Assessment of heavy metal pollution in soils along major roadside areas in Botswana

Assessment of heavy metal pollutants: Al, Co, Cu, Fe, Pb, Mn, Ni and Zn was conducted along major roadside soils of Botswana, lying between latitudes 18°S to 27°S and longitudes 20°E to 29°E using enrichment factor ratios (EF), contamination factor (CF), pollution load index (PLI) and geoaccumulation index (Igeo) methods. The studied sites were demarcated into five zones referred to as FN (Francistown-Nata), NM (Nata-Maun), MG (Maun-Ghanzi), GK (Ghanzi-Kang) and TS (Tshabong-Sekoma). All the four pollution assessment methods revealed that zones FN, NM and MG are pollution impacted as compared to GK and TS zones. Results of multivariate analysis suggest mixed origins of pollution sources including human activities, vehicular emissions and lithogenic occurrences. Al, Cu, Fe, Mn, Zn and Co is of mixed origins of pollutants, with Fe and Mn being predominantly lithogenic, and vehicular emissions characterised by Pb and Ni. The findings in this study will serve to create awareness of vehicular heavy metal pollution to Botswana policy makers in the mitigation of vehicular pollution, as it is barely monitored.Key words: Heavy metal contamination, roadside soils, enrichment factors, contamination factor, pollution load index, geoaccumulation index, cluster analysis, factor analysis

The influence of exogenously applied 2,4- dichlorophenoxyacetic acid on fruit drop and quality of navel oranges (Citrus sinensis L.)

Orchard experiments were carried out in Botswana with the objective of evaluating the effect of 2,4-dichlorophenoxyacetic acid (2,4-D) on reducing premature fruit drop. Different concentration levels ofthe 2,4-D (8, 16 and 20 mg/L were applied exogenously to mature fruit trees of sweet orange (Citrus sinensis L.) in the 2004/2005 season. In the 2005/2006 season the 2,4-D treatments ranged from 20 to 40mg/L concentration. There appeared a general increase in fruit drop for the month of October in all treatments but a decrease in fruit drop was observed in the fruit trees with 16 and 20 mg/L 2,4-D concentration, that is, from November through February; with the latter showing the least number of fruits that dropped throughout the execution of the experiments. The application of 20 mg/L 2,4-D significantly reduced fruit drop by more than 50% but higher concentration levels of the plant growth regulator significantly increased fruit drop. It was also evident that, small sized fruits were more susceptible to fruit drop than larger fruits. These findings suggested that, 2,4-D can be an effective toolto control fruit drop by enhancing retention, as well as improving the quality of navel oranges under dry climatic conditions