Development of a sediment-contact test with rice for the assessment of sediment-bound pollutants.

Despite the key role of higher plants in aquatic ecosystems as functional and structural elements, sediment-contact tests with macrophytes are still scarce. Moreover, due to large differences in exposure routes for pollutants as well as in life cycles between the diverse taxa of macrophytes, sensitivities to pollutants vary between taxa. Therefore, the development of new test systems with aquatic macrophytes, in general, is favorable. This study proposes a protocol for a sediment-contact test with Oryza sativa and addresses the main question whether the rice plant is a suitable test organism for sediment toxicity testing with higher plants. As a first evaluation step, the variability and sensitivity of the test was investigated using spiked artificial sediments. Thus, according to the protocol, rice was exposed to arsenic-, cadmium-, chromium-, and nickel-spiked sediments. Additionally, it was investigated which classical endpoints for plant bioassays, such as root and shoot elongation, are suitable for this bioassay. As a second evaluation step, the test system was used for assessment of natural sediments. Thereupon, a sensitivity profile of the presented test protocol was analyzed in comparison to other plant-based test systems. Inhibition of root and shoot elongation turned out to be the most sensitive endpoints for single-substance testing in spiked artificial sediments. However, regarding testing of natural sediments, rice shoots responded more sensitive than rice roots. In conclusion, the rice plant clearly showed pollutant-induced effects on growth in sediments, and thus, it is likely a promising test organism to complement sediment-contact tests with higher plants.