0141716 



pH of 3.8. Total soil lead levels in the range of 250 ppm to 400 

 ppm had no effect on alfalfa, clover, oats, ryegrass and lettuce 

 (Allinson and Dzialo 1981, Pruves 1977, Taylor and Allinson 1981). 

 Miller et al . (1977) reported the stunting of corn seedlings grown 

 in a silty clay loam with a pH of 6.0 at a total lead level of 125 

 ppm. The reason for the phytotoxici ty of this anomalously low 

 value was not resolved although this study was designed to 

 evaluate the interaction of lead on the uptake of cadmium. Yields 

 of barley grown in loam soil containing 1000 ppm total lead and a 

 pH range of 4.0 to 8.5 were significantly reduced at pH values of 

 4.0 and 6.0 and not affected at pH values of 7.8 and 8.5 (Patel et 

 al. 1977) . 



The above discussion suggests the 1000 ppm total soil lead 

 level is a level at which significant yield reductions may occur 

 in alfalfa, barley and oats in soils with pH values £6.0. It is 

 also the level at which a 30 percent yield reduction has been 

 observed in lettuce. The lead content of some vegetation growing 

 on a soil containing 1000 ppm total lead may exceed the 30 ppm 

 maximum recommended forage limit (NRC 1980) by a considerable 

 amount without any apparent toxicity to the plant (John and 

 VanLaerhoven 1972, Patel et al. 1977). 



A tolerable plant lead level of 250 ppm is based on the 

 observed "no effect" to alfalfa, oats and ryegrass at this level 

 (Allinson and Dzials 1981, Taylor and Allinson 1979). With the 

 exception of one publication (Miller et al . 1977) which reported 

 the stunting of corn seedlings at 125 ppm total soil lead, no 

 phytotoxicity was noted in the reviewed literature for total soil 

 lead values less than 250 ppm. 



3.3.2.2 Extractable soil lead 



Extractable soil lead data were relatively less abundant in 

 the literature than were data for total s'oil lead (Table 40). All 

 elevated extractable soil lead data were derived from the publica- 

 tions of MacLean et al . (1969) and Lagerwerff et al . (1973). The 

 500 ppm hazard level concentration has been estimated based on the 

 mixed experimental results at 367 ppm IN NH4OAC extractable soil 



116 



