HEAVY METALS IN WATER, SOIL AND PUMPKIN (Cucurbita maxima) LEAVES FROM SHIYALU-LURAMBI AREA KAKAMEGA COUNTY KENYA: CONTAMINATION LEVELS AND SPECIATION ANALYSIS

Abstract

Pollution of the environment by heavy metals is a major global concern. Arsenic (As), cadmium (Cd), lead (Pb), nickel (Ni), copper (Cu), and zinc (Zn) present the greatest environmental threat because of their widest distribution and known toxic effects in humans, plants, animals and lower biota. The study was designed to assess the level of selected heavy metals in potable water, soils and Pumpkin leaves (Cucurbita maxima) samples to determine their availability and potential accumulation along the food chain. Samples for the field investigation were collected from randomly selected sites, transported to the research laboratory where they were treated and analyzed for Cd, Pb, Ni, Cu, and Zn using Atomic Absorption Spectroscopy (AAS). Arsenic was determined calorimetrically using Arsenic Test Kit (ATK). Inductive coupled plasma atomic emission spectroscopy (ICP-AES) was used to perform speciation studies for Cd and Pb in soil samples. It was found that whereas the As, Ni, Cu, and Zn concentrations in water, soil and plants were well within the respective World Health Organization (WHO) limits, both the Pb and Cd levels water (Pb -0.0925-0.5680 Cd -0.3911-0.5541); soil (Pb -1.2252-1.9279; Cd -0.6153- 0.7674-) and plants (Pb -1.0482-1.3892); Cd 0.1070-0.11833) respectively exceeded the permissible WHO standards for studied media, respectively. The Soil Pb and Cd were present in the bioavailable exchangeable fractions (0.42 mg/kg, 0.21 mg/kg) and reducible fraction (0.99 mg/kg, 0.28 mg/kg), respectively. Lead (Pb) and Cd in the soils posed significant risk of overexposure because of their high levels and speciation resulting in bioaccumulation and magnification in the plant tissues investigated. Because the overall toxic consequences of excessive exposure to these metals, it is recommended that the levels of heavy metals in plants, water, and soil in the affected areas need to be routinely assessed and measures taken to avert potential environmental and public health damage.