Preprints
https://doi.org/10.5194/soil-2021-70
https://doi.org/10.5194/soil-2021-70

  30 Aug 2021

30 Aug 2021

Review status: a revised version of this preprint is currently under review for the journal SOIL.

Are agricultural plastic covers a source of plastic debris in soil? A first screening study

Zacharias Steinmetz1, Paul Löffler1, Silvia Eichhöfer1, Jan David1, Katherine Muñoz2, and Gabriele E. Schaumann1 Zacharias Steinmetz et al.
  • 1iES Landau, Institute for Environmental Sciences, Group of Environmental and Soil Chemistry, University of Koblenz–Landau, Fortstraße 7, 76829 Landau, Germany
  • 2iES Landau, Institute for Environmental Sciences, Group of Organic and Ecological Chemistry, University of Koblenz–Landau, Fortstraße 7, 76829 Landau, Germany

Abstract. Agricultural plastic covers made from polyethylene (PE) and polypropylene (PP) offer increased yields and an improved crop quality. However, such covers are suspected of partially breaking down into smaller debris and thereby contributing to soil pollution with microplastics. To scrutinize this, we randomly sampled 240 topsoil cores (0–5 cm) from eight fields covered with fleeces, perforated foils, and plastic mulches for less than two years. Samples from the field periphery (50 m perimeter) served as reference. Visual plastic debris > 2 mm was analyzed by Fourier transformed infrared spectroscopy with attenuated total reflection (FTIR–ATR). Smaller, soil-associated plastic debris was dispersed from 50 g of fine soil (≤ 2 mm) using sodium hexametaphosphate solution and density-separated with saturated NaCl solution. The collected PE, PP, and polystyrene (PS) debris was selectively dissolved in a mixture of 1,2,4-trichlorobenzene and p-xylene at 150 °C and quantified by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). We counted six PE and PS fragments > 2 mm in two out of eight fields. By contrast, Py-GC/MS analysis revealed PE, PP, and PS contents > 1 µg g−1 in seven fields (17 % of all samples). In three fields, PE levels of 3–35 µg g−1 were associated with the use of thinner and less durable perforated foils (40 µm thickness). This was slightly more pronounced at field edges where the plastic covers are turned and weighted down. By contrast, 50 µm thick PE films were not indicated to emit any plastic debris. PP contents of 5–10 µg g−1 were restricted to single observations in the field centers of three sites. On one site, we found expanded PS particles >2 mm that concurred with elevated PS levels (8–19 µg g−1) in the fine soil. Both PP and PS were distributed indistinctly across sites so that their source remained unresolved. In addition, the extent to which plastic contents of up to 7 µg g−1 in the field periphery of some sites were attributed to wind drift from the covered fields or from external sources needs to be investigated in future studies. Yet, our results suggest that the short-term use of thicker and more durable plastic covers should be preferred to limit plastic emissions and accumulation in soil.

Zacharias Steinmetz et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on soil-2021-70', Anonymous Referee #1, 07 Oct 2021
    • AC1: 'Reply on RC1', Zacharias Steinmetz, 26 Oct 2021
  • RC2: 'Comment on soil-2021-70', Anonymous Referee #2, 09 Oct 2021
    • AC2: 'Reply on RC2', Zacharias Steinmetz, 26 Oct 2021

Zacharias Steinmetz et al.

Zacharias Steinmetz et al.

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Short summary
To scrutinize the contribution of agricultural plastic covers to plastic pollution, we quantified soil-associated plastic debris (< 2 mm) in and around agricultural fields covered with different plastic types. PP fleeces and 50 μm thick PE films did not emit significant amounts of plastic debris into soil during their four-month use. However, thinner and perforated PE foils (40 μm) were associated with elevated PE contents of up to 35 μg/g. Their long-term use may thus favor plastic accumulation.