Heavy metals, such as lead and mercury, are common pollutants in human-affected ecosystems, including cities. These metals can bioaccumulate, or reach high concentrations in exposed organisms, because heavy metals may be stored in some tissues, like fats, and are difficult for organisms to remove from their bodies. High levels of heavy metals have negative impacts on the health of humans and wildlife, including serious detrimental effects on functioning of the brain and nervous system. The human health impacts of lead pollution in cities are being studied, but we know much less about how lead pollution in water supplies may affect wildlife living in urban habitats.
Lead pollution has been a recurring issue for many urban communities. In 2014, the city of Flint, MI experienced a particularly dramatic episode of lead pollution via a contaminated water system which affected drinking water supplies. While humans were eventually advised to stop drinking the contaminated water, it was still used to irrigate lawns and other surrounding areas. Whether this irrigation exposed wildlife to lead pollution, however, remained unknown. As part of a team at Eastern Michigan University, Kenny Glynn, a masters student in the Cornelius lab, decided to investigate whether wildlife in Flint, MI were exposed to lead via this pathway. Kenny and colleagues measured lead levels in the blood and feathers of three common urban bird species, the American Robin, European Starling, and Gray Catbird in Flint and compared them to level in birds from nearby areas in Ypsilanti without pervasive lead contamination.
Kenny hypothesized that lead levels in bird tissues might vary as a consequence of their behavioral and diet preferences. For instance, while all three bird species are fairly omnivorous, robins eat a high proportion of invertebrates that are present on the ground where lead levels due to irrigation may be highest. Juvenile robins in particular may be vulnerable, as they are preferentially fed earthworms, which can absorb water from irrigated lawns.
Kenny found that robin nestlings, juveniles, and adults from the city of Flint all had significantly higher levels of lead in their blood than birds from nearby sites unaffected by lead pollution. Kenny also found that juveniles in particular experienced higher levels of blood lead than adult robins, suggesting that diet and life stage may play a role in lead exposure. This high blood lead may have serious negative effects on robins, and the neurotoxic effects of lead may be particularly strong on developing brains, meaning juvenile robins may be particularly at risk. Other work has shown that urban birds may be able to adapt to lead pollution, making this an intriguing system for future research.
Kenny plans to continue this work by tracking migration of juvenile birds from Flint to see what the ecological consequences of this pollution may be. Results from Kenny’s data on starlings and catbirds are forthcoming as well as analyses of lead levels in feathers, so stay tuned!
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