Glutathione (GSH) is a soft nucleophile and, as such, can be used to sense the reactivity of electrophilic agents toward the thiol group and other electron-rich sites of molecular structures. A new kinetic GSH chemoassay is introduced that employs a photometric method to quantify GSH loss and enables an efficient determination of second-order rate constants, k(GSH), of the reaction between electrophilic substances and GSH. Comparison with an existing 2 h static assay shows that the new kinetic variant is superior with respect to the detectable range of electrophilic reactivity and to confounding factors such as additional GSH loss due to oxidation. Analysis of the chemoassay degradation kinetics provides insight into the characteristic reaction times and the contributions of GSH-electrophile Michael addition and GSH oxidation to the overall GSH loss. For 15 alpha,beta-unsaturated ketones, nine acrylates, and two propiolates acting as Michael acceptors, the measured k(GSH) values span ca. 5 orders of magnitude. Moreover, log k(GSH) correlates with the compounds' toxicity toward the ciliates Tetrahymena pyriformis in terms of 48 h log EC(50) (50% growth inhibition) values, yielding a squared correlation coefficient (r(2)) of 0.91 and a root-mean-square error of 0.30 log units. It shows that for these and related compounds, aquatic toxicity is driven by electrophilic reactivity. The findings demonstrate that the kinetic GSH chemoassay can be used as an efficient tool to analyze, interpret, and predict correspondingly reactive toxicity in the context of qualitative and quantitative structure-activity relationship studies and as a nonanimal tool of integrated testing strategies for REACH to screen compounds for excess toxicity.

The performance of seven passive sampling devices for the monitoring of dissolved concentrations of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), hexachlorobenzene, and p,p'-DDE was evaluated through simultaneous field exposures of 7-28 days in the River Meuse (The Netherlands). Data from the Chemcatcher, low density polyethylene membranes, two versions of the membrane-enclosed sorptive coating (MESCO) sampler, silicone rods, silicone strips and semipermeable membrane devices (SPMD) was assessed through rate of dissipation of performance reference compounds (PRCs), mass of analyte absorbed by the samplers and time-weighted average concentration (C(TWA)) data. Consistent PRC data throughout the range of samplers tested here confirmed the transition from membrane- to boundary layer-controlled exchange at log K(ow) 4.5-5.0. The comparison of sampler surface area-normalized masses absorbed for analytes under boundary layer-control showed some variability between samplers that can be attributed to the conformation and deployment of the various samplers and to the uncertainty associated with the analysis conducted in different laboratories. Despite different modes of calculation, relatively consistent C(TWA) were obtained for the different samplers. The observed variability is likely to be due to the uncertainty of sampler-water partition coefficients and the extrapolation of analyte uptake rates at the high log K(ow) range (under boundary layer-controlled exchange) from a narrow PRC data range, and these issues require further work. Finally, the usefulness of passive sampler-generated contaminant concentrations is demonstrated through the comparison with institutional monitoring and with European Water Framework Directive Environmental Quality Standards (EQS).