Potentially toxic Metal Loads in Soils Supporting Medicinal Plants in the Ashanti Region of Ghana

The emission of potentially toxic metals from both anthropogenic and natural sources into the ecosystem has resulted in the contamination of soils. This study evaluated the levels of potentially toxic metals accumulation and enrichment in soils supporting medicinal plants in the Ashanti Region of Ghana. Soil physical characteristics (pH), cation exchange capacity, and soil organic matter were evaluated using standard methods. Levels of selected potentially toxic metals (lead, Arsenic, Copper and Cadmium) and mercury in soils were assessed using the X-Ray Fluorescence technique and RA − 915 M mercury analyzer, respectively. The extent of soil contamination was determined using enrichment factor (EF), geo-accumulation index (Igeo), contamination factor (CF), and pollution load index (PLI). Ecological risk (Er) and non-carcinogenic health risks of soils were also evaluated. The pH of the soils ranged from 4.87 to 7.88, and the soil organic matter ranged from 0.35 to 2.63%. The soil cation exchange capacity ranged from 1.14—5.98 meq/100 g. The mean levels of potentially toxic metals were Pb (2.93 ± 0.53–11.22 ± 2.80 mg/kg), As (2.37 ± 0.56–7.52 ± 1.97 mg/kg), Cu (8.87 ± 2.23–23.20 ± 3.62 mg/kg), Cd (4.29 ± 0.90–15.28 ± 3.01 mg/kg) and Hg (4.00 × 10 –3 ± 0.00–1.05 × 10 –3 ± 0.03 mg/kg). The mean EF and CF contents ranged from 238.22 (extremely high contamination) to 0.1 (low contamination), and 0.17 (low contamination) to 76.40 (very high contamination), respectively. The mean PLI and Igeo ranged between 1.04 (moderate polluted) and 1.8180 (strongly polluted), and − 9.35 (practically uncontaminated) to 9.43 (contaminated). The ecological risk was between 0.81 (low risk) and 1134 (very high risk). Levels of all metals were lower than the World Health Organization/Food and Agriculture Organization maximum permissible limits except cadmium, and the soils manifested similar enrichment for the potentially toxic metals but exhibited variable physical properties. Levels of selected metals were within that of naturally occurring concentration in soils except for cadmium that could be from anthropogenic sources.