Plastic Mulch Films in Arid Agroecosystems: A Systematic Review of Microplastic Generation, Transport, and Impacts

Purpose and Rationale: Plastic mulch films are a transformative agricultural technology in arid and semi-arid regions, critically enhancing crop productivity by conserving soil moisture and suppressing weeds. However, their long-term use has led to an unintended and severe consequence: the pervasive contamination of agricultural soils with persistent plastic residues and microplastics (MPs). This research project will be conceived as a systematic review to address a critical knowledge gap. While individual studies have documented aspects of this pollution, a comprehensive, evidence-based synthesis linking agricultural practices to MP generation, their subsequent environmental transport, and their cascading impacts on soil health and ecosystem function in drylands is currently lacking. The overarching purpose will be to consolidate the rapidly growing but fragmented body of recent literature. This synthesis will aim to quantify the scale of the problem, elucidate the unique transport dynamics in arid environments, evaluate the long-term agronomic trade-offs, and critically appraise proposed mitigation strategies. Ultimately, the project will seek to provide a scientific foundation for policymakers, agricultural practitioners, and researchers to navigate the urgent challenge of reconciling food security with environmental sustainability in water-scarce regions. Research Objectives: This systematic review will be designed to achieve four interconnected objectives: (1) To quantify the relationship between specific agricultural practices (especially mulching duration and management) and the accumulation of MPs in dryland soils. (2) To elucidate the dominant transport mechanisms (e.g., wind erosion, irrigation runoff) responsible for redistributing MPs from agricultural fields into adjacent atmospheric, aquatic, and groundwater compartments. (3) To assess the multifaceted impacts of MP accumulation on key indicators of soil health, including physicochemical properties, biological community structure and function, and ultimately, crop productivity. (4) To evaluate proposed mitigation strategies, such as biodegradable mulches and improved film recovery, and identify critical persisting knowledge gaps to inform sustainable policy and practice. Methodology: The project will adhere to the highest standards of evidence synthesis by following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) 2020 guidelines. The methodology will involve: (1) Systematic Search: A comprehensive search will be conducted across major scholarly databases (Scopus, Web of Science, PubMed) and Google Scholar for peer-reviewed literature, using a defined string of keywords related to plastic mulch, microplastics, and arid agriculture. (2) Rigorous Screening & Selection: Identified records will be imported into Covidence software for deduplication and a two-stage screening process (title/abstract, then full-text) based on pre-defined PICOS (Population, Intervention, Comparator, Outcome, Study Design) eligibility criteria. (3) Standardized Data Extraction: Data from included studies will be extracted into a standardized form, capturing details on study design, location, MP characteristics, measured impacts, and mitigation factors. (4) Quality Appraisal: The methodological quality of each included study will be rigorously assessed using the Newcastle-Ottawa Scale (NOS) adapted for cross-sectional studies, ensuring the synthesis is based on robust evidence. Expected Outcomes and Findings: Based on the preliminary scope of work, the project is expected to yield the following key outcomes: (1) A Quantified Source-Pathway: The review will provide clear evidence on whether plastic mulching acts as a primary source of specific polymers (e.g., polyethylene) and will model the relationship between mulching duration and MP accumulation in soil. (2) A Dynamic Transport Model: It will synthesize evidence to confirm and characterize how arid conditions facilitate significant MP redistribution via pathways like wind erosion and irrigation runoff, linking farm-scale practices to broader environmental contamination. (3) An Impact Assessment: The synthesis will document the effects of MP accumulation on soil structure, hydraulic properties, microbial communities, and crop productivity, evaluating the existence of a critical "trade-off" between short-term benefits and long-term soil degradation. (4) A Critical Mitigation Roadmap: The review will evaluate the proposed efficacy of mitigation strategies like biodegradable mulches and will identify critical persisting knowledge gaps regarding their performance, ecological impacts, and socio-economic barriers to adoption. Significance and Impact: This research project will provide a seminal, integrated analysis of the mulch-derived MP pollution crisis in dryland agriculture. Its significance is threefold: (1) For Science: It will synthesize disparate findings into a coherent narrative, establish an integrated understanding of transport mechanisms for arid regions, and definitively chart priority areas for future primary research. (2) For Policy and Practice: The findings will serve as a crucial evidence base for developing regulations on plastic use, informing agricultural extension services about sustainable practices, and designing economic instruments that account for the hidden environmental costs of plastic mulch. (3) For Global Sustainability: The project will directly contribute to achieving United Nations Sustainable Development Goals (SDGs) related to Zero Hunger (SDG 2) and Life on Land (SDG 15) by highlighting the need to protect soil health, the fundamental capital of food systems, from anthropogenic plastic pollution.