0141GS2 



sequently applied to arsenic extraction are: NaHCC>3 (developed 

 for use primarily on alkaline soils); and a mixture of 0.05N HC1 

 and 0.025N H2SO4 (used for neutral and acidic soils). 



In a study by Woolson et al . (1971a) these two methods 

 (NaHCC>3, HCI + H2SO4) and four others were evaluated for determining 

 arsenic availability to corn on 28 different soils from different 

 areas of the United States. Most of the soils were from the east 

 and only five had an alkaline pH, the highest being 7.50. The 

 NaHCC>3 and mixed dilute acid solutions were both recommended for 

 use, because of their relative simplicity and for their good 

 correlations of available arsenic with reduced plant growth. 



A later study by these same researchers (Woolson et al. 1973) 

 revealed the complexity of determining plant-available arsenic in 

 the soil. They found that plants growing on different soils that 

 contained the same extractable arsenic levels experienced varying 

 degrees of arsenic toxicity. This was attributed to the variabil- 

 ity in the chemical and physical properties of the soils (texture, 

 organic matter and pH) . Jacobs and Keeney (1970) also noted the 

 influence of soil texture on arsenic phytotoxici ty , with arsenic 

 being more toxic on sandy soils than on finer-textured soils. 

 Such findings suggest that the general application of extractable 

 soil arsenic levels to estimating phytotoxicity in field situa- 

 tions is limited. Ganje and Rains (1982), in their review of 

 methods of analysis for soil-arsenic, state that when selecting an 

 extracting solution to determine plant-available arsenic, no 

 single extractant can be used as a universal indicator of arsenic 

 availability and that each soil type or soil area must be treated 

 independently. 



The literature indicates that the selection of a soil-arsenic 

 extracting solution is a complicated decision. Present methods 

 have been shown to have limited applicability to field situations 

 where an interpretation of phytotoxic levels is desired. For the 

 Helena Valley study area a decision was made to employ a method 

 for determination of soil extractable arsenic that has been 

 developed and applied successfully to problems of arsenic-contami- 

 nated soils of this region. 



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