Low exposure levels of urban metals induce heterotrophic community tolerance: a microcosm validation

Abstract

The biological response of periphyton chronically exposed to metals of urban origin (Cd, Ni and Zn) was investigated with a Pollution-Induced Community Tolerance (PICT) approach using a previously developed short-term toxicity test based on β-glucosidase (heterotrophic) activity. Periphyton was grown on plastic membranes immersed in indoor aquaria contaminated with metals at realistic contamination levels (0.3, 3 μg/l for Cd, 5, 50 μg/l for Ni, 20, 200 μg/l for Zn). After 3 weeks of exposure, biofilms' parameters (dry-weight, chlorophyll a concentration, heterotrophic activity) were analyzed and tolerance acquisition of the heterotrophic communities was assessed using the toxicity test. Modifications of bacterial and eukaryotic community structure were assessed with Automated Ribosomal Intergenic Spacer Analysis (ARISA). Effects of metal exposure were observed on biofilms parameters in the Cd and Zn experiments. Tolerance levels increased for both Cd-exposed biofilms, and for the high metal treatment biofilms in the Ni and Zn experiments. Analysis of the ARISA profiles showed that metal exposure affected the structure of both bacterial and eukaryotic communities. Moreover, Cd tolerance of the Zn-exposed heterotrophic communities was evaluated, which showed that the Zn-tolerant community (high metal treatment in the Zn experiment) also became tolerant to Cd (co-tolerance). The study shows that tolerance acquisition can be detected after exposure to environmental metal concentrations using β-glucosidase activity as an endpoint in short-term toxicity tests.

Pollution-induced community tolerance of freshwater biofilms: measuring heterotrophic tolerance to Pb using an enzymatic toxicity test

“…A 319 maximum % inhibition inferior to 100% means that -glucosidase activity cannot be fully 320 inhibited by short-term exposure to metals even at high exposure concentrations (the highest 321 metal concentrations tested are 10 mM namely 2.07 g/L for Pb). This phenomenon was already 322 observed in previous studies on laboratory or in situ exposed biofilms with the same toxicity test 323 (Fechner et al, 2011;Fechner et al, 2012a). In the present study, -glucosidase toxicity tests 324 revealed the impact of Pb exposure on the Pb 100 biofilm with a 1.7 increase of normalized EC 50 325 value and a significant decrease of maximum % inhibition (72.30 %) when compared to Pb 0 326 (Figure 2 and Table 5).…”

“…DW and AFDW also decreased for the Pb 100 biofilm but 314 increased slightly for Pb 1 and Pb 10 communities. A similar effect was observed on DW for 315 biofilms exposed to low metal concentrations (Morin et al, 2008;Fechner et al, 2011). 316…”

“…Yet Pb 296 accumulation was much smaller than previously observed for metals like Cd, Ni and Zn (Fechner 297 et al, 2011). For instance, the bioconcentration factor (total biofilm-accumulated metal in µg/g 298 DW divided by the nominal metal concentration in the corresponding microcosm in µg/L) varied 299 16 from 0.50 (Pb 1) to 0.06 (Pb 10 and Pb100) whereas in our previous study the bioconcentration 300 factor reached 11 and 40 for respectively Cd and Zn-exposed biofilms (Fechner et al, 2011). 301…”

“…Aquarel mineral water was chosen for the medium so that physico-chemical parameters were 184 roughly similar to those from the river at site 3 (Fechner et al, 2011). show that, for Pb also, the higher the TSS concentration of the biofilm suspension, the higher the 266 EC 50 value obtained (Figure 1 and Table 1).…”

“…Site 3 was chosen because it is relatively unaffected by the 179 urban area of Paris in terms of metallic contamination (Fechner et al, 2011). 180…”