John Wiley & Sons, Ltd.

Occurrence of glucocorticoids discharged from a sewage treatment plant in Japan and the effects of clobetasol propionate exposure on the immune responses of common carp (Cyprinus carpio) to bacterial infection

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Here we evaluated the environmental risks to common carp (Cyprinus carpio) posed by glucocorticoids present in sewage treatment plant (STP) effluent. To gather information on the seasonal variations in glucocorticoid concentration, we sampled the effluent of a Japanese STP every other week for 12 months. Six out of nine selected glucocorticoids were detected in the effluent, with clobetasol propionate (CP) and betamethasone 17‐valerate detected at the highest concentrations and frequencies. Our results indicated that effluent glucocorticoid concentration may be dependent on water temperature, which is closely related to the removal efficiency of the STP, or to seasonal variations in the public's use of glucocorticoids. In a separate experiment, to clarify whether glucocorticoids in environmental water increase susceptibility to bacterial infection in fish, we examined the responses to bacterial infection (Aeromonas veronii) of common carp exposed to CP. CP exposure did not affect bacterial infection‐associated mortality. In fish infected with A. veronii but not exposed to CP, head kidney weight and number of leukocytes in the head kidney were significantly increased (p < 0.05), whereas these effects were not observed in infected fish exposed to clobetasol, suggesting that CP alleviated bacterial infection‐associated inflammation. Together these results indicate that susceptibility to bacterial infection in common carp is not affected by exposure to glucocorticoids at environmentally relevant concentrations. This article is protected by copyright. All rights reserved

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