Assessment of the Impact of Floods on Availability of Essential Trace Elements in Soils, Selected Vegetables and Water Quality in Budalangi, Busia County

Abstract

This study assessed the impact of floods on essential trace elements in vegetables, water, and soils in Budalangi, Busia County. One hundred and twenty (120) soil samples and twenty (20) vegetables samples comprising of 3 different indigenous vegetables species were collected and analyzed for Iron (Fe), Manganese (Mn), Copper (Cu), and Zinc (Zn) while twenty (20) water samples comprising of 4 different water sources were collected and analyzed for Mercury (Hg), Lead (Pb), Chromium (Cr), Arsenic (As) and Nickel (Ni) using Energy Dispersive X-ray Fluorescence (EDXRF) at the University of Nairobi. Soil pH was also analyzed. The samples were collected under varying climatic conditions; before the floods (in December, 2021) and after the floods (in July 2022). The analysis of soil pH revealed a 7.2% and 7.6% decrease in soil pH for topsoil and subsoil, respectively, indicating a dilution effect. The relative abundance of trace elements in soil decreased in the order Fe>Mn>Cu>Zn, with a 7% reduction in Fe, 4% in Mn, 2.5% in Cu, and 13% in Zn after the floods. Despite the reductions, the measured quantities remained within global limits for agricultural soils. Vegetable concentrations of Fe, Mn, and Zn met global human consumption thresholds, but Cu exceeded recommendations. The increased uptake of Cu by vegetables can be influenced by soil pH, organic matter content brought in due to flooding and also the specific characteristics of the vegetable species, all of which can contribute to variations in copper accumulation. All five elements; Hg, Pb, Cr, As and Ni were below the limits for inorganic contaminants of drinking water according to limits by the Kenya Standard - East African Standard 12: 2014 (KS EAS 12: 2014) and World Health Organization 2011 (WHO 2011) Guidelines for drinking Water Quality. These findings underscore the need for systematic ecosystem monitoring.