Sodium chlorate, a herbicide and major water disinfectant byproduct, generates reactive oxygen species and induces oxidative damage in human erythrocytes

Role of nutraceutical against exposure to pesticide residues: power of bioactive compounds

Pesticides play a crucial role in modern agriculture, aiding in the protection of crops from pests and diseases. However, their indiscriminate use has raised concerns about their potential adverse effects on human health and the environment. Pesticide residues in food and water supplies are a serious health hazards to the general public since long-term exposure can cause cancer, endocrine disruption, and neurotoxicity, among other health problems. In response to these concerns, researchers and health professionals have been exploring alternative approaches to mitigate the toxic effects of pesticide residues. Bioactive substances called nutraceuticals that come from whole foods including fruits, vegetables, herbs, and spices have drawn interest because of their ability to mitigate the negative effects of pesticide residues. These substances, which include minerals, vitamins, antioxidants, and polyphenols, have a variety of biological actions that may assist in the body's detoxification and healing of harm from pesticide exposure. In this context, this review aims to explore the potential of nutraceutical interventions as a promising strategy to mitigate the toxic effects of pesticide residues.

Dietary exposure assessment of perchlorate and chlorate in infant formulas marketed in Shanghai, China

Perchlorate and chlorate are ubiquitous pollutants that can adversely affect the thyroid function in humans. This study assessed the potential health risks associated with the dietary exposure of infants and young children to perchlorate and chlorate present in infant formulas available in Shanghai. The assessment was based on risk monitoring data from 150 samples of infant formulas in Shanghai between 2020 and 2022, along with the dietary consumption data of infants and young children. The detection rates of perchlorate and chlorate in infant formulas were 46.0% and 98.7%, with mean contents of 9.98 μg/kg and 112.01 μg/kg, and the maximum values of 151.00 μg/kg and 1475.00 μg/kg, respectively. The mean and 95th percentile (P 95) values of daily perchlorate exposure of 0-36-month-old infant and young children via infant formulas were 0.07 and 0.17 μg/kg body weight (bw) per day, respectively, which were lower than the tolerable daily intake (TDI) of perchlorate (0.3 μg/kg bw per day). The mean and P 95 values of chlorate exposure via infant formulas in 0-36-month-old infants and young children were 0.83 and 1.89 μg/kg bw per day, which were lower than the TDI of chlorate (3 μg/kg bw per day). The P 95 exposure of different age groups (0-6 months, 7-12 months and 13-36 months) of infants and young children to perchlorate and chlorate in infant formulas was below the TDI. Therefore, the risk associated with the exposure of 0-36-month-old infants and young children to perchlorate and chlorate from infant formulas in Shanghai is considered acceptable. Prioritizing environmental pollution control efforts to reduce the levels of perchlorate and chlorate in food products is important to safeguard the health of the infants and children under the One Health concept.

Chia seeds oil ameliorate chronic immobilization stress-induced neurodisturbance in rat brains via activation of the antioxidant/anti-inflammatory/antiapoptotic signaling pathways

Chronic immobilization stress plays a key role in several neuropsychiatric disorders. This investigation assessed the possible ameliorative effect of chia seed oil (CSO) against the neurodisturbance-induced in rats by chronic immobilization. Rats were randomly allocated into control, CSO (1 ml/kg b.wt./orally), restrained (6 h/day), CSO pre-restraint, and CSO post-restraint for 60 days. Results revealed a significant reduction in serum corticosterone level, gene expression of corticotrophin-releasing factor, pro-inflammatory cytokines, and oxidative biomarkers in restrained rats treated with CSO. The histopathological findings revealed restoring necrosis and neuronal loss in CSO-treated-restraint rats. The immunohistochemical evaluation revealed a significant reduction in the immuno-expression of caspase-3, nuclear factor kappa B, interleukin-6, and cyclooxygenase-2 (COX-2), and an elevation of calbindin-28k and synaptophysin expression compared to non-treated restraint rats. The molecular docking showed the CSO high affinity for several target proteins, including caspase-3, COX-2, corticotropin-releasing hormone binding protein, corticotropin-releasing factor receptors 1 and 2, interleukin-1 receptor types 1 and 2, interleukin-6 receptor subunits alpha and beta. In conclusion, CSO emerges as a promising candidate against stress-induced brain disruptions by suppressing inflammatory/oxidative/apoptotic signaling pathways due to its numerous antioxidant and anti-inflammatory components, mainly α-linolenic acid. Future studies are necessary to evaluate the CSO therapeutic impacts in human neurodisturbances.

Perchlorate and chlorate assessment in drinking water in northern Chilean cities

Perchlorate and chlorate are endocrine disruptors considered emerging contaminants (ECs). Both oxyanions are commonly associated with anthropogenic contamination from fertilizers, pesticides, explosives, and disinfection byproducts. However, the soils of the Atacama Desert are the most extensive natural reservoirs of perchlorate in the world, compromising drinking water sources in northern Chile. Field campaigns were carried (2014-2018) to assess the presence of these ECs in the water supply networks of twelve Chilean cities. Additionally, the occurrence of perchlorate, chlorate and other anions typically observed in drinking water matrices of the Atacama Desert (i.e., nitrate, chloride, sulfate) was evaluated using a Spearman correlation analysis to determine predictors for perchlorate and chlorate. High concentrations of perchlorate (up to 114.48 μg L-1) and chlorate (up to 9650 μg L-1) were found in three northern cities. Spatial heterogeneities were observed in the physicochemical properties and anion concentrations of the water supply network. Spearman correlation analysis indicated that nitrate, chloride, and sulfate were not useful predictors for the presence of perchlorate and chlorate in drinking water in Chile. Hence, this study highlights the need to establish systematic monitoring, regulation, and treatment for these EC of drinking water sources in northern Chilean cities for public health protection.

Health risk assessment of perchlorate and chlorate in red swamp crayfish (Procambarus clarkii) in China

Perchlorate and chlorate are both strong oxidants and thyroid toxicants that are widely distributed in soil, water and human foods. The red swamp crayfish (Procambarus clarkii) is a common aquatic organism that is popular in Chinese culinary dishes. Dietary intake is the main route of human exposure to perchlorate and chlorate, though the health risks of crayfish consumption are unknown. Thus, this study investigated the quantities of perchlorate and chlorate in red swap crayfish from sampling sites in five provinces located near the Yangtze River in China, along with the associated health risks of consuming this species. Perchlorate was detected in 55.6-100 % of crayfish samples in each sampling location, and chlorate was found in 100 % of samples cross all sites. Concentrations of perchlorate in crayfish from upstream provinces (Hubei, Hunan and Jiangxi) were higher than those from downstream provinces (Anhui and Jiangsu). Perchlorate and chlorate concentrations were positively correlated in crayfish, suggesting that chlorate may be a degradation byproduct of perchlorate. The quantities of both pollutants in hepatopancreas tissue were higher than in muscle tissues (p < 0.05), such that we do not recommend ingesting crayfish hepatopancreas. Hazard quotient (HQ) values for chlorate in crayfish were <1 across all provinces, suggesting no potential health risk of chlorate exposure through crayfish consumption. However, perchlorate concentrations in crayfish from the Jiangxi province had an associated HQ value >1, suggesting potential risks for human health. These results will be useful in informing mitigation measures aimed at reducing perchlorate exposure associated with crayfish consumption.

Kinetic and mechanistic understanding of chlorite oxidation during chlorination: Optimization of ClO2 pre-oxidation for disinfection byproduct control

Chlorine dioxide (ClO₂) applications to drinking water are limited by the formation of chlorite (ClO₂^-) which is regulated in many countries. However, when ClO₂ is used as a pre-oxidant, ClO₂^- can be oxidized by chlorine during subsequent disinfection. In this study, a kinetic model for the reaction of chlorine with ClO₂^- was developed to predict the fate of ClO₂^- during chlorine disinfection. The reaction of ClO₂^- with chlorine was found to be highly pH-dependent with formation of ClO₃^- and ClO₂ in ultrapure water. In presence of dissolved organic matter (DOM), 60-70% of the ClO₂^- was transformed to ClO₃^- during chlorination, while the in situ regenerated ClO₂ was quickly consumed by reaction with DOM. The remaining 30-40% of the ClO₂^- first reacted to ClO₂ which then formed chlorine from the DOM-ClO₂ reaction. Since only part of the ClO₂^- was transformed to ClO₃^-, the sum of the molar concentrations of oxychlorine species (ClO₂^- + ClO₃^-) decreased during chlorination. By kinetic modelling, the ClO₂^- concentration after 24 h of chlorination was accurately predicted in synthetic waters but was largely overestimated in natural waters, possibly due to a ClO₂^- decay enhanced by high concentrations of chloride and in situ formed bromine from bromide. Understanding the chlorine-ClO₂^- reaction mechanism and the corresponding kinetics allows to potentially apply higher ClO₂ doses during the pre-oxidation step, thus improving disinfection byproduct mitigation while keeping ClO₂^-, and if required, ClO₃^- below the regulatory limits. In addition, ClO₂ was demonstrated to efficiently degrade haloacetonitrile precursors, either when used as pre-oxidant or when regenerated in situ during chlorination.

Synergistic cytotoxicity of binary combinations of inorganic and organic disinfection byproducts assessed by real-time cell analysis

Chlorine, chlorine dioxide, and ozone are widely used as disinfectants in drinking water treatments. However, the combined use of different disinfectants can result in the formation of various organic and inorganic disinfection byproducts (DBPs). The toxic interactions, including synergism, addition, and antagonism, among the complex DBPs are still unclear. In this study, we established and verified a real-time cell analysis (RTCA) method for cytotoxicity measurement on Chinese hamster ovary (CHO) cell. Using this convenient and accurate method, we assessed the cytotoxicity of a series of binary combinations consisting of one of the 3 inorganic DBPs (chlorite, chlorate, and bromate) and one of the 32 regulated and emerging organic DBPs. The combination index (CI) of each combination was calculated and evaluated by isobolographic analysis to reflect the toxic interactions. The results confirmed the synergistic effect on cytotoxicity in the binary combinations consisting of chlorite and one of the 5 organic DBPs (2 iodinated DBPs (I-DBPs) and 3 brominated DBPs (Br-DBPs)), chlorate and one of the 4 organic DBPs (3 aromatic DBPs and dibromoacetonitrile), and bromate and one of the 3 organic DBPs (2 I-DBPs and dibromoacetic acid). The possible synergism mechanism of organic DBPs on the inorganic ones may be attributed to the influence of organic DBPs on cell membrane and cell antioxidant system. This study revealed the toxic interactions among organic and inorganic DBPs, and emphasized the latent adverse outcomes in the combined use of different disinfectants.

Provenances, preponderances, and distribution of humic acids and organic pollutants in hydro-geosphere: The co-existence, interaction and isotopic biomarkers in the riverine ecosystem

This paper aims to critically review the importance of geochemical fingerprinting and tracing using biomarkers and stable isotopes in the riverine ecosystem and depicts that isotopic ratios of δ¹³C, δ¹⁵N, and δ³⁴S can be used for tracing pollution sources. Stable isotopes like carbon, hydrogen, nitrogen, oxygen, and sulfur are being used for this purpose, and their isotopic signatures are primarily used to distinguish close sources of organic matter through dual isotopes. The present review is articulated to bridge the critical research gaps of the previous and contemporary documented literature on the genesis and transport of OM between freshwater and marine systems. This review comprehensively provides methods and techniques in geochemical tracing and discusses the future directions to address the challenges of the current methods to enhance the knowledge about the source identification of organic matter in the riverine environment. Tracer geochemistry emphasizes the implications of elemental abundances and isotope ratio variations in geologic substances to track natural earth processes, anthropogenic contaminants, and geochemical signatures in the hydrologic system. The principal constituent of organic matter comprises humic substances like humic acid, fulvic acid, and humin, and these comprise 50-75% of the sediments and DOC in natural waters. Their structural and functional characterization is required to elucidate the transport and fate of organic matter, which are often influenced by several paleoenvironmental factors.

The contamination and estimation of dietary intake for perchlorate and chlorate in infant formulas in China

The contents of perchlorate and chlorate were determined in a total of 278 samples of infant formulas marketed in China. The associated health risk via infant and young child formulas consumption for 0-36 month old children in China was also assessed. The contents of perchlorate and chlorate were measured by a validated method with LC-MS and the limit of detection (LOD) was 1.5 μg kg^-1 and 3.0 μg kg^-1 for perchlorate and chlorate, respectively. Perchlorate and chlorate were detected in about 85.8% (median 6.92 μg kg^-1, maximum 74.20 μg kg^-1) and 99.3% (median 52.80 μg kg^-1, maximum 2780 μg/kg) of the samples. The exposures of infant and young children to perchlorate from formulas were lower than the provisional maximum tolerable daily intake (PMTDI, 0.7 μg/kg bw/day), which was established by U.S. Environmental Protection Agency (EPA). The European Food Safety Authority (EFSA) in 2015 also proposed a tolerable daily intake (TDI) of 3 μg/kg bw/day for chlorate based on the mean and average concentrations. Only for infants 0-6 month at the 95th percentile did exposures exceed the TDI of 3 μg/day for chlorate. Therefore, the safety of infant and young child formulas is excellent. To our knowledge, this is the first report to assess the exposure of infant and young child formulas in China to perchlorate and chlorate.

Wild garlic extract reduces lipid peroxidation in terbuthylazine-treated human erythrocytes

Background: Among other negative effects, herbicides induce oxidative stress, leading to lipid peroxidation and protein oxidation. Therefore, there is a growing need to identify natural compounds with sufficient antioxidant capacity and mitigate the negative effects of herbicides without side effects.Objective: Our study aimed to examine the protective effect of the phenolic extract of wild garlic (WG) leaves on terbuthylazine-treated erythrocytes.Material and methods: In human erythrocytes treated with the herbicide terbuthylazine (4.5 mg/L) alone and a combination of terbuthylazine and WG extract, we measured malondialdehyde (MDA) and haemoglobin (Hb) concentrations and the antioxidant activities of CuZn superoxide dismutase (SOD1; EC 1.15.1.1) and catalase (CAT; EC 1.11.1.6) in vitro.Results: In comparison with terbuthylazine, WG extract reduced the concentrations of MDA and Hb from 59.69 to 43.45 nmol/gHb (27%, p < 0.001) and 165.08 to 128.64 g/L (22%, p < 0.05), respectively. Catalase activity was induced for samples treated with both WG extract and terbuthylazine compared with terbuthylazine alone (p < 0.05).Conclusions: The results demonstrated that WG may reduce the toxicity of terbuthylazine, and the erythrocyte membrane may be the primary site of phenolic action. Therefore, the lipid peroxidation intensity could be a biomarker of oxidative damage caused by terbuthylazine and the protective effect of WG.

Bioelectrochemical chlorate reduction by Dechloromonas agitata CKB

Chlorate has been described as an emerging pollutant that compromises water sources. In this study, bioelectrochemical reactors (BERs) using Dechloromonas agitata CKB, were evaluated as a sustainable alternative for chlorate removal. BERs were operated under flow-recirculation and batch modes with an applied cell-voltage of 0.44 V over a resistance of 1 kΩ. Results show chlorate removal up to 607.288 mg/L. After 115 days, scanning electron microscopy showed biofilm development over the electrodes, and electrochemical impedance spectroscopy confirmed the biocatalytic effect of CKB. The theoretical chlorate bioreduction potential (ε° = 0.792 V) was proven, and a kinetic study indicated that 6 electrons were involved in the reduction mechanism. Finally, a hypothetical bioelectrochemical mechanism for chlorate reduction in a BER was proposed. This research expands upon current knowledge of novel electrochemically active microorganisms and widens the scope of BER applications for chlorate removal.

Detection of chlorite, chlorate and perchlorate in ozonated saline

Medical ozone is used to treat various diseases, including numerous pathologies associated with chronic pain. Chronic pain may be treated by systemic administration of ozone, with ozonated autohemotherapy (OAH) being the commonly used method. In the clinic, intravenous infusion of ozonized saline has been used to treat various diseases. Compared with OAH, ozonized saline infusion is less technically demanding and causes minimal damage to veins. However, it has been indicated that ozone may oxidize saline and generate toxic substances, and therefore, the safety of ozone treatment has been questioned. In the present study, the potential chemical compounds produced from ozone and saline, including chlorite, chlorate and perchlorate, were examined at various time-points with ion chromatography-mass spectrometry (IC-MS). A control group (pure oxygen group) and an ozone group were included in the present study. Two subgroups were included within each group: A saline bottle (made from polypropylene) subgroup and an ozone-resistant blood transfusion bag [made from medical polyvinyl chloride, di(2-ethyl) hexyl phthalate plasticized] subgroup. For the ozone group, 100 ml saline and 100 ml medical ozone at various concentrations (20, 40 or 60 µg/ml in pure oxygen) were injected into the saline bottle or blood bag, and for the control group, 100 ml of pure oxygen was injected into the saline bottle or blood bag. The presence and the content of chlorite, chlorate and perchlorate were determined at different time-points (3, 6 and 15 days after mixing) by IC-MS. Chlorate was detected in the ozone groups at three time-points and its content increased as the ozone concentration and the reaction time increased. Under the same conditions (the same ozone concentration and the same incubation time), the chlorate content (0.90±0.14-7.69±0.48 µg/l) in the blood bag subgroup was significantly lower than that in the saline bottle subgroup (45.23±6.14-207.6±15.63 µg/l). However, chlorite and perchlorate were not detected at any time-point in the two groups. In addition, in the control group (pure oxygen group), chlorite, chlorate and perchlorate were not detected at any time-point. These results indicate that ozone reacts with saline to produce chlorate. Ozone may also react with the polypropylene saline bottle to increase the chlorate content in the bottled solution. Due to a lack of toxicology studies of chlorate in blood, it remains elusive whether ozonated saline and chlorate at the range of 0.90±0.14-7.69±0.48 µg/l has any toxic effects. The potential toxicity of chlorate should be considered when ozonated saline is used for clinical infusions.

Behavioral and Biochemical Effects of Mukia madrespatana Following Single Immobilization Stress on Rats

BACKGROUND AND OBJECTIVES

Elevated oxidative stress has been shown to play an important role in the diagnosis and prognosis of stress and memory-related complications. Mukia madrespatana (M. madrespatana) has been reported to have various biological and antioxidant properties. We intended to evaluate the effect of M. madrespatana peel on single immobilization stress-induced behavioral deficits and memory changes in rats. Materials and Methods: M. madrespatana peel (2000 mg/kg/day, orally) was administered to control and immobilize stressed animals for 4 weeks. Anxiolytic, antidepressant, and memory-enhancing effects of M. madrespatana were observed in both unstressed and stressed animals. Results: Lipid peroxidation was decreased while antioxidant enzymes were increased in both unstressed and stressed animals. Acetylcholine level was increased while acetylcholinesterase activity was decreased in both M. madrespatana treated unstressed and stressed rats. There was also an improvement in memory function. Serotonin neurotransmission was also regulated in M. madrespatana treated rats following immobilization stress with anxiolytic and anti-depressive effects. Conclusion: Based on the current study, it is suggested that M. madrespatana has strong antioxidant properties and may be beneficial as dietary supplementation in stress and memory-related conditions.

Reduced Sulfation Enhanced Oxytosis and Ferroptosis in Mouse Hippocampal HT22 Cells

Sulfation is a common modification of extracellular glycans, tyrosine residues on proteins, and steroid hormones, and is important in a wide variety of signaling pathways. We investigated the role of sulfation on endogenous oxidative stress, such as glutamate-induced oxytosis and erastin-induced ferroptosis, using mouse hippocampal HT22 cells. Sodium chlorate competitively inhibits the formation of 3′-phosphoadenosine 5′-phosphosulfate, the high energy sulfate donor in cellular sulfation reactions. The treatment of HT22 cells with sodium chlorate decreased sulfation of heparan sulfate proteoglycans and chondroitin sulfate proteoglycans. Sodium chlorate and β-d-xyloside, which prevents proteoglycan glycosaminoglycan chain attachment, exacerbated both glutamate- and erastin-induced cell death, suggesting that extracellular matrix influenced oxytosis and ferroptosis. Moreover, sodium chlorate enhanced the generation of reactive oxygen species and influx of extracellular Ca²⁺ in the process of oxytosis and ferroptosis. Interestingly, sodium chlorate did not affect antioxidant glutathione levels. Western blot analysis revealed that sodium chlorate enhanced erastin-induced c-Jun N-terminal kinase phosphorylation, which is preferentially activated by cell stress-inducing signals. Collectively, our findings indicate that sulfation is an important modification for neuroprotection against oxytosis and ferroptosis in neuronal hippocampal cells.

Acute renal toxicity of sodium chlorate: Redox imbalance, enhanced DNA damage, metabolic alterations and inhibition of brush border membrane enzymes in rats

Sodium chlorate (NaClO₃ ) is widely used in paper and pulp industries and as a non-selective herbicide. Humans can be exposed to NaClO₃ through contaminated drinking water due to its improper and unchecked usage in industries and as herbicide. NaClO₃ is also present as a major stable by-product in drinking water that has been disinfected with chlorine dioxide. In this study, we have investigated the effect of a single acute oral dose of NaClO₃ on rat kidney. Adult male Wistar rats were divided into one control and four NaClO₃ treated groups that were orally given different doses of NaClO₃ and euthanized 24 hr after the treatment. Oral administration of NaClO₃ resulted in increased hydrogen peroxide levels, lipid, and protein oxidation while thiol and glutathione content and activities of brush border membrane enzymes were decreased in kidney in a NaClO₃ dose-dependent manner. Significant alterations in the activities of enzymes involved in carbohydrate metabolism and antioxidant defense were also observed. Administration of NaClO₃ induced DNA fragmentation and increased DNA-protein cross-linking. Histological studies showed marked damage in kidney from NaClO₃ treated animals. These results strongly suggest that NaClO₃ induces nephrotoxicity via redox imbalance that results in DNA and membrane damage, metabolic alterations and brush border membrane enzyme dysfunction.

Chlorate origin and fate in shallow groundwater below agricultural landscapes

In agricultural lowland landscapes, intensive agricultural is accompanied by a wide use of agrochemical application, like pesticides and fertilizers. The latter often causes serious environmental threats such as N compounds leaching and surface water eutrophication; additionally, since perchlorate can be present as impurities in many fertilizers, the potential presence of perchlorates and their by-products like chlorates and chlorites in shallow groundwater could be a reason of concern. In this light, the present manuscript reports the first temporal and spatial variation of chlorates, chlorites and major anions concentrations in the shallow unconfined aquifer belonging to Ferrara province (in the Po River plain). The study was made in 56 different locations to obtain insight on groundwater chemical composition and its sediment matrix interactions. During the monitoring period from 2010 to 2011, in June 2011 a nonpoint pollution of chlorates was found in the shallow unconfined aquifer belonging to Ferrara province. Detected chlorates concentrations ranged between 0.01 and 38 mg/l with an average value of 2.9 mg/l. Chlorates were found in 49 wells out of 56 and in all types of lithology constituting the shallow aquifer. Chlorates concentrations appeared to be linked to NO₃^-, volatile fatty acids (VFA) and oxygen reduction potential (ORP) variations. Chlorates behaviour was related to the biodegradation of perchlorates, since perchlorates are favourable electron acceptors for the oxidation of labile dissolved organic carbon (DOC) in groundwater. Further studies must take into consideration to monitor ClO₄^- in pore waters and groundwater to better elucidate the mass flux of ClO₄^- in shallow aquifers belonging to agricultural landscapes.

Anti-oxidative effects of safranal on immobilization-induced oxidative damage in rat brain

Safranal, a major constituent of saffron, possesses antioxidant and anti-apoptotic properties showing considerable neuroprotective effects. The present study was designed to investigate the effects of safranal against restraint stress induced oxidative damage in the rat brain. For inducing the chronic restraint stress, rats were kept in the restrainers for 1h every day, for 21 consecutive days, then, the animals received systemic administrations of vehicle (0.1% DMSO) acted as the control group or safranal daily for 21days. Results indicated that the rats submitted to restraint stress showed an increase in the immobility time versus the non-stress rats. In addition, stress decreased number of crossing in the rats submitted to restraint stress versus the non-stress animals. Treatment with safranal (0.75mg/kg) showed a significant reduction in the immobility time compared to the non-treated stress group, while, the treatment improved the number of crossing in rats submitted to restraint stress versus the vehicle-treated stress rats. In the stressed animals that received vehicle, the MDA level was significantly higher and the levels of GSH and antioxidant enzymes were significantly lower than the non-stressed rats. Safranal ameliorated the changes in the stressed animals as compared with the control groups. The present findings indicate that safranal might be effective against depressant-like effects induced by chronic stress via modulating brain oxidative response.

Sodium chlorate induces DNA damage and DNA-protein cross-linking in rat intestine: A dose dependent study

Sodium chlorate (NaClO₃) is widely used in paper and pulp industries and as a non-selective herbicide. It is also a major by-product generated upon disinfection of drinking water by chlorine dioxide. In this study, we have investigated the genotoxicity of NaClO₃ on the small intestine of rats. Adult male rats were divided into 5 groups: one control and four NaClO₃ treated groups. The NaClO₃ treated groups were given a single acute oral dose of NaClO₃ (100, 250, 500 and 750 mg/kg body weight) and sacrificed 24 h later. Administration of NaClO₃ caused significant DNA damage in a dose dependent manner in the rat intestine. This was evident from the comet assay which showed DNA strand breaks and was further confirmed by agarose gel electrophoresis and release of free nucleotides. Increased DNA protein cross-linking in NaClO₃ administered groups showed formation of a critical lesion which hampers activities of proteins/enzymes involved in DNA repair, transcription and replication. Thus, oral administration of NaClO₃ induces DNA damage in the rat intestine, probably through chlorate induced production of reactive oxygen species.

Concurrent Haloalkanoate Degradation and Chlorate Reduction by Pseudomonas chloritidismutans AW-1T

Haloalkanoates are environmental pollutants that can be degraded aerobically by microorganisms producing hydrolytic dehalogenases. However, there is a lack of information about the anaerobic degradation of haloalkanoates. Genome analysis of Pseudomonas chloritidismutans AW-1^T, a facultative anaerobic chlorate-reducing bacterium, showed the presence of two putative haloacid dehalogenase genes, the l-DEX gene and dehI, encoding an l-2-haloacid dehalogenase (l-DEX) and a halocarboxylic acid dehydrogenase (DehI), respectively. Hence, we studied the concurrent degradation of haloalkanoates and chlorate as a yet-unexplored trait of strain AW-1^T The deduced amino acid sequences of l-DEX and DehI revealed 33 to 37% and 26 to 86% identities with biochemically/structurally characterized l-DEX and the d- and dl-2-haloacid dehalogenase enzymes, respectively. Physiological experiments confirmed that strain AW-1^T can grow on chloroacetate, bromoacetate, and both l- and d-α-halogenated propionates with chlorate as an electron acceptor. Interestingly, growth and haloalkanoate degradation were generally faster with chlorate as an electron acceptor than with oxygen as an electron acceptor. In line with this, analyses of l-DEX and DehI dehalogenase activities using cell-free extract (CFE) of strain AW-1^T grown on dl-2-chloropropionate under chlorate-reducing conditions showed up to 3.5-fold higher dehalogenase activity than the CFE obtained from AW-1^T cells grown on dl-2-chloropropionate under aerobic conditions. Reverse transcription-quantitative PCR showed that the l-DEX gene was expressed constitutively independently of the electron donor (haloalkanoates or acetate) or acceptor (chlorate or oxygen), whereas the expression of dehI was induced by haloalkanoates. Concurrent degradation of organic and inorganic halogenated compounds by strain AW-1^T represents a unique metabolic capacity in a single bacterium, providing a new piece of the puzzle of the microbial halogen cycle.IMPORTANCE Halogenated organic and inorganic compounds are important environmental pollutants that have carcinogenic and genotoxic effects on both animals and humans. Previous research studied the degradation of organic and inorganic halogenated compounds separately but not concurrently. This study shows concurrent degradation of halogenated alkanoates and chlorate as an electron donor and acceptor, respectively, coupled to growth in a single bacterium, Pseudomonas chloritidismutans AW-1^T Hence, besides biogenesis of molecular oxygen from chlorate reduction enabling a distinctive placement of strain AW-1^T between aerobic and anaerobic microorganisms, we can now add another unique metabolic potential of this bacterium to the roster. The degradation of different halogenated compounds under anoxic conditions by a single bacterium is also of interest for the natural halogen cycle in different aquatic and terrestrial ecosystems where ample natural production of halogenated compounds has been documented.