The use of halophyte Spartina alterniflora for phytoremediation of Tributyltin (TBT) in coastal sediments
Aquatic superior plants exposed to coastal soils contaminated by inorganic and organic compounds, such as rhizomatous grass in intertidal areas Spartina alterniflora Loisel., Have shown potential to be used as phytoremediation. Tributyltin (TBT) is considered one of the most toxic organostanins released into the environment, capable of causing changes in the development of bivalves and the imposex effect on gastropods (masculinization of females), as well as affecting the human immune system. Since the 1960s, it has been used on a global scale as an active biocide in antifouling paints, and this practice was banned by the International Maritime Organization in 2008. A wide range of concentrations of TBT and other butyltins,resulting from its degradation (DBT and MBT) are detected in estuarine soils close to the main Brazilian ports, indicating its illegal use, commercialization and high environmental persistence. The present study investigated, through cultivation under controlled laboratory conditions, the tolerance and the ability to phytoremediate soils contaminated with tributyltin (TBT) from the grass S. alterniflora. S. alterniflora seedlings were grown in pots with 450g of fortified sediment with initial average concentrations of 0 (control), 179.04 ngTBT.g⁻¹ (low level) and 834.72 ngTBT.g⁻¹ (high level) for 90 days. On days 0, 60 and 90 of the experiment, the development of plants was quantified and the concentrations of butyl tin measured in the soil of pots with plants, as in additional pots without plants. S.alterniflora showed a high tolerance to sedimentary contamination by TBT. No plants died during the experiment. Stems initially planted (“mother plants”) and the various tillers formed grew vigorously (average height 40-70 cm and 3-6 live leaves per stem) in the control soil and contaminated with TBT. Mother plants in soils contaminated with TBT showed a small reduction in leaf renewal (possibly less metabolic activity) in the first 60 days. Leaf biomass in pots at all TBT levels has doubled in the last 30 days, but plants at low TBT level had significantly higher root biomass (p <0.05) and lesser allocations in leaf biomass than other TBT levels. . The presence of S.alterniflora resulted in a 196% greater degradation of total butyl tin at the high level of TBT contamination than in non-vegetated control vessels after 90 days of growth. The reductions observed in pots with and without plants were 72.05% and 25.35%, respectively. The rapid metabolism of TBT in contaminated soils and the increase in fractions of DBT and MBT in the bioassay in the first 60 days suggest an important role of microorganisms in the degradation of TBT. The marked reduction in DBT, MBT and total butyl tin levels in the last 30 days of cultivation in vegetated soils with a high level of TBT suggests an increase in phytoremediation capacity due to plant growth. Within the experimental conditions of S. alterniflora it was able to remedy soils contaminated by high levels of TBT.