TABULATION AND USE OF DATA 

 FROM BIOASSAYS 



Hourly observations of test specimens were re- 

 corded on the test card for each jar (fig. 4) until the 

 pattern of mortality was well established- -usually a 

 period of 5 to 12 hours. Animals still alive were then 

 observed at more extended intervals until they had 

 been exposed to the chemical for approximately 20 

 hours. 



The combined data from the four replications 

 at each concentration were tabulated at the comple- 

 tion of a bioassay to indicate mortality at each obser- 

 vation period. An example of this tabulation for a 

 bioassay in water from the West Branch of the Onto- 

 nagon River, Ontonagon County, Michigan, may be 

 found in figure 5, which is adapted from a standard 

 field form. The purpose for which the bioassay in- 

 formation was used was met adequately by records 

 according to arithmetic dosage intervals and observa - 

 tion periods. 



Bioassays were designed primarily to provide 

 data from which two levels of concentration - -mini - 

 mum lethal and maximum allowable --could be de- 

 termined. For our purposes the minimum lethal val- 

 ue was considered to be the lowest concentration in 

 any series producing 100 -percent mortality among 

 larval lampreys. The maximum allowable was the 

 highest concentration which did not kill more than 

 25 percent of the other test species, rainbow trout. 

 These two levels define the range within which con- 

 centrations must be maintained in all parts of a 

 stream during treatment. 



The difference between the maximum allow- 

 able and minimum lethal concentrations is the work- 

 ing range. For a stream to be treated successfully, 

 a working range clearly is required. The most sig- 

 nificant figure obtained from a bioassay is not, how- 

 ever, the range itself but the ratio of the working 

 range to the minimum lethal concentration. This 

 ratio indicates the amount by which volume of flow 

 may increase in a stream treated at the maximum al- 

 lowable concentration before the concentration will 

 reach the minimum lethal level. The importance of 

 the ratio is best illustrated by the examples of table 1 

 in which various maximum and minimum concentra- 

 tions are assumed to have been obtained from bioassays. 

 The working ranges are identical in the four hypothet- 

 ical bioassays, but the practical problems of stream 

 treatment increase progressively from stream A to 

 stream D. 



If the original application in stream A is at the 

 maximum allowable concentration of 5 p.p. m. , the 

 treated water moving downstream is extremely tol- 

 erant of dilution from streambed springs and the in- 

 flow of untreated tributaries; additional flow of 4 

 cubic feet per second (c. f. s. ) is permissible for each 

 c. f. s. at the treatment point. Furthermore, treat- 

 ment in this stream is highly resistant to "washout" 

 by a sudden, unexpected rain. 



The increase of the maximum allowable and 

 minimum lethal concentration by a mere 1 p. p. m. 

 (stream B) cuts the permissible additional flow in 

 half- -from 4 to 2. This flow is halved once more at 

 concentration limits of 8 and 4 p. p. m. (stream C) 

 and still again at 12 and 8 p. p. m. (stream D). 



Table 1. --Hypothetical results of bioassays in four streams to illustrate significance of 

 ratio of working range to minimum lethal concentration 



1/ Per 1 c. f. s. of flow at point of treatment at the maximum allowable concentration. 



6 



