Microplastics have shape- and polymer-dependent effects on soil aggregation and organic matter loss – an experimental and meta-analytical approach

Abstract

Microplastics are a diverse and ubiquitous contaminant, a global change driver with potential to alter ecosystem properties and processes. Microplastic-induced effects in soils are manifold as microplastics differ in a variety of properties among which the shape is of special interest. Our knowledge is limited regarding the impact of various microplastic shapes on soil processes. Therefore, we conducted this two-part research comprising a meta-analysis on published literature and a lab experiment focusing on microplastic shapes- and polymer-induced effects on soil aggregation and organic matter decomposition. We here focus on fibers, films, foams and particles as microplastic shapes.In the meta-analysis, we found a strong research focus on fibrous and particulate microplastic materials, with films and foams neglected.Our experiment showed that microplastic shapes are important modulators of responses in soil aggregation and organic matter decomposition. Fibers, irrespective of their chemistry, negatively affected the formation of aggregates. However, for other shapes like foams and particles, the polymer identity is an important factor co-modulating the soil responses.Further research is needed to generate a data-driven foundation to permit a better mechanistic understanding of the importance and consequences of microplastics added to soils.

Towards a Circular Economy of Plastics: An Evaluation of the Systematic Transition to a New Generation of Bioplastics

“…The term microplastic has been commonly used in literature to describe a broad assortment of plastic-derived particles classified according to their size. Although the term is widespread and standard, the complexity and variety of microplastic compositions and morphologies are often overlooked in categorizing these contaminants [ 71 , 72 ]. This simplification has led to the inadequacy of studies and protocols that assess the environmental effect of microplastics, the irreproducibility of strategies for microplastic detection, and the ineffectiveness of pollutant-mitigation governance strategies [ 73 ].…”

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“…Microfibers thus have the potential to alter the soil structure [128] , [129] , which is at least in part mediated by the presence of soil microorganisms [128] . For other polymer shapes like foams and particles, the polymer type is an important factor that co-modulates the soil physicochemical properties [130] .…”

“…Third, the presence of MPs can change the soil bulk density and porosity [126] , [127] , [128] , [129] , [130] . The change in soil porosity can result and explain the increase of the soil microbial respiration.…”

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“…1. The percentage of newly formed aggregates (> 600 µm; NFA), according to Lehmann et al (2021): where W >600 is the weight of the > 600 µm fraction after the air drying or wet sieving process, and W sample is the total weight of the sample.…”