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1 EUGENE P. HAYDU 



2 they occur in high concentrations, the lignins constitute 



3 an appropriate substance for tracing in receiving waters 



4 and for chemical analysis. 



5 The PBI test has been developed to determine 



6 concentrations of lignin and related compounds as a measure 



7 of SWL. It is important to note that the test measures 



8 only the stable lignins and related compounds in SWL. 



9 It does not measure a substantial portion of SWL which is 



10 degradable. Since PBI measures only some of the compounds 



11 in SWL, it is not a measure of total SWL and, therefore, the 



12 two terms cannot and should not be used interchangeably. 



13 The toxicological and other physical and 



14 chemical characteristics of pulp mill effluents, including 



15 SWL, have been found to vary considerably during any given 

 15 day in any given plant due to changes in pulp grades, 



17 species and sources of wood, and so forth. Considerable 



18 variation in effluent characteristics occurs even with a 

 Ij) given pulp mill using similar cooking conditions. In view 



20 of the great complexity and variability of the characteris- 



21 tics of pulp mill wastes, it has been very difficult to 



22 find a satisfactory expression for concentration. For 



23 example, attempts have been made to relate toxicity to 



24 various dilutions of waste and to BOD, COD, total solids, 



25 PBI and various reference animals. None have yet proven 



