Preliminary investigation of transfer of metals from soil to vegetables: Case study of Spinacia oleracea L.

The objective of the study was to measure concentrations of Cu, Ni and Zn in Spinacia oleracea cultivated at a site near the copper and nickel mine in Selebi Phikwe. The mean concentrations (in dry matter-basis) of Cu, Zn and Ni in the whole plant system were 7.30 ± 2.51, 6.02 ± 2.16 and 0.03 ± 0.02, mg/kg, respectively. Enrichment factors (EF) of Cu, Ni and Zn were far below the EF value of 1.5 suggesting that the soils at the study site were either good in retention of metals and/or there was minimal translocation of metals in the plants. The authors recommend a multiple exposure effect of heavy metal monitoring to be conducted regularly at the study site.Key words: Dietary toxicity, estimated dietary intake, Spinacia oleracea, target hazard quotient

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 Topography and Vegetation Canopy on the Deposition of Atmospheric Particulates Studied with 210Pb and 137Cs Soil Inventory Measurements

Naturally occurring radioactive isotopes of 210Pb and 7Be in the atmosphere, plant material and soil have been used to investigate the transport and removal of atmospheric aerosols from the atmosphere by precipitation and turbulent deposition to natural surfaces. Concentrations of 210Pb and 7Be contained in aerosols in surface air were measured using a high volume sampler at the King’s Buildings site of the University of Edinburgh (55.9°N, 03.2°W) over a 12 month period (July 2002-June 2003). The log-normally distributed concentrations of 210Pb, with a median of 0.141 mBq m−3 over the monitoring period, indicated a surface source and dispersion by wind. The concentrations were largest in air with trajectories over terrestrial surfaces, consistent with soil as the source, and smallest in air with marine trajectories and also air masses subject to precipitation, the main removal process for aerosol bound 210Pb. Concentrations of 7Be were largest during spring which is consistent with a stratospheric origin and, like 210Pb, concentrations were smaller in air masses subject to precipitation. Measurements of 210Pb and 7Be in tree foliage, precipitation and throughfall water beneath tree canopies were used to investigate the transport pathway of these isotopes from the atmosphere to soil. The measurements showed that the 210Pb aerosols attach and bind effectively to foliar surfaces, so that deposition to soil relies mainly on leaf fall. In open parkland trees, the distribution of the falling leaves determines the deposition of the 210Pb. Foliar surfaces effectively filter 7Be from precipitation as it passes through the woodland canopy. Studies of soil inventories of 210Pb beneath woodland and grassland, undisturbed for several half-lives of the isotope, were used to deduce annual average fluxes, wet deposition, cloud droplet deposition and dry deposition of aerosols onto these surfaces. The measurements showed dry deposition velocities of 210Pb containing aerosols of 7.4 +/- 1.8 mm s−1 on mature mixed deciduous woodland, and 2.6 +/- 1.3 mm s−1 on grassland, substantially larger than current theoretical values but consistent with much recent work by a range of methods

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

Inventories of fallout 210Pb and 137Cs radionuclides in moorland and woodland soils around Edinburgh urban area (UK)

Inventories of fallout 210Pb and 137Cs have been measured in moorland and woodland soils around the Edinburgh urban area, using a high purity germanium detector. The 210Pb inventories in moorland soils were relatively uniform, with a mean value of 2520 ± 270 Bq m−2. The mean 137Cs inventory in moorland soils varied greatly from 1310 to 2100 Bq m−2, with a mean value of 1580 ± 310 Bq m−2. The variability was ascribed mainly to the non-uniform distribution of fallout Chernobyl 137Cs. The mean 210Pb and 137Cs inventories in woodland canopy soils were found to be 3630 ± 380 Bq m−2 and 2510 ± 510 Bq m−2, respectively. At sites for which both moorland and woodland data were available, the mean inventories provided fairly similar average enhancements of (47 ± 7)% and (46 ± 18)% of 210Pb and 137Cs under woodland canopy soils relative to open grassland soils, respectively. The enhancement factors are broadly in line with other independent findings in literature. Enhancement of both 210Pb and 137Cs in woodland soils relative to moorland soils is, in part, due to deposition by impaction during air turbulence, wash-off, gravitational settling and deposition during leaf senescence. Results of this study suggest that these processes affect both 210Pb and 137Cs carrier aerosols in a similar way