Seasonal Trend of Potentially Toxic Trace Elements in Soils Supporting Medicinal Plants in the Eastern Region of Ghana

Investigation was conducted into the occurrence and extent of potentially toxic heavy metals and/or trace elements in soils from three study areas in the Eastern Region of Ghana namely Abonse, Pepease and Mamfe. A protocol for soil sampling, preparation and analysis was developed to yield sufficient information on elemental concentrations in the soils. The soil samples were analysed for As, Co, Cr, Cu, Sb, Th, U, V and Zn, using Instrumental Neutron Activation Analysis (INAA) coupled with conventional counting system. Concentrations of Co, Cr, Th and Zn positively correlate with As, and regressions performed on Co-Zn, Co-Cr, Co-Th, Cr-Th and Zn-Cr values also show strong correlations. The regressions suggest that these elements are geochemically associated and might be enriched simultaneously. Though there are relatively high concentrations of Cu (maximum; 46.3 mg/kg), Co (maximum; 9.17 mg/kg), Th (maximum; 15.1 mg/kg) and U (maximum; 2.38 mg/kg) in some of the soils compared with their levels in world average soils, the average concentrations of the trace elements in general are below or within levels in world average soils/uncontaminated soils. Also, the enrichment index computed in the soils indicates that all the study areas are not enriched with toxic elements, particularly As, Cu, Sb and Zn, and the enrichment index values decrease in the order of Pepease > Mamfe > Abonse. When the average composition of the soils was normalized to the average composition of the underlying rocks, the soils were depleted in the trace elements determined, indicative of background concentration values. Lack of correlations between soil characteristics such as texture, organic carbon, organic matter, total nitrogen and available phosphorous, and most of the trace elements suggests that the influence of these parameters on the distribution of the trace elements is not important in the surface soils.     

Characterization and Liming Effect of Wood Ash Generated from a Biomass-Fueled Commercial Power Plant

Laboratory and greenhouse experiments were carried out to characterize and examine wood ash from a biomass-fueled commercial power plant as a lime. Experimental treatments include wood ash and two commercial limes applied at six application rates. The effective calcium carbonate equivalence (ECCE) of wood ash ranged from 22 to 49%. Wood ash increased soil pH by 0.31–3.18 over unlimed soils, and these changes in pH were similar to the effect of commercial limes. The soil pH at three weeks after wood ash application was constant through week seventeen. Wood ash increased electrical conductivity by 0.13–0.63 dS m^?1 compared to unlimed soils at three weeks after liming; however, a 39–69% decreased was observed by week seventeen. Common bermudagrass did not respond to the application of wood ash and commercial limes. The results of this study suggest that wood ash from the biomass-fueled commercial power plant with low ECCE could be a liming material.