EFFECTS OF PULP MILL POLLUTION ON OYSTERS 
159 
neutralized liquor produced a diminished feeding rate. Further, the oxygen require- 
ment of the liquor, while it might be of significance if experiments were carried on in 
stagnant water, is not the important factor. Both in the above described experi- 
ments, in which running, newly pumped water was continuously provided, and in 
the experiments of Galtsoff , in which the solution was constantly stirred and aerated , 
the possibility of insufficient dissolved oxygen was eliminated. 
Acidity and oxygen demand have generally been considered to be the cause of 
the harmful effect of sulphite pollution. While this may be the case to a great extent 
in fresh-water streams, it is of little significance from the point of view of pollution of 
waters near oyster grounds. The customary recommendations that liquor be neu- 
tralized and exposed to air in ponds before allowing it to enter bodies of water may 
not be made with any confidence where the body of water concerned contains oyster 
beds. Until all toxicity is removed from such wastes, if such is possible, they should 
be completely excluded from waters where oysters are grown. 
In order to work out all of the problems connected with removal of toxicity from 
the liquor, a great amount of research would be required. It would be of importance 
to determine whether the toxicity is slowly destroyed in sea water. It might possibly 
be expected that oxidation would slowly eliminate such substances. However, in 
this case there is no reason for assuming that this would occur, since the actual toxic 
agents are unknown. The results of the present work as correlated with those of 
McMillin and Galtsoff, in accompanying reports, rather indicate that destruction of 
the toxicity of the liquor in Oakland Bay has not progressed very rapidly. 
McMillin was able to calculate, with reasonable accuracy, the maximum concen- 
tration of liquor which would develop in Oakland Bay following regular dumping of 
known quantities by the mill. He found that when an average of about 70,000 gal- 
lons of liquor is dumped daily, the equilibrium developed in the bay would be stronger 
than 1 part per thousand, and that in the neighborhood of a year would be required 
to reach this equilibrium. These calculations assume that no destruction of the toxic 
agents takes place. In the laboratory experiments described above, it was shown 
that liquor in concentrations of 1 part per thousand or above kill oysters within less 
than a month. Lower concentrations produce death after a longer period of time. 
There appears to be a clear relationship between the time required to kill and the 
concentration of liquor. Oysters died in concentrations as low as 0.67 part per 
thousand. 
While the oysters in the laboratory were constantly subjected to the same con- 
centration, this would be true of the oysters in the bay only if complete mixing took 
place. However, complete mixing and distribution of the liquor throughout the bay 
would be a slow process. Further, at low tide the oysters are subjected to the rela- 
tively pure seepage water, which would allow for some recovery. In Oakland Bay 
oysters were first observed to be dying about a year after the mill started operations, 
which is about the same time as McMillin calculated would be necessary for develop- 
ment of equilibrium if complete mixing and distribution should take place at a 
rapid rate. 
The close correlation, therefore, between the time of theoretical building up of 
the equilibrium concentration, the beginning of mortality of oysters in the bay, and 
the results of laboratory experiments on the effect of different concentrations, appears 
to indicate that toxic substances in the liquor were at least partly responsible for the 
abnormal mortality of oysters in Oakland Bay. This agreement between the results 
of the several phases of these investigations is of the utmost importance, for on the 
