OIL AND TAR POLLUTION OF WATERS. 7 
as from lack of oxygen, or from the destruction or spoiling of emergent 
or littoral vegetation with an oil coating, particularly in tidal areas 
(by which means wild fowls may also greatly suffer), and the conse- 
quent loss of a productive habitat. 
From gas houses, tarred roads, and refineries much of the contam- 
ination eventually finds its way to the bottom to render it more or 
less sterile according to thickness and completeness of the deposit 
and the constancy with which the deposit is maintained. Wadham 
indicates that he found apparently complete strata for each. fresh 
tarring of road, and that it took two or more years for a trout brook 
to recover proper productivity of fish. 
In some waters the basic fish food consists in part of air-breathin 
larvee and pup of insects, which, if a layer of oil is present, as is wel 
known, will be unable to come to the surface to breathe and so will 
be destroyed. Young of food fishes or the small fish on which food 
fishes feed will in consequence be deprived of an important source 
of food, and the productivity of the region will be correspondingly 
decreased. In 1920, through the Gulf States, Mr. Hildebrand found 
that Gambusia and Fundulus, which feed largely on such larve and 
pup, disappeared from oil-covered water. He took no special notes 
in regard to larger species, but believed they disappeared also, pre- 
sumably because their food had disappeared. 
SUMMARY. 
Three main sources of oil and tar pollution have been found: Road 
washings, carrying great quantities of lubricating oil; gas houses and 
oil refineries; tankers, oil burners, and oil-engined shipping. Tars, 
tar oils, and crude distillery products are found generally to be highly 
oisonous, whether in weak or great dilution. Some oils have been 
ound to emulsify to a sufficient degree, with continued agitation, 
to coat the gills of fish and so produce death by suffocation. An oil 
film, through prevention or checking of aeration, is dangerous, par- 
ticularly in busy harbors. The deleterious effect on spawning, by 
rendering spawning grounds unfit or inaccessible, is a grave danger 
arising from the pollution of harbors and streams. Another serious 
danger is found to lie in the possible effects on the diminution of the 
food supply. Through whatever means, it is an observed fact, 
according to Weigelt, that in Germany fish have completely disap- 
peared from pools and ponds following the discharge of mineral oil 
into the water. In the sea a great danger is suggested by the fact 
that the eggs of sea fishes are typically floating, and that oil-burning 
and oil-engied shipping is greatly increasing. 
Remedial measures may (now or in the future) be found: (1) In 
the recovery of oils from drainage water, as already has been pro- 
posed; (2) in the prevention of gas-house and refinery pollution, 
which prevention should be helped by the increased use of ‘‘wastes’’ 
in by-products; and (3) in prevention, by international arrange- 
ments, of the dumping of oil from ships in harbors or in the region of 
spawning grounds or special feeding areas. 
