Correlation Analysis of Toxic Metals Distribution and Pollution Indices in Soil, Beans and Maize Samples of Kano State, Nigeria

Abstract

Correlational study and evaluation of pollution indices of toxic metals distribution in soil and crops of a population are imperative for assessing the risk of chronic diseases associated with these metals. Correlational analysis for the distribution of; lead (Pb), cadmium (Cd), chromium (Cr) and mercury (Hg) in soil (S), bean (B) and maize (M) was conducted around Bunkure (BKR), Danbatta (DBT), Gwarzo (GRZ), Ungogo (UGG) and Wudil (WDL) as sampling zones around Kano State, Nigeria. The samples were collected from farm harvests in each of the sampling zones. The metal concentration was determined using atomic absorption spectrometry (AAS). Results in mg/kg across the local governments indicate respective ranges for Hg, Pb, Cd, and Cr of; 0.33 - 3.13, 0.14 - 0.84, 0.02 - 0.05 and 0.01- 0.49 in soil, 0.04-4.23, 0.06-0.23, 0.02-0.04 and 0.00-0.10 in maize and 0.20-4.23, 0.16-0.19, 0.03-0.04 and 0.00-0.03 in beans. Although with the exception of mercury, the ranges of the toxic metals are within the tolerable range set by International Standard Tolerable Limits and European Regulatory Standard. Potential hazard may be speculated because the detected levels are on higher tolerable ranges. A higher level of mercury in almost all the samples indicates potential hazards associated with human activities in those areas. A strong positive correlation between soils samples in respect to the level of some of the toxic metal may suggest a common nature of the soil, while the negative correlation may be due to variation in agrochemicals in-use. For the pollution load index, Wudil had the highest soil pollution load index for Hg (3.13 ± 0.16), Cd (1.6×10-2 ± 0.01) and Cr (4.9×10-3 ± 0.01), while Ungogo had the highest pollution load for Pb. Also, all grains within the study zones exhibited a positive transfer factor, except Cr in Bunkure, Danbatta and Gwarzo. It may be concluded that crops grown in those areas may bioaccumulate some of these toxic metals, thereby incorporating them into the food chain, hence potential health risk.