Photocatalytic degradation of 1,5-naphthalenedisulfonate on colloidal titanium dioxide.

Photocatalytic degradation of 1,5-naphthalenedisulfonate (NDS) was investigated by monitoring the absorption and emission spectral changes, chemical oxygen demand, total organic carbon (TOC) content as well as pH and sulfate concentration. Intermediates formed during the irradiation were also detected by liquid chromatographic-mass spectrometric analysis. The results obtained by the applied analytical techniques clearly indicate that the initial step of degradation is oxygenation (hydroxylation) of the starting surfactant resulting in the formation of an 8-hydroxy derivative, although desulfonation and some mineralization, that is, decrease of TOC indicating carbon dioxide generation, also take place at this stage. Further oxygenation and desulfonation lead to the destruction of the diaromatic naphthalene system, then to ring fission, producing diols, aldehydes, and carboxylic acids on the side-chains. A tentative scheme involving possible pathways of degradation is proposed, taking the intermediates detected by mass spectrometry into consideration. On the basis of the results of quantum chemical calculations, the most possible points of attack by HO radical were identified, supplementing the MS results, and elucidating the initial oxidation step in the degradation of NDS and the benzenesulfonate (BS) intermediate. Thus, in the case of NDS para position is favored for hydroxylation, while for BS, formation of the ortho-hydroxy derivative is preferred.

The ecotoxicological evaluation of Cylindrospermopsis raciborskii from Lake Balaton (Hungary) employing a battery of bioassays and chemical screening.

Ecotoxicity of four Cylindrospermopsis raciborskii strains (ACT 9502, ACT 9503, ACT 9504, ACT 9505) isolated from Lake Balaton (Hungary) was evaluated in four aquatic bioassays including the Thamnocephalus platyurus acute lethality test; Daphnia magna acute immobilization assay; D. magna feeding inhibition assay and Danio rerio embryo developmental toxicity assay, assisted by chemical screening for known toxins by HPLC-MS. For reference, we analyzed in parallel the toxin content and toxic effects of two previously characterized toxin-producing strains: the Australian cylindrospermopsin producer AQS C. raciborskii and the anatoxins producer Oscillatoria sp. PCC 6506. Bioassays were used to evaluate the overall toxicity of the hydrophilic bioactive metabolites pool synthesized by the selected cyanobacteria. Chemical screening has proven that the ACT C. raciborskii extracts investigated did not contained cylindrospermopsins and anatoxins. The relative toxicity of the ACT C. raciborskii aqueous extracts observed in each bioassay was comparable to the effects recorded for the anatoxins producer PCC 6506 strain while toxicity values (EC50/LC50) calculated for the AQS extract were in general one order of magnitude lower. Concerning sublethal effects of ACT C. raciborskii extracts to the D. rerio embryogenesis, the general morphological abnormality observed was a significant retardation of development. Overall, our results suggest that C. raciborskii populating Lake Balaton produce metabolites with significant bioactive potencies. Therefore, continued investigation of these unknown compounds is required.

Photocatalytic degradation of benzenesulfonate on colloidal titanium dioxide.

Titanium dioxide-mediated photocatalyzed degradation of benzenesulfonate (BS) was investigated by monitoring chemical oxygen demand (COD), total organic carbon (TOC) content, sulfate concentration, pH as well as the absorption and emission spectral changes in both argon-saturated and aerated systems. Liquid chromatography-mass spectrometry analysis was utilized for the detection of intermediates formed during the irradiation in the UVA range (λ(max) = 350 nm). The results obtained by these analytical techniques indicate that the initial step of degradation is hydroxylation of the starting surfactant, resulting in the production of hydroxy- and dihydroxybenzenesulfonates. These reactions were accompanied by desulfonation, which increases [H(+)] in both argon-saturated and aerated systems. In accordance with our previous theoretical calculations, the formation of ortho- and meta-hydroxylated derivatives is favored in the first step. The main product of the further oxygenation of these derivatives was 2,5-dihydroxy-benzesulfonate. No decay of the hydroxy species occurred during the 8-h irradiation in the absence of dissolved oxygen. In the aerated system much more efficient desulfonation and hydroxylation, moreover, a significant decrease of TOC took place at the initial stage. Further hydroxylation led to cleavage of the aromatic system, due to the formation of polyhydroxy derivatives, followed by ring fission, resulting in the production of aldehydes and carboxylic acids. Total mineralization was achieved by the end of the 8-h photocatalysis. It has been proved that in this photocatalytic procedure the presence of dissolved oxygen is necessary for the cleavage of the aromatic ring because hydroxyl radicals photochemically formed in the deaerated system too alone are not able to break the C-C bonds.

Screening the toxic potential of Cylindrospermopsis raciborskii strains isolated from Lake Balaton, Hungary.

Cylindrospermopsis raciborskii is becoming a major concern among cyanobacteria, due to its potential ability to produce toxic metabolites. We assessed the cytotoxic potential of four C. raciborskii strains (ACT 9502, ACT 9503, ACT 9504 and ACT 9505) isolated from Lake Balaton (Hungary), by lactate dehydrogenase (LDH) leakage measurements and by detecting morphological alterations in CHO-K1 (Chinese Hamster Ovary) cells. The Australian AQS (cylindrospermopsin producer) strain of C. raciborskii and purified cylindrospermopsin (CYN) were used as positive references in both the biochemical and morphological studies. Chemical analysis for known cyanotoxins was performed on aqueous extracts of ACT and AQS strains by the HPLC-MS technique. Comparing threshold values of LDH leakage data, different toxic potentials of cyanobacterial extracts are suggested in short term (3 h) and long (24 h) exposure regimes. In the acute (3 h) experiments the aqueous extract of the ACT 9505 strain proved to be most toxic (EC(50) = 7.4 mg mL(-1)), while after 24 h the ACT 9504 extract was the most effective (EC(50) = 0.65 mg mL(-1)). The extract of the AQS strain and the purified CYN exerted most of their toxic effects after 3 h exposure (EC(50) = 0.74 mg mL(-1), and 0.9 µg mL(-1) respectively). The morphological changes of CHO-K1 cells induced by the crude extracts of the ACT strains included fragmentation of the actin filaments then relocation of the depolymerized actin to the perinuclear region, resulting cell rounding and loss of adhesion. Exposure of CHO-K1 cells to the crude extract of the AQS strain, moreover, resulted cell shrinking and formation of filopodia, i.e. distinctly different cytological alterations from that induced by the ACT extracts and the purified CYN. Chemical analysis of the cyanobacterial crude extracts confirmed the presence of cylindrospermopsin in the extract of the AQS strain (8.5 mg CYN g(-1) dry weight), and none of the presently known cyanotoxins have been analytically confirmed in the extracts of the ACT strains isolated from the Lake Balaton. Although a significant toxicity of all four ACT C. raciborskii strains is confirmed by both biochemical and morphological studies, our results also pointed out the necessity of further studies to identify the toxic, but still unknown metabolic components produced by these cyanobacterial members of the phytoplankton communities.