Mapping Geospatial Processes Affecting the Environmental Fate of Agricultural Pesticides in Africa

The application of agricultural pesticides in Africa can have negative effects on human health and the environment. The aim of this study was to identify African environments that are vulnerable to the accumulation of pesticides by mapping geospatial processes affecting pesticide fate. The study modelled processes associated with the environmental fate of agricultural pesticides using publicly available geospatial datasets. Key geospatial processes affecting the environmental fate of agricultural pesticides were selected after a review of pesticide fate models and maps for leaching, surface runoff, sedimentation, soil storage and filtering capacity, and volatilization were created. The potential and limitations of these maps are discussed. We then compiled a database of studies that measured pesticide residues in Africa. The database contains 10,076 observations, but only a limited number of observations remained when a standard dataset for one compound was extracted for validation. Despite the need for more in-situ data on pesticide residues and application, this study provides a first spatial overview of key processes affecting pesticide fate that can be used to identify areas potentially vulnerable to pesticide accumulation.

Uranium Speciation in Glass Corrosion Layers: an XAFS Study

ABSTRACTUranium L3 X-ray absorption data were obtained from two borosilicate glasses, which are considered as models for radioactive wasteforms, both before and after leaching. Surface sensitivity to uranium speciation was attained by a novel application of simultaneous fluorescence and electron-yield detection. Changes in speciation are clearly discernible, from U(VI) in the bulk to (UO2)2+-uranyl in the corrosion layer. The uranium concentrations within the corrosion layer also show variations with leaching times that can be determined from the data.

Nutrient Cycling in a Stand of Acacia holosericea A. Cunn. Ex G. Don. III. Calcium, Magnesium, Sodium and Potassium.

Nutrient cycling by a 3-year-old Acacia holosericea plantation (1111 trees ha-1) was studied over a 13-month period. The gross accumulation of each nutrient in the various above-ground organs was calculated from the net increase over the study period plus the amounts lost by leaching and litterfall. Gross accumulation was greatest for calcium (22.4 kg ha-1), and potassium (18.8 kg ha-1), sodium (6.8 kg ha-1), followed by magnesium (5.2 kg ha-1). Biochemical recycling was greatest for calcium (10%) magnesium (8%), sodium (3%) and potassium (2%); however, this may be an overestimate as some of the apparent mobilization was undoubtedly due to leaching. Litter return accounted for 14% of the gross accumulation for potassium, 11% of magnesium, 10% of sodium and 9% of calcium. Litterfall accounted for 90% of the return of calcium to the soil and 75% of the return of magnesium. On the other hand, transfer in solution (leaching, surface wash) accounted for 88% of the return of sodium from the canopy to the soil and 59% of the return of potassium. Over the period 1 January 1979 to 28 February 1980 (total rainfall 2261 mm), the addition of nutrients in area precipitation was greatest for sodium (23.6 kg ha-1), followed by potassium (11.2 kg ha-1), calcium (6.8 kg ha-1) and magnesium (1.8 kg ha-1). Throughfall and stemflow increased the concentration of nutrients, such that the total nutrient addition to the soil was greatest for sodium (28.8 kg ha-1) followed by potassium (15.0 kg ha-1), calcium (7.0 kg ha-1) and magnesium (2.0 kg ha-1). These additions to the soil are significant in relation to the gross accumulation of these elements by Acacia holosericea.