This is wild: humans have been eating oily fish for millennia, it's probably quite important for brain development, but as a species we've now managed to dump so much mercury in the sea it might not be safe for kids to eat anymore.
Tinned #tuna: Acorns Nurseries ban over #mercury levels concern - BBC News
https://www.bbc.co.uk/news/articles/c3e800kn14no