No abstract

1984. Weiationships between the partitioning of trace metals in sediments and their accumulation in the tissues of the freshwater mollusc E88iptio complanata in a mining area. Can. 1. Fish. Aquat. Sci. 41: 1463-1472.Surficial sediment samples and specimens of a benthic freshwater pelecypod, Elliptio compbawata, were collected at eight sites located along a metal contamination gradient downstream from the mining and smelting complex in Wouyn-Noranda, Quebec. The molluscs were dissected, digested, and analysed for Cu, Pb, Zn, Fe, and Mn by flame atomic absorption spectrophotometry. Each sediment sample was wet sieved and the ~9 0 -p m gragaulometric fraction was subjected to a sequential extraction procedure designed to determine the partitioning of the trace metals among various geochemical phases. Regression analysis indicates that Cu, Pb, and Zn levels in various tissues of E. complanab (or in the whole organism, without the shell) are best related, not to total metal concentrations in the adjacent sediment, but rather to one or more of the relatively easily extracted fractions. Accumulation of Cu, Pb, and Zn was also influenced by the protective or competitive effect of other sediment constituents, notably amorphous iron oxyhydroxides and, to a lesser degree, organic matter. Des echantilions d e skdiments de surface et des specimens du pelecypode d'eau douceElliptio compbanata csnt ete pr6leves A huit sites situes dans ken gradient d e contamination en metaux, en aval daa complexe dfop6rations minieres et d e raffinage de Rouyn-Noranda, Quebec. bes mollusques ont et6 disseques, dig6r6s et analyses poker Cu, Pb, Zn, Fe et Mn par spectrophotometrie d'absorption atomique. Chaque 6chantillon d e sediments etait tamis6 par voie humide et la fraction granulometrique C90 ym etait soumise 3 une proc6dure d'extractions sequentielles eoncue pour determiner la repartition de metaux traces entre diverses phases geochimiques. L%aplIyse d e regressions indique que Oes niveaux de Cu, Pb et Zn dans divers tissus de E. csrnp/anab (ou dans Iforganisme entier, sans la coquille) sont mieux correles avec I'une ou plusieurs des fractiogas de metaux extraites relativement facilement des sediments plutdt qu'avec les concentrations totales des metaux dans ces sediments. b'accumulation de Cu, Pb et Zn 6tait aussi influencee par B'effet protecteur ou cornpetitif d'autres constituants des sediments, notamment des oxyhydroxydes de fer amorphe et, h un degre moindre, d e la matiere organique.

This paper reports a net snow‐to‐air Hg transfer from the remote and temperate Experimental Lakes area (Ontario, Canada). More than 40% loss of total Hg concentration was observed in surface snow within 24 hours of its deposition on the ground. Stratigraphic profiles of total Hg in various snowpacks demonstrated a systematic decrease in total Hg concentration with snow depth pointing to snow‐to‐air Hg transfer and not snow‐to‐ground transfer. These results confirm observations made in a suburban area (Sainte‐Foy, Quebec, Canada) receiving higher atmospheric deposition of Hg perhaps differently associated chemically. The occurrence of this phenomenon is therefore extended geographically to include snow from pristine regions. It is hypothesized that the loss of Hg is caused by a sunlight‐initiated Hg(II) reduction in snow and subsequent gas transfer of Hg0 to the atmosphere. Polychromatic action spectra demonstrated that Hg(II) reduction in snow was mostly mediated by UV‐B irradiation and not visible, or UV‐A wavelengths. In addition to Hg(II) reduction in snow, we observed Hg0 oxidation in snow samples spiked with Cl−. Hg0 oxidation could limit the potential for Hg loss from snowpacks from coastal polar or subpolar regions (where snow often contains high chloride levels) by competing with Hg(II) reduction and slowing the snow‐to‐air Hg transfer. However, in regions under minimal marine influences, watershed budgets of Hg should consider the possibility of Hg loss from snow with time of deposition on the ground. Also, snow core studies should consider historic sunlight irradiation if extrapolation from snow cores is desired to estimate past ambient Hg levels.

As for other mRNA measurement methods, quantitative RT-PCR results need to be normalized relative to stably expressed genes. Widely used normalizing genes include β-actin and glyceraldehyde-3-phosphate dehydrogenase. It has, however, become clear that these and other normalizing genes can display modulated patterns of expression across tissue types and during complex cellular processes such as cell differentiation and cancer progression. Our objective was to set the basis for identifying normalizing genes that displayed stable expression during enterocytic differentiation and between healthy tissue and adenocarcinomas of the human colon. We thus identified novel potential normalizing genes using previously generated cDNA microarray data and examined the alterations of expression of two of these genes as well as seven commonly used normalizing genes during the enterocytic differentiation process and between matched pairs of resection margins and primary carcinomas of the human colon using real-time RT-PCR. We found that ribosomal phosphoprotein P0 was particularly stable in all intestinal epithelial cell extracts, thereby representing a particularly robust housekeeping reference gene for the assessment of gene expression during the human enterocytic differentiation process. On the other hand, β-2-microglobulin generated the best score as a normalizing gene for comparing human colon primary carcinomas with their corresponding normal mucosa of the resection margin, although others were found to represent acceptable alternatives. In conclusion, we identified and characterized specific normalizing genes that should significantly improve quantitative mRNA studies related to both the differentiation process of the human intestinal epithelium and adenocarcinomas of the human colon. This approach should also be useful to validate normalizing genes in other intestinal contexts.

Cadmium concentrations were measured at 49 littoral sites in 38 lakes distributed over 350,000 km2 in the provinces of Québec and Ontario, both in the abiotic environment (oxic sediments and overlying water, diagenetic iron oxyhydroxide deposits on Teflon collectors) and in the soft tissues of the freshwater bivalve Anodonta grandis collected along a Cd contamination gradient. Concentrations of dissolved Cd above the water‐sediment interface were highly undersaturated with respect to CdCO3(s). The partitioning of Cd between water and surficial oxic sediments is interpreted in terms of sorption of this metal to sedimentary organic matter and Fe oxyhydroxides, by means of surface complexation concepts. Binding intensity values for the sorption of Cd to Fe oxyhydroxides (KFe−Cd) and organic matter (KOM−Cd) are estimated from field data (i.e. Cd concentrations in diagenetic Fe deposits, in the sediments, and in the water). The following empirical relationships between binding intensities and lake pH are found: log KFe−Cd = 0.82 pH − 1.30 (r2 = 0.89) and log KOM−Cd = 0.97 pH − 2.45 (r2 = 0.78). Calculated Cd partitioning with these binding intensities indicates that Cd is bound mainly to organic matter in these sediments. Linear regression analysis indicates that Cd concentrations in the soft tissues of the bivalves, [Cd(Org)] (µg g−1 dry wt), are related to dissolved Cd concentrations: [Cd(Org)] = 44[Cd2+] + 10 (r2 = 0.81) for [Cd2+] expressed in nmol liter−1. In these lakes, simple normalization of sedimentary extractable Cd with respect to sedimentary Fe oxyhydroxide or organic C concentrations proved inadequate for predicting Cd concentrations in A. grandis. Combining surface complexation concepts with the free‐metal ion model of trace metal‐organism interactions, we show that Cd concentrations in the soft tissues of A. grandis can be predicted with similar success as with the dissolved Cd concentration from water pH and sediment chemistry (total sedimentary Cd, Fe oxyhydroxides, and organic C concentrations).