Ecotoxicology of contaminated marine sediments in Tasmanian estuaries

Sediments are components of marine and estuarine ecosystems. Toxicants most often become sorbed to suspended particulate matter, then fall to the bottom to become incorporated into bed sediments. The bioavailability of the toxicants is difficult to measure chemically and the interpretation of biological significance is unclear. Toxicants stored in sediments can be released due to physical and chemical changes in the environment. The extent of the effects of these changes is also not well established and there is little knowledge of what levels of contaminants may be mobilised, and the ecological effect of that mobilisation. Although recently, pore water toxicity and chemistry has been included in sediment testing, there is a lack ofresearch characterising pore water from Australian marine sediments. Further, there is a paucity of multidisciplinary research of the quality of marine sediments in Australia to provide information on factors affecting quality and remediation of marine sediments that will contribute to improved environmental management of marine sites and allow for successful remediation practices. The primary aim of this study was to apply a multidisciplinary approach to form a weight of evidence assessment of sediment quality in northern Tasmanian estuaries. The technical objectives associate with this aim were to: • determine whether shallow subtidal sediments adjacent to a heavy metals industrial estate was chemically contaminated relative to other northern Tasmanian locations, and relative to numerical, effects-based guidelines • determine ifbenthic communities exposed to chemical contamination differed relative to benthic communities exposed to non-contaminated sediments • establish whether the contaminated sediments were toxic relative to non-contaminated sediments • determine the relationships between toxicity, chemical composition and benthic communities of the subtidal sediments at contaminated and non-contaminated sites • generate background data for future assessment of sediment remediation. The relationship between the toxicity, chemical composition and benthic communities was investigated through a field program. Over two years, samples were collected at four locations. One of these, Deceitful Cove in the Tamar River estuary, has been heavily contaminated by past industrial effluents from aluminium refining and ferro-manganese smelting industrial plants, another (East Ann in the Tamar River estuary) has intermediate contamination, while the other two (Squeaking Point and North East Arm in the Port Sorell estuary) are effectively free of pollution. A Sediment Quality Triad (SQT) assessment of shallow subtidal marine sediments within the two adjacent northern Tasmanian estuaries was conducted to assess sediment quality in terns of potential to elicit adverse biological effects. The SQT provides a weight-of-evidence approach integrating toxicological and chemical analysis with benthic community structure to determine likely impacts of contaminants. Generic effects-based sediment quality guideline (SQG) values were also used to facilitate evaluation of sediment quality by identification of potential contaminants or mixtures of contaminants, likely to cause adverse biological effects. Chemical analysis involved assessment of total trace metals and organics concentrations within sediments. Assessment of toxicity involved the adaptation of a suite of first tier screening bioassays, currently used for testing toxicity of marine water: Micro lox®, sea urchin larval development inhibition and algal growth inhibition tests. Benthic macroinvertebrate community structure was evaluated using univariate, distributional and multivariate analysis of assemblages: species diversity indices, hierachical cluster analysis and nonmetric multi-dimensional scaling ordination. Differential SQT analysis indicated strong evidence of contaminant-induced stress, and possible environmental degradation in the Tamar River estuary at Deceitful Cove. Additionally, contaminant-induced stress was not restricted to a geographically isolated area adjacent to the industrial estate. Multi-dimensional scaling ordination and univariate analyses identified significant differences between the patterns of distribution and abundance of benthic fauna from contaminated and non-contaminated estuaries. There was a significant correlation between patterns of assemblages and concentrations of trace metals. The overall findings from the SQT and multivariate analyses strongly suggest that a combination of metal contaminants are directly related to elevated pore water toxicity and alteration in macroinvertebrate community structure. The liquid phase Microtox® and algal growth bioassays are suitable for testing pore water toxicity of Tasmanian coastal marine sediments. However, difficulty in interpreting Microtox® solid phase test results limits the use of this assay for routine testing. Additionally, research on extending the spawning period of the sea urchin Heliocidaris tuberculata is necessary before this species can be used for routine bioassay work