Toxic Effects Of Lead On Growth,Reproduction,Behavior And Nutrients Of Daphnia Magna

Lead is a non-essential metal element for human beings and animals.Due to its high toxicity and strong accumulation,it widely exists in the natural environment.Because of the development of industry in recent years,a large amount of lead-containing sewage has been flowed into water sources.A large amount of lead-containing soil pollutes groundwater due to rainwater subsidence,which will damage to aquatic ecosystems.Therefore,the studies included that the growth,reproduction,phototactic behavior and nutrients of Daphnia magna,when exposed to lead.The experiments were designed as four lead concentration groups(0.5,1,1.5,2 mg/L)and a control group,according to 5,10,15 and 20 times of the standard limit of lead concentration in Class V water quality standard.Firstly,the heart rate,body length and reproductive capacity of Daphnia magna were measured after lead exposure.Secondly,the optimum water temperature and light intensity of Daphnia magna was determined.On this basis,we were studied the phototaxis behavior of Daphnia manga after exposure 5 h,10 h,24 h and 48 h.The acetylcholinesterase of Daphnia magna was detected after 24 h and 48 h.Finally,The main nutrient were detected when exposed to lead,such as protein,glycogen,triglyceride and fatty acid.The experimental results are as follows:(1)With the increase of lead concentration,the growth rate of body length of Daphnia magna showed a gradually decreasing trend,and after exposure for 48 h,lead concentrations of 1.5 mg/L and 2 mg/L were lower than those of the control group(P<0.01).The heart rate increased after 24 h.With the increase of exposure time,the heart rate gradually decreased at 2 mg/L(p<0.01),the difference was very significantly compared with the control group.The net reproductive rate(R0),finite increase rate(?),generation time(T),and intrinsic rate(rm)of Daphnia magna showed a downward trend with the increase of lead concentration,and the lowest at 2 mg/L(P<0.05).In addition,the pre-reproductive period of Daphnia magna were prolonged,and the second reproduction period and reproduction period were significantly were prolonged.(2)The optimum temperature and light intensity of the phototaxis behavior experiment of Daphnia magna were determined to be 20? and 10000 lx respectively.Based on this,the phototactic value of Daphnia magna was determined.With the increase of lead concentration and exposure time,the phototactic index of Daphnia magna decreased and tended to negative.After exposure to lead for 24 h and 48 h,the phototactic index was negative when the concentration is 1.5-2 mg/L.Acetylcholinesterase activity decreased with the increase of lead concentration and exposure time,and showed significant difference compared with the control group(P<0.05).(3)After exposure in lead for 24 h,the protein content increased with the increase of lead concentration,reaching the maximum at 2 mg/L(P<0.05).After 48 h,the protein content gradually decreased,and the values reached the lowest at 2 mg/L(P<0.05).Glycogen decreased at 24 h and 48 h with the increase of lead concentrations(P<0.01).Fatty acids increased significantly in lead treatment for 24 h,1.5 mg/L when comparing with the control group(P<0.01).After 48 h,the fatty acid content of Daphnia magna decreased,and it was significantly lower than that of the control group at 2 mg/L(P<0.05).The content of triglyceride decreased after lead treatment for 24 h,and it showed no significant difference when compared with control group after treatment for 48 h.Conclusion:(1)Lead adversely affects the heart rate of Daphnia magna,which significantly inhibits the growth of Daphnia magna,reduces its reproductive capacity,and inhibits its population growth.(2)We optimize and determine the optimal temperature and light intensity of the phototactic behavior of Daphnia magna.It is found that lead increases the sensitivity of Daphnia magna to light and makes it produce negative phototaxis.Meanwhile,the study also finds that the decrease of acetylcholinesterase activity may be involved in the regulation of phototactic behavior.(3)Lead reduces the content of protein,glycogen,triglyceride and fatty acid in Daphnia magna,and generates more energy for basic metabolism by mobilizing nutrients in the body,thus affecting the growth and reproduction of Daphnia magna,which consistent with the results of Conclusion 1.