Degradation of carbendazim by UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript> investigated by kinetic modelling

The transformation of the fungicide carbendazim (methyl-2 benzimidazole carbamate) induced by hydroxyl radical generated by the UV photolysis of H₂O₂ has been studied in dilute aqueous solution. The efficient reaction of hydroxyl radicals with carbendazim led to the rapid degradation of carbendazim. The study of reaction kinetics yielded a second order rate constant of 2.2±0.3 10⁹ M⁻¹ s⁻¹ for HO^· radicals with carbendazim. This value is in agreement with a high reactivity of HO^· radicals with carbendazim. Most degradation products were identified by high performance liquid chromatography mass spectrometry (HPLC-MS). In the presence of hydrogenocarbonate and carbonate ions, hydroxyl radicals were quenched and in turn carbonate radicals CO₃ ^·− were formed. Carbonate radicals are indeed known to react efficiently with compounds containing electron-rich sites such as nitrogen or sulfur atoms. The use of a kinetic modelling software gave evidence for the occurrence of such reactions with carbendazim. The second order rate constant of carbonate radical with carbendazim was equal to 6±2 10⁶ M⁻¹ s⁻¹. Electronic Publication     

Removal of carbamazepine from urban wastewater by sulfate radical oxidation

The occurrence of bioactive trace pollutants such as pharmaceuticals in natural waters is an emerging issue. Numerous pharmaceuticals are not completely removed in conventional wastewater treatment plants. Advanced oxidation processes may represent an interesting alternative to completely mineralize organic trace pollutants. In this article, we show that sulfate radicals generated from peroxymonosulfate/Co^II are more efficient than hydroxyl radicals generated from the Fenton’s reagent (H₂O₂/Fe^II) for the degradation of the pharmaceutical compound, carbamazepine. The second-order rate constant for the reaction of SO₄ ^·− with carbamazepine is 1.92·10⁹ M⁻¹ s⁻¹. In laboratory grade water and in real urban wastewater, SO₄ ^·− yielded a faster degradation of carbamazepine compared to HO^· . Under strongly oxidizing conditions, a nearly complete mineralization of carbamazepine was achieved, while under mildly oxidizing conditions, several intermediates were identified by LC–MS. These results show for the first time in real urban wastewater that sulfate radicals are more selective than hydroxyl radicals for the oxidation of an organic pollutant and may represent an interesting alternative in advanced oxidation processes.     

Photocatalytic oxidation of humic substances with TiO<Subscript>2</Subscript>-coated glass micro-spheres

The photocatalytic oxidation of humic substances in aqueous solutions and natural waters with TiO₂ attached to buoyant, hollow glass micro-spheres was studied. A maximum oxidation efficiency of 3.6 mg W^–1 h^–1 was achieved in neutral or alkaline media at a plane surface concentration of the catalyst attached to the micro-spheres of 25 g m^–2. Proceeding by different mechanisms in acidic and alkaline media, the photocatalytic oxidation efficiency did not benefit from an excessive presence of hydroxyl radical promoters, hydrogen peroxide and alkali.     

Degradation of azo dyes in water by Electro-Fenton process

The degradation of the azo dyes azobenzene, p-methyl red and methyl orange in aqueous solution at room temperature has been studied by an advanced electrochemical oxidation process (AEOPs) under potential-controlled electrolysis conditions, using a Pt anode and a carbon felt cathode. The electrochemical production of Fenton's reagent (H₂O₂, Fe²⁺) allows a controlled in situ generation of hydroxyl radicals (^·OH) by simultaneous reduction of dioxygen and ferrous ions on the carbon felt electrode. In turn, hydroxyl radicals react with azo dyes, thus leading to their mineralization into CO₂ and H₂O. The chemical composition of the azo dyes and their degradation products during electrolysis were monitored by high performance liquid chromatography (HPLC). The following degradation products were identified: hydroquinone, 1,4-benzoquinone, pyrocatechol, 4-nitrocatechol, 1,3,5-trihydroxynitrobenzene and p-nitrophenol. Degradation of the initial azo dyes was assessed by the measurement of the chemical oxygen demand (COD). Kinetic analysis of these data showed a pseudo-first order degradation reaction for all azo dyes. A pathway of degradation of azo dyes is proposed. Specifically, the degradation of dyes and intermediates proceeds by oxidation of azo bonds and aromatic ring by hydroxyl radicals. The results display the efficiency of the Electro-Fenton process to degrade organic matter. Electronic Publication     

Removal of the herbicide amitrole from water by anodic oxidation and electro-Fenton

Here we demonstrate that an aqueous solution of the herbicide amitrole can be completely depolluted at pH 3.0 by anodic oxidation and electro-Fenton process. Anodic oxidation gives faster degradation with a boron-doped diamond anode than with a Pt anode. Electro-Fenton with a Pt anode and 1 mmol l ^–1 Fe²⁺ as catalyst yields the quickest depollution. Amitrole decay always follows a pseudo first-order reaction. NO₃^– and NH₄⁺ are accumulated in the medium during mineralization, although volatile N-products are also formed. These environmentally friendly electrochemical treatments could be applied to the remediation of wastewaters containing amitrole.     

Nitrite and nitrate induced photodegradation of monolinuron in aqueous solution

Here we evidenced the photo-induced degradation of monolinuron, a phenylurea herbicide, through the 300–450 nm light excitation of nitrite and nitrate species. The degradation pathways were compared to those obtained under direct photolysis at 254 nm. When using NO₃^– and NO₂^– as photoinducers, hydroxyphenyl-substituted photodegradation products were found to be formed specifically through the involvement of OH° radicals. NO^– and NO₂-phenyl substituted compounds were also observed as a result of the production of NO° and NO₂° radicals. Half-lives of monolinuron in aqueous solutions were measured in various conditions of concentrations of substrate and inducer, oxygen content and pH.     

Degradation of the herbicide imazapyr by Fenton reactions

The degradation of the herbicide imazapyr has been carried out by three advanced oxidation processes involving iron ions as catalysts: Fentons reagent, photo-Fenton and electro-Fenton. We show that all processes are rapid and efficient. The kinetic rate constant was found to be k=5.4×10⁹ M^–1 s^–1. The mineralization of imazapyr is almost complete using the photo-Fenton and electro-Fenton processes.     

Fast and complete removal of the 5-fluorouracil drug from water by electro-Fenton oxidation

Cytostatic drugs are a troublesome class of emerging pollutants in water owing to their potential effects on DNA. Here we studied the removal of 5-fluorouracil from water using the electro-Fenton process. Galvanostatic electrolyses were performed with an undivided laboratory-scale cell equipped with a boron-doped diamond anode and a carbon felt cathode. Results show that the fastest degradation and almost complete mineralization was obtained at a Fe²⁺ catalyst concentration of 0.2 mM. The absolute rate constant for oxidation of 5-fluorouracil by hydroxyl radicals was 1.52 × 10⁹ M^?1 s^?1. Oxalic and acetic acids were initially formed as main short-chain aliphatic by-products, then were completely degraded. After 6 h the final solution mainly contained inorganic ions (NH₄ ⁺, NO₃ ^? and F^?) and less than 10% of residual organic carbon. Hence, electro-Fenton constitutes an interesting alternative to degrade biorefractory drugs.     

Thallium in marine plankton

Concentrations of thallium in phytoplankton (0.02 to 0.8 g g^–1), zooplankton (0.03 to 0.5 g g^–1) and ichthyoplankton (0.1 g g^–1) from the central Pacific were comparable , as were the atomic ratios of thallium to calcium (3x10^–6) and to potassium (1x10^–6) in those organisms. These relatively constant ratios, plus the biounlimited ocean profile of thallium, indicate that it is rapidly cycled through plankton in the same manner as potassium, its principal biogeochemical analogue. The higher atomic ratios of thallium to potassium in pelagic clays (6x10^–6) and ferromanganese nodules (4x10^–3) suggest that both biological transport processes and abiotic transport processes influence this trace element's oceanic cycle.     

Humic substances shorten human plasma prothrombin time

The prothrombin time of the normal human pooled plasma was shortened by Aldrich humic acid well water humic substances and lignin at final concentrations ranging from 5 × 10^–3 mg mL^–1 to 5 × 10^–2 mg mL^–1, with a maxmum effect at 1 × 10^–2 mg mL^–1. At this concentration the shortening was 5.5 s, 4.4 s, and 3.5 s by Aldrich humic acid, well water humic substances and lignin respectively. However, monomeric components of humic acid such as syringic acid, protocatechuic acid, pyrogallol, vanillic acid, gallic acid, resorcinol, ferulic acid, catechol, caffeic acid and p-coumaric acid did not have such ability to shorten prothrombin time at the same final concentration ranges. Certain reducing agents such as t-butanol (2.5 × 10^– –2.0 × 10^–2 mg mL^–1), glutathione (8.0 × 10^–2–1 .0 mg mL^–1), ascorbic acid (4.2 × 10^–2–5.0 × 10^–1 mg mL^–1) and dithiothreitol (1.0 × 10^–2–1.7 × 10^–1mg mL^–1) could prevent the shortening effects of humic substances or lignin on prothrombin time. These results suggested that humic substances and lignin with a polymerised structure had an ability to affect activities of some blood coagulating enzymes.     

Effect of the neurotransmitters dopamine,serotonin and norepinephrine on the ciliary activity of mussel (Mytilus edulis) larvae

The acute and long-term effects of neurotransmitters dopamine (DA), serotonin (SE) and norepinephrine (NE) on the feeding rates of Mytilus edulis veliger larvae were investigated through concentration-response curves. Increasing DA concentrations increasingly inhibited food uptake. Acute exposure to high levels of DA caused long-term inhibitory effects on feeding rates (10^–5 MDA) and growth rates (3x10^–4 MDA). Feeding activity was also inversely related to NE concentration. SE concentrations between 10^–8–3x10^–7 M supported enhanced feeding rates. Neither NE nor SE showed long-term inhibitory effects on feeding at concentrations <10^–4 M. These results were consistent with the observed effects of the different neurotransmitters on the swimming pattern of the larvae. The experimental evidence supports the model of ciliary control in adult mussels, involving dual innervation of the ciliated cells of the velum, with excitatory serotonergic and inhibitory dopaminergic fibers.     

Acute toxicities of eleven metals to early life-history stages of the yellow crab Cancer anthonyi

We report findings from the first laboratory experiments to assess toxicities of metals found in drilling muds to embryos and prezoeae of a brachyuran crab. Embryos of Cancer anthonyi are brooded externally on the abdomen of female crabs; thus, embryos may be continuously exposed to pollutants contained in sediments of contaminated benthic habitats. Lethal concentrations of metals to embryos after 7 d exposures were: iron and barium (sulfate), 1 000 mg l^–1; barium (chloride), 100 mg l^–1; aluminum and nickel, 10 mg l^–1; copper and lead, l mg l^–1; cadmium, chromium VI and manganese, 0.01 mg l^–1; mercury, 0.001 mg l^–1. All metals effectively retarded embryos from hatching at concentrations equal or lower to those causing mortality, except for cadmium. Particularly impressive was iron, which suppressed hatching at l to 10 mg l^–1, concentrations previously found non-deleterious to marine organisms and 100 times more dilute than concentrations causing significant embryo mortality. The effects of metals on embryos increased as a function of exposure duration. Embryo mortality was delayed for at least 120 h at concentrations 1.0 mg l^–1, with the exception of mercury. Lethal concentrations established at 96 h were meaningless for crab embryos, because acute toxic thresholds were not attained by that time. Larval survivorship to chromium VI, copper, and zinc increased following exposure of embryos to these metals at low concentrations (1.0 mg l^–1), suggesting induction of biochemical pathways for products which bind or metabolize metals. Identical exposures of embryos to lead failed to enhance subsequent larval survivorship, showing that inductions may be metal-specific. We suggest that exposures of brachyuran embryos at field sites and the success of their subsequent hatching in the laboratory may be a means of assessing environmental contamination otherwise difficult to monitor.     

Environmental impact of heavy metals (Fe, Ni, Cr, Co) in soils waters and plants of triada in euboea from ultrabasic rocks and nickeliferous mineralisation

Soil, water and vegetation samples were collected from the Triada area of Central Euboea and analysed for heavy metals in order to evaluate their environmental impact. The geology of the area studied includes ultrabasic rocks that are overlaid by Upper Cretaceous limestones whereas Fe–Ni mineralisation is intercalated between either the ultrabasic parent rocks or the karstified Jurassic/Triassic carbonates and the transgessive Upper Cretaceous limestones. All the samples were analysed for heavy metals by using atomic absorption spectroscopy. The heavy metal ranges (in g g^–1) for soils samples are: Ni 480–4000, Cr 240–2720, Co 40–208, Fe 24,000–380,000, Mn 46–1680, Pb 16–56, Zn 40–144, Cu 2–82. The values of soil samples of the Triada area are much higher than the values found for Ni, Cr, Co and Fe, in normal soils of the world. The heavy metal ranges (in g L^–1) for water samples are: Ni 19–24, Cr 19–476, Co <5, Fe <100, Mn <100, Mg 5.7–220.5, As 30–69, Cd <2, Pd <10, Zn 5–11, Cu 2–7. The water samples of the Triada area have Cr and Mg concentrations higher than the permittable values. The heavy metal ranges (in g g^–1) for vegetation samples are: Ni 1–135, Cr 0–24, Co 1–21.5, Fe 20–680, Mn 10–206, Cd 0–10, Pb 0–14, Zn 14–70, Cu 0–10.5. The vegetation samples of the Triada area have so high values of Ni, Cr and Co that are considered toxic. The intercorrelated elements Fe, Ni, Cr, Co of the Triada soils, waters and vegetation reflect their association with the ultrabasic rocks and with the Fe–Ni mineralisation.     

Response of the microbial food web to manipulation of nutrients and grazers in the oligotrophic Gulf of Aqaba and northern Red Sea

The control mechanisms within the pelagic microbial food web of the oligotrophic Gulf of Aqaba and the northern Red Sea were investigated in the spring of 1999. Nutrient conditions and potential grazer impact were manipulated in a series of dilution experiments. Ambient nutrient concentrations and autotrophic biomass were very low (0.23–1.21 µmol NO₃ l^–1, 0.06–0.98 µmol NH₄ l^–1, 1.08–1.17 µmol Si l^–1, 0.08–0.12 µmol P l^–1, 0.15–0.36 µg chlorophyll a l^–1). The planktonic community was characterized by low abundances [3.0–5.5×10⁵ heterotrophic bacteria ml^–1, 0.58–7.2×10³ ultraphytoplankton <8 µm ml^–1 (small eukaryotic photoautotrophs and Prochlorococcus sp., excluding Synechococcus sp.), 0.45–4.4×10⁴ Synechococcus sp. ml^–1, 0.32–1.2×10³ heterotrophic nanoflagellates ml^–1, 1.3–3.8×10³ phytoplankton >8 µm l^–1, 0.93–5.4×10² microzooplankton l^–1] and dominated by small forms (0.2–8 µm). Dinoflagellates and oligotrichous ciliates were the most common groups in initial samples among the phytoplankton >8 µm and microzooplankton, respectively. Results show that bottom-up and top-down control mechanisms operated simultaneously. Small organisms were vulnerable to grazing, with maximum grazing rates of 1.1 day^–1 on heterotrophic bacteria and 1.3 day^–1 on ultraphytoplankton. In contrast, algae >8 µm showed stronger signs of nutrient limitation, especially when the final assemblages were dominated by diatoms. Synechococcus sp. were not grazed and only showed moderate to no response to nutrient additions. The high spatial and temporal variation of our results indicates that the composition of the planktonic community determines the prevailing control mechanisms. It further implies that, at this transitional time of the year (onset of summer stratification), the populations fluctuate about an equilibrium between growth and grazing.Communicated by O. Kinne, Oldendorf/Luhe     

Ammonium excretion by the ophiuridOphiothrix fragilis as a function of season and tide

Ammonium excretion of a dense population (~1 500 individuals m^–2) of the ophiuridOphiothrix fragilis (Abildgaard) was measured in the Dover Straits (French coast) between May 1989 and March 1990: the excretion rate varied from 4.8 µg N g^–1 dry wt h^–1 in November to 12.8 µg N g^–1 dry wt h^–1 in June. Mean individual ammonium excretion,E, wasE=0.019t +1.26 (whereE=µg N individual^–1 andt=time in min;r=0.80;N=81). Variations in the ammonium excretion rate during a tidal cycle appeared to arise from variations in the duration of the suspension-feeding activity ofO. fragilis, which was governed by the strength of the tidal current. During short-term starvation, excretion was low (E=0.009t+1.47;r=0.91;N=17), increasing with increasing length of starvation [E=4.62lnt–2.5;r=0.95;N=17], as observed for other echinoderms; this could be due to catabolism of tissue. The daily ammonia flux from thisO. fragilis population to the water column was estimated at 41 mg N m^–2 d^–1.     

Biodegradation of phenylurea herbicide diuron by microorganisms from long-term-treated sugarcane-cultivated soils in Kenya

The phenylurea herbicide diuron [N-(3,4-dichlorophenyl)-N,N-dimethylurea] is widely used alone or in a broad range of herbicide formulations. Its degradation in sugarcane-cultivated soils which have been impacted by the herbicide through repeated applications was studied. Liquid culture experiments with diuron as the only carbon source led to the isolation of different bacterial strains capable of degrading diuron. The bacterial species belonging to the genera Bacillus, Vagococcus, and Burkholderia, identified through biochemical and molecular characterization, degraded diuron to different extents. The isolated Bacillus cereus, Vagococcus fluvialis, Burkholderia ambifaria, and Bacillus spp1 degraded diuron by 21%, 25%, 22%, and 19% of the initially applied concentration of 40?mg?L^?1, respectively, after 35 days of incubation in liquid culture media. Small amounts of 3,4-dichloroaniline and the de-methylated metabolite N-(3,4-dichlorophenyl)-N-methylurea were detected in liquid culture media. The combination of V. fluvialis and B. ambifaria showed an enhanced degradation of up to 30% of the initially applied concentration of 40?mg?L^?1. Degradation by pure isolates was low (18–25%) compared to the capacities of diuron degradation shown by the bacterial communities (58–74%). This study showed the presence of diuron degraders in sugarcane-cultivated soils impacted by diuron due to repeated applications.     

Influence of food concentration,temperature and salinity on the larval development ofBalanus amphitrite

Influence of food concentration (0.5, 1 and 2 x 10⁵ cell ml^–1 ofSkeletonema costatum), temperature (20 and 30°C) and salinity (15, 25 and 35) on the larval development ofBalanus amphitrite (Cirripedia: Thoracica) was examined. The mortality rate at 20°C was lower than at 30°C in general. Increase in food concentration from 0.5 to 1 x 105 cells ml^–1 improved the survival rate, but this was not evident when food concentration was increased to 2 x 105 cells ml^–1. The results indicate that food availability and temperature jointly determine the energy allocation for metamorphic progress. It was observed that the influence of the tested variables varied with instar. At 20 °C the mean duration of the second instar exceeded 3 d and was much longer than other instar durations. The fourth, fifth and sixth instars and the total naupliar period showed that the effect of different salinities at given food concentrations was negligible at 20°C, while at 30°C there was a marked decrease in duration with increasing salinity.     

Hydroxyl radical generation by redox cycling of some chemotherapeutic antibiotics

The anticancer drugs: adriamycin, farmorubicin and mitomycin C greatly enhance the generation of hydroxyl radicals (HO^.) from H₂O₂ in the presence of Co(II) ions (CoCl2) at pH 7.4 and 8, as measured by the deoxyribose assay. Catalase, hydroxyl radical scavengers (mannitol, cysteine, glutathione, thiourea, lactic dehydrogenase) inhibited the degradation of deoxyribose confirming that HO‐radicals are responsible for the degradation of the carbohydrate.     

Seasonal variations of organic-carbon and nutrient transport through a tropical estuary (Tsengwen) in southwestern Taiwan

This paper reports the fluvial fluxes and estuarine transport of organic carbon and nutrients from a tropical river (Tsengwen River), southwestern Taiwan. Riverine fluxes of organic carbon and nutrients were highly variable temporally, due primarily to temporal variations in river discharge and suspended load. The sediment yield of the drainage basin during the study period (1995–1996, 616 tonne km^–2 year^–1) was ca. 15 times lower than that of the long-term (1960–1998) average (9379 tonne km² year^–1), resulting mainly from the damming effect and historically low record of river water discharge (5.02 m³ s^–1) in 1995. The flushing time of river water in the estuary varied from 5 months in the dry season to >4.5 days in the wet season and about 1 day in the flood period. Consequently, distributions of nutrients, dissolved organic carbon (DOC) and particulate organic carbon (POC) were of highly seasonal variability in the estuary. Nutrients and POC behaved nonconservatively but DOC behaved conservatively in the estuary. DOC fluxes were generally greater than POC fluxes with the exception that POC fluxes considerably exceeded DOC fluxes during the flood period. Degradation of DOC and POC within the span of flushing time was insignificant and may contribute little amount of CO₂ to the estuary during the wet season and flood period. Net estuarine fluxes of nutrients were determined by riverine fluxes and estuarine removals (or additions) of nutrients. The magnitude of estuarine removal or addition for a nutrient was also seasonally variable, and these processes must be considered for net flux estimates from the river to the sea. As a result, nonconservative fluxes of dissolved inorganic phosphorus (DIP) from the estuary are –0.002, –0.09 and –0.59 mmol m^–2 day^–1, respectively, for dry season, wet season and flood period, indicating internal sinks of DIP during all seasons. Due to high turbidity and short flushing time of estuarine water, DIP in the flood period may be derived largely from geochemical processes rather than biological removal, and this DIP should not be included in an annual estimate of carbon budget. The internal sink of phosphorus corresponds to a net organic carbon production (photosynthesis–respiration, p–r) during dry (0.21 mmol m^–2 day^–1) and wet (9.5 mmol m^–2 day^–1) seasons. The magnitude of net production (p–r) is 1.5 mol m^–2 year^–1, indicating that the estuary is autotrophic in 1995. However, there is a net nitrogen loss (nitrogen fixation–denitrification < 0) in 1995, but the magnitude is small (–0.17 mol m^–2 year^–1).     

An assessment of lead absorption from soil affected by smelter emissions

The purpose of this study was to assess the oral bioavailability of lead in soil collected from a former smelter site in Sandy, Utah, USA. Sprague-Dawley rats (approximately 4 weeks of age, 5 of each sex in group) were given either soil lead or lead acetate mixed in a purified diet (AIN-93G ) at four different concentrations for 31 consecutive days. Food consumption measurements were used to compute mean daily lead exposures for the soil lead and lead acetate groups. The lead acetate treatment yielded higher concentrations of lead in the blood and bone than the soil lead treatment. Mean blood lead values ranged from below the detection limit (3 g dL^–1) to 27.25 g lead dL^–1 for the lead acetate groups at dose levels of 0.10–2.91 mg lead kg body weight^–1 and from below the detection limit to 8.8 g lead dL^–1 for the soil lead groups at doses of 0.11–3.43 mg lead kg body weight^–1. At these same doses, mean bone values ranged from 0.52 to 26.92 g lead g^–1 for the lead acetate groups and from 0.64 to 13.1 g lead g^–1 for the soil lead groups. Relative per cent bioavailability was estimated by modelling the dose-blood concentration curves for the lead acetate treatment and the dosed soil lead treatment, and then comparing doses that produce an equivalent blood lead concentration. The ratio of the doses of lead acetate and soil lead that produced the same tissue response (i.e., concentration) provided an index of relative bioavailability. For lead, the bioavailability of soil lead relative to lead acetate was 41% at a blood concentration of 6 g lead dL^–1.