Background, Aim and Scope:
Restoration of lakes and reservoirs with extensive cyanobacterial water bloom often require complex assessment of the sediment quality. Next to the chemical analysis of known pollutants, sediment bioassays should be employed to assess toxicity of the present contaminants and to make predictions of associated risk. Brno reservoir in the Czech Republic is a typical example of water body with long-term problems with cyanobacterial water blooms. Comprehensive assessment of reservoir sediment quality was conducted since successful reservoir restoration might require sediments removal. In this survey we have also examined the applicability of Tubifex tubifex and its sublethal biochemical markers for the assessment of direct sediment toxicity.
Materials and Methods:
This complex study included chemical analysis of contaminants (heavy metals, organic pollutants), ecotoxicity testing (tests with Daphnia magna, Pseudomonas putida, Sinapis alba, Scenedesmus subspicatus) and other parameters. We have tested in more detail the applicability of Tubifex tubifex as a test organism for direct evaluation of sediment toxicity. Survival test after 14 days exposure was complemented by assessment of parameters serving as biomarkers of sublethal effects (such as GPx, GR, GSH, and GST). The data matrix was subjected to multivariate analysis to interpret relationships between different parameters and possible differences among locations.
Results:
The multivariate statistical techniques helped to clearly identify the more contaminated upstream sites and separate them from the less contaminated and reference samples. The data document closer relationship of the results of direct sediment exposure in Tubifex tubifex test regarding mortality, but namely the sublethal endpoints to the sediment contamination than the results obtained with other test organisms exposed to sediment elutriates. Next to the reduction of T.tubifex survival, the sediments with organic pollution caused increase in glutathione content, increased activities of glutathione S-transferase and glutathione peroxidase in the exposed T.tubifex worms.
Discussion:
Results of our study confirm suitability of Tubifex tubifex for toxicity testing of raw waters and sediments. This longer-lasting direct contact test can be more sensitive and appropriate to reflect the lower level of pollution than the elutriate tests. Sensitive biochemical changes in T.tubifex including the elevation of GSH levels and GST activities reflect general stimulation of detoxification metabolisms in the presence of xenobiotics. The results also suggest an important role of glutathione and related enzymes in detoxification processes and possible involvement of oxidative stress in toxicity mechanism in benthic sediment-dwelling worms such as T.tubifex.
Conclusions:
The complex assessment has identified the more contaminated samples with locally increased concentration of organic pollutants and significant ecotoxicity. The direct sediment contact test with T.tubifex and especially the biochemical parameters corresponded better to the lower level of pollution than the other tests with sediment elutriates. Despite its greater time- and cost-demand the direct sediment contact test can provide more realistic picture of exposure.
Recommendations and
Perspectives:
Sediment bioassays should be always included as an integral part of the sediment quality assessment. The direct contact tests take into account also the more hydrophobic pollutants that are not easily available for the water elution but can be still accessible to the organisms. The T.tubifex test is a suitable option for contact sediment toxicity test also because these animals show measurable sublethal biochemical changes that can be associated with the exposure.
|
