IDENTIFYING THE SOURCE AND CHANGE IN SPECIATION OF ARSENIC IN SOILS AND STREAM SEDIMENTS OF NEW HAMPSHIRE, USA

Recent studies have found an association between agricultural land use and high levels of arsenic in the sediment of some New England streams. We investigate a potential source of this arsenic, orchard soils. Arsenic-based pesticides were heavily applied to farmland, particularly to apple orchards, throughout New England between 1900 and 1950. If left undisturbed, these arsenical pesticides remain tightly bound up within the upper few cm of orchard soils, effectively immobilizing the arsenic. However, if the orchard soils are disturbed, such as occurs during tilling or development, the arsenic can be mobilized by physical erosion and enter nearby stream channels. Less clear is what happens to the arsenic after it enters the streams. We report on a field and laboratory-based study to further understand the transport and fate or arsenical pesticides to, and within, New England stream channel sediments.

Two watersheds were studied which contain orchards that were in production at least since the 1950s and have now been developed into residential areas. The receiving stream sediments for these orchards have been previously shown to have arsenic concentrations above the probable effects concentration (33 mg/kg) set by the EPA. Stream sediment and orchard soil samples were collected to determine if the orchards are a source of contamination and to determine how, and in what mineral phase, the arsenic might be being transported to, and within, the stream channel. Sequential extractions coupled with ICP element analysis and synchrotron based X-ray techniques provide precise mineral phases of arsenic in the soil and sediment samples. This provides knowledge of how arsenic is transported and changes phase from application, within the soil, and within the stream sediment.