Data for: Assessment of cryogenic pretreatment for simulating environmental weathering in the formation of surrogate micro- and nanoplastics from agricultural mulch film

Microplastics (MPs) and nanoplastics (NPs) from mulch films and other
plastic materials employed in vegetable and small fruit production pose a
major threat to agricultural ecosystems. For conducting controlled studies
on MPs' and NPs' (MNPs') ecotoxicity to soil organisms and
plants and fate and transport in soil, surrogate MNPs arerequired that
mimic MNPs that form in agricultural fields. We have developed a procedure
to prepare MPs from plastic films or pellets using mechanical milling and
sieving, and conversion of the resultant MPs into NPs through wet
grinding, both steps of which mimic the degradation and fragmentation of
plastics in nature. The major goal of this study was to determine if
cryogenic exposure of two biodegradable mulch films effectively mimics the
embrittlement caused by environmental weathering in terms of the
dimensional, thermal, chemical, and biodegradability properties of the
formed MNPs. We found differences in size, surface charge, thermal and
chemical properties, and biodegradability in soil between MNPs'
prepared from cryogenically treated vs. environmentally weathered films,
related to the photochemical reactions occurring in the environment that
were not mimicked by cryogenic treatment, such as depolymerization and
cross-link formation. We also investigated the size reduction process for
NPs and found that the size distribution was bimodal, with populations
centered at 50 nm and 150–300 nm, and as the size reduction process
progressed, the former subpopulation's proportion increased. The
biodegradability of MPs in soil was greater than for NPs, a
counter-intuitive trend since greater surface area exposure for NPs would
increase biodegradability. The result is associated with differences in
surface and chemical properties and to minor components that are readily
leached out during the formation of NPs. In summary, the use of weathered
plastics as feedstock would likely produce MNPs that are more realistic
than cryogenically-treated unweathered films for use in experimental
studies.