Naturally occurring metal that, when released by mining, chlor-alkali manufacture, coal combustion, gold-amalgamation, or dental and medical waste, becomes methylated by anaerobic bacteria to methylmercury, a potent neurotoxin that bioaccumulates through aquatic food webs.
Mercury occurs in three forms with different exposure profiles: elemental (Hg0), inorganic (Hg(II) salts), and organic (methylmercury, MeHg). Elemental mercury vapour is the dominant inhalation hazard at industrial sites. Methylmercury is the dominant chronic toxicity concern, formed when inorganic mercury in sediment is methylated by sulfate-reducing bacteria and biomagnified up to a million-fold from water to predatory fish.
Mercury-contaminated soil is typically remediated by ex-situ thermal desorption (which volatilizes elemental mercury for capture and recovery), stabilization/solidification with sulfide reagents, or excavation and secure disposal. In-situ remedies including PRBs with iron sulfide media and capping with reactive amendments are increasingly used for sediment.
Also known as: mercury, Hg, methylmercury, elemental mercury.
A globally-regulated heavy metal — listed under the Minamata Convention — whose remediation is dominated by indirect thermal desorption that vaporizes elemental Hg from soil and condenses it as a recoverable stream for offsite reclamation.
Per- and polyfluoroalkyl substances: a class of more than 12,000 synthetic compounds built around exceptionally stable carbon-fluorine bonds. PFAS is the family name, not a single chemical. PFOA and PFOS are two specific members of this class.
Perfluorooctanoic acid: a specific eight-carbon long-chain PFAS compound, historically used in non-stick coatings and AFFF firefighting foam. Classified by IARC in 2023 as Group 1, carcinogenic to humans.
Perfluorooctane sulfonic acid: a specific eight-carbon long-chain PFAS compound, historically the active surfactant in 3M Scotchgard and AFFF firefighting foam. Classified by IARC in 2023 as Group 2B, possibly carcinogenic to humans.
Polychlorinated dibenzo-p-dioxins and related furans: highly persistent, fat-soluble chlorinated compounds formed as unintended byproducts of combustion, chlorine-based manufacturing, and herbicide production, with TCDD among the most toxic substances ever characterized.