a
b
c
12
15
18
21 I-Ig/I Hg
Fig. 60. Even extremely small concentrations of mercury in a culture medium influence the
growth of phytoplankton algae. Considerable differences between anorganic mercury (mercurychloride, closed circles) and mercury in an organic compound (phenylmercuryacetate, open
circles) emerge. Compared with the control experiments without mercury (100%), the 3 diagrams
show at what percentage the cell concentration is reduced by the influence of the poison in
a Chlamydomonas sp. (control: 2.2 million cells/ml), b Chlorella sp. (control: 6.5 million cells/mi),
and c Phaeodactylum tricomutum (control: 27.4 million cells/mO (Nuzzi 1972)
Other ecological factors must also be taken into consideration. As a rule, an organism
living under optimum conditions is more resistant than an animal under stress
(Fig. 61). For a species to continue living in an environment, the tolerance at the
most sensitive stage is the decisive factor. Marine organisms are often particularly sen·
sitive when hatching out of an egg or during metamorphosis. Full·grown Echinometra
mathaei sea urchins manifested 50% mortality (96 h LCso ) in a copper concentration
of 0.3 mg/I in seawater. But even at concentrations of 0.02 mg/I, the formation of
the calcareous skeleton is disturbed in developing larvae (Heslinga 1976). Finally, the
sensitivity of organisms vis-a-vis toxic substances also depends on whether or not
they have previously been able to adapt to toxic concentrations or whether they are
coming into direct contact with poisonous substances for the first time in an experiment (Table 25; Fig. 62).
Experiments are also influenced by the fact that they have to be conducted in small
containers where it is possible that poisonous substances are harbored on the walls of
the container instead of being effective in the experimental water. Then too, the
organisms themselves often react in an uncontrollable manner in the experiment.
Sometimes they store up poisonous substances so intensively that the poison in the
experimental medium itself diminishes. Under certain conditions, plankton algae
grow even better in a culture experiment if lead nitrate is added (Fig. 63). Sometimes,
organisms transform poisons into a form that reacts differently than the lab scientist
expects. For example, mercurychloride in a watery solution is not very volatile.
121
b
c
12
15
18
21 I-Ig/I Hg
Fig. 60. Even extremely small concentrations of mercury in a culture medium influence the
growth of phytoplankton algae. Considerable differences between anorganic mercury (mercurychloride, closed circles) and mercury in an organic compound (phenylmercuryacetate, open
circles) emerge. Compared with the control experiments without mercury (100%), the 3 diagrams
show at what percentage the cell concentration is reduced by the influence of the poison in
a Chlamydomonas sp. (control: 2.2 million cells/ml), b Chlorella sp. (control: 6.5 million cells/mi),
and c Phaeodactylum tricomutum (control: 27.4 million cells/mO (Nuzzi 1972)
Other ecological factors must also be taken into consideration. As a rule, an organism
living under optimum conditions is more resistant than an animal under stress
(Fig. 61). For a species to continue living in an environment, the tolerance at the
most sensitive stage is the decisive factor. Marine organisms are often particularly sen·
sitive when hatching out of an egg or during metamorphosis. Full·grown Echinometra
mathaei sea urchins manifested 50% mortality (96 h LCso ) in a copper concentration
of 0.3 mg/I in seawater. But even at concentrations of 0.02 mg/I, the formation of
the calcareous skeleton is disturbed in developing larvae (Heslinga 1976). Finally, the
sensitivity of organisms vis-a-vis toxic substances also depends on whether or not
they have previously been able to adapt to toxic concentrations or whether they are
coming into direct contact with poisonous substances for the first time in an experiment (Table 25; Fig. 62).
Experiments are also influenced by the fact that they have to be conducted in small
containers where it is possible that poisonous substances are harbored on the walls of
the container instead of being effective in the experimental water. Then too, the
organisms themselves often react in an uncontrollable manner in the experiment.
Sometimes they store up poisonous substances so intensively that the poison in the
experimental medium itself diminishes. Under certain conditions, plankton algae
grow even better in a culture experiment if lead nitrate is added (Fig. 63). Sometimes,
organisms transform poisons into a form that reacts differently than the lab scientist
expects. For example, mercurychloride in a watery solution is not very volatile.
121