『Abstract
Sorption of phosphorus (P) onto particulate surfaces significantly
influences dissolved P concentrations in aquatic environments.
We present results of a study contrasting the sorption behavior
of several dissolved organic phosphorus (DOP) compounds and phosphate
onto three commonly occurring iron (oxyhydr)oxides (FeOX):
ferrihydrite, goethite, and hematite. The DOP compounds were chosen
to represent a range of molecular weights and structures, and
include: adenosine triphosphate (AT), adenosine monophosphate
(AMP), glucose-6-phosphate (G6P), and aminoethylphosphonic acid
(AEP).
All P compounds displayed decreasing sorption as a function of
crystallinity of the FeOX substrate, with
ferrihydrite adsorbing the most, hematite the least. In general,
maximum sorption density decreased with increasing molecular weight
of P compound; sorption of G6P onto goethite and hematite excepted.
P compound size and structure, and the nature of the FeOX
substrate all appear to play a role dictating relative sorption
capacity. Failure of a simple, 1-step sorption-desorption model
to describe the data suggests that P sorption cannot be explained
by a simple balance between sorption and desorption. Instead,
the data are consistent with a 2-step sorption model consisting
of a initial rapid surface sorption, followed by a slow, solid-state
diffusion of P from surface sites into particle interiors. Desorption
experiments provide additional support for the 2-step sorption
model.
Without exception, DOP compounds showed less efficient sorption
than did orthophosphate. This suggests that in aquatic systems
enriched in reactive FeOX, whether as suspended
particulates in the water column or in benthic sediments, DOP
bioavailability may exceed that of orthophosphate. Since biological
uptake of P from DOP requires enzymatic cleavage of orthophosphate,
a system enriched in DOP relative to orthophosphate may impact
ecosystem community structure.』
1. Introduction
2. Materials and methods
2.1. Chemicals and equipment
2.2. Phosphorus compounds
2.3. Iron phases
2.4. Sorption isotherm experiments
2.5. Sorption kinetics experiments
2.6. Desorption experiments
3. Results
3.1. Iron phase characteristics
3.2. Isotherm experimental results
3.3. Sorption kinetics results
3.4. Desorption results
4. Discussion
4.1. Isotherms: sorption equilibrium conditions
4.2. Phosphorus uptake kinetics
4.3. Phosphorus desorption
4.4. Physical aspects of the 2-step sorption process
4.5. Implications for P cycling in marine systems
5. Conclusions
Acknowledgements
Appendix A. Evaluation of an alternative model for sorption kinetics
Appendix B. The model
References