STABILITY OF BACTERIUM-MERCURY COMPLEXES AND SPECIATION OF SOLUBLE INORGANIC MERCURY SPECIES

Soluble inorganic mercury ions from aqueous solutions were retained on the external membrane of both lyophilized bacterial cells and living cells. Desorption studies were performed using both types of cells, Di stribution coefficients of mercury between the aqueous and solid phase s, as well as the conditional stability constants of mercury ions for the external membranes of bacteria were calculated. Loaded membranes a nd the amount of the unadsorbed ions were measured by electrothermal a tomic absorption spectrometry (ETAAS) and/or gamma spectrometry. The H g-203 radiotracer (t(1/2) = 46.6 days) was used to monitor recoveries using gamma spectrometry in combination with an optimized extraction p rocedure. Depending on the pH of the solution mercury ions can be sele ctively retained by the bacterial external membrane and the speciation of the mercury(II) and mercury(I) ions is possible. Best retention pH s for both mercury ions and bacteria were the following: mercury(II): 1 (E. coli) and 3 (P. putida), and mercury(I): 4 (E. coli) and 8 (P. p utida). Interelement effects from other ions in the retention process of mercury were also investigated. A technique involving a solid extra ction stage of mercury from aqueous samples at ng ml(-1) level was dev eloped and applied to the determination of mercury by ETAAS. The mercu ry-biomass pellet is separated by centrifugation and treated with a ni tric acid solution determining the content of mercury in the supernata nt solution. The best detection limit (3 times stand. dev. of the blan k) and the best sensitivity (Hg concentration for an absorbance peak o f 0.0044 s) of the method for the applied concentration procedure were , respectively, of 15.0 ng ml(-1) and 3.0 ng ml(-1) for mercury(I) and 22.0 ng ml(-1) and 5.5 ng ml(-1) for mercury(II).