spiUs or other accidents occur. It is much more 

 common to encounter problems related to slime 

 growths, depressed DO's, and to long-term or 

 chronic effects on the biota. 



A substantial portion of pulpmill wastes includ- 

 ing the toxic components are very amenable to 

 microbial degradation. In one study, kraft mill 

 wastes were found to be nontoxic to oysters at a 

 dilution of 1:20 when the BOD of the waste was 

 reduced by 80 percent employing biological treat- 

 ment. In a similar study, the toxicity of kraft 

 wastes to silver salmon was found to diminish pro- 

 portionally to the degree of BOD reduction above 

 50 percent, again using biological treatment. The 

 results of a recent study by scientists of the Inter- 

 national Pacific Salmon Commission indicate a 

 fairly close relationship between BOD reduction 

 and decrease in the toxicity of kraft wastes. They 

 found no apparent toxicity to salmon when the 

 BOD was reduced by 65 percent. While similar 

 studies have not been made with sulfite liquors, 

 there is some evidence that the toxic components 

 of this waste are also degradable. It is important to 

 recognize that the biological mechanism or degra- 

 dation involved in secondary treatment is essen- 

 tially similar to that in receiving waters. Given 

 sufficient time, the process of degradation of the 

 toxic components of pulp wastes also take place in 

 receiving waters. 



Because of the great complexity and variability 

 of pulpmill wastes, it is difficult to find a satisfac- 

 tory expression for concentration. Attempts have 

 been made to relate toxicity to BOD, COD, total 

 solids, PBI (Pearl Benson Index — a measure of 

 the lignin content of pulp wastes), and various 

 reference animals. There is a general relationship 

 with all of these criteria; i.e., the higher the values, 

 the greater the toxicity. Pulpmill dosages or dilu- 

 tions have been used in bioassays on the basis of 

 applied initial BOD. The response of the test ani- 

 mals has been found to vary considerably to given 

 concentrations of applied BOD even from the 

 wastes of the same mill. This would indicate that 

 the concentration of toxicants in the total biolog- 

 ically amenable fraction is subject to considerable 

 variation. This would not only explain the lack of 

 a good relationship between the toxicity and initial 

 BOD, but it would also explain why, on the other 

 hand, there can coexist a good relationship be- 

 tween BOD reduction and reduction in toxicity. 

 The latter is subject to degradation regardless of 

 the proportions of toxicants and the other to bio- 

 degradable substances- 



The shortcomings of BOD as an expression of 

 the concentration of toxicity would seem to be 

 equally applicable to the PBI test. This test has 



been recommended as a measure of SWL (sulfite 

 waste liquor) concentration. It measures the 

 lignins in SWL which constitute an appropriate 

 substance for tracing in receiving waters and for 

 analysis due to their stability and high concentra- 

 tions. As indicated earlier, critical tests to deter- 

 mine the relationship between BOD reduction and 

 reduction in toxicity have not been conducted with 

 SWL. Nevertheless, there is sufficient evidence to 

 indicate that the toxic components of SWL also 

 reside in the biodegradable fraction and are also 

 degradable. The composition of SWL in receiving 

 waters at different distances from the point of dis- 

 charge would therefore differ even though similar 

 PBI values may occur. The toxicity of fresh SWL 

 at a PBI concentration of 50 mg/1 would be much 

 greater than of biologically stabilized SWL at the 

 same PBI concentration. There is clear indication 

 that further study of SWL toxicity and biodegrada- 

 tion is necessary. 



The toxicity of kraft and sulfite wastes to 

 aquatic life is amply reported in the literature. 

 Deleterious effects produced by SWL (generally 

 considered less toxic than kraft wastes) are re- 

 ported from PBI values as low as 2.0 mg/1 for 

 oyster larvae to concentrations greater than 1,000 

 mg/1 for the adult clams Mya and Macoma. Long- 

 term bioassays with Pacific and Kumamoto 

 oysters, carried out at Oregon State University 

 using calcium-base SWL (10 percent solids), 

 showed no adverse effects at 50 mg/1 after 266 

 days of exposure. Slightly deleterious effects were 

 noted at 100 mg/1, indicating maximum safe 

 limits lie between 50 to 100 mg/1. Continuing field 

 studies at Grays Harbor, Wash., support these 

 findings. In bioassays conducted in salt water by 

 the Washington State Department of Fisheries, sal- 

 mon exposed for 30 days to concentrations of ap- 

 proximately 500 mg/1 of 10-percent SWL showed 

 no apparent ill effects. Herring eggs, on the other 

 hand, were adversely affected at concentrations 

 greater than 96 mg/1. 



The apparent tolerance level for salmon in salt 

 water using kraft wastes was found by the above 

 investigation to range from dilutions of 1:16 to 

 1:90 after 14 to 30 days of exposure. Growth 

 studies conducted at Oregon State University by 

 the National Council for Stream Improvement 

 using raw kraft wastes in fresh water showed no 

 adverse effects to salmonid fishes after 3 to 5 

 weeks exposure in dilutions of 1:100. English (in 

 press), in his field studies of the English sole in 

 Puget Sound, reports a sustained and thriving 

 fishery in an area affected by SWL. Recent work 

 by the Federal Water Pollution Control Adminis- 

 tration (USDI 1967a) in Puget Sound showed 



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