Background, Aim and Scope:
Situated in the transboundary belt between Montenegro and Albania, the Lake Skadar is the largest freshwater reservoir in Southeastern Europe. Because of the wide range of endemic, rare or endangered plant and animal species it supports, Lake Skadar and its extensive adjacent wetlands are internationally recognised as a site of significance and importance (Ramsar site). Within the last 10 to 20 years, Lake Skadar was exposed to intensive pollution. For the assessment of the ecotoxic load of the sediments sampled in Lake Skadar, recently a triad approach was applied. Overall, a complex spectrum of ecotoxic loads was elucidated. The aim of the present study was to use plant-based bioassays for assessing the sediment quality of Lake Skadar in order to facilitate and complement the triad test battery. The newly developed sediment contact test with Myriophyllum aquaticum and the aquatic growth inhibition test with Lemna minor were applied to native sediments and pore water, respectively, allowing the investigation of different toxicity-effects caused by particle-bound pollutants as well as pollutants in the interstitial water. This investigation is the first application of the novel sediment contact test with Myriophyllum aquaticum to lake sediments.
Materials and Methods:
Sediment samples were taken from nine selected sites at Lake Skadar and investigated by the sediment contact assay with Myriophyllum aquaticum. The pore water was extracted from these sediment samples to be analysed in the aquatic growth inhibition test with Lemna minor. The results of the sediment contact tests were compared with each other and with those of the aquatic growth inhibition test.
Results:
The Myriophyllum sediment contact test revealed significant toxicity in the sediment samples from Radus and Kamenik, whereas the aquatic Lemna test showed inhibition effects in the samples from Sterbeq, Plavnica and Kamice. Comparable results for some of these sampling sites have been obtained before using the newly developed Danio rerio contact test and the Arthrobacter globiformis contact test. Analyses of the heavy metal content in the sediments revealed low or moderate contamination levels. Correlation analyses between the content of heavy metals in the sediments and growth inhibition of Myriophyllum aquaticum showed a significant correlation between Cr concentrations and growth inhibition.
Discussion:
Comparable findings are available for a German river system. In contrast, with Lemna minor no significant correlation between inhibition rates and concentration of metals could be observed.
Conclusions:
It was shown, that the newly developed sediment contact test with Myriophyllum aquaticum is applicable to lake sediments. Both, the sediment contact test with Myriophyllum aquaticum on whole sediments and the aquatic growth inhibition test with Lemna minor on pore water were found suitable for the detection of phytotoxic effects due to sediments. Myriophyllum aquaticum as test organism of the contact test is able to detect toxicity caused by particle-bound phytotoxic substances as well as pore water related ones. However, Lemna minor can only detect effects emanating from pore water. High variability of the results was observed between these two different exposure scenarios. Hence, none of the tests can replace the other one, and as a consequence both should be included into a test battery for the assessment of sediment toxicity.
Recommendations and
Perspectives:
Both plant assays were shown to be reliable tools for the evaluation of the eco-toxicological risk potentials of pore water and solid-phase sediment. They should become a complement to the standardised test battery generally used for comprehensive hazard assessment.
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