Lagrangian ocean analysis, where virtual parcels of water are tracked through hydrodynamic fields, provides an increasingly popular framework to predict the dispersal of water parcels carrying particles and chemicals. We conduct the first direct test of Lagrangian predictions for emerging contaminants using (1) the latitude, longitude, depth, sampling date, and concentrations of UV filters in raft cultured mussel ( Mytilus galloprovincialis) of the estuary Ria de Arousa, Spain (42.5°N, 8.9°W); (2) a hydrodynamic numerical model at 300 m spatial resolution; and (3) a Lagrangian dispersion scheme to trace polluted water parcels back to pollution sources. The expected dispersal distances (mean ± SD) are 2 ± 1 km and the expected dispersal times (mean ± SD) are 6 ± 2 h. Remarkably, the probability of dispersal of UV filters from potential sources to rafts decreases 5-fold over 5 km. In addition to predicting dispersal pathways and times, this study also provides a framework for quantitative investigations of concentrations of emerging contaminants and source apportionment using turbulent diffusion. In the coastline, the ranges of predicted concentrations of the UV-filters 4-methylbenzylidene-camphor, octocrylene, and benzophenone-4 are 3.2 × 10-4 to 0.023 ng/mL, 2.3 × 10-5 to 0.009 ng/mL, and 5.6 × 10-4 to 0.013 ng/mL, respectively. At the outfalls of urban wastewater treatment plants these respective ranges increase to 8.9 × 10-4 to 0.07 ng/mL, 6.2 × 10-5 to 0.027 ng/mL, and 1.6 × 10-3 to 0.040 ng/mL.