Acid rain is back: the sequel nobody wanted

Just when you thought it was safe to go out in wet weather, acid rain "may have a sequel", said Popular Mechanics, and "like most sequels, it's arguably worse".

And it might not have a happy ending because dealing with a "forever chemical", which is now coming down in rain and being found in "everything from drinking water to human blood", may be an "impossible task".

Forever chemical

Scientists started studying acid rain in the 1960s and by the 1980s it had become the most discussed environmental issue of the time, in news media and also in popular culture.

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"At its worst", the first era of acid rain "stripped forests bare in Europe, wiped lakes clear of life in parts of Canada and the US", and damaged human health and crops in China, said the BBC.

It came from rising concentrations of sulphuric acid produced mostly from petrol-driven cars and coal-fired power stations. Acid rain became less of a problem as power sources evolved, but now there's a "new anthropogenic source" that is "possibly more pervasive, more persistent, and more sinister".

When rain, or snow, falls, a human-made chemical called trifluoroacetic acid (TFA) is falling with it. It has "shown up in lakes and rivers; bottled water and beer; cereal crops and animal livers", said Nature, and "even in human blood and urine".

Researchers say the concentrations of this "forever chemical" are rising around the planet – from the "leaves and needles" of tree species in Germany, to the Canadian Arctic ice cores, and in groundwater in Denmark.

Insidious problems

Last October, European environmental scientists "raised the TFA alarm", said Popular Mechanics. They warned that the rise in concentrations could be a threat to "planetary boundaries" – a system designed to make sure Earth remains habitable for human life.

Whether it has a direct effect on human health itself is "less clear", said Nature. The UN Environment Programme, which has been investigating TFA since 1998, says it considers the chemical to pose "minimal risk for now", but UN member states have asked it to re-evaluate its assessment.

Meanwhile, experts are discussing ways to tackle the problem but TFA's water-solubility could be a "long-term headache", said Popular Mechanics, because current filtration technologies "are not up to the task" of removing it from drinking water, so "ridding the world" of TFA will be "immensely difficult" and "incredibly expensive".

There are other imposters in rain, including "plastic rain", which is the "new acid rain", said Wired. In 2020, researchers found that more than 1,000 tonnes of microplastic fell on 11 national parks and protected areas in the western US each year, or the equivalent to more than 120 million plastic water bottles. This "could prove to be a more insidious problem than acid rain".