Some fundamental (and often overlooked) considerations underlying the free ion activity and biotic ligand models

Hassler, CS; Slaveykova, VI; Wilkinson, KJ

Some fundamental (and often overlooked) considerations underlying the free ion activity and biotic ligand models

Hassler, CS Slaveykova, VI Wilkinson, KJ

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Publication Type:: Journal Article
Citation:: Environmental Toxicology and Chemistry, 2004, 23 (2), pp. 283 - 291
Issue Date:: 2004-02-01

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Field	Value	Language
dc.contributor.author	Hassler, CS	en_US
dc.contributor.author	Slaveykova, VI	en_US
dc.contributor.author	Wilkinson, KJ	en_US
dc.date.issued	2004-02-01	en_US
dc.identifier.citation	Environmental Toxicology and Chemistry, 2004, 23 (2), pp. 283 - 291	en_US
dc.identifier.issn	0730-7268	en_US
dc.identifier.uri	http://hdl.handle.net/10453/13123
dc.description.abstract	Trace metal bioavailability is often evaluated on the basis of steady-state models such as the free ion activity model (FIAM) and the biotic ligand model (BLM). Some of the assumptions underlying these models were verified by examining Pb and Zn uptake by the green microalga Chlorella kesslerii. Transporter bound metal {(M-Rcell}) and free ion concentrations ([MZ+]) were related to experimentally determined uptake fluxes (Jint). Although the BLM and FIAM correctly predicted Pb uptake in the absence of competing ions, they failed to predict competitive interactions with Ca2+, likely because of modifications of the algal surface charge and the active nature of Ca2+ transport. Zinc transport is also active; in this case, both the internalization rate constant (kint) and the equilibrium constant for the binding of Zn to the transport sites (KZn-Rcell) varied as a function of [Zn 2+] in the bulk solution. For this reason, Zn uptake could not be modeled by the steady-state models either in the presence or absence of competitors (Cd and Ca). Furthermore, the role of Cu on Pb and Zn adsorption and uptake could not be predicted by either model because of secondary effects on the algal physiology and membrane permeability. Finally, a 17°C reduction in temperature resulted in a two- to fivefold decrease in membrane permeability of the metals, an observation that also is unaccounted for by either the FIAM or BLM. This paper emphasizes the limitations of the models in well-controlled laboratory systems with the goal of extrapolating the results to complex environmental systems.	en_US
dc.relation.ispartof	Environmental Toxicology and Chemistry	en_US
dc.relation.isbasedon	10.1897/03-149	en_US
dc.subject.classification	Environmental Sciences	en_US
dc.subject.mesh	Chlorella	en_US
dc.subject.mesh	Calcium	en_US
dc.subject.mesh	Metals, Heavy	en_US
dc.subject.mesh	Trace Elements	en_US
dc.subject.mesh	Ligands	en_US
dc.subject.mesh	Temperature	en_US
dc.subject.mesh	Biological Transport, Active	en_US
dc.subject.mesh	Biological Availability	en_US
dc.subject.mesh	Kinetics	en_US
dc.subject.mesh	Models, Chemical	en_US
dc.title	Some fundamental (and often overlooked) considerations underlying the free ion activity and biotic ligand models	en_US
dc.type	Journal Article
utslib.citation.volume	2	en_US
utslib.citation.volume	23	en_US
utslib.for	0399 Other Chemical Sciences	en_US
utslib.for	03 Chemical Sciences	en_US
utslib.for	05 Environmental Sciences	en_US
utslib.for	06 Biological Sciences	en_US
pubs.embargo.period	Not known	en_US
pubs.organisational-group	/University of Technology Sydney
pubs.organisational-group	/University of Technology Sydney/Faculty of Science
utslib.copyright.status	closed_access
pubs.issue	2	en_US
pubs.publication-status	Published	en_US
pubs.volume	23	en_US

Abstract:

Trace metal bioavailability is often evaluated on the basis of steady-state models such as the free ion activity model (FIAM) and the biotic ligand model (BLM). Some of the assumptions underlying these models were verified by examining Pb and Zn uptake by the green microalga Chlorella kesslerii. Transporter bound metal {(M-Rcell}) and free ion concentrations ([MZ+]) were related to experimentally determined uptake fluxes (Jint). Although the BLM and FIAM correctly predicted Pb uptake in the absence of competing ions, they failed to predict competitive interactions with Ca2+, likely because of modifications of the algal surface charge and the active nature of Ca2+ transport. Zinc transport is also active; in this case, both the internalization rate constant (kint) and the equilibrium constant for the binding of Zn to the transport sites (KZn-Rcell) varied as a function of [Zn 2+] in the bulk solution. For this reason, Zn uptake could not be modeled by the steady-state models either in the presence or absence of competitors (Cd and Ca). Furthermore, the role of Cu on Pb and Zn adsorption and uptake could not be predicted by either model because of secondary effects on the algal physiology and membrane permeability. Finally, a 17°C reduction in temperature resulted in a two- to fivefold decrease in membrane permeability of the metals, an observation that also is unaccounted for by either the FIAM or BLM. This paper emphasizes the limitations of the models in well-controlled laboratory systems with the goal of extrapolating the results to complex environmental systems.

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http://hdl.handle.net/10453/13123