Heavy Metals in Soils and Vegetables Irrigated with Urban Grey Waste Water in Fagge, Kano, Nigeria.

There is currently an increased consumption of vegetables within the local urban community. However, contamination of these vegetables with heavy metals poses a potential health hazard. Consequently, the potential contamination problem due to the effect of levels of some heavy metals (Fe, Mg, Zn, Mn, Cu and Cr) in soils and vegetables irrigated with drainage urban grey waste water were investigated. The maximum levels of Fe, Zn, Mn, Cu and Cr in the urban grey waste waters were respectively 2.8, 2.1, 19.5, 2.3 and 143.1 times, higher than the maximum recommended concentrations of these metals: 5.0 µg/mL, 2.0 µg/mL, 0.2 µg/mL, 0.2 µg/mL and 0.1 µg/mL, respectively, for irrigation waters. The soils were found to be contaminated with these metals to levels that range between 24 to 84 percent contaminations. Although the heavy metals concentration ranking in vegetable parts vary with plant specie, the concentrations of Fe, Zn, Mn, Cu and Cr in most parts of the vegetables were above their critical concentrations of 750 - 1000 µg/g, 100 - 400 µg/g, 300 - 500 µg/g, 20 - 100 µg/g and 5 - 30 µg/g, respectively, in plants. This suggests potential toxicity of these parts of vegetables. It was however found that over 40 percent of the concentrations of Fe, Mg, Zn and Cu in Onions, Fe in Okro, Cr in Bushgreen, Cu in Roselle and Zn, Cu in Carrot leaves can be easily removed by washing the leaves with water. However, only Cu concentration in Onions and Bushgreen leaves met the acceptable permissible level in plants after washing.

Potential application of recycled rubber in oil pollution control.

The abundance and indiscriminate disposal of scrap tyres in urban areas in Nigeria create serious health and environmental problems. The potential of using rubber recycled from scrap tyres as an absorbent in crude oil clean up was investigated. Rubber particles of mesh sizes within the range of 0.15 to 2.36 mm were used to absorb crude oil at different temperatures (5 to 40 degrees C). The rapid increase in oil absorption within the first 20 min was followed by a much slower rate, with the equilibrium absorption being attained after 30 min. The equilibrium absorption increased with decreasing particle size and decreasing temperature of absorption. At 30 degrees C, the oil absorption for the 0.15 mm rubber particles was more than twice that of the 2.36 mm particle size. When regenerated recycled rubber was used, the equilibrium absorption decreased by about 15-40%. The extent of reduction was higher for the larger particles and at lower temperature of absorption.