# Insights from a Long-Term Outdoor Mesocosm Study: eDNA Metabarcoding Reveals Exacerbated but Transient Impacts from a Nanoenabled Pesticide Formulation (Nano-TiO2-Coated Carbendazim) on Freshwater Microbial Communities

## TL;DR

This study shows that a nanoenabled pesticide temporarily harms freshwater microbes more than traditional pesticides, but the effects fade over time.

## Contribution

The study provides new experimental data on the ecological impacts of nanoenabled pesticides on microbial communities.

## Key findings

- Nano-TiO2-coated carbendazim had more pronounced effects on bacterial diversity than noncoated carbendazim.
- Bacterial communities recovered to control levels within 5 weeks after treatment.
- eDNA metabarcoding revealed time-dependent effects of nanoformulated pesticides.

## Abstract

Fungicides currently
encompass the second-most-used class of agricultural
pesticides globally. Residues are frequently detected in freshwater,
leading to undesired ecological impacts. Nanoenabled pesticide formulations
have recently gained prominence in the scientific literature and have
been suggested to exhibit favorable properties over conventional pesticide
formulations by facilitating reductions in emissions toward nontarget
locations. However, data on unintended effects on nontarget aquatic
communities are scarce, especially concerning microbial communities.
In this study, long-term effects of nano titanium-dioxide- (nTiO2)-coated carbendazim and its constituents on (pelagic) freshwater
microbial communities in simulated agricultural ditches were investigated
over a period of 14 weeks using environmental DNA (eDNA) metabarcoding.
Impacts on bacterial diversity (α and β) were observed
2 weeks after the treatment application and most pronounced in the
nTiO2-coated carbendazim treatment, followed by its active
substance, i.e., noncoated carbendazim. The observed patterns possibly
imply that nTiO2-coated carbendazim imposed more pronounced
and potentially delayed or extended effects compared to the noncoated
form of carbendazim. Bacterial communities also proved to be resilient
under the tested conditions as they returned to the control-state
within 5 weeks after the treatment application. Overall, our data
suggest that eDNA metabarcoding data on microbial communities can
help uncover time-dependent effects of nanoformulated pesticides.

Using eDNA metabarcoding, this study
demonstrates exacerbated
yet transient impacts of a nanoenabled pesticide formulation on freshwater
microbial communities. With experimental data to this end currently
being scarce, our findings can support ongoing regulatory developments.