**6. Conclusions**

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 EDCs in the sediments. The specific agents responsible for the toxic effects were not identified because it was beyond the scope of this study. Future research is needed to identify the causal agents (natural or synthetic) and to determine exposure routes (e.g., grazing on sediments or bioconcentration from the water column). Finally, in relation to the adequacy of the bioassay developed to be applied as a monitoring tool, since Juan Lacaze sediments generated the greatest changes in the analyzed biomarkers, confirming their inclusion as a positive control. Likewise, the selection of negative controls (without sediment exposure) showed the lowest levels of changes as well as the lowest dispersion of values between replicates.
