Influence of pH Variation on Lead Uptake and Accumulation in Raphanus raphanistrum and Brassica napus Grown in Spiked and Limed Agricultural Soils of Moiben Sub-County, Kenya

Abstract

This study assessed Pb uptake and distribution in Raphanus raphanistrum (RR) and Brassica napus (BN) grown in agricultural soils from Moiben Sub-County, Kenya, under three soil treatments: Pb-spiked soil (to ≈1000 mg/kg), non-spiked soil, and spiked soil amended with lime (to achieve pH≈7.4). Pb concentrations were quantified using Atomic Absorption Spectrophotometry (AAS), and the Bioaccumulation Factor (BAF) was calculated for roots, stems, leaves and seeds. Data were analyzed using SPSS v25. Descriptive statistics (means, standard deviations) were computed for Pb concentrations in soil and plant tissues. One-way ANOVA tested differences among treatments (control, spiked, limed), with Tukey’s HSD applied for post hoc comparisons. Results showed that Raphanus raphanistrum accumulated mean Pb concentrations of 1043.80 ± 18.34 mg/kg in spiked soils, 25.49 ± 0.39 mg/kg in non-spiked soils, and 548.24 ± 17.75 mg/kg in spiked and limed soils. Brassica napus followed a similar trend, with significantly higher Pb accumulation in spiked compared to non-spiked soils, while liming reduced uptake by nearly 50%. In both species, roots exhibited the highest BAF across treatments, while stems consistently recorded the lowest. In spiked soils, the accumulation trend was roots > seeds > leaves > stem, whereas in limed soils it shifted to roots > leaves > seeds > stem, with overall BAF values reduced to <1. Although liming effectively reduced Pb uptake, both Raphanus raphanistrum and Brassica napus accumulated Pb levels in edible parts above FAO/WHO permissible limits (0.3 mg/kg for leafy vegetables, 0.1 mg/kg for root/tuber crops, and 0.2 mg/kg for cereals and oilseeds), raising concerns over food safety. The findings highlight the influence of soil