Integrated biological–chemical approach for the isolation and selection of polyaromatic mutagens in surface waters

Tracking Aromatic Amines from Sources to Surface Waters

This review examines the environmental occurrence and fate of aromatic amines (AAs), a group of environmental contaminants with possible carcinogenic and mutagenic effects. AAs are known to be partially responsible for the genotoxic traits of industrial wastewater (WW), and AA antioxidants are acutely toxic to some aquatic organisms. Still, there are gaps in the available data on sources, occurrence, transport, and fate in domestic WW and indoor environments, which complicate the prevention of adverse effects in aquatic ecosystems. We review key domestic sources of these compounds, including cigarette smoke and grilled protein-rich foods, and their presence indoors and in aquatic matrices. This provides a basis to evaluate the importance of nonindustrial sources to the overall environmental burden of AAs. Appropriate sampling techniques for AAs are described, including copper-phthalocyanine trisulfonate materials, XAD resins in solid-phase extraction, and solid-phase microextraction methods, which can offer insights into AA sources, transport, and fate. Further discussion is provided on potential progress in the research of AAs and their behavior in an aim to support the development of a more comprehensive understanding of their effects and potential environmental risks.

Application of effect-directed analysis to identify mutagenic nitrogenous disinfection by-products of advanced oxidation drinking water treatment

Advanced oxidation processes are important barriers for organic micropollutants in (drinking) water treatment. It is however known that medium pressure UV/H₂O₂ treatment may lead to mutagenicity in the Ames test, which is no longer present after granulated activated carbon (GAC) filtration. Many nitrogen-containing disinfection by-products (N-DBPs) result from the reaction of photolysis products of nitrate with (photolysis products of) natural organic material (NOM) during medium pressure UV treatment of water. Identification of the N-DBPs and the application of effect-directed analysis to combine chemical screening results with biological activity would provide more insight into the relation of specific N-DBPs with the observed mutagenicity and was the subject of this study. To this end, fractions of medium pressure UV-treated and untreated water extracts were prepared using preparative HPLC and tested using the Ames fluctuation test. In addition, high-resolution mass spectrometry was performed on all fractions to assess the presence of N-DBPs. Based on toxicity data and read across analysis, we could identify five N-DBPs that are potentially genotoxic and were present in relatively high concentrations in the fractions in which mutagenicity was observed. The results of this study offer opportunities to further evaluate the identity and potential health concern of N-DBPs formed during advanced oxidation UV drinking water treatment.

Improving the accuracy of effect-directed analysis: the role of bioavailability

Aquatic ecosystems have been suffering from contamination by multiple stressors. Traditional chemical-based risk assessment usually fails to explain the toxicity contributions from contaminants that are not regularly monitored or that have an unknown identity. Diagnosing the causes of noted adverse outcomes in the environment is of great importance in ecological risk assessment and in this regard effect-directed analysis (EDA) has been designed to fulfill this purpose. The EDA approach is now increasingly used in aquatic risk assessment owing to its specialty in achieving effect-directed nontarget analysis; however, a lack of environmental relevance makes conventional EDA less favorable. In particular, ignoring the bioavailability in EDA may cause a biased and even erroneous identification of causative toxicants in a mixture. Taking bioavailability into consideration is therefore of great importance to improve the accuracy of EDA diagnosis. The present article reviews the current status and applications of EDA practices that incorporate bioavailability. The use of biological samples is the most obvious way to include bioavailability into EDA applications, but its development is limited due to the small sample size and lack of evidence for metabolizable compounds. Bioavailability/bioaccessibility-based extraction (bioaccessibility-directed and partitioning-based extraction) and passive-dosing techniques are recommended to be used to integrate bioavailability into EDA diagnosis in abiotic samples. Lastly, the future perspectives of expanding and standardizing the use of biological samples and bioavailability-based techniques in EDA are discussed.

Quantifying the contribution of dyes to the mutagenicity of waters under the influence of textile activities

The combination of chemical analyses and bioassays allows the identification of potentially mutagenic compounds in different types of samples. Dyes can be considered as emergent contaminants and were detected in waters, under the influence of textile activities. The objective of this study was to evaluate the contribution of 9 azo dyes to the mutagenicity of representative environmental samples. Samples were collected along one year in the largest conglomerate of textile industries of Brazil. We analyzed water samples from an important water body, Piracicaba River, upstream and downstream two main discharges, the effluent of a wastewater treatment plant (WWTP) and the tributary Quilombo River, which receives untreated effluent from local industries. Samples were analyzed using a LC-MS/MS and tested for mutagenicity in the Salmonella/microsome microsuspension assay with TA98 and YG1041. Six dyes were detected in the collected samples, Disperse Blue 291, Disperse Blue 373, Disperse Orange 30, Disperse Red 1, Disperse Violet 93, and Disperse Yellow 3. The most sensitive condition for the detection of the mutagenicity was the strain YG1041 with S9. The concentration of dyes and mutagenicity levels varied along time and the dry season represented the worst condition. Disperse Blue 373 and Disperse Violet 93 were the major contributors to the mutagenicity. We conclude that dyes are contributing for the mutagenicity of Piracicaba River water; and both discharges, WWTP effluent and Quilombo River, increase the mutagenicity of Piracicaba River waters in about 10-fold. The combination of chemical analysis and bioassays were key in the identification the main drivers of the water mutagenicity and allows the selection of priority compounds to be included in monitoring programs as well for the enforcing actions required to protect the water quality for multiple uses.

Identification of Mutagenic Aromatic Amines in River Samples with Industrial Wastewater Impact

Aromatic amines are one of the most important classes of compounds contributing to surface water mutagenicity due to their widespread occurrence as precursors and transformation products of dyes, pharmaceuticals, agrochemicals, and other compound classes. In this study, we implemented a workflow including novel analytical and data evaluation methods aiming to identify aromatic amines in six mutagenic wastewater effluents from a chemical-industrial area in Germany, collected by the passive sampler Blue Rayon. We identified 14 amines including the two potent mutagenic aromatic amines 2,3- and 2,8-phenazinediamine, which were reported for the first time as environmental contaminants. These two isomers accounted between 4.2 and 86% of the mutagenicity of the blue rayon extracts and may be byproducts of dye production at the studied site.

Mutagenicity in Surface Waters: Synergistic Effects of Carboline Alkaloids and Aromatic Amines

For decades, mutagenicity has been observed in many surface waters with a possible link to the presence of aromatic amines. River Rhine is a well-known example of this phenomenon but responsible compound(s) are still unknown. To identify the mutagenic compounds, we applied effect-directed analysis (EDA) utilizing novel analytical and biological approaches to a water sample extract from the lower Rhine. We could identify 21 environmental contaminants including two weakly mutagenic aromatic amines, and the known alkaloid comutagen norharman along with two related β-carboline alkaloids, carboline, and 5-carboline, which were reported the first time in surface waters. Results of mixture tests showed a strong synergism of the identified aromatic amines not only with norharman, but also with carboline and 5-carboline. Additionally, other nitrogen-containing compounds also contributed to the mutagenicity when aromatic amines were present. Thus, comutagenicity of β-carboline alkaloids with aromatic amines is shown to occur in surface waters. These results strongly suggest that surface water mutagenicity is highly complex and driven by synergistic mechanisms of a complex compound mixture (of which many are yet unidentified) rather than by single compounds. Therefore, mixture effects should be considered not only from mutagens alone, but also including possible comutagens and nonmutagenic compounds.

Nontargeted detection and identification of (aromatic) amines in environmental samples based on diagnostic derivatization and LC-high resolution mass spectrometry

The presence of aromatic amines in the environment has been in the focus of research, as many of these compounds are known or suspected mutagens and carcinogens. To facilitate the detection of aromatic amines in complex environmental samples by LC-high resolution mass spectrometry, an on-line-post-column and a pre-column derivatization method to label (in an ideal case) all aromatic amines was evaluated by applying different derivatization reagents. 4-Fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) was found to be the most promising labeling reagent due to its high reactivity with both primary and secondary amines and its low signal in positive mode electrospray ionization (ESI+). Post-column on-line derivatization did not result in sufficient signal intensities of derivatives. With pre-column derivatization most of the selected aromatic amines resulted in a derivative that shows common fragments of diagnostic value. The selectivity of NBD-F was studied in depth with a data set of 220 compounds with different functional groups showing that also aliphatic amines and some thiols yield a derivative. The developed method was successfully applied to wastewater effluent samples and several derivatives were confirmed by diagnostic neutral losses.

Anthropogenic Stressors Shape Genetic Structure: Insights from a Model Freshwater Population along a Land Use Gradient

Environmental pollution including mutagens from wastewater effluents and discontinuity by man-made barriers are considered typical anthropogenic pressures on microevolutionary processes that are responsible for the loss of biodiversity in aquatic ecosystems. Here, we tested for the effects of wastewater treatment plants (WWTPs), weirs and other stressors on the invertebrate species Gammarus pulex at the population genetic level combining evolutionary ecotoxicology, body burden analysis and testing for exposure to mutagens. Exposure to chemical pollution alone and in combination with the presence of weirs resulted in a depression of allelic richness in native G. pulex populations. Our results suggest that the input of a mutagenic effluent from a WWTP resulted in a strong increase in private alleles over the affected populations. In addition, the presence of weirs along the river disrupted the migration across the river and thus the gene flow between G. pulex upstream and downstream. This study provides strong evidence that the assessment of genetic variation including private alleles together with the contamination of mutagenic and nonmutagenic chemical pollution offers new insights into the regulation of genetic population structure and highlights the relevance of emerging anthropogenic pressures at the genetic level.

Effect-directed analysis supporting monitoring of aquatic environments--An in-depth overview

Aquatic environments are often contaminated with complex mixtures of chemicals that may pose a risk to ecosystems and human health. This contamination cannot be addressed with target analysis alone but tools are required to reduce this complexity and identify those chemicals that might cause adverse effects. Effect-directed analysis (EDA) is designed to meet this challenge and faces increasing interest in water and sediment quality monitoring. Thus, the present paper summarizes current experience with the EDA approach and the tools required, and provides practical advice on their application. The paper highlights the need for proper problem formulation and gives general advice for study design. As the EDA approach is directed by toxicity, basic principles for the selection of bioassays are given as well as a comprehensive compilation of appropriate assays, including their strengths and weaknesses. A specific focus is given to strategies for sampling, extraction and bioassay dosing since they strongly impact prioritization of toxicants in EDA. Reduction of sample complexity mainly relies on fractionation procedures, which are discussed in this paper, including quality assurance and quality control. Automated combinations of fractionation, biotesting and chemical analysis using so-called hyphenated tools can enhance the throughput and might reduce the risk of artifacts in laboratory work. The key to determining the chemical structures causing effects is analytical toxicant identification. The latest approaches, tools, software and databases for target-, suspect and non-target screening as well as unknown identification are discussed together with analytical and toxicological confirmation approaches. A better understanding of optimal use and combination of EDA tools will help to design efficient and successful toxicant identification studies in the context of quality monitoring in multiply stressed environments.

Linking mutagenic activity to micropollutant concentrations in wastewater samples by partial least square regression and subsequent identification of variables

We deployed multivariate regression to identify compounds co-varying with the mutagenic activity of complex environmental samples. Wastewater treatment plant (WWTP) effluents with a large share of industrial input of different sampling dates were evaluated for mutagenic activity by the Ames Fluctuation Test and chemically characterized by a screening for suspected pro-mutagens and non-targeted software-based peak detection in full scan data. Areas of automatically detected peaks were used as predictor matrix for partial least squares projections to latent structures (PLS) in combination with measured mutagenic activity. Detected peaks were successively reduced by the exclusion of all peaks with lowest variable importance until the best model (high R(2) and Q(2)) was reached. Peaks in the best model co-varying with the observed mutagenicity showed increased chlorine, bromine, sulfur, and nitrogen abundance compared to original peak set indicating a preferential selection of anthropogenic compounds. The PLS regression revealed four tentatively identified compounds, newly identified 4-(dimethylamino)-pyridine, and three known micropollutants present in domestic wastewater as co-varying with the mutagenic activity. Co-variance between compounds stemming from industrial wastewater and mutagenic activity supported the application of "virtual" EDA as a statistical tool to separate toxicologically relevant from less relevant compounds.

Multicriteria approach to select polyaromatic river mutagen candidates

The identification of unknown compounds remains one of the most challenging tasks to link observed toxic effects in complex environmental mixtures to responsible toxicants in effect-directed analysis (EDA). Here, a workflow is presented based on nontarget liquid chromatography-high resolution mass spectrometry (LC-HRMS) starting with molecular formulas determined in a previous study. A compound database search (ChemSpider) was performed to retrieve candidates for each formula. Subsequently, the number of candidates was reduced by applying MS-, physical-chemical, and chromatography-based selection criteria including HRMS/MS fragmentation and plausibility, ionization efficiency with different ion sources and detection modes, acid/base behavior, octanol/water partitioning, retention time prediction and finally toxic effects (mutagenicity caused by aromatic amines). The workflow strongly decreased the number of possible candidates and resulted in the tentative identification of possible mutagens and the positive identification of the nonmutagen benzyl(diphenyl) phosphine oxide in a mutagenic fraction. The positive identification of mutagens was hampered by a lack of commercially available standards. The workflow is an innovative and promising approach and forms an excellent basis for possible further advancements.

Metabolic transformation as a diagnostic tool for the selection of candidate promutagens in effect-directed analysis

To implement metabolic activation by S9 rat liver homogenate in the selection of candidate promutagens in effect-directed analysis, we critically assessed the capability of LC-HRMS measurements to detect depletion and formation of metabolites by S9 exposure. The exposure of a reference mixture to S9 led to a depletion by >70% for most compounds. Other processes than metabolism were excluded as significant contribution to compound depletion. Metabolites formed by S9 exposure were identified and S9 metabolism was incorporated in the identification of candidate promutagens in a wastewater treatment plant (WWTP) effluent with mutagenic activity only after metabolic activation by S9. The metabolism by S9 in the WWTP effluent was confirmed. Based on a candidate exclusion of all peaks not depleted, thus not activated by the S9 mix, the number of candidate promutagens was reduced by 40%. Selected remaining candidates were evaluated and identified, but could not be confirmed as promutagens.

The Critical Assessment of Small Molecule Identification (CASMI): Challenges and Solutions

The Critical Assessment of Small Molecule Identification, or CASMI, contest was founded in 2012 to provide scientists with a common open dataset to evaluate their identification methods. In this article, the challenges and solutions for the inaugural CASMI 2012 are presented. The contest was split into four categories corresponding with tasks to determine molecular formula and molecular structure, each from two measurement types, liquid chromatography-high resolution mass spectrometry (LC-HRMS), where preference was given to high mass accuracy data, and gas chromatography-electron impact-mass spectrometry (GC-MS), i.e., unit accuracy data. These challenges were obtained from plant material, environmental samples and reference standards. It was surprisingly difficult to obtain data suitable for a contest, especially for GC-MS data where existing databases are very large. The level of difficulty of the challenges is thus quite varied. In this article, the challenges and the answers are discussed, and recommendations for challenge selection in subsequent CASMI contests are given.