Old meets new: How emerging contaminants reshape the environmental behavior of legacy contaminants in soils-interaction mechanisms, remediation reassessment, and the regulatory role of soil organic matter.

Abstract

Microplastics, per- and polyfluoroalkyl substances (PFAS), and antibiotics coexist in soils with legacy metal(loid)s, polycyclic aromatic hydrocarbons (PAHs), and pesticides. These mixtures can alter contaminant fate, microbial selection, and remediation performance, but direct soil evidence remains uneven. This review synthesizes studies mainly from 2015 to 2025, earlier work, and selected early-online papers through June 2026. Soil evidence supports microplastic interactions with metals and PAHs; PFAS-metal evidence remains limited, mainly to retention. Antibiotic-metal evidence primarily concerns resistance co-selection rather than altered metal fate. We organize candidate processes into overlapping diagnostic tiers (physical co-location, interfacial chemical coupling, and biologically mediated feedback) and appraise evidence by study design, environmental relevance, mechanistic support, and risk of bias. A comparative map specifies required observations, alternative explanations, endpoint direction, and direct-evidence confidence. Concentration addition, independent action, and the combination index apply only to commensurable toxicological dose-response endpoints; transport, speciation, accumulation, and resistance require factorial or response-surface analyses. HIX, SUVA254, and PARAFAC components remain conditional dissolved organic matter proxies requiring method controls and independent validation. We classify remediation conclusions as direct mixture evidence, transferred single-contaminant principles, or author recommendations. The synthesis separates established findings from provisional interpretations.