Investigations on Boron contaminated sediment (Tuscany, Italy): Phytotoxicity and phytoextraction test

The greatest part of Cecina river basin is located in the geothermal zone of Larderello, where for about a hundred years mine activities were practiced and the geothermoelectric industry spilled in the Possera and Pavone creeks (tributaries of Cecina River) until the 70'es. Recent studies indicates that contamination is still present in certain areas of the basin. The study was performed analyzing total and available B fraction in sediment samples. The sediment was investigated for its genotoxicity effect on plants by micronuclei assay on Vicia faba. In micronuclei test the cytological analysis on primary root tips (3rd day) showed no effect on mitotic activity of meristematic centers however, a big presence of micronuclei was found (a frequency of 5% of micronuclei in contaminated soils compared to 1% in control). Moreover, mitotic anomalies, as chromosome bridges, chromosome lagging and c-metaphases, were found. Phytoextraction tests was performed to assess boron-tolerant plant species able to reduce the content of this metal in the sediments. Experiments were conducted in the laboratory and on the lysimeter scale. At laboratory scale three high biomass crops (B. juncea, Z. mays and H. annuus) grew in the most contaminated sample in two consecutive grown (each of 35-day period). Results showed that B. juncea was able to remove about 45% of the initial available B fraction in only two growing cycles. On the lysimeter scale, B. juncea and nitrogen fertilization were tested at three different doses and plants were allowed to grow until the end of the vegetative phase (70 days). Results showed that nitrogen application had effectively increased plant biomass production, while boron (B) uptake was not affected. Total B phytoextracted increased threefold when the highest nitrogen dose was applied. Phytotoxicity on Brassica plants was also evaluated by biochemical parameters. The activity of antioxidant enzymes SOD, APX and PPX increased, whereas CAT decreased with respect to the control (B. juncea plants grown in uncontaminated sediment). These alterations suggest that B induced oxidative stress. Moreover, addition of N progressively mitigated the alteration of enzymatic activity, thus suggesting that N can alleviate the oxidative stress. Results suggest that appropriate N fertilization increases phytoremediation efficiency by increasing the aerial B-rich biomass. Phytoextraction technology could reduces boron level in sediments from the Cecina basin (Tuscany, Italy) and limits its diffusion through the environment. Moreover, B-rich biomass may provide an additional value to the process as a source of bioenergy, stock fodder, or as an amendment for B-deficient soil. Keywords: Boron contamination, genotoxicity, sediment, phytoextraction, Vicia faba l., N fertilization, oxidative stress Acknowledgements: Authors thanks to I. Rosellini and M. Scatena for their technical assistance.