Improved short-term toxicity test protocol to assess metal tolerance in phototrophic periphyton: toward standardization of PICT approaches

Abstract

Pollution-induced community tolerance (PICT) approaches involve comparing tolerance levels of natural communities to a particular contaminant or a contaminant mixture using short-term toxicity tests performed under controlled conditions. However, results from toxicity tests can be modulated by various environmental and experimental conditions, raising questions about their reproducibility and comparability. In this context, the present study aimed to determine the influence of exposure duration, periphyton suspension concentration, and periphyton maturation stage on the measurement of short-term effects of copper on phototrophic periphyton communities. Our results showed the very weak influence of exposure duration in the tested range (2-6 h) on toxicity level, whereas periphyton biomass in the tested suspension (in terms of both chlorophyll a concentrations and dry weight), proved a crucial determinant in toxicity assessment. Results also highlighted the potential tolerance increase with the periphyton maturation stage. This parameter conditioned the positive linear relationship between tolerance level and periphyton suspension concentration, leading to an increase in the linear regression slope with the maturation stage. This suggests that such a relationship is probably highly periphyton-dependent. Consequently, to enable data toxicity comparisons, an a priori normalization of the periphyton suspension biomass is necessary, and PICT approaches require the use, as much of possible, of periphyton with similar maturation stage. Finally, the present study clearly shows that a better standardization of PICT approaches could help to improve reproducibility. It could thus facilitate the comparison of tolerance levels measured in the same study (e.g., spatial and/or temporal and/or inter-treatment comparison) as well as the comparison obtained from different experimental and in situ research.

A Time-Dose Response Model to Assess Diuron-Induced Photosynthesis Inhibition in Freshwater Biofilms

“…To sum up, our results lead to the same conclusion reached by Lambert et al (2015) that there is a considerable influence of biofilm biomass in the outputs of ecotoxicity tests with biofilms, which complicates between-sample comparisons. However, both time-response curves, for very different biofilms, yielded comparable t 1/2 values, making the latency parameter a unique response favoring between-date comparisons.…”

Experimental Warming Differentially Influences the Vulnerability of Phototrophic and Heterotrophic Periphytic Communities to Copper Toxicity

“…In each tank, six microcosms were filled with reconstituted water consisting of 3:1 (v/v) distilled water:groundwater, supplemented with nutrients in order to adjust conductivity (i.e., about 180 μS cm -1 ) and nutrient concentrations (i.e., 15 mg L -1 of silica; 8 mg L -1 of nitrates; 0.2 mg L -1 of orthophosphates) to the characteristics of the river water at the periphyton sampling site ( Table 1 ). Water mixing, oxygenation, and lighting were operated as previously described in Lambert et al (2015) . Three microcosms were used as Control microcosms (“Control,” without Cu addition) and three Cu-exposed microcosms (“Cu”) were supplemented with CuSO 4 , 5H 2 O to obtain a Cu concentration close to the highest concentrations recorded in the downstream section of Morcille River (i.e., about 15 μg Cu L -1 ; Montuelle et al, 2010 ; Rabiet et al, 2015 ).…”

Pollution-induced community tolerance for in situ assessment of recovery in river microbial communities following the ban of the herbicide diuron

“…Most of other pesticides frequently detected in the river (before and after the ban of diuron) belong to fungicides (Montuelle et al, 2010) and especially dimetomorph and tebuconazole (Rabiet et al, 2010;Foulquier et al, 2015), which can reach concentrations higher than 0.5 µg/L during post-treatment periods due to their intensive use on vineyards (unpublished). In 2011, annual organic pesticide application were about 10.6, 5.3, and 0.14 kg ha−1, respectively, for active ingredients of fungicides, herbicides, and insecticides during the growing season (Peyrard et al, 2016).…”

“…The fact that these two independent studies performed with periphytic communities exhibiting different characteristics produced largely comparable reference values together with the relative temporal stability observed over the three years studied here reopens an important question on the feasibility (or not) of defining reference levels or tolerance baselines for PICT approaches. This perspective, which could promote the field use of PICT as diagnostic tool, requires significantly more research attention to encourage the standardization of PICT measurements ( Lambert et al, 2015 andTlili et al, 2016) and significantly greater extension to a large geographical scale in order to better estimate the weight of confounding effects of abiotic factors on the baseline tolerance estimates. One strategy to achieve this goal would be to select representative model compounds for chosen modes of action and to mobilize international collaborative projects in order to collect data from different regions (Tlili et al, 2016).…”