BIOACCUMULATION OF HEAVY METALS IN CROPS IRRIGATED WITH WATER FROM ABANDONED MINING PONDS IN KUNET, BOKKOS LGA

ABSTRACT This study investigated the bioaccumulation of selected heavy metals Lead (Pb), Cadmium (Cd), Arsenic (As), Zinc (Zn), Copper (Cu), and Nickel (Ni) in vegetable crops irrigated with water from abandoned mining ponds in Kunet District of Bokkos Local Government Area, Plateau State, Nigeria. Soil, root, and aerial plant samples were analyzed to determine the distribution and uptake of these metals. Physicochemical soil parameters (pH, bulk density, organic matter, and electrical conductivity) were examined to understand their influence on heavy-metal mobility. Metal concentrations were quantified using Atomic Absorption Spectrophotometry after wet-digestion. Bioaccumulation coefficients (BCF) and translocation factors (TF) were calculated to assess plant uptake and internal translocation. The results showed that soils contained elevated levels of some metals particularly Copper (Cu) up to 2.08 mg/kg in Kunet soils and 1.75 mg/kg in Butura, and Lead (Pb) up to 1.60 mg/kg in Butura soils. In roots, Pb reached 0.48 mg/kg in the control site and 0.29 mg/kg in Kunet, while Cd reached 0.20 mg/kg at the control site and 0.14 mg/kg in Butura C. Several of these values exceeded FAO/WHO permissible limits for agricultural soils and edible plant parts (e.g., FAO/WHO limit for Cd = 0.02 mg/kg, Pb = 0.3 mg/kg). BCF and TF results indicated active uptake and internal mobility. Notably, the translocation factor for nickel reached 8.36 in Butura, indicating extremely high movement from roots to shoots. Copper translocation was also significant (TF = 2.23 in Butura C and 1.20 in the control). Zinc exhibited high soil-to-root accumulation (BCF up to 2.18 in Kunet). Overall, the study demonstrates that irrigation with water from abandoned mining ponds significantly increases heavy-metal load in soils and crops, posing potential human-health risks. The study recommends routine monitoring, soil remediation, and safer irrigation practices to reduce exposure to toxic metals.