The production of plastic reached 368 million tons in 2019 due to its widespread use (PlasticEurope, 2020) In Europe, an average of 60 million tons of plastic is produced every year, and 27 million tons of this is stored as waste in landfills (WWF, 2018). As of the end of 2020, the total plastic production in Turkey was approximately 9.54 million tons, of which 8.4 million tons were consumed domestically (PAGEV, 2021). Excessive consumption of plastic also causes a significant amount of plastic waste. It is estimated that approximately 32 million tons of municipal waste were produced in Turkey in 2018, of which approximately 10% was plastic (Gündoğdu and Walker, 2021)
Plastic waste in the environment may undergo degradation and decomposition due to physical, chemical, and biological factors. Recent studies have revealed that many plastics, including plastics reported as biodegradable, break down into smaller fragments rather than decompose (Barnes et al., 2009; de Souza Machado et al., 2018). Therefore, plastics larger than 5 mm, turn into particles smaller than 5 mm, often called microplastics (MP), due to the aforementioned factors. MPs can also be released directly into the environment as micro-sized particles designed for various purposes (e.g. resin pellet, microbead, etc.). MPs were first reported in the Sargasso sea by (Carpenter and Smith, 1972). Since this first report, early studies have mainly focused on the marine and freshwater environments. It is now widely known that MPs now can be found in all ecosystems (including, air, water and soil), personal care products, table salt and seafood (Dehghani et al., 2017; Duis and Coors, 2016; Gündoğdu, 2018; Gündoğdu et al., 2021, 2020; Gündoğdu and Çevik, 2017; Lusher et al., 2018). Although most of the information we have about MP pollution today is from aquatic environments, in the last ten years, the number of MP studies that have focused on terrestrial environments has increased (Bläsing and Amelung, 2018; Büks and Kaupenjohann, 2020; Schell et al., 2021). Even with this increase, little is still known about the abundance and impact of MPs in soils, and in particular, within agricultural settings.
The use of plastics in agriculture has increased significantly in recent years (Maraveas, 2020). Plasticulture practices are varied and for a multitude of purposes, including improving crop productivity, animal nutrition, water use, and reducing food losses. For example, mulching films are used in crop production to suppress weed growth, increase soil temperatures, reduce topsoil and nutrient losses, and reduce soil water evaporation after heavy rainfall (Adhikari et al., 2016; Li et al., 2021). These factors increase crop yields, extend the growing season, and reduce the need for irrigation as well as fertilizer and herbicide applications. However, plastic mulch films are also known to be a significant source of macro and microplastic pollution. Their widespread and long-term use, coupled with a lack of systematic collection and management, has led to their accumulation in the soil (Ren et al., 2021). Soil pollution caused by micro and nanoplastics is not limited to mulching films. Disposable irrigation pipes, fruit protection films, and empty agrochemical containers that are poorly managed and abandoned on farms also contribute to agricultural plastic pollution. Büks and Kaupenjohann (2020) state that soils, where plastic-containing agricultural applications are made, contain significant MP residues. The low-tunnel greenhouse plastic films are an important source of MP in arable soils (Huang et al., 2020). This thin-film type plastic (8-50 µm thick polyethylene) is thought to be unaffected by biodegradation processes and therefore, limiting entry to the soil (Qi et al., 2020a; Steinmetz et al., 2016). The use of sewage sludge as a source of organic matter and effluent water for irrigation risks mixing micro and nanoplastics into agricultural soils, as all wastewater treatment plants do not effectively remove these particles. MPs in soil threaten human and ecosystem health due to their potential to bioaccumulate in the food web. MPs also risk carrying other pollutants such as pesticides that enter the food chain and harm human and environmental health. MP accumulation in agricultural soil affects soil water holding capacity, soil aggregation, performance, and composition of soil microbial community, soil fauna, and flora which can affect agricultural productivity (Büks et al., 2020; de Souza Machado et al., 2018; Fei et al., 2020; Lehmann et al., 2019; Rillig et al., 2019). MPs also affect organisms that live within and are reliant on the soil environment including earthworms, snails and soil nematodes (Lei et al., 2018; Song et al., 2019; Wang et al., 2019).
Plastic applications in agricultural activities are escalating in Turkey as well as all over the world. According to PAGEV (2020), 382 thousand tons of plastic produced by Turkey as of 2020, is used for agricultural purposes, with the primary application types being greenhouse and disposable drip irrigation piping. Turkey ranks in the top four in the world in greenhouse cultivation, and ranks second in Europe after Spain (Tüzel et al., 2020). Turkey's total greenhouse area has reached 77209.1 ha as of 2018. The low plastic tunnel application is 27.36% of the total greenhouse area (Tüzel et al., 2020). It is worth noting that plastic material in greenhouse applications is relatively high, especially for low tunnel applications. Although there is not enough data, it can be proposed that disposable drip irrigation pipe applications are also increasing in parallel with greenhouse cover applications. This is the first study to quantify MPs from greenhouse covers and irrigation piping conducted on agricultural soils in Turkey. The purpose of this study was to investigate the abundance of MPs in agricultural soils, specifically those that originated from greenhouse cover plastics and disposable drip irrigation pipes.
This study aims to investigate the following hypotheses: both greenhouse films and disposable irrigation pipes (GFSUP) usage causes MP pollution in the soils; removal of plastics after use affects both the number and the size of MPs originated from GFSUP in the soil. The results aim to guide farmers and decision-makers in better managing the MP pollution in the fields and further the understanding of the behavior of plastics in GFSUP applied agricultural soils.