Spatial variation in Heavy Metal residue in Corchorus olitorious cultivated along a Major highway in Ikorodu- Lagos, Nigeria

This study focused on heavy metals (Lead (Pb), Zinc (Zn) and Cadmium (Cd)) contamination in the vegetable Corchorus olitorius (C.olitorius) leaves cultivated along a major road. Samples the vegetable, C. olitorius leaves) were collected from two sites, one of which is located on a major highway and the other remotely located from any form of industrial activity and which served as the control site. These samples were collected at distances of 10, 20 and 30m from the roadside and analyzed for Pb, Zn and Cd content by atomic absorption spectrophotometer. The mean concentration of heavy metals in the studied vegetable with effect to distance from the road was compared with the permissible values given by WHO/FAO. Mean concentration of heavy metal in C. olitorius leaves ranged from 0.013 to 0.310mg/kg, 2.500 to 4.850mg/kg and 0.063 to 0.205mg/kg at 10m, 20m and 30m distances respectively from the road. In all cases, it was observed that the closer the plants were to the road, the higher the heavy metal burden. The result of this study shows that, while the concentration of heavy metals in C. olitorius leaves from the control site remains constant, (i.e. showing no sign of contamination) the concentration of heavy metals in C. olitorius leaves cultivated along major road decreased with an increasing distance from the road. @JASEM Many anthropogenic sources such as waste incineration, industrial processes and most importantly, vehicular traffic emits heavy metals into the atmosphere (Turkdogan et al; 2002). The contamination of vegetables with heavy metals due to soil and atmospheric contamination poses a threat to its quality and safety. Dietary intake of heavy metals also poses risk to animals and human health. High concentrations of heavy metals such as copper (Cu), cadmium (Cd) and lead (Pb) in fruits and vegetables were related to high prevalence of upper gastrointestinal cancer (Turkdogan et al, 2002). The uptake and bioaccumulation of heavy metals in vegetables are influenced by many factors such as the prevailing climatic condition, depositions from the atmosphere, the concentration of heavy metals in soil, the nature of soil and the degree of maturity of the plants at harvest. (Scott et al, 1996; Vousta et al, 1996). Cultivation areas near highways are exposed to atmospheric pollution in the form of metal containing aerosols. These aerosols can be deposited on soils and absorbed by vegetables, or alternatively deposited on leaves and fruits and then absorbed. Voutsa et al ( 1996) and De Nicola et al ( 2008) reported in their work high accumulation of Pb, Cr and Cd in leafy vegetables due to atmospheric depositions. The levels of heavy metals such as zinc (Zn), manganese (Mn), copper(Cu) and lead(Pb) in Talinum triangulare in dumpsites in Lagos, Nigeria were found to be high due to vehicular traffic emission. (Adeniyi, 1996). In many cities in the developing world, lack of access to land make other lands including hazardous places such as road verges, banks of drainage channels and dumpsites converted to vegetable gardens. All setbacks along major highways are used by farmers for vegetable cultivation. (Adeniyi, 1996). Corchorus olitorius is one of the popular edible vegetables in Nigeria. Corchorus olitorius is usually recommended for pregnant women and nursing mothers because it is believed to be rich in iron (Oyedele et al, 2006). C. olitorius is widely consumed with a variety of food particularly in South Western Nigeria where it is locally referred to as “ewedu”, “ooyo” or “obeeyo”. The Hausa people of Nigeria and their Fulbe neighbors call it “rama.” They use it to produce soup (“taushe”) or boil the leaves and mix it with “Kuli-kuli” or groundnut cake and consume the mixture which they call “kwado” in Hausa (Denton, 1997). According to Burkill (2000), C. olitorius is used in Kenya to treat toothache, in Congo, the leafy twigs are used against heart troubles, an infusion from the leaves is taken in Tanzania against constipation and in Nigeria, and the seeds are taken as a purgative. The objectives of this work are to determine the extent of contamination of vegetables cultivated along major road with toxic heavy metals from traffic emission and to determine the effect of distance from the road on the heavy metal content of the vegetables. MATERIALS AND METHODS