The rankings are out and three metals top the chart: arsenic, lead, and mercury. The Agency for Toxic Substances and Disease Registry (ATSDR) has released its 2017 list of substances at EPA-managed contamination sites posing the most significant risk to human health.  A total of 275 substances are listed on the entire ATSDR 2017 Substance Priority list.  Here are the Top 50 substances listed.