Real-time monitoring of bioaccessibility tests for solid samples using automatic flow methods

Resumo

Total extraction methods for risk assessment/exposure of potentially contaminated solid samples of environmental interest tend to overestimate the actual hazard of such samples. Bioaccessibility tests have been developed during the past few decades in order to assess the real hazard of environmental solid samples more closely by resorting to mild extractions in environmentally mimetic conditions. Those tests present however a series of drawbacks, including the operationally defined conditions that should be adapted between samples (but are not), the risk of readsorption and redistribution processes, and the lack of sink capacity of the extraction media. A novel insight into the fundamentals of bioaccessibility of organic pollutants is presented in this dissertation by the so-called Membrane Enhanced Bioaccessibility Extraction (MEBE) approach (chapter 3), which uses semipermeable membranes in order to separate the extraction medium and the final acceptor of the pollutants, and thus foster maintaining the desorption flux from the matrix. To assess the suitability of the operationally defined conditions and detect readsorption and redistribution processes the international community proposed dynamic extraction tests and kinetic monitoring of the ongoing extraction processes, in spite of complicating and lengthening the analyst workload. In this dissertation, we propose the development of automatic methodologies resorting to low pressure flow methods for simplification of bioaccessibility tests from solid matrices followed by extract clean-up and preconcentration (whenever needed) for monitoring the kinetics of the leaching of nutrients, trace elements and organic pollutants. To control this instrumentation and to ease the data treatment, CocoSoft, an automation suite has been developed (chapter 4). At-line and on-line hyphenation of flow-based bioaccessibility tests to appropriate detectors allows for real time leachate monitoring with added benefits of deconvolution of several bioaccessible pools, early prediction of pollutant content or test duration. Those hyphenations have been applied to molecular fluorimetry (chapter 5), atomic spectrometry (chapters 6 and 7) and reverse phase HPLC (chapters 8, 9 and 10).