Changes In Phototaxical Index Of Daphnia Carinata In Response To Heavy Metals,Pesticides And NH₄⁺

The serious aquatic pollution restricts the sustainable development of economy and is also dangerous to the human health and survival.In order to protect water resources free from pollution,it is urgent to increase the precision and extend the detection range in water monitoring.The bio-monitoring is important for monitoring water qualities.Scientists have paid an increasing attention to set up sensitive,quick,and reliable biomonitoring methods,even though that is a quite difficult issue in water monitoring.To use of phototatic index of Daphnia to monitor water qualities is a new and fast method.It was reported that appropriate current could stimulate the growth,metabolisms,and behavior reaction of living things.Therefore,we used 4 d old Daphnia carinata,self-bred mono-clones,to study influence of direct current on the phototaxity and their changes in water solutions added with heavy metals,pesticides and NH4+,respectively or together.The main object is to improve phototatic index method and increases their sensibilities in water monitoring.The main results as follow:(1)The treatment of current intensity from 0 to 0.05 mA for 5 min to 10 min influenced greatly the phototaxity of daphnia.Phototatic index changed from the positive to negative values as the electric intensity increased and the time prolonged in direct current,indicating the effect of micro-field of direct current on phototaxity of this animals.Phototatic index began to change significantly when treated with current intensity over 0.01 mA for more than 5 min.Consequently,0.01 mA/5 min could be considered as the critical point to treat daphnia for varying their phototatic index.(2)The detection limits of detecting Cr6+,Hg2+,Cd2+,Cu2+,and alphaeypermethrin by the phototatic index of daphnia decreased significantly after pre-treatment with 0.01 mA/5 min.After that treatment above,they decreased from 56 ?g L-1 to 32 ?g L-1 for Cr6+,5.6 ?g L-1 to 4.2 ?g L-1 for Hg2+,32 ?g L-1 to 24 ?g L-1 for Cd2+,18 ?g L-1 to 10 ?g L-1 for Cu2+,and 3.2 ?g L-1 to 2.4 ?g L-1 for alphaeypermethrin.Therefore,use of appropriate current to pre-treat daphnia could decrease detection limits and increase sensibilities in water monitoring.(3)The sensibilities of the phototaxity to PCP-Na did not vary much by treatment with current.It indicated that there were some exceptions that the use of appropriate current to pre-treat daphnia could increased the sensibilities in water monitoring.(4)Phototatic index of Daphnia carinata in response to mixture of the two poisons by treatment with appropriate current varied by the type and concentration of poison.The use of micro-field of direct current to pre-treat daphnia could increased the sensibilities in mixture of Cr6+ and Hg2+ contained water solutions while the pre-treatment was not obvious to mixture of Cd2+ and Hg2+,mixture of Cu2+ and PCP-Na and mixture of Hg2+ and alphaeypermethrin.(5)The significant effects of NH4+ in water on phototatic index of Daphnia carinata.Phototatic index of Daphnia carinata reduced gradually as the concentration of NH4+ in water increased.Meanwhile Daphnia carinata by treatment with current were more sensitive to NH4+than one treatment without current.(6)When NH4+ and heavy metals coexisted in water,NH4+ in a certain range(Cr6+ and Cd2+the concentration of NH4+ below 1.5 mg·L-1,Hg2+:the concentration of NH4+ below 0.5 mg·L-1)showed strong inhibitory effect on the biotoxicity of heavy metals in waters.The positive phototaxity of Daphnia carinata significantly reduced in response to the mixture of NH4+ and Cr6+,NH4+ and Hg2+,NH4+ and Cd2+ after the treatment of micro-field of direct current.The study suggested to improvethe sensibilities of daphnia to the mixture of NH4+and heavy metals by pre-treating Daphnia with micro-field of direct current.