PFAS "Forever Chemicals" in Rainwater

For generations, rainwater was viewed as the ultimate source of pristine, fresh water. However, a groundbreaking study has fundamentally shifted that understanding. Researchers have determined that rainwater across the globe is no longer safe to drink according to the latest health guidelines. This article explores the specifics of the study, the nature of these chemicals, and what this means for environmental safety and personal health.

The Stockholm University Study

A team of researchers from Stockholm University and ETH Zurich published alarming findings in the journal Environmental Science & Technology. Their research concluded that rainwater everywhere on Earth contains levels of per- and polyfluoroalkyl substances (PFAS) that exceed safety limits.

This is not a localized issue restricted to industrial zones. The study collected data from some of the most remote places on the planet, including Antarctica and the Tibetan Plateau. Even in these isolated regions, the levels of specific PFAS chemicals in rainwater were higher than the drinking water advisory levels set by the United States Environmental Protection Agency (EPA).

The lead author of the study, Ian Cousins, noted that based on the latest US guidelines for PFOA (a specific type of PFAS), rainwater everywhere would be judged unsafe to drink. This suggests that the planetary boundary for chemical pollution has been crossed.

What Are "Forever Chemicals"?

To understand the gravity of this finding, it is necessary to understand what PFAS are. The acronym stands for per- and polyfluoroalkyl substances. This is a family of thousands of synthetic chemicals that have been used in industry and consumer products since the 1940s.

They are widely known as “forever chemicals” because of their molecular structure. They possess a carbon-fluorine bond, which is one of the strongest bonds in organic chemistry. This bond does not break down naturally in the environment. Consequently, these chemicals persist in water, soil, and human bodies for years or even centuries.

Common Sources of PFAS

You likely interact with materials containing these chemicals daily. They are prized for their ability to repel grease, water, and oil. Common applications include:

  • Non-stick cookware: Pans coated with Teflon (PTFE) historically used PFOA in production.
  • Food packaging: Grease-resistant wrappers for fast food, pizza boxes, and microwave popcorn bags.
  • Textiles: Water-repellent clothing (like rain jackets), stain-resistant carpets, and upholstery.
  • Firefighting foam: Aqueous film-forming foam (AFFF) used at airports and military bases to extinguish fuel fires.

The Gap Between Rainwater Levels and Safety Limits

The reason rainwater is now considered “unsafe” is largely due to a drastic tightening of health guidelines. As scientists learn more about the toxicity of PFAS, the “safe” level drops lower and lower.

In June 2022, the EPA issued interim updated drinking water health advisories for two of the most common and dangerous PFAS: PFOA and PFOS. The new advisories are near zero.

  • PFOA Limit: The EPA set the interim advisory limit at 0.004 parts per trillion (ppt).
  • PFOS Limit: The limit was set at 0.02 parts per trillion (ppt).

To put this in perspective, 1 part per trillion is roughly equivalent to a single drop of water in 20 Olympic-sized swimming pools. The EPA is essentially saying that no amount of these chemicals is safe.

The Stockholm University study found that rainwater often contains levels of PFOA that are hundreds or even thousands of times higher than these minute 0.004 ppt limits. While the levels in the rain have not necessarily increased drastically in recent years, the definition of what is toxic has changed dramatically.

How PFAS Enters the Water Cycle

If these chemicals are manufactured on land, you might wonder how they end up in the rain falling over Antarctica. The answer lies in the global water cycle and the ocean.

PFAS are mobile in water. They wash out of landfills, factories, and fields into rivers, eventually reaching the oceans. Once in the ocean, they do not just sit there. The process involves sea spray aerosols.

  1. Transport: Ocean waves crash and create bubbles.
  2. Aerosolization: When these bubbles burst, they release aerosols (tiny particles) into the air.
  3. Atmospheric Travel: PFAS attach to these aerosols and travel into the atmosphere.
  4. Precipitation: The chemicals eventually fall back to Earth as rain or snow.

This creates a continuous cycle where the chemicals are recirculated rather than diluted. Even if we stopped all manufacturing of PFAS today, the chemicals currently in the ecosystem would continue to cycle through the rain for decades.

Health Risks Associated with Exposure

The EPA lowered its safety limits because recent science links long-term exposure to minute levels of PFAS to serious health problems. These chemicals are bioaccumulative, meaning they build up in the body over time faster than they are excreted.

Peer-reviewed studies have linked high levels of certain PFAS to the following health issues:

  • Cancer: Increased risk of kidney and testicular cancer.
  • Immune System: Reduced ability of the body’s immune system to fight infections, including reduced response to vaccines in children.
  • Hormones: Disruption of natural hormone regulation and thyroid disease.
  • Reproductive Health: Decreased fertility and pregnancy-induced hypertension.
  • Development: Low birth weight and developmental delays in children.

Industry Changes and Regulation

The news regarding rainwater is grim, but there is movement toward phasing out these chemicals. Major manufacturers are facing immense pressure from regulators and lawsuits.

For example, 3M, one of the largest manufacturers of these substances, announced it will exit all PFAS manufacturing and work to discontinue the use of PFAS across its product portfolio by the end of 2025.

Governments are also taking action beyond advisory limits. The European Union is currently evaluating a proposal to ban the entire class of PFAS chemicals (over 10,000 substances), which would be the most extensive chemical restriction in history. In the United States, the EPA is moving to designate PFOA and PFOS as hazardous substances under the Superfund law, which would force polluters to pay for cleanup.

Protecting Yourself at Home

While you cannot scrub the atmosphere, you can take steps to reduce your exposure at home. It is important to note that boiling water does not remove PFAS. In fact, boiling evaporates the water and leaves the chemicals behind, effectively increasing their concentration.

Effective Filtration

Not all water filters are created equal. Simple pitcher filters often lack the density to capture these chemicals. To effectively remove PFAS from tap water (or collected rainwater), look for these technologies:

  • Reverse Osmosis (RO): These systems are highly effective. They push water through a semipermeable membrane that catches contaminants as small as ions. High-quality under-sink RO units can reduce PFAS levels by more than 90%.
  • Activated Carbon: High-quality granular activated carbon or carbon block filters can be effective, but they must be changed regularly. If the carbon becomes saturated, the chemicals can break through.
  • Ion Exchange: These resins act like tiny magnets for contaminants and are often used in whole-house filtration systems.

Frequently Asked Questions

Is it safe to drink rainwater? Based on the new EPA lifetime health advisories and the findings of the Stockholm University study, drinking untreated rainwater is generally unsafe anywhere on Earth due to PFAS contamination levels.

Does boiling water remove PFAS? No. PFAS are heat-resistant chemicals. Boiling water will actually concentrate the chemicals because the water volume decreases while the amount of chemicals stays the same.

Can plants absorb PFAS from rainwater? Yes. If you water your garden with contaminated rainwater, plants can uptake these chemicals. However, the risk of ingestion through eating vegetables is generally considered lower than the risk of drinking contaminated water directly.

Do bottled waters contain PFAS? They can. Bottled water is not immune to contamination. However, many reputable brands purify their water using Reverse Osmosis before bottling, which removes the vast majority of PFAS. You should check the water quality report of the specific brand you buy.