The use of halophyte Sarcocornia ambigua (Michx.) M.A.Alonso & M.B.Crespo for Tributyltin (TBT) phytoremediation in coastal sediments
Tributyltin (TBT) is an organostannic compound that, for many years, has been used as the main active ingredient with biocidal function in the formulation of antifouling paints. Several studies have associated its use with metabolic imbalances in different groups of animals. Although this compound was banned worldwide from the formulation of antifouling paints by the International Maritime Organization in 2008, significant concentrations of TBT and its degradation products, dibutyltin (DBT) and monobutyltin (MBT), can still be found in port regions and coastal estuarine environments, including in Brazil. The toxicity of this compound is poorly described for the plant kingdom, especially when it comes to coastal plants.Some plants grow in contaminated areas and may perhaps be used to increase the process of remediation of organotin compounds in coastal sediments. Sarcocornia ambigua (Michx.) M.A.Alonso & M.B.Crespo (Amaranthaceae) is a halophyte with wide distribution in salt marshes and mangroves on the Brazilian coast, and also a possible phytoremediation agent of TBT. The objective of this work was to evaluate the ability of S. ambiguade to tolerate and decontaminate sediments with different concentrations of TBT. Seedlings of S. ambigua were grown for 78 days in pots with sediments without contamination (control; n = 15) and contaminated with two concentrations of TBT (low level: 67.4 ± 7.5 ngSn.g-1; high level 499 , 8 ± 52.1 ngSn.g-1; mean ± standard error; n = 15 vessels per treatment level). An additional group of vessels with sediment,but without plants, it was subjected to the same levels of TBT contamination and also monitored. The phytotechnical performance was monitored through biometric analyzes of height of the main stem, number of branches and length of the largest branch in three sampling times (0, 53 and 78 days). Contaminated sediments and control of pots with plants and without plants were collected in the same sampling period, with the organotins present identified and quantified. All plants exposed to the two TBT levels survived and grew vigorously, with no significant differences in the phytotechnical parameters in relation to the control plants. Regardless of the presence or absence of S. ambigua, the degradation of TBT in its metabolites (DBT and MBT) was observed shortly after the sediment fortification,at the beginning of the experiment (6-20% of total organotin; OTs), and increased markedly over the first 53 days (up to 42% of OTs), both at high and low levels of contamination. At the high level of contamination, the presence of S. ambigua significantly increased the degradation of organotin in the last 25 days of the experiment. At the end of the 78 days of cultivation, the average TBT value in vegetated sediments (142 ngSn.g-1) was 55.6% lower and significantly different from the average value in non-vegetated sediments (320 ngSn.g-1). Additionally, on this date, the average concentration of OTs in vegetated sediments reduced to 56.2% of the value of the first day of the experiment, while in non-vegetated sediments this reduction was only 13.1%. Consequently,the presence of plants also resulted in reduced concentrations of the metabolites DBT and MBT, which may have happened due to changes induced by the plant in the physical-chemical characteristics and / or microorganisms in the sediment, or even by incorporating the contaminant into the plant matrix. Halophyte S. ambigua showed tolerance to concentrations of organotins that are potentially capable of causing adverse effects to biota, found in sediments from Brazilian estuaries. This plant was able to potentiate the degradation of TBT, proving to be a possible phytoremediation agent of organotins.