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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.

Natural and synthetic steroid estrogens have been detected in sewage treatment work effluents discharged into rivers. An understanding of the partitioning of these estrogens between water and sediment is critical for the prediction of their fates in river systems. Hence, a series of experiments was conducted to ascertain the effects of differing environmental conditions on estrogen partitioning to sediment. Fugacity level 1 (sediment phase) output data demonstrated a good correlation with removal of estrogens from the water phase. Synthetic estrogens, with their higher K ow values, were removed more readily from the water phase than the natural estrogens. Maximum sorption to the sediment phase was attained after 1 h of shaking. At higher estrogen concentrations, there was a decrease in estrogen removal, while higher levels of sediment induced greater removal. The sorption of estrogen to sediments correlated with total organic carbon content. However, the presence of organic carbon was not a prerequisite for sorption. Iron oxide alone was demonstrated to have a sorption capacity of 40% of that of a sediment containing 1.1% total organic carbon. Laboratory saline water was found to increase estrogen removal from the water phase which was found to be consistent with partitioning experiments using actual field water samples. The addition of estradiol valerate, a synthetic estrogen with a particularly high K ow , suppressed sorption of other estrogens suggesting that it competed with the other compounds for binding sites.

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