**Conflict of interest**

None.

from agricultural surrounding areas [54]. Additionally, phytoestrogens released by crops as a defense strategy may be reaching the river in overland runoff. In particular, soybeans contain high levels of genistein, daidzein, and glycitein, which can elicit alterations in endocrine function in wildlife and humans [55]. Juan Lacaze receive untreated municipal sewage effluent containing a complex cocktail of natural (estrone or 17b-estradiol) and synthetic estrogens used in oral contraceptives as well as surfactants used in soaps and detergents (alkylphenols and alkylphenolpolyethoxylates) Furthermore, the plasma VTG concentrations in fish were highest where deposition processes were predominant at Juan Lacaze and where pulp mill effluent was discharged near the sampling site. In that sense, several works worldwide have documented the increase in vitellogenin plasma in juvenile individuals exposed to effluents from cellulose plants [14, 56, 57]. Elevated levels of VTG in males and immature females were clearly an estrogen-mediated response. It is important to note that VTG levels were not affected by the sex ratio, as shown by similar VTG concentrations in the Las Cañas and Juan Lacaze groups with opposite sex ratios, same when

The gonad histology analyses indicated that female fish did not exhibit differences in maturation state. Unlike other works carried out under similar conditions, not differences in the stage of oocyte development were observed [33, 58, 59]. Whereby it could only be a trophoblastic but not protoplasmic growth, this could be checked by increasing the exposure time to see if there are changes in the stages in the individuals with the highest number of cells. However, sediment-exposed males presented delayed testicular maturation than that in the unexposed group. Jobling et al. reported that the induction of VTG in males is negatively correlated with testicular maturation, and Devlin and Nagahama observed retarded gonadal maturation in *C. carpio* males exposed to estrogenic compounds [60, 61]. Changes in sex ratios and intersex individuals have been reported in common carp exposed to EDCs [40, 41, 61]. However, the intersex condition occurs naturally in approximately 5% of the population in this species [7]. Thus, the presence of individuals with testis-ova observed in our study was possibly a natural

phenomenon and may not have been caused by exposure to contaminated sediments.

The condition factor showed higher values in all the treatments with respect to the control group; however, the differences are not statistically significant, and this agrees with the results obtained by Orrego et al. [14]. The significant increase in liver mass at Juan Lacaze may have been caused by induction of the hepatic mixed function oxidase system in response to discharge of persistent organic compounds from the pulp mill effluent [62–64]. Increased protein synthesis generates proliferation of endoplasmic reticulum, which can be reflected in

This study is the first report about endocrine disruption in fish exposed to sediment from the lower Uruguay river. The results can be considered a reference condition for monitoring the impacts of the new ECF bleached Kraft Eucalyptus pulp mill. Nonpoint (soybeanwheat crops) and point sources (municipal sewage and pulp mill effluent) can explain the VTG induction observed in immature fish and suggest the presence and bioavailability of

comparing the Paysandu and Nuevo Berlin treatments.

increased hepatocyte size [65–69].

**6. Conclusions**

26 Endocrine Disruptors
