A new version of an additive scheme for the prediction of gas chromatographic retention indices of the 211 structural isomers of 4-nonylphenol

Linking electron ionization mass spectra of organic chemicals to toxicity endpoints through machine learning and experimentation

Quantitative structure-activity relationship (QSAR) modeling has been widely used to predict the potential harm of chemicals, in which the prediction heavily relies on the accurate annotation of chemical structures. However, it is difficult to determine the accurate structure of an unknown compound in many cases, such as in complex water environments. Here, we solved the above problem by linking electron ionization mass spectra (EI-MS) of organic chemicals to toxicity endpoints through various machine learning methods. The proposed method was verified by predicting 50% growth inhibition of Tetrahymena pyriformis (T. pyriformis) and liver toxicity. The optimal model performance obtained an R² > 0.7 or balanced accuracy > 0.72 for both the training set and test set. External experimentation further verified the application potential of our proposed method in the toxicity prediction of unknown chemicals. Feature importance analysis allowed us to identify critical spectral features that were responsible for chemical-induced toxicity. Our approach has the potential for toxicity prediction in such fields that it is difficult to determine accurate chemical structures.

The development of isomer-specific analysis of branched 4-nonylphenol in food for dietary exposure - a critical review of analytical methods and occurrence in foodstuffs

4-Nonylphenol (4-NP) is a para-substituted phenolic compound comprising a straight or branched carbon chain group while branched 4-NP consists of 211 possible structural isomers. NP is recognised as an environmental pollutant and exists ubiquitously in both the environment and in food. 4-NP, especially branched 4-NP, has been shown to have the potential role of endocrine disruptor and xeno-oestrogen. Moreover, different NP isomers also exhibit different oestrogen-like activities. Recently, it was reported that the isomer-specific profile of 4-NP in foodstuffs varies greatly between and within food groups. Hence, risk assessment based on total branched 4-NP cannot reflect dietary risk. This study reviews the analytical methods applicable to conduct an isomer-specific analysis of 4-NP and its occurrence in foodstuffs. Lastly, research gaps are identified for future research.

Molecular docking simulation on the interactions of laccase from Trametes versicolor with nonylphenol and octylphenol isomers

The biodegradation of nonylphenol (NP) and octylphenol (OP) isomers by laccase has attracted increasing concerns. However, the interaction mechanism between these isomers and laccase remains unclear, especially for fungal laccase. In this work, molecular docking was employed to study this issue. The results indicated that the structural characteristic of alkyl chain (position and branching degree) affected the interactions between Trametes versicolor (T. versicolor) laccase and isomers. The binding affinity between them was closely related to the position and branching degree of alkyl chain in isomers. The binding affinities between linear isomers and T. versicolor laccase were para-position < meta-position < ortho-position. For selected branched 4-NP, the isomers with bulky α-substituent in alkyl chain had higher binding affinities. In addition, hydrophobic contacts between T. versicolor laccase and NP or OP isomers were necessary, while H-bonds were optional. The isomers with similar structure may have more common residues involved in hydrophobic contacts. The H-bonds of selected NPs and OPs were all connected with phenolic hydroxyl. These findings provide an insight into detailed interaction mechanism between T. versicolor laccase and isomers of NP and OP. It is helpful to broaden the knowledge of degradation technology of NPs and OPs and provide theoretical basis on biological remediation of these contaminants.

Analysis, toxicity, occurrence and biodegradation of nonylphenol isomers: a review

Over the last two decades, nonylphenols (NPs) have become to be known as a priority hazardous substance due primarily to its estrogenicity and ubiquitous occurrence in the environment. Nonylphenols are commonly treated as a single compound in the evaluation of their environmental occurrence, fate and transport, treatment or toxicity. However, technical nonylphenols (tNPs) are in fact a mixture of more than 100 isomers and congeners. Recent studies showed that some of these isomers behaved significantly differently in occurrence, estrogenicity and biodegradability. The most estrogenic isomer was about 2 to 4 times more active than tNP. Moreover, the half lives of the most recalcitrant isomers were about 3 to 4 times as long as those of readily-biodegradable isomers. Negligence of NP's isomer specificity may result in inaccurate assessment of its ecological and health effects. In this review, we summarized the recent publications on the analysis, occurrence, toxicity and biodegradation of NP at the isomer level and highlighted future research needs to improve our understanding of isomer-specificity of NP.

Isomer-specific biodegradation of nonylphenol in river sediments and structure-biodegradability relationship

Nonylphenol (NP), a well-known environmental estrogen with numerous isomers, is frequently found in surface water and sediments. Recent studies showed that NP isomers exhibited different estrogenicity. However, at present little information is available on its isomer-specific degradation in the bed sediment, which is the primary sink of NP in surface aquatic systems. In this study, we investigated the biodegradability of 19 NP isomers in two river sediments under oxic and anoxic conditions. Under oxic conditions, the half-lives of NP isomers in an upper river sediment ranged from 0.9 to 13.2 d. Under reduced conditions, the persistence of NP isomers generally increased, with negligible dissipation under strongly reduced conditions. In the well-aerated sediment, NP isomers with short side chain and/or bulky α-substituents were found to be more recalcitrant to degradation. Moreover, when a total of 57 molecular descriptors were examined, the degree of branching as quantified by IDWbar was found to result in the best linear correlation with half-lives of NP isomers (R(2) = 0.88). These results indicated that the isomer-specificity of NP in environmental processes should be considered, and that simple molecular descriptors may be used to identify the more recalcitrant isomers, thus allowing prioritization in the evaluation of environmental fate and risks of NP isomers.

Recent trends in biomonitoring of bisphenol A, 4-t-octylphenol, and 4-nonylphenol

Bisphenol A (BPA), 4-t-octylphenol (4-t-OP), and 4-nonylphenol (4-NP) are man-made alkylphenolic environmental contaminants possessing controversial endocrine disruption properties. Nowadays, an increased interest is raised for their accurate determination in biological media in order to estimate the exposure to these compounds and the associated health risk. The aim of this review is to present the available analytical methodologies for biomonitoring these three EDCs in human population. In non-occupational human exposure, they are detected in human matrices in trace level concentrations, commonly lower than 1ng/mL. The use of mass spectrometry based methods is particularly emphasized due to their well known superiority over sensitivity, selectivity and precision, even in difficult matrices, such as blood plasma and serum. Recent and most applicable sample preparation techniques are thoroughly presented. The benefits of solid phase extraction (SPE) and expected developments are demonstrated. Recent results from exposure assessment and epidemiologic studies for BPA, 4-t-OP and 4-NP are summarized and future trends are discussed.