0141602 



Abstracts, CRIS-USDA, ENVIROLINE, MEDLINE, NTIS, Pollution 

 Abstracts, SCISEARCH and Water Resources Abstracts. A brief 

 description of these data bases is included in section 6.3. 

 Conventional library methods were also employed for researching 

 abstracts, periodicals and other materials. No attempt was made 

 to determine the relative importance of field studies versus 

 greenhouse studies, but study settings are given in appropriate 

 tables to enable the reader to evaluate this variable. No attempt 

 was made to evaluate synergistic or antagonistic effects of these 

 metals although some of these mechanisms are documented in the 

 text. Levels of impact or an evaluation of an acceptable impact 

 have not been determined but this data is included in appropriate 

 tables when reported in the referenced literature. 



The authors conducted a meeting to establish normal, tolera- 

 ble, uncertain and toxic levels of metals in soils, plants, and 

 livestock. At this meeting all literature was discussed followed 

 by establishment of hazard levels based on the reviewed litera- 

 ture . 



Background values for all parameters were generally derived 

 directly from data in the reviewed literature and are the minimum 

 and maximum or only value reported for normal or control parame- 

 ters. The background range will no doubt expand as more data 

 become available. 



The tolerable level represent the maximum concentrations at 

 which no toxicity has been noted. These levels were not available 

 for many parameters. 



The uncertain range represents the chemical level at which 

 both nontoxic and toxic results have been reported by various 

 studies. This result stems from variations in individual animal 

 tolerances, variations in experimental designs, and by synergistic 

 or antagonistic effects of other constituents. 



Toxic concentrations have been derived from two major 

 sources: 1) the results of individual studies and 2) criteria 

 reported as toxic in toxicology manuals, texts, and special 

 Dubli cat ions. 



