Application of Hydrophobicity Parameters to Prediction of the Acute Aquatic Toxicity of Commercial Surfactant Mixtures

Abstract

Ethoxylated alcohols are the most extensively used nonionic surfactants in detergent products. The application of QSAR to their aquatic toxicity is complicated by the fact that they are multicomponent mixtures, the parent alcohols being often mixtures of isomers and homologues, each one being ethoxylated to varying degrees. A spreadsheet method for calculation of aquatic toxicity of such nonionic surfactant mixtures is presented. The method is based on a combination of the Könemann narcosis QSAR and mixture toxicity equations based on the principle of concentration addition. Log P values used in the spreadsheet calculations are themselves calculated by spreadsheet formulae based on the Leo and Hansch method modified by incorporation of the position dependent branching factor originally applied to linear alkylbenzene sulphonates. Close agreement between calculated and experimental EC50 values (48 hr Daphnia tests) is obtained for a range of ethoxylated alcohols having a diversity of branching patterns, carbon numbers and degrees of ethoxylation. The effects of increasing carbon number (decreasing EC50), branching (increasing EC50) and increasing degree of ethoxylation (increasing EC50) are all quantified.     

Ecotoxicological modelling of cosmetics for aquatic organisms: A QSTR approach

In this study, externally validated quantitative structure–toxicity relationship (QSTR) models were developed for toxicity of cosmetic ingredients on three different ecotoxicologically relevant organisms, namely Pseudokirchneriella subcapitata, Daphnia magna and Pimephales promelas following the OECD guidelines. The final models were developed by partial least squares (PLS) regression technique, which is more robust than multiple linear regression. The obtained model for P. subcapitata shows that molecular size and complexity have significant impacts on the toxicity of cosmetics. In case of P. promelas and D. magna, we found that the largest contribution to the toxicity was shown by hydrophobicity and van der Waals surface area, respectively. All models were validated using both internal and test compounds employing multiple strategies. For each QSTR model, applicability domain studies were also performed using the “Distance to Model in X-space” method. A comparison was made with the ECOSAR predictions in order to prove the good predictive performances of our developed models. Finally, individual models were applied to predict toxicity for an external set of 596 personal care products having no experimental data for at least one of the endpoints, and the compounds were ranked based on a decreasing order of toxicity using a scaling approach.     

Interlaboratory studies on wastewater toxicity using Daphnia magna

In order to verify the quality of biological measurements, the National Institute of Chemistry in Slovenia is regularly organizing interlaboratory comparisons to estimate the analytical precision of different laboratories using the same test and to determine if statistically significant differences exist between results. Several interlaboratory trials named “ILC-Waste Water” (ILC-WW) were organized in the last 7 years. Acute toxicity testing with Daphnia magna mobility inhibition assay (ISO 6341) was included in eight successive rounds and about 20 laboratories from Slovenia and a few adjacent countries took part in each study with two samples (T1 and T2) at two different concentration levels. Variation coefficients of the mean 24 h EC50s were determined for each exercise and the evaluation of the interlaboratory variability was analysed. Comparisons were also made of the results and the variability laboratories using organisms taken from laboratory cultures versus those who used daphnias hatched from dormant eggs (Daphtoxkits).     

Validation and extension of a similarity-based approach for prediction of acute aquatic toxicity towards Daphnia magna

Quantitative structure–activity relationship (QSAR) models for predicting acute toxicity to Daphnia magna are often associated with poor performances, urging the need for improvement to meet REACH requirements. The aim of this study was to evaluate the accuracy, stability and reliability of a previously published QSAR model by means of further external validation and to optimize its performance by means of extension to new data as well as a consensus approach. The previously published model was validated with a large set of new molecules and then compared with ChemProp model, from which most of the validation data were taken. Results showed better performance of the proposed model in terms of accuracy and percentage of molecules outside the applicability domain. The model was re-calibrated on all the available data to confirm the efficacy of the similarity-based approach. The extended dataset was also used to develop a novel model based on the same similarity approach but using binary fingerprints to describe the chemical structures. The fingerprint-based model gave lower regression statistics, but also less unpredicted compounds. Eventually, consensus modelling was successfully used to enhance the accuracy of the predictions and to halve the percentage of molecules outside the applicability domain.     

Flow-based in vivo NMR spectroscopy of small aquatic organisms

NMR applied to living organisms is arguably the ultimate tool for understanding environmental stress responses and can provide desperately needed information on toxic mechanisms, synergistic effects, sublethal impacts, recovery, and biotransformation of xenobiotics. To perform in vivo NMR spectroscopy, a flow cell system is required to deliver oxygen and food to the organisms while maintaining optimal line shape for NMR spectroscopy. In this tutorial, two such flow cell systems and their constructions are discussed: (a) a single pump high-volume flow cell design is simple to build and ideal for organisms that do not require feeding (i.e., eggs) and (b) a more advanced low-volume double pump flow cell design that permits feeding, maintains optimal water height for water suppression, improves locking and shimming, and uses only a small recirculating volume, thus reducing the amount of xenobiotic required for testing. In addition, key experimental aspects including isotopic enrichment, water suppression, and 2D experiments for both ¹³C enriched and natural abundance organisms are discussed.