The Ranger Uranium Mine has ceased operation in January 2021 and has entered the rehabilitation phase. Contaminated site assessments were undertaken to guide the rehabilitation, during which PFAS were recorded on the mining lease and close to areas where PFAS chemicals were known to be used.
The Office of the Supervising Scientist (OSS), in collaboration with the local Djurrubu Rangers, sampled the streams and billabongs in the wider region and downstream of both, the Jabiru township and the Ranger Uranium Mine. Water samples at locations close to the mine and township showed up to nine PFAS compounds of 28 analysed, and fewer compounds were recorded further downstream. Perfluorooctane sulfonate (PFOS) was measured at low concentrations with an apparent concentration gradient where higher PFOS concentrations closer to the Jabiru township and Ranger mine and lower PFOS at increasingly greater distances were recorded. Of all surface water samples 29.6% were below the reporting limit and 8.6 % measured concentrations above the (new) 99% species protection guideline value (GV) of 0.0091 µg/L, but below the 95% GV of 0.48 µg/L. There was limited seasonal variability in PFAS in these streams and billabongs. Seven percent of billabong sediment samples were positive for low PFOS concentrations.
The local residents are concerned about the potential contamination of traditional aquatic food sources. A preliminary investigation focussed on freshwater mussels from Mudginberri Billabong, and recorded 1 µg/kg of PFOS in one of 13 composite samples, which is below safe concentrations for consumption.
OSS are planning to sample tissue of fish, turtle and file snake commonly consumed from Mudginberri Billabong, to conduct a human-health risk assessment and determine if there has been bioaccumulation and biomagnification in the food chain.