Are wastewater treatment wetlands safe for waterbirds?

Abstract

(south-central Spain) waterbirds are increasingly dependent on wastewater treatment wetlands (WTW). However, the use of wastewater may increase the risk of avian botulism outbreaks. With this in mind we have studied the hypothesis that the presence of some avian enteropathogens in sewage may cause waterbirds mortalities and consequently start botulism outbreaks. To assess this possibility, between April 2010 and March 2011 we collected samples of sediment, water and waterbird faeces in three wetlands situated in Ciudad Real: two WTWs (Navaseca and Alcázar de San Juan) and one natural wetland (NW, Tablas de Daimiel National Park). We tested the samples for the presence of avian enteropathogens [Avian Pathogenic Escherichia coli (APEC), Salmonella spp., Clostridium perfringens] and C. botulinum following different culture and PCR protocols. The prevalence of C. perfringens was significantly higher in all the samples from WTWs than in those from the NW. APEC were significantly more prevalent in faeces from the two WTWs and in sediments from one of them than in the NW. Finally, the prevalence of Salmonella spp. and C. botulinum was low, but again it was higher in the WTWs. Moreover, in one of the WTWs (Navaseca) botulism outbreaks have occurred in 2010 and 2011. This high prevalence of avian enteropathogens observed in WTWs may be a determining factor in the occurrence of botulism outbreaks.