Contamination of vegetables with toxic metals is one of the most important contributing factors to ill health throughout the world, more so because vegetables are considered essential for human health and their consumption is highly recommended by health authorities. The aim of this study was to determine the concentrations of selected essential elements (Fe, Cu, Mn, Mo, Zn) and toxic elements (As, Cd, Cr, Pb) in common vegetables sold for human consumption in supermarkets and open market of Maun village, Botswana. Five vegetables (cabbage, rape, tomatoes, onions and potatoes) were purchased from different selling points, washed with de-ionised water, cut into small pieces and digested with aqua regia on a block digester, following the US. EPA method 200 -7 and analysed for metal content using Inductively Coupled Plasma -Atomic Emission Spectroscopy (ICP-AES). The results showed that concentrations of essential and toxic metals varied with the type of vegetable and also with the market category (supermarket or street vendor). The highest concentration of essential elements was obtained from cabbage with a Zn concentration of 135.4mg/Kg and the lowest was from onion with a Mo concentration of 1.35mg/Kg. For toxic elements the highest concentration was obtained from rape vegetable with a Pb concentration of 4.73mg/Kg and the lowest from the same vegetable with Cr concentration below the detection limit. Also observed was that leafy vegetables, especially cabbage, had the highest concentrations of most trace metals. It was concluded that vegetables sold in Maun had sufficient levels of essential elements but also some had high concentrations of toxic metals. We thus recommend consumption of vegetables from the studied markets with reduced frequency to avoid metal poisoning.

Climate change and adaptive land management in southern Africa-assessments, changes, challenges, and solutions. Biodiversity & Ecology, 6, Klaus Hess Publishers, Göttingen & Windhoek.

No abstract

Pristine aquatic environments are the preferred state for maintaining ecosystem integrity, supporting biodiversity and preserving human health. However, world ecosystems have been altered by anthropogenic activities which release chemical contaminants into the environment and threaten terrestrial and aquatic life. In order to protect water bodies from pollution, monitoring water quality indicators and levels of trace metals is critical. The Okavango Delta is regarded pristine, but concentrations of trace metals in the river have not been adequately studied. This study quantifies concentration of 10 trace metals, determines their spatiotemporal distribution and assesses associated health risks. Water samples were collected monthly between 2014 and 2017 from five sites and concentrations determined by ICP-OES. The results indicate that all metals studied were present at all study sites with a concentration in the order of Fe > Mn > Ni > V>Zn > Pb > Cd ≫ Cu > Cr > Co, a wide occurrence of metals reflecting a possible presence of mafic and ultramafic rocks in the catchment. Concentrations of trace metals were variable, but these were not statistically significant at p ≤ 0.05, indicating a relatively uniform water composition. However, Fe occurred in distinctively higher concentrations compared to other metals. When compared with US EPA guidelines for freshwater ecosystems and WHO drinking water standard, mean concentrations of all metals except Pb were below EPA guidelines for freshwater ecosystems and WHO drinking water standard. The risk assessment revealed that none of the metals posed health risks to the communities that use river water as a direct drinking source. Continuous monitoring is necessary for the protection of human health and sustainability of the delta.

Flood recession farming locally known as molapo farming in the Okavango Delta is practiced along the edges of the river channels or seasonally flooded depressions on its fringes. It relies on residual moisture and natural fertilization of the floodplains, and is promoted as being more productive than dryland farming. However, the productivity of this low-input farming system has not been extensively investigated. The objective of this study was to evaluate the yield potential of hybrid maize (Zea mays L.) in molapo farming. Two molapo field experiments and one dry-land experiment were conducted at Matsaudi and Lake Ngami, and Shorobe, respectively, in a randomized complete block design with four replications. Maize grain yield and plant height were measured from six consecutive plants from the centre row. The results showed that maize grain yield and plant height were significantly (P < 0.05) higher at Lake Ngami than at either Matsaudi or Shorobe. Late planting at Lake Ngami coincided with rainfall in November providing even and abundant soil moisture which contributed to better productivity of maize. Similarly, soil fertility was also better at Lake Ngami. Maize grain yield although lower (2.41 t ha-1) at Matsaudi and Shorobe (2.58 t ha-1) than at Lake Ngami (3.4 t ha-1), it is much higher than yields normally obtained by smallholder farmers in semi-arid zones in sub-Saharan Africa, where actual yields are often less than half of the potential yields. Similarly, plant height was significantly (P < 0.05) higher at Lake Ngami (235 cm) than either Matsaudi (194 cm) or Shorobe (192 cm). It could be concluded that timely planting of maize in molapo fields supplemented by rainfall is capable of producing better yields in semi-arid regions where water is the most limiting resource to crop production