Nicolas Mazzella

It is now widely recognized that the sampling rate of Polar Organic Chemical Integrative Samplers (POCIS) is significantly affected by flow velocity, which can cause a consequent bias when determining time-weighted average concentrations (TWAC). In previous works, we observed the desorption of a compound such as deisopropylatrazine (DIA) over time when added to the receiving phase of a POCIS. In particular, it was found in situ that its desorption rate was also influenced by flow velocity, in an agitated water environment. In the method presented here, we calibrated 30 pesticides under controlled laboratory conditions, varying the flow velocity over four levels. At the same time, we studied the desorption rate of DIA-d5 (a deuterated form of DIA) over time. An empirical model based on a power law involving flow velocity was used to process the information provided by the accumulation kinetics of the compounds of interest and the elimination of DIA-d5. With this type of model, it was possible to take into account the effect of this crucial factor on exchange kinetics, and then to obtain more accurate TWACs, with reduced bias and more acceptable dispersion of the results.

Environmental factors, such as light intensity and exposure to contaminants, may significantly influence the lipid composition of algae in periphytic communities. In this study, we investigated the joint effects of dodecylbenzyldimethylammonium chloride (BAC 12), as biocide, and light photoperiods on the polar lipidome of a freshwater biofilm. Exposure to BAC 12 in a microcosm experiment increased the heterotrophic compartment, while phototrophic organisms were severely affected, with corresponding shifts in lipid composition. The overall decrease in polyinsaturated fatty acids suggested a significant impact of the biocide on biofilm microalgae. However, it was difficult to distinguish the influence of light from that of contamination, as there was no observable effect of photoperiod on conventional fatty acid determination. Thus, the molecular species compositions of both glycolipids and phospholipids were explored in additional multivariate analyses. The results suggested that certain molecular species can serve as more specific markers of light duration at the biofilm scale, independently of the chemical pressure caused by other pollutants.

This study examines the polar lipid profiles of two freshwater algae, Scenedesmus costatus and Nitzschia palea. HILIC-ESI-MS/MS analysis was used to determine and quantify the major phospholipids and glycolipids, as well as their relative molecular species, extracted from the two microalgal cultures. Glycolipids were eluted first, followed by phospholipids partially co-eluting with a sulfoglycolipid. The fragmentation pattern in the negative ionization mode for galactolipids was studied, revealing the stereospecific distribution of fatty acids on the glycerol backbone. Green algae frequently include 18:3 fatty acid in both phospholipids and galactolipids, while monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) were more saturated and contained shorter acyls. The diatom phospholipids contained mainly molecular species with saturated or monounsaturated fatty acids, while MGDG and DGDG exhibited a higher proportion of polyunsaturated fatty acids, such as the unique and abundant MGDG (20:5/20:2).

This work reports the polar lipid profiles of two freshwater algae: the diatom Nitzschia palea, widespread alga that typically inhabits freshwater ponds and rivers, and the Scenedesmus costatus, a common green alga. HILIC-ESI-MS/MS analysis was used to determine and quantify the major phospholipids and glycolipids, and their relative molecular species, extracted from the two microalgal cultures. Glycolipids were eluted first, followed by phospholipids partially co-eluting with the sulfoglycolipids. We also studied the fragmentation pattern in the negative ionization mode for galactolipids. The most intense daughter ion corresponded to the fatty acyl chain located at the sn-2 position, which allowed us to determine the stereospecific distribution of the following fatty acids on the glycerol backbone. For green algae, 18:3 fatty acid was frequently occurring in both phospholipids and galactolipids. We also found 16:4 in some molecular species of mono- and digalactosyldiacylglycerol (MGDG and DGDG). The most abundant and characteristic molecular species of MGDG in green algae exhibited the combination (18:3/16:4), whereas DGDG was more saturated than MGDG and contained mainly 18:1, 18:2, or 18:3 at sn-1 and shorter fragments 16:0, 16:1, 16:2, and 16:3 at sn-2. It is also remarkable that in the diatom, the phospholipids contained mainly molecular species with saturated or monounsaturated fatty acids such as 16:0, 16:1 and 18:1. In contrast, MGDG and DGDG contained a higher proportion of polyunsaturated fatty acids, such as the unique and abundant MGDG (20:5/20:2).

This paper presents a multi-step methodology to identify relationships between integrative pesticide quantifications and land uses on a given watershed of the Adour-Garonne Basin (Southwestern France). In fact, a large amount of pesticide concentration data was collected from 51 sites located in the Adour-Garonne Basin for a 1 year monitoring period in 2016. The sampling devices used here were polar organic chemical integrative samplers (POCIS), which provided time-weighted average concentration estimates. For each study site, its associated watershed and land cover distribution were determined using Corine Land Cover 2012 (CLC 2012) and Geographic Information System (GIS). The large-scale data were analyzed using multivariate statistical analyses, such as hierarchical cluster analysis (HCA) and principal component analysis (PCA). HCA grouped the 51 sites into five clusters with similar primary land uses. Next, the integrated pesticide concentration and land use distribution data sets were analyzed in a PCA. The key variables responsible for discriminating the sample sites showed distribution patterns consistent with specific land uses. To confirm these observations, pesticide fingerprints from sites with contrasting land uses were compared using a waffle method. The overall multivariate approach allowed for the identification of contamination sources related to their likely initial use, at the watershed level, that could be useful for preventing or containing pesticide pollution beyond simply acting on areas at risk.

This work reports the polar lipid profiles of two freshwater algae: the diatom Nitzschia palea, widespread alga that typically inhabits freshwater ponds and rivers, and the Scenedesmus costatus, a common green alga. HILIC-ESI-MS/MS analysis was used to determine and quantify the major phospholipids and glycolipids, and their relative molecular species, extracted from the two microalgal cultures. Glycolipids were eluted first, followed by phospholipids partially co-eluting with the sulfoglycolipids. We also studied the fragmentation pattern in the negative ionization mode for galactolipids. The most intense daughter ion corresponded to the fatty acyl chain located at the sn-2 position, which allowed us to determine the stereospecific distribution of the following fatty acids on the glycerol backbone. For green algae, 18:3 fatty acid was frequently occurring in both phospholipids and galactolipids. We also found 16:4 in some molecular species of mono- and digalactosyldiacylglycerol (MGDG and DGDG). The most abundant and characteristic molecular species of MGDG in green algae exhibited the combination (18:3/16:4), whereas DGDG was more saturated than MGDG and contained mainly 18:1, 18:2, or 18:3 at sn-1 and shorter fragments 16:0, 16:1, 16:2, and 16:3 at sn-2. It is also remarkable that in the diatom, the phospholipids contained mainly molecular species with saturated or monounsaturated fatty acids such as 16:0, 16:1 and 18:1. In contrast, MGDG and DGDG contained a higher proportion of polyunsaturated fatty acids, such as the unique and abundant MGDG (20:5/20:2).