Environmental toxicology requires spatially resolved chemical evidence because contaminants are retained, transformed and expressed unevenly across tissues, roots, biofilms, sediment interfaces and particle-contact zones. Mass spectrometry imaging (MSI) can provide this evidence only when the ionization modality matches the contaminant class, the spatial scale of interest and the chemical claim being made. This study defines Spatial Toxicant–Modality Concordance (STMC), a class-resolved analytical method for selecting primary and confirmatory MSI platforms for organic, inorganic and particulate pollutants. The calculation uses five instrument routes–MALDI, LDI, SIMS, DESI and LA-ICP-MS–and nine pollutant subclasses: pharmaceutically active compounds, plastic additives, industrial chemicals, personal care products, pesticides, heavy metals, micro- and nanoplastics, particulate matter and engineered nanoparticles. Five modality attributes are scored: spatial granularity, molecular compatibility, quantitative confidence, operational simplicity and contaminant-class concordance. The resulting class scores identify a clear modality switch: MALDI ranks first for organic pollutants at 0.80, LA-ICP-MS ranks first for heavy metals at 0.83, and SIMS ranks first for particulate pollutants at 0.86. LDI provides a matrix-free route for selected surface and low-mass organic questions, whereas DESI is best used for rapid ambient screening. STMC strengthens environmental analytical chemistry by tying pollutant images to the specific molecular, elemental or fragment evidence that each platform can support.