CSIRO Study Shows Declining PFOS but Persistent Heavy Metals in SA Dolphins

Overview

A peer-reviewed study published by CSIRO and the South Australian Environment Protection Authority (SA EPA) has documented three decades of contaminant trends in South Australian dolphins, providing one of the most comprehensive long-term datasets on PFAS and heavy metal contamination in Australian marine mammals. The research, covering specimens from 1993 to 2023, reveals a clear downward trend in PFOS concentrations in dolphins from the Adelaide Dolphin Sanctuary and Port River Estuary, validating the effectiveness of regulatory bans on PFOS and fluorinated firefighting foams. However, the same study found persistently elevated concentrations of mercury, lead, and tin, raising important questions about legacy heavy metal contamination in urbanised estuarine environments.

Key details

The study analysed hepatic (liver) tissue samples from Indo-Pacific bottlenose dolphins across two sampling periods: 1993 to 2015 and 2021 to 2023. Key findings include:

• PFAS screening: Researchers tested for 29 PFAS compounds and identified 21 different PFAS in dolphin liver tissue. PFOS was the dominant compound, comprising approximately 80 per cent of the total PFAS load.
• Declining PFOS trend: Total PFAS concentrations showed a clear downward trend between the two sampling periods, correlating with the 2002 phase-out of PFOS and PFOA importation into Australia and subsequent state-level bans on fluorinated aqueous film-forming foams (AFFF).
• Persistent heavy metals: Mercury concentrations were recorded at up to 2,350 mg/kg dry weight in hepatic tissue. Lead and tin also remained persistent across the sampling periods, indicating ongoing bioaccumulation of legacy heavy metals in the marine food web.
• 18 metals screened: The study included comprehensive metals analysis, providing baseline data for ecological risk assessments in the Port River Estuary and surrounding marine environments.

The study’s use of marine apex predators as biomonitors provides an integrated measure of environmental contamination across the entire catchment and food web, rather than point-source sampling alone.

Australian context

The Port River Estuary and Adelaide Dolphin Sanctuary sit within one of South Australia’s most heavily urbanised and industrialised catchments. Historical land uses in the catchment include defence facilities, industrial manufacturing, fuel storage, and wastewater treatment, all of which have contributed to legacy contamination of sediments and groundwater.

The PFAS findings align with the trajectory of Australian PFAS regulation. The PFAS National Environmental Management Plan (NEMP), now in its third edition, has progressively tightened screening levels and management expectations for PFAS-contaminated sites. The observed decline in dolphin PFOS concentrations provides ecosystem-level evidence that source control measures, including import restrictions and AFFF bans, are delivering measurable environmental outcomes.

However, the persistent heavy metal contamination presents a different challenge. Mercury, lead, and tin are not subject to the same source-elimination strategies available for synthetic chemicals. These metals persist in sediments and bioaccumulate through marine food webs over decades. For sites in urbanised estuaries across Australia, including Sydney Harbour, the Brisbane River, and the Derwent Estuary in Hobart, similar legacy metal contamination is well documented.

The study reinforces that environmental risk assessments in these settings must consider the additive and synergistic toxicity of co-occurring contaminants. Regulators will not accept PFAS remediation success as sufficient if legacy metals continue to pose unacceptable ecological risks.

Practical implications

For contaminated land consultants, ecological risk assessors, and remediation practitioners, this study delivers several important messages:

• Co-contaminant assessment is essential. Sites with PFAS contamination in urbanised catchments almost always have co-occurring heavy metal contamination. Environmental site assessments must screen for both contaminant groups. Remediation strategies that address PFAS alone may not achieve regulatory closure if metals remain above guideline values.
• Biomonitoring provides powerful lines of evidence. Dolphin tissue concentrations integrate contaminant exposure across the entire food web and catchment. For sites near sensitive marine environments, biomonitoring data can supplement conventional groundwater and sediment sampling to provide a more complete picture of environmental risk.
• Legacy metals require long-term management. Unlike PFAS, where source elimination can drive declining environmental concentrations, heavy metals in estuarine sediments are effectively permanent on human timescales. Remediation strategies must account for ongoing exposure pathways and include long-term monitoring commitments.
• Regulatory expectations are tightening. The PFAS NEMP and state EPA guidelines are progressively raising the bar for site assessment and remediation. Practitioners should anticipate that future updates will incorporate the growing body of ecological monitoring data, including studies like this one, into refined screening levels and risk assessment frameworks.
• Defence and industrial legacy sites require comprehensive assessment. Many PFAS-impacted sites in Australia are former defence facilities or industrial sites with multiple contaminant sources. Site investigations must characterise the full contaminant profile, not just the headline PFAS compounds.

References and related sources

• Original peer-reviewed study (Springer)
• PFAS National Environmental Management Plan (DCCEEW)
• SA Environment Protection Authority
• View the iEnvi LinkedIn post

How iEnvi can help

iEnvi specialises in PFAS and contaminated land assessment, remediation, and management across Australia. Our relevant services include:

• Contaminated land assessment, including PFAS detailed site investigations, human health and ecological risk assessments, and multi-contaminant site characterisation
• Remediation design and implementation for PFAS, heavy metals, and co-contaminated sites, including sediment and groundwater remediation in estuarine environments
• Expert witness services for PFAS litigation, contaminated land disputes, and regulatory enforcement proceedings

If you need specialist PFAS assessment, ecological risk evaluation, or remediation advice for contaminated sites, contact iEnvi.

This is an iEnvi Machete news summary. Prepared by iEnvi to summarise the source article for contaminated land, groundwater, remediation, approvals and site risk professionals.

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