Environment and Resource Management

Soil, sediment and water testing - dioxins

Summary

Soil and sediment testing carried out by the Environmental Protection Agency both near and distant from the site of last year's Chemical fire at Narangba has found dioxins at levels similar to those commonly found in urban and industrial areas in Australia. Testing of water samples from ponds close to the site of the fire showed dioxin concentrations very much less than those in the soils and sediments. This is consistent with the very low solubility of dioxins in water.

Professor Michael Moore, Director of The National Research Centre for Environmental Toxicology, and Professor in Medicine at the University of Queensland, has advised the department that the dioxin levels outside of the fenced the department site remediation area were low, and there is no greater health risk associated with exposure to these soils and sediments than from exposure to soils and sediments from other parts of Australia. He also advised that water is a very unlikely source of human exposure to dioxins. Read Professor Moore's independent advice (PDF, 223K)*.

How testing was done

Sediments from the bottom of four containment ponds used to store water contaminated by chemicals from the fire, as well as soil collected approximately a kilometre away from the Binary site and sediment samples from Saltwater Creek as far as Lipscombe Road were tested.

Sampling and analysis was done in the same way as used by the National Dioxins Program so that there could be a comparison with background dioxin levels in other parts of Australia.

Most testing involved soils and sediments because dioxins have extremely low water-solubility. However, water samples from Ponds 1 and 2 within the fenced remediation area and also the on-site treatment pond for contaminated water were tested. Water could not be sampled from ponds 3 and 4 because they had already been pumped out to the treatment pond before sampling for dioxins took place.

The results

To quantify the risk of human and ecological exposure by different dioxin-like chemicals which have different toxicities, the World Health Organization (WHO) expresses the overall toxicity of a mixture of dioxins using a single number, the "WHO Toxic Equivalent" (TEQ). The results of sampling at Narangba are given in this way.

Most of the dioxins found were the least toxic dioxins.

The results from the samples are shown on the attached aerial photographs.

The Laboratory Analysis Result Certificates from the NATA-accredited National Measurement Institute show the measured concentrations of individual dioxins and how the TEQ was calculated for each sample.

Analysis of the sample results by the department scientists and by independent environmental toxicologists found the dioxin levels in soil and sediment samples were within background levels at 10 sites and slightly above background levels at four sites.

The sediment samples from the bottom of two of the four containment ponds used to store contaminated firewater contained slightly higher than normal dioxin levels for urban and industrial areas in Australia. The results for the other two containment ponds were within normal dioxin levels for urban and industrial areas in Australia.

Contaminated sediments are being removed from all of the ponds and replaced with clean fill as part of the department's remediation works.

Soil and sediment samples taken about 1km to the north and northwest of the Binary site were also found to contain dioxin levels slightly above background levels. However, these levels are not considered to be high. The department has been advised these dioxin levels are not linked to the Binary factory fire last year.

Reviews of the department's dioxin test results by University of Queensland environmental toxicologists, Associate Professor Barry Noller, and Associate Professor Jochen Mueller, found no evidence that the Binary fire last year caused the dioxin contamination of soils and sediments outside the area directly affected by the fire.

The department has been advised that the slightly higher than background levels found to the north and northwest of the Binary site may be due to bushfires or vehicle activities in the past.

This advice has been supported by further testing of all the soil samples, which did not detect any of the pesticide chemicals present at the Binary site at the time of the fire.

The wind was blowing towards the northeast on the night of the fire. The dioxin levels in soils from the sampling point to the northeast of the Binary site were within background levels.

Tests showed that the levels of dioxins found in the sediments from the bottom of the four ponds were 1.5, 5.7, 13 and 17 pgTEQ/g (pg = picogram which is 0.000000000001g).

100 - 520 Parramatta River estuary

1.5 - 17 containment ponds

2.1 - 12 sampling outside containment area

0.095 - 11 Queensland background soils

Table: TEQ comparisonsTests to the north and northwest of the Binary site found levels of 11 and 12 pgTEQ/g. All other samples collected outside the area directly affected by contaminated firewater were within background levels for urban and industrial areas in Australia.

To put the Narangba results into perspective, an Australia-wide study, the National Dioxins Program published by the Australian government Department of Environment and Heritage in 2004, found that 'background', or commonly occurring, levels of dioxin in Queensland soils ranged from 0.095 to 11 pgTEQ/g.

Background levels in New South Wales reached up to 23 pgTEQ/g whereas sediments taken from Sydney's Parramatta River around the polluted industrial area of Homebush Bay had levels up to 520 pgTEQ/g.

For comparison, the levels of dioxins found in soils and sediments at Narangba are shown together with levels found in the National Dioxins Program on a box and whiskers plot.

This national study did not include contaminated sites where there had been accidental contamination, like the containment ponds at the Binary site.

Test results for the Narangba water samples were in the range 0.0046 to 0.053 pgTEQ/mL which is some 100 to 1000 times less than those measured in the soil and sediment samples (note that the analysing laboratory reported the water results in pgTEQ/L, these have been converted to pgTEQ/mL to simplify comparison with the soil and sediment results). This result is consistent with the very low water solubility of dioxins.

Risk of exposure

Dioxins bind to soils and sediments which means people would have to ingest soils or sediments to be at risk from the dioxins. Water is not regarded as a significant source of exposure as dioxins are very poorly soluble in water.

The containment ponds where the highest readings were found are fenced off and not accessible to the public. The area is also being cleaned up by the department as part of the comprehensive remediation works underway at the site.

What are dioxins?

There are more than 200 different substances which form the chemicals collectively known as 'dioxins'.

They fall into two families of chlorine-containing chemicals: the polychlorinated dibenzodioxins (PCDDs) and the polychlorinated dibenzofurans (PCDFs). Their chemical structure is a pair of aromatic rings bound together with oxygen atoms, and with chlorine atoms attached. The individual dioxins are named according to the number of chlorine atoms and the points of attachment.

How are they produced? What are some common sources of dioxins?

Dioxins are produced from burning materials containing chlorine. This includes many natural materials, for example many plants accumulate chlorine in the form of salt. Accordingly, there are thousands of different sources - some natural such as bushfires and volcanic action, and anthropogenic sources such as incineration (of many kinds of wastes), some manufacturing processes involving burning, smoking tobacco, and vehicle emissions.

Where are they commonly found in the environment?

The National Dioxins Program conducted across all of Australia in 2003-2004 showed that dioxins are widespread throughout Australian soils and sediments, with the highest levels found in urban areas. However, most of the mixture found during the study comprised the least toxic dioxins. They are found in most soils and sediments, particularly in urban areas where there are many sources.

How long does it take for dioxins to break down in the environment?

Dioxins are persistent pollutants. They are very resistant to being broken down in the environment, and tend to be passed up the food chain. Breakdown takes many years.

How are humans exposed to dioxins?

Dioxins are also found in animal tissues, including humans. Most of the dioxins found in humans come from food. Diet is estimated to account for about 95 percent of dioxin exposure in the general community. For example, traces of dioxins in the soil are swallowed with grass when cattle graze, and passed on to humans in dairy products and meat. Dioxins accumulate in fats and oils because they are more soluble in fats and oils than in water.

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Last updated: 28 November 2007

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