Water Quality and Crop Contamination in Peri-Urban Agriculture

The quality of untreated water used by dry season vegetable growers determines the safety of the vegetables produced for human consumption. Traditionally, small scale vegetable farmers site their farms along banks of streams which gradually dry up during the dry season resulting in isolated pockets of ponds at different intervals along the path of the streams which are used by farmers to irrigate. A field experiment was initiated at Ibadan to ascertain the quality of irrigation water used to produce vegetables along Ona-stream during the dry season. Five isolated ponds and one locally dug well were sampled and analysed to ascertain the heavy metals status. Results of soil analysis from five farms (A - E) sited very close to the stream revealed high concentrations of heavy metals ranging from 0.96 to 2.34 mg kg^-1 for Pb, 0.72 to 2.16 mg kg^-1 for Cr and 0.30 to 0.92 mg kg^-1 for Co while farmland F sited about 90m away from the stream was free of Pb, Cr and Co contaminants. Locally dug well F water was free of Cr, Co and Pb while isolated ponds had Cr, Co and Pb in the range of 0.01 to 0.23 mg kg^-1 which is beyond safe consumption thresholds. There were strong correlations between heavy metals in water and vegetable for Cr (0.992**), Cd (0.599**), Ni (0.614*) and Pb (0.552**) indicating that the hygienic status of dry season vegetables is largely determined by the quality of irrigation water. In addition, all vegetables irrigated with untreated isolated ponds contained Cd, Pb and Ni concentrations above maximum permissible standard which could pose risk to human health. Therefore, farmers should be enlightened on the need to use hygienic water for irrigation. Construction of shallow wells on the farms instead of using contaminated stream water directly could be a better option for healthy and sustainable agriculture.