Integrating bioassays, chemical analysis and in silico techniques to identify genotoxicants in surface water

High-efficiency effect-directed analysis (EDA) advancing toxicant identification in aquatic environments: Latest progress and application status

Facing the great threats to ecosystems and human health posed by the continuous release of chemicals into aquatic environments, effect-directed analysis (EDA) has emerged as a powerful tool for identifying causative toxicants. However, traditional EDA shows problems of low-coverage, labor-intensive and low-efficiency. Currently, a number of high-efficiency techniques have been integrated into EDA to improve toxicant identification. In this review, the latest progress and current limitations of high-efficiency EDA, comprising high-coverage effect evaluation, high-resolution fractionation, high-coverage chemical analysis, high-automation causative peak extraction and high-efficiency structure elucidation, are summarized. Specifically, high-resolution fractionation, high-automation data processing algorithms and in silico structure elucidation techniques have been well developed to enhance EDA. While high-coverage effect evaluation and chemical analysis should be further emphasized, especially omics tools and data-independent mass acquisition. For the application status in aquatic environments, high-efficiency EDA is widely applied in surface water and wastewater. Estrogenic, androgenic and aryl hydrocarbon receptor-mediated activities are the most concerning, with causative toxicants showing the typical structural features of steroids and benzenoids. A better understanding of the latest progress and application status of EDA would be beneficial to further advance in the field and greatly support aquatic environment monitoring.

Effects of the antidepressant mirtazapine on the swimming behaviour and gene expression rate of Danio rerio embryos - Is the sedating effect seen in humans also evident for fish?

In the last decade, mirtazapine has become an important antidepressant in clinical use and has also been found at many different environmental sampling sites. Several homologies between the zebrafish Danio rerio and humans, combined with a number of advantages for behavioural and gene expression research using zebrafish embryos, make their use for the analysis of mirtazapine appropriate. The sedative effect of mirtazapine in humans was also found for a specific concentration range in zebrafish embryos (1333.4 μg/L - 2666.9 μg/L). Specifically, 116 hpf old zebrafish embryos showed a reduced swimming distance when exposed to 1334.4 μg/L mirtazapine. Furthermore, changes at the gene regulatory level could be measured (1333.4 μg/L), in particular in the superordinate regulatory systems. For selected transporters of all regulatory systems, an up regulation of the genes by a factor of more than five times could be measured at the highest mirtazapine exposure concentration that was tested. Finally, studies on the protein levels demonstrated an increase in acetylcholinesterase activity for several exposure concentrations (83.3 μg/L and 666.7 μg/L). The physiological changes in zebrafish embryos caused by mirtazapine demonstrate the relevance of these types of studies in aquatic non-target organisms. Such neuroactive substances could pose a potential risk for aquatic organisms below the previously considered concentration threshold for morphological effects.

Subcritical and supercritical water oxidation for dye decomposition

The total annual output of synthetic dyes exceeds 7 × 10⁵ tons. About 1,000 tons of non-biodegradable synthetic dyes are released every year into the natural streams and water sources from textile wastes. The release of these colored wastewater exerts negative impact on aquatic ecology and human beings because of the poisonous and carcinogenic repercussions of dyes involved in coloration production. Therefore, with a growing interest in the environment, efficient technologies need to be developed to eliminate dyes from local and industrial wastewater. Supercritical water oxidation as a promising wastewater treatment technology has many advantages, such as a rapid reaction and pollution-free products. However, due to corrosion, salt precipitation and operational problems, supercritical water oxidation process did not gain expected industrial development. These technical difficulties can be overcome by application of non-corrosive subcritical water as a reaction medium. This work summarizes the negative impacts of dyes and role of subcritical and supercritical water and their efficiencies in dye oxidation processes.

Assessment of source and treated water quality in seven drinking water treatment plants by in vitro bioassays - Oxidative stress and antiandrogenic effects after artificial infiltration

Drinking water quality and treatment efficacy was investigated in seven drinking water treatment plants (DWTPs), using water from the river Göta Älv, which also is a recipient of treated sewage water. A panel of cell-based bioassays was used, including measurements of receptor activity of aryl hydrocarbon (AhR), estrogen (ER), androgen (AR), peroxisome proliferator-activated receptor alpha (PPARα) as well as induction of oxidative stress (Nrf2) and micronuclei formation. Grab water samples were concentrated by solid phase extraction (SPE) and water samples were analyzed at a relative enrichment factor of 50. High activities of AhR, ER and AR antagonism were present in WWTP outlets along the river. Inlet water from the river exhibited AhR and AR antagonistic activities. AhR activity was removed by DWTPs using granulated activated carbon (GAC) and artificial infiltration. AR antagonistic activity was removed by the treatment plants, except the artificial infiltration plant, which actually increased the activity. Furthermore, treated drinking water from the DWTP using artificial infiltration exhibited high Nrf2 activity, which was not found in any of the other water samples. Nrf2 activity was found in water from eight of the 13 abstraction wells, collecting water from the artificial infiltration. No genotoxic activity was detected at non-cytotoxic concentrations. No Nrf2 or AR antagonistic activities were detected in the inlet or outlet water after the DWTP had been replaced by a new plant, using membrane ultrafiltration and GAC. Neither target chemical analysis, nor chemical analysis according to the drinking water regulation, detected any presence of chemicals, which could be responsible of the prominent effects on oxidative stress and AR antagonistic activity in the drinking water samples. Thus, bioanalysis is a useful tool for detection of unknown hazards in drinking water and for assessment of drinking water treatments.

Optimization of a pre-metabolization procedure using rat liver S9 and cell-extracted S9 in the Ames fluctuation test

Many environmental pollutants pose a toxicological hazard only after metabolic activation. In vitro bioassays using cell lines or bacteria have often no or reduced metabolic activity, which impedes their use in the risk assessment. To improve the predictive capability of in vitro assays, external metabolization systems like the liver S9 fraction are frequently combined with in vitro toxicity assays. While it is typical for S9 fractions that samples and testing systems are combined in the same exposure system, we propose to separate the metabolism step and toxicity measurement. This allows for a modular combination of metabolic activation by enzymes isolated from rat liver (S9) or a biotechnological alternative (ewoS9^R) with in vitro bioassays that lack metabolic capacity. Benzo(a)pyrene and 2-aminoanthracene were used as model compounds to optimize the conditions for the S9 metabolic degradation/activation step. The Ames assay with Salmonella typhimurium strains TA98 and TA100 was applied to validate the set-up of decoupling the S9 activation/metabolism from the bioassay system. S9 protein concentration of 0.25 mg_protein/mL, a supplement of 0.13 mM NADPH and a pre-incubation time of 100 min are recommended for activation of samples prior to dosing them to in vitro bioassays using the regular dosing protocols of the respective bioassay. EwoS9^R performed equally well as Moltox S9, which is a step forward in developing true animal-free in vitro bioassays. After pre-incubation with S9 fraction, chemicals induced bacteria revertants in both the TA98 and the TA100 assay as efficiently as the standard Ames assay. The pre-incubation of chemicals with S9 fraction could serve for a wide range of cellular in vitro assays to efficiently combine activation and toxicity measurement, which may greatly facilitate the application of these assays for chemical hazard assessment and monitoring of environmental samples.

Testing the low dose mixtures hypothesis from the Halifax project

In 2013, 60 scientists, representing a larger group of 174 scientists from 26 nations, met in Halifax, Nova Scotia to consider whether - using published research - it was logical to anticipate that a mixture of chemicals, each thought to be non-carcinogenic, might act together in that mixture as a virtual carcinogen. The group identified 89 such chemicals, each one affecting one or more Hallmark(s) - collectively covering all Hallmarks of Cancer - confirming the possibility that a chemical mixture could induce all the Hallmarks and function as a virtual carcinogen, thereby supporting the concern that chemical safety research that does not evaluate mixtures, is incomplete. Based on these observations, the Halifax Project developed the Low-Dose Carcinogenesis Hypothesis which posits "…that low-dose exposures to [mixtures of] disruptive chemicals that are not individually carcinogenic may be capable of instigating and/or enabling carcinogenesis." Although testing all possible combinations of over 80,000 chemicals of commerce would be impractical, prudence requires designing a methodology to test whether low-dose chemical mixtures might be carcinogenic. As an initial step toward testing this hypothesis, we conducted a mini review of published empirical observations of biological exposures to chemical mixtures to assess what empirical data exists on which to base future research. We reviewed studies on chemical mixtures with the criteria that the studies reported both different concentrations of chemicals and mixtures composed of different chemicals. We found a paucity of research on this important question. The majority of studies reported hormone related processes and used chemical concentrations selected to facilitate studying how mixtures behave in experiments that were often removed from clinical relevance, i.e., chemicals were not studied at human-relevant concentrations. New research programs must be envisioned to enable study of how mixtures of small doses of chemicals affect human health, starting, when at all possible, from non-malignant specimens when studies are done in vitro. This research should use human relevant concentrations of chemicals, expand research beyond the historic focus on endocrine endpoints and endocrine related cancers, and specifically seek effects that arise uniquely from exposure to chemical mixtures at human-relevant concentrations.

QSAR models for the acute toxicity of 1,2,4-triazole fungicides to zebrafish (Danio rerio) embryos

In recent decades, the 1,2,4-triazole fungicides are widely used for crop diseases control, and their toxicity to wild lives and pollution to ecosystem have attracted more and more attention. However, how to quickly and efficiently evaluate the toxicity of these compounds to environmental organisms is still a challenge. In silico method, such like Quantitative Structure-Activity Relationship (QSAR), provides a good alternative to evaluate the environmental toxicity of a large number of chemicals. At the present study, the acute toxicity of 23 1,2,4-triazole fungicides to zebrafish (Danio rerio) embryos was firstly tested, and the LC₅₀ (median lethal concentration) values were used as the bio-activity endpoint to conduct QSAR modelling for these triazoles. After the comparative study of several QSAR models, the 2D-QSAR model was finally constructed using the stepwise multiple linear regression algorithm combining with two physicochemical parameters (logD and μ), an electronic parameter (Q_N1) and a topological parameter (X^vPC₄). The optimal model could be mathematically described as following: pLC₅₀ = -7.24-0.30X^vPC₄ + 0.76logD - 26.15Q_N1 - 0.08μ. The internal validation by leave-one-out (LOO) cross-validation showed that the R²_adj (adjusted noncross-validation squared correlation coefficient), Q² (cross-validation correlation coefficient) and RMSD (root-mean-square error) was 0.88, 0.84 and 0.17, respectively. The external validation indicated the model had a robust predictability with the q² (predictive squared correlation coefficient) of 0.90 when eliminated tricyclazole. The present study provided a potential tool for predicting the acute toxicity of new 1,2,4-triazole fungicides which contained an independent triazole ring group in their molecules to zebrafish embryos, and also provided a reference for the development of more environmentally-friendly 1,2,4-triazole pesticides in the future.

Synthesis, extracorporeal nephrotoxicity, and 3D-QSAR of andrographolide derivatives

Andrographolide is a traditional Chinese medicine monomer with many pharmacological activities, but has potential nephrotoxicity. Here, we aim to investigate the relationship between modification of andrographolide structure and its nephrotoxicity. Twenty-three andrographolide derivatives were synthesized, and their structures were confirmed by ¹ H-NMR and HRMS. Nephrotoxicity of these compounds against human renal tubular epithelial (HK-2) cells was evaluated using the MTT assay. The results indicated that most of them had significantly reduced nephrotoxicity, especially compounds III, V, and IX_c , with IC₅₀ values of 1,985, 1,300, and 806.9 μmol/L, respectively, which were obviously superior to andrographolide (IC₅₀ 30.60 μmol/L). However, compounds I_a -I_f (IC₅₀ values < 30 μmol/L), the 14-OH derivatives of andrographolide, showed higher nephrotoxicity than that of andrographolide. Three-dimensional quantitative structure-activity relationship (3D-QSAR) models of COMFA and COMSIA were established (COMFA: q²  = 0.639, r²  = 0.951; COMSIA: q²  = 0.569, r²  = 0.857). This model allowed proposing five new compounds with lower theoretical nephrotoxicity, which would be worthwhile to synthesize and evaluate. We believe that predicted models will help us to understand the structural modification requirements of andrographolide to reduce the nephrotoxicity, and further investigations will be needed to determine the mechanism involved in the effect of less nephrotoxic compounds.

Catalytic Oxidation Process for the Degradation of Synthetic Dyes: An Overview

Dyes are used in various industries as coloring agents. The discharge of dyes, specifically synthetic dyes, in wastewater represents a serious environmental problem and causes public health concerns. The implementation of regulations for wastewater discharge has forced research towards either the development of new processes or the improvement of available techniques to attain efficient degradation of dyes. Catalytic oxidation is one of the advanced oxidation processes (AOPs), based on the active radicals produced during the reaction in the presence of a catalyst. This paper reviews the problems of dyes and hydroxyl radical-based oxidation processes, including Fenton's process, non-iron metal catalysts, and the application of thin metal catalyst-coated tubular reactors in detail. In addition, the sulfate radical-based catalytic oxidation technique has also been described. This study also includes the effects of various operating parameters such as pH, temperature, the concentration of the oxidant, the initial concentration of dyes, and reaction time on the catalytic decomposition of dyes. Moreover, this paper analyzes the recent studies on catalytic oxidation processes. From the present study, it can be concluded that catalytic oxidation processes are very active and environmentally friendly methods for dye removal.

Toxicity of 10 organic micropollutants and their mixture: Implications for aquatic risk assessment

Micropollutants, as a serious water pollution issue, raise considerable toxicological concerns, particularly when present as components of complex mixtures. Due to the interactions of environmental pollution components (contaminant), the micropollutant problem is increasingly complex, thus, water quality of organic chemical contamination assessed substance-by-substance might lead to underestimation in aquatic environmental risk assessment. To assess the aquatic environmental risk of micropollutants mixture, a total of 10 organic micropollutants were selected and analysed by an approach of integration of literature data, laboratory experiments and prediction techniques. The experiment results showed that all 10 micropollutants were capable of causing toxicity in zebrafish embryos, aquatic invertebrates and algae with the LC50 (50% lethal concentration) values from 1.14 mg/L to 14.37 mg/L. Triclosan, carbamazepine, diazinon and diuron were the most hazardous compounds in the Danube River and the Rhine River. The artificial mixture presented a strong antagonistic relationship, which demonstrated an independent action (IA) model of the mixture. Based on the observed toxicity data, the risk quotients (RQs) of environmental mixtures of the Danube River and the Rhine River were extrapolated. It can be concluded that the micropollutant mixture may pose a potential risk for aquatic ecosystems with the present environmentally measured concentrations in the Danube River and Rhine River. Mixture risk assessment results suggested that the toxicity of studied chemicals might be induced by dissimilar actions, which is in agreement with the mixture toxicity prediction of the IA model. The observed findings could be useful to establish an overview of the pressures, vision, measures and expectations for hazardous substances pollution, which can help in making to informed decisions to reduce the concentration and bioactive fraction of pollutants.