Melbourne Rain Drops 10.6 kg of PFAS on the Bay

Researchers from RMIT University and EPA Victoria estimated that rain delivers about 10.6 kilograms of PFAS a year onto Port Phillip Bay. They found eight of these chemicals in Melbourne rain sampled in 2024 and 2025, at levels they said sat below national drinking water limits.

The tank-water reading is the part that travelled. The load on the bay is the part that changes how the city accounts for the same chemicals, because that rain never goes through a treatment plant.

Rain Puts 10.6 kg of PFAS on Port Phillip Bay Each Year

PFAS are a large family of human-made chemicals used in firefighting foams, food packaging, textiles, cosmetics and nonstick cookware. They move on dust and on tiny water droplets, then come down in rain far from the place they were made or used.

Lead researcher Professor Oliver Jones, from RMIT’s School of Science, said finding them in rain was not a shock. “Finding PFAS in rain isn’t surprising given how widespread these chemicals are in the environment,” Jones said.

The team scaled the levels in its Melbourne samples against local rainfall and the bay’s surface of 1,930 km². That produced about 10.6 kilograms a year, or 23.4 pounds, equal to about 5.5 grams per square kilometre. Doctoral student Navneet Singh is lead author of the paper on PFAS in south-eastern Australian rainwater, published in Environmental Toxicology and Chemistry.

Jones put the health question in dose language, not presence language.

The more useful question isn’t whether a chemical is toxic, but whether it’s present at a concentration that could actually cause harm. Dose and exposure matter.

Oliver Jones, Professor, RMIT School of Science

He also said the two best-known compounds, PFOS and PFOA, were below current Australian drinking water guideline values, which “should provide some reassurance for people who use rainwater as a source of drinking water.” The public summary does not name the other six of the eight compounds that cleared the lab’s limit of quantitation.

A Bay Already Loaded by Rivers and Sewage

Direct rain on the water is a separate input from the rivers that drain Melbourne. In 2025, EPA Victoria scientist Phoebe Lewis and colleagues published a catchment study of the same bay in Environmental Research. They sampled seven waterways that feed it: the Werribee, Maribyrnong and Yarra rivers, and Kororoit, Merri, Eumemmerring and Dandenong creeks.

Those catchments cover almost 10,000 km² around a city of about 5.2 million people, with mean annual rainfall of 518 mm. Grab samples found 25 of 52 PFAS screened, with a mean sum of 76.4 ng/L. The group estimated 57.4 kg a year from seven waterways for that 52-compound list. Treated sewage, counted on a shorter 19-compound list, was put at 26.7 kilograms a year, and the paper said surface water exported more than twice that sewage figure on the matched list.

PFAS LOADS TO PORT PHILLIP BAY

The three rows are not the same chemical list, so they should not be added into one total. They still show the same direction. Rain on the 1,930 km² of open water is smaller than the river figure and smaller than the sewage figure, and it is not a subset of either. It lands on the bay without passing a pipe.

Lewis and colleagues also found that a wide range of land uses, including ones not usually treated as point sources, shaped the PFAS mix in those creeks and rivers. Airports and sewer land did not dominate their catchment model. Diffuse cover did more of the work.

Land Air Left More PFAS in the Rain

EPA Victoria added atmospheric modelling to the rain project, so the team could trace the air that sat over Melbourne for each sampled storm. Rain tied to air that had travelled over land held higher PFAS levels than rain tied to air that had travelled over the ocean.

That split points at the city itself. Urban and industrial ground, not a long marine fetch, looks like the stronger local source of what the rain then washes out. Jones has spent years on the other version of this puzzle, the remote site with no factory and no foam pit. “Sometimes there’s an obvious source where they’re coming from, but sometimes you find it in a remote area where you’ve got no industry,” he said.

Rain is the missing link in those maps. Site models used for contaminated land already count foam training grounds, landfills and sewage plants. Atmospheric fallout now belongs on the same list, including at places that never hosted those uses. The chemicals can leave a city on dust, ride an air mass, and arrive in someone else’s gauge.

The ocean-air samples being cleaner also cuts against a simple sea-spray story for these Melbourne events. Whatever the global debate about spray lifting PFAS off seawater, the dirtier Melbourne rain in this set had crossed land.

What the Samples Mean for Tank Water

Jones’s reassurance is aimed at people who drink from tanks, and it is tied to numbers the National Health and Medical Research Council set on 25 June 2025. NHMRC published updated PFAS drinking water guideline values after a two-year review. The health-based limits are 8 ng/L for PFOS, 200 ng/L for PFOA, 30 ng/L for PFHxS and 1,000 ng/L for PFBS.

NHMRC PFAS DRINKING WATER VALUES

Jones said the rain levels were generally measured in nanograms per litre. “For context, one nanogram per litre is one part per trillion, so we are talking very low concentrations indeed,” he said. He also told AAP that all the concentrations the team found were well below the NHMRC PFAS drinking water guidelines. Those guidelines exist for four compounds. The paper’s public summary names PFOS and PFOA against the limits and does not say whether the other six detections have a national drinking-water value at all.

Protected catchments sit in a different place. Melbourne Water’s 2024-2026 program has catchment source water tested below 2 ng/L for PFOS, PFHxS, PFOA and PFBS. Tank water is roof runoff, not closed-catchment water, and the rain study is the first Australian look at that pathway.

Tanks are common enough for the question to matter. In October 2011 the Australian Bureau of Statistics counted 706,900 Victorian households with a rainwater tank, including 27 percent of Melbourne homes, with 127,600 Melbourne tanks plumbed into the dwelling. Many tanks feed gardens, toilets and laundry rather than the kitchen tap. The rain paper does not sort those uses. It only measures what fell.

Lingering Chemicals After the July Ban

On 1 July 2025, two months after the new drinking-water values, Australia’s Industrial Chemicals Environmental Management Standard listed PFOS, PFOA and PFHxS in its highest-risk schedule. The rules include an import and manufacture ban on PFOA, with matching prohibitions on PFOS and PFHxS, except for narrow cases such as research, trace contamination, and articles already in use.

Rain sampled across 2024 and 2025 still carried PFOS and PFOA. A ban on new import and manufacture does not empty the air of chemicals that already left factories, foams, landfills and everyday goods. Jones has been arguing that the popular label for this family misleads on that point.

PFAS are often called ‘forever chemicals,’ but that term can be misleading because it suggests they never break down, which isn’t actually the case. A more accurate description is that they are highly persistent, or ‘lingering,’ chemicals that can remain in the environment for a long time, which is why understanding their behaviour is so important.

Oliver Jones, Professor, RMIT School of Science

Lingering is the word that fits a 10.6 kilogram rain load after a national ban. The chemicals can still move. They just move slowly, and rain is one of the ways they relocate.

WHAT THE JULY 2025 RULES STOP

• New supply: Import, export and manufacture of PFOS, PFOA and PFHxS are prohibited except in listed cases.
• Trace leftovers: Unintentional contamination at or below 0.025 mg/kg for PFOA and its salts can still pass.
• Goods already here: Articles in use on 1 July 2025 are not pulled from homes and sheds by the new schedule.
• The rain: Nothing in the standard filters a storm that scavenges dust already in the air.

Jones said he hopes policymakers use the rain findings when they set future rules on PFAS use. The July list closes the front door on three well-known members of the family. It does not inventory what is already cycling through Melbourne air.

Measuring 30 PFAS in Small Rain Samples

The project began as a methods test. Rain samples are small, and the team wanted a way to quantify very low levels of contaminants in that volume. They collected rain on three occasions, screened 30 PFAS compounds, and reported eight detections, generally in nanograms per litre.

HOW THE RAIN STUDY WAS BUILT

1. 2024 to 2025: Rain is collected in Melbourne on three separate occasions.
2. Laboratory screen: The samples are tested for 30 PFAS compounds; eight are found above the limit of quantitation.
3. Air-mass step: EPA Victoria modelling assigns each event to land-origin or ocean-origin air.
4. Bay estimate: Measured levels are combined with Melbourne rainfall and the 1,930 km² bay surface to produce 10.6 kg a year.

Three storms are a thin base for an annual mass. The 10.6 kilogram figure is an estimate from that set, not a gauge network running all year. The land-versus-ocean contrast is also only as strong as those three air histories. Singh called the work a contribution to a hard environmental problem, not a finished map of the city’s sky.

That honesty is useful. A first Australian rain data set is still a first data set. It is enough to put rain next to sewage, landfill and runoff as a pathway. It is not enough to rank every suburb’s roof.

Broader Rain Monitoring Across Australia

EPA Victoria Deputy Chief Environmental Scientist Caroline Martino said the regulator was proud to sit on the paper. She treated it as evidence for the job the agency already has, not as a scare about taps.

This study provides valuable insights into how PFAS moves through the environment. Robust, peer-reviewed evidence is essential for effective regulation, risk assessment and management.

Caroline Martino, Deputy Chief Environmental Scientist, EPA Victoria

Jones wants the same method used more widely. He asked how much is there, where it came from, and what that says about movement, and he hoped for broader monitoring of PFAS in rainfall across Australia. A Melbourne trio of storms cannot speak for Darwin, Hobart or a farm tank west of the divide.

The practical change is narrower and closer to home. Port Phillip Bay already had a river number and a sewage number. It now has a rain number for the water surface itself, 10.6 kilograms a year, from air that was dirtier after it crossed land. That is the line the first Australian rain study actually added.

Frequently Asked Questions

What Are the Current Australian PFAS Drinking Water Guideline Values?

From 25 June 2025 the health-based values are 8 ng/L for PFOS, 200 ng/L for PFOA, 30 ng/L for PFHxS and 1,000 ng/L for PFBS. NHMRC’s Water Quality Advisory Committee moved PFOS from a draft of 4 ng/L to 8 ng/L after choosing a Gamma benchmark-dose model; the 2018 pair had been 70 ng/L for PFOS and PFHxS together and 560 ng/L for PFOA. No health-based value could be set for GenX chemicals on the evidence then available.

Has Melbourne Water Found PFAS in Catchment Source Water?

Melbourne Water’s 2024-2026 testing at seven protected and open catchment sites, including the Yarra Ranges, Tarago, Maroondah, mid-Yarra and Yan Yean, has not detected PFOS, PFHxS, PFOA or PFBS above 2 ng/L in source water. That closed-catchment result is not a reading of roof runoff into household tanks, which is the pathway the RMIT rain samples describe.

When Did Australia Ban PFOS, PFOA and PFHxS?

The IChEMS Schedule 7 listings took effect on 1 July 2025 and prohibit import, export, manufacture and new use of those three groups, with exceptions for research, environmentally sound disposal, unintentional trace contamination, and articles already in use on that date. Therapeutic goods sit outside IChEMS, which is why the Therapeutic Goods Administration said medical devices were not caught by the environmental standard.

Why Did the Draft PFOS Limit Move From 4 ng/L to 8 ng/L?

Public consultation in October 2024 used 4 ng/L. NHMRC’s Water Quality Advisory Committee then selected the Gamma model from an SLR assessment, which produced 8.49 ng/L, rounded to 8 ng/L under the rounding rules in Chapter 6 of the Australian Drinking Water Guidelines. NHMRC CEO Professor Steve Wesselingh said the final set was reviewed by that committee, an independent expert review, and jurisdictional public health experts including the Chief Health Officers.

What Does One Nanogram Per Litre Mean in Plain Terms?

Jones described one nanogram per litre as one part per trillion. Melbourne Water uses a household picture for the same unit: 1 ng/L is like one drop of water in 20 Olympic-sized swimming pools. The rain detections sat in that nanogram-per-litre range, which is why the team built a method for small samples rather than relying on a routine tap-water run.

Disclaimer: This article is news reporting on a published environmental chemistry study and related Australian water-quality rules. It is for information only and is not drinking-water advice, medical advice, or a risk assessment of any household tank, roof, or bay fishery. Anyone who drinks rainwater, manages a tank, or has a health concern about PFAS exposure should speak with a qualified doctor and, for tank or plumbing decisions, a licensed water or environmental health professional. The figures and statuses here reflect the cited papers, NHMRC values, Melbourne Water testing notes and IChEMS listings as those sources stood on the dates given, and later tests or rule changes can move them.