Effect of seasonal variation on the removal of Pb and Cd from a polluted field using Helianthus annuus L. and Tithonia diversifolia (Hemsl.)

Abstract

Presently, there is increase in public awareness and attention on environmental pollution, but very scanty information is available on heavy metal pollution of the tropical soil ecosystem and the possibility of removing these pollutants from the soils. This work, therefore, investigated the possibility of removing Pb and Cd, in situ from soil polluted with effluents from a paint industry in Ibadan, southwestern Nigeria using Helianthus annuus L. and Tithonia diversifolia (Hemsl.) and the possible contributions of seasonal variation to phytoremediation technique. The experiment consisted of three treatments (H. annuus, T. diversifolia and control) each replicated three times to give nine plots of 2 × 4 m² each arranged in a randomized complete block design. Each plot was planted with the seeds of phytoplants at a spacing of 60 × 30 cm² and the seed rate of four seeds per hole. The seedlings were thinned to two stands per hole two weeks after planting (WAP) and also weeded twice (2 and 5 WAP). A significantly (p < 0.05) higher value of 0.88 mg Pb kg⁻¹ was removed and stored in the shoot of T. diversifolia as against 0.31 mg Pb kg⁻¹ by H. annuus in the dry season at 8 WAP. However, in the wet season, lower values of Pb with no significant (p < 0.05) difference were remediated by the two plants. Also, values of Cd remediated by the two plants were much lower with no significant difference during the two seasons.

Keywords:

• seasonal variation
• phytoremediation
• factory effluents
• Helianthus annuus
• Tithonia diversifolia
• Ibadan