Determination of Cadmium, Chromium, Lead and Mercury in Honey Samples from Mbeere, Meru, and Kirinyaga Districts

Abstract

This study focuses on quantitative analysis of toxic heavy metals; cadmium, chromium, lead and mercury in unrefined and refined honey, honeycombs, bees, flowers, soils and water samples from selected districts in Kenya; namely Mbeere, Meru and Kirinyaga. The work is based on the use of atomic absorption spectrophotometric technique. The mean concentrations of the metals in honey have been compared to their acceptable concentration limits of cadmium (0.008 to 0.010 ppm). chromium, (less than 1 ppm), lead (0.02 to 0.6 ppm), and mercury (less than 0.001 ppm) proposed by World Health Organization (WHO), Food Agricultural Organization (FAO), and Kenya Bureau of Standards (KBS). The mean concentration levels of cadmium, chromium, lead and mercury in all 60 unrefined honey samples from the three districts showed that, while the concentration of chromium and cadmium in all honey samples fall within the acceptable levels, those of lead in some areas were slightly higher than the WHO, FAO and KBS recommendations. This is particularly so for honey samples from Mbeere and Meru districts where the highest concentrations of lead in Mbeere unrefined honey collected from lshiara approximately 0.5 km from a major road was 1.39 ppm while unrefined honey collected from Kangoro in Meru had 0.73 ppm of lead. With cadmium, the concentration was above the WHO, FAO and KBS limit in all districts. Refined honey samples from USA and Kenya bought from Kenyan Supermarkets were also analyzed and found to contain 0.022 ppm, 0.027 ppm, 0.45 ppm and 0.8 ppb of cadmium, chromium, lead and mercury respectively for the USA honey; while refined honey from Kenya contained 0.018 ppm of chromium, 0.032 ppm of cadmium, 0.10 ppm of lead and 0.5 ppb of mercury. The two commonly used digestion methods; the wet oxidation and dry ashing oxidation methods were used to digest the samples. Comparison of the effectiveness of the two methods was performed by subjecting them to t-tests at 95 % confidence level. The I-critical which was found to be 2.06 was compared to the I-calculated for chromium, lead and cadmium which were 3.22, 10.53 and 11.5 respectively. These values were higher than t-critical values suggesting that the two digestion methods gave significantly different results. The effect of cation interference on the determination of lead, cadmium and chromium showed that the presence of Cur", Mn2+, Ni“, Fe”, Ca2+, Mg” and Na+ at concentration levels below 4 ppm had no significant effect on the concentration levels of the heavy metals. However, it was observed that concentration higher than 4 ppm of interfering cations enhanced or depressed concentration levels of the heavy metals. Good recoveries ranging from 95.5%—lO0.4 % for lead, 92.5%—lOl.5 % for chromium, and 98 °/>—l00.5 % for cadmium, were obtained from unrefined honey samples. Correlation studies of cadmium, chromium and lead concentrations in honey, honeycombs, bees, flowers and soil samples were performed using excel software. Results indicate that chromium showed positive correlation between the soil and the flower samples, the honey and the bee samples and between the honeycombs and the flower samples. For cadmium, the significant correlation was observed between the soil and the flower samples. For lead, positive correlations were observed between all the samples.