|Sloan, John - TEXAS A&M UNIVERSITY|
Submitted to: Proceedings Effects of Land Application of Biosolids in Arid & Semiarid Env
Publication Type: Proceedings
Publication Acceptance Date: July 11, 1999
Publication Date: N/A
Interpretive Summary: There is a great concern within the population that once biosolids applications have ceased, toxic heavy metals will become available for plant uptake because of the breakdown of organic matter added to the soil as biosolids. To answer this concern, we established that biosolids applied cadmium (Cd) and zinc (Zn) were still available for plant uptake eighteen years following excessive biosolids applications, although concentrations in plant tissue were very low. Increased levels of Cd, and to a lesser extent Zn, were observed in corn stover (stalk plus leaves) as a result of previous biosolids loadings; but biosolids borne Cd, the heavy metal of concern to the food and feed chain, never accumulated in corn grain. Stover Cd and stover and grain levels of Zn appeared to stabilize by Year 3 following biosolids applications, dispelling fear of enhanced biovailability of heavy metals 10 to 15 years post biosolids applications due to the breakdown of the biosolids organic matter that, in turn, released the heavy metals. Treatment plant managers, consultants, and producers will use this information for designing management plans for beneficial use of biosolids in agriculture.
Technical Abstract: Post application bioavailability of biosolids-borne trace metals over extended periods of time is unresolved, a result of the lack of controlled, well-documented, long-term field studies. Waste activated municipal biosolids were applied annually for 3 y for cumulative biosolids loadings of 0 (control), 60 (low), 120 (medium), and 180 (high) Mg ha**-1, a total Cd and Zn loading of 25 and 343 kg ha**-1, respectively, for the high treatment. Biosolids applied Cd and Zn were still available for uptake by maize 18 y post application. Differences in stover Cd, and to a lesser extent Zn, concentrations were greater between the control vs biosolids treatments. Biosolids borne Cd never accumulated in maize grain, while biosolids derived Zn did accumulate in the grain. Stover Cd and stover and grain Zn levels appeared to stabilize by Year 3 post biosolids applications.