Heavy metal contamination of river systems can occur from a variety of sources including the erosion of naturally mineralised rocks, mining activities and from urban and industrial wastes and effluents. 

The Upper Macleay River is scattered with known naturally occurring deposits of mineral resources that have been historically mined. 

Council has undertaken programs to monitor heavy metals in the Macleay River, at Bellbrook, for water supply purposes. 

In 2005 to 2007, intensive metals analysis was undertaken following elevated levels of arsenic found in the drinking water at Bellbrook. 

The monitoring of the river and bore water indicated the arsenic levels were associated with the groundwater and not the river surface water.

Council has continued to monitor the surface water quality for heavy metals. Sampling has been associated with events such as flooding and overflows of the stormwater detention ponds from the disused Hillgrove mine site. 

Council director of infrastructure services Robert Scott said while previous studies had identified the presence of naturally abundant minerals in the Macleay River catchment, the current research effort is examining the forms in which the metals are present in the environment. 

“Some forms are far more susceptible to bioaccumulation than others, which may explain why there doesn’t appear to be a carryover from the sediments into food production or the resident population,” Mr Scott said.

“The latest results for monitoring of the heavy metals in the river water at Bellbrook show levels of antimony at generally 0.001mg/l with one recent result of 0.006mg/l.  

“With the exception of the recent result of 0.006mg/l, overall these are low levels and well below the guideline value in the Australian drinking water guidelines of 0.003mg/l. 

“It should be noted that there is no guideline for antimony in relation to recreational and agricultural uses. "The levels of arsenic have been around 0.002-0.004mg/l through most of the data on our website which is much lower than both the Australian Drinking Water Guidelines (ADWG) and Australian and New Zealand Environment Conservation Council (ANZEC) guidelines.”

Mr Scott said arsenic naturally occurring in water supplies happens all over the world and as a result has been studied to a far greater extent than antimony. 

“This level of understanding and the reduced risk is reflected in the higher guidelines values for arsenic,” Mr Scott said. 

“There is a far lower level of scientific understanding of the long term impacts of antimony in drinking water hence the guideline values are much lower in order to be conservative until proven otherwise.

“So even though the guideline values vary quite a bit this is not to say that one is any worse that the other, just that we know more about one and therefore can adopt a less conservative approach. The guidelines for recreational waters are much higher again.”

To see the NSW Health report on the Macleay River water quality go to the council website at www.kempsey.nsw.gov.au/environment/estuary-management/upper-macleay