Sorption and leaching of benzalkonium chlorides in agricultural soils

Quaternary ammonium salts for water treatment with balanced rate of sterilization and degradation

The growing number of infections caused by drug-resistant bacteria which arise from the overuse of antibiotics has severely affected the normal operation of human society. The high antibacterial activity of QAS makes it promising as an alternative to antibiotics, but it suffers from secondary pollution due to its non-degradation. Here we have synthesized a class of gemini quaternary ammonium salts (GQAS) with different carbon chain lengths containing ester groups by using facile methylation reaction. Quaternary ammonium groups contribute to insert negatively charged bacterial membranes, resulting in membrane damage and bacteria death. Compared with conventional single-chain QAS, except for the more efficient antibacterial efficiency attribute to the presence of the second carbon chain, GQAS with alterable antibacterial properties can minimize the possibility of bacterial resistance and reduce the accumulation of GQAS in the environment through the introduction of degradable ester groups. GQAS is completely superior to the commercial bactericide benzalkonium chloride (BAC) in both antibacterial activity and degrade performance, which can be used as a more environmentally friendly bactericide.

Microbial biofilm metabolization of benzalkonium compounds (benzyl dimethyl dodecyl ammonium & benzyl dimethyl tetradecyl ammonium chloride)

Benzalkonium chlorides (BACs) are quaternary ammonium compounds (QUATs) that are used as biocides. The degradation of these compounds in wastewater treatment plants is essential to reduce their spread into the environment and thus prevent the development of QUAT-resistant genes. The biodegradation of two BACs (BAC-12 and BAC-14) was investigated in moving bed biofilm reactors (MBBRs). Degradation half-lives of 12 and 20 h for BAC-12 and - 14, respectively, were detected as well as the formation of 42 metabolites. Two new degradation pathways for the BACs were identified in this study: 1) one involving an ω-oxidation, followed by β-oxidation and 2) one via an ω-oxidation followed by an α-oxidation that was succeeded by β-oxidation. Similar metabolites were detected for both BAC-12 and BAC-14. Additional metabolites were detected in the study, that could not be assigned to the above-mentioned pathways, revealing even more metabolic pathways in the MBBR which is probably due to the complexity of the microbial community in the biofilm. Interestingly, both TP194 (Benzyl-(carboxymethyl)-dimethylazanium) and TP208B (Benzyl-(2-carboxyethyl)-dimethylazanium) were identified as end products of the ω/β-pathway and the α/β-pathway. TP208B, TP152 and TP250 that were identified in this study, as well as the known BDMA were discovered in the effluent of a wastewater treatment plant.

Benzalkonium Chloride and Benzethonium Chloride Effectively Reduce Spore Germination of Ginger Soft Rot Pathogens: Fusarium solani and Fusarium oxysporum

Ginger soft rot is a serious soil-borne disease caused by Fusarium solani and Fusarium oxysporum, resulting in reduced crop yields. The application of common chemical fungicides is considered to be an effective method of sterilization, and therefore, they pose a serious threat to the environment and human health due to their high toxicity. Benzalkonium chloride (BAC) and benzethonium chloride (BEC) are two popular quaternary ammonium salts with a wide range of fungicidal effects. In this study, we investigated the fungicidal effects of BAC and BEC on soft rot disease of ginger as alternatives to common chemical fungicides. Two soft rot pathogens of ginger were successfully isolated from diseased ginger by using the spread plate method and sequenced as F. solani and F. oxysporum using the high-throughput fungal sequencing method. We investigated the fungicidal effects of BAC and BEC on F. solani and F. oxysporum, and we explored the antifungal mechanisms. Almost complete inactivation of spores of F. solani and F. oxysporum was observed at 100 mg/L fungicide concentration. Only a small amount of spore regrowth was observed after the inactivation treatment of spores of F. solani and F. oxysporum in soil, which proved that BAC and BEC have the potential to be used as an alternative to common chemical fungicides for soil disinfection of diseased ginger.

Excessive disinfection aggravated the environmental prevalence of antimicrobial resistance during COVID-19 pandemic

During COVID-19 pandemic, chemicals from excessive consumption of pharmaceuticals and disinfectants i.e., antibiotics, quaternary ammonium compounds (QACs), and trihalomethanes (THMs), flowed into the urban environment, imposing unprecedented selective pressure to antimicrobial resistance (AMR). To decipher the obscure character pandemic-related chemicals portrayed in altering environmental AMR, 40 environmental samples covering water and soil matrix from surroundings of Wuhan designated hospitals were collected on March 2020 and June 2020. Chemical concentrations and antibiotic resistance gene (ARG) profiles were revealed by ultra-high-performance liquid chromatography-tandem mass spectrometry and metagenomics. Selective pressure from pandemic-related chemicals ascended by 1.4-5.8 times in March 2020 and then declined to normal level of pre-pandemic period in June 2020. Correspondingly, the relative abundance of ARGs under increasing selective pressure was 20.1 times that under normal selective pressure. Moreover, effect from QACs and THMs in aggravating the prevalence of AMR was elaborated by null model, variation partition and co-occurrence network analyses. Pandemic-related chemicals, of which QACs and THMs respectively displayed close interaction with efflux pump genes and mobile genetic elements, contributed >50 % in shaping ARG profile. QACs bolstered the cross resistance effectuated by qacEΔ1 and cmeB to 3.0 times higher while THMs boosted horizon ARG transfer by 7.9 times for initiating microbial response to oxidative stress. Under ascending selective pressure, qepA encoding quinolone efflux pump and oxa-20 encoding β-lactamases were identified as priority ARGs with potential human health risk. Collectively, this research validated the synergistic effect of QACs and THMs in exacerbating environmental AMR, appealing for the rational usage of disinfectants and the attention for environmental microbes in one-health perspective.

Anthropogenic antimicrobial micropollutants and their implications for agriculture

Antibiotics and disinfectants have saved millions of human lives and cured uncountable animal diseases, but their activity is not limited to the site of application. Downstream, these chemicals become micropollutants, contaminating water at trace levels, resulting in adverse impacts on soil microbial communities and threatening crop health and productivity in agricultural settings and perpetuating the spread of antimicrobial resistance. Especially as resource scarcity drives increased reuse of water and other waste streams, considerable attention is needed to characterize the fate of antibiotics and disinfectants and to prevent or mitigate environmental and public health impacts. In this review, we hope to provide an overview of why increasing concentrations of micropollutants such as antibiotics are concerning in the environment, how they can pose health risks for humans, and how they can be countered using bioremediation strategies.

Widespread occurrence of quaternary alkylammonium disinfectants in soils of Hesse, Germany

Quaternary alkylammonium compounds (QAACs) are cationic organic compounds with amphiphilic properties that are widely used as surfactants and disinfectants in industry, households and agriculture. Several studies suggest that QAACs co-select for antibiotic resistant microorganisms and thus may contribute to the spread of antibiotic resistance in the environment. Data on QAAC occurrence in soil are scarce and limited to soils that are prone to direct exposure to QAACs. Therefore, we conducted a comprehensive study on the occurrence of QAACs in soils of Hesse, a federal state in Germany, covering an area of 21,115 km². Sixty-five soil samples that comprised different land uses (arable, grassland, forest, vineyard) and area types (rural, agglomeration) were analysed for concentrations of alkyltrimethylammonium (ATMACs, with alkyl chain lengths C8-C16), benzylalkyldimethylammonium (BACs, C8-C18) and dialkyldimethylammonium compounds (DADMACs, C8-C18) via HPLC-MS/MS after ultrasonic-assisted extraction with acidified acetonitrile. QAACs were detected in 97 % of the soil samples irrespective of land use and area type. The most abundant QAAC homologues were DADMACs > BACs > ATMACs. The highest total QAAC concentrations were detected in alluvial soils influenced by the deposition of suspended particles during flood events, with DADMAC-C16 and -C18 as the dominant homologues. The high abundance of long-chain DADMACs suggests that legacy pollution and accumulation govern QAAC concentrations in soils. The presence of QAACs in forest soils points to a potential input via atmospheric deposition. Our work highlights the widespread occurrence of QAACs in soils of Hesse and the need for more research on their entry paths and fate in the soil ecosystem.

Adsorption of cationic surfactant as a probe of the montmorillonite surface reactivity in the alginate hydrogel composites

Adsorption of a cationic surfactant allowed to probe the surface reactivity of montmorillonite encapsulated in a composite of alginate hydrogels (A-MMT). Dodecylbenzyldimethylammonium chloride (BAC-12) was the surfactant used for these studies. BAC-12 is part of the widely used surfactant mixture known as benzalkonium chloride. XRD showed that up to three different types of basal spacing (d 001) were present within the composite indicating that as the concentration of adsorbed BAC-12 increases, populations with different adsorption conformational arrangements are present, even unexpanded clay remains. From the SEM-EDS spectra it is observed that the clay is distributed in the whole composite. In addition, the effect of the presence of cationic and anionic biocides on BAC-12 adsorption was studied. Cationic biocides such as tetradecyllbenzyldimethylammonium chlorides (BAC-14) and paraquat (PQ) show a competitive behavior for the clay adsorption sites at BAC-12 low concentration indicating an electrostatic adsorption mechanism. However, the presence of anionic contaminants such as 2,4-D and metsulfuron methyl do not affect surfactant adsorption. In all scenarios is observed an abrupt increase of BAC-12 adsorbed amount reaching values higher than the clay CEC suggesting strong tail-tail interactions. This occurs at concentrations 10 times lower than the CMC of BAC-12 promoted by clay encapsulation in the composite. In these composites the alginate does not affect the surface reactivity of the clay, but the formation of the hydrogel allows it to be easily extracted from aqueous media which makes it an interesting material with a potential use in water remediation.

Ecological Risk Analysis for Benzalkonium Chloride, Benzethonium Chloride, and Chloroxylenol in US Disinfecting and Sanitizing Products

Use of three topical antiseptic compounds-benzalkonium chloride (BAC), benzethonium chloride (BZT), and chloroxylenol (PCMX)-has recently increased because of the phaseout of other antimicrobial ingredients (such as triclosan) in soaps and other disinfecting and sanitizing products. Further, use of sanitizing products in general increased during the coronavirus (COVID-19) pandemic. We assessed the environmental safety of BAC, BZT, and PCMX based on best available environmental fate and effects data from the scientific literature and privately held sources. The ecological exposure assessment focused on aquatic systems receiving effluent from wastewater-treatment plants (WWTPs) and terrestrial systems receiving land-applied WWTP biosolids. Recent exposure levels were characterized based on environmental monitoring data supplemented by modeling, while future exposures were modeled based on a hypothetical triclosan replacement scenario. Hazard profiles were developed based on acute and chronic studies examining toxicity to aquatic life (fish, invertebrates, algae, vascular plants) and terrestrial endpoints (plants, soil invertebrates, and microbial functions related to soil fertility). Risks to higher trophic levels were not assessed because these compounds are not appreciably bioaccumulative. The risk analysis indicated that neither BZT nor PCMX in any exposure media is likely to cause adverse ecological effects under the exposure scenarios assessed in the present study. Under these scenarios, total BAC exposures are at least three times less than estimated effect thresholds, while margins of safety for freely dissolved BAC are estimated to be greater than an order of magnitude. Because the modeling did not specifically account for COVID-19 pandemic-related usage, further environmental monitoring is anticipated to understand potential changes in environmental exposures as a result of increased antiseptic use. The analysis presented provides a framework to interpret future antiseptic monitoring results, including monitoring parameters and modeling approaches to address bioavailability of the chemicals of interest. Environ Toxicol Chem 2022;41:3095-3115. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Molecular evidence for suppression of swimming behavior and reproduction in the estuarine rotifer Brachionus koreanus in response to COVID-19 disinfectants

The increased use of disinfectants due to the spread of the novel coronavirus infection (e.g. COVID-19) has caused burden in the environment but knowledge on its ecotoxicological impact on the estuary environment is limited. Here we report in vivo and molecular endpoints that we used to assess the effects of chloroxylenol (PCMX) and benzalkonium chloride (BAC), which are ingredients in liquid handwash, dish soap products, and sanitizers used by consumers and healthcare workers on the estuarine rotifer Brachionus koreanus. PCMX and BAC significantly affected the life table parameters of B. koreanus. These chemicals modulated the activities of antioxidant enzymes such as superoxide dismutase and catalase and increased reactive oxygen species even at low concentrations. Also, PCMX and BAC caused alterations in the swimming speed and rotation rate of B. koreanus. Furthermore, an RNA-seq-based ingenuity pathway analysis showed that PCMX affected several signaling pathways, allowing us to predict that a low concentration of PCMX will have deleterious effects on B. koreanus. The neurotoxic and mitochondrial dysfunction event scenario induced by PCMX reflects the underlying molecular mechanisms by which PCMX produces outcomes deleterious to aquatic organisms.

Can Alkyl Quaternary Ammonium Cations Substitute H2O2 in Controlling Cyanobacterial Blooms-Laboratory and Mesocosm Studies

Mitigation of harmful cyanobacterial blooms that constitute a serious threat to water quality, particularly in eutrophic water, such as in aquaculture, is essential. Thus, in this study, we tested the efficacy of selected cyanocides towards bloom control in laboratory and outdoor mesocosm experiments. Specifically, we focused on the applicability of a group of cationic disinfectants, alkyltrimethyl ammonium (ATMA) compounds and H₂O₂. The biocidal effect of four ATMA cations with different alkyl chain lengths was evaluated ex situ using Microcystis colonies collected from a fish pond. The most effective compound, octadecyl trimethyl ammonium (ODTMA), was further evaluated for its selectivity towards 24 cyanobacteria and eukaryotic algae species, including Cyanobacteria, Chlorophyta, Bacillariophyta, Euglenozoa and Cryptophyta. The results indicated selective inhibition of cyanobacteria by ODTMA-Br (C18) on both Chroccocales and Nostocales, but a minor effect on Chlorophytes and Bacillariophytes. The efficacy of ODTMA-Br (C18) (6.4 μM) in mitigating the Microcystis population was compared with that of a single low dose of H₂O₂ treatments (117.6 μM). ODTMA-Br (C18) suppressed the regrowth of Microcystis for a longer duration than did H₂O₂. The results suggested that ODTMA-Br (C18) may be used as an effective cyanocide and that it is worth further evaluating this group of cationic compounds as a treatment to mitigate cyanobacterial blooms in aquaculture.

Validation of an Analytical Workflow for the Analysis of Pesticide and Emerging Organic Contaminant Residues in Paddy Soil and Rice

Contamination of agricultural soil with organic contaminants is a global problem due to the risks associated with food security and ecological sustainability. Besides the use of agrochemicals, hundreds of emerging contaminants enter arable lands through polluted irrigation water. In this study, an analytical workflow based on QuEChERS extraction coupled with LC-MS/MS quantification was applied to measure 65 emerging contaminants (42 pesticides and 23 multiclass industrial chemicals) in soil and rice for the first time. The method was validated on paddy and yard soil and rice plants. A recovery efficiency ranging between 70 and 120% (RSD <20%) was achieved for more than 70% of the analytes. Then, the validated method was used to quantify target contaminants in 22 soil and 9 rice samples collected mainly from paddy fields close to the Ergene River (Turkey), which is a highly polluted river used for irrigation in the region. Pesticide residues were present in all soil samples up to 2.4 mg/kg. However, their concentrations were below their maximum residual limits in rice. Azoxystrobin, prochloraz, propiconazole, imidacloprid, and epoxiconazole were the most frequently detected pesticides. In addition, industrial pollutants such as benzyldimethyldodecylammonium and tris(2-butoxyethyl) phosphate were detected in paddy soil samples at concentrations between 0.1 and 691 μg/kg. Benzyldimethyldodecylammonium and 5-methyl-1H benzotriazole were also measured in rice at concentrations up to 0.26 and 2.13 μg/kg, respectively.

A Review on the Fate of Legacy and Alternative Antimicrobials and Their Metabolites during Wastewater and Sludge Treatment

Antimicrobial compounds are used in a broad range of personal care, consumer and healthcare products and are frequently encountered in modern life. The use of these compounds is being reexamined as their safety, effectiveness and necessity are increasingly being questioned by regulators and consumers alike. Wastewater often contains significant amounts of these chemicals, much of which ends up being released into the environment as existing wastewater and sludge treatment processes are simply not designed to treat many of these contaminants. Furthermore, many biotic and abiotic processes during wastewater treatment can generate significant quantities of potentially toxic and persistent antimicrobial metabolites and byproducts, many of which may be even more concerning than their parent antimicrobials. This review article explores the occurrence and fate of two of the most common legacy antimicrobials, triclosan and triclocarban, their metabolites/byproducts during wastewater and sludge treatment and their potential impacts on the environment. This article also explores the fate and transformation of emerging alternative antimicrobials and addresses some of the growing concerns regarding these compounds. This is becoming increasingly important as consumers and regulators alike shift away from legacy antimicrobials to alternative chemicals which may have similar environmental and human health concerns.

Application of an algal growth inhibition assay to determine distribution coefficients of benzalkonium ions between kaolinite and water

Benzalkonium compounds are widely used and found in environmental samples. Due to their amphiphilic nature, it is important to know sorption coefficients to account their bioavailability. However, currently available models describing their partitioning were developed using low molecular weight homologues and it cannot be ascertained whether they are applicable to their higher molecular weight homologues. Reasons for the scarcity of data on highly sorptive compounds include the lack of reliable quantification techniques for analyzing these chemicals at environmentally relevant levels. This study, therefore, reports on an algal growth inhibition assay-based method for the determination of kaolinite/water distribution coefficients for benzalkonium compounds at their environmentally relevant concentration range. Sorption to clay was computed using the difference between median effective concentration determined in a culture with kaolinite and that derived from a culture grown in standard medium. A kinetic model was used to account for uptake into algal cells and to calculate free concentrations. Due to the sensitivity of the algal species, Pseudokirchneriella subcapitata, it was possible to determine distribution coefficients below micromole per liter concentrations. The computed distribution coefficients showed a linear increase with number of carbon atoms in the alkyl chain up to 14. The proposed bioassay-based method should be applicable to determine distribution coefficients for highly hydrophobic chemicals and ionic liquids at a concentration range lower than typical analytical limits.

Effect of plants and their root exudate on bacterial activities during rhizobacterium-plant remediation of phenol from water

We investigated remediation of phenol from water using microbe-plant partnerships. Co-introduction of maize seedlings, Pseudomonas fluorescens rifampicin-resistant P13 and P. stutzeri P7 carrying self-transmissible TOL-like plasmids reduced phenol content in water at lower phenol concentrations (25, 50, and 75 mg/L), similar to individual introduction of the bacteria. Co-introduction of plants and bacteria significantly reduced phenol content in water at higher phenol concentrations (100, 125, and 150 mg/L) compared to using individual introduction of the bacteria. Moreover, TOL-like plasmids were transferred from P7 to P13. Addition of plants promoted the growth of both strains, leading to increased plasmid transfer. At higher phenol concentrations, addition of plants resulted in increases of catechol 2, 3-dioxygenase (C23O) activity and reduction in level of reactive oxygen species (ROS) of bacteria in the degradation experiments. Increased plasmid transfer and C23O activity and reduction in ROS level might be the major reasons why plants promote bacterial degradation of phenol at higher phenol concentrations. Furthermore, root exudate of maize seedlings and artificial root exudate (ARE) constructed using major components of the root exudate had the same effects on bacterial activities. Unlike the ARE, deletion of glucose, arabinose, or fructose or all the monosaccharides from ARE resulted in no increase in numbers of both strains and in plasmid transfer. At the higher phenol concentrations, deletion of glutamic acid, aspartic acid, alanine, or glycine or all the amino acids did not stimulate bacterial C23O activity. Deletion of fumaric, oxaloacetic or citric acids still reduced bacterial ROS level as ARE did, but, deletion of all the organic acids or DIMBOA, a hydroxamic acid, did not reduce bacterial ROS level as ARE did. The data showed that each monosaccharide might be important for sufficient numbers of plant-associated bacteria and increased plasmid transfer while each amino acid might be important for maintaining bacterial C23O activity and that DIMBOA might be responsible for the decrease in ROS levels. These results are the basis for efficient remediation of phenol from water by microbe-plant partnerships and further studies on the mechanism of rhizobacterium-plant interaction.