Specific objectives of the contaminants component of the North West Shelf Joint
Environmental Management Study were to:
Establish an inventory of contaminant inputs (nutrients and toxicants) from all known point and diffuse sources;
Review the pathways, fates and bioavailability of the contaminants of concern
in the water, sediments and biota;
Establish environmental quality criteria to assess environmental health and provide early indications of environmental degradation; and
For the contaminants of concern, collate and evaluate the applicability of
available toxicological data, and if necessary develop acute and chronic toxicity data using local marine indicator species.
The North West Shelf (NWS) has been subject to inputs of contaminants (toxicants and nutrients) from a variety of point and diffuse sources over the last 35 years. The various types of contaminants behave differently and can have different effects depending on their loads to, and concentrations in, the environment. Effective environmental management relies on an understanding of the types and quantities of wastes discharged, the sources of those discharges and their environmental consequences viewed individually and from a cumulative perspective, and considering both acute and chronic effects.
An electronic database of annual loadings of point source contaminants discharged into NWS waters has been compiled for the period 1985 to 2001. The contaminants include toxicants such as heavy metals and petroleum compounds and nutrients such as nitrogen. Concentrations of heavy metals in the waters surrounding the offshore petroleum facilities were lower than the highest level of protection specified in the ANZECC & ARMCANZ (2000) guidelines. There are significant discharges of heavy metals from the Parker Point Power Station where the annual loads in 2000 range from 252 kg/yr for cadmium to 8 145 kg/yr for zinc. There appears to be no data on the concentration levels of these metals in the waters or the sediments surrounding the discharge sites.
In 2000, 12 million tonnes of produced formation water containing 214 tonnes of oil was discharged from nine offshore petroleum facilities. This compares with an estimated 3,300 tonnes of oil naturally seeping into NWS waters. Few studies of the fates and effects of petroleum-based compounds have been undertaken on the NWS. These studies report no acute effects, but suggest that chronic and sub-lethal effects on marine plankton and bacteria have occurred in the vicinity of some of the production platforms. Concentrations of the antifouling chemical, tributyltin (TBT), were found in coastal waters of the Dampier Archipelago to be at levels ranging from 0.003 to 0.025 μg/L.
In chapter 3 we review what is known about fates, pathways and potential bioavailability for the key contaminants of concern identified as part of the contaminants inventory and the review of toxicological data (chapter 4). These contaminants were identified as: six metals; barium, cadmium, chromium, copper, lead, mercury and zinc; one organometalloid: tributyltin (TBT); one nutrient: nitrogen; a waste stream; produced formation waters (PFW); and hydrocarbons (oil).
The results of the water quality study indicate that the coastal waters of the North West Shelf are generally of very high quality. The concentrations of metals were low by world standards, with localised elevations of some metals adjacent to industrial centres and ports. No organic chemicals were detected. The reporting limits were well below the guideline trigger values recommended in ANZECC & ARMCANZ (2000) for a very high level of ecological protection for the five organics for which guideline values were available.
The findings of this study suggest that ANZECC & ARMCANZ (2000) 99% species protection guidelines are relevant to the region for all metals analysed, except cobalt, for which the 95% species protection guideline is recommended for u
