Measuring in-stream retention of copper by means of constant-rate additions.

Human practices entail inputs of nutrients and toxicants such as heavy metals to the fluvial ecosystems. While nutrient dynamics in fluvial ecosystems have been widely studied for over three decades, dynamics of toxicants still remain unclear. In this investigation, the nutrient spiraling concept and associated methodologies to quantify nutrient retention in streams were applied to study copper (Cu) dynamics in streams. The present study aimed to quantify total dissolved Cu retention using a simplified system of indoor channels colonized with fluvial biofilms. Cu retention was studied at sub-toxic concentrations to avoid negative/lethal effects on biota. In addition, Cu retention was compared with retention estimates of a macronutrient, phosphate (PO(4)(3-)), which has been widely studied within the context of the nutrient spiraling concept. The methodology used allowed a successful quantification of Cu and PO(4)(3-) retention. The results showed higher retention efficiency for PO(4)(3-) than for Cu. The biofilm played a key role in retaining both solutes. Although retention efficiency for both solutes was higher in the experiments with colonized substrata compared to uncolonized substrata, we found a positive relationship between uptake rate and chlorophyll-a only for PO(4)(3-). Finally, retention efficiency for both solutes was influenced by water discharge, showing lower retention efficiencies under higher flow conditions. These results suggest that the fate and toxic effects of copper on stream biota may be strongly influenced by the prevailing environmental conditions. Our results indicate that the experimental approach considered can provide new insights into the investigation of retention of toxic compounds in fluvial systems and their controlling mechanisms.

Determination of an arsenosugar in oyster extracts by liquid chromatography-electrospray mass spectrometry and liquid chromatography-ultraviolet photo-oxidation-hydride generation atomic fluorescence spectrometry.

HPLC-UV-HG-AFS analysis of aqueous extracts of oysters (Crassostrea gigas) taken from the southwestern Atlantic coast of Spain showed the presence of arsenite, arsenate, dimethylarsinic acid and an unidentified arsenic peak. Subsequent analysis of the oyster samples by LC-electrospray MS and comparison with four standard dimethylarsinoylribosides (arsenosugars), showed that the previously unidentified peak was an arsenosugar (arsenosugar 2). When the arsenosugar in the oyster was quantified using the two detection methods and external calibration with standard arsenosugar, there was a large discrepancy between the two sets of results. The LC-MS analysis was strongly affected by the sample matrix and gave concentrations 50% lower than those obtained by AFS detection. When the method of standard addition was applied to the LC-MS analysis, the results were comparable to the AFS data. The matrix effects were eliminated by subjecting the extract to a clean-up procedure with anion-exchange and gel permeation preparative chromatography before the LC-MS analysis. The arsenosugars gave a small signal without photo-oxidation when they were analysed by HPLC-HG-AFS. Possibly this resulted from partial decomposition of the arsenosugar to dimethylarsinic acid under the acidic conditions employed in the hydride generation step.

Arsenic biotransformation by the brown macroalga, Fucus serratus.

The brown alga Fucus serratus was maintained in aquaria with added arsenate (0, 20, 50, and 100 microg As/L, four individuals per treatment) for up to 19 weeks. Biotransformation of arsenic by Fucus was monitored by high-performance liquid chromatography/inductively coupled plasma mass spectrometry and liquid chromatography/electrospray mass spectrometry analysis of aqueous extracts of algal frond tips removed periodically throughout the experiment. Major arsenic species monitored were arsenate, arsenite, methylarsonate, dimethylarsinate, and the four arsenosugars 1 to 4 found naturally in Fucus. Algae accumulated arsenate readily and transformed it into several arsenic compounds depending on the exposure concentration. At 100 microg As/L, the major metabolite was arsenite with smaller quantities of methylarsonate and dimethylarsinate, but only traces of arsenosugars were formed. In contrast, the 20-microg-As/L group accumulated only small quantities of arsenite and methylarsonate, while dimethylarsinate and arsenosugars were major arsenic metabolites. At 50 microg As/L exposure, algae had significant quantities of all arsenic metabolites monitored. Arsenate was toxic to the algae at 100 microg As/L but had no obvious detrimental effect at 20 microg As/L. The data are consistent with a process of arsenate detoxification by reduction and alkylation; at higher exposures, however, the alkylation processes become saturated, leading to an accumulation of arsenite and subsequent toxicity.