Fate and Transport of Arsenical Feed Amendments in Chesapeake Bay Watersheds

Hancock, T.C., USGS, Richmond, VA; Miller, C.V., USGS, Baltimore, MD; Denver, J.M., USGS, Dover, DE; Riedel,
G.F., Academy of Natural Sciences, St. Leonard, MD.

Because of the high concentration of poultry feeding operations in many Chesapeake Bay watersheds and the extensive use of arsenic feed amendments, we are investigating the fate and transport of several arsenic compounds in water and sediment in the Pocomoke
River Basin in Maryland and Christians Creek Basin in Virginia. Roxarsone (3-nitro-4-hydroxyphenylarsonic acid), the most commonly used arsenical compound in poultry feed in the U.S., is amended at 23-45 grams chemical/ton feed. Concentrations of total arsenic in poultry manure usually range from 15 to 35 mg/kg. Although the initial input of arsenic is organic, we found mostly inorganic arsenic, and relatively lower concentrations of methylated arsenic. Concentrations of the dissolved arsenic species in surface water from both basins were <1 g/L; however,
we observed a pulse of arsenic (III) and (IV) and total arsenic (inorganic + organic) in samples collected during storm runoff compared to base flow.

In Christians Creek water, total arsenic concentrations increased from 0.21 g/L at base flow to 0.37 g/L at streamflow recession. In the Pocomoke River and its tributaries, base-flow concentrations of arsenic in suspended particles and bed sediment were moderate to high (0.8 to 21 mg/kg) when compared to national averages. Dissolved arsenic concentrations in shallow ground water from the Pocomoke Basin were as high
as 7.6 g/L. It appears that roxarsone may be mineralized to inorganic arsenic during transport; however, the relatively low concentrations of arsenic detected in surface waters from these basins suggests that there is an unidentified sink. Roxarsone possibly remains un-reacted or degrades to another organic form for which analytical methods have not been developed.

Hancock, T.C., Miller, C.V., Denver, J.M., Riedel, G.F., 2000, Fate and Transport of Arsenical Feed Amendments in Chesapeake Bay Watersheds, [abs.], Society of Environmental Toxicology and Chemistry 21st Annual Meeting, November 12-16, 2000, Nashville, Tenn.

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