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Title: DISTRIBUTION AND MOVEMENT OF SLUDGE-DERIVED TRACE METALS IN A NIGERIAN ULTISOL

Author
item MBILA, MONDAY - IOWA STATE UNIVERSITY
item THOMPSON, MICHAEL - IOWA STATE UNIVERSITY
item MBAGWUA, JOE - UNIVERSITY OF NIGERIA
item Laird, David

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/26/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: In Nigeria and many third world countries, there is a large need for fertilizers to increase fruit, vegetable and grain production. However local farmers often can not afford chemical fertilizers. Sewage sludge is potentially an inexpensive source of plant nutrients which local farmers can afford. Studies of sewage sludge application on soils in temperate regions have raised concerns about the accumulation of heavy metals. Little work has been done with sewage sludge application on tropical soils. We found substantial downward movement of heavy metals and accumulation of organic matter and plant nutrients in tropical soils near Nsukka, Nigeria that had been amended with sewage sludge for 30 years. The research will help governmental agencies evaluate the potential risk of heavy metal accumulation associated with long-term application of sewage sludge on tropical soils. The main beneficiaries of this research will be farmers in tropical regions.

Technical Abstract: Use of metal-enriched sewage sludge as a soil fertilizer may result in trace metal contamination of soils. This study was conducted to evaluate the effects of long-term sludge application on trace metal (Zn, Cu, Pb, and Ni) distribution and potential bioavailability in a Nigerian Ultisol. Total metal analyses, sequential chemical fractionation and DPTA extractions were carried out on samples of control and sludge-amended pedons (a Rhodic Kandiustult and two Rhodic Kandiustalfs from Nigeria). Soil enrichment factors (EF) were calculated for each metal. The sewage sludge contained high levels of Zn and Cu but low levels of Pb and Ni. The control soil contained low levels of all four metals. Compared with the control soil, the sludge-amended soils showed elevated levels of Zn and Cu, reflecting the trace metal composition of the sewage sludge. Zn and Cu in the sludge-amended soils were strongly enriched at all depths in the profile, indicating that they had moved from the zone of sludge application. The sequential extraction and DPTA analyses indicated that the sludge-amended soils contained more readily extractable and bioavailable metal ions than the unamended soil.