There is growing public concern in Zimbabwe over the illegal cultivation of vegetables on soils amended with sewage sludge or irrigated with admixtures of sewage and sewage sludge. Excessive accumulation of heavy metals in agricultural soils may not only result in environmental contamination, but lead to elevated heavy metal uptake by crops, which may affect food quality and safety. The work reported here studied concentrations of Pb were 6.77 mg kg -1 , over 22 times the permissible levels allowed by both EU standards and UK guidelines (0.3 mg kg -1 ); Zn concentrations were 221 mg kg -1 , over 4 times the guideline value (50 mg kg -1 ). The other plants (beans, maize, peppers and sugarcane) also contained concentrations of heavy metals above the permissible levels. Furthermore the concentrations observed in this study were higher than those reported by other workers who have examined vegetation from other contaminated sites. This study highlights the potential risks involved in the cultivation and consumption of vegetables on plots irrigated with sewage sludge, a practice which may place at risk the health of the urban population who consume these vegetables.

No abstract

The objective of the study was to determine and compare the effect of several solvents namely hot water, 50 % methanol, ethanol, 50 % ethanol, acetone, 50 % acetone and ethyl acetate on phenolic composition and free radical scavenging activity in black tea and selected herbal infusions from Zimbabwe and Brazil. For the black tea, made from Camellia sinensis, Quickbrew™ was used. Zimbabwean herbal infusions used were Lippia javanica and Ficus sycamore while those from Brazil were Syzygium j a m b o l a n u m , C u p h e a c a r t h a g e n e n s i s a n d I l e x paraguariensis. Total phenolic content and free radical scavenging activity were determined using Folin-Ciocalteu and 2, 2-diphenyl-1-picrylhydrazyl (DPPH) assay, respectively. IC 50 values for each solvent were calculated and used to interpret radical scavenging activity. Aqueous organic solvents extracted higher quantities of phenolic compounds than in their absolute organic nature. Acetone (50 %) extracted a higher total phenolic content (TPC) in C. sinensis, L. javanica and I. paraguariensis. Hot water extracted the highest TPC in F. sycamore and S. jambolanum while 50 % ethanol was highest in C. carthagenensis. Free radical scavenging activity (FRSA) was not necessarily in the same order as TPC, indicating that high TPC does not always mean high FRSA and vice versa. The highest FRSA for S. jambolanum and C. carthagenensis extracts was in 50 % ethanol, F. sycamore in 50 % methanol, and I. paraguariensis, C. sinensis and L. javanica extracts in 50 % acetone. Ethyl acetate recorded the lowest TPC and FRSA in all plant samples analysed. Generally, solvent used affected TPC and free radical scavenging activity. Organic solvents may need to be separated from phenolics after extraction, as some of them namely acetone, methanol and ethyl acetate can be toxic to humans. Water and ethanol are the least toxic solvents which may need no further separation from extracts.

No abstract

No abstract