Endocrine disruption in thicklip grey mullet (Chelon labrosus) from the Urdaibai Biosphere Reserve (Bay of Biscay, Southwestern Europe)

Endocrine disruptors (EDs) interfere with the development and functioning of the endocrine system, causing reproductive disturbance in aquatic wildlife. The aim of the present work was to determine the presence of EDs in sediments and to investigate possible exposure and effects of EDs in the estuary of the Urdaibai Biosphere Reserve (Gernika) in comparison with the Arriluze marina. For this, gonad histology, plasma vitellogenin (VTG) protein levels and mRNA levels of vitellogenin (vtg), cyp19 aromatases, estrogen receptor (er) and retinoid X receptor (rxr) were studied in Chelon labrosus. The presence of alkylphenols (APs) in fish bile was also assessed. In sediments, estrogenic hormones were below the detection limit and levels of bisphenol A were very low. In Gernika organotin compounds were low but in Arriluze levels of up to 12μg/g were found. Moderate levels of APs and phthalate levels of up to 8μg/g were found in sediments. In fish, a high prevalence up to 33% of intersex gonads was found in Gernika, whereas only one intersex was found in Arriluze. Accordingly, mullets from Gernika showed higher concentrations of APs in bile. VTG protein levels were detected not only in females but also in some undifferentiated, male and intersex fish. mRNA of vtg was detected in one male from Gernika. mRNA of er and rxr showed significant differences between seasons. In conclusion, the present study demonstrated that C. labrosus from the Urdaibai estuary were exposed to EDs and showed clear signs of endocrine disruption. ► High prevalence of intersex gonads was found in the Urdaibai Biosphere Reserve. ► High levels of alkylphenols were measured in fish bile. ► VTG protein was detected in the plasma of undifferentiated, male and intersex fish. ► Levels of phthalate and organotins measured in sediments are of great concern. ► This study provided evidence of EDs presence in the Urdaibai Biosphere Reserve.