María Rosende

Fluidized-bed column method for automatic dynamic extraction and determination of trace element bioaccessibility in highly heterogeneous solid wastes

Dynamic flow-through extraction/fractionation methods have recently drawn much attention as appealing alternatives to the batchwise steady-state counterparts for the evaluation of environmentally available pools of potentially hazardous trace elements in solid matrices. The most critical weakness of flow-based column approaches lies in the small amount of solid that can be handled, whereby their applicability has been merely limited to date to the extraction of trace elements in highly homogeneous solid substrates; otherwise the representativeness of the test portion might not be assured. To tackle this limitation, we have devised an automated flow-through system incorporating a specially designed extraction column with a large volume capacity, wherein up to 2 g of solid sample could be handled without undue backpressure. The assembled flow setup was exploited for fast screening of potentially hazardous trace elements (namely, Cd, Cr, Cu, Pb, and Zn) in highly inhomogeneous municipal solid waste incineration (MSWI) bottom ashes. The pools of readily mobilizable metal forms were ascertained using the Toxicity Characteristic Leaching Procedure (TCLP) based on the usage of 0.1 mol L(-1) CH(3)COOH as leachant and analysis of extracts by inductively coupled optical emission spectrometry. The application of a two-level full factorial (screening) design revealed that the effect of sample fluidization primarily but other experimental factors such as the solid to liquid ratio and extractant flow rate significantly influenced the leachability of given elements in raw bottom ashes at the 0.05 significance level. The analytical performance of the novel flow-based method capitalized on fluidized-bed extraction was evaluated in terms of accuracy, through the use of mass balance validation, reproducibility and operational time as compared to batchwise extraction and earlier flow injection/sequential injection microcolum-based leaching tests.

Assessing oral bioaccessibility of trace elements in soils under worst-case scenarios by automated in-line dynamic extraction as a front end to inductively coupled plasma atomic emission spectrometry

A novel biomimetic extraction procedure that allows for the in-line handing of ≥400 mg solid substrates is herein proposed for automatic ascertainment of trace element (TE) bioaccessibility in soils under worst-case conditions as per recommendations of ISO norms. A unified bioaccessibility/BARGE method (UBM)-like physiological-based extraction test is evaluated for the first time in a dynamic format for accurate assessment of in-vitro bioaccessibility of Cr, Cu, Ni, Pb and Zn in forest and residential-garden soils by on-line coupling of a hybrid flow set-up to inductively coupled plasma atomic emission spectrometry. Three biologically relevant operational extraction modes mimicking: (i) gastric juice extraction alone; (ii) saliva and gastric juice composite in unidirectional flow extraction format and (iii) saliva and gastric juice composite in a recirculation mode were thoroughly investigated. The extraction profiles of the three configurations using digestive fluids were proven to fit a first order reaction kinetic model for estimating the maximum TE bioaccessibility, that is, the actual worst-case scenario in human risk assessment protocols. A full factorial design, in which the sample amount (400-800 mg), the extractant flow rate (0.5-1.5 mL min(-1)) and the extraction temperature (27-37°C) were selected as variables for the multivariate optimization studies in order to obtain the maximum TE extractability. Two soils of varied physicochemical properties were analysed and no significant differences were found at the 0.05 significance level between the summation of leached concentrations of TE in gastric juice plus the residual fraction and the total concentration of the overall assayed metals determined by microwave digestion. These results showed the reliability and lack of bias (trueness) of the automatic biomimetic extraction approach using digestive juices.

Dynamic fractionation of trace metals in soil and sediment samples using rotating coiled column extraction and sequential injection microcolumn extraction: a comparative study.

Dynamic fractionation has been recognized as an appealing alternative to conventional equilibrium-based sequential extraction procedures (SEPs) for partitioning of trace elements (TE) in environmental solid samples. This paper reports the first attempt for harmonization of flow-through dynamic fractionation using two novel methods, the so-called sequential injection microcolumn (SIMC) extraction and rotating coiled column (RCC) extraction. In SIMC extraction, a column packed with the solid sample is clustered in a sequential injection system, while in RCC, the particulate matter is retained under the action of centrifugal forces. In both methods, the leachants are continuously pumped through the solid substrates by the use of either peristaltic or syringe pumps. A five-step SEP was selected for partitioning of Cu, Pb and Zn in water soluble/exchangeable, acid-soluble, easily reducible, easily oxidizable and moderately reducible fractions from 0.2 to 0.5 g samples at an extractant flow rate of 1.0 mL min(-1) prior to leachate analysis by inductively coupled plasma-atomic emission spectrometry. Similarities and discrepancies between both dynamic approaches were ascertained by fractionation of TE in certified reference materials, namely, SRM 2711 Montana Soil and GBW 07311 sediment, and two real soil samples as well. Notwithstanding the different extraction conditions set by both methods, similar trends of metal distribution were in generally found. The most critical parameters for reliable assessment of mobilizable pools of TE in worse-case scenarios are the size-distribution of sample particles, the density of particles, the content of organic matter and the concentration of major elements. For reference materials and a soil rich in organic matter, the extraction in RCC results in slightly higher recoveries of environmentally relevant fractions of TE, whereas SIMC leaching is more effective for calcareous soils.

A mesofluidic platform integrating restricted access-like sorptive microextraction as a front end to ICP-AES for the determination of trace level concentrations of lead and cadmium as contaminants in honey

An automatic programmable-flow system capitalizing upon mesofluidic Lab-On-Valve (LOV) sample processing coupled on-line to inductively coupled plasma atomic emission spectrometry (ICP-AES) is proposed in this work as a quality control tool for expedient assessment of potential contamination episodes of food safety elements (namely, Cd and Pb) in a variety of undigested ripened honeys, taken as a model of an edible matrix. On-chip micro-solid phase extraction (μSPE) is effected in a bead-injection disposable sorbent mode using a cationic exchange restricted access-like material (viz., Bond Elut Plexa PCX). We have proven that the lifetime of the miniaturized solid reactor on-chip (11 ± 0.6 mg) is limited to processing less than 6 mL of unfiltered sample suspension (5% (w/w) honey buffered at pH 4.5) after which the analytical performance is severely deteriorated because of strong adherence of the sample matrix to the bead surface. Several physicochemical parameters including the nature of the sorbent material and its ionic form were investigated in detail so as to maximize absolute recoveries and enrichment factors of Pb and Cd. Variables for the elution process were explored by means of a full factorial design. Using 4.0 mL of sample and 200 μL of 3.0 mol L−1 HNO3 as an eluent, enrichment factors of ca. 15 with extraction/elution efficiencies close to 80% and relative recoveries ranging from 90–111% in honey were obtained for both Pb and Cd. The limits of detection (LODs), based on the 3sintercept criterion, were 26 ng g−1 and 68 ng g−1 for Cd and Pb, respectively, which are far below those endorsed by current regulatory agencies (namely, 100 and 300–500 ng g−1 for Cd and Pb, respectively). Demonstrated by the analysis of a suite of off-the-shelf honey brands, the proposed LOV-μSPE platform hyphenated to ICP-AES is deemed suitable for the reliable quantitation of trace level concentrations of Pb and Cd in honey and the detection of heavy metal contamination episodes.

Automatic kinetic bioaccessibility assay of lead in soil environments using flow-through microdialysis as a front end to electrothermal atomic absorption spectrometry.

In-line microdialysis is in this work hyphenated to electrothermal atomic absorption spectrometry via a dedicated flow-based interface for monitoring the batchwise leaching test endorsed by the Standards, Measurements and Testing Program (SM&T) of the European Commission. The bioaccessible pool of lead in soils is measured using 0.43 mol/L AcOH as extractant. The proposed method allows to gain knowledge of leaching kinetics at real-time, simplify the overall procedure by accurate detection of steady-state conditions and overcome sample filtration or centrifugation. Soil leachates were automatically sampled at specified timeframes (e.g, every 20 or 80 min), processed in an external container (where dilution can be applied at will) and further injected into the atomizer. The method was experimentally validated by comparison of in situ microdialysis sampling results with in-line microfiltration in two soils of varying physicochemical properties. A mathematical framework was used for discrimination of different metal fractions (that is, readily mobilizable against slowly mobilizable lead) and also for estimating the total extractable lead under actual steady-state conditions. We have demonstrated that bioaccessibility tests lasting 16 h as endorsed by SM&T might not suffice for ascertainment of maximum (steady-state) bioaccessibility of lead in terrestrial environments as demanded in risk assessment programs.

In-vitro estimation of bioaccessibility of chlorinated organophosphate flame retardants in indoor dust by fasting and fed physiologically relevant extraction tests

This paper reports the evaluation of in-vitro physiologically relevant extraction tests for ascertainment of the bioaccessible fractions of emerging flame retardants from indoor dust in the gastric and gastrointestinal compartments. Standardized bioaccessibility tests under both fasting (UBM-like test) and fed (FOREhST test) conditions simulating the macronutrient composition of an average child diet were harnessed for investigation of the oral bioaccessibility of chlorinated organophosphate esters, namely, tris(2-chloroethyl) phosphate (TCEP), tris(1-chloro-2-propyl) phosphate (TCPP) and tris(1,3-dichloro-2-propyl) phosphate (TDCP), in household and automobile cabin dust samples with varying concentration levels of contaminants. Minimal processing of the biomimetic extracts (only protein precipitation using acetonitrile) was proven feasible by analysis with liquid chromatography-mass spectrometric detection (LC-MS/MS). An inversely proportional relationship was identified between log Kow and oral bioaccessibility concentrations for TCEP, TCPP and TDCP in both dust samples with maximum bioaccessibility fractions for TCEP within the range of 50-103%. Non-bioaccessible fractions were determined by matrix-solid phase dispersion. Limits of quantification of LC-MS/MS in surrogate digestive fluids ranging from 0.4-0.8ng/mL suffice for determination of freely dissolved fractions of the two less hydrophobic species. Our results indicate that lipophilic food commodities used under fed-state gastrointestinal extraction conditions do not increase availability of TCEP, TCPP and TDCP in body fluids, and therefore conservative conditions in human health risk explorations for the target moderately polar flame retardants might be obtained with simplified tests under fasting conditions. This also holds true for the UBM/FOREhST bioaccessibility data for SRM 2585 (organic contaminants in house dust). Estimated average daily intake doses for toddlers incorporating oral bioaccessibility data afforded body burdens for the three chlorinated alkyl phosphates of ca. 3000 to 700 times below reference dose values, which indicate that long-term exposure to chlorinated organophosphate esters via accidental ingestion of indoor dust does not pose health risks to toddlers.

Automatic flow-through dynamic extraction: A fast tool to evaluate char-based remediation of multi-element contaminated mine soils

An automatic in-vitro bioaccessibility test based upon dynamic microcolumn extraction in a programmable flow setup is herein proposed as a screening tool to evaluate bio-char based remediation of mine soils contaminated with trace elements as a compelling alternative to conventional phyto-availability tests. The feasibility of the proposed system was evaluated by extracting the readily bioaccessible pools of As, Pb and Zn in two contaminated mine soils before and after the addition of two biochars (9% (w:w)) of diverse source origin (pine and olive). Bioaccessible fractions under worst-case scenarios were measured using 0.001 mol L(-1) CaCl2 as extractant for mimicking plant uptake, and analysis of the extracts by inductively coupled optical emission spectrometry. The t-test of comparison of means revealed an efficient metal (mostly Pb and Zn) immobilization by the action of olive pruning-based biochar against the bare (control) soil at the 0.05 significance level. In-vitro flow-through bioaccessibility tests are compared for the first time with in-vivo phyto-toxicity assays in a microcosm soil study. By assessing seed germination and shoot elongation of Lolium perenne in contaminated soils with and without biochar amendments the dynamic flow-based bioaccessibility data proved to be in good agreement with the phyto-availability tests. Experimental results indicate that the dynamic extraction method is a viable and economical in-vitro tool in risk assessment explorations to evaluate the feasibility of a given biochar amendment for revegetation and remediation of metal contaminated soils in a mere 10 min against 4 days in case of phyto-toxicity assays.

High-throughput automatic flow method for determination of trace concentrations of aluminum in dialysis concentrate solutions using salicylaldehyde picolinoylhydrazone as a turn-on fluorescent probe.

A simple and expedient flow-based assembly capitalizing on programmable flow is herein proposed for reliable determination of trace level concentrations of aluminum as a potential contaminant in dialysis concentrate solutions without any prior sample clean-up/preconcentration procedure. Using salicylaldehyde picolinoylhydrazone in weakly acidic media as a turn-on fluorescent probe, the manifold is devised to handle three samples concurrently in stopped-flow reaction mode for simultaneous improvement of the analytical sensitivity and sample throughput. Analytical parameters influencing the sensitivity and repeatability of the assays, namely, probe concentration, reaction temperature and reaction time were investigated using a multivariate optimization protocol composed of a full factorial screening design followed by a Doehlert matrix model. The analysis of the Pareto chart and surface response revealed that the reaction time and amount of fluorescent probe were critical parameters for reliable assays of aluminum at the low ng mL(-1) level. Under the optimized chemical and physical variables, a detection limit of 1.1ngmL(-1) Al(III) at the 3s(blank) level, relative standard deviations better than 1.0%, a dynamic linear range of 5.0-80 ng mL(-1) and a sample throughput up to 25 h(-1) were obtained with no need for either sample preconcentration or the use of organized supramolecular systems. Demonstrated with the analysis of hemodialysis and peritoneal concentrate solutions, and dialysis waters, the flow-through method copes with the requirements of regulatory bodies (e.g., European Pharmacopeia) for quality control of aluminum in high salinity containing dialysis concentrates.

Automated Microdialysis-Based System for in Situ Microsampling and Investigation of Lead Bioavailability in Terrestrial Environments under Physiologically Based Extraction Conditions

In situ automatic microdialysis sampling under batch-flow conditions is herein proposed for the first time for expedient assessment of the kinetics of lead bioaccessibility/bioavailability in contaminated and agricultural soils exploiting the harmonized physiologically based extraction test (UBM). Capitalized upon a concentric microdialysis probe immersed in synthetic gut fluids, the miniaturized flow system is harnessed for continuous monitoring of lead transfer across the permselective microdialysis membrane to mimic the diffusive transport of metal species through the epithelium of the stomach and of the small intestine. Besides, the addition of the UBM gastrointestinal fluid surrogates at a specified time frame is fully mechanized. Distinct microdialysis probe configurations and membranes types were investigated in detail to ensure passive sampling under steady-state dialytic conditions for lead. Using a 3-cm-long polysulfone membrane with averaged molecular weight cutoff of 30 kDa in a concentric probe and a perfusate flow rate of 2.0 μL min(-1), microdialysis relative recoveries in the gastric phase were close to 100%, thereby omitting the need for probe calibration. The automatic leaching method was validated in terms of bias in the analysis of four soils with different physicochemical properties and containing a wide range of lead content (16 ± 3 to 1216 ± 42 mg kg(-1)) using mass balance assessment as a quality control tool. No significant differences between the mass balance and the total lead concentration in the suite of analyzed soils were encountered (α = 0.05). Our finding that the extraction of soil-borne lead for merely one hour in the GI phase suffices for assessment of the bioavailable fraction as a result of the fast immobilization of lead species at near-neutral conditions would assist in providing risk assessment data from the UBM test on a short notice.

New Insights into the Reliability of Automatic Dynamic Methods for Oral Bioaccessibility Testing: A Case Study for BGS102 soil

Dynamic flow-through extraction is attracting a great deal of attention for real-time monitoring of the bioaccessible fraction of metal species in environmental solid substrates compared to its batchwise manual counterparts. There is however a lack of studies on the harmonization and validation of in vitro dynamic methods for physiologically based extraction tests against in vivo bioavailability methods. This work is aimed at evaluating the reliability of dynamic flow-through extraction methods for estimation of oral bioaccessible fractions of Cu, Zn, Pb, Ni, Cr, and As under worst-case extraction conditions in the gastric compartment based on the BGS102 guidance soil using the in vivo validated Unified BARGE (UBM) test, commonly performed under batchwise mode. Good overall agreement between batch and dynamic UBM results was obtained for the tested elements, except for Pb, as a consequence of the slow leaching kinetics identified with the dynamic method and the contribution of readsorption phenomena in the course of the gastric digestion. Metal-soil phase associations and their relationship with gastric bioaccessible fractions were elucidated using the so-called Chemometric Identification of Substrates and Element Distributions method based on sequential extraction with a variety of chemicals of increasing acidity as applied to both static and dynamic bioaccessibility data.