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 ...

Wageningen University & Research

Plastic pollution is one of the global pressing environmental problems, threatening the health of aquatic and terrestrial ecosystems. However, the influence of plastic residues and microplastics (MPs) in soil ecosystems remains unclear. We conducted a global meta-analysis to quantify the effect of plastic residues and MPs on indicators of global soil ecosystem functioning (i.e. soil physicochemical properties, plant and soil animal health, abundance and diversity of soil microorganisms). Concentrations of plastic residues and MPs were 1-2700 kg ha and 0.01-600,000 mg kg, respectively, based on 6223 observations. Results show that plastic residues and MPs can decrease soil wetting front vertical and horizontal movement, dissolved organic carbon, and total nitrogen content of soil by 14%, 10%, 9%, and 7%, respectively. Plant height and root biomass were decreased by 13% and 14% in the presence of plastic residues and MPs, while the body mass and reproduction rate of soil animals decreased by 5% and 11%, respectively. However, soil enzyme activity increased by 7%441% in the presence of plastic residues and MPs. For soil microorganisms, plastic residues and MPs can change the abundance of several bacteria phyla and families, but the effects vary between different bacteria.

Effects of plastic residues and microplastics on soil ecosystems: A global meta-analysis.

Microplastics (MPs) pollution is becoming one of the most pressing environmental issues globally. MPs in the marine, freshwater and terrestrial environments have been fairly well investigated. However, knowledge of the atmospheric-mediated deposition of MPs within rural environments is limited. Here, we present the results of bulk (dry and wet) atmospheric MPs deposition in a rural region of Quzhou County in the North China Plain (NCP). Samples of MPs in the atmospheric bulk deposition were collected for individual rainfall events over a 12-month period from August 2020 to August 2021. The number and size of MPs from 35 rainfall samples were measured by fluorescence microscopy, while the chemical composition of MPs was identified using micro-Fourier transform infrared spectroscopy (μ-FTIR). The results showed that the atmospheric MPs deposition rate in summer (892-75,421 particles/m/day) was highest compared to 735-9428, 280-4244 and 86-1347 particles/m/day in spring, autumn, and winter, respectively. Furthermore, the MPs deposition rates in our study were 1-2 orders of magnitude higher than those in other regions, indicating a higher rate of MPs deposition in the rural region of the NCP. MPs with a diameter of 3-50 μm accounted for 75.6 %, 78.4 %, 73.4 % and 66.1 % of total MPs deposition in spring, summer, autumn, and winter, respectively, showing that the majority of MPs in the current study were small in size. Rayon fibers accounted for the largest proportion (32 %) of all MPs, followed by polyethylene terephthalate (12 %) and polyethylene (8 %). This study also found that a significant positive correlation between rainfall volume and MPs deposition rate. In addition, HYSPLIT back-trajectory modelling showed that the farthest source of deposition MPs may have come from Russia.

Atmospheric deposition of microplastics in a rural region of North China Plain.

The macroplastics (MaPs) and microplastics (MiPs) polluting agricultural soils raise great concerns. Unfortunately, scientists know little about the occurrence of MaPs/MiPs in soil among different farming systems. In this study, we analyzed MaPs/MiPs in soils (0-30 cm) collected from six different farming systems (wheat-maize rotations, cotton, vegetables, permanent orchards, greenhouses with and without mulching) in Quzhou county, the North China Plain, by using fluorescence microscope and micro-Fourier transform infrared spectroscopy. The results showed that the abundance of MaPs and MiPs ranged from 0.2 to 46.8 kg ha, and 4.1 × 10-3.7 × 10 items kg, respectively. The prominent colors of the MaPs were white and black. The predominant shape, size and chemical composition of soil MiPs were fragments (45-62%), <1 mm (98-99%), and polyethylene (38-43%), respectively. MaPs were mainly detected in the 0-10 cm soil layer. MiP abundance in the 0-10 cm soil layer was significantly higher than that in the 20-30 cm soil layers among different farming systems, except for the fields with wheat-maize rotations and permanent orchards (p < 0.05). Overall, cotton fields showed the highest MaP and MiP abundance, followed by vegetable fields and orchards. Redundancy analysis revealed that tillage practices and plastic film management greatly influence the size distribution of MiPs. A strong negative correlation between large-sized plastic fractions (0.2-1 mm) and tillage frequency was tested while the years of application of plastic films and the abundance of plastic residues showed a strong positive correlation with small-sized plastic fractions (<0.2 mm). Our findings conclude that agricultural mulch films are an important source of MaPs and MiPs in agricultural soil and distributions are strongly influenced by agricultural management practices and farming systems. Further studies should take farming systems and farming practices into account, thereby exploring the potential mechanisms of plastic fragmentation and granularization in agricultural soil.

Hanyue Zhang

Soil Physics and Land Management Group

Wageningen University & Research

Separation and Identification of Conventional Microplastics from Farmland Soils