Review and assessment of road-derived metals as a major contributor of metallic contaminants to urban stormwater and the estuarine environment (Sydney estuary, Australia).

Sydney Harbour (Australia). is one of the most metal-contaminated in the world and sediments are toxic over large areas. The major source of metals is stormwater, however there remains considerable debate regarding the source of metals in water entering the estuary. The current review and critical assessment of a large source of data accumulated from over three decades of research, supplemented by global studies, identified road-derived metals (RDMs) as the chief contributor of metals to stormwater and consequently to pollution of the estuary. Roads comprise almost 25% of a typical urban catchment and generate a considerable metal load from highly effective impervious surfaces and RDM is transported directly to the adjacent receiving basin with enhanced connectivity. In Sydney, industrial waste is delivered to the sewage system and is disposed of offshore, leaving RDM as a major contributor of metals to the stormwater system and estuarine environment. RDMs are modelled to be hazardous to the ecology and human health (carcinogenic and non-carcinogenic diseases) in the catchment environment driven by high metal concentrations, small size and elevated bioavailability. Remediation of RDMs is complex, requiring extensive knowledge and an experienced management team. The enormous potential for water re-use is often neglected.