The oxygen isotope composition of dissolved anthropogenic phosphates: a new tool for eutrophication research?

High-precision oxygen isotope analyses were carried out on dissolved phosphate extracted from discharge waters from three wastewater treatment plants (WTP) located in western France, as well as on the different phosphate-based fertilizers applied by farmers in the same region. Measured delta(18)O values of phosphate from chemical fertilizers range from 19.6 to 23.1 per thousand, while those of phosphate from WTP discharge waters are more tightly grouped between 17.7 and 18.1 per thousand. The variability in delta(18)O values of phosphate fertilizers is attributed to oxygen isotope variations of the phosphorite deposits from which France's fertilizers are manufactured. The significance of the delta(18)O values of phosphate from WTP discharge waters is less straightforward. At present, it is not clear whether these values are primary isotopic compositions corresponding, e.g., to the oxygen isotope composition of phosphate builders included in detergents (delta(18)O(P)=17.9 per thousand), or represent secondary values reflecting biological recycling of the phosphate in equilibrium with ambient WTP water The restricted difference in isotopic composition obtained between phosphate from fertilizers and phosphate from WTP discharge waters (<2 per thousand), as well as the fairly large internal isotopic variability observed in both end-members (>/=1.5 per thousand), cast doubt about the possibility that the oxygen isotope composition could serve as a tracer for the source of anthropogenic phosphates in waters.

Release of trace elements in wetlands: role of seasonal variability.

Dissolved concentrations were determined for Fe, Mn, Al, Cu, Zn, La, U, Th, Cd and As in a wetland and its recipient stream to reveal the effect of seasonal changes in environmental conditions on the cycling and transfer of trace elements at the transition between terrestrial and aquatic ecosystems. These preliminary results from the wetland show marked seasonal changes in dissolved concentration for all elements except Zn and Cu. Concentrations are found to be low until about mid-February and then increase abruptly. The onset of trace element release appears to coincide with a marked decline in redox potential and increase of organic carbon content. Because this decline is itself correlated with a pronounced increase in temperature and dissolved Fe. Mn and organic carbon content, we suggest that the microorganisms which use soil iron and manganese oxy-hydroxides as electron acceptors catalyzed the change in redox conditions and induced an increase of DOC. Temporal changes were also observed in the recipient stream which showed marked positive concentration peaks during stormflow events (except Zn). The seasonal processes occurring in the wetland appear to play a major role in determining the amount of trace elements which are transferred from the wetland to the river.

Delivery of extraterrestrial amino acids to the primitive Earth. Exposure experiments in Earth orbit.

A large collection of micrometeorites has been recently extracted from Antarctic old blue ice. In the 50 to 100 micrometers size range, the carbonaceous micrometeorites represent 80% of the samples and contain 2% of carbon. They might have brought more carbon to the surface of the primitive Earth than that involved in the present surficial biomass. Amino acids such as "-amino isobutyric acid have been identified in these Antarctic micrometeorites. Enantiomeric excesses of L-amino acids have been detected in the Murchison meteorite. A large fraction of homochiral amino acids might have been delivered to the primitive Earth via meteorites and micrometeorites. Space technology in Earth orbit offers a unique opportunity to study the behaviour of amino acids required for the development of primitive life when they are exposed to space conditions, either free or associated with tiny mineral grains mimicking the micrometeorites. Our objectives are to demonstrate that porous mineral material protects amino acids in space from photolysis and racemization (the conversion of L-amino acids into a mixture of L- and D-molecules) and to test whether photosensitive amino acids derivatives can polymerize in mineral grains under space conditions. The results obtained in BIOPAN-1 and BIOPAN-2 exposure experiments on board unmanned satellite FOTON are presented.