Speciation of cadmium mixed ligand complexes in salt water lakes

Amalgam voltammetry has been used to study heavy metal interaction in model lake water in KNO3 at 23 oC at concentration levels of genuine lake water. The hanging drop amalgam electrode was prepared in situ before exchanging the medium for the sample solution. Half-wave potentials at two metal ion concentrations were measured, one at the actual concentration in the lake while the other at a much lower one. The experimentally determined shifts in half-wave potentials are used to compute several formation constants. At the natural [CO32-] of 0.5 M in the lake, the main contributor to the speciation of cadmium is [Cd(CO3Cl2)]2-. At high [Cd2+], the DPASV detects the presence of free Cd2+ ions, hence, potential polluting effect, while the amalgam reports [Cd(CO3)2Cl)]3- to be dominant above [CO32-] = 0.8 M. There is a variation in the number of complexes detected, their stabilities and percentage distribution in the two methods. Cd2+ ion concentration also affects the number of complexes formed and their stabilities. KEY WORDS: Heavy metals, Hanging drop electrode, Amalgam voltammetry, Speciation, Cadmium mixed ligand complexes  Bull. Chem. Soc. Ethiop. 2003, 17(1), 85-94

Comparison of soil phosphorous extraction by Olsen and double acid methods in acid soils of Western Kenya

hosphorous is an essential nutrient in plants required for root establishment. In the soil, it is applied as DAP, TSP or phosphate rocks. In acid soils, aluminium and iron are dominant and tend to “fix” phosphorous, making it unavailable for plant uptake. Phosphorous deficiencies are monitored through soil chemical analysis. There are many methods for the extraction of available forms; however the choice is dependent on several factors among them soil pH. Forty soil samples were collected from three different acid soils in Western Kenya. The samples were air dried, sieved under 2.0 mm sieve and stored in sample bags for subsequent analysis. Phosphorous extraction of was carried out using a basic extractant (Olsen bicarbonate method) and acid extractant (double acid method). The extracts were measured colorimetricaly by the ascorbic acid method at 880 nm wavelength. The methods were compared in terms of extracting efficiency, correlations and soil critical levels. The soils had a pH range of between 4.5 – 6.1; phosphorous, 1.66 – 55.37 mg P/ kg by Olsen method and 3.01 – 158.17 mg P /kg by double acid method. The methods were linearly correlated (r = 0.95), however, double acid extracted more phosphorous than Olsen by a factor of 2.67

Fluoride distribution in selected foodstuffs from Nakuru County, Kenya, and the risk factors for its human overexposure

Abstract Critical data on the impacts of fluoride (F) in food systems along the Eastern Africa Rift Valley System (EARS) is needed for public health risk assessment and for the development of strategies for ameliorating its deleterious effects among the affected communities. Long-term F overexposure causes dental and skeletal fluorosis, and leads to neurotoxicity, which impacts several important body functions. Investigating F exposure pathways is of essence to inform and safeguard public health of the affected communities. The current study assessed the F levels in potatoes (Solanum tuberosum L.), beans (Phaseolus vulgaris L.) and garden peas (Possum sativa) from Nakuru County, Kenya, by potentiometric analysis using F ion-selective electrodes. It then evaluated the risk factors for excessive human exposure to F through contaminated foodstuffs. The mean F levels in the potatoes (8.50 ± 4.70 mg/kg), beans (8.02 ± 4.12 mg/kg) and peas (4.99 ± 1.25 mg/kg) exceeded recommended dietary allowances (RDA) level of 4 mg/kg endorsed by US Institute of Medicine for the different categories of people. The F distribution trends in beans and potatoes reflected the environmental patterns of F contamination of the study area but the spatial extent Fin the peas indicated existence of partial resistance of the pea plants to environmental F uptake. The results indicated that both the beans and the potatoes were more liable to accumulating greater amounts of F from the environment than garden peas and that all the three foodstuffs contained high F levels that posed greater risk of F overexposure and its deleterious impacts among the young children, male populations, and in people of greater body weight and high physical activity levels