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Xz~nmary: In batch expcrinients wit,li the metals labelled with their rudionuclides the culnttlation of zinc, cadmium and mercury on Sc~n,~des?nus obliquus in dependence on the pH-value is measured, because the original pH-value of the solution is changed by t'he algae due t,o their absorpt,ioii of hydrogen-ions. For thc: uptake of zinc and cadmium the logarithm of the cunialation factor in the range of 2 ... 5 is a linear function of the pH-value in the range of 5 ... 9, cutnulaOion increasing with rising pH-value. 111 contrast, the mercury cumulation is pH-iudependent. If the changedpH-value is taken into account, the curnulation fact'ors are independent of the metal concent,ration in the range =10-4 inolil. The degree of cumulation is not changed by t.he presence of other met.aIs. The cumulation factor. is reduced by substances forming negatively charged complexes with t'he metals.The studies dealing with the cuniulation of metals by fresh water algae (KEENEY et al. ; GERHARDS iind WELLER; ALBERGOXI Yrccin-~ and COPPELLOTTI; etc.) demonstrate the differences of the curnulation of individual elements or chemical compounds. The cumulation factor F (the ratio of the concentration of metal in algal cells and iri the medium) depends on the species of algae, on the type of metal, its chemical form, concentration etc. The generally described characteristic of this process I S iisually disciissed together with the evaluation of the studied metal for the nietabolisni and living conditions of the tested organism (ALBERGONI, PICCWI and COPPELLOTTI). The coiirsc of Zri and Cd uptake by algae just as the kinetics of iiptake of a niimbcr of other iiietals has a typical curve. The greatest concentration of the studied inetxl in the biomass of algae 1s found very early after addition of the metal, maximallwithin one hour. This is followed by the stagnation or the decrease, and a further gradual increase in concentration occurs a t longer exposures, lasting for 3 ... 14 d. (1976) reporled, for cxaniple, for zinc that in the alga Clilorella vulgaris sorption was inaximuni within 1 ... 3 h andat anexposure to I niinol/l %nC12 for 10 d the zinc content decreased in algae from 0.34 minol/g dry weight to 0.04 mniol/g A siniilar course of the culllidation curve is reported by WIHLIDAL and BRODA i n the alga Chlorella fitsca, by BRAEK, MALNES and JENSEN in iuarine diatoms and by KAMEDA, SHIMIZA and HIYAMA in sea fish and molluscs. SAKAGUCHI et al. report in the alga Chlorella regularis, strain 5-50, at exposure to cadniiuiii n niaxiiiiuin uptake within 30 niin, and GPPS and COLLER who studied the uptake of cadniiii~ii by Chlorella pyrenoidosa describe a so-called "rapid uptake" within 8 min of expo- DE F~LIPPIS and PALLAGHY

Adsorption of hexavalent uranium (4.2X10 -5 mol/I) from aqueous solutions on "cypris" clay was studied as a function of pH (1 -12), concentration of coal humate (0, 0.3 and 3 g/1) and clay concentration (5 and 50 g/1). A batch method was used for the experiments. Uranium remaining in the solution after the adsorption was determined by spectrophotometry of its arsenazo-III complex. Simultaneously, the distribution of coal humate between the solid and liquid phases was measured by UV spectrophotometry. Both the adsorption of uranium and the distribution of coal humate were strongly pH-dependent. The adsorption of uranium passed through two maxima whose form and position on the pH-scale depended on the concentration of clay and on the humate to clay ratio. The precipitation/adsorption of humate on clay was high at low pH values and decreased with increasing pH. The slope of the decrease and its position on the pH-scale depended on the humate to clay ratio. Presence of humate enhanced the adsorption of uranium at pH<4-7.5 (depending on the concentrations of clay and humate) and suppressed it at pH>4-8. The results were compared with literature data and qualitatively interpreted. Conclusions were drawn on probable mechanisms of uranium adsorption in the absence and presence of humate, and on possible applications of cypris clay as barrier or filling material and of the clay-humate system for wastewater treatment.

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