iron is turned into steel and bauxite into aluminum, both vital to humanity’s advanced societies. Image courtesy of Guilherme Garbin.
Amazon deforestation threatens one of Brazil’s key pollinators, study shows
Citations:
Barillaro, J., Soto da Costa, L., Gómez-Corea, W. N., García, F. J., Pereira de Souza, A., & Bovendorp, R. (2024). Landscape degradation drives metal bioaccumulation in bats from Atlantic Forest cacao region, Brazil. Environmental Science and Pollution Research, 31(55), 63819-63833. doi:10.1007/s11356-024-35478-x
Destro, A. L., Gonçalves, D. C., Alves, T. D., Gregório, K. P., Da Silva, V. M., Santos, V. R., … Freitas, M. B. (2024). Iron and aluminum ore mining pollution induce oxidative and tissue damage on fruit-eating bats from the Atlantic Forest. Journal of Hazardous Materials, 465, 133285. doi:10.1016/j.jhazmat.2023.133285
Hernout, B. V., Arnold, K. E., McClean, C. J., Walls, M., Baxter, M., & Boxall, A. B. (2016). A national level assessment of metal contamination in bats. Environmental Pollution, 214, 847-858. doi:10.1016/j.envpol.2016.04.079
Ocampo‐Ariza, C., Vansynghel, J., Bertleff, D., Maas, B., Schumacher, N., Ulloque‐Samatelo, C., … Tscharntke, T. (2023). Birds and bats enhance cacao yield despite suppressing arthropod mesopredation. Ecological Applications, 33(5). doi:10.1002/eap.2886
FEEDBACK: Use this form to send a message to the author of this post. If you want to post a public comment, you can do that at the bottom of the page.
Credits
