Trace Metals in Natural Waters
45
toxic above a certain concentration. Very toxic elements include the cations Ag
+
,Be
2 +
,
Cu
2+ , Hg
2+ , Sn
2+ , Co
2+ , Ni
2+ , and Pb
2+ . Some of these elements may be lethal to some
organisms (algae) at concentrations as low as 1CT
7 M and may interfere with metabolic
functions and give deficiency symptoms even at lower concentrations. Nutritional
requirements also differ from organism to organism. The fungus Aspergillus niger for
example increases its growth with Mo concentrations as low as 1CT
12 M (1).
Addition of an organic complex forming substance may have the following
consequences:
(1) It may reduce the free metal ion concentrations in the solution (See Table 3). Such a
reduction may increase or decrease the growth of organisms (e.g., productivity). As a
consequence of complex formation, the latter condition might result from the decrease in
concentration of one or more essential micronutrients, the former condition might result
because one or more toxic elements become masked. As Table 3 shows for a hypothetical
example, the addition of a few organic ligands at concentrations of 1CT
6 M or smaller
indeed tends to decrease the concentrations of free Cu
2 + , Ni
2 + , Zn
2 + and Cd
2 + by factors
of 160, 6, 2 and 1.4, respectively.
(2) It increases total soluble metal concentration. Depending on whether the organisms
can take up or break down the metal chelates, the metal species may become better
available to the cells. Some chelates may be more readily transportable through the cell
walls. EDTA and NTA chelates which have repeatedly been shown to increase (16) and
decrease (13) productivity do not appear to penetrate cell walls; but other chelate
formers may penetrate and may change the coordination chemistry of the inside of the
cell.
Logical interpretation of observed phenomena is furthermore rendered more difficult
because the results of many nutrient enrichment experiments carried out as batch tests in
closed bottles are not amenable to unambiguous interpretations. For example in a bottle
test, trace metals that might readily be available in the aquatic environment — become
soon depleted because the routes of replenishment have been cut off, or because trace
metals have become adsorbed on the glass wall.
45
toxic above a certain concentration. Very toxic elements include the cations Ag
+
,Be
2 +
,
Cu
2+ , Hg
2+ , Sn
2+ , Co
2+ , Ni
2+ , and Pb
2+ . Some of these elements may be lethal to some
organisms (algae) at concentrations as low as 1CT
7 M and may interfere with metabolic
functions and give deficiency symptoms even at lower concentrations. Nutritional
requirements also differ from organism to organism. The fungus Aspergillus niger for
example increases its growth with Mo concentrations as low as 1CT
12 M (1).
Addition of an organic complex forming substance may have the following
consequences:
(1) It may reduce the free metal ion concentrations in the solution (See Table 3). Such a
reduction may increase or decrease the growth of organisms (e.g., productivity). As a
consequence of complex formation, the latter condition might result from the decrease in
concentration of one or more essential micronutrients, the former condition might result
because one or more toxic elements become masked. As Table 3 shows for a hypothetical
example, the addition of a few organic ligands at concentrations of 1CT
6 M or smaller
indeed tends to decrease the concentrations of free Cu
2 + , Ni
2 + , Zn
2 + and Cd
2 + by factors
of 160, 6, 2 and 1.4, respectively.
(2) It increases total soluble metal concentration. Depending on whether the organisms
can take up or break down the metal chelates, the metal species may become better
available to the cells. Some chelates may be more readily transportable through the cell
walls. EDTA and NTA chelates which have repeatedly been shown to increase (16) and
decrease (13) productivity do not appear to penetrate cell walls; but other chelate
formers may penetrate and may change the coordination chemistry of the inside of the
cell.
Logical interpretation of observed phenomena is furthermore rendered more difficult
because the results of many nutrient enrichment experiments carried out as batch tests in
closed bottles are not amenable to unambiguous interpretations. For example in a bottle
test, trace metals that might readily be available in the aquatic environment — become
soon depleted because the routes of replenishment have been cut off, or because trace
metals have become adsorbed on the glass wall.