Heavy metals content of grains commonly sold in markets in south-east, Nigeria

Abstract

Heavy metals levels in legume and cereal grains were determined using atomic absorption spectrophotometry. The ranges of concentrations (mg/kg) in legume grains were: Ni (1.23 – 5.91); Cd (0.03-0.11); Cu (3.03 – 7.94); Zn (38.46 – 57.72); Fe (59.00 – 102.40); Mn (12.86 – 27.65); and Co (0.43 – 0.66); while Pb was below detectable level in all the samples. In the cereal grains, the ranges were; Cd (0.007 – 0.023); Cu (0.351 – 0.764); Zn (0.05 – 0.119); Fe (6.393 – 12.643) and Pb (0.007 – 0.032), in mg/kg, dry weight. The much higher concentrations of these metals in the legume grains is attributable to the fact that legume grains have high protein content, thereby easily accumulate these trace metals which have high affinity for active sites of proteins. The presence of lead in all the cereal grain samples could be possibly attributed to one or more of these factors-soil pollution, use and type of fertilizers and pesticides in the farms. All concentrations in this study were below the WHO recommended limits. However, the legume grains were found to be fairly rich sources of some of the essential nutrients, namely; Fe, Zn, Mn, Cu, Cr, and Ni. The low levels of heavy metals are indicative of low levels of contamination of farmlands by these trace metals in spite of increasing use of fertilizers and pesticides in modern agriculture, as well as emissions from other anthropogenic sources. The data show largely the background levels of the trace heavy metals in the farms.