How to confirm identified toxicants in effect-directed analysis

Abstract

Due to the production and use of a multitude of chemicals in modern society, waters, sediments, soils and biota may be contaminated with numerous known and unknown chemicals that may cause adverse effects on ecosystems and human health. Effect-directed analysis (EDA), combining biotesting, fractionation and chemical analysis, helps to identify hazardous compounds in complex environmental mixtures. Confirmation of tentatively identified toxicants will help to avoid artefacts and to establish reliable cause-effect relationships. A tiered approach to confirmation is suggested in the present paper. The first tier focuses on the analytical confirmation of tentatively identified structures. If straightforward confirmation with neat standards for GC-MS or LC-MS is not available, it is suggested that a lines-of-evidence approach is used that combines spectral library information with computer-based structure generation and prediction of retention behaviour in different chromatographic systems using quantitative structure-retention relationships (QSRR). In the second tier, the identified toxicants need to be confirmed as being the cause of the measured effects. Candidate components of toxic fractions may be selected based, for example, on structural alerts. Quantitative effect confirmation is based on joint effect models. Joint effect prediction on the basis of full concentration-response plots and careful selection of the appropriate model are suggested as a means to improve confirmation quality. Confirmation according to the Toxicity Identification Evaluation (TIE) concept of the US EPA and novel tools of hazard identification help to confirm the relevance of identified compounds to populations and communities under realistic exposure conditions. Promising tools include bioavailability-directed extraction and dosing techniques, biomarker approaches and the concept of pollution-induced community tolerance (PICT). [figure: see text]

Characterization of AhR agonist compounds in roadside snow

“…Another study investigating AhR agonists in indoor dust from electronic waste recycling sites could only explain between 8 and 29 % of the activity by chemical analysis [42]. Other factors that could contribute to this discrepancy, such as matrix effects in the complex mixture and non-additive effects of mixtures of compounds [43,44], have been proposed for lack of coherence between the measured AhR activity and the presence of AhR agonists in complex samples.…”

Effect-directed analysis (EDA) in aquatic ecotoxicology: state of the art and future challenges

“…Finally, a confirmation step in the EDA procedure evaluates how much of the observed toxicity in the environmental sample can be attributed to the mixture of identified toxicants (Brack 2003). More recent approaches focus on the development of methodologies aiming at the assessment of mixture toxicity accounting for unknown modes of action and heterogeneity of concentration-response curves (Brack et al 2008b). …”

Behavioural ecotoxicology, an “early warning” signal to assess environmental quality

“…Borja and Dauer (2008) describe the four corners of environmental quality assessment as: “(1) assessing ecological integrity, (2) evaluating if significant ecological degradation has occurred, (3) identifying the spatial extent and location of ecological degradation and (4) determining causes of unacceptable degradation in order to guide management actions.” The identification of cause represents a major issue that has been addressed in toxicity identification evaluation (TIE) or in effects evaluation analysis studies. Recent publications by Perron et al (2010), Hecker and Hollert (2009), Schaeffer et al (2009), Brack et al (2008) and Gomez-Gutierrez et al (2007) provide a wealth of references on this aspect of risk assessment and outline the critical role played by chemical analyses. The importance of chemical analyses is also apparent in the work described in a large section of the present manuscript (Section 7).…”