Mercury human health risk assessment — Tasmanian mine site
iEnvi (iEnvironmental) completed a targeted surface water, sediment and soil sampling programme in March 2018 on behalf of a community group near a municipal potable water intake and an open scheelite mine pit on an island in Tasmania (tagged as King Island). The project responded to community concerns about elevated mercury reported in residents’ hair and blood samples and sought to determine whether the mine and associated tailings were a likely source.
What we did
- Planned and implemented sampling of surface water, creek-bed sediment (grab samples), bank and floodplain soils, rock and sediment from the open mine pit and the scheelite tailings dam.
- Prioritised locations near the municipal water-supply intake and within the downstream flood zone.
- Considered mine history and the large volume of tailings and sediments when designing a limited, targeted sampling programme.
Why this matters — plain English
- Mercury risk: Mercury can pose human health risks if people are exposed via drinking water, food (e.g. fish), dust or direct soil contact, and hair and blood testing can indicate prior exposure.
- Receptor focus: The municipal potable intake and local residents were the primary receptors of concern; assessing sediment and soil near the intake helped evaluate potential pathways.
- Site context: Scheelite (calcium tungstate, CaWO4) deposits are often associated with mercury in ores and tailings, so mine-derived materials are a credible potential source.
Key findings and practical implications
The study concluded that, for the locations sampled, there was likely minimal human health risk associated with mercury. However, the sampling was limited relative to the overall extent and volume of tailings, soils and sediments on site. Practical implications include:
- For community reassurance: the sampled locations did not show evidence of widespread elevated mercury risk, which helps reduce acute community exposure concerns.
- For regulators and developers: limited sampling provides an initial risk screen but is unlikely to satisfy due-diligence requirements for subdivision, redevelopment or transaction without follow-up work.
- For ongoing protection: targeted follow-up sampling, comparison to relevant health and environmental guideline values, and clear communication of results and uncertainties are recommended.
Recommended next steps
- Undertake a staged follow-up programme focused on data gaps: additional soil/sediment sampling around the largest tailings accumulations, upstream/downstream transects from the water intake, and media likely to influence human exposure (e.g. edible fish, drinking water if abstraction is unfiltered).
- Compare measured concentrations to current Australian and state human-health and ecological guideline values and document exposure assumptions used in risk calculations.
- Implement simple ongoing monitoring of the potable intake and key downstream locations if the water supply is potentially vulnerable.
- Prepare a targeted risk communication package for the community and stakeholders summarising findings, uncertainties and next steps.
Communications and stakeholder management
A communications plan on this project managed interactions with multiple government bodies, community groups and media. Early, transparent engagement and clear explanation of limitations in the dataset were central to maintaining community confidence.
Practical takeaways
- Limited, well-targeted sampling can quickly clarify immediate risks but rarely removes the need for further work where there is a large volume of tailings or heterogeneous deposits.
- Matching the sampling design to the decision (community reassurance vs. regulatory approval vs. property transaction) determines whether results are sufficient.
- Stakeholder engagement and clear reporting of uncertainties are as important as laboratory results in managing community concerns.
Want help with a similar community or site risk issue? Contact iEnvi on 13000 43684 or via our contact page for a pragmatic next-step plan tailored to your project.