Fates of selenium and other metals in estuarine lakes receiving inputs from coal-fired power stations, NSW, Australia

Abstract

In New South Wales (NSW), on the east coast of Australia bordered by the Pacific Ocean, the existence of major coal deposits close to the estuaries has led to a history of coal-fired power station activities in the area and metal inputs in to these estuaries. The purpose of this study was to measure and understand inputs and fate of selenium and other metals from nearby coal-fired power stations. The study focuses on three lakes in NSW, Lake Macquarie, Lake Budgewoi and Lake Illawarra. Previous studies provide evidence of high metal concentrations in sediment and biota in these lakes. In this thesis, selenium, copper, zinc, arsenic, cadmium and lead concentrations in sediment from the three lakes were measured to determine the extent of metal inputs from the power stations. The full selenium cycle has not been completely characterised in Australian marine ecosystems, information needed for management plans. A major focus of this thesis, therefore, was to characterise the cycling of selenium in Lake Macquarie which has the highest selenium sediment concentrations of the three lakes studied. Metals and metalloids, for convenience, are referred to as metals in this study. Of the three lakes, Lake Macquarie has the highest metal concentrations in sediments from input of metals from two coal-fired power stations and because of its embayments which enable concentration of metals in sediments. Metal concentration profiles from sediment cores collected in the three lakes correlated well with historical industrial development, with the exception of arsenic and selenium due to their mobility over a wide range of redox conditions. Ash handling procedures at power stations in Lake Macquarie have shown to be efficient in reducing metal inputs to the sediments. Metal concentration in Lake Illawarra sediment samples close to Tallawarra Power Station are low as a result of its location in an open area of the lake allowing metals to disperse to below background levels. Port Kembla industrial activity, located in Griffins Bay, is the main source of metals to the lake and has generated high sediment metal concentrations. In addition, Windang Peninsula, an area where copper slag from Port Kembla industries was stock piled, was found to be an important source of metals. Lake Budgewoi was the lake with lowest sediment metal concentrations and metal concentrations are correlated with power stations activities in the lake. Some Lake Macquarie and Lake Illawarra sediment metal concentrations are above the Australian and New Zealand sediment quality guidelines high trigger values, while Lake Budgewoi sediments were under these threshold limits. A seagrass ecosystem in Lake Macquarie, which had the most significant levels of selenium, was analysed for selenium bioaccumulation and biomagnification. Selenium concentrations in organisms from Lake Macquarie are greater than other Australian estuaries, but are considerably lower than selenium concentrations in organisms in aquatic ecosystems in the USA, Canada and elsewhere in the world due to low metal concentrations in Australian coal. Selenium biomagnification is occurring in this ecosystem. The high potential for selenium to enter Lake Macquarie food webs is a result of long water residence time which enables selenium partitioning to particulate material. Habitat and feeding zone were found to be important factors influencing selenium bioaccumulation in invertebrates, while feeding zone only influenced vertebrates. These results demonstrated that invertebrates are accumulating selenium both via body absorption and diet, while vertebrates are bioaccumulation selenium mainly via diet. The fish Sillago maculata is the only species with selenium concentrations above the Food Standards Australia New Zealand (FSANZ) general expected level (GEL) guidelines of 6.6 μg/g dry mass for human consumption. Other metals, including copper, zinc, arsenic, cadmium and lead, are accumulated by organisms of the Lake Macquarie seagrass food web, but they are not being biomagnified through food chains. Omnivores and detritivores-suspension feeders were the organisms with the highest metal concentrations, with the exception of lead and arsenic which was higher in plants and algae. This difference in metal concentrations per feeding group is related to differences in regulation mechanisms and physiology. Feeding zone influences arsenic accumulation for both invertebrate and vertebrate organisms. Metal concentration patterns within groups were species-specific and indicate the importance of measuring metal concentrations at the species level. Arsenic, zinc and copper concentrations in biota were detected above the maximum level (ML) recommended by the FSANZ. No maximum limits of these metals has been developed in regards of the health of the animals themselves, showing the urgent need for a risk assessment of metal on organisms of Lake Macquarie food web for ecosystem health and for human consumption. A method was developed to measure volatile selenium fluxes in Morisset Bay, in Lake Macquarie, to comprehend the magnitude of losses of volatile selenium to the atmosphere. The system was designed to sample water incubated in domes placed in sediments of Morisset Bay. Lake water samples were then purged for 30 min at 100 mL/ L helium flow and moisture removed using a Teflon water trap at -30º C. A cryogenic trap absorbed and Introduction concentrated the selenium and a heating system was used to release the selenium species to be measured by Atomic Fluorescence Spectrometry. DMSe was the only volatile selenium species found in waters from Lake Macquarie, with DMDSe measurements below the detection limit of ~1 ng/L or 4 ng/ m2/ h. A preliminary estimation has indicated an annual flux of around 24 kg/ year of volatile selenium from Lake Macquarie. Overall, these data suggest that selenium and other inputs metal have been decreasing in the sediments of Lake Macquarie and that improved ash handling procedures have reduced metal inputs to this estuarine lake. Selenium was shown to have potential to enter food webs. Physiological effects of selenium exposure should be further studied to understand the toxic effects in the wildlife of Australian Ecosystems. Volatilization of selenium by bacteria is a potential removal mechanism of selenium from the lake and the method developed in this study should be applied in more comprehensive studies to further understand the volatilization of selenium species.

Date of Award	2014
Original language	English
Supervisor	Bill Maher (Supervisor), Bernd GRUBER (Supervisor), Anne Taylor (Supervisor) & Arthur GEORGES (Supervisor)