I have been reading up on mercury poisoning which has an affinity for the hearing nerve. As well as amalgam fillings there are unsafe levels found in certain fish, as reported by the FDA. Interestingly though Zinc and NAC will help protect against mercury toxicity. Useful to know if we are Tuna lovers.
https://www.ncbi.nlm.nih.gov/pubmed/26302927
https://www.ncbi.nlm.nih.gov/pubmed/26302927