Copper in water-soil-plant interactions: food chain toxicity due to irrigation with Asa River in Ilorin, Nigeria

Asa River is the most important river that serves as a cheaper and easier disposal alternative to industries and at the same time as a less expensive and dependable water supply to farmers for the production of vegetables in dry season in Ilorin, the capital city of Kwara State, Nigeria. To investigate the effect of Asa River water pollution on water-soil-plant copper (Cu) mobility, a two factor factorial in randomized complete block design (RCBD) survey was conducted. The factors comprised of Factor A: distance between irrigation water sources and Factor B: irrigation history (irrigation duration in years). Four (4) farming locations, which corresponded to a control location 200 m upstream (– 200 m location), 200, 400 and 600 m downstream were selected. At each location, 4 farmers with different irrigation history were selected and the study was replicated thrice. The irrigation history was 0, 10, 20 and 30 years of irrigation with Asa river water. The results indicated that Cu levels in Asa River obtained 600 m downstream of control location, exceeded permissible limits with levels as high as 4.51 mg/L. Soil and plant tissue Cu concentrations were also found to exceed permissible levels, with plant tissue Cu reaching as high as 81.86 mg/kg in Corchorus olitorius.