Reactions to heavy metal salts 

The salts of heavy metals occupy a special position among the pollutants of  the ecosystem.  It is
known that not only the different species of  plants, but also separate types and even clones are distinguished by their sensitivity to the specific contaminant. Special bioassays for determining the effectiveness of the general/common action of pollutants are reduced to the estimation/evaluation of the degree of a change in readily measured morphometric and biochemical indices, the estimation/evaluation of germination vigor, energy of an root growth, vulnerability of plants to the effect of the contaminant. The degree of the depression of the plants after a treatment is determined by physiological methods. 

For the purpose of our studies, we made a search for rapid and adequate tests with which it would be possible to determine the pollution/contamination of soil and water by salts of heavy metals, pesticides, to analyze soil from the diverse variants of field  monitoring with the complex pollution/contamination.  Different forms of duckweeds, which are encountered in the territory of Krasnodar edge, served successful as test object. 

During the first stage of our work we began to determine the reaction of each specific contaminant (metal or pesticide), and then to conduct complex soil testing.

Reactions to the metals.

Studies were undertaken on the aqueous solutions of the following salts:  ZnSO4, CuSO4, CuCl2, Co(NO3)2, BaCl2, MnSO4, and Fe2(S04)3. We show the reaction of duckweeds to the metals by means of the three tables below.  This presentation, in our view, allows us to most fully illustrate entire spectrum of the responses to each concentration of these metals. 

Two forms - ivy-leaf duckweed (Lemna trisulca) and rootless water meal (Wolffia arrhiza) reacted to the action of pollutants with a change in the color of the fronds and there was little other information. For these species we, therefore, limited themselves  to a brief description, without the introduction of a table.

Ivy-leaf duckweed is completely immersed in the water.  Therefore it more rapidly responds to pollution/contamination - either it dies off completely or is the intensity of its pigmentation changed .  Apparently for this form it is necessary to search for other evaluation criteria, with
the use of color and other cytological methods capable of giving complete information
about the degree of contamination of water. 

The rootless Wolffia plant is very small, without roots which hamper analysis upon transfer from one concentration of metal to another.  This plant, nevertheless can be used successfully for phytotoxicity testing for passive monitoring of pollution/contamination of natural reservoirs. 

Concentrations 0,1- 0,25 of all the metals tested proved to be lethal for all representatives of Lemnaceae, in this connection we combined them in one graph (tables 1, 2, 3). 
 
Figure 1. Lemna minor. Cu -copper - 0,001-0,0001 mg/mL (reaction five hours after experiment) Fronds are decolorized from the edge to the center,
frond disconnection is complete. 

Copper (Cu) -  the first reaction to the metal with the concentrations:0,1 - 0,25 - 0,025 -appeared 4 hours after the beginning of the experiment.  Fronds were decolorized, (Fig. 1) and by the next day they had acquired a bluish pigmentation.  Wolffia fronds at a concentration 0.001 Cu were decolorized.  Green pigmentation was preserved in ivy-leaf and lesser duckweed only at the points of increase/growth with complete disconnection of fronds.  In greater duckweed, fronds became light green and disconnected (Fig. 2). 
 
a) b)
Transparent thread, which
connects four fronds and
two turions.
Specific reaction to copper:  a) control, all fronds of
 small duckweed are assembled into groups; b) version
with copper, all fronds were disconnected and the fronds
turned brown.
Figure  2.

 
Table 1 
Reaction of lesser duckweed (Lemna minor) to the salts of heavy metals 
Metal and its concentration Text Indices
Frond color Disconnection of Fronds Coefficient of Growth Reaction
control intense green none 1,55 none
Cu 0,1-0,25 white none none none
0,025 white 100% none none
0,001-0,0001 loss of color from the edge to the center 100% none none
Fe 0,1-0,25 white 100% none  white roots 
0,025 -- -- -- --
0,001 light green none 1,2  
0,0001 white none 1,55  
Zn 0,1-0,25 loss of color from the edge to the center none none  white roots 
0,025 -- none none none
0,001  green none 1,2 none
0,0001 light green none 1,1 none
Ba 0,1-0,25 from white to dark yellow 100% none none
0,025 white, but the ends of fronds are green 100% none none
0,001 white only at the growing point 70% none none
0,0001 green none 1,4 none
Co 0,1-0,025 white, only the veins 100% none none
0,001 light green 100% none none
0,0001 pale green, white in places none none fronds dry up
Mn 0,1-0,25 green, slightly yellow on the edges 100% none roots fall off
0,025  green, slightly yellow none none none
0,001 yellow-green none 1,4 none
0,0001 light green none 1,5 none

 
Table  2
Reaction of swollenduckweed (Lemna gibba) to the salts of heavy metals 
Metal and its concentration Text Indices
Frond color Disconnection of Fronds Coefficient of Growth Reaction
control intensely green none 1,35 none
Cu 0,1-0,25 серо-зеленая none none white roots
0,025 white none none none
0,001 оливковая 100% none none
0,0001 white -- -- --
Fe 0,1-0,25 white 100% none white roots
0,025 -- -- -- --
0,001 decolorized from the edge to the center none 1,4 none
0,0001 green none 1,5  
Zn 0,1-0,25 decolorized from the edge to the center none none white roots
0,025 light green none none white roots
0,001 green none none white roots
0,0001 light green none none none
Ba 0,1-0,25  yellowish-green 100% none roots fell off
0,025 white, but the ends of the fronds are green 100% none roots fell off
0,001 light green none none roots fell off
0,0001 light green none 1,2 none
Co 0,1-0,25 light green none none none
0,025 -- -- -- --
0,001 light green none none none
0,0001 yellowish-green, white in places none none fronds dried up
Mn 0,1-0,25 green 100% none roots fell off
0,025 pale green none none none
0,001 yellowish green none 1,2 none
0,0001 light green none 1,2 none

 
Table  3
Reactions of greater duckweed (Spirodella polyrhiza) to the salts of heavy metals 
Металл и его концентрации Text Indices
Frond color Disconnection of Fronds Coefficient of Growth Reaction
Control intense green none 1,25 none
Cu 0,1-0,25   gray green none none white roots
0,025  olive 100% none none
0,001 olive 100% none wrinkled fronds
0,0001  light green 70% 1,2 none
Fe 0,1-0,25 white none none none
0,025 gray -- -- --
0,001 green none 1,2 none
0,0001 green none 1,3 none
Zn 0,1-0,25 decolorized from the edge to the center none none white roots
0,025 light green none none white roots
0,001 green none none white roots
0,0001 green none 1,2 none
Ba 0,1-0,25  yellowish-green none none roots fell off
0,025  yellowish-green none none roots fell off partially
0,001 green none 1,5  roots fell off 40% of the plants
0,0001 light green none 1,2 fronds became partly dry
Co 0,1-0,25 light green none none fronds sluggish
0,025 -- -- -- --
0,001 light green none 1,3 none
0,0001 green none 1,5 none
Mn 0,1-0,25 light green, but the edges dried strongly and turned yellow none none roots fell off, fronds dried off
0,025  yellowish-green none none none
0,001 green none 1,2 none
0,0001 light green none 1,3 none

 

Reaction to iron (Fe) began 6 hours after the beginning of the experiment.  Fronds of duckweeds became steel white, and then in 2 days acquired a light-orange color.

Reaction to zinc (Zn) is characteristic for all forms of duckweeds.  Fronds with concentrations 0,1- 0,25 - 0,025 (in L. minor) become almost colorless at the growing  points.
 
Figure 3. Spirodela polyrhiza.  Ba - barium - 0,1-0,25 mg/ml (reaction to 2 days).  Fronds light yellow, complete disconnection of fronds; roots die and drop off. 

The actions of barium (Ba) on the duckweeds is manifested in the loss of painting/color, the separation of fronds, and the death of roots (fig 3).
 
Figure 4. Spirodela polyrhiza. Co - cobalt - 0,1-0,025 mg/ml (reaction at 2 days).  Fronds are sluggish, but are green, there is no increase in fronds. Figure 5. Lemna minor. Co - cobalt - 0,1-0,025 mg/ml (reaction at 2 days).  Fronds green; begin to die off on the edges; all fronds are disconnected 

Cobalt (Co) In comparison with all forms of duckweeds, more sensitive than all reacts the Lemna minor (table 1, 2, 3).  It is noted:the loss of painting/color, fronds they get dry from the edges and are separated.Apparently, the way this of entering it threw it passes along the vascular beams is caused lightening the cloths of fronds along the veins (fig 4, 5).

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Краснодар, 2002