Cocaine effects on the gills of the European eel, Anguilla anguilla”

Many illicit drugs and their breakdown products are detected in the aquatic environment due to the worldwide use of these substances and the variable efficiency with which they are removed from sewage effluent in sewage treatment plants.1 These substances have strong pharmacological activity; indeed, despite their low concentrations in surface waters, the first studies showed toxic effects for aquatic organisms.2,3,4,5 The aim of this study was to evaluate the influence of environmental concentrations of cocaine, an illicit drug widespread in surface waters, on the gills of the European eel (Anguilla anguilla). A stock solution of 0.006 mg mL-1 cocaine free-base in ethanol was prepared. Male silver eels were exposed for fifty days to 20 ng L-1 of cocaine, corresponding to the mean cocaine concentration detected in surface waters.1 The gills of cocaine exposed eels were compared to untreated control and vehicle control groups. The morphology of the gills and plasma levels of prolactin and cortisol, involved in gill physiology regulation, were evaluated. The gills of cocaine-exposed eels showed an hyperplasic epithelium, in which many mucous cells were observed, and lamellar fusion. Moreover, cocaine increased plasma prolactin and cortisol levels. The changes observed in the gills epithelium agree with those observed in the intestine4 of cocaine-exposed eels. Since in fish prolactin and cortisol stimulate epithelial cell proliferation and the differentiation and proliferation of mucous cells, these hormones might be involved in the changes induced by cocaine. Fish gills are involved in gas exchange, in the exchange of salt and water and excretion of nitrogenous waste products; therefore, even slight structural changes can render a fish vulnerable to osmoregulatory and respiratory difficulties. This study shows that even low cocaine concentrations affect the gills, suggesting potential impact on the survival of this species. 1. Rosi Marshall EJ et al. J Hazard Mater 2015,282;18-25. 2. Capaldo A et al. Water Air Soil Pollut 2012, 223:2137-2143. 3. Gay F et al. Water Air Soil Pollut 2013, 224:1579. 4. Gay F et al. J Fish Dis 2016, 39:295-308. 5. Monaco A et al. Eur J Histochem 2016,9.