A non-invasive observation parameter to complement sediment bioassays using Myriophyllum aquaticum

Abstract

Purpose The objective of this study was to modify a sediment contact protocol to a multiwell plate exposure system which supplements measurement of the fresh weight change (FWC) using the non-invasive effective quantum yield of energy conversion at photosystem II (PS II) reaction centres (Y(II)) in parallel. Since Y(II) is a functional parameter and FWC represents a whole-plant structural response, the determination of a more pronounced response in one of these parameters may hint at the mode of action of contaminants. By the observation of Y(II) at different time points, extrapolation of effect development over time may be gained from modelling. Material and methods An established sediment contact protocol was adapted to an exposure in multiwell plates. During exposure, the Y(II) of exposed Myriophyllum aquaticum was measured using an imaging-pulse amplitude-modulated chlorophyll fluorometer. At the end of the 13-day exposure, the FWC was determined and the IC 50 for FWC and Y(II) was estimated using concentrationresponse modelling. A concentration-time-response model was used to describe the effect development on Y(II) over time. This protocol was applied to natural sediments and to artificial sediments which were spiked with different contaminants. Results and discussion It was shown that for the PS II inhibitor atrazine, the IC 50 was four times lower on the Y(II) compared to the value for the FWC. In contrast, for the acetolactate-synthase inhibitor metsulfuron methyl, no effect on the Y(II) of exposed M. aquaticum could be found, while a 100% inhibition in FWC was detected. For dinitro-ocresol, a decoupler of oxidative phosphorylation, the IC 50 for the FWC and the Y(II) were of the same order of magnitude. These results are in agreement with the current mode of action understanding and show the potential of this method to interpret differences in determined IC values as mode of action dependent. Moreover, a clear decrease in estimated I Y(II),tx C 50 values by the end of the 13-day exposure was found for atrazine. This strengthens the hypothesis that effects of contaminants in sediment are not immediately evident but may evolve over time.Conclusions With the miniaturised sediment contact assay, mode of action dependent differences in IC values on the Responsible editor: Marc Babut Electronic supplementary material The online version of this article (FWC and the Y(II) could be determined. Based on results from the concentration-time-response modelling, it could be assumed that during the 13-day exposure all contaminants may not fully exert their effects. Since investigated natural sediments did not show inhibitions on Y(II), while pronounced effects on the FWC were found, the FWC may also be worthwhile to be studied over time.

Metabolic Effect Level Index Links Multivariate Metabolic Fingerprints to Ecotoxicological Effect Assessment

“…In addition to the MELI, the end points main shoot length change (SLC), dry weight change (DWC) and photosynthetic efficiency [ Y (II)] of M. spicatum plants, as well as their inhibition ( I SLC , I DWC , I Y(II) ), were calculated for each treatment as previously reported . Concentration–response relationships were determined by use of the Hill model with the equation given in Table .…”

“…In addition to the metabolic fingerprints, main shoot length change (SLC) and dry weight change (DWC) were observed as apical observation parameters and photosynthetic efficiency [Y(II)] was determined as a functional end point closely related to the primary target site of the PS II inhibitor. Hereby, the measurement of variable chlorophyll fluorescence was adapted as noninvasive observation parameter in the bioassay, based on a protocol of Schreiber et al 25 using a maxi-imaging pulse-amplitude-modulated (I-PAM) chlorophyll fluorometer (Walz, Effeltrich, Germany). For measurement details on growth-related and functional end points, see Supporting Information (section 3 and Table S1).…”

“…In addition to the MELI, the end points main shoot length change (SLC), dry weight change (DWC) and photosynthetic efficiency [Y(II)] of M. spicatum plants, as well as their inhibition (I SLC , I DWC , I Y(II) ), were calculated for each treatment as previously reported. 25 Concentration−response relationships were determined by use of the Hill model with the equation given in Table 1. Model parameters for the end points MELI hyd , MELI lip , Y(II), and SLC were estimated by the maximum likelihood method, with an intercept fixed to the mean and I DWC (here from the range-finding experiment; please refer to Supporting Information, section 6 and Figure S2, for more information), and the min−max scaled MELI hyd response was performed with fixed intercept (b = 0) and maximum (v = 1 or 100) value (OriginPro 8.5.1G SR2, OriginLab Corp., Northampton, MA).…”