Are long-term exposure studies needed? Short-term toxicokinetic model predicts the uptake of metal nanoparticles in earthworms after nine months

Marta Baccaro,Johannes H.J Van Den Berg,Nico W Van Den Brink

doi:10.1016/j.ecoenv.2021.112371

Marta Baccaro, Johannes H.J Van Den Berg + Show 1 more

Open Access

https://doi.org/10.1016/j.ecoenv.2021.112371

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Abstract

Uptake of most metal nanoparticles (NPs) in organisms is assumed to be mainly driven by the bioavailability of the released ions, as has been verified in controlled and short-term exposure tests. However, the changeability of NPs and the dynamic processes which NPs undergo in the soil environment, bring uncertainty regarding their interactions with soil organisms over a long period of time. To assess the potential impacts of long-term exposure scenarios on the toxicokinetic of metal NPs, earthworms Eisenia fetida were exposed to soils spiked with pristine Ag-NP, aged Ag-NP (Ag2S-NP) and ionic Ag for nine months, and results were compared to those from a similar short-term (28 days) experiment, conducted under similar conditions. Overall, there were no statistical differences between long-term accumulation patterns in earthworms exposed to pristine Ag-NP and AgNO3, while for Ag2S-NP, the amount of Ag internalized after 9 months was five times lower than for the other treatments. Average Ag concentrations in soil pore water in all treatments did not change over time, however the soil pH decreased and electrical conductivity increased in all treatments. Metallothionein concentrations in exposed earthworms were not statistically different from levels in untreated earthworms. Finally, the short-term toxicokinetic models predicted the bioaccumulation in earthworms exposed to Ag-NP, AgNO3 after nine months on the whole. Although the bioaccumulation for Ag2S-NPs was somewhat under-predicted, the rate of accumulation of Ag2S-NPs is much lower than that of Ag-NPs or AgNO3 and thus potentially of lower concern. Nevertheless, better understanding about the exposure kinetics of Ag2S-NP would help to address potential nano-specific toxicokinetic and toxicodynamics, also of other sulfidized metal NPs.

Highlights

Highlighting communalities and differences between the tox icokinetics and toxicodynamics of metal nanoparticles (NPs) and bulk materials in organisms has been the focus of many studies in the last decade (Unrine et al, 2010; Croteau et al, 2011; Diez-Ortiz et al, 2015)
In our previous study (Baccaro et al, 2018) we demonstrated that in earthworms exposed to Ag-NP and AgNO3 for 28 days, ~ 85% of the accumulated Ag was present in the earthworms as ions while accumulation patterns did not statistically differ between ionic Ag and pristine Ag-NPs
The Ag concentrations in pore water measured at the sam pling time points did not reflect the uptake pattern since a lower Ag concentration in pore water would be expected for the Ag2S-NP expo sure group

Summary

Introduction

Highlighting communalities and differences between the tox icokinetics and toxicodynamics of metal nanoparticles (NPs) and bulk materials in organisms has been the focus of many studies in the last decade (Unrine et al, 2010; Croteau et al, 2011; Diez-Ortiz et al, 2015). Besides dissolution other processes such as heteroaggregation and adsorption of NPs to soil particles and dissolved organic matter occur (Cornelis et al, 2014) Since such speciation processes can strongly affect long-term bioavailability, they should be studied, using dynamic approaches under long-term exposure conditions (Coutris et al, 2012; Vijver et al, 2018). In the present study we exposed earthworms Eisenia fetida to pristine Ag-NP, aged Ag-NP (Ag2S-NP) and AgNO3 in natural soil for nine months and quantified and modeled their uptake over time, deriving uptake rate constants for each Ag form

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