Sophie Gangloff

Removal of pesticide mixtures in a stormwater wetland collecting runoff from a vineyard catchment

Wetlands can collect contaminated runoff from agricultural catchments and retain dissolved and particle-laden pesticides. However, knowledge about the capacity and functioning of wetland systems with respect to the removal of pesticides is very limited. Here we show that stormwater wetlands can efficiently remove pesticides in runoff from vineyard catchments during the period of pesticide application, although flow and hydrochemical conditions of the wetland largely vary over time. During the entire agricultural season, the inflowing load of nine fungicides, six herbicides, one insecticide and four degradation products was 8.039g whereas the outflowing load was 2.181g. Removal rates of dissolved loads by the wetland ranged from 39% (simazine) to 100% (cymoxanil, gluphosinate, kresoxim methyl and terbuthylazine). Dimethomorph, diuron, glyphosate, metalaxyl and tetraconazole were more efficiently removed in spring than in summer. More than 88% of the input mass of suspended solids was retained, underscoring the capability of the wetland to trap pesticide-laden particles via sedimentation. Only the insecticide flufenoxuron was frequently detected in the wetland sediments. Our results demonstrate that stormwater wetlands can efficiently remove pesticide mixtures in agricultural runoff during critical periods of pesticide application, although fluctuations in the runoff regime and hydrochemical characteristics can affect the removal rates of individual pesticides.

High performance automated ion chromatography separation for Ca isotope measurements in geological and biological samples

Natural mass-dependent fractionation of calcium isotopes is a promising tool for investigating Ca pathways and cycling in geological and biological materials. But since natural isotope fractionation of Ca appears to be extremely limited (∼1.25‰/amu), excellent external precision and sensitivity are needed to make full use of its potential. Here, we describe a new Ca purification procedure that consists of a high selectivity automated ionic chromatography separation protocol, which is suitable for Ca isotope measurements by mass spectrometry and applicable to multiple natural matrixes (waters, mineral and organic samples). The analytical progress in this automated technique are multiple: (1) saving time with a minimum of handling, (2) unique operating protocol whatever the nature of the sample, (3) complete separation of Ca from K, Mg and Sr, avoiding isobaric interferences which are critical during TIMS analysis, and (4) Ca separation by peak recognition optimising the full recovery of Ca even if its retention time is shifted from one sample to another. The two latter advantages ensure a Ca recovery yield close to 100%, leading to the absence of any fractionation of Ca isotopes during the chemical clean-up. Thus, this chemical separation will be of special interest for applications not compatible with the use of the double spike technique such as MC-ICP-MS and 40Ca excesses measurements. Additionally this procedure leads to a twofold improvement of the long-term repeatability of the Ca isotopes determination by TIMS (±0.11 δ44/40Ca, 2SD) as compared with a classical resin chemistry protocol and is similar to the best repeatability published so far (±0.10 δ44/40Ca, 2SD).

Siderophore‐promoted dissolution of smectite by fluorescent Pseudomonas

Siderophores are organic chelators produced by microorganisms to fulfil their iron requirements. Siderophore-promoted dissolution of iron-bearing minerals has been clearly documented for some siderophores, but few studies have addressed metabolizing siderophore-producing bacteria. We investigated iron acquisition from clays by fluorescent Pseudomonads, bacteria that are ubiquitous in the environment. We focused on the interactions between smectite and Pseudomonas aeruginosa, a bacterium producing two structurally different siderophores: pyoverdine and pyochelin. The presence of smectite in iron-limited growth media promoted planktonic growth of P. aeruginosa and biofilm surrounding the smectite aggregates. Chemical analysis of the culture media indicated increases in the dissolved silicon, iron and aluminium concentrations following smectite supplementation. The use of P. aeruginosa mutants unable to produce either one or both of the two siderophores indicated that pyoverdine, the siderophore with the higher affinity for iron, was involved in iron and aluminium solubilization by the wild-type strain. However, in the absence of pyoverdine, pyochelin was also able to solubilize iron but with a twofold lower efficiency. In conclusion, pyoverdine and pyochelin, two structurally different siderophores, can solubilize structural iron from smectite and thereby make it available for bacterial growth.