Metal and polycyclic aromatic hydrocarbon contaminants in benthic sediments of Port Curtis

In this study funded by the Coastal CRC, benthic surficial sediments and sediment cores from Port Curtis were analysed for 10 metals and 17 polycyclic aromatic hydrocarbons (PAHs). The concentrations were compared to the ANZECC (2000) interim sediment quality guidelines. The intertidal (mangrove) sediments tended to collect fine sediments, which contained higher levels of metals and PAHs than did estuarine sediments. The top 28 cm of subsurface sediments at intertidal or subtidal sites were estimated to have been deposited since 1958 in Port Curtis, which is roughly the start of the industrialisation of Gladstone. The rate of sediment deposition was at least 0.6 cm/yr. The sediment depositional zones were demonstrated to be largely at the intertidal (mangrove) sites, particularly at the northern Narrows, lower Calliope River and South Trees Inlet-Boyne River areas. Sediment cores exhibited fairly constant metal concentrations with depth. Stable Lead isotope ratios suggested generally low Lead contamination in the region. ANZECC (2000) trigger values for Nickel, Arsenic and Chromium were exceeded in many sediment samples. Background metal levels were established using regression models. Concentrations of Nickel, Arsenic and Chromium appeared to have local geological sources, with the estimated natural levels being fairly close to their respective ANZECC (2000) trigger values. This is important to remember when undertaking sediment quality assessments. PAHs from combustion or pyrolytic sources were dominant around intertidal sites along the industrial area of Gladstone, particularly at the Clinton Coal Facility, near the industrial areas (eg QAL-Red Mud Dam outlet and Calliope River near NRG power station) and at the Gladstone Marina. Perylene, a naturally-occurring PAH, dominated sediments in the northern Narrows. Several other types of PAHs were detected, some of pyrolytic sources. Naphthalene levels were below 5 μg/kg, in contrast to high levels (exceeding the ANZECC guideline of 160 μg/kg) reported in 2000. Port Curtis may be considered as still a relatively low to moderately polluted estuary. It would be important to monitor changes in levels of the metal and PAH contaminants and their ecological impacts in the estuary, especially with the continuing rapid industrialisation of Gladstone and the expansion of port activities in the harbour.