Effect of pH, sulphate concentration and total organic carbon on mercury accumulation in sediments in the Volta Lake at Yeji, Ghana.

In this study, pH, total organic carbon, sulphate concentration and mercury concentrations of sediment samples from the Volta Lake at Yeji in the northern part of Ghana were determined. The results indicate that pH ranged from 6.32 to 8.21, total organic carbon ranged from 0.17 to 3.02 g/kg and sulphate concentration from 10.00 to 57.51 mg/kg. Total mercury concentrations ranged from 32.61 to 700 ng/g which is below the International Atomic Energy Agency recommended value of 810 ng/g. Humic substance-bound mercury ranged from 81.15 to 481.31 mg/kg in sediments and its two fractions existed as humic acid-bound mercury > fulvic acid-bound mercury with the ratio of humic substance-bound mercury to fulvic acid-bound mercury as 1.62 on the average. Humic substance-bound mercury and the two fractions fulvic acid-bound mercury and humic substance-bound mercury in sediments were favorably determined and found to correlate significantly positive with total organic carbon (r = 0.538) and total mercury (r = 0.574). However, there were poor correlations between SO(4) (2-) concentrations and humic substance-bound mercury (r = -0.391) as well as the two fractions; fulvic acid (r = -0.406) and humic acid (r = -0.381). By assuming that methyl mercury is mostly formed in sediments, these significant relations suggest that the efficiency of mercury being methylated from a given inorganic form depends on the amount, and most likely biochemical composition of total organic carbon in the lake sediment but not the SO(4) (2-) concentration.

Total mercury distribution in different tissues of frigate tuna (Auxis thazard thazard) from the Atlantic Coastal Waters of Ghana, Gulf of Guinea.

Total mercury concentrations in different tissues of frigate tuna fish (Auxis thazard thazard) was determined by the cold vapour atomic absorption spectrometry technique using an automatic mercury analyzer. A mixture of HNO3, HClO4 and H(2)SO(4) was used for complete oxidation of organic tissue. The concentration of mercury obtained was in the order Gills < Stomach < Gonads < Intestine < Heart < Duodenum < Liver < Muscle. The concentration of total mercury detected in the edible muscle tissue of the tuna fish tested ranged from 0.044 to 0.201 microg g(-1) (mean = 0.108 microg g(-1)) wet weight. These levels are all within the maximum allowed/recommended level in fish (0.5 mug g(-1) wet weight) set by the Food and Agriculture Organisation/World Health Organisation (FAO/WHO) and are therefore unlikely to constitute any significant mercury exposure to the general population because of consumption of tuna fish. The results of the study suggest a relatively clean marine environment that has not been significantly impacted by mercury contamination probably due to minimal industrial activity in the region.

Europium complexation by an aquatic fulvic acid - effects of competing ions.

Effects of competing ions, Fe (2+)Fe (3+) and Al(3+), on Eu(3+) complexation with an aquatic fulvic acid (FA), have been investigated using an ion exchange technique. The influence of different concentrations (10(-6), 10(-4) M) of the competing ions on the distribution coefficient for Eu was measured, and the overall complex formation function, beta(ov), was resolved for the Eu systems with Fe and Al. All systems showed pH-dependent beta(ov)-functions. The presence of 10(-4) M concentration of competing ion reduced the resolved complex formation function (logbeta(ov)) for Eu complexation with fulvic acid by 0.6 and 0.4 log units at pH 5 for Fe and Al, respectively. this indicates that Fe has a more perturbing effect on Eu-FA complexation than Al. In similar competition studies Sr and Eu were found not to perturb each others complexation with fulvic acid, suggesting therefore that the two metals probably bind to different sites on the fulvic acid molecule.

Binding of cadmium to Laurentide fulvic acid. Justification of the functionalities assigned to the predominant acidic moieties in the fulvic acid molecule.

The binding of cadmium to a fulvic acid (FA) extracted from peat was studied as a function of pH (4-8), ionic strength (0.01 and 0.10 M NaNo(3)) and ratio of fulvic acid to metal ion concentrations (FA Cd = 8, 4 , and 2). An overall complex formation function of approximately 10(3.14) was determined to enable comparison with previous studies. Additionally, literature values of complex formation constants were employed to describe the interaction between Cd(II) and the individual acidic sites. A good prediction of the experimental results is considered as a justification of the functionalities assigned to the predominant acidic sites in the fulvic acid molecule.

Dissociation properties of laurentide fulvic acid: Identifying the predominant acidic sites.

Application of the unified physicochemical approach to the description of the dissociation properties of Laurentide fulvic acid, extracted from peat, has shown that five predominant acidic moieties may account for the observed potentiometric titrations in aqueous medium. Information from non-aqueous titrations and titrations in presence of excess metal ions, e.g. Cu(2+) and Eu(3+), has shown that three of the acidic moieties are carboxylic in nature while the other two are of alcoholic nature. A comprehensive description of the dissociation properties of natural organic acids, as ligands, is advocated as a pre-requisite step towards understanding their interaction with metal ions in the environment.

Calcium binding by fulvic acids studied by an ion selective electrode an ultrafiltration method.

The interaction between Ca(2+) and two well-characterized fulvic acids (Armadale and Laurentide FA) has been studied at 0.100 and 0.010M sodium nitrate using a fixed concentration of fulvic acid (100 ppm) and varying amounts of calcium (0.005-0.020 mmoles). Free calcium concentration was determined by in situ measurements employing a calcium electrode. For Armadale FA, free calcium was additionally determined via an ultrafiltration technique followed by atomic absorption measurements. For both fulvic acids, Ca(2+) binding was observed to be decreased by an increase in the ionic strength of the system. At the lower ionic strength the tendency for binding is dependent on the fulvic acid-to-metal ratio while at the higher ionic strength, the binding is insensitive to changes in the fulvic acid-to-metal ratio (an observation corroborating the contention that calcium binding to humic substances is primarily electrostatic). Comparison of the computed overall complex formation functions shows that values obtained from the ultrafiltration method were higher than those obtained using the calcium electrode. The binding of calcium was similar for the two fulvic acids.

Complex-forming properties of natural organic acids Fulvic acid complexes with cobalt, zinc and europium.

The complex-forming properties of a fulvic acid sample have been studied by an ion-exchange distribution method. The results have been analysed by a novel physicochemical approach which attempts to take into account complications introduced by the polyelectrolyte nature and functional heterogeneity of the fulvic acid molecule. These studies with trace level concentrations of cobalt, zinc and europium show that these metal ions are selectively complexed by the weakly acidic enol grouping of the fulvic acid molecule. The logarithms of the stability constants (beta(1)) for the cobalt, zinc and europium chelates are 6.5, 6.4 and 10.3 respectively.

Non-aqueous titration of a fulvic acid sample, with use of an internal reference compound.

The use of an internal reference compound in non-aqueous acid-base titrations as a relatively simple, reliable and accurate means of obtaining information on the acidity spectrum of natural organic acids is reported. Acid-base titrations in dimethylformamide, DMF, with tetrabutylammonium hydroxide as the titrant and p-hydroxybenzoic acid as an internal reference compound have been performed to determine the carboxylic acid and the acidic hydroxyl components of a fulvic acid sample isolated from surface water in the Bersbo area, south-east of Sweden. A carboxylic acid capacity of 4.78 +/- 0.05 meq/g and an acidic hydroxyl group capacity of 1.35 +/- 0.03 meq/g were found for the aquatic fulvic acid.