Background, Aim and Scope:
Risk assessment for herbicides and the evaluation of contaminated sediments based on algae and the macrophyte Lemna sp. alone may underestimate the potential hazard of certain compounds. Therefore, various test systems with Myriophyllum spp. have been developed recently to assess the phytotoxicity in surface waters and natural sediments. In the present study, experiments investigating plant development of Myriophyllum spp. were performed in the laboratory under defined conditions and in mesocosms under environmental realistic exposure conditions in order to evaluate the suitability of this species as an additional standard test organism in risk assessment. This study provides data on the endpoints biomass, plant length, and root development.
Materials and Methods:
Six separate experiments were performed to investigate plant development of Myriophyllum spp. under control conditions. The main differences in the experiments were the complexity of the test systems ranging from simple laboratory experiments to complex outdoor mesocosm studies. At the start of each experiment uniform cuttings of Myriophyllum spp. were placed in vessels with or without sediments to reduce variability between replicates. The endpoints considered in this investigation were biomass (fresh weight of the whole plant), length of the main shoot, length of the side shoots, total length of the plant (calculated from the length of main and side shoots) and root formation. Root:shoot ratios were calculated as a further measure for plant development. Relative growth rate (RGR) based on plant length (RGLR) and on biomass (RGBR) were calculated.
Results:
Despite the various experimental conditions, comparable growth was obtained in all test systems and the variability of endpoints such as total length and biomass of plants was low. It was observed, that the RGR of M. spicatum in the simple laboratory test system with sediment were comparable to growth data obtained for M. verticillatum and M. spicatum grown in indoor and outdoor mesocosms indicating that Myriophyllum growth tends to increase by the addition of sediment. High variability was determined for the endpoints length of the side shoots, total root length and biomass of roots.
Discussion:
One challenge for a test design to investigate phytotoxicity on aquatic plants is to obtain good growth of the plants. From the results, it can be concluded that the experimental conditions in the various test systems were suitable to study plant development of Myriophyllum spp. since obtained growth rates were comparable between laboratory and field investigations. Another challenge for developing a plant biotest system is the definition of sensitive endpoints. Low variability is preferred in order to detect minor effects of chemicals or polluted sediments on plant development. In our studies, the variability of the endpoints biomass and total length of plant was low and therefore they have much potential as endpoints for assessing toxicity.
Conclusions:
Recommendations and
Perspectives:
Setting safe quality criteria for surface water and sediments is one of the challenges authorities are facing today. Myriophyllum spp. is recommended as suitable test species to investigate phytotoxicity in surface water and sediments. These results, thus, might serve as the basis for the compilation of a new harmonised guideline for ecotoxicological testing with aquatic macrophytes.
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