# Uptake rate

Uptake rate indicates the speed at which an organism takes in material from the medium. It is measured as the increase in concentration of material in the organism per unit of concentration in the medium per day. The overall unit of the uptake rate constant ($$k_{1}$$) is

$$g_{medium}*g_{organism}^{-1} \ast day^{-1}$$

where $$g$$ is gram of the medium or organism.

Generally, the modelling of bio-uptake in invertebrates does not take into consideration specific routes of uptake, but rather a summation of routes, e.g. both oral and dermal uptake. However, when needed, uptake rate can be assessed per specific route. Similarly, uptake rates can be assessed for either total concentrations of nanomaterials or for specific forms, although quantification of the different forms of a material in kinetic experiments can be difficult.

Concentration in an organism over time of a given material during uptake phase (conceptual graph of exposure experiment)

Bio-uptake

## Procedure

 $$C_{org} = C_{env} \ast k_{1}\ast SF\ast t + C_{env}\ast \frac{k_{1}}{k_{2}+k_{g}}\ast (1-e^{-(k_{2}+k_{g})\ast t})\ast (1-SF)$$  Uptake calculation