A naturally occurring metalloid, Class 1 human carcinogen, and one of the most prevalent groundwater contaminants worldwide. Anthropogenic sources include mining and smelting tailings, coal combustion, historical pesticides, and wood-preservation operations.
Arsenic exists in groundwater predominantly as arsenate (As(V), oxic conditions) and arsenite (As(III), anoxic conditions, more mobile and more toxic). The U.S. EPA drinking water MCL is 10 micrograms per litre; Health Canada's guideline is also 10 µg/L. Naturally elevated arsenic in groundwater affects an estimated 200 million people worldwide, with the Bengal Basin the most studied case.
Anthropogenic arsenic contamination is concentrated at former mining and smelting sites, chromated copper arsenate (CCA) wood-treating operations, and pesticide manufacture and orchard application sites. Remediation routes include stabilization with ferric and aluminium salts, PRBs with iron-based media, and ex-situ excavation with thermal treatment or secure landfill. In-situ treatment is constrained by arsenic's tendency to remobilize under changing redox conditions.
Also known as: arsenic, As, arsenate, arsenite.
A naturally-occurring metalloid regulated at 10 μg/L in drinking water whose remediation is driven by oxidation state — mobile, toxic As(III) is oxidized to less mobile As(V) and coprecipitated with iron or bound into a stabilized matrix.
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.