We conducted water and soil sampling at Cabbage Tree Island on 7 and 8 April 2022. The sampling was undertaken to help community understand the health of soil and water on and around the island after the recent floods.
Water samples from the river and puddles were collected to check for bacteria, nutrients, metals and organic compounds. Soil samples were collected to check for metals and organic compounds.
Results and safety recommendations
We found levels of potentially harmful bacteria above the guideline levels for healthy water. Nutrient levels were also high. At present, community should limit contact with the water on and around the Island to protect community health.
- Do not swim in or use water from the river or puddles on the island.
- Do not consume produce from gardens on the island.
- Prevent pets from swimming.
Environmental health on the Island will improve over time as bacteria die off. This process can occur over a few weeks or months depending on environmental conditions such as how warm it is and the amount of sunlight during the day. Levels of metals and organic compounds were low and considered safe. We will continue to monitor and review the situation and provide advice.
The results from this sampling does not indicate any outstanding issues that would stop the rebuilding process.
Sampling sites included the river system at the southern point of the island as well as the eastern and western channels. We collected six water and three soil samples.
Tests for microorganisms indicate if waters have been impacted by sewage, which contains bacteria and other pathogenic organisms that may pose a risk to community health. Levels of indicator bacteria found in sewage called Enterococci are tested to check the level of risk for illness.
|Bacteria Tested||Units||Water 1||Water 2||Water 3||Water 4||Water 5||Water 6|
- Enterococci levels were very high, recording above 500 cfu/100mL.1 Generally, levels of enterococci below 40 cfu/100mL have been shown to not have any adverse effect on human health in epidemiological studies.
- There may be significant risk of gastrointestinal or respiratory illness in the community if people ingest or inhale the water 2.
1 cfu = colony-forming unit of bacterial cells
2 NHMRC (2008) Table 5.7, Guidelines for managing risks in recreational waters (https://www.nhmrc.gov.au/about-us/publications/guidelines-managing-risks-recreational-water)
These guidelines have been developed to assess risks to people swimming in contaminated water at coastal beaches, but are also relevant to help assess potential health risks to people exposed to other waters potentially contaminated with sewage.
Nutrients such as compounds containing nitrogen (for example nitrate) or phosphorus act as food for aquatic microorganisms such as cyanobacteria (blue-green algae). High levels of these nutrients can allow these organisms to grow rapidly forming a ‘bloom’ that can be toxic if touched or ingested.
- Total nitrogen and total phosphorus levels were above estuary ecological guideline levels (ANZECC 2000, Table 3.3.2).
- River samples were up to seven times higher than the guideline value for total nitrogen, and 19 times higher than the guideline level for phosphorus.
- Growth of visible algal blooms are possible if these nutrients remain elevated due to continued rainfall in the Richmond River, leading to poor water quality in the river. However, no algal blooms were observed by the sampling team.
- Nutrients go through a cycling process known as nutrient cycles, where bacteria convert nitrogen compounds like ammonia into nitrite and nitrate. These nitrogen compounds can cause harm to aquatic organisms. Based on the nutrient results, ammonia, nitrite and nitrate were low, and it is not expected to result in harm in the Richmond River.
- Mass fish kills can occur after flood events. Once blue-green algae have used up all the nutrients, they can die off and decompose in the river. This causes dissolved oxygen in the water to drop to low levels and becomes a problem for aquatic animals, like fish that need oxygen to survive.
- The Department of Planning and Environment is continuing to monitor dissolved oxygen in the river following the recent flood.
Many heavy metals are vital for humans and animals to stay healthy and only pose a risk if they are found at high levels in the environment. The results found that all metal values were within safe guidelines. Aluminium is high in water by drinking water standards but is not a health concern. A summary of key metals found in water and soils are below.
|Metal in Water||NHMRC3||Sample4|
|Recreational Water Guidelines
3NHMRC (2008) Guidelines for managing risks in recreational waters & NHMRC Australian Drinking Water Guidelines. For recreational guidelines, NHMRC suggest ten times the current drinking water guideline (DWG) values to be used. Ten times the value of the most up to date DWG (NHMRC Version 3.7 Updated 2022, Table 10.6) were used.
4Concentrations are for unfiltered samples (as total metal concentrations).
*Aluminium and Zinc guideline values are based on aesthetics and taste rather than health effects.
|Metal in Soil||NEPM (2013) Guideline5||Sample|
|Residential soil with garden (HIL-A)(mg/kg)||
|Aluminium||No guideline value||16000||30000||20000|
5NEPM (2013) Health Investigation Levels (HIL-A, from Table 1A(1)). HIL-A is protective of home garden settings with accessible soil (assumes home grown produce with <10% fruit and vegetable intake), and includes childcare centres, preschools and primary schools.
Organic Compound Results
Organic compounds can include a range of petroleum products like bitumen or chemicals from agricultural run-off. Tests for organic compounds found total polyaromatic hydrocarbons (PAHs) were low with no health concerns for the community or environment.
|Total Polyaromatic Hydrocarbons (PAH)||NEPM Guideline (2013)||Sample|
|HIL-A5 (mg/kg)||Soil 1 (mg/kg)
||Soil 2 (mg/kg)||Soil 3 (mg/kg)
||Water 4 (mg/kg)
Note: No organic compounds were found in the other five samples.
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