581^1 



WOELKE ON PACIFIC OYSTER EMBRYO BIOASSAY 1 1 9 



the waste streams bioassayed to the and 20 per cent response levels 

 are summarized in Table 3. 



In a further refinement of this bioassay procedure, water samples are 

 collected by airplane from various estuarine environments and are flown 

 to the laboratory where they are bioassayed within a few hours of the 

 time collected. In this type of bioassay, a control water sample is carried 

 from the laboratory on the airplane and is subject to the same handling 

 stresses as the samples to be bioassayed. The water is collected in one- 

 gallon polyethylene containers. As many as 50 water samples have been 

 collected for a single bioassay. These samples are divided between four 

 one-liter beakers. Three samples are inoculated with freshly spawned 

 oyster embryos, and the fourth is used for chemical analysis. At the end 

 of the 48-hr bioassay, further chemical measures are often made on the 

 waters in which the embryos actually developed. The flow diagram in 

 Fig. 1 outlines the procedure followed in this type of bioassay. Average 

 per cent abnormal larvae and average PBI values from seven consecutive 

 monthly bioassays in one area of Washington state are summarized in 

 Fig. 2. High larva response levels in the Port Angeles area which decrease 

 with increasing distance from Port Angeles are readily apparent. At 

 present, water quality is being monitored annually with oyster larvae at 

 more than 130 stations, which include 95 per cent of the oyster growing 

 areas of Washington state and over 80 per cent of the estuarine areas 

 of the state. 



Conclusions 



I feel that the results achieved with the oyster embryo bioassay justi- 

 fies considering it for general use in: 



1. Evaluating existing estuarine water quality. 



2. Monitoring estuarine water quality. 



3. Determining toxicity of new potentially toxic materials. 



4. Measuring relative toxicity of wastes or potential wastes and esti- 

 mating their probable effect on moliuscan populations. 



5. Aiding in determining the degree and type of treatment a particular 

 waste might require. 



6. Evaluating the effectiveness of waste treatment facilities discharg- 

 ing into estuarine waters. 



7. Establishing estuarine water quality standards. 



Among the advantages of this method are its speed (relative to many 

 other types of bioassays), its simplicity, its low cost, the fact that it is 

 based on a commercially valuable species, the availability of test organ- 

 isms on a 12-month basis, and the clear-cut response of the oyster em- 

 bryos. While not mentioned previously, biological problems such as age, 

 size, sex, and prior exposure of the animals to stress, which tend to 

 confound the results of bioassays with many other organisms, are not 



