New sensitive tools to characterize meta-metabolome response to short- and long-term cobalt exposure in dynamic river biofilm communities.

Untargeted metabolomics is a non-a priori analysis of biomolecules that characterizes the metabolome variations induced by short- and long-term exposures to stressors. Even if the metabolite annotation remains lacunar due to database gaps, the global metabolomic fingerprint allows for trend analyses of dose-response curves for hundreds of cellular metabolites. Analysis of dose/time-response curve trends (biphasic or monotonic) of untargeted metabolomic features would thus allow the use of all the chemical signals obtained in order to determine stress levels (defense or damage) in organisms. To develop this approach in a context of time-dependent microbial community changes, mature river biofilms were exposed for 1 month to four cobalt (Co) concentrations (from background concentration to 1 × 10-6 M) in an open system of artificial streams. The meta-metabolomic response of biofilms was compared against a multitude of biological parameters (including bioaccumulation, biomass, chlorophyll a content, composition and structure of prokaryotic and eukaryotic communities) monitored at set exposure times (from 1 h to 28 d). Cobalt exposure induced extremely rapid responses of the meta-metabolome, with time range inducing defense responses (TRIDeR) of around 10 s, and time range inducing damage responses (TRIDaR) of several hours. Even in biofilms whose structure had been altered by Co bioaccumulation (reduced biomass, chlorophyll a contents and changes in the composition and diversity of prokaryotic and eukaryotic communities), concentration range inducing defense responses (CRIDeR) with similar initiation thresholds (1.41 ± 0.77 × 10-10 M Co2+ added in the exposure medium) were set up at the meta-metabolome level at every time point. In contrast, the concentration range inducing damage responses (CRIDaR) initiation thresholds increased by 10 times in long-term Co exposed biofilms. The present study demonstrates that defense and damage responses of biofilm meta-metabolome exposed to Co are rapidly and sustainably impacted, even within tolerant and resistant microbial communities.

Metal localisation in gastropod shells: New insights from mass spectrometry techniques.

Gastropod shells are calcified structures made of several crystal layers. They grow throughout the lifecycle of mollusks by integrating some of the chemical elements present in their environment, including metals. This characteristic means mollusks can be useful bioindicators of metal exposure. The present study aimed to better understand the role of layer composition on metal accumulation. To that end, the gastropods Radix balthica were collected in a French river adjacent to a municipal wastewater treatment plant. Microchemical metal analyses in the different shell layers were performed by Femtosecond-Laser Ablation Inductively Coupled Plasma Mass Spectrometry (Fs-LA-ICP-MS) and analyses of the molecular environment of the metals were performed by Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). Strontium, Ba and Mn were well distributed within the whole shell and the high concentrations of these elements were found to be related to the aragonite structure of the shell. Copper, Ni, Pb and Zn were mostly present at the outer surfaces of the shell where the organic constituents were more concentrated. The analysis of metal distribution in shell layers could improve our understanding of the relationships between metal exposure and accumulation in mollusks, therefore providing evidences of their use as powerful integrated bioindicator of metal contamination.

Investigating predictive tools for refinery effluent hazard assessment using stream mesocosms.

Hazard assessment of refinery effluents is challenging because of their compositional complexity. Therefore, a weight-of-evidence approach using a combination of tools is often required. Previous research has focused on several predictive tools for sophisticated chemical analyses: biomimetic extraction to quantify the potentially bioaccumulative substances, 2-dimensional gas chromatography, modeling approaches to link oil composition to toxicity (PETROTOX), and whole-effluent toxicity assessments using bioassays. The present study investigated the value of these tools by comparing predicted effects to actual effects observed in stream mesocosm toxicity studies with refinery effluents. Three different effluent samples, with and without fortification by neat petroleum substances, were tested in experimental freshwater streams. The results indicate that the biological community shifted at higher exposure levels, consistent with chronic toxicity effects predicted by both modeled toxic units and potentially bioaccumulative substance measurements. The present study has demonstrated the potential of the predictive tools and the robustness of the stream mesocosm design to improve our understanding of the environmental hazards posed by refinery effluents. Environ Toxicol Chem 2019;38:650-659. © 2018 SETAC.