Helen Keenan

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 Scherrers 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.

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.

Chitosan beads as barriers to the transport of azo dye in soil column

The development of chitosan-based materials as useful adsorbent polymeric matrices is an expanding field in the area of adsorption science. Although chitosan has been successfully used for the removal of dyes from aqueous solutions, no consideration is given to the removal of dyes from contaminated soils. Therefore this study focuses on the potential use of chitosan as an in situ remediation technology. The chitosan beads were used as barriers to the transport of a reactive dye (Reactive Black 5, RB5) in soil column experiments. Batch sorption experiments, kinetic and equilibrium, were performed to estimate the sorption behavior of both chitosan and soil. The chitosan beads were prepared in accordance with published literature and a synthetic soil was prepared by mixing quantities of sand, silt and clay. The synthetic soil was classified according to British Standards. Calcium chloride was used as tracer to define transport rates and other physical experimental parameters. Dye transport reaction parameters were determined by fitting dye breakthrough curves (BTCs) to the HYDRUS-1D version 4.xx software. Fourier Transform-Infra Red (FT-IR) spectroscopy was used to reveal the sorption mechanism. The study showed that chitosan exhibited a high sorption capacity (S(max)=238 mg/g) and pseudo-first sorption rate (k(1)=1.02 h(-1)) coupled with low swelling and increased retardation for the azo dye tested. Thus it has potential as a Permeable Reactive Barrier (PRB) for containment and remediation of contaminated sites.

Effects of salinity pH and temperature on the Octanol-water partition co-efficient of Bisphenol A

Bisphenol A (BPA) has been widely used as an industrial plasticizer and is considered an endocrine disrupting chemical (EDC). BPA can be released into the aquatic environment and magnify in the food chain, resulting in human exposure. To understand and predict the environmental fate and toxicity in the aquatic environment, the octanol-water partition coefficient (Kow) was determined at various salinity, pH and temperatures using the OECD guideline 107 shake flask method. With increasing salinity the log Kow of BPA at 25˚C increased from 3.44 to 3.55. The log Kow also changed at different pH, it decreased at pH > pKa, at pH between 6 and 8 a small increase (from 3.39 – 3.47) was observed which was then followed by a decrease at pH 10 (to 2.99). Increasing temperatures (between 25°C and 45°C) affect log Kow leading to decreased log Kow values (3.42 to 3.18). The log Kow for the natural seawater (salinity 29 psu and pH 8) was also determined at 3.52. The experimental and the default values were input into the prediction program EPI Suite™, which was used to assess environmental fate and toxicity of BPA. Using the experimental values enables a more accurate model for site specific samples can be defined. The model using the experimental Kow values of natural seawater indicated higher bioaccumulation and higher sediment adsorption but slightly lower aquatic toxicity than the default values. These findings imply that BPA in the marine environment is more bioaccumulative therefore has a greater biomagnification potential in fish species, particularly benthic feeders. This may adversely impact on human health and prove detrimental to humans that consume these marine species compared to similar species from a freshwater environment.

Measurement of polymer residuals in an alum sludge

This note outlines a method for measuring polymer residuals in an alum sludge on the basis of size exclusion chromatography (SEC). In our approach we established reference standards of polymer in a sludge supernatant and compared the derived chromatogram with that of the supernatant alone, this allowing us to clearly distinguish the polymer response from the response of the supernatant in the samples. Much of the work focused on a nonionic polymer using nanopure water as the mobile phase for the SEC. Later tests showed that the techniques, which were developed, could be applied to a wider variety of polymers using a 0.8 M sodium sulphate solution as the mobile phase. All polymers examined were excluded without interfering chromatographic mechanisms and the method could handle about 12 samples per hour. In the context of an alum sludge being conditioned with a nonionic polymer, the polymer-sludge interaction was characterised by an apparent adsorption isotherm.

Measurement of arsenic and gallium content of gallium arsenide semiconductor waste streams by ICP-MS

The chemistry of semiconductor wafer processing liquid waste, contaminated by heavy metals, was investigated to determine arsenic content. Arsenic and gallium concentrations were determined for waste slurries collected from gallium arsenide (GaAs) wafer processing at three industrial sources and compared to slurries prepared under laboratory conditions. The arsenic and gallium content of waste slurries was analyzed using inductively coupled plasma mass-spectrometry (ICP-MS) and it is reported that the arsenic content of the waste streams was related to the wafer thinning process, with slurries from wafer polishing having the highest dissolved arsenic content at over 1,900 mgL−1. Lapping slurries had much lower dissolved arsenic (< 90 mgL−1) content, but higher particulate contents. It is demonstrated that significant percentage of GaAs becomes soluble during wafer lapping. Grinding slurries had the lowest dissolved arsenic content at 15 mgL−1. All three waste streams are classified as hazardous waste, based on their solids content and dissolved arsenic levels and treatment is required before discharge or disposal. It is calculated that as much as 93% of material is discarded through the entire GaAs device manufacturing process, with limited recycling. Although gallium can be economically recovered from waste slurries, there is little incentive to recover arsenic, which is mostly landfilled. Options for treating GaAs processing waste streams are reviewed and some recommendations made for handling the waste. Therefore, although the quantities of hazardous waste generated are miniscule in comparison to other industries, sustainable manufacturing practices are needed to minimize the environmental impact of GaAs semiconductor device fabrication.

Development of a low-cost method of analysis for the qualitative and quantitative analysis of butyltins in environmental samples

Most analytical methods for butyltins are based on high resolution techniques with complicated sample preparation. For this study, a simple application of an analytical method was developed using High Performance Liquid Chromatography (HPLC) with UV detection. The developed method was studied to determine tributyltin (TBT), dibutyltin (DBT) and monobutyltin (MBT) in sediment and water samples. The separation was performed in isocratic mode on an ultra cyanopropyl column with a mobile phase of hexane containing 5% THF and 0.03% acetic acid. This method was confirmed using standard GC/MS techniques and verified by statistical paired t-test method. Under the experimental conditions used, the limit of detection (LOD) of TBT and DBT were 0.70 and 0.50 μg/mL, respectively. The optimised extraction method for butyltins in water and sediment samples involved using hexane containing 0.05–0.5% tropolone and 0.2% sodium chloride in water at pH 1.7. The quantitative extraction of butyltin compounds in a certified reference material (BCR-646) and naturally contaminated samples was achieved with recoveries ranging from 95 to 108% and at %RSD 0.02–1.00%. This HPLC method and optimum extraction conditions were used to determine the contamination level of butyltins in environmental samples collected from the Forth and Clyde canal, Scotland, UK. The values obtained severely exceeded the Environmental Quality Standard (EQS) values. Although high resolution methods are utilised extensively for this type of research, the developed method is cheaper in both terms of equipment and running costs, faster in analysis time and has comparable detection limits to the alternative methods. This is advantageous not just as a confirmatory technique but also to enable further research in this field.

The ecological complexity of the Thai-Laos Mekong River: I. Geology, seasonal variation and human impact assessment on river quality.

The objective of this study is to assess the variation of pollution in the Thai–Laos Mekong associated with seasonal dynamics concomitant with the natural geological features and human activities that impact on the adverse quality of the river. The complex ecology of the 1500 km stretch of the Thai-Laos Mekong River has been studied in this paper to understand the relationship with the geomorphology, with the sub-tropical monsoonal climate and the impact of human activity. Sub-surface geology controls the nature and extent of the drainage basin and of the river channel. The volume flow of the river varies naturally and dynamically in phase with the rainfall; traditional models based on steady state hydraulics are inappropriate. Continuous erosion of the river banks and bed generates a sediment load of impure silt, mica, quartz and clay minerals that inhibits light penetration and limits the primary productivity of the river. The river separates two countries at different stages of development; it flows through or close to eight non-industrial conurbations (Populations 350,000–2,000,000) but is otherwise sparsely populated. The river is used for subsistence agriculture, village transport, fishing including aquaculture and as a source of domestic water. Hydroelectricity is generated from the Laos tributaries. The river is a depository for partially treated urban waste and untreated village waste, hence populations of E.coli bacteria sometimes render the water unsuitable for drinking unless treated with the highest value of 240/100ml found at station 7 during the summer season of 2003. Furthermore the river is polluted by trace metals, notably cadmium and mercury, and by Polycyclic Aromatic Hydrocarbons (PAHs), which are particularly concentrated in the sediments. Previous work has shown that cadmium and mercury exceed the Probable Effect Level (PEL) values of Canadian Environmental Quality Guidelines and that the PAH concentrations were also greater than the Interim Sediment Quality Guidelines (ISQG). Consequently the fish stock, a vital source of protein for the local human population maybe seriously affected. As conflict between the demands of human activities will be exacerbated by the continuing development of the basin; monitoring must be continued and a better model of the rivers ecology is needed to predict the impact of development.

Isolation of tributyltin-degrading bacteria citrobacter braakii and enterobacter cloacae from butyltin-polluted sediment

Tributyltin compound (TBT) released into the aquatic environment is generally degraded by bacteria in water and sediment. The isolation of TBT-degrading bacteria from TBT polluted sediment leads to the indication of specific potential TBT degraders. Two new strains of bacteria designated as B2 and B3 were successfully isolated using glycerol medium containing tributyltin chloride (TBTC) at 130 μM from contaminated sediment collected from Bowling Basin in Glasgow. The observed degradation after 14 days of the microcosm from the sediment and the isolated bacteria were investigated at an initial concentration of 1 μM TBTC. It was found that TBT was degraded by the bacterial strains B2 and B3 at 8.3 and 16.9 %, respectively. The results indicate that B2 and B3 are effective as TBT degraders. EC50 of B2 and B3 in water were 88.73 and 112.53 μM TBTC, which were significantly higher than the concentration of TBT measured at the basin, suggesting a low effect of TBT on the growth and activity of bacteria. After identification using API 20E and 16S sequencing, the bacterial isolate strain B2 is Citrobacter braakii and B3 is Enterobacter cloacae. Therefore, this study has discovered two species of high resistance TBT degrader which have never been previously studied or isolated based upon TBT degradation ability.