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The accumulation of Cd(II), Cu(II), Pb(II) and Zn(II) at mg L(-1) concentration levels by inactive freeze-dried biomass of Pseudomonas Putida has been investigated. These metals could be efficiently removed from diluted aqueous solutions. A contact time of 10 min was sufficient to reach equilibrium. The pH has a strong effect on metal biosorption and the optimal pH values were 6.0, 5.0-6.0, 6.0-6.5 and 7.0-7.5 for Cd(II), Cu(II), Pb(II) and Zn(II) respectively. Under these conditions there was 80% removal for all metals studied. The process of biosorption can be described by a Langmuir-type adsorption model. This model accounts for 98% of the data variance. The K(A) and q(max) parameters for each metal are strongly correlated (at confidence levels greater than 98%) with the metal acidity, quantified by the constant of the corresponding M(OH)(+) complex, thus confirming previous assertions by other authors.

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A new procedure for the direct determination of picomolar levels of cobalt in seawater is presented. Cathodic stripping voltammetry is preceded by adsorptive accumulation of the cobalt-nioxime (cyclohexane-1,2-dione dioxime) complex from seawater containing 6 μM nioxime and 80 mM ammonia at pH 9.1, onto a hanging mercury drop electrode, followed by reduction of the adsorbed species. The reduction current is catalytically enhanced by the presence of 0.5 M nitrite. Optimized conditions for cobalt include a 30 s adsorption period at -0.7 V and a voltammetric scan using differential pulse modulation. According to the proposed reaction mechanism, dissolved Co(II) is oxidized to Co(III) upon addition of nioxime and high concentrations of ammonia and nitrite; a mixed Co(III)-ammonia-nitrite complex is adsorbed on the electrode surface; the Co(III) is reduced to Co(II) (complexed by nioxime) during the voltammetric scan, followed by its chemical reoxidation by the nitrite, initiating a catalytically enhanced current. A detection limit of 3 pM cobalt (at an adsorption period of 60 s) enables the detection of this metal in uncontaminated seawater using a very short adsorption time. UV digestion of seawater is essential, as part of the cobalt may occur strongly complexed by organic matter and rendered nonlabile. The method was applied successfully to the determination of the distribution of cobalt in the water column of the Mediterranean.