Exposure States, Environmental Fate, and Functional Effects of Microplastics in Soil: Bibliometric Mapping and Critical Mechanistic Synthesis.

Reported effects of microplastics in soil vary with particle properties, exposure conditions, and measured endpoints. We combined bibliometric mapping with a critical mechanistic synthesis to examine these differences. A 3200-record Web of Science Core Collection corpus was tested against broad (4787) and title-strict (2375) sensitivity corpora. A year-stratified manual relevance audit judged 115 of 120 sampled records (95.8%) to be in scope. An article-only subset of 2756 records retained positive directions for all twelve principal title-concept trends and preserved 112 of 119 primary co-citation nodes. Twelve title concepts increased consistently across corpus definitions and start years, led by plant and crop performance, biodegradable plastics, and aging and weathering. Only co-contamination and nitrogen cycling remained significant under every robust model specification. The mechanistic synthesis indicates that differences in particle state, soil-mediated contact, endpoints, and inferential scope can contribute to apparently contradictory findings. We propose an exposure-to-function framework that integrates exposure descriptors with a bounded sequence linking particle characterization, fate and biological contact, process change, functional consequences, and persistence or recovery. Risk and management claims should remain within the links supported by evidence.