not very surprising since anything in large quantities is bad
"Problems are likely in people who take supplements, which can contain up to 50 times as much polyphenol as a single cup of tea." ... "liver toxicity" in humans... dont know what the actual findings were - probably just by liver enzyme blood tests, not by biopsy to see if any real damage happened.
But they did manage to kill a couple lab animals with large doses of polyphenols, i guess from liver failure.