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Metal mobility at an old, heavily loaded sludge application site
B K Richards1, T S Steenhuis, J H Peverly
1Department of Agricultural and Biological Engineering, Riley-Robb Hall, Cornell University, Ithaca, NY 14853, USA. bkr2@cornell.edu
Environmental Pollution (Barking, Essex : 1987)
|April 20, 2004
Summary
Sludge-applied metals persist in soil, with elevated concentrations found in leachate and grass nearly 20 years later. Despite this, bulk subsoil showed no significant metal increase, suggesting complex mobility patterns.
Area of Science:
- Environmental Science
- Soil Science
- Geochemistry
Background:
- Wastewater sludge application to land can introduce trace metals into soil ecosystems.
- Understanding the long-term fate and mobility of these metals is crucial for environmental risk assessment.
Purpose of the Study:
- To investigate the distribution and mobility of metals applied via wastewater sludge nearly 20 years after application.
- To compare metal concentrations in soil, leachate, and plant tissue between a sludge-applied site and a control site.
Main Methods:
- Analysis of trace metal concentrations in soil extracts (4 M HNO3), soil leachates (passive wick lysimeters), and plant tissue.
- Use of blue dye to trace preferential flow paths in the soil.
- Comparison of metal levels between the sludge-applied plot and an adjacent control plot.
Main Results:
- Leachate from the sludge plot showed significantly higher concentrations of cadmium (Cd), nickel (Ni), zinc (Zn), and boron (B) compared to the control plot, exceeding drinking water standards.
- Elevated levels of Cd, copper (Cu), and Ni were detected in grass from the sludge plot.
- Despite evidence of leaching, bulk subsoil analysis revealed no statistically significant increase in metal concentrations in the sludge plot compared to the control, even in a calcareous horizon.
Conclusions:
- Metals applied via wastewater sludge remain mobile in soil nearly two decades after application, as indicated by leachate and plant tissue concentrations.
- Preferential flow paths and metal complexation with soluble organics may facilitate leaching without significant subsoil accumulation.
- The absence of detectable metal increases in bulk subsoil does not confirm the immobility of sludge-applied metals.