Soil Heavy Metal Concentration Patterns at Two Speed Zones along the Gaborone- Tlokweng Border Post Highway, Southeast Botswana

Since 1988 Botswana has been experiencing an unprecedented increase in vehicular traffic which is suspected to be having contamination effects on soils along heavily used roads in the country. This study aimed atunderstanding the contamination trends of heavy metals on soils due to vehicular emissions. The soil physicochemistry (bulk density, particle size distribution, pH, electrical conductivity and cation exchange capacity),mineralogy (using x-ray diffraction techniques) and heavy metals (Cd, Pb, Cu and Zn) concentrations were determined for soil samples obtained along the roadside at 2m, 4m, 6m and 100 m of the Gaborone – TlokwengEmigration/Immigration Boarder Post Road, which is one of the busiest in the country. Bulk density of soil samples were from 1.19 to 1.4; and sand, loamy sand and sandy loam textural classes constituted the soil samples. The soil pH was from 5.09 to 8.57; the EC ranged from 6.27 ìS cm-1to 20.3 27 ìS cm-1 and the CEC values were from 10.2 meq100g-1 to 27.2 meq100g-1. Clay minerals were identified in the samples as well as feldspar and quartz. The concentration levels for Pb were from 0 mgkg-1 to 71 mgkg-1; Zn were from 5.23 mgkg-1 to 51.26 mgkg-1 ; Cu werefrom 0.3 mgkg-1 to 18.1 mgkg-1 and Cd 0 mgkg-1 to 2.4 mgkg-1 . The interplay of soil physico-chemistry and mineralogy on heavy metals concentrations is discussed. Although levels of heavy metals concentrations fell below normal ranges, the values obtained were generally higher than those from some developed and developing countries.@JASE

The Southern African Regional Science Initiative (SAFARI 2000) : wet season campaigns

The Southern African Regional Science Initiative (SAFARI 2000) involved two wet season and one dry season field campaigns. This paper reports on the wet season campaigns. The first was conducted at five sites along the Kalahari Transect in Zambia (Kataba Forest) and Botswana (Pandamatenga, Maun, Okwa River Crossing, Tshane) during February 2000 and concentrated primarily on characterizing the land surface with respect to exchanges of matter and energy with the atmosphere. The second, conducted in February 2001, focused on fluxes of water, gases and energy between the canopy and the atmosphere at Maun, Botswana, and at Skukuza in the Kruger National Park, South Africa. Eddy covariance measurements at Skukuza and Maun were designed to collect a near-continuous record of the seasonality and inter-annual variability in savanna carbon, water and energy exchanges in representative savanna ecosystems. This paper gives brief descriptions of the sites, the measurements made, and the methods used. It highlights some preliminary results, particularly from the first campaign, and outlines the next stages of the SAFARI 2000 projec

Short-term response of three soil types in Botswana to sewage sludge application

Changes in the moisture content (MC), volatile solid content (VS), water retention capacity (WRC), bulk density (Db), porosity, pH, electrical conductivity (EC), organic matter content (OM), and cation exchange capacity (CEC) of 2 luvisols, a vertisol and an arenosol from Botswana brought about by sludge addition were investigated. Each soil type was mixed separately with a 36 months and 3 months old sludge at volume per volume percent ratios of 5:95, 10:90, 20:80, and 40:60 sludge:soil. Ninety days after sludge addition, there was an increase in the porosity, WRC, VS, CEC OM and EC of the soils and a decrease in the pH and Db. Changes were more evident in soils amended with the 3 months old sludge than in soils amended with the 36 months old sludge. Sludge application rate and soil type affected the changes observed in the pH, EC, VS Db and WRC of the different soils types. Application of sludge to these soils significantly improved their physical condition after 90 days.Keywords: Soil physico-chemistry; sludge application rate; sludge ag

Physico-chemical and Mineralogical Characterisation of Subsurface Sediments around Gaborone Landfill, Botswana

Studies were carried out on subsurface sediments obtained around the Gaborone landfill area Botswana, in order to characterize their mineralogy and physico-chemistry, appraise any contaminant inputs from the landfill and assess their ability to attenuate contaminants from the landfill. Physico-chemical properties investigated included particle size distribution (PSD), moisture content, bulk density (Db), porosity, surface area, pH, electrical conductivity (EC), and cation exchange capacity (CEC). The mineral phases occurring in the subsurface sediments were identified by use of X-ray powder diffraction (XRPD) technique. Grain size analyses of the subsurface sediments revealed sandy loam, silty loam, and silt as the main textural classes. The values obtained for Db and porosity is reflective of the textural classes of the different samples. Moisture content values of the studied samples are characteristic of sediments in semi-arid environments. Apart from two samples, which were acidic, others were alkaline. The EC values were indicative of significant amounts of total dissolved salts (TDS) especially along the eastern corner of the landfill. Cation exchange capacity values were relatively low. Minerals identified by XRPD included quartz, microcline, muscovite and kaolinite in bulk subsurface sediments, whereas kaolinite, smectite and /or illite occurred in the clay fractions. Sediment pH, EC and TDS suggests inputs from the landfill. The sediments seem to have a low attenuation capacity as a result of their physico-chemical and mineralogical properties. Further geophysical and hydrogeochemical research is needed to verify if the Gaborone landfill area is environmentally safe. Journal of Applied Sciences and Environmental Management Vol. 8 (1) 2004: 49 - 5

Mineralogy of Tailings Dump around Selebi Phikwe Nickel-Copper Plant, Botswana

This study aimed at mineralogically characterizing the tailings dump emanating from the mining and smelting of nickel-copper (Ni-Cu) at Selebi Phikwe, Botswana, Southern Africa. Samples of tailings dump around the Selebi Phikwe Ni-Cu plant were studied using petrographic microscopy and X-ray Powder Diffraction (XRPD) technique. The tailings dump comprised of the following minerals: nickelblodite, pyrrhotite, quartz, pentlandite, malachite, chalcopyrite, actinolite, cristobalite, tremolite, kaolinite, mica and albite. Nickelblodite and malachite were mineralized from the primary ore minerals in the tailings dump. The sulfur-rich minerals contained in the tailings dump serve as principal promoting sources for acid mine drainage in the immediate surrounding environment. Consequently, aspects of pollution management such as phytoremediation and phytomining, and environmental desulfurization could be introduced as pollution control measures at Selebi Phikwe. @JASE

Mineralogy of Tailings Dump around Selebi Phikwe Nickel-Copper Plant, Botswana

This study aimed at mineralogically characterizing the tailings dump emanating from the mining and smelting of nickel-copper (Ni-Cu) at Selebi Phikwe, Botswana, Southern Africa. Samples of tailings dump around the Selebi Phikwe Ni-Cu plant were studied using petrographic microscopy and X-ray Powder Diffraction (XRPD) technique. The tailings dump comprised of the following minerals: nickelblodite, pyrrhotite, quartz, pentlandite, malachite, chalcopyrite, actinolite, cristobalite, tremolite, kaolinite, mica and albite. Nickelblodite and malachite were mineralized from the primary ore minerals in the tailings dump. The sulfur-rich minerals contained in the tailings dump serve as principal promoting sources for acid mine drainage in the immediate surrounding environment. Consequently, aspects of pollution management such as phytoremediation and phytomining, and environmental desulfurization could be introduced as pollution control measures at Selebi Phikwe. Journal of Applied Sciences and Environmental Management Vol. 8 (1) 2004:37 - 4

Speciation and mobility of lead in shooting range soils

The mobility and bioavailability of lead (Pb) in seven military shooting range soils found in eastern and north eastern Botswana were studied using sequential extraction procedure. The different forms of Pb and their reactivity in the soil help explain their speciation, mobility and bioavailability in the environment. Mobility of Pb in the berm soils in all the seven shooting ranges was found to be over 90% implying high Pb lability. The bioavailability index of Pb was in the range 60–90%, an indication that most of the Pb can be available for plant uptake. Sequential extraction studies indicate that the partitioning of Pb was mostly confined to the carbonate compartment in all the shooting ranges. All the seven shooting ranges failed the Synthetic Precipitation Leaching Procedure (SPLP) with SPLP Pb concentrations exceeding United States Environmental Protection Agency (USEPA) 0.015 mg/kg critical level of hazardous waste, posing a pollution threat to surface and groundwater