The effect of wastewater treatment works on foraging ecology, haematology, detoxification organs and reproduction in an urban adapter, the banana bat (Neoromicia nana).

Abstract

Natural land is rapidly becoming urbanized. Wastewater Treatment Works (WWTWs) are a ubiquitous component of this urban landscape. WWTWs may provide profitable foraging areas for insectivorous bats because of their association with a high abundance of pollution-tolerant chironomid midges (Diptera). However, bats that feed on these insects may also accumulate metal pollutants in their tissues, with acute or chronic effects on their health. There have been no studies to investigate whether African bats utilize these WWTWs as foraging grounds, and the potential physiological impacts from foraging at such sites. The aim of this study was to investigate the impact of WWTWs on foraging ecology and multiple tiers of physiology (haematology and genotoxicity, detoxification organs and reproduction) in an urban adapter, the banana bat (Neoromicia nana, family Vespertilionidae) in KwaZulu-Natal, South Africa. N. nana exhibited a significantly higher abundance and feeding activity at wastewaterpolluted sites than at unpolluted reference sites. Additionally, the most abundant insect order at wastewater-polluted sites and in the diet of resident bats was Diptera, compared to a diverse insect diet at unpolluted sites. Thus, WWTWs provide an optimal food resource to bats in the short-term. However, I found significantly higher levels of essential and non-essential metals at WWTW-polluted sites, and in the tissues of WWTW bats than at unpolluted sites. Further, I found sub-lethal haematological and genotoxic responses related to increased metals in WWTW bats. Specifically, N. nana at WWTWs had significantly lower antioxidant capacity and significantly higher levels of DNA damage and haematocrits than bats from unpolluted sites. An accumulation of DNA damage, especially from double-stranded breaks ultimately leads to tissue damage and disease. These longer-term effects of chronic pollutant exposure should be most evident in the organs involved in detoxification, the liver and kidneys. Indeed, I found evidence of disrupted balance of essential metals and mineral nutrients, histopathological tissue damage and whole organ effects in the liver and kidneys. Finally, I found reproductive system alterations in male N. nana at WWTWs. Although I did not find significant effects on the sex organs, testosterone hormone concentrations were significantly lower in male N. nana at WWTWs than in males from unpolluted sites. In addition, body condition indices for N. nana from the WWTWs were significantly lower than at unpolluted sites, suggesting lower quality male bats at WWTWs. Taken together, these results suggest the potential for serious long-term health risks, negative fitness implications and ultimately, population effects for these top predators within the urban landscape.