Based on the OP, it wasn't at all accidental. They knew it was dangerous and chose it because they could make more money than with safer alternatives such as ethanol.
He's not 'the public' but a highly educated and experienced leading expert in the subject. You have no idea what he knew (afaict) and even if the chronic problems were indeed unknown to him, anyone, even a member of 'the public', could infer that the acute problems certainly risked long-term problems
He's not some incidental commentator. He's an engineer and a principle force behind this technology. He is responsible for the outcomes - 'I didn't know' is reckless negligence. And if there were clear acute problems, chronic problems weren't hard to guess at for anyone, much less an engineer, with all those resources, working on it for years.
And plenty of stuff is toxic in large quantities but harmless (or even vital!) in small quantities.