Effect Of Heavy Metal On Chlorophyll A Contents Of Cladophora Fracta And Research For Toxic Mechanism

Water pollution of heavy metal is an issue of environmental concern. Various undesirable toxic heavy metals such as mercury, cadmium, copper, zinc, lead, nickel, etc, are well-known as fresh water and marine pollutants. They are contaminating many sites through industrial discharge. Much interest has recently been invested in their effects on algae.Algae are the primary producer of the water system.Cladophora fracta is found in a variety of marine and freshwaters and provides habitat and food for numerous organisms. It may be the most ubiquitous macroalga in freshwaters worldwide. Representatives of the genus Cladophora are distributed worldwide and dominate the benthos in fresh and marine waters. Cladophora fracta is a filamentous chlorophyte with varied degrees of branching and has a relatively long life span.Because local abundance, widespread distribution, sedentary nature and capacity to accumulate trace metals to levels well above those found in water, macroalgae can integrate short-term temporal fluctuations in environmental concentrations and have been used as biomonitors to indicate heavy metal levels in waters.Many experiments have shown that Cladophora has a high removal efficiency of heavy metals such as cadmium and N, P nutriments in the eutrophic water. And Cladophora also can be used to make fine paper.So we choose Cladophora fracta as our experimental materials to study the toxicity on Cladophora fracta induced by four heavy metals: mercury( II) > cadmium( II) -> copper( II) -. and zinc( II) under different experimental conditions such as different temperatures, different ions concentrations. The aim of the experiment is to reveal the toxic mechanisms of heavy metals to the Cladophora fracta and to offer some useful information for the biomonitoring of water body and the bioremoval of heavy metal from aqueous system. So we can use Cladophora fracta as a better bioindicator and biosorbent of wastewaters.We have studied the effects of exposure time, heavy metal concentration, temperature and cross effects among these three factors through the experiment method of orthogonal design on the growth of Cladophora fracta, which is measured by the content of chlorophyll a. It is suggested that Hg24\"~)4- 0-1- 0-1-Cd nCu ^ Zn all have toxic effects on the Cladophora fracta, chlorophyll a contents have shown a decreasing tendency with the exposure time increased.In the acute toxicity experiments of Hg2\ Cu2~\ Zn2+, temperature is the major factor affecting the Chlorophyll a(Chl.a). Otherwise, the exposure time is the major factor in the CdCl2 acute toxicity experiment to the Cladophora fracta.ThQ effects of temperature and concentration of heavy metals on Chi.a are different in four heavy metals.In the short term experiments, exposure time is the major factors...