Occurrences and toxicological risk assessment of eight heavy metals in agricultural soils from Kenya, Eastern Africa

Abstract

The concentration distribution and toxicological assessment of eight heavy metals including lead (Pb), cadmium (Cd), copper (Cu), chromium (Cr), nickel (Ni), mercury (Hg), arsenic (As), and zinc (Zn) in agricultural soils from Kenya, Eastern Africa, were investigated in this study. The results showed mean concentrations of eight heavy metals of Zn, Pb, Cr, Cu, As, Ni, Hg, and Cd in agricultural soils as 247.39, 26.87, 59.69, 88.59, 8.93, 12.56, 8.06, and 0.42 mg kg(-1), respectively. These mean values of eight heavy metals were close to the toxicity threshold limit of USEPA standard values of agricultural soils, indicating potential toxicological risk to the food chain. Pollution index values revealed that eight heavy metals severely decreased in the order Hg > Cd > As > Cu > Pb > Zn > Ni > Cr and the mean value of the overall pollution index of Hg and Cd was 20.31, indicating severe agriculture ecological risk. Potential pollution sources of eight heavy metals in agricultural soils were mainly from anthropogenic activities and natural dissolution. The intensification of human agricultural activities, the growing industrialization, and the rapid urbanization largely influenced the concentration levels of heavy metals in Kenya, Eastern Africa. Moreover, the lack of agricultural normalization management and poor enforcement of environmental laws and regulations further intensified the widespread pollution of agricultural soils in Kenya.

Occurrences and Ecotoxicological Risk Assessment of Heavy Metals in Surface Sediments from Awash River Basin, Ethiopia

“…A microwave digester (Milestone ETHOS ONE, Leutkirch im Allgau, Germany) was used for the sample digestion process. The procedures for sample extraction by microwave digester were described previously [21]. Operation pressure, temperature, and output power were adjusted to 300 psi, 165 • C, and 900 W, respectively, and kept constant for 10 min; in the second step, the temperature was raised to 175 • C while pressure and output power were kept the same (300 psi and 900 W) for five minutes; at the last step, the parameters were maintained at 100 psi, 170 • C, and 900 W, respectively, for 10 min.…”

“…Eri describes the sensitivity of a biological community to a given heavy metal and can be used to illustrate the risk posed to that community by the specific contaminant [33] while ERI is used to identify locations which need special considerations due to the risks associated with pollutants. The toxic response factors T i f of the eight heavy metals investigated are As = 10, Cd = 30, Cr = 2, Cu = 5, Pb = 5, Hg = 40, Ni = 5, and Zn = 1 [21,[32][33][34]. Hakson [32] defined five classes of Eri and four classes of ERI.…”

Heavy metal pollution in suburban topsoil of Nyeri, Kapsabet, Voi, Ngong and Juja towns, in Kenya

“…The topsoil (0-30 cm depth) was sampled using a small shovel and packed in zip lock bags. The heavy metals were extracted using a method previously reported by Mungai et al [6]. Sample preparation involved the following steps: approximately five grams of the resultant sample was freeze-dried at high pressure, pulverized, and sifted using a 60-mesh sieve [27].…”

“…Human activities also contribute to the dissemination of pollutants in the surroundings leading to toxic pollution in major cities [3]. Some of the anthropogenic activities include; improper disposal of municipal waste, and domestic effluent, agricultural fertilizers, mining activities, small-scale manufacturing industries, burning of fossil fuel, and vehicular traffic emissions [4][5][6]. Additionally, human interference with the biogeochemical systems of the earth, lead to the enhanced release of naturally occurring heavy metals into the environment and soils act as the significant sink [7].…”

Evaluating cadmium bioavailability in contaminated rice paddy soils and assessing potential for contaminant immobilisation with biochar

“…Indeed, ecological and/or human health concerns linked with elevated soil metal concentrations have been reported in every continent (e.g. Basta and Gradwohl, 2000;de Lima Neto et al, 2017;Farmer et al, 2011;Flynn et al, 2002;Mungai et al, 2016;Pereira et al, 2017;Taylor et al, 2010;Zhao et al, 2015). Contamination can arise from many potential sources, including mining and smelting activities, the use of rock phosphate or sewage sludge in agriculture, gaseous and particulate emissions from coal combustion, other industrial releases, and vehicular emissions (e.g.…”