THE DERWENT RIVER is not only an iconic symbol of Hobart’s identity, but it also marks the electoral boundary between seats of Denison and Franklin (House of Assembly) and the northern boundary of the seat of Wellington (Legislative Council).

For that reason, the river is a political and environmental arena.

The health of the Derwent River and its various bays (such as Cornelian Bay) has been a topical issue and has also been an intriguing feature in election material for some candidates in the recent Upper House elections (Wellington).

The state of the Derwent drifts in and out of the public consciences from time to time — some may recall that during the recent summer, Cornelian Bay was one of the three (from a total of 38) swimming venues closed to the public due to pollution concerns. But what’s wrong at Cornelian Bay and what’s the real state of the Derwent?

When science becomes spin

In understanding the context of Cornelian Bay we need to consider the current status of the greater Derwent River.

Both immediately prior to and during the state election campaign the public were inundated with a spate of ‘good news’ stories. Some suggested that the state government was moving through a check-list of contentious issues (mostly environmental).  The Government Media Unit (also referred to as ‘Pravda’) appeared to be busily churning out imaginative stories with just a touch of truth-engineering.

The Sunday Tasmanian [Mercury] on 15 January 2006 reported the glowing news that the Derwent River had been brought “back to life” — according to a recent environmental report card by the Derwent Estuary Program (DEP). No fewer than four articles, all authored by the one person in a two-page spread — an advertorial.

Even the front-page banner of the newspaper heralded the ‘good news’ about the estuary. According to the lead article, the ‘good news’ seems to be based on hard-hitting scientific data such as ‘anecdotal’ evidence and positive comments from local fishermen.

It was somewhat ironic that only 9 days later the Sydney Morning Herald reported that the public of Sydney were advised by their State Government Environment and Health Departments that dioxin levels in Bream caught within Sydney Harbour were dangerously high, owing to industrial pollution, and that fishing in the harbour would be banned immediately.

What would an Environmental Protection Agency — if it existed in Tasmania — say about the state of the Derwent?

Whilst there has been some commendable improvement in the state of the Derwent, this has mainly been determined from some measures of water quality (mainly microbiological) — but this is only one aspect of environmental assessment. What the Sunday Tasmanian failed to mention was the ongoing (and in some areas increasing) levels of heavy metal pollution in the extensive mud sediments of the estuary.

As with all estuarine systems, heavy metals (commonly sourced from industrial processes and vehicle exhausts) become trapped within the clay and silt matrix of deposited sediments. Here they pose a major problem owing to their incredible longevity. Heavy metals in sediments tend to re-enter the food chain through benthic dwelling filter-feeders and can be remobilised into the environment if the sediments are disturbed by storm events, shipping or dredging activities.

Ooops! — We forgot about those heavy metals

In 1974 the CSIRO reported that shellfish in the Derwent contained zinc and cadmium levels well above national guidelines. In 2005 (31 years later) Zinc levels in Derwent shellfish were still being reported well above standard (particularly north of the Tasman Bridge) and Derwent Estuary Program advice was that they were not safe to eat (as stated in an interview with ABC radio 2005). Likewise in 2004 the Tasmanian Conservation Trust warned that Flathead caught north of the Tasman Bridge and in Ralphs Bay tended to contain Mercury levels above the 0.5 mg/kg national food guideline.

The polluted state of the Derwent was revealed by Professor Harry Bloom of the University of Tasmania in the mid-1970’s. However these early studies were not based on water quality data and organic content analysis (the focus of the DEP Report Card and Sunday Tasmanian article). Indeed Bloom based his observations on heavy metal concentrations measured from 102 sediment sample sites.

Whilst the Sunday Tasmanian mentioned the work of Harry Bloom, it didn’t reveal that his findings were based on sediment samples. Consequently, the DEP reported ‘good news’ seems to be based on a confused and inappropriate comparison of Bloom’s early analysis of heavy metals in sediment versus contemporary measures of water quality.

In 1996 and 1997 an additional 70 sites in the Derwent were sampled for sediment heavy metal content using modern geochemical techniques by Professor Brian Jones (University of Wollongong). Jones’ findings published in the Australian Journal of Earth Sciences (2003) show that heavy metal concentrations in the Derwent mud have only improved slightly for surface sediments in some parts of the river since the initial studies of Bloom in 1975.

Jones found no definable improvements in the upper Derwent Estuary and in fact the middle estuary (from Bridgewater to the Zinifex electrolytic zinc smelter at Lutana) suffered an increase in contamination. The Derwent Estuary Program (DEP) also conducted its own studies on heavy metal pollution in the Derwent sediments in 1997 and 2000, with similar results to those of Jones and his colleagues in 2003, and concluded that there had been no improvement in heavy metal concentrations since the 1997 study.

Likewise a 2003 University of Tasmania study also reported heavy metal concentrations in sediment samples from Cornelian Bay well above the Australian Interim Sediment Quality Guidelines. There was no mention of these facts in the Sunday Tasmanian in 2006 and seemingly no new data either.

The Derwent — international benchmark for heavy metal sediment pollution

The sediments of the Derwent contain a cocktail of heavy metals (all toxic to humans) including Zinc, Lead, Arsenic, Copper, Antimony and Cobalt — all well above the Australian Interim Sediment Quality Guidelines (2 to 55 times above). Maximum contamination values for heavy metals are 40 to 565 times greater than baseline levels (compared to relatively unpolluted rivers such as the Huon).

Bottom sediments in the centre of the river directly east of Hobart CBD and Sandy Bay contain Zinc concentrations in the order of 3000-6000 ppm and Lead in the order of 150-1200 ppm. This means that every 1 ton of sediment deposited in this part of the river centre may also contain up to 6 kilograms of Zinc and 1.2 kilograms of Lead. In the most heavily polluted areas (just north of the Tasman Bridge) these values are 12kg and 2.4kg per ton of sediment for Zinc and Lead respectively. When one considers the phenomenal amount of sediment deposited annually in the Derwent, the volume of heavy metals entrapped within the sediments must be equally staggering.

On an international basis, there are few river systems which can match the Derwent for excessive heavy metal pollution of sediments. Maximum Lead concentrations in the Derwent sediments are 10 times those of Sydney Harbour and 45 times those of the Hudson River. With the exception of a few Norwegian ports, the Derwent eclipses all other ports for sediment heavy metal pollution. According to Professor Jones: ‘… the bottom sediments in the middle Derwent estuary have some of the highest concentrations of Zinc pollution in the world …’ (Jones et al, 2003).

Cornelian Bay — a tarnished gem

Up to the end of World War I Cornelian Bay was a popular and pristine recreational reserve for the inhabitants of Hobart. The Bay derives its name from its Yorkshire equivalent and both are noted for the presence of semi-precious “cornelian” stones — the mineral Agate (silicon dioxide) which wash-up on the foreshore. In 1836 Charles Darwin walked the along the beach of Cornelian Bay to study the shell horizons during the Hobart visit of the HMS Beagle. Boating, fishing and swimming bathes remained popular in the Bay during the 1920s.

However after 1917 with the advent of heavy industrialization and urbanization, the Estuary became a source of the heavy metal and urban effluents. By 1954 local residents were up in arms about the reclamation of land at Selfs Point to build the oil refinery and sewerage plant. With increasing discharges of polluted water into the Bay, by 1972 Hobart City Council was forced to erect warning signs at Cornelian Bay, closing the beach to swimming.

Whilst much has been said about the polluted stormwater entering Cornelian Bay (mainly containing faecal coliforms), little has been said publicly about the accumulation of heavy metals in the silt and sand of Cornelian Bay. The 2003 UTAS study noted that Lead and Mercury concentrations in the near shore sandy sediments of Cornelian Bay exceeded ISQG levels and concluded that: ‘As disturbance of sediments could potentially result in re-suspension of the most highly contaminated sediments, it is recommended that activities which could disturb the silty sediments in the central bay area are restricted’.

Consequently one would think that any proposal for development at Cornelian Bay may have to account for the thorny issue of what to do with contaminated sediments and the equally thorny issue of whom is going to pay for the clean-up. A political and environmental hot potato!

Monitoring the monitors

In other States and Territories, the ongoing environmental monitoring of local waterways is typically the responsibility of the independent EPA. In the absence of such a body in Tasmania one may expect that monitoring is outsourced to a local environmental organisation with a board or committee comprised of local researchers, academics, environmental practitioners and community members; not so in Tasmania.

A cursory review of their website reveals that the Derwent Estuary Program (DEP) is comprised of staff who are employees of the Department of Primary Industry Water & Environment (DPIWE). Indeed the DEP Steering Committee is a collection of Local Council officers, DPIWE officers and Industry representatives (the same industries who may be contributing to pollution). The Chair of Committee is in fact the DPIWE Secretary (Kim Evans) who answers directly to the Minister (probably only David Llewellyn).

The annual DEP Report Card is notable for its dearth of quantitative data and the fact that it makes no mention whatsoever of heavy metal concentrations. Similarly the Sunday Tasmanian article made no mention of these facts and the journalist didn’t bother to sift through the 120 page State of the Derwent Report 2003, where, towards the end of the document, he may have found a brief discussion on the alarming status of heavy metal pollution in the estuary sediments.

And I haven’t even touched on the role of a Tasmanian EPA to monitor for persistent organic pollutants (POPs) like dioxins and organochlorines in the marine ecology of the estuary. As a duty of care to fishers and consumers of fish, these bioaccumulated pollutants should be part of ongoing river monitoring.

The total ban on the fishing and consumption of fish from Sydney Harbour — based on the human health risk — should be a trigger for Tasmanian authorities to wake up to the need for a properly resourced, independent EPA; maybe DPIWE could be re-badged and re-born!

Tasmania has a tendency to take its rivers for granted, the history of the Derwent River is a prime example, and there are other troubled rivers. If we want future generations to value it and enjoy it perhaps we should occasionally scratch through the thin veneer of beauty and health that is commonly presented to us.

*Picture: Enjoying the sand beach at Cornelian Bay (1860s).  Photo by Alfred Winter, State Library of Tasmania.