Interactions between heavy metal lead and two freshwater algae

To get a better understanding of interactions between heavy metal lead and freshwater algae Microcysis aeruginosa Kutz.and Scenedesmus obliquus(Turp.) Kutz.,the algal biomass,electrical conductivity(EC) of supernatant,concentration of superoxide anion radical(O-· 2),activities of POD and CAT as well as the absorption of Pb2+by algal were determined respectively at different concentrations of Pb2+,and the surface structure of two algae cells was contrasted by scanning electron microscopy.The results showed as follows:(1) 3 mg/L of Pb2+accelerated the growth of M.aeruginosa,and the opposite effects were observed when exposed to more than 9 mg/L of Pb2+;however,the growth of S.obliquus was obviously inhibited when the concentrations of Pb2+ranged from 3 to 12 mg/L.The effects of Pb2+on the two kinds of freshwater algae indicated that S.obliquus was more sensitive to the Pb2+pressure.(2) The membrane permeability of the two algae cells was changed under the stress of Pb2+.The photos of scanning electron microscopy showed that the superficial flocs of the two algae cells increased with the increasing of Pb2+,and numerous cells deformed or ruptured evidently,especially for S.obliquus.Meanwhile,the increases of O-2contents were exhibited and the activities of POD and CAT in the two algae were advanced with increasing of Pb2+concentration at the early stage,which indicated that the main mechanisms of Pb2+acting on two algae involve the increasing production of superoxide anion radical and the accompanying physiologicaland biochemical changes of the algae.(3) Pb2+can be absorbed by the two algae,and moreover S.obliquus had higher capacity of Pb2+absorption than M.aeruginosa did at the unit cells.From the above points,compared with the M.aeruginosa,S.obliquus can be used not only as a biological indicator for monitoring heavy metal pollution levels,but also as a biological material to deal with water Pb2+contamination due to its ability of Pb2+absorption.