Growth Parameters and Toxicity of Cowpea (Vigna unguiculata) Grown in Copper Polluted Soil

Abstract

Heavy metals find their way into the soil and eventually the food chain via anthropogenic activities. The deleterious effects of some heavy metals depend on the concentration of the metal and the tolerant capacity of the plant. The present study investigated the morphological and toxicological effects of copper on cowpea. Exactly 2 kg of soil was treated with 10 mg/mL, 50 mg/mL, 100 mg/mL and 200 mg/mL of copper sulphate (1 g/L stock solution), and 5.20 g/L of kocide (lower dose of kocide), 6.67 g/L of kocide (positive control) and 10.70 g/L of kocide (higher dose of kocide) and no treatment (negative control) to obtain eight groups. The experimental plant was cultivated for five weeks. Data were collected within and after the first week of cultivation and subsequent weeks until the fifth week. The data obtained from the various growth parameters considered were subjected to analysis of variance (ANOVA) using Statistical Product and Service Solutions (SPSS) software (version 16). The result obtained showed inconsistent increase with no significant difference in the percentage seed germination, leaf area and plant height as against the control between the weeks, while an inconsistent decrease within the weeks. There was reduction in the copper content in the leaf and steam, though, the content in the leaf exceeded in all the groups. Finally, the results of health risk factors/indices considered showed a decrease in the leaf in most of the treatments, and an increase in the stem when compared to United States Environmental Protection Agency (USEPA) permissible units. Data from the target hazard quotient and carcinogenic or health risk of the plant leaf and stem indicate that there is little or no risk associated in consuming the plant at certain level of copper contamination.