The Earth's capacity to absorb “novel entities” such as synthetic chemicals like plastic, without endangering the global ecosystem has been exceeded, 14 scientists argue. These entities span a wide range – primarily chemicals that do not biodegrade or do so only poorly.

In 2009, the Stockholm Resilience Center identified nine planetary boundaries within which human activities threaten Earth's stability, which has survived for at least 10,000 years. The Center has brought together experts to make assessments of where we stand on each boundary compared to the safe operating space. Some of these measures are truly global – notably, climate-changing gasses – whereas others – such as freshwater use – are experienced more locally.

In Environmental Science and Technology a team, including the Center's Patricia Villarubia-Gómez, consider the threat novel entities pose, and the aspects of the nine boundaries where they think we have most exceeded planetary capacities.

“There has been a 50-fold increase in the production of chemicals since 1950. This is projected to triple again by 2050,” Villarubia-Gómez said in a statement. 

Novel entities are defined as “new substances, new forms of existing substances, and modified life forms.”

Environmental Science and Technology is a publication of the American Chemical Society, so the publishers, and presumably the authors, are aware of the benefits novel chemical entities have provided to humanity. However, the authors argue in excess they have become a global threat when they persist in the environment, move on a large scale, and accumulate in organisms and the environment. The paper represents an effort to define the point at which these things can disrupt large-scale processes that keep the planet stable, rather than being merely a local threat.

The problem of chemicals to which living things are not adapted is exceptionally diverse. An estimated 350,000 different types are manufactured and on the global market. The authors argue this “outstrip[s] our efforts at safety assessment and monitoring.”

Some novel entities, such as many pharmaceuticals, only leave the body after being broken down and therefore pose no risk to the wider environment. Others are biologically inert and fairly safe. However, pesticides and plastics are posing much wider threats. Currently used plastics, the authors note, contain 10,000 other chemicals, which get released as the originals break down, sometimes forming new combinations.

“The rate at which these pollutants are appearing in the environment far exceeds the capacity of governments to assess global and regional risks, let alone control any potential problems,” said co-author Professor Bethanie Carney Almroth from the University of Gothenburg. "Some of these pollutants can be found globally, from the Arctic to Antarctica, and can be extremely persistent.  We have overwhelming evidence of negative impacts on Earth systems, including biodiversity and biogeochemical cycles.”

“Shifting to a circular economy is really important. That means changing materials and products so they can be reused not wasted, designing chemicals and products for recycling, and much better screening of chemicals for their safety and sustainability along their whole impact pathway in the Earth system,” Villarubia-Gómez said.

Carney Almroth's prescription may prove an even harder sell: “We need to be working towards implementing a fixed cap on chemical production and release."