Editing Lead (section)

=== Toxicity ===
Lead is a highly poisonous metal (whether inhaled or swallowed), affecting almost every organ and system in the human body.{{sfn|United States Food and Drug Administration|2015|p=42}} <!--The permitted daily exposure limit for lead of 5&nbsp;μg (five millionths of a gram) is a recommended test benchmark for pharmaceuticals.--> At airborne levels of 100&nbsp;mg/m<sup>3</sup>, it is [[Immediately dangerous to life or health|immediately dangerous to life and health]].{{sfn|National Institute for Occupational Safety and Health}} Most ingested lead is absorbed into the bloodstream.{{sfn|Occupational Safety and Health Administration}} The primary cause of its toxicity is its predilection for interfering with the proper functioning of enzymes. It does so by binding to the [[Thiol|sulfhydryl groups]] found on many enzymes,{{sfn|Rudolph|Rudolph|Hostetter|Lister|2003|p=369}} or mimicking and displacing other metals which act as [[cofactor (biochemistry)|cofactors]] in many enzymatic reactions.{{sfn|Dart|Hurlbut|Boyer-Hassen|2004|p=1426}} The essential metals that lead interacts with include calcium, iron, and zinc.{{sfn|Kosnett|2006|p=238}} High levels of calcium and iron tend to provide some protection from lead poisoning; low levels cause increased susceptibility.{{sfn|Luckey|Venugopal|1979|pp=177–178}}