Derwent Dilema — Rod Holden

The River Derwent looks beautiful, but it is one of the worst polluted waterways in the world.

AUSTRALIA’S BEST BREAM ESTUARY IS ALSO THE MOST POLLUTED

ROD HOLDEN explains how this great estuary needs love and help.

The River Derwent…one of Tasmania’s best Bream estuaries…can we fix it?

Look out over the River Derwent, from almost anywhere in the estuary, and you’d easily believe this stunning river, with its mountain backdrop, is a picture of health and a great spot to catch a feed of fish.

You’d be wrong in spades and in fact, the Derwent estuary is documented as one of the worst polluted waterways in the world! If you’re a local, you’ll know the official advice is…DO NOT eat the shellfish or Bream at all and limit consumption of ALL other fish from the Derwent to twice each week. If you’re breastfeeding, pregnant, planning to get pregnant, 6 years old or younger eat fish from the Derwent only once each week.

How did we get to this tragic point?

Industry is still directly on the waterfront.

In 1804 a settlement was established on a permanent freshwater stream, which became known as Hobart Rivulet. The settlement was named Hobart Town and had a population of 262, which was mostly convicts and soldiers.

For the first 15 years of settlement, the town didn’t expand much. The inhabitants drank straight from the stream and filled cooking pots and buckets to carry back to their homes.

As the population increased a number of small industries started to harness the energy of the stream. With increased use for both industry and domestic purposes the rivulet was rapidly changed from a clean natural stream to basically a drain. Residents disregarded the impact their effluent and rubbish had on the stream, at the same time expecting the water flowing past their door to be clean enough to drink. This was despite the fact that their neighbours upstream had polluted the water in the same manner. The streets became so dirty and the water so polluted that Governor Sorell issued regulations in an effort to clean the place up.

Animals were prohibited from wandering the streets. Constables made a daily check of footpaths and drains to make sure rubbish was not being dumped anywhere. In 1829 it was found that effluent from the overcrowded Female Factory (female convicts) was being discharged into the rivulet. A town water supply was built in 1832 after “an inspection of the rivulet found it fouled by sawdust, greenhides, effluent from a distillery, and pig’s dung and muck running off properties all the way along its banks”.

28 years that transformed the Derwent

In as little as 28 years, a sparkling clean rivulet that everyone relied on was transformed into a stinking drain. Unfortunately, the same story continues for the next 187 years with the exponential growth of population and industry. A lot of their pollutants also ended up in the river with the biggest industries creating a legacy of heavy metals and industrial waste.

Heavy metals

Public awareness of this legacy issue started in 1972 when a group of people eating oysters from Ralphs Bay became very ill. The oysters were found to have extremely high levels of zinc. Since then scientists have been studying the heavy metals in the Derwent. The following summaries show the extent of the issue.

Professor Harry Bloom reported in 1975 that mercury levels in the Derwent were second only to Minamata Bay, where 900 people died from mercury related disease. It must be noted that even though his numbers were disputed, the mercury levels are still some of the highest in the world.

Chapman said in her Master thesis (1992) that the cadmium levels in the Derwent sediments were almost three times higher than anywhere else in the world.

Dr Graeme Batley, a recently retired Chief Research Scientist from CSIRO said in 2014 the zinc levels in the Derwent are the second highest in the world (by a whisker) and 13 times higher (yes, thirteen) than number three on the list.

The Hughes report in 2014 states there’s about 150,000 tonnes of heavy metals in the Derwent sediments. His breakdown was roughly 122,000t of zinc, 19,900t of lead, 5,100t of copper and 2,200t of arsenic. Cadmium and mercury could not be estimated due to the equipment used. There’s also another 10,000 tonnes of zinc concentrate still sitting in the SS Lake Illawarra, which is the ship that took out the Tasman Bridge in 1975.

These metals are natural elements, but when they become soluble (which they are in the Derwent through various means) they enter the food chain. When you eat anything out of the Derwent, you’re absorbing these metals into your body. At this point it’s worth considering what the World Health Organisation says about high levels of these metals and the effects on people. It’s a bit technical, but I bet you a beer it will be on your mind when you hit the Derwent for a fish sometime in the future.

Exposure to mercury (even small amounts) may cause serious health problems and is a threat to the development of children. It has toxic effects on the nervous, digestive and immune systems, and on lungs, kidneys, skin and eyes. People are mainly exposed to methylmercury, an organic compound, when they eat fish and shellfish that contains it.

Cadmium has toxic effects on the kidney, the skeletal and the respiratory systems, and is classified as a human carcinogen (known to cause cancer). It is readily accumulated in many organisms, notably molluscs (oysters, mussels, shellfish, etc) and crustaceans (prawns, crabs, crayfish, etc) or in other words it accumulates in the food source of a lot of fish species.

Lead is a cumulative toxicant that affects multiple body systems and is particularly harmful to young children. Lead in the body is distributed to the brain, liver, kidney and bones. It is stored in the teeth and bones, where it accumulates over time. Lead in bone is released into the blood during pregnancy and becomes a source of exposure to the developing foetus. There is no known level of lead exposure that is considered safe.

Arsenic is highly toxic in its inorganic form and can cause death. It has been associated with cardiovascular disease and diabetes. In utero and early childhood exposure has been linked to negative impacts on cognitive development and increased deaths in young adults. Absorption occurs mostly through the small intestine (when you eat fish), although some absorption occurs from skin contact and inhalation (e.g. don’t smoke rollies when you fish).

Those four are the worst of a bad bunch, but wait there’s more. Copper-induced toxicity affects the liver, bones the central nervous and immune systems. Soluble zinc (which the Derwent is full of) is highly toxic to bacteria, plants, invertebrates, and fish.

So, the ‘what’ and ‘how’ show it’s from bad to worse and back again, especially for our kids.

It should be remembered that there is also a significant amount of other pollutants in the Derwent. These include various catchment pollutants, sewage effluent, storm water runoff, a large range of synthetics (microplastics, pharmaceuticals, pesticides, etc) and the list goes on. to the heavy metals in the Derwent estuary anyway, its climate change making the ocean more acidic. Let me explain…

Science tells us the oceans are becoming more acidic due to climate change. It also tells us that estuaries have an amplifying affect on this. Add to the mix the nutrients coming down from the catchment. The affect is that the bottom waters in estuaries is becoming more acidic and much faster than the ocean. This change in pH causes a chemical reaction that releases the heavy metals into the environment in its soluble form. The whole estuary, all at the same time, is releasing soluble heavy metals which are bioavailable. The King and Queen rivers on the west coast of Tasmania provides an example of the potential outcome. They are completely saturated with heavy metals and are now totally devoid of life because of it.

Won’t flushing make it better?

Don’t think for a second that the fresh water coming down from the catchment will save the day as estuaries have a salt wedge (the freshwater flows over the top of the salt water) and this salt wedge runs all the way up to New Norfolk. Basically, the whole estuary is salt water along the bottom.

Can it be fixed?

It looks extremely bad, but the main question in the title of this article is “can we fix it?” We believe we can.

We spent 4 years identifying the solutions, the technology is there. We also know how to fund it without waiting for the government to pick up the whole tab. We also changed our constitution to be a profit-for-purpose company. That means we’re legally bound to drive all profit we make into our purpose, which is fixing the Derwent. We have some of Australia’s best scientists and water remediation professionals on board and we’re establishing a Youth Advisory Council and a large Citizen Science Project Cluster to give the public ownership. We’re drawing a line in the mud, bringing all stakeholders into the tent and fixing the river.

Make no mistake, the job at hand is massive and will take decades. It’s actually the largest holistic river remediation project in the world…ever. Apart from fixing the river, the next best part is that it will inject billions into the Tasmanian economy in the process. Then our kids will enjoy some of the best Bream fishing on the plant and they’ll also be able to catch a feed of flatties too.

There’s a catch, (yeah, there’s always a catch) we need to get the politicians to put some of our tax dollars into getting it started. We need to prove Tasmanians are behind our plan and that simply means subscriber numbers. Each subscriber adds one more pressure point for the pollies and the best time to leverage these guys is during an election… which is now.

Jump onto our website, check out the plan and subscribe. With your help, we have a shot at our kids being able to eat the fish from the River Derwent without it killing them. www.derwentremediation.com.au

Rod Holden, Managing Director, Derwent Remediation Pty Ltd

Is it bad - or getting better?

We now know how we ended up with this issue and that it’s getting into the food chain, but is it really that bad?

We’ve been told for the last 20 years that it’s getting better because inputs are being addressed and the heavy metals in the sediment is stable. Also, clean sediments are coming down from the catchment and slowly covering up the heavy metals. That’s true to some degree, but it’s not the whole truth. Don’t get me wrong, there has been some excellent strides in improving the impacts on the river from industry over the last 20 years. We want to see that not only continue, but expand significantly. We know there are at least four major events that happen in the Derwent estuary which stirs up and remobilises those “stable” sediment on a regular basis. One of these major events happens almost weekly, another one fortnightly.

Having said that, the physical disturbance is not the real issue relative Whilst the Derwent gets a lot of attention from bream fishers they rarely kill or take fish. www.tasfish.com - Get the knowledge - Get the fish.