2012/13: Goorambat Gross Alpha Activity 0.69 (Bq/L)
The maximum gross alpha activity result at Goorambat unexpectedly exceeded the ADWG screening level of >0.5 Bq/L which was suspected an anomalous result and prompted further investigation in accordance with ADWG 2011. The initial retest for gross alpha and gross beta activity at Goorambat returned lower levels (<0.28 Bq/L respectively) which were in the normal test range. In accordance with North East Water’s risk management plan and risk-based monitoring program, testing for radiological parameters (including individual radionuclides) is now scheduled quarterly for Goorambat until levels can be verified. (North East Water 2012/13).
Radionuclides (Other beta- and gamma-emitting)
No specific guideline values are set for beta- or gamma-emitting radionuclides.
Specific beta- or gamma-emitting radionuclides should be identified and determined only
if gross beta radioactivity (after subtracting the contribution of potassium-40) exceeds 0.5 Bq/L (27.6 Bq of beta activity per gram of stable potassium).
Several radionuclides that are classified as beta-particle or gamma-ray emitters may occasionally be present in drinking water. The significant long-lived nuclides in this group are the naturally occurring isotopes potassium-40, lead-210 and radium-228, and artificial radionuclides caesium-137 and strontium-90. Tritium, another nuclide in this group, is present in the environment both from natural sources and as a result of nuclear fall-out and nuclear power generation.
Levels of strontium-90 and caesium-137 in the Australian environment have decreased substantially since atmospheric testing of nuclear weapons ceased, and these radionuclides are not detectable in drinking water. In the absence of a nuclear power industry in Australia, these nuclides are likely to be present in significant concentrations in drinking water only as a result of transient contamination following an event such as a nuclear accident.
Potassium‑40 occurs naturally in a fixed ratio to stable potassium. Potassium is an essential element for humans, and is absorbed mainly from ingested food. Potassium-40 does not accumulate in the body but is maintained at a constant level independent of intake. The average concentration of potassium in an adult male is about 2 g/kg of bodyweight, which gives an activity mass concentration of potassium-40 of 60 Bq per kg of bodyweight. The corresponding value for females is slightly less.
Lead-210, like radium-226, is a decay product of the uranium-238 series. Food is the most important route by which lead-210 enters the human body, and the annual intake depends on diet: highest concentrations are found in fish and other aquatic species. Generally, lead-210 concentrations in drinking water are considerably less than concentrations of either radium-226 or radium-228.
TYPICAL VALUES IN AUSTRALIAN DRINKING WATER
Concentrations of potassium-40 in Australian drinking water supplies vary widely, from below 0.05 Bq/L in surface water sources to more that 1 Bq/L in some supplies drawn from groundwater.
There are only limited data on concentrations of other beta- or gamma-emitting radionuclides such as lead-210, strontium-90 and caesium-137 in Australian drinking water supplies. Lead-210 concentrations are probably below 0.05 Bq/L and concentrations of artificial radionuclides are negligible.