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Plastics in soil: municipal compost possible major entry path

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  • At least 300 million tons of plastic are produced annually, from which large parts end up in the environment, where it persists over decades, harms biota and enters the food chain. Yet, almost nothing is known about plastic pollution of soil.
  • Soils may receive plastic inputs via plastic mulching or the application of plastic containing soil amendments.
  • In compost up to 2.38–1200 mg plastic kg−1 have been found so far. Compost, especially of municipal origin, must be considered as a serious entry path of plastic in soil.

Highlights

•Analytical methods and possible input pathways of plastic in soil were discussed.
•Organic matter challenges plastic quantification in soil.
•Soil amendments and irrigation are likely major plastic sources in agricultural soils.
•Flooding, atmospheric input and littering can potentially pollute even remote soil.
•Leaching of small plastics from soil into groundwater cannot be excluded

Abstract

At least 300 Mio t of plastic are produced annually, from which large parts end up in the environment, where it persists over decades, harms biota and enters the food chain. Yet, almost nothing is known about plastic pollution of soil; hence, the aims of this work are to review current knowledge on i) available methods for the quantification and identification of plastic in soil, ii) the quantity and possible input pathways of plastic into soil, (including first preliminary screening of plastic in compost), and iii) its fate in soil. Methods for plastic analyses in sediments can potentially be adjusted for application to soil; yet, the applicability of these methods for soil needs to be tested. Consequently, the current data base on soil pollution with plastic is still poor. Soils may receive plastic inputs via plastic mulching or the application of plastic containing soil amendments. In compost up to 2.38–1200 mg plastic kg− 1 have been found so far; the plastic concentration of sewage sludge varies between 1000 and 24,000 plastic items kg− 1. Also irrigation with untreated and treated wastewater (1000–627,000 and 0–125,000 plastic items m− 3, respectively) as well as flooding with lake water (0.82–4.42 plastic items m− 3) or river water (0–13,751 items km− 2) can provide major input pathways for plastic into soil. Additional sources comprise littering along roads and trails, illegal waste dumping, road runoff as well as atmospheric input. With these input pathways, plastic concentrations in soil might reach the per mill range of soil organic carbon. Most of plastic (especially > 1 μm) will presumably be retained in soil, where it persists for decades or longer. Accordingly, further research on the prevalence and fate of such synthetic polymers in soils is urgently warranted.

Melanie Bläsing and Wulf Amelung. Plastics in soil: Analytical methods and possible sources. Science of The Total Environment Volume 612, 15 January 2018, Pages 422-435

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