Bioremediation of tributyltin contaminated sediment: degradation enhancement and improvement of bioavailability to promote treatment processes.

Bioremediation of tributyltin (TBT) contaminated sediment was studied and degradation enhancement and improvement of bioavailability were also investigated. In TBT spiked sediment, the half-life of TBT in the control sample, representing natural attenuation, was 578 d indicating its persistence. In the stimulated sample (pH 7.5, aeration and incubated at 28°C), the half-life was significantly reduced to 11 d. Further stimulation by nutrient addition (succinate, glycerol and l-arginine) or inoculation with Enterobacter cloacae (∼10(7) viable cells g(-1) of sediment) resulted in half-life reduction to 9 and 10d, respectively. In non-spiked sediment, the indigenous microorganisms were able to degrade aged TBT, but the extended period of contamination decreased the degradation efficiency. To improve bioavailability, addition of surfactant, adjustment of salinity and sonication were studied. The highest percentage solubilisation of TBT in water was obtained by adjusting salinity to 20 psu, which increased the solubility of TBT from 13% to 33%. Half-lives after bioavailability was improved were 5, 4 and 4d for stimulation, stimulation w/nutrient addition and stimulation w/inoculation, respectively. However, natural attenuation in the control sample was not enhanced. The results show that providing suitable conditions is important in enhancing TBT biodegradation, and bioavailability improvement additionally increased the rate and degraded amount of TBT. Unfortunately, nutrient addition and inoculation of the degrader did not enhance the degradation appreciably.

Enhancement of tributyltin degradation under natural light by N-doped TiO2 photocatalyst.

Photo-degradation of tributyltin (TBT) has been enhanced by TiO(2) nanoparticles doped with nitrogen (N-doped TiO(2)). The N-doped catalyst was prepared by a sol-gel reaction of titanium (IV) tetraisopropoxide with 25% ammonia solution and calcined at various temperatures from 300 to 600°C. X-ray diffraction results showed that N-doped TiO(2) remained amorphous at 300°C. At 400°C the anatase phase occurred then transformed to the rutile phase at 600°C. The crystallite size calculated from Scherrer's equation was in the range of 16-51 nm which depended on the calcination temperature. N-doped TiO(2) calcined at 400°C which contained 0.054% nitrogen, demonstrated the highest photocatalytic degradation of TBT at 28% in 3h under natural light when compared with undoped TiO(2) and commercial photocatalyst, P25-TiO(2) which gave 14.8 and 18% conversion, respectively.

The partition behavior of tributyltin and prediction of environmental fate, persistence and toxicity in aquatic environments.

Tributyltin (TBT) is one of the most toxic anthropogenic compounds introduced into the aquatic environment. It has a relatively high affinity for particulate matter, providing a direct and potentially persistence route of entry into benthic sediments. To understand TBT behavior, computational programs are an exceptionally helpful tool for modeling and prediction. EPISuite program was used for evaluation of the prediction data including fate, persistence and toxicity from the partition coefficient values. Without experimental data, the model is useful for prediction but is essentially a default model. A site specific assessment is possible by measuring the partition coefficients and entering the experimental values obtained into the model. This paper describes the results of a study undertaken to determine the partition coefficients and the effect of various parameters on such partition coefficients. The octanol-water partition coefficient (K(ow)) was determined by the OECD shake-flask method, with the logarithm values obtained ranging from 3.9 to 4.9 depending on salinity. The sediment-water partition coefficient (K(d)) was determined by ASTM method of generating Freundlich adsorption isotherms, the obtained values ranged from 88 to 4909 L kg(-1) depending on sediment properties, salinity, pH, and temperature. The experimental partition coefficient K(ow) and K(oc) (calculated from K(d)) were used as input data into the prediction program to provide accurate values for the natural samples in situ. The experimental prediction showed lower toxicity than the default model, but represent actual toxicity and accumulation at the natural site. Moreover, the environmental fate was significantly different when the experimental values and the default values were compared.

Environmental fate and partition co-efficient of oestrogenic compounds in sewage treatment process.

The presence of residual pharmaceuticals and environmental endocrine disrupters (EEDs) is increasingly significant due to their impact on human health and wildlife. Of the compounds implicated as EEDs, the most potent in their oestrogenic effect are the natural and synthetic oestrogens. As these compounds will be present in the sewage matrix, it is necessary to establish their fate during sewage treatment with a view of removal and safe disposal to avoid unnecessary exposure. Using methodology developed by the author this paper describes the results of a study undertaken to determine both the K(ow) and the adsorption characteristics of these oestrogens. The experimental values obtained were compared to a computational default model. However, there was disparity between the default model and the values determined experimentally. This was especially the case in the determination of the K(oc) which impacts directly on the sludge adsorbance potential. The calculated results ranged from log4.21 for beta-oestradiol to log4.68 for 17alpha-EE-3-ME, the experimental results were higher log(5.04-log5.83), respectively. The implications of the findings in terms of water recycling and sewage sludge disposal are also discussed.