separation-identification-conventional-microplastics-from-farmland

Separation and Identification of Conventional Microplastics from Farmland Soils

Microplastics (MPs) pollution in the terrestrial environment has received increasing attention over the last decade, with increasing studies describing ...

Bangor University

Micro and macroplastics are emerging contaminants in agricultural settings, yet their impact on nitrogen (N) cycling and partitioning in plant-soil-microbial systems is poorly understood. In this mesocosm-scale study, spring barley (Hordeum vulgare L.) was exposed to macro or microplastic produced from low density polyethylene (LDPE) or biodegradable plastic at concentrations equivalent to 1, 10 and 20 years of plastic mulch film use. Partitioning of N-labelled fertiliser into plant biomass, soil and leachate yielded a partial mass balance. Soil N partitioning was probed via compound-specific N-stable isotope analyses of soil microbial protein. Concentration-dependent decreases in plant N uptake occurred with increased leached nitrogen for LDPE microplastic. Assimilation into soil microbial protein was higher for biodegradable plastics, which we associate with early-stage biodegradable plastic degradation. Partitioning of N into inorganic soil N pools was affected by LDPE size, with lower assimilation into the microbial protein pool. While microplastics and macroplastics altered soil N cycling, the limited impacts on plant health indicated the threshold for negative effects was not reached at agriculturally relevant concentrations. This study highlights the difference between conventional and biodegradable plastics, and emphasises that the interplay of micro and macroplastics on soil N cycling must be considered in future studies.

LDPE and biodegradable PLA-PBAT plastics differentially affect plant-soil nitrogen partitioning and dynamics in a Hordeum vulgare mesocosm.

Over the last 50 years, the intense use of agricultural plastic in the form of mulch films has led to an accumulation of plastic in soil, creating a legacy of plastic in agricultural fields. Plastic often contains additives, however it is still largely unknown how these compounds affect soil properties, potentially influencing or masking effects of the plastic itself. Therefore, the aim of this study was to investigate the effects of pure plastics of varying sizes and concentrations, to improve our understanding of plastic-only interactions within soil-plant mesocosms. Maize (Zea mays L.) was grown over eight weeks following the addition of micro and macro low-density polyethylene and polypropylene at increasing concentrations (equivalent to 1, 10, 25, and 50 years mulch film use) and the effects of plastic on key soil and plant properties were measured. We found the effect of both macro and microplastic on soil and plant health is negligible in the short-term (1 to <10 years). However, ≥ 10 years of plastic application for both plastic types and sizes resulted in a clear negative effect on plant growth and microbial biomass. This study provides vital insight into the effect of both macro and microplastics on soil and plant properties.

Increasing concentration of pure micro- and macro-LDPE and PP plastic negatively affect crop biomass, nutrient cycling, and microbial biomass.

Plastic mulch films support global food security, however, their composition and the potential release rates of organic, metal and metalloid co-contaminants remains relatively unknown. This study evaluates the low molecular weight organic additives, metal and metalloid content and leaching from low density polyethylene (LDPE) and biodegradable plastic mulch films. We identified 59 organic additives, and non-intentionally added substances in the new LDPE films (39.8 mg m) and 60 in the new biodegradable films (129 mg m). The leaching of organic compounds of high concern for ecosystem and human health (e.g. phthalates, organophosphite antioxidants) was comparable to those of low concern (fatty acids, fatty amides, alkanols). However, the majority of leached compounds have undergone no regulatory scrutiny and their environmental fate and toxicity remain unknown. Leaching of heavy metals (Cu, Zn, Pb) was low relative to inert fillers (Ca, Na). Leaching was higher for both organic and metal/metalloid additives from the biodegradable films (74.6 mg m) than the LDPE films (23.7 mg m). This untargeted approach allowed assessment of the chemical burden posed to individual farms, based on existing use patterns of plastic mulch films, with higher chemical burden coming from biodegradable films, raising the potential for pollution swapping. This research emphasises the need to include the complex mixture of leached additives when assessing the environmental risks presented by plastic mulch films, balancing yield benefits with the protection of our agricultural soils.

Higher potential leaching of inorganic and organic additives from biodegradable compared to conventional agricultural plastic mulch film.

Artificial degradation is often used to recreate and accelerate the natural aging of plastic for small-scaled simulation experiments assessing their environmental impact. However, current artificial aging methods are rarely compared against reference materials or validated using field-aged samples, creating uncertainties when extrapolating results to naturally aged plastics, making it difficult to place findings in an environmentally applicable context. Therefore, here we compared four accessible, cost-effective, and easily replicable methods (heat, UVA, and UVC irradiance at two intensities) to produce artificially degraded materials. The artificial aging methods were assessed over a duration of 5 months against degradation rate, efficiency, and similarity to field-aged samples of conventional and biodegradable plastic mulch film over a 6-month field exposure period. We utilised attenuated total reflectance-Fourier transform infrared spectroscopy to calculate the carbonyl index and measure chemical changes of the mulch film surface, as well as differential scanning calorimetry and thermogravimetric analysis. Physical changes were assessed by thickness and surface roughness measurements. We found that UVA was the most suitable and realistic artificial degradation method at a medium rate, whilst UVC is recommended for rapid degradation without the need to simulate realistic changes, and heat for processing large volumes of samples without a requirement for realistic degradation over a prolonged time period. However, the methods compared in this study yielded differential results depending on polymer type and parameter of interest. We therefore recommend establishing the degradation aim, identifying the spectral region of interest, and accounting for different polymer types to select the most appropriate method.

Martine Graf

School of Environmental & Natural Sciences

Bangor University

Separation and Identification of Conventional Microplastics from Farmland Soils

Martine Graf

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Bangor University

Separation and Identification of Conventional Microplastics from Farmland Soils

School of Environmental & Natural Sciences