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One of benefits of Sydney’s clean green Olympics in 2000 has been the remediation of the grossly industrially polluted Homebush Bay and Sydney Olympic Park sites. Thanks to an ARC Linkage Grant involving the Department of Environmental Science at UTS and industry partners in Australia (Sydney Olympic Park Authority, CSIRO Land and Water, Department of Environment and Climate Change in NSW) and Landcare Research in New Zealand, funding was provided for a comprehensive study of the current success of the remediation.
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| Chris Rawson's Doctoral research into the remediation in the area focussed on the fresh water bodies, rather than Homebush Bay or the Parramatta River because of the potentially greater health risk for the public.
The study looked at several characteristics.
One was the chemistry of the sediments to see if current levels of selected chemicals were typical of urban sites around Sydney and whether they were reduced from the high levels recorded in there historically.
From 1993, following the announcement of the Olympic Games the chemistry data of the area had been studied in detail and were used for comparisons.
Another characteristic was possible effects on the living organisms - the biota.
Fish and invertebrates, were chosen because of ease of capture in the area.
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The sites at Olympic Park were compared with a series of 12 control sites selected from around Sydney for levels of various contaminants and richness of invertebrate life typically living in and around water sediments.
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How successful has the remediation been? |
| In terms of Chemistry - a definite thumbs up.
The level of contaminants studied has fallen dramatically.
In terms of availability of remaining contaminants, when contaminant availability was compared with 12 different sites around Sydney and the levels at Olympic Park were in the range expected from urban sites.
Left: contaminated waste treatment plant
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In terms of species richness and biodiversity - species richness was decreased
When Chris Rawson looked at the invertebrates at the site - the little organisms that turn into dragon flies and flies, there were much reduced numbers of different species compared with the other Sydney sites. Statistical analysis showed this was related to the contaminants in the sediments and especially the group known as persistent organic pollutants (these include dioxins, PCBs and organochlorine pesticides).
The insecticides of most interest to the researchers were DDT and its breakdown products. While these were still in high enough concentrations in the environment to be picked up by chemical analysis, at the sites, these insecticides were very tightly bound to the sediments and not available to the organisms and so were not the cause of the reduction of any of the invertebrates.
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The culprit was the dioxin availability - measured as ‘dioxin equivalency’ - in the sediments. | Dioxin equivalency measures the amount of chemicals that act in the same way in an organism as does dioxin. This means, for example, that there may be a number of these chemicals, all in very low concentrations, that together will produce a higher dioxin equivalency measure.
So it seems to be the sum of the levels of these chemicals that is driving the differences in the number of species found in different sediments.
Right: sampling for Gambusia
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Some animals, including copepods and some mayfly larvae, were found to be particularly sensitive and their numbers more likely to be reduced. It is important to maintain species richness because decrease in diversity of lower level creatures in the food web is known to result in decreased diversity of higher level creatures.
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Were all sites equally well remediated? |
| The success of the chemical remediation was related to the type of remediation used... the most highly remediated, and particularly some of the wetlands that have been created anew, are the cleanest while the least remediated remain the most contaminated. However the levels of contamination involved are all in the sort of range to be expected in urban sites.
Left: constructed habitat pond
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| Left: replanted saltmarsh
In terms of biological remediation the entire site has been remediated and replanted with native vegetation. Even the containment mounds are attractive hills planted out thickly with Spinifex grass.
Chris Rawson regards the most positive outcome from his research was the finding that on almost every measure the sites at Olympic Park are in the range expected for Sydney sites.
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| | Prior to 1993 they would have been way below the cleanliness levels for the rest of Sydney and the risk of having activity out there was so high that the whole area was closed off. Now it is a very valuable recreational bushland enjoyed widely by the community. In terms of negatives - part of Chris Rawson’s study examined the effect of stirring up the sediments in the ponds on the dioxin equivalency and found it increases about three times.
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| This was the case for both Homebush Bay and freshwater pond sediments.
This suggests caution if further treatment of such water bodies is contemplated and that some care needs to be taken.
Fishway, Bicentenniel Park
All photos from Chris Rawson
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