engleski

Lead concentrations in the hepatic and gill cytosol of European chub (Squalius cephalus) as promising indicators of lead exposure in the river water

Within European Water Framework Directive (WFD), Pb and its compounds were included in the list of priority pollutants which should be regularly monitored in the natural waters. During the study of the water quality of Sutla River in Croatia, in September 2009, dissolved Pb concentrations in the river water, determined at five sites covering the entire course of the river, were mainly below 0.1 μg L-1. At only one site, Pb concentration was prominently increased (site 2: 0.91 μg L-1), but still well below environmental quality standard set in WFD, recommending 7.2 μg L-1 as acceptable annual average Pb concentration in the river water. The aim of this study was to examine if the exposure of fish to increased Pb concentrations in the river water up to the level which is still regarded as legally acceptable, would result in Pb accumulation in fish tissues, which eventually could be hazardous to fish organism. With that purpose, lead concentrations were determined in the cytosolic fractions of two organs of European chub (Squalius cephalus), gills as the site of uptake and liver as the main detoxification organ. Lead was directly measured in the diluted cytosols by high resolution inductively coupled plasma mass spectrometry (Element 2, Thermo Finnigan, Germany), with the detection limit of 0.1 μg of Pb per litre of cytosol. Total number of studied fish was 75, with 15 specimens per site. The spatial distribution of Pb concentrations measured in both tissues was identical to spatial distribution of Pb dissolved in the water, with the highest levels obtained at the site 2. In the chub hepatic cytosol, median Pb concentration at the site 2 (16.2 μg L-1) was 13 times higher than median Pb concentration at the remaining four sites (1.21 μg L-1). In the chub gill cytosol, the difference was even more prominent, with 24 times higher median Pb concentration at the site 2 (19.5 μg L-1) compared to the remaining sites (0.82 μg L-1). The differences between Pb concentrations at the site 2 and the remaining sites were statistically significant for both tissues (p<0.001). Since fish included in this study were heterogeneous regarding the age (1-4 years old), sex (both males and females) and the size (chub mass in the range from 33.0 to 400.5 g), the analysis of the physiological variability of Pb concentrations in the hepatic and gill cytosol was also performed based on the data obtained for the fish caught at the four sites with low Pb exposure. The dependence of basal gill and hepatic Pb concentrations on chub mass, Fulton condition index, hepatosomatic index, gonadosomatic index, sex or age was not observed, which excluded the possibility that increased Pb concentrations in the chub gills and liver at the site 2 could be associated to any of the biotic parameters. The fact that increases of Pb concentrations in both gill and hepatic cytosols of the European chub were spatially restricted to the one site with increased dissolved Pb concentration in the river water, without the dependence on the fish physiology, points to the importance and applicability of these parameters in the regular monitoring of the natural waters, as the promising indicators of Pb exposure in the river water.

lead ; hepatic and gill cytosol ; European chub ; Sutla River

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