Metal speciation dynamics and bioavailability. 2. Radial diffusion effects in the microorganism range

Area of Science:

• Environmental Chemistry
• Biogeochemistry
• Toxicology

Background:

• The free ion activity model (FIAM) for metal biouptake is limited in complex media where mass transfer is not flux-determining.
• Previous work analyzed metal speciation and bioavailability using bioconversion kinetics and coupled metal transport and dissociation kinetics.
• This established a framework for understanding when labile metal complexes contribute to biouptake, indicating deviations from FIAM.

Purpose of the Study:

• To theoretically extend metal flux expressions with a radial diffusion term for application to microorganism-sized surfaces.
• To analyze the influence of surface dimensions on metal complex lability and limiting metal fluxes.
• To investigate the impact of varying bioaffinities and bioconversion capacities on metal ion biouptake rates.

Main Methods:

• Theoretical extension of metal flux equations to incorporate radial diffusion.
• Systematic analysis of metal complex lability and limiting fluxes across different surface dimensions.
• Consideration of diverse bioaffinities and bioconversion capacities.

Main Results:

• The transition from macroscopic to microscopic surfaces significantly alters flux characteristics and metal complex lability.
• Surface dimensions dramatically influence the rate of metal ion biouptake.
• The study provides a more comprehensive model for metal biouptake in complex environmental scenarios.

Conclusions:

• The FIAM is insufficient for predicting metal biouptake in complex media, especially at micro-scales.
• Metal complex lability and diffusion dynamics are critical factors governing metal bioavailability.
• This research offers a refined theoretical framework for assessing metal ion uptake by organisms in diverse environmental conditions.