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bermuda grass at concentrations which ranged from 45 to 90 ppm in 

 sand and clay soils respectively. Phytotoxic criteria reported in 

 the literature for total arsenic in soils ranged from 15 to 50 ppm 

 (Kitagishi and Yamane 1981, Kloke 1979, Linzon 1978 and El-Bassam 

 and Tietjen 1977). Numerous cases of phytotoxici ty were reported 

 in the 45 to 100 ppm range (Table 30). For many situations, a 

 phytotoxic level of 50 ppm would appear appropriate. A tolerable 

 level of 25 ppm total soil arsenic is based on the low or no yield 

 reductions that have been reported at or below this level (Table 

 30). The only important exception is the 22 percent yield 

 reduction for oats at a 10 ppm total soil arsenic concentration 

 that was noted by Woolson et al. (1973). 



3.1.2.2 Extractable soil arsenic 



It is highly probable that extractable arsenic soil concen- 

 trations greater than the 50 ppm hazard level suggested for the 

 Helena Valley will be phytotoxic (Table 31). Jacobs et al. (1970) 

 reported 100 percent yield reductions (no growth) for snap beans 

 and peas at the 100 ppm extractable (Bray P-l) arsenic level. 

 Considerable phytotoxici ty was noted at levels less than 50 ppm 

 extractable (various methods) soil arsenic (Table 31) and a 

 phytotoxic concentration as low as 10 ppm may be an appropriate 

 hazard level in some circumstances.- It is apparent from the 

 reviewed data that soil factors have much less influence on 

 phytotoxic extractable arsenic levels as compared to phytotoxic 

 total arsenic levels in soils (Tables 30, 31). 



The tolerable extractable soil arsenic concentration of 2 ppm 

 is based on the limited work of Vandecaveye et al. (1936) , who 

 noted no toxicity in barley and alfalfa at or below that level, 

 and the observations of Walsh et al . (1977), who reported phyto- 

 toxicity to soybeans at an extractable arsenic level of 3 ppm 

 (Table 31) . 



3.1.3 Arsenic in plants 



Phytotoxic arsenic levels in plant tissues have been reported 

 from 5 to 20 ppm (Table 32). The suggested 20 ppm hazard concen- 



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