Q&A-The ins and outs of 'forever chemicals' as EU weighs complete ban

Feb 7 (Reuters) - Five European countries on Tuesday called time on widely used substances known as PFAS or "forever chemicals", proposing a ban because they accumulate in the environment, leading to potential harm to human health and ecosystems.

What are PFAS, why are they in such pervasive use and what is the harm to humans and the environment? WHAT ARE PFAS?

Depending on the definition, PFAS - or per- and polyfluorinated substances - are a class of synthetic chemicals comprising between about 4,000 and 9,000 substances.

The five-country initiative to bring a EU-wide ban into force as early as 2026 is defining PFAS widely, covering at least 10,000 compounds that contain bonds between carbon and fluorine atoms, one of the strongest connections in organic chemistry.

They can take solid, liquid or gaseous forms. But according to Chemservice, a consultancy firm on chemical regulation, only 256 of these substances are commercially relevant globally.

HOW WIDELY ARE THEY USED?

The EU proposal dossier mentions 14 industrial sectors affected by the ban and a lobby group of PFAS makers and users has said PFAS are used in industries including aerospace, agriculture, food handling, construction, electronics, healthcare, automotive, renewable energy and textiles.

WHY ARE PFAS SO UBIQUITOUS?

Their ability to make materials resist extreme heat, corrosion and aggressive chemicals have made PFAS ideal candidates to go into heavy-duty parts in weapon systems, aircraft, machinery and industrial plants.

The water and dirt repellent properties of PFAS are upheld over time, adding long-term durability to construction materials, car parts and fabrics.

WHY DO PFAS ACCUMULATE IN THE ENVIRONMENT The strong carbon-fluorine bonds prevent PFAS molecules from breaking down or decomposing long after their useful life in commercial products, causing them to build up in soils and circulate globally in the water and atmosphere.

Some non-PFAS molecules, such as widely used cooling agents for commercial refrigerators, later break down into more durable PFAS when released into the environment.

WHAT ARE THE HEALTH AND ENVIRONMENTAL HAZARDS LINKED TO PFAS?

Animal tests have yielded possible links to conditions including cancer, liver damage, hormonal dysfunction and a weaker immune system.

While the exact harmful effects remain unclear and need more research, the main concern voiced by scientists is that these effects, however small, may pile up as PFAS accumulate in the environment and in the human body over time.

WHAT ARE THE ALTERNATIVES?

The search for alternatives is as varied as the different uses and there is no one-size-fits-all substitute. Many companies have been doing research into alternatives but in many cases no substitutes are available.

The proposed EU ban will grant longer grace periods of up to 12 years for important products where work on alternative materials is in early stages.

The chemical industry has said that the use of alternative materials often poses trade-offs in product design at the expense of durability, safety, resource efficiency or maintenance frequency. (Reporting by Ludwig Burger Editing by Tomasz Janowski)