Regulatory groundwater monitoring: Realistic residues of pinoxaden and metabolites at vulnerable locations.

A bespoke groundwater monitoring programme was designed to generate a database of pinoxaden and metabolite concentrations in shallow groundwater at agricultural locations across Europe. The data generated from this programme represent a higher tier refinement of modelled exposure estimates and provide realistic information on groundwater quality at vulnerable locations which will aid plant protection product (PPP) assessment in Europe in relation to Regulation (EC) No. 1107/2009. The Regulatory GeoPEARL_3.3.3 model developed by RIVM was used to estimate the vulnerability of cereal growing regions to leaching of two pinoxaden metabolites across the entire EU at a 1 km2 level using 20 years of daily weather data (MARS, EU JRC). Seventy sites located within the upper 50th percentile of leaching vulnerability from this modelling exercise, crop density and shallow groundwater were selected for monitoring groundwater. Retrospective and prospective pinoxaden product applications at candidate sites were recorded and these data used to place sites in the distribution for Europe. The 70 sites all fulfil the site assessment criteria and have no confining layers which may prevent or delay leaching. All sites equipped with groundwater wells had a minimum of two pinoxaden applications in the preceding four years to cereal crops. A total of 1326 samples were analysed from up to 90 down hydraulic gradient wells at 70 locations between June 2015 and July 2018. Results indicate that pinoxaden and pinoxaden metabolites are very unlikely to reach shallow groundwater at concentrations greater than 0.1 µg/L for relevant metabolites, or 10 µg/L for non-relevant metabolites, respectively (Sanco/221/2000-rev.10). Over 38 months of groundwater monitoring the annual average and 90th percentile for pinoxaden or its metabolites never exceeded 0.1 µg/L and it is proposed that these data infer that exposure to these metabolites is minimal.

Microcosm experiments of oil degradation by microbial mats. II. The changes in microbial species.

The influence of microbial mats on the degradation of two crude oils (Casablanca and Maya) and the effect of oil pollution on the mat structure were assessed using model ecosystems, prepared under laboratory conditions subject to tidal movements, from pristine Ebro Delta microbial-mat ecosystems. Both selected oils are examples of those currently used for commercial purposes. Casablanca crude oil is aliphatic with a low viscosity; Maya represents a sulphur-rich heavy crude oil that is predominantly aromatic. In the unpolluted microcosms, Microcoleus chthonoplastes-, Phormidium- and Oscillatoria-like were the dominant filamentous cyanobacterial morphotypes, whilst Synechoccocus-, Synechocystis- and Gloeocapsa-like were the most abundant unicellular cyanobacteria. After oil contamination, no significant changes of chlorophyll a and protein concentrations were observed, though cyanobacterial diversity shifts were monitored. Among filamentous cyanobacteria, M. chthonoplastes-like morphotype was the most resistant for both oils, unlike the other cyanobacteria, which tolerated Casablanca but not Maya. Unicellular cyanobacteria seemed to be resistant to pollution with both essayed oils, with the exception of the morphotype resembling Gloeocapsa, which was sensitive to both oils. The crude-oil addition also had a significant effect on certain components of the heterotrophic microbial community. Casablanca oil induced an increase in anaerobic heterotrophic bacteria, whereas the opposite effect was observed in those heterotrophs when polluted with Maya oil. The overall results, microbiological and crude-oil transformation analysis, indicate that the indigenous community has a considerable potential to degrade oil components by means of the metabolic cooperation of phototrophic and heterotrophic populations.

Microcosm experiments of oil degradation by microbial mats.

Several microcosm experiments were run in parallel to evaluate the efficiency of microbial mats for crude oil degradation as compared with physico-chemical weathering. The oils used in the experiments constituted representative examples of those currently used for commercial purposes. One was aliphatic and of low viscosity (33.4 American Petroleum Institute degrees, degrees API) and the other was predominantly aromatic, with high sulphur content (ca. 2.7%) and viscosity (16.6 degrees API). After crude oil introduction, the microcosms were kept under cyclic changes in water level to mimic coastal tidal movements. The transformations observed showed that water weathering leads to more effective and rapid elimination of low molecular weight hydrocarbons than microbial mat metabolism, e.g. n-alkanes with chain length shorter than n-pentadecane or n-heptadecane, regular isoprenoid hydrocarbons with chain length lower than C16 or C18 or lower molecular weight naphthalenes. Microbial mats preserved these hydrocarbons from volatilization and water washing. However, hydrocarbons of lower volatility such as the C24-C30 n-alkanes or containing nitrogen atoms, e.g. carbazoles, were eliminated in higher proportion by microbial mats than by water weathering. The strong differences in composition between the two oils used for the experiments were also reflected in significant differences between water weathering and microbial mat biodegradation. Higher oil viscosity seemed to hinder the former but not the later.

Changes in the composition of polar and apolar crude oil fractions under the action of Microcoleus consortia.

Cultures of Microcoleus consortia polluted with two different types of crude oil, one with high content in aliphatic hydrocarbons (Casablanca) and the other rich in sulphur and aromatic compounds (Maya), were grown for 50 days and studied for changes in oil composition. No toxic effects from these oils were observed on Microcoleus consortia growth. In fact, the interface layer between the oils and the water culture medium proved to be the ideal site for consortia development, leading to a wrapping effect of the oil layers by these organisms. Despite this affinity of cyanobacteria for the oil substrate, the changes in oil composition were small. Microcoleus consortia did not induce transformation in the aliphatic-rich oil, and the modifications in the sulphur and aromatic-rich oil were small. The latter essentially involved degradation of aliphatic heterocyclic organo-sulphur compounds such as alkylthiolanes and alkylthianes. Other groups of compounds, such as the alkylated monocyclic and polycyclic aromatic hydrocarbons, carbazoles, benzothiophenes and dibenzothiophenes, also underwent some degree of transformation, involving only the more volatile and less alkylated homologues.

Characterization of functional bacterial groups in a hypersaline microbial mat community (Salins-de-Giraud, Camargue, France).

A photosynthetic microbial mat was investigated in a large pond of a Mediterranean saltern (Salins-de-Giraud, Camargue, France) having water salinity from 70 per thousand to 150 per thousand (w/v). Analysis of characteristic biomarkers (e.g., major microbial fatty acids, hydrocarbons, alcohols and alkenones) revealed that cyanobacteria were the major component of the pond, in addition to diatoms and other algae. Functional bacterial groups involved in the sulfur cycle could be correlated to these biomarkers, i.e. sulfate-reducing, sulfur-oxidizing and anoxygenic phototrophic bacteria. In the first 0.5 mm of the mat, a high rate of photosynthesis showed the activity of oxygenic phototrophs in the surface layer. Ten different cyanobacterial populations were detected with confocal laser scanning microscopy: six filamentous species, with Microcoleus chthonoplastes and Halomicronema excentricum as dominant (73% of total counts); and four unicellular types affiliated to Microcystis, Chroococcus, Gloeocapsa, and Synechocystis (27% of total counts). Denaturing gradient gel electrophoresis of PCR-amplified 16S rRNA gene fragments confirmed the presence of Microcoleus, Oscillatoria, and Leptolyngbya strains (Halomicronema was not detected here) and revealed additional presence of Phormidium, Pleurocapsa and Calotrix types. Spectral scalar irradiance measurements did not reveal a particular zonation of cyanobacteria, purple or green bacteria in the first millimeter of the mat. Terminal-restriction fragment length polymorphism analysis of PCR-amplified 16S rRNA gene fragments of bacteria depicted the community composition and a fine-scale depth-distribution of at least five different populations of anoxygenic phototrophs and at least three types of sulfate-reducing bacteria along the microgradients of oxygen and light inside the microbial mat.