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.