EFFECT OF CRUDE OIL POLLUTION ON OYSTERS 
183 
fact is clear: That a concentration between 20 and 30 percent soluble fraction will, 
on the average, reduce the rate of feeding of the oyster to one-half its normal value. 
RESULTS OBTAINED WITH THE DROP COUNTING METHOD 
Two series of experiments were made with the water-soluble fraction of crude 
oil, using the drop counting technique previously described. 
The first group of 12 experiments (table 12) represents winter conditions, as they 
cover the period of November and December 1933. Two Louisiana crude oils were 
used, one from the Lake Barre wells, the other from the Pelto wells. Both fields 
are located in Terrebonne Parish and are operated by the Texas Co. 
In the second series (table 13) are 19 experiments completed during May 1934, 
using only Lake Barre oil. The results of all experiments are summarized in these 
tables, which give the rate of pumping, in drops per minute, before, during, and after 
treatment. A column marked “Effect of treatment” gives the percent of the normal 
rate of flow obtained by dividing the average rate of flow during treatment by the 
average rate before treatment, making it possible to evaluate the inhibiting effect of 
oil extract on various oysters. In table 14 the results of the experiments are presented 
in a more detailed manner, showing for every 5-minute interval, the average number 
of drops of water per minute passed by the gills. 
Heavy type indicates observations made when the soluble-fraction solution was 
running through the experimental chamber. 
In both series of experiments a full-strength solution was used. There was a 
slight increase in the specific gravity of the sea water after it was stirred with oil, but 
there was no correlation between the specific gravity of the extract and its toxicity. 
Table 12. — The effect of soluble fraction of crude oil of Lake Pelto and Lake Barre wells on the rate of 
pumping of water by the gills of the oyster 
[Drop counting method, winter experiments, Beaufort, 1933] 
Experiment 
no. 
Date 
Drops per 
minute 
Effect 
of 
treat- 
ment 
Dura- 
tion 
test 
in 
min- 
utes 
Specific gravity, 
17.5“ C. 
Tempera- 
ture, “ C. 
pH 
sol- 
uble 
frac- 
tion 
Increase 
in spe- 
cific 
gravity 
of sol- 
uble 
fraction 
Recovery 
time 
Source 
of oil 
Be- 
fore 
treat- 
ment 
Dur- 
ing 
treat- 
ment 
After 
treat- 
ment 
Labora- 
tory 
sea 
water 
Soluble 
frac- 
tion 
Be- 
gin- 
ning 
End 
Per- 
cent 
Min- 
utes 
Percent 
fit) 
Nov. 28 
92.0 
109. G 
95.2 
119. 1 
5 
1. 0261 
1. 0277 
13.6 
128 
5 
60 A 
65.8 
41. 3 
69.7 
62. 8 
5 
1. 0261 
1. 0262 
15. 0 
15. 1 
7 3 
0 0001 
1 16 
30 
Dn 
62 
Dec. 
1 
31.2 
19.0 
27.0 
61. 1 
5 
1. 0261 
1. 02638 
15.4 
15.2 
7.3 
.00028 
93 
15 
Do. 
63 A 
Dec. 
4 
112.2 
92.0 
108.2 
82.0 
5 
1.0262 
1.0262 
17. 4 
17. 3 
7. 3 
107 
15 
Dn 
64 A 
Dec. 
5 
77.2 
30.0 
71.5 
38. 9 
1. 0260 
1.0260 
16.5 
16. 3 
97 
15 
Do 
65A 
Dec. 
7 
41.4 
46. 6 
39.0 
112.7 
5 
1. 0265 
14.8 
14.8 
123 
5 
66 
Dec. 
11 
36.0 
35.0 
39. 5 
97. 2 
10 
1. 0267 
13. 2 
13. 5 
145 
5 
Dn 
67 
...do. 
60.5 
54.7 
58.2 
90.4 
10 
1. 0267 
13.8 
14. 1 
103 
20 
Do. 
68 
Dec. 
12 
67.2 
52.0 
57.2 
77. 4 
10 
1. 0267 
11.8 
11. 6 
77 
10 
Dn 
69 
Dec. 
15 
77.0 
60.4 
79.6 
78.4 
in 
1. 0267 
1. 0279 
12.3 
12.5 
7.5 
.0012 
109 
15 
Do. 
70 
Dec. 
21 
1 120. 7 
0 
36.5 
i 30. 2 
15 
1.0256 
1. 0260 
15.6 
16. 5 
7.6 
Do. 
70 A 
Dec. 
22 
i 83.5 
0 
64.9 
> 77.7 
15 
1. 0256 
15.0 
15.4 
Sea water. 
Average.. 
66.0 
54.06 
62.2 
82.0 
14. 48 
109.8 
13.5 
1 Numbers omitted in making average. 
