Formation of chloroform and tetrachloroethene by Sinorhizobium meliloti strain 1021

The mechanisms and organisms involved in the natural formation of volatile organohalogen compounds (VOX) are largely unknown. We provide evidence that the common and widespread soil bacterium Sinorhizobium meliloti strain 1021 is capable of producing up to 3338·6 ± 327·8 ng l(-1) headspace volume of chloroform (CHCl3 ) and 807·8 ± 13·5 ng l(-1)  headspace volume of tetrachloroethene (C2 Cl4 ) within 1 h when grown in soil extract medium. Biotic VOX formation has been suggested to be linked to the activity of halogenating enzymes such as haloperoxidases. We tested if the observed VOX formation by S. meliloti can be attributed to one of its chloroperoxidases (Smc01944) that is highly expressed in the presence of H2 O2. However, addition of 10 mmol l(-1) H2 O2 to the S. meliloti cultures decreased VOX formation by 52% for chloroform and 25% for tetrachloroethene, while viable cell numbers decreased by 23%. Interestingly, smc01944 gene expression increased 450-fold. The quantification of extracellular chlorination activity in cell suspension experiments did not provide evidence for a role of S. meliloti chloroperoxidases in the observed VOX formation. This suggests that a momentarily unknown mechanism which requires no H2 O2 might be responsible for the VOX formation by S. meliloti. Regardless of the underlying mechanism our results suggest that the soil bacterium S. meliloti might be an important source of VOX in soils.

SIGNIFICANCE AND IMPACT OF THE STUDY

Volatile organohalogen compounds (VOX) strongly influence atmospheric chemistry and Earth's climate. Besides anthropogenic emissions they are naturally produced by either abiotic or biotic pathways in various environments. Particularly in soils, microbial processes drive the natural halogen cycle but the direct link to microbial VOX formation has not been studied in detail yet. In this study we provide evidence that the common and widespread soil bacterium Sinorhizobium meliloti strain 1021 forms chloroform and tetrachloroethene. The potential contribution of S. meliloti to soil VOX release could significantly influence soil and atmospheric chemistry.

Oxidation of Fe(II)-EDTA by nitrite and by two nitrate-reducing Fe(II)-oxidizing Acidovorax strains

The enzymatic oxidation of Fe(II) by nitrate-reducing bacteria was first suggested about two decades ago. It has since been found that most strains are mixotrophic and need an additional organic co-substrate for complete and prolonged Fe(II) oxidation. Research during the last few years has tried to determine to what extent the observed Fe(II) oxidation is driven enzymatically, or abiotically by nitrite produced during heterotrophic denitrification. A recent study reported that nitrite was not able to oxidize Fe(II)-EDTA abiotically, but the addition of the mixotrophic nitrate-reducing Fe(II)-oxidizer, Acidovorax sp. strain 2AN, led to Fe(II) oxidation (Chakraborty & Picardal, 2013). This, along with other results of that study, was used to argue that Fe(II) oxidation in strain 2AN was enzymatically catalyzed. However, the absence of abiotic Fe(II)-EDTA oxidation by nitrite reported in that study contrasts with previously published data. We have repeated the abiotic and biotic experiments and observed rapid abiotic oxidation of Fe(II)-EDTA by nitrite, resulting in the formation of Fe(III)-EDTA and the green Fe(II)-EDTA-NO complex. Additionally, we found that cultivating the Acidovorax strains BoFeN1 and 2AN with 10 mM nitrate, 5 mm acetate, and approximately 10 mM Fe(II)-EDTA resulted only in incomplete Fe(II)-EDTA oxidation of 47-71%. Cultures of strain BoFeN1 turned green (due to the presence of Fe(II)-EDTA-NO) and the green color persisted over the course of the experiments, whereas strain 2AN was able to further oxidize the Fe(II)-EDTA-NO complex. Our work shows that the two used Acidovorax strains behave very differently in their ability to deal with toxic effects of Fe-EDTA species and the further reduction of the Fe(II)-EDTA-NO nitrosyl complex. Although the enzymatic oxidation of Fe(II) cannot be ruled out, this study underlines the importance of nitrite in nitrate-reducing Fe(II)- and Fe(II)-EDTA-oxidizing cultures and demonstrates that Fe(II)-EDTA cannot be used to demonstrate unequivocally the enzymatic oxidation of Fe(II) by mixotrophic Fe(II)-oxidizers.

Application of an optimized system for the well-defined exposure of human lung cells to trichloramine and indoor pool air

In this study an in vitro exposure test to investigate toxicological effects of the volatile disinfection by-product trichloramine and of real indoor pool air was established. For this purpose a set-up to generate a well-defined, clean gas stream of trichloramine was combined with biotests. Human alveolar epithelial lung cells of the cell line A-549 were exposed in a CULTEX(®) device with trichloramine concentrations between 0.1 and 40 mg/m(3) for 1 h. As toxicological endpoints the cell viability and the inflammatory response by the cytokines IL-6 and IL-8 were investigated. A decreasing cell viability could be observed with increasing trichloramine concentration. An increase of IL-8 release could be determined at trichloramine concentrations higher than 10 mg/m(3) and an increase of IL-6 release at concentrations of 20 mg/m(3). Investigations of indoor swimming pool air showed similar inflammatory effects to the lung cells although the air concentrations of trichloramine of 0.17 and 0.19 mg/m(3) were much lower compared with the laboratory experiments with trichloramine as the only contaminant. Therefore it is assumed that a mixture of trichloramine and other disinfection by-products in the air of indoor pool settings contribute to that effect.

Nanofiltration for enhanced removal of disinfection by-product (DBP) precursors in swimming pool water-retention and water quality estimation

Three nanofiltration (NF) membranes with a chlorine tolerance > or = 1 mg L-1 were applied to reduce DBPs and their precursors in swimming pool water. A lab scale plant with crossflow modules was installed in by-pass at the sand filter outlet of a swimming pool for a period of several weeks. The chlorine tolerances of the membranes SB90 and NP030 were found to be adequate for filtration under swimming pool water conditions over the given experimental period. Retention of dissolved organic carbon (DOC) and adsorbable organic halogens (AOX) were about 70% and 80% for SB90 and 50% and 40% for NP030, respectively. DOC accumulation in the pool and the expected fresh water consumption for a treatment system consisting of ultrafiltration (UF) and NF with backwash water treatment were estimated by mass balances based on the results. Mass balances were calculated also for a German public swimming pool with a conventional water treatment system (flocculation-sand filtration-chlorination) and were compared to DOC on-line measurements. Calculation of DOC mass balances for different UF-NF treatment scenarios showed that pool water quality could be improved significantly compared to the conventional treatment system.

Short-term tests with a pilot sewage plant and biofilm reactors for the biological degradation of the pharmaceutical compounds clofibric acid, ibuprofen, and diclofenac

The biodegradation of three active compounds of pharmaceuticals clofibric acid, ibuprofen, and diclofenac was investigated in short-term tests with a pilot sewage plant (PSP) and biofilm reactors (BFR, oxic and anoxic) as model systems for municipal sewage treatment. The PSP was characterized with respect to mixing behavior, the BFR with respect to biofilm content and sorption of the pharmaceutical compounds. The short-term experiments were carried out for 55 h in the PSP and for 48 h in the BFR. The concentration of the pharmaceuticals was in the microgram per liter range in presence of readily biodegradable substances in the milligram per liter range. Therefore, a too short time period and too low concentration to promote adaption of the microorganisms were applied. Under the operating conditions applied the biodegradation of the lipid lowering agent clofibric acid and the analgesic agents ibuprofen and diclofenac in the oxic BFR resembled that in the PSP. Clofibric acid and diclofenac were not eliminated and reached a level of approximately 95% of their initial concentration, whereas the concentration of ibuprofen was decreased to approximately 40% in the PSP and to approximately 35% in the oxic BFR. Both systems showed, therefore, an inherent ability for ibuprofen biodegradation. Elimination in the anoxic BFR resulted in a decrease of the concentration of all three substances to values between 60 and 80% of their initial concentration. In contrast to the PSP acetone revealed as inhibitor in the BFR. In both systems acetone was not degraded in the short-term tests.

Method optimization for the determination of carbonyl compounds in disinfected water by DNPH derivatization and LC-ESI-MS-MS

A method has been developed for quantitative determination of carbonyl disinfection by-products (DBP) from aqueous samples by derivatization with 2,4-dinitrophenylhydrazine combined with high-performance liquid chromatography (HPLC) and electrospray ionization (ESI) tandem mass spectrometry (MS-MS). The effect of excess of derivatization reagent and derivatization time, the effect of buffer and dry-gas temperature in the ESI process, and the effect of focus potential and collision energy in MS measurement are shown. Major fragment ions for compound identification on the basis of collision-induced dissociation (CID) mass spectra (MS) are given, as are common fragments for screening analyses by MS experiments such as the use of precursor ion scans. Detection limits in the microg x L(-1) range could be achieved by selected ion monitoring measurements without sample preconcentration. Solid-phase extraction improved the sensitivity by a factor of 25 to 250. The applicability of the method is illustrated by DBP analyses of samples from outdoor swimming pools after chlorination. Several carbonyl compounds, e.g. aldehydes, ketones, hydroxybenzaldehyde, and dicarbonyl compounds were identified.

Metabolites from the biodegradation of pharmaceutical residues of ibuprofen in biofilm reactors and batch experiments

The three metabolites hydroxyibuprofen (OH-Ibu), carboxyibuprofen (CA-Ibu), and carboxyhydratropic acid (CA-HA), also known from human metabolism of ibuprofen, could be identified in biodegradation experiments. Identification was based on EI mass spectra and comparison with literature data. Detection was performed by selective MS-MS measurements by GC-ion-trap MS and online methylation. Ibuprofen (Ibu), OH-Ibu, and CA-Ibu could be detected with a signal-to-noise ratio of 10:1 at a concentration of 2 nmol L(-1), CA-HA at 0.5 nmol L(-1). Degradation experiments in both biofilm reactors (BFR) and batch experiments with activated sludge (BAS) reveal OH-Ibu as the major metabolite under oxic conditions, and CA-HA under anoxic conditions. CA-Ibu was found under oxic and anoxic conditions almost only in the BAS. The metabolites together do not account for more than 10% of the initial concentration of Ibu.

Determination of the strong mutagen 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) and its analogues by GC-ITD-MS-MS

A new analytical method has been developed for the determination of chlorinated and brominated hydroxyfuranones. The method is based on separation by GC and selective determination of the compounds by use of an ion-trap mass detector. MS-MS fragmentation in an ion-trap detector can be regarded as an alternative to high-resolution mass spectrometry. Unique precursor ions were selected from the EI mass spectra and product-ion patterns were studied for a variety of collision energies. From these data, abundant mass transitions were selected for quantification and confirmation of compound identity. The method was applied to a spiked sample of chlorine-disinfected drinking water and it was found that the GC-MS-MS procedure is at least as sensitive and selective as previously published methods.

Sample cleanup and reversed-phase high-performance liquid chromatographic analysis of polar aromatic compounds in groundwater samples from a former gas plant

A method for the analysis of the polar aromatic compounds 1H-quinolin-4-one (Q), 10H-acridin-9-one (A), 5H-phenanthridin-6-one (P) and 9H-fluoren-9-one (F) in aqueous solutions has been developed. The method comprises steps for sample preparation (solid-phase extraction, cleanup) and analytical determination by means of reversed-phase high-performance liquid chromatography (RP-HPLC). For the cleanup step the suitability of two different sorbents (alternative A: silica gel, alternative B: LiChrolut EN) was investigated. Alternative B depicted several advantages, in particular higher sorbent capacity, faster and less complicated handling, higher recovery and better reproducibility. For Q, A and P, reproducibility of all method steps is better than 13%, with recovery rates ranging from 76% to 105% (n=3). Alternative B was applied to groundwater samples from a former gas plant. The analytes A and P could be detected at concentrations in the micro/l range.