0141688 



tration is based on two publications, Davis et al . (1978) and 

 Weaver et al . (1984). Davis et al . (1978) reported arsenic 

 concentrations in the shoots of barley were toxic in a range of 11 

 to 26 ppm and determined a level of 20 ppm was the "upper critical 

 level" at which a 10 percent yield reduction could be expected. 

 Bermuda grass leaves containing 20 ppm arsenic were associated 

 with plants exhibiting reduced growth (Weaver et al . 1984). These 

 authors found bermuda grass leaves, stems and roots often exceeded 

 15, 25, and 200 ppm respectively in plants grown in soils contain- 

 ing 45 ppm arsenic. All plant tissue arsenic concentrations >20 

 ppm found in the reviewed literature were associated with phyto- 

 toxicity. Kabata-Pendias and Pendias (1984) reported a phytotoxic 

 range of 5 to 20 ppm for arsenic in unspecified plant tissue. 



Numerous references reported "intermediate range" arsenic 

 levels (those values between traces and toxicity). Typical values 

 for plant tops of alfalfa, red clover, and oats were reported as 

 0.05, 0.37, and 0.62 ppm respectively (Liebig, 1966). This source 

 reported high range (elevated but not showing toxicity symptoms) 

 values for alfalfa, red clover and barley as 3.15 to 14 ppm, 6.26 

 ppm and 12.3 ppm, respectively. Data from the reviewed literature 

 indicated that no cereal and forage crops or edible vegetable 

 portions contained a concentration of arsenic greater than the 3 

 ppm tolerable level suggested for the Helena Valley. Woolson 

 (1973) calculated, through the use of regression equations, the 

 phytotoxic tissue levels producing a yield reduction of 50 percent 

 in 6 vegetables. This study indicated only lima beans, an arsenic 

 sensitive crop, had a tolerance level less than 3 ppm for the 

 calculated yield reductions. 



3.2 Cadmium in soils and plants 



3.2.1 Cadmium literature review 



Cadmium levels in plants and soils rarely exceed 1 ppm 

 (Kabata-Pendias and Pendias 1984). Areas with naturally occurring 

 high levels of cadmium in soils have been documented to have up to 

 22 ppm total cadmium, with soil parent material up to 33 ppm total 



35 



