The Contaminant Impacts Research Program at the Australian Nuclear Science and Technology Organization (ANSTO) studies how contaminants, such as mercury, have a lasting impact on the environment. Researchers Tom Cresswell and Alexandra Boyd recently shared their findings with Hidex and Australian distributor Skudtek Scientific, emphasising their use of the Hidex AMG gamma counter in contamination research related to the decommissioning of offshore oil and gas infrastructure.

Offshore decommissioning and environmental impact

Tom Cresswell’s research group in Sydney focuses on radioecology and environmental ecotoxicology. Early in our discussion, we took a deep dive into the challenges of offshore infrastructure decommissioning and its environmental implications. Australia is home to numerous offshore oil and gas extraction facilities, and national legislation mandates the removal of this infrastructure from the ocean once operations cease.

However, decommissioning comes with substantial financial burdens, often costing tens of billions of dollars. In some cases, exemptions to the legislation are granted if companies can demonstrate a net environmental benefit to leaving structures in place. For example, certain infrastructure may serve as artificial reefs, supporting entire aquatic ecosystems and possibly fisheries.

Contaminants in decommissioned pipelines

While subsea pipelines may provide ecological benefits, they can also accumulate harmful contaminants over time. Two significant contaminants of concern that may form as mineral scales or films on the internal surfaces of production pipelines are naturally occurring radioactive material (NORM) and mercury. These substances may leach into the environment over time, posing risks to marine life and the broader food web.

Mercury exists in various chemical forms, including methylmercury, metacinnabar (mercuric sulfide), and elemental mercury. Due to its persistence and ability to bioaccumulate, mercury contamination can have severe consequences for fisheries, marine ecosystems, and ultimately human health also.

Retention of mercury in marine organisms

One of the research team’s key applications involves assessing the persistence of mercury in the food web using radioisotope tracers of mercury (²⁰³Hg). Their lab workflows include introducing small marine organisms, such as prawns, into seawater containing radioisotopes of mercury, generated using ANSTO’s OPAL research reactor.

Marine organisms are exposed to sources of radioactive mercury under controlled conditions in the laboratory, from either spiked seawater, sediment or food. The quantification of mercury radioactivity in live animals are then quantified using the Hidex AMG counter. The AMG allows to quantify a range of different radionuclides and is used by the ANSTO researchers to determine bioaccumulation kinetics of contaminants (e.g., mercury), which helps to understand how organisms will accumulate and retain contaminants from the environment.

Bioaccumulation studies and mercury retention

In a pulse-chase experiment studying mercury chloride and mercury sulfide retention in marine snails using mercury radiotracers, the team observed how these contaminants were processed by organisms when ingested. Over a four-day period, more than half of the mercury chloride was retained in the muscle tissue, while mercury sulfide, due to its insolubility, did not have a tendency to bioaccumulate and passed through the gut.

These bioaccumulation and toxicity studies are critical in understanding how contaminants interact with marine organisms, and ultimately, the impact contaminants have.

This research provides critical insights into environmental risk assessments, guiding policymakers and advisors toward effective strategies for offshore decommissioning and marine ecosystem protection. With the help of these findings, decision-makers can take a more sustainable approach to preserving ocean health.