0141711 



mobile of the heavy metals, resulting in generally low lead levels 

 in the soil solution and minimal plant uptake. Chumbley and Unwin 

 (1982) determined that there was no significant correlation 

 between total soil lead and plant lead levels. The low mobility of 

 lead is governed primarily by soil pH, texture, cation exchange 

 capacity and organic matter content (Zimdahl and Arvik 1973, 

 Pepper et al . 1983) . 



Little specific research has been directed toward the deter- 

 mination of plant and soil lead toxicity levels. Rather, concern 

 has centered around the introduction of lead into the human food 

 chain from plants (either from lead taken up from the soil or from 

 aerially deposited lead on plant surfaces), or from ingestion of 

 lead that is in soil or dust. Tables 39, 40 and 41 summarize the 

 limited number of studies where the phytotoxic concentration of 

 lead in soil and plant tissue has been documented. 



3.3.2 Lead in soils 



3.3.2.1 Total lead in soils 



The suggested total soil lead hazard concentration for the 

 Helena Valley is 1000 ppm. Phytotoxic levels of total soil lead 

 were reported by many authors (Table 39). Values ranged from 100 

 ppm to 1000 ppm. It must be noted that considerable crop damage 

 may occur to sensitive crops or other crops grown in soils with 

 higher available lead content (i.e. lower pH) at levels considera- 

 bly lower than the selected hazard level (Table 39). The above 

 problem was exemplified in the following reviewed literature. 



McLean et al . (1969) noted significant reductions in alfalfa 

 yields at total soil lead levels of 100 to 1000 ppm in soils with 

 a pH range of 4.9 to 5.7. These authors reported nonsignificant 

 yield reductions at 1000 ppm total soil lead at a pH of 6.3 and no 

 yield reductions at a pH of 7.5. Similar results were reported by 

 these authors for oats: the only significant yield reduction 

 occurred at 1000 ppm total lead at a pH of 5.2. John and VanLaer- 

 hoven (1972) found a 30 percent yield reduction in lettuce but no 

 effect to oat yield at a total soil lead level of 1000 ppm and a 



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