Inżynieria Ekologiczna (Dec 2016)
SHORT-TERM EXPOSURE OF FRESHWATER ALGAE TO LEAD ORGANIC COMPOUNDS STUDIED WITH NON-INVASIVE ELECTRICAL AND LUMINESCENT METHODS
Abstract
In this paper the non-invasive biophysical methods were applied to assess the organic lead compounds absorption by freshwater algae Nitellopsis obtusa. Two biophysical techniques were used: the electrical method AC bridge with four external electrodes and the luminescent with the registration of ultraweak photon radiation emitted by plants. They allow to study the electrical and luminescent cell membrane properties. Research was performed with the lead acetate and trimethyl-lead chloride to verify whether algae cells were able to absorb Pb ions from water medium contaminated by these compounds. When the concentration of lead acetate solution increased up to 25 -100 µM the membrane resting potential changed from -140 mV to -175 mV. On the other hand, the electrical resistance of cell membrane (for 12-50 µM) increased with exposure time exceeding its starting value up to 1.5 times. In contrast to these electrical changes, the intensity of ultraweak luminescence was constant at concentrations below 1 µM lead acetate. These results with comparison of literature data can suggest that there was no lipid peroxidation in cell membranes for such organic lead compound concentrations. Chemiluminescent responses of algae were observed in the first 5 hours of experiments for lead concentration higher than 1 µM. The luminescence intensity increased immediately for both reagents, but no more than 4 times for concentrations of 1-10 µM lead acetate. For tetramethyl-lead chloride, the luminescence intensity started to increase slowly about 40 minutes after injection. These results with comparison of literature data may suggest lipid peroxidation in cell membrane for higher, toxic lead concentrations. It means that higher concentrations of lead can trigger lethal processes in the living cells. We conclude that the return of the electrical and chemiluminescent plant parameters to the starting values (before the action of lead ions) can indicate whether living cells are able to cope with detoxifying from heavy metals and whether they can survive when exposed to certain concentration of lead compounds. Algae of Nitellopsis obtusa in the first stage of exposure (5 hours) are able to accumulate organic compounds of lead without essential perturbations only up to specified concentrations (for example 1 µM of lead acetate). For higher lead content, an increase of ultraweak luminescence occurred which was probably associated with free radical productions and lipid peroxidation, as many researchers suggested.
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