Phosphorus-Associated Viral Indicators Override pH as Predictors of Heavy Metal Mobility in Urban Storm Drain Sediments

Urban storm drain sediments (SDSs) accumulate heavy metals from building façades and road surfaces, yet the biogeochemical controls governing metal mobility remain poorly understood. This study investigated biotic and abiotic controls on metal mobility along the urban dust transport chain (Xiamen-Quanzhou-Zhangzhou, China), using four sample types-façade dust (FD), road-deposited sediment (RDS), SDS, and runoff suspended solids (RSS)-from nine sites across three functional zones. Metal concentrations (Pb, Cu, Zn, Cr, Cd), phosphorus fractions, and microbial functional genes were quantified to test the hypothesis that viral abundance indicators, rather than pH, are more strongly associated with metal mobility in near-neutral urban sediments. Results showed that SDS served as metal accumulation hotspots with enrichment factors of 2.0-2.3× relative to FD, while total phosphorus declined by 34% along the transport chain. Contrary to conventional expectations, pH exhibited weak correlation with Pb mobility (r = -0.21; 95% CI: -0.62 to 0.27), whereas the T4-type bacteriophage gene <i>g23</i> showed strong positive correlation (r = 0.85, <i>p</i> < 0.01; 95% CI: 0.52-0.96). Partial least squares path modeling revealed that viral abundance (<i>g23</i> gene copies) showed the strongest statistical association with metal mobility among biotic variables (β = +0.48, <i>p</i> < 0.001), mediated through phosphorus-supported microbial activity. The model explained 76% of variance in metal mobility, with phosphorus cycling positively influencing viral abundance (β = +0.28). These findings challenge the pH-centric paradigm of metal geochemistry and reveal a novel phosphorus-virus-metal coupling mechanism in urban environments. The textile industrial site QZ-2 exceeded chromium screening values by 45%, demonstrating the framework's utility for pollution hotspot identification.