Janusz Dominik

Factors controlling 7Be and 210Pb atmospheric deposition as revealed by sampling individual rain events in the region of Geneva, Switzerland

Bulk atmospheric deposition of 7Be and 210Pb has been measured at Versoix, close to Geneva, Switzerland. Collectors were continuously deployed from November 1997 through November 1998 for periods from 1 to 22 days depending on the frequency of rain. The activities of 7Be and 210Pb integrated over the sampling interval were moderately well correlated with rainfall (r2 of 0.66 and 0.55, respectively; p < 0.001) and well correlated one with the other (r2 of 0.91; p < 0.001). The 7Be/210Pb activity ratio is close to 13.5, except for samples collected in the periods of very low precipitation which have a distinctly lower ratio. A simple model accounting for rainfall, seasonal variations and reload of the local atmosphere after a rain event explains 90% of the variance of 7Be and 210Pb deposition. Concentrations of 210Pb and Ca++ in rain were correlated with transport time of air masses over the continent as indicated by reconstruction of air mass trajectories over three days.

Transport of the environmental radionuclides in an alpine watershed

Abstract The radionuclides137Cs,210Pb and7Be have been examined in the alpine Rhoˆne watershed (Switzerland) during a period of two years in order to evaluate their usefulness as tracers of the removal and transport rate of top-soil particles and particle-reactive contaminants of atmospheric origin. The specific activities of the radionuclides in fluvial suspension show a distinct seasonal pattern which depends on the hydrologic regime of the stream and the sources of the suspended matter. Input-output budgets based on the atmospheric deposition and fluvial removal of three radionuclides in the alpine Rhoˆne watershed are used to estimate their erosional residence times. The simplest one box model yields mean residence times of about 800 and 1400 years for137Cs and210Pb, respectively. The removal rate of short-lived7Be suggests that a part of the watershed (0.6–2.3% of the total surface) is exposed to a rapid erosion, in which the mean residence time of the radionuclides is in the range of 1–220 days. This has little influence on the calculated residence time of137Cs but increases the estimated residence time of210Pb in soil to over 1800 years. The use of210Pb-7Be pair in fluvial output may be very helpful in the assessment of the impact of atmospheric pollutants on the water quality in rivers and lakes.

Evolution of the Upper Rhone River discharge and suspended sediment load during the last 80 years and some implications for Lake Geneva

Abstract: During this century, the characteristics of the Upper Rhone River discharge, flowing into Lake Geneva, have been altered in response to the changes which have occurred in its watershed. Principally, numerous hydroelectric dams have been constructed on the course of the Rhone River tributaries. At present the major reservoirs can hold about 1220106m3 of water, which represents 1/5 of the total annual Rhone River flow. Flow regime characteristics of the river have been modified by the dam operations. Water is released from reservoirs during winter and stored in summer. Large floods have also been reduced in amplitude and frequency. From the available literature data, sediment rating curves have been calculated and used to estimate the evolution of the sediment load from the Rhone River to Lake Geneva. They show that sediment input has decreased by at least a factor 2. This reduction has impacted the occurrence of underflows along the lake bottom, due to the reduction of sediment-laden floods, which in turn may have considerable negative effects on the reoxygenation of Lake Geneva deep waters.

Partitioning of trace metals between particulate, colloidal and truly dissolved fractions in a polluted river: the Upper Vistula River (Poland)

Metal partitioning depends on the physical–chemical conditions of a system and can be affected by anthropogenic inputs. In this study, the authors report the results of trace metal partitioning between particulate (>1.2 μm), colloidal (1.2 μm–1 kDa) and truly dissolved (<1 kDa) fractions in the polluted section of the Upper Vistula River compared with the non-polluted headwaters. It was found that the salt input in the Vistula River induced a decrease of colloid concentration and the increase of suspended particulate matter. Compared with upstream from the polluted section, the metal concentrations (Co, Cu, Cr, Mn and Zn) in the colloidal fraction were lower. It was mainly due to the rapid colloid coagulation at increased salinity, the competition with ligands and major ions (Ca and Mg) and the weak mobility of metals associated with particles at the pollution sources.

Organic colloid separation in contrasting aquatic environments with tangential flow filtration

The use of tangential flow filtration (TFF) for size fractionation of natural dissolved organic matter was investigated. The performance of regenerated cellulose membrane with a nominal molecular weight cut-off of 1 kDa was examined on 20 samples from lake, river and estuary systems, characterised by contrasting dissolved organic carbon (DOC) contents and conductivity. The evaluation was based on absorbance, fluorescence and DOC measurements. Detailed protocols of membrane cleaning and conditioning nation are proposed. The ultrafiltration membrane can efficiently be cleaned to provide low carbon blank (<0.01 mg/L). Fluorescence measurements confirmed that the higher molecular weight compounds were isolated in the retentate and the lower molecular weight remain in the permeate. Mass balance for natural samples show good recovery for DOC (109 +/- 12%, n = 20) and fluorescence measurements (106 +/- 9%, n = 13). No relation between factors of concentration (fc) and mass balance quality was observed for the fc range 1.5-11. Moreover, high ionic strength and high DOC contents did not enhance membrane fouling. These findings demonstrate that reliable fractionations by TFF of natural organic colloids in aquatic systems can be achieved.

Water toxicity and metal contamination assessment of a polluted river: the Upper Vistula River (Poland)

In aquatic systems, the bioavailability of an element to microorganisms is greatly influenced by its chemical speciation. The goal of this work was to assess metal toxicity to a green algae (Pseudokirchneriella subcapitata) and a bacterium (Vibrio fisheri) as a function of size fractionation and chemical speciation (using the program MINTEQA2) in contaminated water of the Upper Vistula River. Water samples were collected at 1 reference site, 4 polluted sites and one polluted site on the Vistulas main tributary, the Przemsza River. Toxicity measurements were performed on unfiltered samples and, total dissolved (<1.2 μm), and truly dissolved (<1 kDa) fractions. Trace metal (Cd, Co, Cr, Cu, Mn, Pb, Zn) concentrations were measured in these samples and also in the colloidal fraction (1 kDa–1.2 μm). At the reference site, the low metal concentrations were in agreement with the absence of measurable toxicity. In the polluted section of the river, free metal concentrations were largely below the potential toxic levels for bacteria, which was in agreement with the absence of toxicity. Although Zn2+ was at potentially toxic-level concentrations in total dissolved and truly dissolved fractions in the polluted riverine section, toxicity for algae was observed, only in truly dissolved fractions from two stations. The absence of toxicity in most samples was related to metal association with particles and with low molecular weight ligands as well as the presence of organic ligands (phenol). The reason for toxic effects in two ultrafiltered samples is not clear, but may be related to the elimination of the colloidal organic fraction and thus the eradication of its protective effect occurring in natural samples.

Insights into low fish mercury bioaccumulation in a mercury-contaminated reservoir, Guizhou, China

We examined Hg biogeochemistry in Baihua Reservoir, a system affected by industrial wastewater containing mercury (Hg). As expected, we found high levels of total Hg (THg, 664-7421 ng g(-1)) and monomethylmercury (MMHg, 3-21 ng g(-1)) in the surface sediments (0-10 cm). In the water column, both THg and MMHg showed strong vertical variations with higher concentrations in the anoxic layer (>4m) than in the oxic layer (0-4 m), which was most pronounced for the dissolved MMHg (p < 0.001). However, mercury levels in biota samples (mostly cyprinid fish) were one order of magnitude lower than common regulatory values (i.e. 0.3-0.5 mg kg(-1)) for human consumption. We identified three main reasons to explain the low fish Hg bioaccumulation: disconnection of the aquatic food web from the high MMHg zone, simple food web structures, and biodilution effect at the base of the food chain in this eutrophic reservoir.

Chromium(VI) is more toxic than chromium(III) to freshwater algae: A paradigm to revise?

The behavior and toxicity of Cr(III) and Cr(VI) to the green algae Pseudokirchneriella subcapitata and Chlorella kessleri were studied in a standard culture medium (ISO medium) and, for P. subcapitata only, in ultrafiltered natural water enriched with all ISO components (modified ISO medium). In all solutions amended with Cr(III), initial chromium concentrations decreased by 60-90% over 72h (the duration of algal tests) indicating that protocols for testing poorly soluble substances are required to properly evaluate Cr(III) toxicity. After accounting for its behavior in test solutions, chromium(III) was 5-10 times more toxic than Cr(VI) in both media. For P. subcapitata, the average 72h EC50 of Cr(III) in ISO medium was 17.4+/-4.7 microg/L (n=9); lower than corresponding hardness-corrected Continuous Concentration Criteria of the US EPA and well within the range of Cr concentrations found in waters impacted by tannery discharges. These results follow from intrinsic chemical properties of Cr(III) in circumneutral solutions, so that the actual toxicity of Cr(III) to aquatic organisms may be generally underestimated.

Identification of stoichiometric iron-phosphorus colloids produced in a eutrophic lake

Abstract: Iron-rich colloids formed at the oxic-anoxic interface of a eutrophic lake (Lake Lugano; CH) were characterized by bulk chemical methods and analytical electron microscopy. Fractionation of raw waters showed that non-dissolved iron is particulate above the oxicline and mainly colloidal in the anoxic part of the hypolimnion, while non-dissolved ortho-phosphate is mostly colloidal through the water column. Because of these differences, filtration did not prove helpful for the determination of the role of iron-rich species in the scavenging of ortho-phosphate. On the other hand, analytical electron microscopy revealed that iron-rich nano-granules (ca. 50nm) are associated to the surface of bacterially produced fibrillar polysaccharides. Iron colloids in these complex entities contain important and constant amounts of phosphorus ([PO4]part:[Fe]part = 0.48 ± 0.11, n = 1096 Fe-rich entities analyzed by electron microscopy), which suggests that phosphates are stoichiometrically incorporated into the hydrous iron oxide phase, with a tentative composition Fe2[OOH]1-x[(OH)3]x[PO4], during its genesis.

Possible evidence for dissimilatory bacterial magnetite dominating the magnetic properties of recent lake sediments

Rock magnetic measurements, including low temperature susceptibility and Curie Temperature experiments, show that the most recent sediments from the Bay of Vidy, close to Lausanne on the north shore of Lake Geneva, Switzerland, are rich in superparamagnetic magnetite. The 137Cs dated increase in magnetite concentration coincides with the beginning of sewage de-phosphatization by the addition of iron chloride. Extracts of fine-grained magnetite, imaged by transmission electron microscopy, form amorphous masses visually comparable to those detected as the product of extracellular magnetite production by bacteria. This is the first indication that extracellular, dissimilatory magnetite may survive and make a dominant contribution to the magnetic properties of sediments. Final confirmation of the bacterial origin of the magnetite will depend on rRNA sequencing.