Assessing the risk from chemical contaminants in the Port Curtis Estuary, Australia

"The Port Curtis estuary is a heavy industrial centre and an international harbour. Sources of chemical stressors are many and multiple contaminants anre likely to be transported to the estuary by air and/or water. To assess whether contaminants are accumulating in the estuary and to identify those of potential concern in the Port Curtis estuary a screening level ecological risk assessment (SLERA) and a screening level human health risk assessment (HHRA) were performed." -- abstract.. The Port Curtis estuary is a heavy industrial centre and an international harbour. Sources of chemical stressors are many and multiple contaminants arelikely to be transported to the estuary by air and/or water. To assess whether contaminants are accumulating in the estuary and to identify those of potential concern in the Port Curtis estuary a screening level ecological risk assessment (SLERA) and a screening level human health risk assessment (HHRA) were performed. The basic risk assessment framework developed by the USEPA (1998) was applied in this study. Conceptual models were developed to assist with planning and design of the study. Assessment endpoints were chosen through consultations with experts and stakeholders. For the SLERA, the study area was divided into seven geographical zones. Existing water and sediment data were collated and data gaps identified. Additional data were gathered from two water and sediment surveys conducted by the CRC for Coastal Zone Estuary and Waterway Management. Al, As, Cd, Cu, Cr, Fe, Hg, Ni, Pb, Se, Zn, fluoride, cyanide, polycyclic aromatic hydrocarbons (PAHs) and tributyltin (TBT) were chemicals examined in the SLERA. Chemicals were measured in water and sediments, and in seagrass (Zostera capricorni), oysters (Saccostrea sp.), and mud whelks (Telescopium telescopium). For the HHRA, levels of Al, As, Cd, Cu, Cr, Fe, Hg, Ni, Pb, Se, and Zn were measured in fish and shellfish likely to be consumed by humans, namely, barramundi (Lates calcarifer), sea mullet (Mugil cephalus), mud crab (Scylla serrata) and banana prawns (Penaeus merguiensis) and TBT was measured in the edible flesh of mud crab. A compilation of all the data for the SLERA was assessed by comparing the observed water and sediment concentrations with water quality and sediment quality guidelines (ANZECC/ARMCANZ 2000) and comparing the observed contaminant concentrations in biota at study sites with benchmarks derived from concentrations in biota at control sites and the literature. It was found that concentrations of dissolved metals in waters of the Port Curtis estuary were low and below levels of regulatory concern. Concentrations of metals in sediments were also low, except for As, Cr and Ni. However, background concentrations of these metals were high. At some sites, As was higher than background levels, therefore As was included as a contaminant of potential ecological concern (COPEC). Tributyltin and naphthalene concentrations in water and/or sediments also exceeded guideline values and were identified as COPECs. Contaminants found to be enriched in biota in the estuary were Al, As, Cu, Cr, Fe, Hg, Ni, Se, Zn, and TBT. Possible adverse effects to the assessment endpoints from enrichment of metals in the Port Curtis estuary and from concentrations ofTBT and naphthalene in water/sediments were discussed. For the screening level HHRA, chronic daily intakes (CDIs) of contaminants by adults and children consuming seafood from this region were compared to threshold toxicity values set by regulatory agencies (ATSDR 2001). To account for additivity of other chemicals, a hazard quotient greater than 0.1 indicated contaminant of potential concern (COPC). It was found that Hg in barramundi from this region was a COPC. The inclusion of concentrations in biota was important in the SLERA of the Port Curtis estuary as several metals were accumulating to high concentrations in biota, but were not accumulating to high concentrations in water and sediments. The concentrations of metals in the dissolved form and/or in sediments were determined as being of low ecological risk. The ability of biota to integrate fluctuating concentrations of metals over time and to reflect exposure via dietary uptake meant the inclusion of concentrations in biota allowed a more thorough investigation of the exposure of biota to contaminants in the Port Curtis estuary.