Toxic equivalent concentrations (TEQs) for baseline toxicity and specific modes of action as a tool to improve interpretation of ecotoxicity testing of environmental samples

Abstract

The toxic equivalency concept is a widely applied method to express the toxicity of complex mixtures of compounds that act via receptor-mediated mechanisms such as induction of the arylhydrocarbon or estrogen receptors. Here we propose to extend this concept to baseline toxicity, using the bioluminescence inhibition test with Vibrio fischeri, and an integrative ecotoxicity endpoint, algal growth rate inhibition. Both bioassays were validated by comparison with literature data and quantitative structure-activity relationships (QSARs) for baseline toxicity were developed for all endpoints. The novel combined algae test, with Pseudokirchneriella subcapitata, allows for the simultaneous evaluation of specific inhibition of photosynthesis and growth rate. The contributions of specific inhibition of photosynthesis and non-specific toxicity could be differentiated by comparing the time and endpoint pattern. Photosynthesis efficiency, measured with the saturation pulse method after 2 h of incubation, served as indicator of specific inhibition of photosynthesis by photosystem II inhibitors. Diuron equivalents were defined as toxicity equivalents for this effect. The endpoint of growth rate over 24 h served to derive baseline toxicity equivalent concentrations (baseline-TEQ). By performing binary mixture experiments with reference compounds and complex environmental samples from a sewage treatment plant and a river, the TEQ concept was validated. The proposed method allows for easier interpretation and communication of effect-based water quality monitoring data and provides a basis for comparative analysis with chemical analytical monitoring.

Treatment of micropollutants in municipal wastewater: Ozone or powdered activated carbon?

“…This specific effect of substances acting on the photosystem II (Escher et al, 2008a) was not strongly reduced during the biological treatment (14 ± 37%, 228 ± 155 ng DEQ l -1 ), suggesting low biodegradability of these compounds. However, both advanced treatments led to a clear decrease in this effect with 82 ± 8% removal (32 ± 9 ng DEQ l -1 ) during ozonation and 87 ± 11% removal (18 ± 11 ng DEQ l -1 ) during PAC-UF treatment.…”

“…A relatively high algae growth inhibition was observed in the raw wastewater (Figure 3b), with a non-specific toxicity of 26 ± 7.3 mg l -1 (baseline toxic equivalent concentration, Escher et al, 2008a). This was clearly reduced (73 ± 6%, 6.9 ± 1 mg l -1 ) during the biological treatment.…”

“…The combined algae assay on the green algae Pseudokirchneriella subcapitata was conducted as described by Escher et al (2008a) and in the SI. Photosynthesis inhibition was measured by means of effective quantum yield (after 2 h of exposure) and algae growth by means of absorbance at 685 nm (after 24 h of exposure).…”

“…Both, the reference substance and the wastewater samples, were tested in triplicates in a 1:2 dilution series, with the highest concentration of diuron being 3 × 10 -7 M (69.9 µg l -1 , in ethanol) and maximum enrichment factors of the wastewater samples of 20 (WWTP influent) and 83.3 (all additional treatment steps). The toxicity of the wastewater samples was expressed as diuron-equivalent concentrations (DEQs) for the endpoint "inhibition of Photosystem II" and toxic equivalent concentrations (TEQs, virtual baseline toxicant) for growth inhibition (Escher et al, 2008a).…”

Electrochemical degradation of the β-blocker metoprolol by Ti/Ru0.7Ir0.3O2 and Ti/SnO2-Sb electrodes

“…The Microtox assay with Vibrio fischeri and the combined algae test with the green algae Pseudokirchneriella subcapita were performed as described previously (Escher et al, 2008), on the samples pre-treated by SPE. Three endpoints were assessed in the combined algae test: the direct inhibition of photosynthesis after 2 h and 24 h incubation via measurement of the quantum yield of photosystem II using Imaging pulse-amplitude modulated fluorometry (2 h IPAM and 24 h IPAM) and the inhibition of growth rate (24 h growth rate).…”