Ireland has a poor environmental record, despite its green image. In the 1980s it had more than 500 rivers and lakes with pristine water, now there are just 20, according to the Environmental Protection Agency.
The definition of “pristine” has changed over those years.
That’s about the period of time in which measurement techniques have advanced from parts per million to parts per billion and then trillion.
As I say, I don’t actually know this but I’d most certainly want to disprove that contention before I believed the statement.