Toxicants are chemical contaminants that may harm living organisms at concentrations found in the environment . The ANZECC/ARMCANZ Guidelines for Fresh and Marine Water Quality  provide a large list of potential toxicants under the broad headings: metals & metalloids; non-metallic inorganics; organic alcohols; chlorinated alkanes; chlorinated alkenes; anilines; aromatic hydrocarbons (e.g. polyaromatic hydrocarbons, polychlorinated biphenyls and dioxins); phenols & xylenols; organic sulphur compounds; phthalates; miscellaneous industrial chemicals; organochlorine pesticides (e.g. DDT); organophosphorus pesticides (e.g. chlorpyrifos); carbamates (e.g. carbaryl) & other miscellaneous pesticides; pyrethroids; and herbicides and fungicides.
Figure 1. Conceptual model of the movement of toxicants through Moreton Bay (From Dennison and Abal (1999) ). Reproduced with permission of Healthy Waterways Library.
Chemicals are used everywhere. They are essential components in the production of the foods, equipment, fuels, goods, cosmetics, and medicines that maintain and improve our quality of life. When appropriately managed, they deliver major benefits to the community in the fields of agriculture, medicines, manufacturing and in and around the home. There are around 50,000 industrial, agricultural and veterinary chemicals available for use in Australia, and between 70,000 and 100,000 chemicals in use worldwide. Along with their many benefits, in some circumstances they can cause harmful impacts on the environment and public health, ranging from fish kills to potential long-term chronic impacts on children's health and development. Many metals & metalloids are essential to life (e.g. copper, zinc and chromium etc). However they become toxicants when they are present at higher concentrations.
In the immediate areas of high concentration, toxic contaminants in water or sediment can kill marine life (e.g. fish and invertebrates). Other acute effects may include changes in the abundance, composition and diversity of biological communities and habitats. Some toxicants persist in the environment and may progressively accumulate in sediments or in biological tissues to levels that are much higher than water column concentrations (e.g. bioaccumulation). Chronic effects of bioaccumulated toxicants in organisms include alterations of growth, reproductive success, competitive abilities and deformities such as imposex. Elevated toxicant concentrations in organisms (e.g. fish and shellfish) may also pose health risks to consumers of those organisms (including humans). For this reason, toxicant concentrations in food are regulated by Food Standards Australia and New Zealand (FSANZ).
Toxicants in coastal waterways are derived from a range of agricultural, industrial and domestic sources. Agricultural activities can result in erosion and run-off of sediment, fertilisers (phosphate and nitrogen) and pesticides. Such pollutants have been found to impact on the health and reproductive capacity of corals, seagrasses and fauna of the Great Barrier Reef . The "Pestcide Hazard" indicator can be used to assess toxicant risk from agricultural sources. Common toxicants from industrial and domestic sources include paints & primers, petrol & oil, garden pesticides & fertilisers and anti-freeze. Urban and industrial toxicant risks can be assessed using the "Industrial Point Source Hazard" and "Wastewater Discharges" indicators.
Many toxicants reaching estuaries have a high affinity for fine-grained sediment. The concentrations of some toxicants are therefore controlled to a certain extent by processes governing sediment transport and deposition. In tide-dominated waterways (e.g. deltas, estuaries and tidal creeks), flanking environments are the main traps for fine sediments, and these include mangroves , saltmarsh areas  and intertidal flats . Fine sediments also accumulate in mangroves, saltmarsh and intertidal flats in wave-dominated coastal waterways (e.g. estuaries and strandplains/coastal lagoons), but the central basin is usually the main sink. The baffling of water movement by seagrass leaves can also cause fine sediments and toxicants to deposit in seagrass meadows. Physical disturbance of these habitats (e.g. dredging, reclamation, erosion and re-suspension) can remobilise toxicants from the sediments into the water column .
DOM can enhance the solubilities of some organic pollutants and pesticides , and this might be important in areas where there is lots of decaying vegetation.
At the request of the Premier's Lake Macquarie Taskforce, the NSW Department and Conservation investigated the concentration of metals in the lake sediment as well as any environmental and biological problems they might be causing. The concentrations of metals in Lake Macquarie sediments fell significantly between 1985 and 1998. This reduction was most likely a result of lower pollution loads entering the lake and the input of less contaminated sediments from the catchment. Despite these decreases, the levels of cadmium, copper, lead, mercury, selenium, silver and zinc were still above natural levels in the lake sediments. The study also found elevated levels of selenium, cadmium, lead and zinc in the tissues of adult fish from the lake. Of these, only selenium exceeded health guidelines for human consumption and the exceedences were small and at just one location. The rates of skeletal abnormalities in larval fish were higher in some contaminated areas of the lake compared with rates in populations from relatively unpolluted locations. While these results show that trace metals are having an impact in some areas of Lake Macquarie, the study concluded that most of the ecosystem and biological effects are localised. There appears to have been little impact on the commercial and recreational fish stocks of the lake with most not affected by trace metal contaminants. The study also concurred with the NSW Health finding that there is little risk to human health from eating fish from the lake. Future monitoring of Lake Macquarie will determine the effectiveness of the projects implemented and help to further improve its sediment and water quality. If successful, these may provide a guide for the management of other areas with sediment contamination. Further information on this study can be found in reference .
In the late 1980s it was found that contamination in the sediments of Homebush Bay from the activities of a chemical manufacturing facility was significant. Fishing restrictions were put in place and some limited remediation works were put in place on the land to limit further contamination of the Bay. It was not possible at the time to consider full remediation of the area due to a lack of appropriate technology. The contaminants in the Bay sediments are polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) which were formed as by-products in the process of manufacturing 2,4,5-T, a herbicide that was part of Agent Orange, as well as DDT and other organochlorine pesticides and related chemicals. In 2002, an environmental impact statement was submitted to allow the remediation of the land and the Bay sediments and work is currently underway on the land and will commence on the sediments in 2007. During 2005 and 2006 fish were sampled to see how much of these persistent and bioaccumulative chemicals were present in fish in the harbour. Levels were found to be quite high and additional fishing restrictions were put in place. Further information about the fish sampling and an overview of results can be found at www.foodauthority.nsw.gov.au. Further information about the work being undertaken to clean up these areas can be found at www.rhodesremediation.nsw.gov.au and www.rhodesremediation.com.au.
There are inherent problems associated with the analysis of both water and sediment for contaminant concentrations . Contaminant concentrations in water are often below detection limits, and are highly variable both spatially and temporally . By comparison, contaminants in sediments are easy to measure and can provide a degree of time integration not found with water samples . If one undertakes an assessment of sediment quality, it is worthwhile also to determine the severity of impact and identification of contaminant sources and dispersion pathways (more information).
It is recommended that sampling for toxicants be undertaken in accordance with the ANZECC/ARMCANZ Australian Guidelines for Water Quality Monitoring and Reporting . Table 5.2 (pg 5-4) in the guidelines is a source of appropriate analytical methods. Decision tree frameworks for assessing toxicants in ambient waters are provided in Figures 3.4.1 (water pg. 3.4-14) and 3.5.1 (sediments pg. 3.5-6) of the ANZECC/ARMCANZ Australian and New Zealand Guidelines for Fresh and Marine Water Quality . There is no formal guidance for incorporating bioaccumulation into these guidelines, however chemicals having the potential to bioaccumulate are indicated with a 'B' in Table 3.4.1.
Aquatic organisms are used increasingly in contamination assessments  because the concentrations in water and sediment do not reliably indicate toxicity to biota . Even the demonstrated bioaccumulation of a contaminant does not necessarily mean that there has been environmental harm. The exposure of marine organisms to high environmental levels of contaminants can induce biomarker synthesis . Such biomarkers are being used increasingly as accurate and cost-effective methods for identifying the toxic effects of pollutants on biota (see review in ).
Limited toxicant data for estuaries and coastal waterways is held by the collecting agencies (Federal, State and Local Government, Universities and environmental consultants). Trigger values for different toxicants in water and sediment are listed in Tables 3.4.1 (pg 3.4-5) and 3.5.1 (pg 3.5-4) respectively of the ANZECC/ARMCANZ Monitoring and Reporting Guidelines . Detailed background information pertaining to different toxicants and to the derivation of trigger values is provided in Section 8 of the ANZECC/ARMCANZ Guidelines for Fresh and Marine Water Quality . Recommendations for direct toxicity assessment are also provided in Section 8 of the guidelines.
Information on the Guidelines for Fresh and Marine Water Quality and information about types of guidelines for chemicals in Australia can be found at the Chemical Reference Guide website at http://hermes.erin.gov.au/pls/crg_public/!CRGPPUBLIC.pStart
The The National Pollutant Inventory website contains data on the types and amounts of 36 substances (90 in the future) that are emitted into the environment, mainly from urban industrial sources. The NPI excludes the following: veterinary and agricultural chemicals; emissions from petrol stations, dry cleaners (<20 people employed), scrap metal handling facilities that do not reprocess batteries or engage in smelting metal and from mobile sources operating outside the boundaries of a fixed facility (e.g. an aircraft in flight or a ship at sea). Agricultural processing and production facilities, including the growing of trees, aquaculture, horticulture or livestock raising, are also excluded from the inventory, unless they involve intensive livestock production such as piggeries or cattle feedlots.
The ECOTOX database at the U.S. Environmetal Protection Agency website has chemical toxicity information for aquatic and terrestrial life, and can be used to examine the impacts of chemicals on the environment. CSIRO's online website called Restoring Contaminated Environments describes research that improves our understanding of the biogeochemical fate of chemicals and identifies relevant biochemical indicators and risk assessment protocols.
More information on Toxicants.
There are still many challenges to understanding the fate, transport and interactions of contaminants in marine systems. In particular, more information is needed on contaminant concentrations and processes governing their distribution in Australian coastal environments. Section 8.5.3 of the ANZECC Guidelines for Fresh and Marine Water Quality  lists several other deficiencies in knowledge.
Simon Apte, CSIRO Centre for Advanced Analytical Chemistry
Gavin Birch, Environmental Geology Group, School of Geosciences, The University of Sydney
Karina Budd, Water Sciences Program, Bureau of Rural Sciences
Robyn Gatehouse, the Department of Environment, Water, Heritage and the Arts
Therese Manning, NSW Department of Environment and Conservation