Modelling of leachates from dolomitic mine tailings.

The REDEQL.EPAK computer model was used to study speciation of Pb, Cd, Zn, and Ca in leachates from dolomitic Pb mine tailings. By allowing or disallowing precipitation of solids and equilibration of the modelled leachate with atmospheric C02, comparison of fresh and aged leachates was made. The effects of treatment of the tailings with phosphate containing fertilizer were studied through addition of P04 (3-) to the modelled solution. Equilibrium constants pertaining to metal ion-humic acid complexation were added to the thermodynamic data base of the model in order to study the effects of decaying plant material on tailings leachate.Initial leachate of the tailings is found to be supersaturated with Cd and Zn. Non-complexed ("free") Cd(2+) and Zn(2+) is predicted to comprise most of the soluble form of these metals in the leachate; Pb is predicted to be present largely as PbCO3 ion pair. Equilibration of the leachate with the atmosphere is predicted to lead to extensive precipitation of CdCO3 and ZnSiO3. Precipitation of Pb5(PO4)3Cl is predicted at high PO4 (3-) concentration and at low pH. Complexation by the humic acid is predicted to compete effectively with other ligands in the leachate for the metal ions. The results are compared with experimental findings.

Food analysis for lead using furnace atomic absorption and a L'vov platform.

Furnace atomic absorption is a very sensitive method for determination of lead and other trace metals in a variety of samples, but it is prone to matrix interferences. A major improvement in the method is achieved by the use of a L'vov platform, a small piece of graphite placed inside the furnace tube, onto which the sample solution is pipetted. The temperature of the platform rises more slowly than that of the tube wall during the atomization cycle, and sample vaporization is delayed until the furnace atmosphere is at a high and nearly constant temperature. The resulting atomization behavior is more consistent and less matrix-dependent for numerous analyte elements, including lead. Results are further improved by addition of ammonium phosphate to all samples and standards as a matrix modifier. For example, in comparing analyte sensitivity (slope of the absorbance vs concentration curve) in a variety of food sample types to the sensitivity in dilute HNO3, the average lead response showed 60 +/- 15% suppression due to the sample matrices. Use of the L'vov platform and matrix modifier virtually eliminated the suppression and improved the precision.

Zinc, copper, cadmium and chromium in polished and unpolished rice.

One hundred samples of polished and 27 of unpolished rice were collected from 22 countries and areas and analyzed for Zn and Cu by flame atomic absorption, for Cd by carbon furnace atomic absorption, and for Cr by neutron activation. Unpolished rice contains on average 16.4 mug/g Zn, 4 mug/g Cu, 0.029 mug/g Cd and 0.011 mug/g Cr. Polished rice contains 13.7 mug/g Zn, 3 mug/g Cu, 0.029 mu/g Cd and 0.012 mug/g Cr. Thus, polishing brings about a loss of the essential elements Zn and Cu, but not of Cd, a toxic pollutant. Japanese rece has high Cd content. In countries where rice is a major staple food, high Cd content in rice may cause excessive absorption of this toxic metal.

Calcium content of river water, trace element concentrations in toenails, and blood pressure in village populations in New Guinea.

Several studies carried out on industrialized population groups have revealed the presence of an inverse relationship between hardness of drinking water and certain cardiovascular parameters, e.g., death rates, blood pressure, blood cholesterol, etc. In the present paper an attempt was made to see whether such an association also exists in primitive population groups who drink untreated water collected directly from rivers. Blood pressure was measured in persons living in villages along the banks of the Wogupmeri river in New Guinea. The water was analyzed for calcium content. Trace element concentrations were also determined in toenails from the same subjects to see whether a correlation existed. Calcium content of river water decreases as the river flows downstream, while blood pressure of the villagers living along this river increases. The trace element analysis of toenails revealed strong correlations between aluminium and vanadium. The concentrations of these two elements decrease with age. This association is present in both sexes, in adults and in children. A similarly strong correlation also exists between these two elements in staple food. The results of the present investigation tend to confirm the findings of other studies indicating an apparently beneficial effect of relatively hard water on cardiovascular parameters. The concentration of aluminium and vanadium in toenails show interesting trends, the biological meaning of which, if any, is still unknown.