Department of Geology

Accumulation of potentially harmful elements in edible parts of vegetables grown on two different geological substrates in Zimbabwe.

Thu, 12 Sep 2019 00:00:00 GMT

Accumulation of potentially harmful elements in edible parts of vegetables grown on two different geological substrates in Zimbabwe. Meck, Maideyi L.; Mudimbu, D.; Davies, T.C. This study investigated the bioaccumulation of potentially harmful elements (PHEs) in common, locally grown vegetables in Zimbabwean farmlands. The aim of the study was to compare PHE accumulation in vegetables grown on greenstone substrate to those grown on granitic substrate. The greenstone terrain in Zimbabwe hosts some of the most economically viable gold and base metal deposits in the country, an endowment that triggered the establishment and growth of many of Zimbabwe’s main cities. Vegetable samples (n = 44) and soil samples (n = 102) were collected over 4 seasons and analysed by Inductively Coupled Plasma-Mass Spectrometer (ICP-MS). The results indicate that the trend of PHE concentration was the same in vegetables from both substrates, as follows: Cr > Pb > Zn > Cu > Ni > As > Co > Sb > Cd. A comparison of the PHE levels in the vegetables against the FAO/WHO Codex maximum permissible levels (MPL), revealed Pb levels above the limit in all samples from both substrates. Tomatoes revealed a concentration of Pb in the order of 1400 times and 360 times above the MPL in greenstone and granitic substrates, respectively. Arsenic concentrations were also well above the MPL in all vegetable samples from the greenstone substrate, as well as in the tomatoes, pumpkin leaves, cabbage and okra in the granitic substrate. Concentration levels of Cd, a known carcinogen, exceeded the MPL in tomatoes from both substrates. Root vegetables were found to accumulate lesser amounts of PHEs than leafy vegetables. The vegetables grown on the granitic substrate revealed average bioaccumulation factor (BAF) values that were higher than values obtained for vegetables grown on greenstone substrates, in the range of multiples of 16, 15, 5, and 4.5 for Sb, As, Cu, and Cd, respectively. The results of a Kruskal-Wallis test revealed that although there was a significant difference (p <0.05), between the concentration of PHEs in soils in the greenstone and the granitic substrates, the PHE accumulation in vegetables was significantly different (p <0.05) only for As, Ni, and Pb; but there was no significant difference in the accumulation of the rest of the PHEs studied. The study indicates potential human health risks due to ingestion of vegetables having As, Cd and Pb levels above safe limits (MPLs). The study recommends careful selection of vegetables for cultivation in different substrates based on type of geological substrate, type of plant species and the bioaccumulation factor as key in controlling bioaccumulation of PHEs. The results from this study can be applied in human health risk analysis and monitoring of PHE accumulation in food crops.

Semi-quantitative mineralogical valuation of the non-nickeliferous weathering crusts in the northeast of Cuba

Wed, 01 Dec 2010 00:00:00 GMT

Semi-quantitative mineralogical valuation of the non-nickeliferous weathering crusts in the northeast of Cuba Njila, Tendai; Martínez, Roberto Díaz; Fernández, Joaquín Proenza; Melgar, Gerardo Orozco This study presents a semi-quantitative mineralogical evaluation of the non-nickeliferous weathering crusts in the areas of Baconal, El Culebro, Caimanes and Farallones in the northeast of Cuba. The main objective of this study is to determine the main mineral phases, their vertical distribution and concentration, as well as the degree of mineral transformation in the weathering profiles. Sixteen samples were analyzed by X-Ray Diffraction and the diffractograms were used in qualitative and semi-quantitative phase analyses using ANALYZE and AUTOQUAN programs. The degree of mineral transformation in relation to phase distribution and concentration as weathering progressed was evaluated using the Mineralogical Index of Alteration. The main mineral phases present in Baconal and El Culebro are Kaolinite (50-75%), Kaolinite-Montmorillonite (50-75%), Quartz (25-50%), Plagioclase, mainly Albite (25-50%) and Hematite (<10%). In Caimanes and Farallones the principal mineral phases present are Kaolinite, Hematite, Quartz, Potassic feldspars, mainly as Orthoclase, all with more than 75%, Halloysite (<10%), and Montmorillonite (<10%). Extreme primary mineral transformation is evidenced in the intermediate and upper layers in Baconal, El Culebro and Caimanes (Mineralogical Index of alteration values between 29 and 98 %). This transformation is also evidenced in the whole Farallones profile (98-99 %). In conclusion, the non-nickeliferous weathering crusts in Baconal, El Culebro, Caimanes and Farallones are mainly kaolinitic clays.

An overview of non-nickeliferous weathering crusts in Eastern Cuba

Tue, 01 Jun 2010 00:00:00 GMT

An overview of non-nickeliferous weathering crusts in Eastern Cuba Njila, Tendai; Martinez, Roberto Diaz; Melgar, Gerardo Orozco; Puron, Arturo Luis Rojas This paper presents an overview of the studies in non-nickeliferous weathering crusts initiated more than six decades ago in Eastern Cuba. This overview is based on a detailed literature review and a descriptive-critical discussion on these studies with the main objective of highlighting their achievements and failures. These investigations were motivated by the existence of large mineral deposits associated with different types of weathering crusts in this region and were mainly focused on finding bauxites. However, prospects could not be delineated because the alumina contents in these geological objects were below those required to classify them as bauxites. This limited the evaluation of the possibilities of assimilating these crusts in such industries as the ceramic, construction and refractory, among others, which can contribute significantly to the sustainable local development. Generally, in all these investigations there is an absence of solid mineralogical and geochemical criteria for the characterization and classification of different aluminium-rich weathering crusts. The SiO2-Al2O3- Fe2O3 contents in the region show that most of the weathering crusts as ferrosialitic. There are possibilities of finding sialitic, ferrallitic and allitic types in Cayo Guam, Centeno, Quesigua, Puriales de Caujeri, Quemado del Negro and Cantarrana. In overview, the level of study of the non-nickeliferous weathering crusts widely developed on gabbros, volcanic, metamorphic and sedimentary rocks in Eastern Cuba is relatively low. Further investigations including detailed profile sampling, chemical and mineralogical analyses in Téneme, Centeno, Cayo Guam, Quemado del Negro and Cantarrana are proposed which, in our opinion, are perspectives for allitic deposits.