Beyond Waste Utilization: Evidence Boundaries and Receiving-Soil Suitability for Phosphogypsum Land Application

Phosphogypsum (PG), a gypsum-rich by-product of wet-process phosphoric acid production, is increasingly considered for land application because it can supply calcium and sulfur and alleviate constraints such as sodicity, subsoil acidity, and vegetation establishment limitations. However, PG may also contain residual acidity, soluble salts, fluoride, heavy metals, and naturally occurring radionuclides, creating multiple exposure pathways. This critical review distinguishes direct PG evidence from gypsum or sulfate analogue evidence, life cycle assessment/material flow analysis evidence, and risk control studies. It evaluates PG land application according to receiving soil conditions, diagnosed constraints, exposure pathways, and environmental safety boundaries. The strongest evidence supports use in diagnosed sodic and saline–sodic soils, whereas applications in Al-toxic acid subsoils, flooded paddy systems, contaminated or degraded soils, and non-food vegetated systems require conditional assessment. PG should therefore be treated as a context-specific management option rather than an unrestricted disposal route. By linking waste valorization with soil demand, source quality, exposure control, and long-term monitoring, the proposed framework contributes to sustainability by integrating circular resource use with soil health, water protection, food/feed safety, and risk-informed governance, while helping to prevent the transfer of environmental burdens across ecosystems or generations.