Mapping Phosphorus Availability in Soil at a Large Scale and High Resolution Using Novel Diffusive Gradients in Thin Films Designed for X-ray Fluorescence Microscopy.

A novel binding layer (BL) as part of the diffusive gradients in thin films (DGT) technique was developed for the two-dimensional visualization and quantification of labile phosphorus (P) in soils. This BL was designed for P detection by synchrotron-based X-ray fluorescence microscopy (XFM). It differs from the conventional DGT BL as the hydrogel is eliminated to overcome the issue that the fluorescent X-rays of P are detected mainly from shallow sample depths. Instead, the novel design is based on a polyimide film (Kapton) onto which finely powdered titanium dioxide-based P binding agent (Metsorb) was applied, resulting in superficial P binding only. The BL was successfully used for quantitative visualization of P diffusion from three conventional P fertilizers applied to two soils. On a selection of samples, XFM analysis was confirmed by quantitative laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The XFM method detected significant differences in labile P concentrations and P diffusion zone radii with the P fertilizer incubation, which were explained by soil and fertilizer properties. This development paves the way for fast XFM analysis of P on large DGT BLs to investigate in situ diffusion of labile P from fertilizers and to visualize large-scale P cycling processes at high spatial resolution.

Use of fish otoliths as a temporal biomarker of field uranium exposure.

This study aimed to determine uranium (U) pollution over time using otoliths as a marker of fish U contamination. Experiments were performed in field contamination (~20 µg L-1: encaged fish: 15d, 50d and collected wild fish) and in laboratory exposure conditions (20 and 250 µg L-1, 20d). We reported the U seasonal concentrations in field waterborne exposed roach fish (Rutilus rutilus), in organs and otoliths. Otoliths were analyzed by ICPMS and LA-ICP SF MS of the entire growth zone. Concentrations were measured on transects from nucleus to the edge of otoliths to characterize environmental variations of metal accumulation. Results showed a spatial and temporal variation of U contamination in water (from 51 to 9.4 µg L-1 at the surface of the water column), a high and seasonal accumulation in fish organs, mainly the digestive tract (from 1000 to 30,000 ng g-1, fw), the gills (from 1600 to 3200 ng g-1, fw) and the muscle (from 144 to 1054 ng g-1, fw). U was detected throughout the otolith and accumulation varied over the season from 70 to 350 ng g-1, close to the values measured (310 ng g-1) after high exposure levels in laboratory conditions. U in otoliths of encaged fish showed rapid and high U accumulation from 20 to 150 ng g-1. The U accumulation signal was mainly detected on the edge of the otolith, showing two U accumulation peaks, probably correlated to fish age, i.e. 2 years old. Surprisingly, elemental U and Zn signatures followed the same pattern therefore using the same uptake pathways. Laboratory, caging and field experiments indicated that otoliths were able to quickly accumulate U on the surface even for low levels and to store high levels of U. This study is an encouraging first step in using otoliths as a marker of U exposure.

Comparison of analytical methods using enzymatic activity, immunoaffinity and selenium-specific mass spectrometric detection for the quantitation of glutathione peroxidase 1.

Glutathione peroxidase 1 (Gpx1), one of the most responsive selenoproteins to the variation of selenium concentration, is often used to evaluate "selenium status" at a cellular or organismal level. The four major types of analytical methodologies to quantify Gpx1 were revisited. They include (i) an enzymatic assay, (ii, iii) polyacrylamide gel electrophoresis (PAGE) with (ii) western blot detection of protein or (iii) inductively coupled plasma mass spectrometry (ICP MS) detection of selenium, and (iv) size-exclusion chromatography with ICP MS detection. Each of the four methods was optimized for the quantification of Gpx1 with maximum sensitivity. The methods based on the enzymatic and immunodetection offer a much higher sensitivity but their accuracy is compromised by the limited selectivity and limited dynamic range. The advantages, drawbacks and sources of error of each technique are critically discussed and the need for the cross-validation of the results using the different techniques to assure the quality assurance of quantitative analysis is emphasized.