Microplastics transport in soils: A critical review

Microplastics (MPs) in terrestrial environments are an emerging contaminant of huge concern
to ecosystems and human health. However, our understanding of the MPs fate, particularly their
transport mechanisms, remains elusive. This knowledge gap arises from the multiplicity of
coupled physical, chemical and biological processes and parameters affecting MPs transport,
together with scarcity of systematic studies that aim to isolate their individual effects. In this
paper, we provide a critical review of the state-of-the-art in our understanding of MPs transport,
highlight knowledge gaps, and suggest future research to bridge them. We classify the
governing factors into four main categories: (i) MPs properties; (ii) soil properties; (iii)
hydrological conditions; and (iv) biological activity. Our analysis highlights the intricacy of
MPs transport, showing that seemingly non-monotonic trends and even complete lack of
correlation between some parameters and MPs transport could be explained by the interference
(co-effects) with other parameters and processes