The Effects of Periodic Low
Oxygen Upon the Toxicity of
Various Chemicals to
Aquatic Organisms
John Cairns, Jr., Associate Curator Limnology
Arthur Scheier, Scientific Assistant
Department of Limnology
Academy of Natural Sciences of Philadelphia
The toxicity of solutions of various substances to aquatic
organisms may be influenced by numerous factors (Cairns, 1957).
The purpose of these experiments was to establish the effect of
periodic low oxygen upon the tolerance to various chemicals of the
bluegill sunfish, Lepomis macrochirus Raf., and a pulmonate snail,
Physa heterostropha (Say.) These test organisms were selected
because they are widely distributed in streams, lakes and ponds in
the U. S. Several chemicals that are often found in industrial wastes
were chosen for study: potassium dichromate, zinc chloride, naph-
thenic acid and potassium cyanide. All these chemicals were tested
on the fish, only the latter two on the snail.
The selection of a pulmonate for these tests perhaps needs
further explanation, since members of this order are air-breathers.
Usually these snails replenish the air supply of the pulmonary
cavity by atmospheric contact and hence would not be dependent
upon the oxygen supply in the water. However, it has been found
under both natural and experimental conditions that many pulmon-
ates rarely or never come to the surface for air. According to Pennak
(1953), this is particularly true of certain species of Lymnaea,
Physa and Helisoma which may pass their entire life cycle without
access to the surface. Apparently the pulmonary cavity may be filled
with water and serve as a gill. In addition, it has been established
that for many species all oxygen absorption may take place through
the surface of the body. These considerations suggested that periodic
low dissolved oxygen might modify the tolerance of Physa to chemical compounds despite the fact that it is a pulmonate. Dr. Theodore
von Brand, Department of Health, Education and Welfare, Public
Health Service, (personal communication) thought it would be of
interest to include a pulmonate snail in this series.
165