They found that the average temperature at which the droplets froze was 5–10 degrees warmer than droplets without microplastics. Typically, an atmospheric water droplet without any defects freezes at about -38°C.

Any kind of defect in the water droplet, whether that's dust, bacteria or microplastics, can give ice something to form—or nucleate—around. That tiny structure is just enough to trigger the water droplet to freeze at warmer temperatures.

In the case of the researchers' microplastics, 50% of the droplets were frozen by -22°C for most of the plastics studied. It turns out that if you introduce something insoluble, you introduce a defect into that droplet and it can nucleate ice at warmer temperatures.

What this discovery means for weather and climate is not entirely clear with just this experiment, but it suggests that microplastics are likely already making an impact. 

Mixed-phase clouds, such as the puffy cumulus, blanket-like stratus and dark, ominous nimbus clouds, all contain a combination of liquid and frozen water. These clouds can be widespread throughout the atmosphere, including the classic "anvil" shaped clouds that can form during thunderstorms.

When air patterns are such that a droplet gets lifted into the atmosphere and cools, that's when microplastics could be affecting weather patterns and forming ice in clouds.

In a polluted environment with many more aerosol particles, like microplastics, you are distributing the available water among many more aerosol particles, forming smaller droplets around each of those particles. When you have more droplets, you get less rain, but because droplets only rain once they get large enough, you collect more total water in the cloud before the droplets are large enough to fall and, as a result, you get heavier rainfall when it comes.

In general, clouds cool the Earth by reflecting solar radiation, but certain clouds at certain altitudes can have a warming effect by helping to trap energy emitted from the Earth. The amount of liquid water versus the amount of ice is important in determining to what extent clouds will have a warming or cooling effect. If microplastics are influencing mixed-phase cloud formation, the researcher s say, they are likely affecting climate, too, but it's extremely difficult to model their overall effect right now.

We know that the fact that microplastics can nucleate ice has far-reaching effects, we're just not quite sure yet what those are. We can think about this on many different levels, not just in terms of more powerful storms but also through changes in light scattering, which could have a much larger impact on our climate.

The researchers also found that environmental aging, the natural photochemical processes that aerosol particles experience over time, can significantly change how the particles interact with gases and vapors in the atmosphere. The team simulated environmental aging by exposing the microplastics to light, ozone and acids to see if it changed their ability to form ice.

They found that all the tested plastics could form ice, but aging generally reduced the ice-forming ability of LDPE, PP and PET. In contrast, aging increased the ice-forming ability of PVC due to slight changes on its surface caused by aging.

Next, the team is going to study a variety of additives that are commonly put into plastics, such as plasticizers, to get a better sense of how commonly used plastics may affect the Earth's atmosphere.

 The full lifecycle of these plastic items we use every day could be changing the physical and optical properties of the Earth's clouds and, therefore, changing the climate in some way, but we still have a lot to learn about exactly what they are doing, conclude the researchers.

 Heidi L. Busse et al, Pristine and Aged Microplastics Can Nucleate Ice through Immersion Freezing, ACS ES&T Air (2024). DOI: 10.1021/acsestair.4c00146. ChemRxiv : DOI: 10.26434/chemrxiv-2024-86g6r

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Plastics pollution worsens the impacts of all planetary boundaries, new study says

Plastics are not as safe and inert as previously thought. A new research study written by an international team of researchers uses the planetary boundaries framework to structure the rapidly mounting evidence of the effects of plastics on the environment, health and human well-being.

It's necessary to consider the full life cycle of plastics, starting from the extraction of fossil fuel and the primary plastic polymer production.

Five hundred million tons of plastics are now produced yearly but only 9% get recycled globally. Plastics are everywhere: from the top of Mount Everest to the deepest part of the Mariana Trench.

Through a synthesis review of the scientific literature on the impacts of plastics on the natural environment, the research team shows that plastics pollution is changing the processes of the entire Earth system, and affects all pressing global environmental problems, including climate change, biodiversity loss, ocean acidification, and the use of freshwater and land.

The paper, titled "Plastics pollution exacerbates the impacts of all planetary boundaries," emphasizes the need to consider the complexity of plastics. As synthetic polymer-based materials associated with thousands of other chemicals, their impacts occur throughout the full life cycle of these products and materials. The work is published in One Earth.

Plastics are seen as those inert products that protect our favorite products, or that make our lives easier, that can be 'easily cleaned up' once they become waste. But this is far from reality. Plastics are made out of the combination of thousands of chemicals. Many of them, such as endocrine disruptors and chemicals, pose toxicity and harm to ecosystems and human health. We should see plastics as the combination of these chemicals with which we interact on a daily basis.

Until recently, the scientific community has mostly studied these impacts separately, without addressing interactions between them. Also, public discourse and policy tend to address plastics as mainly a waste problem.

The impacts of plastics on the Earth system are complex and interconnected, and this work clearly demonstrates how plastics are acting to destabilize the system.

The team suggests a set of control variables that can be used together to include plastics pollution in the operational use of the Planetary Boundaries framework. Their impact pathway approach considers impacts and indicators at three main stages in the full life cycle of plastics: raw material extraction, plastics production and use; environmental release and fate; and Earth system effects.

The available evidence shows clearly how plastics contribute to environmental problems up to the planetary scale, both directly and via downstream biophysical interactions and cumulative effects.

Many people worldwide already face crisis conditions due to breached planetary boundaries. Understanding the systemic interactions of plastics in the planetary boundaries framework can inform strategies for more sustainable responses, as an integrative part of climate change, biodiversity and natural resource-use policy.

We now find plastics in the most remote regions of the planet and in the most intimate, within human bodies. And we know that plastics are complex materials, released into the environment throughout the plastics life cycle, resulting in harm in many systems. The solutions we strive to develop must be considered with this complexity in mind, addressing the full spectrum of safety and sustainability to protect people and the planet, say the experts. 

As the international Plastics Treaty negotiations approach closure, the research team calls for experts and policymakers to shift away from considering plastics pollution as merely a waste management problem, and instead to tackle material flows through the whole impact pathway. This approach lets Earth system effects of plastics be detected, attributed and mitigated in a timely and effective way.

Patricia Villarrubia-Gómez et al. Plastics pollution exacerbates the impacts of all planetary boundaries, One Earth (2024). DOI: 10.1016/j.oneear.2024.10.017. www.cell.com/one-earth/fulltex … 2590-3322(24)00541-4