title: Tracer test with As(V) under variable redox conditions controlling arsenic transport in the presence of elevated ferrous iron concentrations.
abstract: To study transport and reactions of arsenic under field conditions, a small-scale tracer test was performed in an anoxic, iron-reducing zone of a sandy aquifer at the USGS research site on Cape Cod, Massachusetts, USA. For four weeks, a stream of groundwater with added As(V) (6.7 muM) and bromide (1.6 mM), was injected in order to observe the reduction of As(V) to As(III). Breakthrough of bromide (Br(-)), As(V), and As(III) as well as additional parameters characterizing the geochemical conditions was observed at various locations downstream of the injection well over a period of 104 days. After a short lag period, nitrate and dissolved oxygen from the injectate oxidized ferrous iron and As(V) became bound to the freshly formed hydrous iron oxides. Approximately one week after terminating the injection, anoxic conditions had been reestablished and increases in As(III) concentrations were observed within 1 m of the injection. During the observation period, As(III) and As(V) were transported to a distance of 4.5 m downgradient indicating significant retardation by sorption processes for both species. Sediment assays as well as elevated concentrations of hydrogen reflected the presence of As(V) reducing microorganisms. Thus, microbial As(V) reduction was thought to be one major process driving the release of As(III) during the tracer test in the Cape Cod aquifer.
authors.affiliation: G.E.O.S. Freiberg Ingenieurgesellschaft mbH, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Höhn
authors.forename: M
authors.initials: M
authors.lastname: Isenbeck-Schröter
authors.forename: D B
authors.initials: DB
authors.lastname: Kent
authors.forename: J A
authors.initials: JA
authors.lastname: Davis
authors.forename: R
authors.initials: R
authors.lastname: Jakobsen
authors.forename: S
authors.initials: S
authors.lastname: Jann
authors.forename: V
authors.initials: V
authors.lastname: Niedan
authors.forename: C
authors.initials: C
authors.lastname: Scholz
authors.forename: S
authors.initials: S
authors.lastname: Stadler
authors.forename: A
authors.initials: A
authors.lastname: Tretner
mesh_terms: D001151:Arsenic / Q000032:analysis* / Q000737:chemistry / Q000302:isolation & purification; D005290:Ferric Compounds / Q000737:chemistry; D005296:Ferrous Compounds / Q000032:analysis / Q000737:chemistry*; D019015:Geologic Sediments / Q000032:analysis; D008404:Massachusetts; D010084:Oxidation-Reduction; D014872:Water Movements; D014873:Water Pollutants / Q000032:analysis* / Q000737:chemistry / Q000302:isolation & purification; D014874:Water Pollutants, Chemical; D018508:Water Purification
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D014873:Water Pollutants; D014874:Water Pollutants, Chemical; C000499:ferric oxide; D001151:Arsenic