Anthropogenic radionuclides persist in marine sediment at the Montebello Islands nuclear legacy site in Western Australia
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Date
2022-11-28
Journal Title
Journal ISSN
Volume Title
Publisher
South Pacific Environmental Radioactivity Association
Abstract
In 1952 and 1956 the UK government conducted three atmospheric nuclear fission tests in the Montebello Islands, an archipelago approximately 100 km off the coast of northern Western Australia. Radioactive contamination from the tests was deposited locally across the archipelago in both terrestrial and marine environments but was investigated minimally in the decades that followed. This is particularly true for the marine environment which is composed of various distinct ecosystems – from mangroves to open marine channels and is home to a diverse trophic web of marine organisms. To understand the extent and persistence of anthropogenic radionuclides introduced by the tests into this region, we aim to establish the distribution of anthropogenic radionuclides in the marine surface sediments throughout the archipelago. Here we present the results on activity concentrations and distributions of 90Sr, 137Cs, 238 Pu, 239&240Pu and 241Am due to their long half lives and their potential to impart radiological dose to organisms existing at the sediment-water interface.
Quantification of anthropogenic and naturally occurring radionuclides in surface and core samples was completed by alpha spectrometry, Cherenkov counting and gamma spectrometry.
Activity concentrations of 90Sr, 137Cs, 238 Pu, 239&240Pu and 241Am were highest around the detonation locations in the north of the archipelago in surface sediment samples. Observable activity concentrations also persist in the north-west of the detonation locations, reflecting the direction of the original fallout plumes from the weapons. One additional location showed higher activity concentrations of 90Sr, 137Cs, 238 Pu, 239&240Pu and 241Am in comparison to other locations within the archipelago (121 Bq/kg, 1.6 Bq/kg, 80 Bq/kg, 402 Bq/kg and 28 Bq/kg respectively). This sample was collected 26 km south of the nearest detonation site and was originally selected as an environmental control outside of the state marine park boundaries, suggesting migration of anthropogenic radionuclides has occurred in the 70 years since the detonations took place.
Sediment cores were also taken from different marine environments of the region, including at the bottom of the crater created by Operation Hurricane, which involved the detonation of a naval ship in shallow water in 1952. 210Pb was analysed to assess the sedimentation rates over the last century across the cores. In most instances, mixing dominated throughout the sediment core profiles. This reflects the highly dynamic and turbulent nature of the region, subject to seasonal cyclones and fast-moving tides within the archipelago. The exception to this observed mixing was found in a single core, the ‘Hurricane Core’, taken in the bottom of the Operation Hurricane crater. 137Cs and 241Am activity concentrations of this core showed a clear peak in activity at 50 cm depth; an order of magnitude above those found in similar parts of the region within surface sediments. The maximum activity concentrations of 180 Bq/kg and 66 Bq/kg for 137Cs and 241Am respectively were established in the core at 50 cm depth, with the closest surface sediment activity concentrations established at 56 Bq/kg and 20 Bq/kg.
Description
Keywords
Radioisotopes, Aquatic ecosystems, Islands, Western Australia, Nuclear test sites, Nuclear explosions, Contamination, Plutonium 238, Plutonium 239, Plutonium 240, Strontium 90, Cesium 137, Americium 241
Citation
Williams-Hoffman, M., Johansen, M., Lavery, P., Thiruvoth, S., Serrano. O., & Masqué, P. (2022). Anthropogenic radionuclides persist in marine sediment at the Montebello Islands nuclear legacy site in Western Australia. Paper presented to the SPERA 2022 - SPERA 2022 - Connecting People, developing solutions for a Changing Environment, 28-30 November 2022, Chrischurch, New Zealand, (pp. 27). Retrieved from: https://au-admin.eventscloud.com/file_uploads/baa6bb17538b457fbd436f1552075bea_SPERA2022e-handbook.pdf