Arsenic in wind-blown sediment deposits loess

5 Arsenic in wind-blown sediment deposits (loess) 

Loess refers to deposits of fine-grained wind-blown (eolian) sediments, which may accumulate up to 100 m thick. The material mostly consists of silt grains with perhaps 5-30% clay-sized particles and 5-10% sand (Benn and Evans, 1998), 291. Like other sediments, loess may contain considerable arsenic depending on the chemistry of its source rocks (Table 3.15). 

Loess is especially common in parts of China and US Midwestern states. Chinese loess primarily forms from the wind erosion of the uplifting Himalaya Mountains under arid and semiarid conditions. In the US Midwest, loess accumulated as winds scoured deposits left by retreating glaciers about 10000 years ago (Press and Siever, 2001), 318-319. 

Groundwaters in the loess aquifers of La Pampa, Argentina, may contain 5 mgL-1 of arsenic ((Smed-ley et al., 2005 Smedley et al., 2002) Table 3.13). The aquifers are very oxidizing and As(V) is the dominant arsenic species. The alkalinity of the groundwaters (pH 7.0-8.8) and the unusual presence of vanadium probably hinders the sorption of As(V) onto iron and manganese (oxy)(hydr)oxides. The alkalinity and vanadium may also desorb arsenic from the minerals (Smedley et al., 2005). 

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