In situ measurement and statistical modelling of Escherichia coli decay in small rivers.

Numerous studies have been carried out on the environmental factors associated with the decay of faecal bacteria in open (fresh or marine) waters. The present study aimed at understanding the fate of bacteria in small streams (flow <20 m3 s(-1)) for which there is a lack of knowledge. An original in situ protocol was developed for measuring the die-off of Escherichia coli (E. coli) from wastewater treatment plants. Based upon 80 values of the decay first-order parameter (K or its inverse T90), collected from five rivers in Normandy (France), a median T90 of 10 h and a minimal T90 of 1.3 h were obtained. K was then modelled as a linear function of variables made up from flow, water temperature and suspended particulate matter (SPM). The set of significant co-variables did not include light indicators. E. coli decay is inversely related to the river flow and it becomes highly significant below 0.3 m3 s(-1). The positive effect of small flows on die-off is increased by water temperature over 15 degrees C, whereas it could be reduced by SPM. The major co-variable of the model (p < 10(-9)) is an empiric composite variable integrating the effect of flow and temperature that explains more than 40% of the variance of K. We interpreted this as an expression of predation by benthic micro-grazers which could be the main cause of E. coli die-off in small streams in temperate countries.

Trace metals analysis in estuarine and seawater by ICP-MS using on line preconcentration and matrix elimination with chelating resin.

The main difficulties of trace metals analysis in estuarine and seawater stem from their very low concentration (mug/l to sub-mug/l), and, by contrast, the high salt content (up to 38 g/l in the Mediterranean Sea). ICP-MS allows multi-elemental analysis and offers great sensitivity, but may be strongly affected by matrix effects induced by high salt contents (> 1 g/l). To perform trace metals analysis both in riverine, estuarine and seawater, we have developed a hyphenated method: ion chelation chromatography coupled on-line with ICP-MS. Iminodiacetate resin, Metpac CC-1 (Dionex), was used to concentrate most of the trace metals, and to separate them from alkaline and alkaline-earth metals. Behaviour of 17 elements (Pb, Cu, Cd, Ni, U, Cr, Mn, Al, Co, Ga, In, Zn, V, Tl, Bi, Ag and Sn) towards the resin was qualitatively investigated. A method validation, partly derived from AFNOR standard XPT 90-210, was carried out on 12 elements (Pb, Cu, Cd, Ni, U, Cr, Mn, Al, Co, Ga, Bi and In). Replicate measurements of multi-elemental standard solutions were used to check linearity, and to determine repeatability and detection limits. Method accuracy was then assessed by analysing two certified materials: a synthetic freshwater (SRM 1643d), and a natural filtered coastal seawater (NRCC CASS-3). An application assay of natural samples from the Rhône river (France) was eventually carried out, and the analytical results were found to be consistent with previous works.