Determination of 2,6-dichlorobenzamide and its degradation products in water samples using solid-phase extraction followed by liquid chromatography-tandem mass spectrometry

A sustainable composite of rice-paper/BaMoO4 nanoparticles for the photocatalytic elimination of the recalcitrant 2,6-dichlorobenzamide (BAM) pesticide in drinking water and its mechanisms of degradation

This research reports the use of biodegradable and flexible composites for the removal of the 2,6-dichlorobenzamide (BAM) pesticide from drinking water. Rice paper (a biodegradable substrate) and Ag/BaMoO4 (MOBA) nanoparticles were employed to fabricate these composites. The SEM images showed that the MOBA nanoparticles with sizes of 300-800 nm decorated the surface of the biodegradable substrate and formed porous agglomerates, which have sizes of 1-3 μm. The MOBA powders were dispersed in drinking water polluted with BAM and were exposed to 4 h of UV-VIS irradiation, producing a maximum degradation of 82% for the BAM. Moreover, the flexible and biodegradable rice/MOBA composite produced a maximum removal percentage of 95% for the BAM. Also, we studied the effect of pH of the initial solution utilizing both powders and composites. From here, we found that a pH of 10 leads to a complete degradation of BAM after 4h, while a pH of 3 degraded only 37-47% of BAM for the same reaction time. According to the scavenger experiments, the •OH radical and the h+ were the main oxidizing agents for the BAM. Overall, the biodegradable photocatalytic composites are a reliable and a low-cost alternative to eliminate pesticides from the drinking water and can find application in water purification processes.

Toward Improved Bioremediation Strategies: Response of BAM-Degradation Activity to Concentration and Flow Changes in an Inoculated Bench-Scale Sediment Tank

Compound-specific isotope analysis (CSIA) can reveal mass-transfer limitations during biodegradation of organic pollutants by enabling the detection of masked isotope fractionation. Here, we applied CSIA to monitor the adaptive response of bacterial degradation in inoculated sediment to low contaminant concentrations over time. We characterized Aminobacter sp. MSH1 activity in a flow-through sediment tank in response to a transient supply of elevated 2,6-dichlorobenzamide (BAM) concentrations as a priming strategy and took advantage of an inadvertent intermittence to investigate the effect of short-term flow fluctuations. Priming and flow fluctuations yielded improved biodegradation performance and increased biodegradation capacity, as evaluated from bacterial activity and residual concentration time series. However, changes in isotope ratios in space and over time evidenced that mass transfer became increasingly limiting for degradation of BAM at low concentrations under such stimulated conditions, and that activity decreased further due to bacterial adaptation at low BAM (μg/L) levels. Isotope ratios, in conjunction with residual substrate concentrations, therefore helped identifying underlying limitations of biodegradation in such a stimulated system, offering important insight for future optimization of remediation schemes.

Mass-Transfer-Limited Biodegradation at Low Concentrations-Evidence from Reactive Transport Modeling of Isotope Profiles in a Bench-Scale Aquifer

Organic contaminant degradation by suspended bacteria in chemostats has shown that isotope fractionation decreases dramatically when pollutant concentrations fall below the (half-saturation) Monod constant. This masked isotope fractionation implies that membrane transfer is slow relative to the enzyme turnover at μg L^-1 substrate levels. Analogous evidence of mass transfer as a bottleneck for biodegradation in aquifer settings, where microbes are attached to the sediment, is lacking. A quasi-two-dimensional flow-through sediment microcosm/tank system enabled us to study the aerobic degradation of 2,6-dichlorobenzamide (BAM), while collecting sufficient samples at the outlet for compound-specific isotope analysis. By feeding an anoxic BAM solution through the center inlet port and dissolved oxygen (DO) above and below, strong transverse concentration cross-gradients of BAM and DO yielded zones of low (μg L^-1) steady-state concentrations. We were able to simulate the profiles of concentrations and isotope ratios of the contaminant plume using a reactive transport model that accounted for a mass-transfer limitation into bacterial cells, where apparent isotope enrichment factors *ε decreased strongly below concentrations around 600 μg/L BAM. For the biodegradation of organic micropollutants, mass transfer into the cell emerges as a bottleneck, specifically at low (μg L^-1) concentrations. Neglecting this effect when interpreting isotope ratios at field sites may lead to a significant underestimation of biodegradation.

Solid-phase extraction method for stable isotope analysis of pesticides from large volume environmental water samples

Compound-specific isotope analysis (CSIA) is a valuable tool for assessing the fate of organic pollutants in the environment. However, the requirement of sufficient analyte mass for precise isotope ratio mass spectrometry combined with prevailing low environmental concentrations currently limits comprehensive applications to many micropollutants. Here, we evaluate the upscaling of solid-phase extraction (SPE) approaches for routine CSIA of herbicides. To cover a wide range of polarity, a SPE method with two sorbents (a hydrophobic hypercrosslinked sorbent and a hydrophilic sorbent) was developed. Extraction conditions, including the nature and volume of the elution solvent, the amount of sorbent and the solution pH, were optimized. Extractions of up to 10 L of agricultural drainage water (corresponding to up to 200 000-fold pre-concentration) were successfully performed for precise and sensitive carbon and nitrogen CSIA of the target herbicides atrazine, acetochlor, metolachlor and chloridazon, and metabolites desethylatrazine, desphenylchloridazon and 2,6-dichlorobenzamide in the sub-μg L^-1-range. ¹³C/¹²C and ¹⁵N/¹⁴N ratios were measured by gas chromatography-isotope ratio mass spectrometry (GC/IRMS), except for desphenylchloridazon, for which liquid chromatography (LC/IRMS) and derivatization-GC/IRMS were used, respectively. The method validated in this study is an important step towards analyzing isotope ratios of pesticide mixtures in aquatic systems and holds great potential for multi-element CSIA applications to trace pesticide degradation in complex environments.

Determination and occurrence of phenoxyacetic acid herbicides and their transformation products in groundwater using ultra high performance liquid chromatography coupled to tandem mass spectrometry

A sensitive method was developed and validated for ten phenoxyacetic acid herbicides, six of their main transformation products (TPs) and two benzonitrile TPs in groundwater. The parent compounds mecoprop, mecoprop-p, 2,4-D, dicamba, MCPA, triclopyr, fluroxypr, bromoxynil, bentazone, and 2,3,6-trichlorobenzoic acid (TBA) are included and a selection of their main TPs: phenoxyacetic acid (PAC), 2,4,5-trichloro-phenol (TCP), 4-chloro-2-methylphenol (4C2MP), 2,4-dichlorophenol (DCP), 3,5,6-trichloro-2-pyridinol (T2P), and 3,5-dibromo-4-hydroxybenzoic acid (BrAC), as well as the dichlobenil TPs 2,6-dichlorobenzamide (BAM) and 3,5-dichlorobenzoic acid (DBA) which have never before been determined in Irish groundwater. Water samples were analysed using an efficient ultra-high performance liquid chromatography (UHPLC) method in an 11.9 min separation time prior to detection by tandem mass spectrometry (MS/MS). The limit of detection (LOD) of the method ranged between 0.00008 and 0.0047 µg·L⁻¹ for the 18 analytes. All compounds could be detected below the permitted limits of 0.1 µg·L⁻¹ allowed in the European Union (EU) drinking water legislation [1]. The method was validated according to EU protocols laid out in SANCO/10232/2006 with recoveries ranging between 71% and 118% at the spiked concentration level of 0.06 µg·L⁻¹. The method was successfully applied to 42 groundwater samples collected across several locations in Ireland in March 2012 to reveal that the TPs PAC and 4C2MP were detected just as often as their parent active ingredients (a.i.) in groundwater.

Determination of Organic Acids in Salicornia herbacea by Solid-phase Extraction Combined with Liquid Chromatography

A solid-phase extraction (SPE) method for the determination of procatechuic acid, ferulic acid and caffeic acid in Salicornia herbacea L. (Hamcho) has been developed. The optimal conditions were obtained by using a C18 SPE cartridge. By using ethanol and acetonitrile /water/ trifluoracetic acid as washing and eluting solvents, most interfering compounds originating from the hamcho matrix were eliminated. The extracts were sufficiently clean to be directly injected into the HPLC for further chromatographic analysis. Good linearity was obtained from 0.1 to 200 μg/mL (r > 0.999) for procatechuic acid, 0.2 to 400 μg/mL (r > 0.999) for caffeic acid and 0.3 to 600 μg/mL (r > 0.999) for ferulic acid, with the relative standard deviations being less than 3.6%. The mean recoveries of procatechuic acid, ferulic acid and caffeic acid from hamcho were more than 79.2% and the detection limit (S/N = 3:1) was 0.02 μg/mL for procatechuic acid, 0.01 μg/mL for caffeic acid and 0.04 μg/mL for ferulic acid. This method is a viable alternative to the existing HPLC methods for analyzing the content of procatechuic acid, ferulic acid and caffeic acid in hamcho.

Dichlobenil and 2,6-dichlorobenzamide (BAM) in the environment: what are the risks to humans and biota?

Dichlobenil is a herbicide widely used for weed control, mainly in non-agricultural areas and in the aquatic environment. When released into the environment, dichlobenil can undergo many processes such as vaporization to air, binding to soil and sediment, as well as degradation to a number of new compounds. The main metabolite is 2,6-dichlorobenzamide (BAM) which is water soluble and causes ground water contamination. It is frequently found in levels exceeding maximum allowed concentrations of pesticides and metabolites in ground water (0.1 μg/L) set by the European Commission. The environmental distribution of both dichlobenil and BAM was outlined and the risk quotients were calculated for biota and for humans. For organisms living in aquatic habitats, risk quotients were low for both dichlobenil and BAM, approximately 0.02 for dichlobenil and 2.4·10(-4) to 1.3·10(-3) for BAM. For humans, a margin of safety above 15,000 was estimated for dichlobenil. The most unusual and extreme concentration of BAM ever found in ground water is 560 μg/L. Even at this concentration, the margin of safety for humans was 313 for a 70 kilo man and 56 for a 25 kilo child. The results clearly demonstrate that the risks to biota and humans are very low.

Analysis and environmental concentrations of the herbicide dichlobenil and its main metabolite 2,6-dichlorobenzamide (BAM): a review

Dichlobenil is an herbicide which has been applied in many countries for weed control in non-agricultural areas such as railroads, car parks and private gardens. In the aquatic environment it has been used for control of floating aquatic weeds. Dichlobenil is relatively persistent in the environment, and primarily bound to solid matrices. Of great concern is its main degradation product 2,6-dichlorobenzamide which is water soluble and therefore transported downward in aquifers, contaminating groundwater resources. It is often found in concentrations exceeding 0.1 μg/L, which is the maximum allowed concentration of pesticides in groundwater set by the European Commission. In many countries, the usage of dichlobenil and the problems associated with groundwater contamination by 2,6-dichlorobenzamide have resulted in intensive research and monitoring of these compounds. This review gives the first overview of analytical strategies available for determining dichlobenil and 2,6-dichlorobenzamide in environmental matrices. It also summarizes studies presenting measured environmental concentrations of dichlobenil and 2,6-dichlorobenzamide identified in the literature during the past two decades. Thereby a preliminary picture of the distribution of dichlobenil and 2,6-dichlorobenzamide in the environment can be outlined for the first time.