Driving factors and sources of microplastics in soils in the Yellow River source area

Microplastics (MPs) are widespread in various environments worldwide, they pose a serious threat to ecosystems. As a typical remote area, the Qinghai-Tibetan Plateau (QTP) has a sophisticated road system. However, the contributions of anthropogenic and natural factors to MP accumulation in remote plateau regions remain unclear. Here, we investigated the distribution, driving factors, and main sources of MPs in the source area of Yellow River on the QTP. MPs in soil showed an average abundance of (75.39 ± 49.16) items/kg, which was approximately 1-10³ lower than that in the lower sections of Yellow River. Film, transparent color, and polyethylene were the common shapes, colors, and polymers, respectively. Under different land uses, MP abundance was remarkably higher in nonagricultural soils than in farmland. The influencing factors, source analysis on the basis of MP characteristics, and statistical analysis (redundancy analysis and structural equation modeling) showed that MP abundance was influenced by nonagricultural activities (tourism, traffic, and grazing). Utilizing the conditional fragmentation model, we further revealed that MP abundance in the upstream and downstream regions was related to roadside dust (traffic) and atmospheric dust. It was associated with human activities, including plastic packaging waste from tourism and herdsmen, in the midstream region. Moreover, MPs in farmland were related to local sources (fertilizers). These results provide valuable information on MP distribution in headstream areas and thus contribute to controlling potential MP pollution on the QTP.