Dibenzothiophene oxidation by horseradish peroxidase in organic media: effect of the DBT:H2O2 molar ratio and H2O2 addition mode

Its is well known that in the biodesulfurization (BDS) process the low water solubility of sulfur compounds hinders its transference from the oil phase to the cells being the rate-limiting step in the metabolism of dibenzothiophenes (DBT). Thus sulfur compounds derivatives with high water solubility could be more easily transported increasing the BDS efficiency. The present work performed a stepwise evaluation of the enzymatic oxidation of DBT by horseradish peroxidase (HRP). Reactions were carried out in monophasic organic media containing 25% (v/v) acetonitrile. The following parameters were evaluated: DBT:H2O2 molar ratio (1:1-1:20); H2O2 addition mode (single or stepwise); pH (6.0-8.0) and temperature (37-50 degrees C). Best results were observed in a reaction medium at pH 8.0 presenting HRP 0.06IUml(-1), DBT 0.267mM, DBT:H2O2 molar ratio of 1:20 (stepwise hydrogen peroxide addition) and incubated at 45 degrees C for 60min. Under these conditions 60% of DBT was converted into dibenzothiophene sulfoxide (12%) and dibenzothiophene sulfone (46%). The DBT oxidation rate observed in this work, of 5mmolmin(-1)g(-1) of HRP, was 250-fold higher than the BDS rate, 20mumolmin(-1)g(-1) of catalyst. As such a combined enzyme-microbial desulfurization process could be envisaged. Products were determined by HPLC RP C-18.     

Biodesulfurization of dibenzothiophene by growing cells of Pseudomonas putida CECT 5279 in biphasic media

Several studies have proven that natural or genetically modified bacteria, such as Pseudomonas putida strain, degrade recalcitrant organic sulfur compounds. However, from a practical point of view, the biodesulfurization (BDS) process has to be performed with really high proportions of organic solvents. In this work, the dibenzothiophene (DBT) was selected as recalcitrant model compound, and hexadecane as model organic solvent. It has been observed that P. putida CECT 5279 was able to desulfurize DBT even in the presence of 50% (v/v) of hexadecane. A concentration of 400 ppm of DBT was converted at a specific rate of generation of desulfurized final product, 2-hydroxybiphenyl (HBP), of 2.3 and 1.5 mg HBP L-1 (g DC L-1 h)-1 for 27% and 50% (v/v) of hexadecane, respectively. Finally, the Haldane kinetic model was used to describe the process evolution. The study is relevant as it has been proven that the strain CECT 5279 is a potential biocatalyst for developing an efficient BDS process.     

Methods for the preparation of a biodesulfurization biocatalyst using Rhodococcus sp

Several methods to prepare a biodesulfurization (BDS) biocatalyst were investigated in this study using a strain of Rhodococcus sp. 1awq. This bacterium could selectively remove sulfur from dibenzothiophene (DBT) via the "4S" pathway. DBT, dimethylsulfoxide (DMSO), sodium sulphate and mixed sulfur sources were used to study their influence on cell density, desulfurization activity, desulfurization ability, and the cost of biocatalyst production. In contrast to that observed from bacteria cultured in DBT, only partial desulfurization activity of strain 1awq was induced by DBT after cultivation in a medium containing inorganic sulfur as the sole sulfur source. The biocatalyst, prepared from culture with mixed sulfur sources, was found to possess desulfurization activity. With DMSO as the sole sulfur source, the desulfurization activity was shown to be similar to that of bacteria incubated in medium with DBT as the sole sulfur source. The biocatalyst prepared by this method with the least cost could remove sulfur from hydrodesulfurization (HDS)-treated diesel oil efficiently, providing a total desulfurization percent of 78% and suggesting its cost-effective advantage.     

Thermophilic desulfurization of dibenzothiophene and different petroleum oils by Klebsiella sp. 13T

Purpose

Biodesulfurization (BDS) has the potential to desulfurize dibenzothiophene (DBT) and its alkylated derivatives, the compounds that are otherwise refractory to hydrodesulfurization (HDS). Thermophilic microorganisms are more appropriate to be used for BDS applications following HDS. The aim of the present study was to isolate a thermophilic microorganism and to explore its commercial relevance for BDS process.

Methods

The desulfurizing thermophilic strain was isolated and enriched from various soil and water samples using sulfur free medium (SFM) supplemented with DBT. Microbiological and genomic approach was used to characterize the strain. Desulfurization reactions were carried out using DBT and petroleum oils at 45°C followed by different analytical procedures.

Results

We report the isolation of a thermophilic bacterium Klebsiella sp. 13T from contaminated soils collected from petroleum refinery. HPLC analysis revealed that Klebsiella sp. 13T could desulfurize DBT to 2-hydroxybiphenyl (2-HBP) at 45°C through 4S pathway. In addition, adapted cells of Klebsiella sp. 13T were found to remove 22?C53% of sulfur from different petroleum oils with highest sulfur removal from light crude oil.

Conclusion

Klebsiella sp. 13T is a potential candidate for BDS because of its thermophilic nature and capability to desulfurize petroleum oils.     

Aerobic biodegradation of organotin compounds in activated sludge batch reactors

The biodegradation behavior of four organotin (OT) compounds, namely tributyltin (TBT), dibutyltin (DBT), monobutyltin (MBT) and triphenyltin (TPhT), was studied in lab-scale activated sludge batch reactors. The activated sludge was spiked with the OT compounds at a level of 100 microg l(-1) as Sn. Determination of the OT compounds by GC-FPD after ethylation in the dissolved and particulate phase revealed that 24 h after the start of the experiments, almost the total of OT compounds has been removed from the dissolved phase and is associated with the suspended solids. Calculation of mass balance in batch reactors showed that OT compounds biodegradation was performed via a sequential dealkylation process. Removals due to biodegradation were differentiated according to the parent compound. In experiments with non-acclimatized biomass, a percentage of 27.1, 8.3, 73.8 and 51.3 was still present as TBT, DBT, MBT and TPhT, respectively, at the end of the experiment (18th day). Half-lives (t1/2) of 10.2 and 5.1 days were calculated for TBT and DBT, respectively, whereas apparent t1/2 values could not be determined for MBT and TPhT (t1/2>18 days). The capacity of activated sludge to biodegrade OT compounds in the absence of supplemental substrate indicated that these compounds can be metabolized as single sources of carbon and energy in activated sludge systems. Excluding TBT, the presence of low concentrations of supplemental substrate did not affect the biodegradation potential of activated sludge. The acclimatization of biomass on OT compounds enhanced significantly biodegradation, resulting in significant decreases of half-lives of OT compounds. As a result in the presence of acclimatized biomass, half-lives of 1.4, 3.6, 9.8 and 5.0 days were calculated for TBT, DBT, MBT and TPhT, respectively.     

Biodegradation capacity of tributyltin by two Chlorella species

Two microalgal species, Chlorella vulgaris and Chlorella sp., which showed high tributyltin (TBT) tolerant ability were investigated for their capabilities in degrading TBT at sublethal concentration. The distribution of TBT and its degraded products dibutyltin (DBT) and monobutyltin (MBT) in the incubation medium, extracellular surface and intracellular fraction were monitored during an exposure period of 14 days. Results showed that biosorption of TBT by the algal cell wall was the major mechanism in reducing 40% of the initial TBT from the medium in the first 2 days. The half-life of TBT incubated with C. vulgaris was 60 h while that of Chlorella sp. was 80 h. The occurrence of DBT at Day 1 in the culture medium provided direct evidence to the biodegradation of TBT by both Chlorella species. At the end of the experimental period, 27 and 41% of the original TBT were recovered as DBT and MBT in cultures of C. vulgaris, respectively. In contrast, DBT appeared to be the only degradation product of Chlorella sp. and only 26% of the original TBT was transformed to DBT. Despite the same genus, TBT was debutylated to a greater extent to MBT by C. vulgaris, while DBT was the end degradation product by Chlorella sp. The capability of such debutylating process therefore accounted for the higher tolerant ability of C. vulgaris than Chlorella sp.     

Input/output balance of estrogenic active compounds in a major municipal sewage plant in Germany

24 h samples of untreated and treated wastewater were taken in parallel from a modern municipal sewage plant in southern Germany in March and June 1998. After solid phase extraction, total estrogenic activity was quantitatively measured with a miniaturized E-screen assay and the levels of nine estrogenic phenolic chemicals analyzed by HRGC/LRMS. 17Beta-estradiol equivalent concentrations (EEQ) were 58 and 70 ng/l in the influent and 6 ng/l in the effluent, indicating that the load of estrogenic activity of the wastewater was reduced by about 90% in the sewage plant. Less than 3% of the estrogenic activity was found in the sludge. 4-t-octylphenol, 4-nonylphenol, bisphenol A, 2-hydroxybiphenyl, and 4-chloro-3-methylphenol were detected in the untreated wastewater at levels from 0.13 to 3.6 microg/l. 4-t-octylphenol, 4-nonylphenol, and bisphenol A were present in the effluent at concentrations from 0.16 to 0.36 microg/l, 2-hydroxybiphenyl and 4-chloro-3-methylphenol were not detectable. The contribution of the quantified levels of phenolic xenoestrogens to total estrogenic activity in the sewage was 0.7-4.3%.     

Specific detection of organotin compounds with a recombinant luminescent bacteria

Organotin compounds are widely used as biocides in marine and terrestrial environments. Several currently used techniques allow either the measurement of the chemicals or their effects on living organisms. Our current research focuses on the development of a complementary method based on a bacterial bioluminescence-based bioassay for the specific detection of organotin compounds. The performance of the bioassay was assessed. The Escherichia coli bacterial strain used in this study is specific for TBT and DBT (with Cl, Br or I as the halogen group) with the central tin atom important for light production. The assay is conducted after overnight culture of the bacterial strain, followed by 60 min of contact time with the organotin compound for significant light production. The detection limits were found to be 0.08 microM for TBT (26 microgl(-1)) and 0.0001 microM for DBT (0.03 microgl(-1)) with a linear range of one logarithm. The repeatability of the bioassay is 8% and the reproducibility for TBT and DBT was approximately 14%. Lyophilization of the strains did not significantly modify the detection limit as well as the range of detection. Applications of the bioassay to environmental samples are discussed.     

Toxic effects of anthraquinone and phenanthrenequinone upon Scenedesmus strains (green algae) at low and elevated concentration of CO2

Short-term (24h) experiments were performed to examine the effect of anthraquinone (ANTQ) and phenanthrenequinone (PHEQ) on two Scenedesmus armatus strains (B1-76 and 276-4d) grown in a batch culture system aerated with CO2 at a low (0.1%) or elevated (2%) concentration. ANTQ at concentrations within the range of 0.156-1.250 mg dm-3 inhibited the growth of B1-76 population in a concentration-dependent manner, and calculated EC50 for low-CO2 cells was 0.56 mg dm-3. The toxic effect of ANTQ on this strain was more pronounced in high-CO2 cells, where not only growth but also photosynthesis, respiration and SOD activity were significantly inhibited. In contrast, except for SOD activity, no ANTQ effects on strain 276-4d were found. PHEQ at concentrations within the range of 0.063-0.125 mg dm-3 inhibited the growth of B1-76 population in a concentration-dependent manner. The value of EC50 for low-CO2 B1-76 cells was 0.10 mg dm-3. PHEQ inhibited the growth of both strains regardless of CO2 concentration. In B1-76 cells affected by PHEQ, inhibition of photosynthesis was independent of the CO2 level, whereas the SOD activity was much higher in cultures aerated with 2% than with 0.1% CO2. Higher toxicity of PHEQ to strain 276-4d grown at 2% CO2 was accompanied by strong inhibition of photosynthesis, while in low-CO2 cells this process was slightly stimulated. The SOD activity in both low- and high-CO2 cells of strain 276-4d treated with PHEQ was 2-3 times higher compared with the controls. The pattern of SOD isoforms (PAGE analysis) obtained from cells exposed to ANTQ or PHEQ did not change compared with the controls, but the location of the SOD isoforms bands on gel was affected by the concentration of CO2. The results suggest that the strain-specific toxicity of ANTQ and PHEQ may result from oxidative stress. In addition, carbon dioxide appears to play an important role in the toxicity of quinones to algae.     

氧化镁烟气脱硫反应特性研究

利用实验室规模的鼓泡式反应装置,对比了碳酸钙、氧化镁和氧化镁/硫酸镁脱硫剂的反应活性,证实脱硫液中高浓度硫酸镁的存在是保证镁法脱硫效率高于钙法的重要因素,并考察了硫酸镁浓度、脱硫剂(氧化镁)浓度、烟气量、SO2浓度和吸收液温度等因素对脱硫效率的影响。结果表明,脱硫反应可以根据pH分为2个不同阶段;反应过程中脱硫效率随着硫酸镁浓度的增加而显著升高;烟气量增加将会导致脱硫效率有所下降;入口SO2浓度升高,脱硫效率下降;氧化镁浓度、温度对脱硫效率影响不显著。结合实验现象进行推断,氧化镁脱硫的反应过程受SO2在气液两相界面的传质扩散和其水解产物在液相的扩散控制。     

Lead exposure improves the tolerance of Spodoptera litura (Lepidoptera: Noctuidae) to cypermethrin

Many ecological factors such as heavy metals can affect the tolerance of herbivorous insects to chemical insecticide. Spodoptera litura larvae exposed to lead (Pb) (0-100 mg kg(-1) in artificial diet) did not inhibit their growth. After 96 h of Pb (0-100 mg kg(-1)) exposure, topical application and feeding of cypermethrin to S. litura decreased their mortality and increased weight gain. Moreover, the mortality of S. litura treated with 25 and 50 mg kg(-1) of Pb for five generations was significantly lower than control. In addition, Pb accumulation was detected in midgut, fat body, brain and hemolymph, and its highest level was in the midgut. Furthermore, there was a significant negative correlation between Pb accumulation in fat body and mortality after topical application of cypermethrin. After 96 h of Pb exposure, there was increase expression of detoxification enzymes (CYP9A39 and CYP6B47) in midgut and fat body of S. litura. Therefore, the tolerance of S. litura to cypermethrin is increased by Pb exposure at certain concentrations through Pb accumulation in body and the increase of CYP9A39 and CYP6B47 expression.     

Evaluation of mitogen-induced responses in marine mammal and human lymphocytes by in-vitro exposure of butyltins and non-ortho coplanar PCBs

The effects of exposure to butyltin compounds (BTs: tributyltin; TBT, dibutyltin; DBT and monobutyltin; MBT) and non-ortho coplanar PCBs (IUPAC 77, 126 and 169) on marine mammals and human lymphocyte were evaluated. Peripheral blood mononuclear cells (PBMCs) isolated from Dall's porpoises (Phocoenoides dalli), bottlenose dolphins (Tursiops truncatus), a California sealion (Zalophus californianus), a larga seal (Phocoa largha) and humans (Homo sapiens) were exposed at varying concentrations of BTs and coplanar PCBs. Concanavalin A (Con A)-stimulated mitogenesis found significantly suppressed (P<0.01) when the cells were exposed at 300 nM (89 ng/ml) of TBT and 330 nM of DBT (77 ng/ml), while MBT showed little cytotoxicity at treatment levels of up to 3,600 nM (620 ng/ml). BTs concentrations in the liver of Dall's porpoises from Japanese coastal waters ranged between 81-450 ng/g for TBT and 200-1,100 ng/g (wet wt.) for DBTs, which is greater than the cytotoxic levels registered in this study. In contrast, non-ortho coplanar PCBs did not suppress cell proliferation at concentrations of up to 30 nM (10 ng/ml). The residue levels of coplanar PCBs in the blubber of Dall's porpoises were 0.12-1.3 ng/g, which were one order of lower than those levels that do cell proliferation. When cells were exposed to a mixture of TBT/DBTand coplanar PCBs, the proliferation was significantly reduced to 33 nM DBT plus 34 nM CB-77 and 33 nM DBT plus 28 nM CB-169 mixtures, respectively. The investigations relating the contaminant-induced immunosuppression in marine mammals have been focused on persistent organochlorines such as PCBs. pesticides and dioxin compounds. However, this study suggested the possibility of BTs could also pose a serious threat to the immune functions in free-ranging marine mammals and humans.     

Influence of sorption to dissolved humic substances on transformation reactions of hydrophobic organic compounds in water. Part II: hydrolysis reactions

The effect of dissolved humic acid (HA) on two types of hydrolysis reactions was investigated: (I) dehydrochlorination of gamma-hexachlorocyclohexane (HCH) and 1,1,2,2-tetrachloroethane (TeCA) as a reaction involving hydroxide ions (OH(-)) and (II) hydrolysis of 1-octyl acetate (OA) which is catalyzed by H(+) at the applied pH value (pH 4.5). The rate of TeCA hydrolysis was not affected by addition of 2 g l(-1) of HA at pH 10 (k' = 0.33 h(-1)) but HCH hydrolysis was significantly inhibited (k' = 4.6 x 10(-3) h(-1) without HA and 2.8 x 10(-3)h(-1) at 2 g l(-1) HA). HCH is sorbed by 51% whereas TeCA sorption is insignificant at this HA concentration. Sorbed HCH molecules are effectively protected due to electrostatic repulsion of OH(-) by the net negative charge of the HA molecules. In contrast, OA hydrolysis at pH 4.5 (k' = 1.6 x 10(-5) h(-1)) was drastically accelerated after addition of 2 g l(-1) HA (k' = 1.1 x 10(-3) h(-1)). The ratio of the pseudo-first-order rate constants of the sorbed and the freely dissolved ester fraction is about 70. H(+) accumulation in the microenvironment of the negatively charged HA molecules was suggested to contribute to the higher reaction rate for the sorbed fraction in case of this H(+)-catalyzed reaction. Analogous effects from anionic surfactants are known as micellar catalysis.     

Assessment of adsorption behavior of dibutyltin (DBT) to clay-rich sediments in comparison to the highly toxic tributyltin (TBT)

The sorption behavior of dibutyltin (DBT) to four types of natural clay-rich sediments as a function of pH and salinity was studied. The strongest affinity of DBT was found to the montmorillonite-rich sediment, which is characterized by the highest specific surface area and cation exchange capacity of the four used sediments. Kd values range between 12 and 40 (l/kg) on simulated marine conditions (pH 8, salinity 32%). A maximum of DBT adsorption was found at a salinity of 0% and pH 6. Desorption occurred over the entire studied pH range (4-8) when contaminated sediments interact with butyltin-free water. The maximum of desorption coincided with the minimum of adsorption, and vice versa. The results of DBT adsorption are compared with tributyltin (TBT), and the mechanism of the adsorption process is discussed.     

In-situ partitioning of butyltin compounds in estuarine sediments

The in-situ solid/pore-water partitioning of tributyltin (TBT), dibutyltin (DBT) and monobutyltin (MBT) was determined for an estuarine sediment profile collected from a commercial marina. Total butyltin levels exceeded sediment quality guideline values, and were 220-8750 microg/kg for TBT, 150-5450 microg/kg for DBT and 130-4250 microg/kg for MBT. Pore-water butyltin concentrations ranged from 0.05 to 2.35 microg/l for TBT, 0.07-3.25 microg/l for DBT, and 0.05-0.53 microg/l for MBT. The partitioning of butyltin compounds between the sediment solid-phase and pore-water was described by an organic carbon normalised distribution ratio (D(OC)). The observed D(OC) values were similar for TBT, DBT and MBT, and were 10(5)-10(6) l/kg. Values for the Butyltin Degradation Index (BDI) were larger than 1 at depths greater than 10 cm below the sediment/water-column interface. This indicates that substantial TBT degradation has occurred in the sediments, and suggests that natural attenuation may be a viable sediment remediation strategy.     

连续式生物吸收工艺脱除二氧化硫

运用连续式生物吸收处理工艺,以废糖蜜发酵液作为碳源进行了微生物法去除SO2气体的研究,在简单粗放的实验条件下,研究了脱硫脱硫弧菌对较大气量SO2气体的去除效果,并对产物H2S在第二级生物反应器中的去除率进行了测定。实验结果表明,随着进气量由0.18 m3/h增大至5 m3/h,脱硫率会降低,但是随之提高搅拌速度和补料速度后,脱硫率又恢复到较高水平,当搅拌速度为590 r/min时,5 L生物反应液可以处理5 m3/h的SO2气体,1#反应器SO2去除率和2#反应器H2S去除率分别达到92%和98%以上。在气量增至5 m3/h时,1#和2#反应器补料流速分别为175 mL/h和200 mL/h时,没有亚硫酸盐和硫化物的积累,pH值和菌体浓度稳定,系统运行良好。     

Photocatalytic degradation of azo dyes by nitrogen-doped TiO2 nanocatalysts

This study examined the photocatalytic degradation of three azo dyes, acid orange 7 (AO7), procion red MX-5B (MX-5B) and reactive black 5 (RB5) using a new type of nitrogen-doped TiO2 nanocrystals. These newly developed doped titania nanocatalysts demonstrated high reactivity under visible light (lambda>390 nm), allowing more efficient usage of solar light. The doped titania were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Experiments were conducted to compare the photocatalytic activities of nitrogen-doped TiO2 nanocatalysts and commercially available Degussa P25 powder using both UV illumination and solar light. It is shown that nitrogen-doped TiO2 after calcination had the highest photocatalytic activity among all three catalysts tested, with 95% of AO7 decolorized in 1 h under UV illumination. The doped TiO2 also exhibited substantial photocatalytic activity under direct sunlight irradiation, with 70% of the dye color removed in 1h and complete decolorization within 3 h. Degussa P25 did not cause detectable dye decolorization under identical experimental conditions using solar light. The decrease of total organic carbon (TOC) and evolution of inorganic sulfate (SO4(2-)) ions in dye solutions were measured to monitor the dye mineralization process.     

Dissolution studies on TiO2 with organics

In this work the effect of organic reducing reagents, namely, ascorbic acid, oxalic acid and L-cysteine on dissolution of commercial TiO(2) has been investigated. Kinetic studies showed that a maximum of about 45% of TiO(2) was dissolved by ascorbic acid in 4h when oxide:acid molar ratio was kept at 1:2. The dissolution of TiO(2) increased with increase in ascorbic acid and oxalic acid concentration up to 0.15M in 4h (corresponding to molar ratio of oxide to acid of 1:3) and further addition did not affect the dissolution. Nearly 45% TiO(2) dissolution was obtained with ascorbic acid alone while oxalic acid yielded 40% dissolution. When oxalic acid was added along with ascorbic acid in equi-molar concentrations, dissolution of TiO(2) was enhanced to 60% in 2.5h but when cysteine was added to ascorbic acid the dissolution was about 50% in just 1h.     

Seasonal variation in the composition and concentration of butyltin compounds in marine fish of Taiwan

For the first time, strong evidence is presented to demonstrate that the accumulations of butyltin compounds (BTs) exhibit seasonal variations with respect to their compositions and concentrations in marine fishes. Measurements were made on the benthic ponyfish Leiogenathus splendens and lizardfish Trachinocephalus myops inhabiting the west coast of Taiwan. In the whole body samples of the ponyfish, BT concentrations ranged from 236 to 2501 ng/g wet wt, with those in winter considerably higher than in the other seasons (p < 0.05 ). In a similar vein, proportions of mono- (MBT), di- (DBT) and tributyltin (TBT) differed significantly (p < 0.001) depending upon the season, with TBT (75 and 50%) dominant in winter and spring and DBT (37 and 57%) and MBT (42 and 24%) dominant in summer and autumn, respectively. In the lizardfish, the concentrations of BTs were one to two orders of magnitude higher in the liver than in the muscle, i.e. 3058-11,473 vs. 36-159 ng/g wet wt, respectively. Concentrations of MBT, DBT and TBT in the muscle ranged, respectively, from 5 to 14, 8 to 35 and 23 to 110 ng/g wet wt, with the major compound being TBT (57-69%) in all seasons. However, in the liver, DBT concentrations, ranging from 992 to 7797 ng/g wet wt, differed seasonally with a descending order of autumn>summer>spring (p < 0.05). Meanwhile, TBT (41%) was predominant in spring, whereas DBT (50 and 68%) was most heavily concentrated in summer and autumn (p < 0.001). Seasonally mediated physiological changes, such as dilution due to growth and metabolic compensation, may play important roles in forming different BT accumulation patterns among seasons and organisms.     

Determination of butyltins in harbour sediment and water by aqueous phase ethylation GC-ICP-MS and hydride generation GC-AAS

Sediment and water samples have been collected between 1992 and 1995 for evaluating butyltin contamination in two marinas from the coastal area in The Netherlands, two years after the ban of TBT. Sediments extracts were analysed by capillary gas chromatography-inductively coupled plasma-mass spectrometry. Sediment concentrations for TBT showed no trend of decrease between 1992 and 1995 and were extremely high in the marina secluded from tidal action; 17.5 +/- 8.0 microg g(-1) and much lower for the marina with tidal action; 0.117 +/- 0.073 microg g(-1). High ratios between TBT and DBT in the sediments indicate that degradation mechanisms in the sediments are of minor importance. Dissolved butyltin compounds were analysed in water by means of gas chromatography-atomic absorption spectrometry. Water concentrations of TBT showed no clear trend of decrease between 1992 and 1995 and were high in the marina secluded from tidal action; 139 +/- 166 ng litre(-1) but much lower for the marina with tidal action; 48 +/- 98 ng litre(-1). An active degradation mechanism during summer periods was indicated by low (<1) TBT/DBT ratios in the water phase of the marina secluded from tidal action.