One of the shallowest, most intense oxygen minimum zones (OMZs) is found in the eastern tropical South Pacific, off northern Chile and southern Peru. It has a strong oxygen gradient (upper oxycline) and high N 2 O accumulation. N 2 O cycling by heterotrophic denitrification along the upper oxycline was studied by measuring N 2 O production and consumption rates using an improved acetylene blockage method.

Abstract. The mechanisms of microbial nitrous oxide (N 2 O) production in the ocean have been the subject of many discussions in recent years. New isotopomeric tools can further refine our knowledge of N 2 O sources in natural environments. This study compares hydrographic, N 2 O concentration, and N 2 O isotopic and isotopomeric data from three stations along a coast-perpendicular transect in the South Pacific Ocean, extending from the center (Sts. GYR and EGY) of the subtropical oligotrophic gyre (∼26 • S; 114 • W) to the upwelling zone (St. UPX) off the central Chilean coast (∼34 • S). Although AOU/N 2 O and NO − 3 trends support the idea that most of the N 2 O (mainly from intermediate water (200-600 m)) comes from nitrification, N 2 O isotopomeric composition (intramolecular distribution of 15 N isotopes) expressed as SP (site preference of 15 N) shows low values (10 to 12‰) that could be attributed to the production through of microbial nitrifier denitrification (reduction of nitrite to N 2 O mediated by ammonium oxidizers). The coincidence of this SP signal with high -stability layer, where sinking organic particles can accumulate, suggests that N 2 O could be produced by nitrifier denitrification inside particles. It is postulated that deceleration of particles in the pycnocline can modify the advection -diffusion balance inside particles, allowing the accumulation of nitrite and O 2 depletion suitable for nitrifier denitrication. As lateral advection seems to be relatively insignificant in the gyre, in situ nitrifier denitrification could account for 40-50% of the N 2 O produced in this Correspondence to: J. Charpentier (jcharpentier@profc.udec.cl) layer. In contrast, coastal upwelling system is characterized by O 2 deficient condition and some N deficit in a eutrophic system. Here, N 2 O accumulates up to 480% saturation, and isotopic and isotopomer signals show highly complex N 2 O production processes, which presumably reflect both the effect of nitrification and denitrification at low O 2 levels on N 2 O production, but net N 2 O consumption by denitrification was not observed.

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The dry-wet cycle is a common climatic phenomenon in the tropical regions of monsoon-affected Asia. An intermittent increase in N2O was clearly observed in the Bang Nara River, with a tropical swamp catchment at the beginning of rainy season of November 1997. The intramolecular distribution of isotopes clearly demonstrated that nitrification is the major process for the production of N2O. Using stable isotope data, the production mechanism of N2O in the study areas was found to vary in time and space with changes in the redox boundary along the water flow.

The biogeochemical mechanism of bacterial N 2 O production in the ocean has been the subject of many discussions in recent years. New isotopomeric tools can help further knowledge on N 2 O sources in natural environments. This research shows and compares hydrographic, nitrous oxide concentration, and N 2 O isotopic and isotopomeric 5 20 cesses, which presumably reflect both the effect of nitrification and denitrification at low oxygen levels on N 2 O production, but non N 2 O consumption by denitrification was observed.

This study aimed to investigate the antibiotic concentration at each stage of treatment and to evaluate the removal efficiency of antibiotics in different types of secondary and advanced treatment, as well as the effects of the location of their discharge points on the occurrence of antibiotics in surface water. Eight target antibiotics and four hospital wastewater treatment plants in Bangkok with different conventional and advanced treatment options were investigated. Antibiotics were extracted by solid phase extraction and analysed by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The antibiotic with the highest concentration at influent was cefazolin at 13,166 ng/L, while the antibiotic with the highest concentration at effluent was sulfamethoxazole at 1,499 ng/L. The removal efficiency of antibiotics from lowest to highest was sulfamethoxazole, piperacillin, clarithromycin, metronidazole, dicloxacillin, ciprofloxacin, cefazolin, and cefalexin. The adopted conventional treatment systems could not completely remove all antibiotics from wastewater. However, using advanced treatments or disinfection units such as chlorination and UV could increase the antibiotic removal efficiency. Chlorination was more effective than UV, ciprofloxacin and sulfamethoxazole concentration fluctuated during the treatment process, and sulfamethoxazole was the most difficult to remove. Both these antibiotics should be studied further regarding their contamination in sludge and suitable treatment options for their removal.

The goals of this study were to determine the concentrations of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) in textiles and to determine PFOS and PFOA contamination in textile washing water. Quantification analysis was performed by high performance liquid chromatography coupled with tandem mass spectrometry. Analysis of 32 textile samples by methanol extraction revealed that the average concentrations of PFOS and PFOA were 0.18 µg m(-2) (0.02 to 0.61 µg m(-2)) and 2.74 µg m(-2) (0.31 to 14.14 µg m(-2)), respectively. Although the average concentration of PFOS found in textile samples was below European Union (EU) Commission regulations (<1 µg m(-2)), the average concentration of PFOA was 2.74 µg m(-2), and 68.75% of textile samples had PFOA concentrations exceeding 1 µg m(-2). Thus, based on these results, the concentration of PFOA in products should also be regulated. Experiments on PFOS and PFOA leaching into washing water were conducted. The maximum concentrations of PFOS and PFOA were measured after the first washing; the concentrations gradually decreased with each subsequent washing. PFOS and PFOA migrated from textiles and were released into the environment, with disappearance percentages of 29.8% for PFOS and 99% for PFOA. The data presented in this study showed that textiles could be a significant direct and indirect source of PFOS and PFOA exposure for both humans and the environment.

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