Modeling Transport and Uptake of Heavy Metals In The Presence of Natural Organic Acids Exuded By Plant Roots
Abstract
In response to various environmental stimuli, plant roots produce organic acids which may change the (bio)availability of metals. Models that integrate rhizosphere pro- cesses of organic acid exudation and degradation, metal uptake, and transport of met- als and ligands to soil layers below the root zone, are lacking. The hydrogeochemical model PHREEQC was used to describe the transport and uptake of Cu in the pres- ence of oxalic acid-exuding plant roots in a goethite-coated quartz sand. The effect of oxalate exudation was modeled in the presence and absence of organic matter, repre- sented by chelidamic acid. In the absence of the ligands, the Cu-front moved 5 cm in 50 days at pH 5, and was immobile at a pH above 6. While oxalic acid is exuded, Cu is adsorbed to the goethite surface as a ternary Cu-oxalate surface complex and the migration and uptake of Cu continuously slows down. In the presence of chelidamic acid and at pH 7.5, the stabilizing effect of oxalate is counteracted by an enhanced Cu mobilization by dissolved chelidamic acid. At pH 5, the presence of chelidamic acid further reduces Cu mobility. Root Cu uptake was lower in the presence of chelidamic acid as compared to the uptake in the absence of the ligand at pH 5. At pH 6 and 7.5, uptake was higher in the presence of chelidamic acid. The model can be extended to other sorbents, heavy metals and ligands for which consistent datasets are available. The model will be used for the design of future studies dealing with ligand-assisted metal uptake by plant roots.
- Publication:
-
EGS General Assembly Conference Abstracts
- Pub Date:
- 2002
- Bibcode:
- 2002EGSGA..27.1140S