NanoFASE - nanofase-case-study-uptake-and-elimination-kinetics-of-ag-nps-in-earthworms

Silver nanoparticles (Ag-NPs) are used in a broad variety of industrial applications. Following the use of the final products (including consumer goods), Ag-NPs can end up in waste water treatment plants. Then the silver can reach the soil compartment via the disposition of sewage sludge on agriculture land. In the soil, the nanomaterials may be taken up by e.g. earthworms, which play an important role in soil structure and fertility, influencing soil biochemical and biophysical functioning.

In this NanoFASE case study, bio-uptake kinetics of different forms of Ag nanomaterials in earthworms are quantified. Experiments showed that the uptake and elimination of dissolving Ag-NPs were similar to ionic uptake and elimination, demonstrating that for such dissolving metal nanomaterials, the ionic form is most relevant for uptake. In contrast, the uptake of non-dissolving Ag₂S-NPs (reflecting the main environmentally relevant form of Ag-NPs) in earthworms was extremely low. In order to quantify the toxicokinetics, we calculated uptake kinetic rate constant (k1) and elimination rate constant (k2) by modelling the results of single species exposure studies.

Study aim

Overview

Soil is spiked with different forms of Ag and earthworms are introduced
Contaminated soil sampling of earthworms, soil and soil pore water <see procedure 1 in soil compartment> once per week for a month
Transfer of the earthworms to clean soil for depuration
Clean soil sampling of earthworms, soil and soil pore water once per week for a month
Analysis of Ag concentrations within the organisms distinguishing between ionic Ag and particulate Ag and calculation of the uptake kinetic rate constant (k1) and elimination kinetic constant (k2)

Compartment involved:
Uncontaminated natural soil

NP type/size:

Ag-NP 50 mm
Ag₂S-NP 20nm

Species:
Eisenia fetida

Bioassay:
Bioaccumulation (quantification of Ag as ionic and particulate form)

Results

Figure 1: A. Ag particulate and total Ag+ predicted kinetics in earthworms during uptake and elimination phases. B. Calculated k1 and k2 values per Ag form.

Ionic Ag is the main form which is taken up in the case of dissolving NPs.
The uptake and elimination rate constants for earthworms exposed to dissolving Ag-NPs or AgNO₃ did not significantly differ.
The uptake of Ag₂S-NPs was significantly lower.

Parameters

Emitted to

k1 uptake kinetic rate constant in earthworm kg soil /kg body weight / day
k2 elimination kinetic rate constant in earthworm (per day)

Soil

Read also

Baccaro, Marta, et al. "Ageing, dissolution and biogenic formation of nanoparticles: how do these factors affect the uptake kinetics of silver nanoparticles in earthworms?." Environmental Science: Nano 5.5 (2018): 1107-1116. DOI:10.1039/C7EN01212H