FIGURE.1 Examples of plastics employed by erosion control engineering in China (a. Large-scale of plastic mesh mulching was performed to control soil erosion and reduce dust in river embankment; b. Use plastic mesh mulching to control soil erosion by a wind power project in hilltop; c. Use plastic mesh mulching to control slope erosion in road embankment; d. Use plastic mulching to reduce soil erosion and promote vegetation growth in engineering accumulation; e. Use planting bag to reinforcement river embankment; f. Use planting bag to restoration mine site; g. Use non-woven geotextile to control soil erosion in orchard terrace slope; h. Use plastic geocell as channel lining to control gully erosion; i. Use plastic net to promote vegetation restoration during a watershed management project).

2.2 Wide distribution in various landscapes

Recently, there has been a growing recognition of the significant impact of (micro)plastics pollution in terrestrial ecosystems, primarily due to their great potential to accumulate in large quantities (Rillig & Lehmann 2012; Chen et al., 2022). In particular, agroecosystems are coming into focus as a major entry point for microplastics in soil systems, where contamination might occur through different sources such as sludge amendment or plastic mulching (Chen et al., 2022). In contrast to microplastics in agricultural land, the presence of CEC plastics is widespread across diverse landscapes in China, owing to the extensive implementation of large-scale infrastructure and ecological restoration project. Thereby, these CEC plastics have permeated various ecological environments, including alpine regions, grasslands, forests, rivers, and wetlands. It is important to emphasize that certain ecological environments exhibit a heightened vulnerability compared to agricultural system, making them particularly susceptible to the wide-ranging consequences of CEC plastic contamination (Baho et al., 2021).

2.3 Higher degradation rate

Conventional plastic materials predominantly employed in the field of ECE are polyethylene (PE) and polypropylene (PP). These materials, renowned for their stability and durability, possess an extraordinary capacity to endure in the natural environment for extended durations, ranging from hundreds to even thousands of years. Nevertheless, it is worth noting that PE and PP in soils undergo a gradual process of degradation, progressively disintegrating into microplastics through the mechanisms of photodegradation, thermal degradation, and mechanical degradation (Chamas et al., 2020). While the degradation of plastic products during ECE was yet to be investigated, it is conceivable to predict a relatively elevated rate of degradation, influenced by the exposure to the surrounding environment and the occurrence of vigorous physical disturbances (Zhang et al., 2021). Firstly, the plastic products in ECE mainly work on the soil surface and the very top of soil matrix, thereby usually involve cracking, embrittlement, and flaking induced by ultraviolet (UV) irradiation from solar (Figure. 2). Secondly, the process of slope runoff and streamflow facilitates collisions and abrasions between plastics and rocky or sandy substrates. Furthermore, the disturbances caused by construction activities, such as engineering vehicle rolling and subsequent soil restoration efforts, directly contribute to the fragmentation of larger plastic fragments.

2.4 Prone to transport

Soil erosion is acknowledged as a key mechanism driving the horizontal transport of microplastics form land to aquatic ecosystems (Horton et al., 2017; Rehm et al., 2021). Larger plastic debris undergo a degradation and breakdown into smaller fragments, making them easily transport by wind and runoff due to their lightweight nature and their preferential distribution at the very top of soil matrix. It is worth noting that plastic products in ECE are usually work in erosion hotspots, such as slopes, riverbanks and gullies (Figure.2). Consequently, it can be predicted that the transport capacity of (micro)plastics in ECE will increase, and also augmenting their propensity to be conveyed to aquatic ecosystems, leading to extra pollution.