180 



DONALD J. BENSON 

 levels ac which tiie laboratory-spavmed larvje exhibited a 

 response to spent sulfite liquor. 



The Lest procedure for the oyster larval 

 bioassay is not consider 'd adequate for establishing finite 

 levels of field conditions. It has been the experience 

 of many scientists using bio-issay techniques that small 

 scale laboratory experitRvnts are more critical to living 

 forms than similar conditions found in th.? environment. 



Professor Wilbur Breese of the Yaquina Bay 

 Laboratory at the Oregon State University founil uhat by 

 increasing the temperature of the oyster larval bioassay 

 to a level more nearly suited to natural spawning and egg 

 development conditions, the response to spent sulfite 

 liquor levels was reduced significantly. At norra<3l 

 temperatures only one-half to one-third of the response 

 was observed. This may indicate that the oyster larvae 

 under the test condition reported by the FWPCA were being 

 so stressed that any slight additional stress of a 

 foreign substance such as SSL was enough to indicate a 

 very sensitive response. 



The Pearl-Benson Index is at best an 

 approximate indicator of levels of spent sulfite liquor 

 and is not at all satisfactory at the lower levels of 



sensitivity. The test indicates the presence of materials 



