RESUMO
This study aimed to determine uranium (U) pollution over time using otoliths as a marker of fish U contamination. Experiments were performed in field contamination (~20⯵gâ¯L-1: encaged fish: 15d, 50d and collected wild fish) and in laboratory exposure conditions (20 and 250⯵gâ¯L-1, 20d). We reported the U seasonal concentrations in field waterborne exposed roach fish (Rutilus rutilus), in organs and otoliths. Otoliths were analyzed by ICPMS and LA-ICP SF MS of the entire growth zone. Concentrations were measured on transects from nucleus to the edge of otoliths to characterize environmental variations of metal accumulation. Results showed a spatial and temporal variation of U contamination in water (from 51 to 9.4⯵gâ¯L-1 at the surface of the water column), a high and seasonal accumulation in fish organs, mainly the digestive tract (from 1000 to 30,000â¯ngâ¯g-1, fw), the gills (from 1600 to 3200â¯ngâ¯g-1, fw) and the muscle (from 144 to 1054â¯ngâ¯g-1, fw). U was detected throughout the otolith and accumulation varied over the season from 70 to 350â¯ngâ¯g-1, close to the values measured (310â¯ngâ¯g-1) after high exposure levels in laboratory conditions. U in otoliths of encaged fish showed rapid and high U accumulation from 20 to 150â¯ngâ¯g-1. The U accumulation signal was mainly detected on the edge of the otolith, showing two U accumulation peaks, probably correlated to fish age, i.e. 2â¯years old. Surprisingly, elemental U and Zn signatures followed the same pattern therefore using the same uptake pathways. Laboratory, caging and field experiments indicated that otoliths were able to quickly accumulate U on the surface even for low levels and to store high levels of U. This study is an encouraging first step in using otoliths as a marker of U exposure.
Assuntos
Monitoramento Ambiental/métodos , Membrana dos Otólitos/química , Urânio/análise , Poluentes Químicos da Água/análise , Animais , Biomarcadores/metabolismo , Peixes/metabolismoRESUMO
Ecotoxicological studies have indicated the reprotoxicity of uranium (U) in zebrafish, but its molecular mechanisms remain unclear. Due to the non-covalent nature of U-protein complexes, canonical proteomics approaches are often not relevant as they usually use denaturating reagents or solvents. In this study, non-denaturating (ND) methods were used to obtain insight into the nature of U potential targets in ovaries of reproduced and non-reproduced zebrafish after 20 days of exposure to an environmentally relevant U concentration (20 µg L-1). After the ND sample preparation, 1-dimensional (SEC) and 2-dimensional (OGE × SEC) separations followed by ICP-sector-field MS measurements (U, P, Fe, Cu, and Zn) enabled the determination of chemical characteristics (MW, pI) of the metal-protein complexes. Phosphorus and U coelution confirmed the affinity of U for P-containing proteins. In addition, 2D separation allowed the discrimination of Fe-metalloproteins as potential U targets. Finally, 20 protein candidates for U complexation were identified after tryptic digestion conditions by LC-ESI FT MS and a database search. Potential U targets were mainly involved in three biological processes: oxidative stress regulation (SOD, GST), cytoskeleton structure (actin) and embryo early development (vtg, initiation factor).