The concentration remains practically the same, even when air is blown through the
experimental container. If, however, an algae culture is living in experimental water,
the rapid disappearance of the mercury is in proportion to the concentration of the
algae culture. The mercury cannot be found in the experimental water, nor on the
walls of the container, nor in the algae themselves. The explanation is that the algae
have transformed the mercury chloride into mercury-organic compounds which then
escape from the system with the aquarium's air supply. This experiment also shows
how careful one must be when interpreting the results of toxic experiments with
heavy metals (Ben-Bassat and Mayer 1975).
From all these examples and arguments it is understandable that toxicity experiments
lead to very different results, if one applies one and the same substance to one and
the same species of organism, but under differing environmental and experimental
conditions. On the other hand, toxicity experiments with one and the same substance,
even when conducted with the same experimental setup, come to different results
when different experimental organisms have been tested. According to toxicity
experiments, mercury chloride can have a toxicity threshold between 0.5 and 100 p.gJI
(Table 26).
It does not seem sound to go on with toxicity experiments including more and more
organism species, except when trying to find organisms which are more sensitive than
species known, and which could set up new standards for toxicity evaluation. It
would be more important if future work could pOint to fundamental differences, if
they can be demonstrated, between freshwater and seawater experiments. The higher
concentration of salts in seawater, not only of sodium chloride, could be the reason
for reduced toxicity of some elements. On the other hand, it could be that organisms
from the high seas are more sensitive to stress from pollution than freshwater orgaganisms, because the high sea is an extremely stable environment where even smallscale fluctuations of environmental factors are the exception. In this respect, marine
organisms from nearshore waters and from estuaries should like freshwater organisms
be adapted to cope with changing environmental conditions and stress, and the assumption is made that they may be more resistant to some pollutants, too, compared with
sensitive organisms from the high seas. The dilemma is that many organisms from
the high seas are so sensitive that even without the addition of pollutants it is impossible to keep them for longer periods in culture. But without submitting them to
experiments, science has difficulties in assessing the effect of pollution to such highly
sensitive species.
Anyway, if it should be possible to deduct from experiments with standard freshwater test organisms, or standard terrestrial test organisms the possible effects a certain environmental chemical will have upon the marine environment, this would
economize an enormous amount of laboratory toxicity testing procedures with
marine organisms.
124
experimental container. If, however, an algae culture is living in experimental water,
the rapid disappearance of the mercury is in proportion to the concentration of the
algae culture. The mercury cannot be found in the experimental water, nor on the
walls of the container, nor in the algae themselves. The explanation is that the algae
have transformed the mercury chloride into mercury-organic compounds which then
escape from the system with the aquarium's air supply. This experiment also shows
how careful one must be when interpreting the results of toxic experiments with
heavy metals (Ben-Bassat and Mayer 1975).
From all these examples and arguments it is understandable that toxicity experiments
lead to very different results, if one applies one and the same substance to one and
the same species of organism, but under differing environmental and experimental
conditions. On the other hand, toxicity experiments with one and the same substance,
even when conducted with the same experimental setup, come to different results
when different experimental organisms have been tested. According to toxicity
experiments, mercury chloride can have a toxicity threshold between 0.5 and 100 p.gJI
(Table 26).
It does not seem sound to go on with toxicity experiments including more and more
organism species, except when trying to find organisms which are more sensitive than
species known, and which could set up new standards for toxicity evaluation. It
would be more important if future work could pOint to fundamental differences, if
they can be demonstrated, between freshwater and seawater experiments. The higher
concentration of salts in seawater, not only of sodium chloride, could be the reason
for reduced toxicity of some elements. On the other hand, it could be that organisms
from the high seas are more sensitive to stress from pollution than freshwater orgaganisms, because the high sea is an extremely stable environment where even smallscale fluctuations of environmental factors are the exception. In this respect, marine
organisms from nearshore waters and from estuaries should like freshwater organisms
be adapted to cope with changing environmental conditions and stress, and the assumption is made that they may be more resistant to some pollutants, too, compared with
sensitive organisms from the high seas. The dilemma is that many organisms from
the high seas are so sensitive that even without the addition of pollutants it is impossible to keep them for longer periods in culture. But without submitting them to
experiments, science has difficulties in assessing the effect of pollution to such highly
sensitive species.
Anyway, if it should be possible to deduct from experiments with standard freshwater test organisms, or standard terrestrial test organisms the possible effects a certain environmental chemical will have upon the marine environment, this would
economize an enormous amount of laboratory toxicity testing procedures with
marine organisms.
124