Solid-Embedded Microplastics from Sewage Sludge to Agricultural Soils: Detection, Occurrence, and Impacts

Microplastics (MPs) have been increasingly identified as a global concern because of their ubiquitous distribution and the threats they pose. MPs embedded in the solid matrix remain an underexplored field compared to MPs in aquatic environments. This review focuses on solid-embedded MPs in a binary system consisting of sewage sludge and agricultural soils, which are interconnected through land application of sewage sludge to agricultural soils. The detection, occurrence, and impacts of MPs were summarized for sewage sludge and agricultural soils. Specifically, the latest techniques for detecting solid-embedded MPs are summarized and compared. The occurrence of MPs is presented from three aspects, i.e., the origin, transformation, and properties. Lastly, the impacts of solid-embedded MPs on sewage sludge treatment processes and the agroecosystem are reviewed. As a cutting-edge overview of the current knowledge, this review proposes key challenges to be further investigated with respect to solid-embedded MPs, including a uniform detection procedure, worldwide monitoring programs, rigorous assessments of potential risks, and mitigation measures through collaborative efforts by related liable parties.