0141631 



It has been noted by investigators that chemical analysis of 

 the total soil arsenic is not a reliable indicator of potentially 

 phytotoxic levels in vegetation (Albert and Arndt 1931, 

 Vandecaveye et al. 1936, Woolson et al. 1971b). This has led to 

 attempts to develop soil tests for plant-available soil arsenic 

 that can be correlated with symptoms of plant toxicity. A 

 greenhouse study by Benson and Reisenauer (1951) found no satis- 

 factory correlation between soil extractable arsenic and plant 

 growth by four different extracting solutions (NaCl , NaOAc + 

 CH3COOH, H 2 S0 4 , NH4F+HCL) Vandecaveye et al . (1936) believed that 

 the condition of field crops in the state of Washington was 

 closely related to the amount of readily soluble arsenic. However, 

 others have noted that such easily soluble arsenic is best used as 

 an indicator only for those soils that have had recent arsenic 

 applications (Carrow et al. 1975, Jacobs et al. 1970). 



Johnston and Barnard (1979) evaluated 14 different arsenic 

 extracting solutions on four New York soils. The arsenic extrac- 

 tion ability for the 14 solutions was (in increasing order): water 

 = IN NH4CI = 0.5M CH3COONH4 = 0.5M NH4NO3 < 0.5M (NH 4 ) 2 S04 < 0.5N 

 NH4F = 0.5M NaHC03 < 0.5M (NH 4 ) 2 C03 < 0.5N HC1 + .025N H 2 S0 4 < 

 0.5N HC1 = 0.5M Na 2 CC>3 = . 5M KH 2 PC>4 < 0.5N H 2 SC>4 = 0.1N NaOH. 

 They made no specific recommendations for the use of any particu- 

 lar solution, but noted that basic solutions were more effective 

 in arsenic extraction than were neutral solutions, and that phos- 

 phorus and arsenic reacted ' simi larly to solutions containing 

 bicarbonate or hydrogen ions. 



The soil chemistry of arsenic is similar to that of phospho- 

 rus; its principle chemical form is that of arsenate (As04~3) 

 which has been occluded or adsorbed on hydrous aluminum and iron 

 oxides (Ganje and Rains 1982). Like phosphorus, it is also often 

 present as precipitates of slightly soluble compounds of Al , Fe, 

 Ca and Mg . Lesser amounts of arsenic are associated with soil 

 clays and organic matter. This similarity between arsenic and 

 phosphorus has led to the use of phosphorus extracting solutions 

 for the determination of plant-available arsenic. Perhaps the two 

 most commonly used extractants for phosphorus that have been sub- 



Si 



