Chlorination Of Natural Organic Matter Research Articles

Trichloramine and Hydroxyl Radical Contributions to Dichloroacetonitrile Formation Following Breakpoint Chlorination.

Breakpoint chlorination is applied to remove ammonia in water treatment. Trichloramine (NCl3) and transient reactive species can be present, but how they affect the formation of nitrogenous disinfection byproducts is unknown. In this study, the dichloroacetonitrile (DCAN) formation mechanisms and pathways involved during breakpoint chlorination (i.e., free chlorine to ammonia molar ratio ≥2.0) were investigated. DCAN formation during breakpoint chlorination of natural organic matter (NOM) isolates was 14.3-20.3 μg/L, which was 2-10 times that in chlorination without ammonia at similar free chlorine residual conditions (2.1-2.9 mg/L as Cl2). The probe tests and electron paramagnetic resonance spectra supported the presence of •OH, •NO, and NCl3 besides free chlorine in breakpoint chlorination. 15N-labeled ammonium-N tests indicated the incorporation of ammonium-N in DCAN formation though ammonia was eliminated during breakpoint chlorination. Aromatic non-nitrogenous moieties, such as phenols (i.e., none DCAN precursors in the free-chlorine-only system), became DCAN precursors during breakpoint chlorination. The reactions involved in reactive nitrogen species, such as •NO/•NO2 and NCl3, led to additional nitrogen sources in DCAN formation, accounting for 36-84% of total nitrogen sources in DCAN formation from NOM isolates and real water samples. Scavenging •OH by tert-butanol reduced DCAN formation by 40-56%, indicating an important role of •OH in transforming DCAN precursors. This study improves the understanding of breakpoint chlorination chemistry.

Investigation of trihalomethane formation after chlorine dioxide preoxidation followed by chlorination of natural organic matter

Investigation of trihalomethane formation after chlorine dioxide preoxidation followed by chlorination of natural organic matter

Identification of important precursors and theoretical toxicity evaluation of byproducts driving cytotoxicity and genotoxicity in chlorination

Chlorination, the most widely used disinfection process for water treatment, is unfortunately always accompanied with the formation of hazardous disinfection byproducts (DBPs). Various organic matter species, like natural organic matter (NOM) and amino acids, can serve as precursors of DBPs during chlorination but it is not clear what types of organic matter have higher potential risks. Although regulation of DBPs such as trihalomethanes has received much attention, further investigation of the DBPs driving toxicity is required. This study aimed to identify the important precursors of chlorination by measuring DBP formation from NOM and amino acids, and to determine the main DBPs driving toxicity using a theoretical toxicity evaluation of contributions to the cytotoxicity index (CTI) and genotoxicity index (GTI). The results showed that NOM mainly formed carbonaceous DBPs (C-DBPs), such as trichloromethane, while amino acids mainly formed nitrogenous DBPs (N-DBPs), such as dichloroacetonitrile (DCAN). Among the DBPs, DCAN had the largest contribution to the toxicity index and might be the main driver of toxicity. Among the precursors, aspartic acid and asparagine gave the highest DCAN concentration (200 g/L) and the highest CTI and GTI. Therefore, aspartic acid and asparagine are important precursors for toxicity and their concentrations should be reduced as much as possible before chlorination to minimize the formation of DBPs. During chlorination of NOM, tryptophan, and asparagine solutions with different chlorine doses and reaction times, changes in the CTI and GTI were consistent with changes in the DCAN concentration.

Disinfection byproducts and halogen-specific total organic halogen speciation in chlorinated source waters – The impact of iopamidol and bromide

This study investigated the speciation of halogen-specific total organic halogen and disinfection byproducts (DBPs) upon chlorination of natural organic matter (NOM) in the presence of iopamidol and bromide (Br−). Experiments were conducted with low bromide source waters with different NOM characteristics from Northeast Ohio, USA and varied spiked levels of bromide (2–30 μmol/L) and iopamidol (1–5 μmol/L). Iopamidol was found to be a direct precursor to trihalomethane (THM) and haloacetic acid formation, and in the presence of Br− favored brominated analogs. The concentration and speciation of DBPs formed were impacted by iopamidol and bromide concentrations, as well as the presence of NOM. As iopamidol increased the concentration of iodinated DBPs (iodo-DBPs) and THMs increased. However, as Br− concentrations increased, the concentrations of non-brominated iodo- and chloro-DBPs decreased while brominated-DBPs increased. Regardless of the concentration of either iopamidol or bromide, bromochloroiodomethane (CHBrClI) was the most predominant iodo-DBP formed except at the lowest bromide concentration studied. At relevant concentrations of iopamidol (1 μmol/L) and bromide (2 μmol/L), significant quantities of highly toxic iodinated and brominated DBPs were formed. However, the rapid oxidation and incorporation of bromide appear to inhibit iodo-DBP formation under conditions relevant to drinking water treatment.

Formation and interdependence of disinfection byproducts during chlorination of natural organic matter in a conventional drinking water treatment plant.

It is crucial to explore the source, formation process and interdependence of disinfection byproducts (DBPs) to reduce their risk on public health. In this investigation, a source water was chlorinated to evaluate the initial formation rates and the maximum yields of trichloromethane (TCM), dichloroacetic acid (DCAA), and trichloroacetic acid (TCAA) based on a hyperbola model. The results showed that TCM achieved the highest initial formation rate and maximum theoretical concentration compared with DCAA and TCAA. The TCM yield can be used to forecast the yields of DCAA and TCAA throughout the whole reaction process, and the yields of chloral hydrate (CH), dichloroacetonitrile (DCAN) and 1,1,1-trichloropropanone (1,1,1-TCP) within the initial reaction stage. Besides, the raw water, settled water and filtered water collected from a drinking water treatment plant were divided into five fractions, respectively, by ultrafiltration membranes to evaluate their DBP formation after chlorination. Compared with the medium molecular weight species, high and low molecular weight organic matters exhibited relatively high specific regulated and unregulated DBP yields (expressed as μg/mg C), respectively. Humic acid-like compositions predominantly contributed to regulated DBP yields, while soluble microbial by-product-like compounds preferentially generated DCAN. The correlation study revealed that the TCM could also serve as an indicator for the measured DBPs from chlorination of sample fractions with different molecular weight. Finally, it was found that the theoretical cytotoxicity was enhanced during chlorination of filtered water compared with chlorination of settled water.

Resorcinarene Cavitand Polymers for the Remediation of Halomethanes and 1,4-Dioxane.

Disinfection byproducts such as trihalomethanes are commonly found in drinking water. Trihalomethanes are formed upon chlorination of natural organic matter found in many drinking water sources. Inspired by molecular CHCl3⊂cavitand host-guest complexes, we designed porous polymers composed of resorcinarene receptors. These materials show higher affinity for halomethanes than a specialty activated carbon used for trihalomethane removal. The cavitand polymers show similar removal kinetics as activated carbon and have high capacity (49 mg g-1 of CHCl3). These materials maintain their performance in drinking water and can be thermally regenerated. Cavitand polymers also outperform commercial resins for 1,4-dioxane adsorption, which contaminates many water sources. These materials show promise for water treatment and demonstrate the value of using supramolecular receptors to design adsorbents for water purification.

Radiotracer evidence that the rhizosphere is a hot-spot for chlorination of soil organic matter

AimsThe ubiquitous and extensive natural chlorination of organic matter in soils, leading to levels of chlorinated soil organic matter that often exceed the levels of chloride, remains mysterious in terms of its causes and regulation. While the composition of plant species and the availability of labile organic matter was recently shown to be important, the physical localization of chlorination in soils remains unclear but is a key for understanding regulation and patterns observed. Here we assess the relative importance of organic matter chlorination in (a) bulk soil, (b) the plant roots plus the rhizosphere zone surrounding the roots, and (c) above-ground plant biomass, in an experimental plant-soil system.MethodsA radiotracer, 36Cl, was added to study translocation and transformations of Cl− and Clorg in agricultural soil with and without wheat (Triticum vulgare) over 50 days.ResultsThe specific chlorination rates (the fraction of the added 36Cl− converted to 36Clorg per day) in soil with plants was much higher (0.02 d−1) than without plants (0.0007 d−1) at peak growth (day 25). The plant root and rhizosphere showed much higher formation of 36Clorg than the bulk soil, suggesting that the rhizosphere is a hotspot for chlorination in the soil. In addition, the treatment with plants displayed a rapid and high plant uptake of Cl−.ConclusionsOur results indicate that the rhizosphere harbour the most extensive in-situ chlorination process in soil and that root-soil interaction may be key for terrestrial chlorine cycling.

Effects of carbon materials on the formation of disinfection byproducts during chlorination: Pore structure and functional groups

Release of carbon materials (CMs) into water and wastewater treatment systems occurs due to their increasing utilization as adsorbents for water treatment. When the CMs, mixed with natural organic matter (NOM), interact with disinfectants used during water treatment (e.g. chlorine), the released CMs can affect the formation of disinfection byproducts (DBPs). In this study, three common CMs were investigated to reveal their possible effects and the mechanisms of DBP formation during the chlorination of NOM. The experimental results indicate that DBPs generation decreased by 10–40% in the presence of CMs when Suwannee River humic acid (SRHA) was chlorinated. The adsorption of SRHA by CMs was hypothesized as the major cause for the DBPs inhibition. CMs could irreversibly adsorb DBP precursors in their mesopores through π-π bonding and hydrophobic effects. OH groups on the surface of CMs were shown to be critical for DBPs inhibition through linking with the OH or COOH groups on the surface of NOM via hydrogen bonding. The study also showed that water chemistry parameters, such as pH and salinity, can affect DBP formation by changing the adsorption of NOM onto CMs. With diverse NOM components, the presence of CMs resulted in decreased formation of trichloromethane from 57.1 μg/L to 23.8, 38.4, and 40.4 μg/L when coal-made activated carbon (CAC), wheat straw-made BC pyrolyzed at 300 °C (WSBC300), and multiwalled carbon nanotubes (MWCNTs), respectively, were added to surface water; and from 30.6 μg/L to 20.0, 19.2, and 13.2 μg/L when CAC, WSBC300, and MWCNTs, respectively, were added to wastewater.

Effect of copper corrosion products on the formation and speciation of haloacetamides and haloacetonitriles during chlorination

The catalytic effect of copper corrosion products, including copper ions, cupric oxide, and cuprous oxide, on the formation of haloacetamides and haloacetonitriles during chlorination of natural organic matter (NOM), model nitrogenous precursors, and real water samples was investigated. During chlorination of NOM, the presence of these copper corrosion products facilitated chlorine decay, and enhanced the formation of dichloroacetonitrile (DCAN) and dichloroacetamide (DCAcAm) with enhancement ratios of 45–59% and 64–137% after 10 h contact time, respectively. Six amino acids were selected as nitrogenous NOM surrogates for chlorination, and the results show that the enhancement of DCAN and DCAcAm formation by copper corrosion products was only observed for slow reacting amino acids, including glutamine, glutamic acid, and phenylamine, suggesting that copper corrosion products may enhance DCAN and DCAcAm formation by catalyzing NOM portions that are relatively inefficient precursors. When bromide and copper corrosion products were present, the formation of dihaloacetonitriles (DHANs) and dihaloacetamides (DHAcAms) could be enhanced during chlorination of NOM, but the degrees of bromine substitution for DHANs and DHAcAms decreased. Although copper corrosion products facilitated DHAN and DHAcAm hydrolysis with the facilitation increasing as the halogens shifted from chlorine to bromine, increased DHAN and DHAcAm concentrations was observed during chlorination of real water samples in the presence of copper corrosion products, confirming that the copper corrosion products had a catalytic effect on DHAN and DHAcAm formation that exceeded their catalytic effect on DHAN and DHAcAm hydrolysis. This study provides basic knowledge of disinfectant residuals and the fate of haloacetonitriles and haloacetamides in drinking water distribution systems where copper is used, which will be helpful for the management of safe water distribution.

Influence of Multiple Environmental Factors on Organic Matter Chlorination in Podsol Soil.

Natural chlorination of organic matter is common in soils. The abundance of chlorinated organic compounds frequently exceeds chloride in surface soils, and the ability to chlorinate soil organic matter (SOM) appears widespread among microorganisms. Yet, the environmental control of chlorination is unclear. Laboratory incubations with 36Cl as a Cl tracer were performed to test how combinations of environmental factors, including levels of soil moisture, nitrate, chloride, and labile organic carbon, influenced chlorination of SOM from a boreal forest. Total chlorination was hampered by addition of nitrate or by nitrate in combination with water but enhanced by addition of chloride or most additions including labile organic matter (glucose and maltose). The greatest chlorination was observed after 15 days when nitrate and water were added together with labile organic matter. The effect that labile organic matter strongly stimulated the chlorination rates was confirmed by a second independent experiment showing higher stimulation at increased availability of labile organic matter. Our results highlight cause-effect links between chlorination and the studied environmental variables in podsol soil-with consistent stimulation by labile organic matter that did overrule the negative effects of nitrate.

Vanadium Chloroperoxidases: The Missing Link in the Formation of Chlorinated Compounds and Chloroform in the Terrestrial Environment?

It is well established that the majority of chlorinated organic substances found in the terrestrial environment are produced naturally. The presence of these compounds in soils is not limited to a single ecosystem. Natural chlorination is also a widespread phenomenon in grasslands and agricultural soils typical for unforested areas. These chlorinated compounds are formed from chlorination of natural organic matter consisting of very complex chemical structures, such as lignin. Chlorination of several lignin model compounds results in the intermediate formation of trichloroacetyl-containing compounds, which are also found in soils. These decay, in general, through a haloform-type reaction mechanism to CHCl3 . Upon release into the atmosphere, CHCl3 will produce chlorine radicals through photolysis, which will, in turn, lead to natural depletion of ozone. There is evidence that fungal chloroperoxidases able to produce HOCl are involved in the chlorination of natural organic matter. The objective of this review is to clarify the role and source of the various chloroperoxidases involved in the natural formation of CHCl3 .

Formation of 2,6-dichloro-1,4-benzoquinone from aromatic compounds after chlorination

Halobenzoquinones are a group of disinfection byproducts formed by chlorination of certain substances in water. However, to date, the identities of halobenzoquinone precursors remain unknown. In this study, the formation of 2,6-dichloro-1,4-benzoquinone (DCBQ), a typical halobenzoquinone, from 31 aromatic compounds was investigated after 60 min of chlorination. DCBQ was formed from 21 compounds at molar formation yields ranging from 0.0008% to 4.9%. Phenol and chlorinated phenols served as DCBQ precursors, as reported previously. Notably, DCBQ was also formed from para-substituted phenolic compounds. Compounds with alkyl and carboxyl groups as para-substituents led to relatively higher molar formation yields of DCBQ. Moreover, p-quinone-4-chloroimide, 2,6-dichloroquinone-4-chloroimide (2,6-DCQC), and para-substituted aromatic amines (e.g., aniline and N-methyl aniline) served as DCBQ precursors upon chlorination. It was deduced that DCBQ was formed from the para-substituted aromatic amines via 3,5-dichloroquinone-4-chloroimide, a structural isomer of 2,6-DCQC. These results suggested that DCBQ was formed by chlorination of natural organic matter containing para-substituted phenolic species and para-substituted aromatic amines, despite the absence of phenol in water.

Effects of metal ions on disinfection byproduct formation during chlorination of natural organic matter and surrogates.

The effects of calcium, cupric, ferrous and ferric ions on the formation of trihalomethanes (THMs) and haloacetic acids (HAAs) were investigated using natural organic matter (NOM), small molecular weight NOM surrogates and natural water samples. The results showed that the effects were greatly dependent on the disinfection byproduct (DBP) precursor structure and molecular weight, and metal ions species. While using NOM as precursors, addition of 4.00 mM calcium ions increased the formation of THMs, dihaloacetic acids (DHAAs) and trihaloacetic acids (THAAs) by 24-47%, 51-61% and 15-25%, respectively. Addition of cupric ions at 0.02 mM increased the formation of THMs and DHAAs by 74-83% and 90-100%, respectively, but decreased the formation of THAAs by 26-27%. Similar effect was not observed when 0.04 mM ferrous or ferric ions were added. The effects of calcium and cupric ions on DBP formation were generally more evident for the NOM surrogates than that for NOM. The primary catalytic effect of calcium ions was due to complexation and less sensitive to molecular structure or weight, while that of cupric ions was attributed to redox reactions and greatly dependent on molecular structure. Both ferric and ferrous iron had substantial effects on the DBP formation of surrogates (citric acid and catechol in particular), which implied that the catalytic effects of ferric and ferrous iron mainly depended on molecular weight. The catalytic effect of cupric ions was also observed on natural water samples, while the effects of calcium, ferrous and ferric ions on natural water samples were not evident.

40 years on: what do we know about drinking water disinfection by-products (DBPs) and human health?

2014 marks the 40th anniversary of the seminal discovery by Johannes Rook, in 1974, that trihalomethanes (THMs) were formed by the chlorination of natural organic matter (NOM) in drinking water. Since this discovery, which revolutionized how we viewed drinking water safety and quality, hundreds of other classes of disinfection by-products (DBPs) have been discovered. The finding in 1976 by the US National Cancer Institute that chloroform, the dominant THM, was a rodent carcinogen spurred a large number of epidemiology and toxicology studies into chlorinated drinking water. In 1985, this cancer finding was shown to be wrong. We should now be asking: What do we know about the human health impacts of DBPs in drinking water? Bladder cancer has been the most consistent finding from epidemiologic studies in North America and Europe and the possibility that chlorinated drinking water contributes an increased risk of bladder cancer remains a viable hypothesis. Despite some recent improvements in exposure assessments to focus on inhalation and dermal exposures rather than ingestion, no causal agent with sufficient carcinogenic potency has been identified, nor has a mechanistic model been validated. Consequently, a sensible precautionary approach to managing DBPs remains the only viable option based on four decades of evidence.

Impact of UV/persulfate pretreatment on the formation of disinfection byproducts during subsequent chlorination of natural organic matter

Ultraviolet/persulfate (UV/PS) has been widely used to generate sulfate radicals (SO4−) in degrading organic pollutants. However, its impact on chlorinated disinfection byproducts (DBPs) is unclear. Impact of UV/PS pretreatment on the formation of DBPs during subsequent chlorination of natural organic matter was evaluated in this study. For the samples pretreated by UV/PS, the formation of some carbonaceous disinfection byproducts (C-DBPs) such as chloroform and haloacetic acids only increased a little, but the formation of nitrogenous disinfection byproducts (N-DBPs) including haloacetonitriles and trichloronitromethane decreased slightly. UV/H2O2 pretreatment increased the formation of both C-DBPs and N-DBPs significantly with the initial dosage of H2O2 being 30μM. Chloral hydrate and haloketones followed an increasing and then decreasing pattern, but dichloroacetonitrile and trichloronitromethane followed an opposite pattern with increasing UV/PS pretreatment time. Most of the C-DBPs rose monotonically with increasing dosages of PS, but N-DBPs declined at the dosage of PS being 10μM by UV/PS pretreatment. Preoxidation pH and the presence of nitrate played little role in DBP formation. In the presence of 2.5mg/L ammonia, UV/PS pretreatment increased most of the DBPs except for trichloroacetonitrile and trichloronitromethane. Bromine incorporation factors for trihalomethanes, haloacetic acids and dihaloacetonitriles were affected by UV/PS preoxidation insignificantly. It is suggested that the combination of UV/PS and post chlorination was expected to be a good choice in controlling the formation of DBPs.

Coagulation and Chlorination of NOM and Algae in Water Treatment: A Review

Due to health concerns of natural organic matter (NOM) and algae presence in surface water and difficulties encountered in their removal in the water treatment, this paper reviews coagulation and chlorination processes which are largely used in water treatment technology. In the conventional water treatment, coagulation and slow filtration treatments have better efficiency to reduce the NOM in water especially for the hydrophobic portion than the hydrophilic one. However, the pre-chlorination treatment for raw water has been proved to increase the dissolved organic carbon concentration due to the lysis of algae cells and disinfection by-products formation. The impact of water treatment processes on disinfection by-products formation remains complex and variable, as demonstrated by recent literature. It is concluded that no pre-, no inter-, only post-chlorination preceded by optimised coagulation for NOM and algae removal is the best available technology for the conventional water treatment which would be reinforced by at least adsorption on powdered activated carbon or nanofiltration in the short terms. Finally, the conventional water treatment will not remain a viable solution for drinking water from source waters containing NOM as their quality deteriorates and water quality standards become more difficult to achieve.

Mechanistic insights into the formation of chloroform from natural organic matter using stable carbon isotope analysis

Chloroform can be naturally formed in terrestrial environments (e.g. forest soils, peatland) by chlorination of natural organic matter (NOM). Recently, it was demonstrated that natural and anthropogenic chloroform have a distinctly different carbon isotope signature that makes it possible to identify its origin in soil and groundwater. In order to evaluate the contribution of different functional groups to chloroform production and factors controlling the isotopic composition of chloroform, carbon isotope trends during chlorination of model compounds, soil organic matter (SOM) and humic acids were evaluated, and apparent kinetic isotope effects (AKIEs) quantified. Phenol and propanone were selected as model compounds representing common functional groups in NOM. Chlorination was induced by hypochlorous acid to mimic natural chlorination. The pH ranged between 4 and 8 to cover typical soil conditions. For each model compound and pH, different AKIEs were observed. For phenol, the AKIE was normal at pH 4 (1.0156±0.0012) and inverse at pH 8 (0.9900±0.0007). For 2-propoanol, an opposite pH dependence was observed with an inverse AKIE at pH 4 (0.9935±0.0007) and a normal AKIE at pH 8 (1.0189±0.0016). The variations of the AKIE values suggest that the rate-limiting step of the reaction is either the re-hybridization of the carbon atom involved in chloroform formation or the hydrolysis of trichloroacetyl intermediates depending on the nature of functional group and pH. The chloroform formation from humic acid and SOM gives rise to small isotope variations. A comparison of the isotopic trends of chloroform formed from humic acid and SOM with those found for the model compounds suggest that opposed AKIE associated with the chlorination of phenolic and ketone moieties of NOM partly compensate each other during chlorination of NOM indicating that different types of functional groups contribute to chloroform formation.

Selective Chlorination of Natural Organic Matter: Identification of Previously Unknown Disinfection Byproducts

Natural organic matter (NOM) serve as precursors for disinfection byproducts (DBPs) in drinking water production making NOM removal essential in predisinfection treatment processes. We identified molecular formulas of chlorinated DBPs after chlorination and chloramination in four Swedish surface water treatment plants (WTPs) using ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Chlorine-containing formulas were detected before and after disinfection and were therefore classified to identify DBPs. In total, 499 DBPs were detected, of which 230 have not been reported earlier. The byproducts had, as a group, significantly lower ratio of hydrogen to carbon (H/C) and significantly higher average carbon oxidation state (COS), double bond equivalents per carbon (DBE/C) and ratio of oxygen to carbon (O/C) compared to Cl-containing components present before disinfection and CHO formulas in samples taken both before and after disinfection. Electrophilic substitution, the proposed most significant reaction pathway for chlorination of NOM, results in carbon oxidation and decreased H/C while O/C and DBE/C is left unchanged. Because the identified DBPs had significantly higher DBE/C and O/C than the CHO formulas we concluded that chlorination of NOM during disinfection is selective toward components with relatively high double bond equivalency and number of oxygen atoms per carbon. Furthermore, choice of disinfectant, dose, and predisinfection treatment at the different WTPs resulted in distinct patterns in the occurrence of DBP formulas.

Assessing the role of trichloroacetyl-containing compounds in the natural formation of chloroform using stable carbon isotopes analysis

Chloroform (CHCl3) is an environmental contaminant widely distributed around world, as well as a natural compound formed in various aquatic and terrestrial environments. However, the chemical mechanisms leading to the natural formation of chloroform in soils are not completely understood. To assess the role of trichloroacetyl-containing compound (TCAc) in the natural formation of chloroform in forest soils, carbon stable isotope analyses of chloroform and TCAc in field samples and chlorination experiments were carried out. The isotope analysis of field samples have revealed that the δ13C value of natural chloroform (δ13Cmean=−25.8‰) is in the same range as the natural organic matter (δ13Cmean=−27.7‰), whereas trichloromethyl groups of TCAc are much more enriched in 13C (δ13Cmean=−9.8‰). A similar relationship was also observed for TCAc and chloroform produced by chlorination of natural organic matter with NaOCl. The strong depletion of 13C in chloroform relative to TCAc can be explained by carbon isotope fractionation during TCAc hydrolysis. As shown using a mathematical model, when steady state between formation of TCAc and hydrolysis is reached, the isotope ratio of chloroform is expected to correspond to isotope composition of NOM while TCAc should be enriched in 13C by about 18.3‰, which is in good agreement with field observations. Hence this study suggests that TCAc are likely precursors of chloroform and at the same time explains why natural chloroform has a similar isotope composition as NOM despite large carbon isotope fractionation during its release.

Position‐specific carbon isotope analysis of trichloroacetic acid by gas chromatography/isotope ratio mass spectrometry

Trichloroacetic acid (TCAA) is an important environmental contaminant present in soils, water and plants. A method for determining the carbon isotope signature of the trichloromethyl position in TCAA using gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) was developed and tested with TCAA from different origins. Position-specific isotope analysis (PSIA) can provide direct information on the kinetic isotope effect for isotope substitution at a specific position in the molecule and/or help to distinguish different sources of a compound. The method is based on the degradation of TCAA into chloroform (CF) and CO₂ by thermal decarboxylation. Since thermal decarboxylation is associated with strong carbon isotope fractionation (ε = -34.6 ± 0.2‰) the reaction conditions were optimized to ensure full conversion. The combined isotope ratio of CF and CO₂ at the end of the reaction corresponded well to the isotope ratio of TCAA, confirming the reliability of the method. A method quantification limit (MQL) for TCAA of 18.6 µg/L was determined. Samples of TCAA produced by enzymatic and non-enzymatic chlorination of natural organic matter (NOM) and some industrially produced TCAA were used as exemplary sources. Significant different PSIA isotope ratios were observed between industrial TCAA and TCAA samples produced by chlorination of NOM. This highlights the potential of the method to study the origin and the fate of TCAA in the environment.