Simultaneous assessment of particle and dissolved emerging road pollutants in roadside retention ponds under baseflow conditions

Particle road pollutants (tyre and road wear particles [TRWPs] and road lining paint fragments) and dissolved chemicals (tyre and plastic-related additive chemicals) are emerging aquatic contaminants. Roadside retention ponds are key pathways for their transport. However, studies focus on pollutant influx during storm events. Baseflow conditions between storm events in drainage systems with continuous flow (e.g., in temperate climates) need investigated. Therefore, two retention pond systems alongside a trunk road were monitored during summer and winter baseflow conditions. Particle concentrations (> 50 µm) in inlet water were 0.8 – 18.0 TRWPs/L and 0.1 – 16.0 paint particles/L demonstrating mobility in the road drainage system outside storm conditions. Four additive chemicals in inlet water were ≤ 0.1 µg/L except dimethylphthalate which reached 1.3 µg/L. Inlet pollutant concentrations were considerably lower than observed in stormwaters. Concentrations were similar between summer and winter sampling, but greater winter baseflows increased pollutant mobilisation and loading (≤ 9.5 times). Pollutant presence in pond outlet waters revealed incomplete removal. Sediment profiling demonstrated particle retainment and longer-term trends with slip roads increasing TRWPs and painted rumble strips increasing paint particles. Concentrations were ∼ 1.0 × 106 particles/kg dry weight. Twenty-one additive chemicals were present including N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine-quinone up to 55 µg/kg, which was not detected in water. Hazard quotients were significant (> 1) for 11 chemicals in sediments compared to one (hexamethoxymethylmelamine) in water. Findings demonstrate baseflow monitoring of retention ponds between storm events is essential to better assess the fate of road pollutants and chronic exposure of aquatic organisms.