Identification Of Chemicals Research Articles

Prioritising site-specific micropollutants in surface water from LC-HRMS non-target screening data using a rarity score

BackgroundCurrent compound prioritisation and monitoring approaches within Europe focus mainly on widely occurring priority and river basin specific pollutants but may overlook site-specific contamination from local emission sources. Thus, we propose a robust and semiautomated approach for the identification of site-specific chemicals and a prioritisation of water bodies with specific contamination based on non-target screening data from liquid chromatography coupled to high-resolution mass spectrometry.ResultsFor prioritisation of site-specific contaminants, we calculated rarity scores for all peaks occurring in a set of 31 surface water samples, which combine the maximum signal intensity of a peak in a dataset with its frequency of occurrence in that dataset in one single number. These were a robust measure without the need to address the problems of missing data in more sophisticated multivariate statistical methods. For our dataset, site-specific compounds were defined for rarity scores > 1000, and the studied 31 sites showed a huge difference in the number of such peaks (0–91 in positive and 0–48 in negative ion mode). Together with isotopologue detection, the evaluation of mass defects and the occurrence of homologue series, which all could be obtained from automated data processing, a more detailed characterisation of these site-specific contaminations was possible. For three selected sites with a high number of site-specific peaks, novel or unexpected compounds could be identified, which stem from specific usage or (former) industrial production upstream of these sites.Conclusions and outlookThe proposed approach allows for a rapid screening of large non-target screening datasets for site-specific contaminants, the prioritisation of sites with such a specific contamination and the subsequent identification of these compounds. Thus, the risk of overlooking possibly hazardous chemicals (including unknowns) which are not covered in conventional monitoring and prioritisation schemes is reduced.

Establishment and performance assessment of an in-house 3D Reconstructed Human Cornea-Like Epithelium (RhCE) as a screening tool for the identification of liquid chemicals with potential eye hazard

The objective of this project was to develop an in-house 3D Reconstructed Human Cornea-Like Epithelium (RhCE) to be used as a screening tool in early stages of product development. This study reports the establishment of the experimental procedure and the performance assessment of the model to discriminate liquid chemicals classified as causing serious eye damage/irritation (UN-GHS Category 1/2) from liquid chemicals not requiring such hazard classification (UN-GHS No Category). Histological examination of this ocular equivalent model, based on Normal Human Keratinocytes (NHK) cultured in a chemically defined medium, revealed a stratified and well-organized tissue construct. Moreover, barrier robustness and functionality were demonstrated by the effective time-50 (ET50) of Triton X-100 measurement. The prediction model is based on cytotoxicity assessment following a test chemical exposure. When the mean tissue viability was over 60%, the chemical was defined as No Category; otherwise, it was classified as Category 1/2. In accordance with the applicable OECD guidance document (ENV/JM/MONO (2015)23), the performance of the model for eye hazard identification was evaluated with the minimum list of reference chemicals. As a result, the method scored 84.4% Accuracy, 70.8% Specificity, 100% Sensitivity and 93.3% for Concordance, demonstrating prediction performances close to those of Validated Reference Methods that are commonly used for regulatory purposes. Finally, these results suggest that this in-house RhCE based test method is a qualitative and accurate screening tool for eye hazard identification of liquid chemicals.

Liquid trace detection and identification by spectral reflectance model

A basic concept for detection and identification of liquid phase chemicals that may harm the environment is presented. Reliable detection is shown to be possible using a simplified model describing a uniform layer as well as realistic dispersal, shown to be in nonuniform irregular surface coverage. The results are dependent upon the effect of droplet size and spectral scattering from liquid–air interface on the measured scattered light. This information is crucial for accurate identification for on-site real-time sensing.

Identification of novel agonists by high-throughput screening and molecular modelling of human constitutive androstane receptor isoform 3.

Prediction of drug interactions, based on the induction of drug disposition, calls for the identification of chemicals, which activate xenosensing nuclear receptors. Constitutive androstane receptor (CAR) is one of the major human xenosensors; however, the constitutive activity of its reference variant CAR1 in immortalized cell lines complicates the identification of agonists. The exclusively ligand-dependent isoform CAR3 represents an obvious alternative for screening of CAR agonists. As CAR3 is even more abundant in human liver than CAR1, identification of its agonists is also of pharmacological value in its own right. We here established a cellular high-throughput screening assay for CAR3 to identify ligands of this isoform and to analyse its suitability for identifying CAR ligands in general. Proof-of-concept screening of 2054 drug-like compounds at 10µM resulted in the identification of novel CAR3 agonists. The CAR3 assay proved to detect the previously described CAR1 ligands in the screened libraries. However, we failed to detect CAR3-selective compounds, as the four novel agonists, which were selected for further investigations, all proved to activate CAR1 in different cellular and in vitro assays. In primary human hepatocytes, the compounds preferentially induced the expression of the prototypical CAR target gene CYP2B6. Failure to identify CAR3-selective compounds was investigated by molecular modelling, which showed that the isoform-specific insertion of five amino acids did not impact on the ligand binding pocket but only on heterodimerization with retinoid X receptor. In conclusion, we demonstrate here the usability of CAR3 for screening compound libraries for the presence of CAR agonists.

Standoff Detection and Identification of Explosives and Hazardous Chemicals in Simulated Real Field Scenario using Time Gated Raman Spectroscopy

The detection of hazardous chemicals, explosives, improvised explosive materials, energetic materials and their associated compounds for security screening, forensic applications and detection of unexploded ordnance is an active area of research. The results based on comprehensive experimental study and performance of time gated Raman spectroscopy (TGRS) for stand-off detection of explosives and hazardous chemicals under realistic scenario are presented. Representative results drawn from the experimental study for detection of explosives and hazardous chemicals in simulated real field scenario are given.

In vitro skin irritation assessment using EpiDerm™: applicability for updating toxicity information of oxybenzone and N,N-diethyl-m-toluamide

A skin irritation test using in vitro reconstructed human epidermis (RhE) models was established for hazard identification of irritant chemicals in accordance with UN Globally Harmonized System of Classification and Labelling of Chemicals (GHS) category. In this study, EpiDerm™ was used to assess skin irritation by oxybenzone and N,N-diethyl-m-toluamide (DEET), which are widely used sunscreen and insect repellent components, respectively. EpiDerm™ was applied with oxybenzone and DEET, combined and sequentially with each single dose. Epidermal morphology and differentiation/proliferation were examined microscopically. Oxybenzone and sequential administration groups were determined as nonirritant with cell viability >50% and the morphology was comparable to the human epidermis. Contrastingly, the DEET and coadministration groups exhibited cell viability <50% and poor epidermal morphology. Interleukin (IL)-1α release from substance-treated EpiDerm™ increased inversely to cell viability, suggesting the pro-inflammatory reaction was initiated by DEET. CK-10, E-cadherin, Ki-67, laminin, and ceramide were identified as relevant markers to assess oxybenzone- or DEET-induced epidermal injury. In conclusion, these results may indicate to be aware of the possible skin irritation by indiscriminate use of oxybenzone and DEET without animal testing.

Quality Markers of Traditional Chinese Medicine: Concept, Progress, and Perspective

Abstract As the most important complementary medication against a variety of diseases, traditional Chinese medicines (TCMs) have been extensively applied over thousands of years. Current quality control of herbal medicines, however, is in great dispute. Unlike chemical drugs, which have clear and validated quality standards, the content of only one (or a few) compounds of many herbs and preparations is currently assessed as an indicator of quality, even though the assessed compound(s) is neither closely associated with the efficacy nor representative of the medicine as a whole. Based on the clinical use, compatibility of multiple component prescriptions, and manufacturing process of TCM, the new concept of a TCM quality marker that was proposed in previous work is discussed further here. In addition, practical technological approaches are described for the qualitative analysis and quantification of TCMs including herbs, processed products, and preparations, which lead to the discovery and identification of specific chemicals as quality markers and new quality control patterns. The progress that has been made in TCM quality control is also addressed. This work provides useful information for the quality control of herbal medicines in the future.

Time-course of coiling activity in zebrafish (Danio rerio) embryos exposed to ethanol as an endpoint for developmental neurotoxicity (DNT) – Hidden potential and underestimated challenges

Detection of developmental neurotoxicity (DNT) has been recognized as a major challenge by regulatory bodies and science. In search of sensitive and specific test methods, spontaneous tail coiling of embryonic zebrafish has been recommended as a promising tool for identification of DNT-inducing chemicals. The present study was designed to develop a protocol for a prolonged test to study neurotoxicity during the entire development of coiling movement in zebrafish embryos. Ambient illumination was found to modulate coiling activity from the very onset of tail movements representing the earliest behavioral response to light possible in zebrafish. In the dark, embryos displayed increased coiling activity in a way known from photokinesis, a stereotypical element of the visual motor response. Elevated coiling activity during dark phases allows for the development of test strategies that integrate later coiling movements under the control of a further developed nervous system.Furthermore, zebrafish embryos were exposed to ethanol, and coiling activity was analyzed according to the new test protocol. Exposure of embryos to non-teratogenic concentrations of ethanol (0.4–1%) resulted in a delay of the onset of coiling activity and heartbeat. Moreover, ethanol produced a dose-dependent increase in coiling frequency at 26 h post-fertilization, indicating the involvement of neurotoxic mechanisms. Analysis of coiling activity during prolonged exposure allowed for (1) attributing effects on coiling activity to different mechanisms and (2) preventing false interpretation of results. Further research is needed to verify the potential of this test protocol to distinguish between different mechanisms of neurotoxicity.

Determination of Endocrine Disruption Potential of Bisphenol A Alternatives in Food Contact Materials Using In Vitro Assays: State of the Art and Future Challenges.

Alternatives to bisphenol A (BPA) are developed for food contact materials as a result of increasing evidence of exposure-correlated harmful effects of BPA. In vitro assays provide the fast, affordable, and mechanism insightful ways to screen endocrine disruption (ED), which is a major concern of new BPA alternatives. In this review, we summarize the safety and regulation information on the alternatives to BPA, review the state of the art of in vitro assays for ED evaluation, highlight their advantages and limitations, and discuss the challenges and future research needs. Our review shows that ligand binding, reporter gene, cell proliferation, and steroidogenesis are four commonly used in vitro assays to determine the ED at the response of receptor, gene transcription, and whole cell level. Major challenges are found from in vitro-in vivo translation and identification of ED chemicals in polymers. More studies on these areas are needed in the future.

Towards High-Throughput Chemobehavioural Phenomics in Neuropsychiatric Drug Discovery.

Identifying novel marine-derived neuroactive chemicals with therapeutic potential is difficult due to inherent complexities of the central nervous system (CNS), our limited understanding of the molecular foundations of neuro-psychiatric conditions, as well as the limited applications of effective high-throughput screening models that recapitulate functionalities of the intact CNS. Furthermore, nearly all neuro-modulating chemicals exhibit poorly characterized pleiotropic activities often referred to as polypharmacology. The latter renders conventional target-based in vitro screening approaches very difficult to accomplish. In this context, chemobehavioural phenotyping using innovative small organism models such as planarians and zebrafish represent powerful and highly integrative approaches to study the impact of new chemicals on central and peripheral nervous systems. In contrast to in vitro bioassays aimed predominantly at identification of chemicals acting on single targets, phenotypic chemobehavioural analysis allows for complex multi-target interactions to occur in combination with studies of polypharmacological effects of chemicals in a context of functional and intact milieu of the whole organism. In this review, we will outline recent advances in high-throughput chemobehavioural phenotyping and provide a future outlook on how those innovative methods can be utilized for rapidly screening and characterizing marine-derived compounds with prospective applications in neuropharmacology and psychosomatic medicine.

Improving training on cleaner production through Borich needs assessment model in SAF leather industry, Nowapara, Jessore, Bangladesh

The present study has been undertaken to assess the training needs of employer on cleaner production in SAF leather industry at Jashore district in Bangladesh. Using Borich Need Assessment Model for training needs. A total 60 employers were surveyed including 20 employers from each group and data were collected on socioeconomic condition of responders, management activities in leather processing and environment pollution related issues through the questionnaire. The importance level, competence needs were analyzed and ranked using weighted discrepancy scores (WDS). The study revealed that the highest WDS score (15.38) was found for Beam house worker that indicated the training is strongly needed for them on identification of harmful chemicals and environmental pollution. Crust and fishing unit worker needed high training (WDS score= 15.10) on understanding the types and quantities wastewater discharged from industry during leather processing and its management. The WDS score 14.78 was estimated for administrative employers where they needed high training on controlling odor problem from the industry. Although they have an average knowledge about the environmental pollution, they did not have qualified level of capabilities on understanding how to use some environmental tools e.g. social impact assessment and environmental auditing. Therefore, majority of the respondents preferred training for reduction of environmental pollution.&#x0D; Asian Australas. J. Food Saf. Secur. 2019, 3(1), 15-22

Validation of the GARD™skin Assay for Assessment of Chemical Skin Sensitizers: Ring Trial Results of Predictive Performance and Reproducibility.

Proactive identification of chemicals with skin sensitizing properties is a key toxicological endpoint within chemical safety assessment, as required by legislation for registration of chemicals. In order to meet demands of increased animal welfare and facilitate increased testing efficiency also in nonregulatory settings, considerable efforts have been made to develop nonanimal approaches to replace current animal testing. Genomic Allergen Rapid Detection (GARD™) is a state-of-the-art technology platform, the most advanced application of which is the assay for assessment of skin sensitizing chemicals, GARD™skin. The methodology is based on a dendritic cell (DC)-like cell line, thus mimicking the mechanistic events leading to initiation and modulation of downstream immunological responses. Induced transcriptional changes are measured following exposure to test chemicals, providing a detailed evaluation of cell activation. These changes are associated with the immunological decision-making role of DCs in vivo and include among other phenotypic modifications, up-regulation of co-stimulatory molecules, induction of cellular and oxidative stress pathways and xenobiotic responses, and provide a holistic readout of substance-induced DC activation. Here, results from an inter-laboratory ring trial of GARD™skin, conducted in compliance with OECD guidance documents and comprising a blinded chemical test set of 28 chemicals, are summarized. The assay was found to be transferable to naïve laboratories, with an inter-laboratory reproducibility of 92.0%. The within-laboratory reproducibility ranged between 82.1% and 88.9%, whereas the cumulative predictive accuracy across the 3 laboratories was 93.8%. It was concluded that GARD™skin is a robust and reliable method for the identification of skin sensitizing chemicals and suitable for stand-alone use or as a constituent of integrated testing. These data form the basis for the regulatory validation of GARD™skin.

Mitigating the effects of granular scattering using cepstrum analysis in terahertz time-domain spectral imaging.

Terahertz (THz) imaging is a widely used technique in the study and detection of many chemicals and biomolecules in polycrystalline form because the spectral absorption signatures of these target materials often lie in the THz frequencies. When the size of dielectric grain boundaries are comparable to the THz wavelengths, spectral features can be obscured due to electromagnetic scattering. In this study, we first investigate this granular scattering effect in identification of chemicals with THz spectral absorption features. We then will propose a signal processing technique in the so-called “quefrency” domain to improve the ability to resolve these spectral features in the diffuse scattered THz images. We created a pellet with α-lactose monohydrate and riboflavin, two biologically significant materials with well-known vibrational spectral resonances, and buried the pellet in a highly scattering medium. THz transmission measurements were taken at all angles covering the half focal plane. We show that, while spectral features of lactose and riboflavin cannot be distinguished in the scattered image, application of cepstrum filtering can mitigate these scattering effects. By employing our quefrency-domain signal processing technique, we were able to unambiguously detect the dielectric resonance of lactose in the diffused scattering geometries. Finally we will discuss the limitation of the new proposed technique in spectral identification of chemicals.

Chemical Response Emergency Medical Information System in Chemical Disaster

Introduction:There are many database sets and websites which provide chemical information, but they do not perform an adequate role for emergency medical support in a chemical disaster.Aim:To make the basis of a chemical emergency medical information system.Methods:We reviewed the database sets, mobile applications and websites in the world which provide chemical database and emergency medical response information from a chemical accident or disaster site to hospitals. Also, we examined chemical accident cases which developed during disasters. A chemical database set for emergency medical response was proposed and the algorithm for elicitation of chemicals suitable for emergency medical response and information providing. We performed a survey about chemical emergency medical information system to related personnel.Results:By four steps of elicitation of chemicals, the number of chemicals more than 100,000 was decreased to less than 1,000. The standard of steps includes accident preparedness, toxicity and circulating amount and expert consultation. Algorithm for elicitation of chemicals was made and 82% of related personnel supported the chemical emergency response algorithm. The emergency medical real-time consultation system for chemical disaster was placed under control of the call center.Discussion:When mass exposure by toxic chemicals occurs, the chemical emergency medical information system will be helpful for acute identification of chemicals, protection of related personnel and emergency medical response. Also, it can be possible to guide citizens immediately in case of a chemical disaster.

A hazard classification system based on incorporation of REACH regulation thresholds in the USEtox method

REACH regulation classifies persistent, bioaccumulative, and toxic (PBT) substances based on regulatory thresholds established for selected physicochemical and toxicity properties. The underlying ideas behind this hazard classification system are: i) that is essentially dependent on the individual value of a restricted number of the substance properties, ii) the combinatory effect of the different substances properties is not relevant, iii) the regulatory thresholds established for the different substance properties are equivalent. These ideas have never been verified before, so the main aim of this paper is to do a critical appraisal of the REACH PBT classification. For that purpose, a conceptual framework is developed based on the use of the USEtox model to calculate characterization factors (CFs) associated with virtual substances (VS): hypothetical substances whose properties are based on the thresholds established to PBT substances. The analysis of the CFs calculated for the VS suggested that the essential ideas from the PBT classification are not verified, and important aspects that can affect the identification of hazardous substances are missing: a) the regulatory thresholds are not all equivalent; b) the combinatorial effect of the different physicochemical and toxicity properties is not negligible, so the hazard potential of a substance cannot be evaluated based on the value of individual properties; c) other properties not included in the PBT classification are as relevant as others currently included to evaluate the potential hazard on human health. A hazard classification system based on the use of the CFs of the virtual substances as a hazardous reference is proposed to help perform a preliminary screening, which can be integrated with other criteria to facilitate the identification of PBT chemicals.

Volumetric enhancement of Raman scattering for fast detection based on a silver-lined hollow-core fiber.

Fast detection and identification of chemicals are of utmost importance for field testing and real-time monitoring in many fields. Raman spectroscopy is the predominant technique in principle, but its wide application is limited on account of weak scattering efficiency. Surface Enhanced Raman Spectroscopy (SERS) technique provides a solution for signal enhancement, but may not good at fast detection due to cross contamination and bulky instruments. Hollow-core fiber-based Raman cell with long interaction length can achieve high detection sensitivity, but it also suffers from low flow rate, bulky high-pressure equipment and light coupling structure, which also restricts its application for fast detection. In order to solve those problems, we proposed a portable Raman cell, by using metal-lined hollow-core fibers (MLHCF) with large bandwidth, good field confinement, extremely large numerical aperture and arbitrary length. With our proposed fiber inserted light coupling and light reflecting method, a Raman cell of 3.1 cm in length provides nearly 50 times of signal enhancement compared with direct detection using bare fiber tip. Furthermore, the sample exchange rate could be as fast as 1 second even under normal pressure without any cross contamination. At last, we also demonstrated the underlying general mechanism of signal enhancement and summarized it as volumetric enhancement of Raman scattering (VERS). Both the experiment results and the theoretical analysis demonstrated that our device has the potential for fast online Raman detection, which also possesses high-sensitivity and high-accuracy.

Transfer learning for predicting human skin sensitizers.

Computational prioritization of chemicals for potential skin sensitization risks plays essential roles in the risk assessment of environmental chemicals and drug development. Given the huge number of chemicals for testing, computational methods enable the fast identification of high-risk chemicals for experimental validation and design of safer alternatives. However, the development of robust prediction model requires a large dataset of tested chemicals that is usually not available for most toxicological endpoints, especially for human data. A small training dataset makes the development of effective models difficult with insufficient coverage and accuracy. In this study, an ensemble tree-based multitask learning method was developed incorporating three relevant tasks in the well-defined adverse outcome pathway (AOP) of skin sensitization to transfer shared knowledge to the major task of human sensitizers. The results show both largely improved coverage and accuracy compared with three state-of-the-art methods. A user-friendly prediction server was available at https://cwtung.kmu.edu.tw/skinsensdb/predict . As AOPs for various toxicity endpoints are being actively developed, the proposed method can be applied to develop prediction models for other endpoints.

The development and prevalidation of an in vitro mutagenicity assay based on MutaMouse primary hepatocytes, Part II: Assay performance for the identification of mutagenic chemicals.

As demonstrated in Part I, cultured MutaMouse primary hepatocytes (PHs) are suitable cells for use in an in vitro gene mutation assay due to their metabolic competence, their “normal” phenotype, and the presence of the MutaMouse transgene for reliable mutation scoring. The performance of these cells in an in vitro gene mutation assay is evaluated in this study, Part II. A panel of 13 mutagenic and nonmutagenic compounds was selected to investigate the performance of the MutaMouse PH in vitro gene mutation assay. The nine mutagens represent a range of classes of chemicals and include mutagens that are both direct‐acting and requiring metabolic activation. All the mutagens tested, except for ICR 191, elicited significant, concentration‐dependent increases in mutant frequency (MF) ranging from 2.6‐ to 14.4‐fold over the control. None of the four nonmutagens, including two misleading, or “false,” positives (i.e., tertiary butylhydroquinone [TBHQ] and eugenol), yielded any significant increases in MF. The benchmark dose covariate approach facilitated ranking of the positive chemicals from most (i.e., 3‐nitrobenzanthrone [3‐NBA], benzo[a]pyrene [BaP], and aflatoxin B1 [AFB1]) to least (i.e., N‐ethyl‐N‐nitrosourea [ENU]) potent. Overall, the results of this preliminary validation study suggest that this assay may serve as a complimentary tool alongside the standard genotoxicity test battery. This study, alongside Part I, illustrates the promise of MutaMouse PHs for use in an in vitro gene mutation assay, particularly for chemicals requiring metabolic activation. Environ. Mol. Mutagen. 60:348–360, 2019. © 2019 The Authors. Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.

Screening and identification of a non-peptide antagonist for the peptide hormone receptor in Arabidopsis

Intercellular signaling mediated by peptide hormones and membrane-localized receptor kinases plays crucial roles in plant developmental processes. Because of their diverse functions, agonistic or antagonistic modulation of peptide signaling holds enormous promise for agricultural applications. Here we established a high-throughput screening system using a bead-immobilized receptor kinase and fluorescent-labeled peptide ligand to identify small molecules that bind peptide hormone receptors in competition with natural ligands. We used the Arabidopsis CLE9-BAM1 ligand-receptor pair to screen a library of ≈30,000 chemicals and identified NPD12704 as an antagonist for BAM1. NPD12704 also inhibited CLV3 binding to BAM1 but only minimally interfered with CLV3 binding to CLV1, the closest homolog of BAM1, demonstrating preferential receptor specificity. Treatment of clv1-101 mutant seedlings with NPD12704 enhanced the enlarged shoot apical meristem phenotype. Our results provide a technological framework enabling high-throughput identification of small non-peptide chemicals that specifically control receptor kinase–mediated peptide hormone signaling in plants.

Assessing effects of germline exposure to environmental toxicants by high-throughput screening in C. elegans

Chemicals that are highly prevalent in our environment, such as phthalates and pesticides, have been linked to problems associated with reproductive health. However, rapid assessment of their impact on reproductive health and understanding how they cause such deleterious effects, remain challenging due to their fast-growing numbers and the limitations of various current toxicity assessment model systems. Here, we performed a high-throughput screen in C. elegans to identify chemicals inducing aneuploidy as a result of impaired germline function. We screened 46 chemicals that are widely present in our environment, but for which effects in the germline remain poorly understood. These included pesticides, phthalates, and chemicals used in hydraulic fracturing and crude oil processing. Of the 46 chemicals tested, 41% exhibited levels of aneuploidy higher than those detected for bisphenol A (BPA), an endocrine disruptor shown to affect meiosis, at concentrations correlating well with mammalian reproductive endpoints. We further examined three candidates eliciting aneuploidy: dibutyl phthalate (DBP), a likely endocrine disruptor and frequently used plasticizer, and the pesticides 2-(thiocyanomethylthio) benzothiazole (TCMTB) and permethrin. Exposure to these chemicals resulted in increased embryonic lethality, elevated DNA double-strand break (DSB) formation, activation of p53/CEP-1-dependent germ cell apoptosis, chromosomal abnormalities in oocytes at diakinesis, impaired chromosome segregation during early embryogenesis, and germline-specific alterations in gene expression. This study indicates that this high-throughput screening system is highly reliable for the identification of environmental chemicals inducing aneuploidy, and provides new insights into the impact of exposure to three widely used chemicals on meiosis and germline function.