Ecological Toxicological Effects Of Heavy Metals Cd²⁺and Pb²⁺on Chironomus Kiiensis

At present,heavy metal pollution is widespread in rivers,lakes and the other aquatic environments,which not only causes serious damage to aquatic ecosystems,but also indirectly threatens human health.Chironomus kiiensis are dominant species in Chironomidae.They widely distributed in freshwater environment in China and play an important role in the food chain of aquatic ecosystem.To investigate the response of C.kiiensis to the stresses of heavy metals Cd2+ and Pb2+,we determined the effects of Cd2+ and Pb2+ on acute and combined toxicity,pupation rate and emergence rate of 4th instar larvae of C.kiiensis,teratogenicity of mouthparts,in vivo activities of five biomarkers(SOD,CAT,GST,P450,MT)and enrichment of two heavy metals.The main results are as follows:1.When the larvae of C.kiiensis were exposed to two heavy metals,their sensitivity to heavy metals increased with the prolongation of exposure time,and their activity slowed down at the initial stage of exposure,and the stimulated stress response weakened.However,the poisoning larvae were stiff in the late stage of exposure alongwith the "S" curve in the tail and grey-green body color.The results indicated that heavy metals Cd2+ and Pb2+ had toxic effects on C.kiiensis.The LC50 of Cd2+was 9.29 and 6.35 mmol/L while the LC5O of Pb2+was 45.98 and 27.71 mmol/L for fourth instar larvae of C.kiiensis at 24 h and 48 h,respectively.The tolerance of the larvae of C.kiiensis to heavy metal pollutants was higher.2.The evaluation results of the combined toxicity for three groups of mixed ions are not entirely consistent by four index methods.The qualitative judgment of the combined toxicity by TU and MTI is identical,but there are differences between them and AI and ?.Under 24 h treatment,When mixed at the ratio of 1:1,the results assessed by TU and MTI methods were partial additive,while those assessed by AI and X methods were antagonistic;When mixed ions are mixed at the ratio of 1:2 and 2:1,The results assessed by TU?MTI and AI were all antagonistic;Under 48 h treatment,the results assessed by TU and MTI methods were partial additive,while those assessed by AI was antagonistic and ?,was synergistic.3.Both Cd2+ and Pb2+ have effects on pupation and emergence of the larvae of C.kiiensis,and Pb2+ has stronger inhibition on pupation and emergence of the larvae of C.kiiensis.Two heavy metals and their mixed ions have teratogenic effects on the mouthparts of the larvae of C.kiiensis,mainly manifested by the brittle mouthparts,broken mandible,initial wear of teeth on the mentum and asymmetry between left and right,seriously.The mentum will be notched and the central teeth will be missed.Under heavy metal stresses,the teratogenic rate of the C.kiiensis larvae was positively correlated with the duration of action.The teratogenic rate is higher while the treatment time is longer,but the type of distortion was not related to the types of heavy metals.4.The Cd2+ and Pb2+ of heavy metal pollutants have acute and chronic toxicity to the larvae of C.kiiensis,and the mixed ions of the two heavy metals(1:1,1:2,2:1)have combined toxicity and time-dose effects on biochemical markers in the C.kiiensis larvae.The theoretical sublethal concentrations of Cd2+and Cd2+and their mixed ions mainly inhibited the activities of protective enzymes(SOD,CAT)in the C.kiiensis larvae,while the maximm allowable residual concentration in actual water mainly showed the activation effect.The response of GST to the stress of two heavy metals in the larvae of C.kiiensis at theoretical sublethal concentration was different,showing a wave-like change,while P450 was inhibited.The activity of GST was mainly inhibited and then returned to the normal level at the actual water concentration,while P450 was activated and then inhibited,while the theoretical and actual concentrations of Cd2+ and Pb2+ and their mixed ions were mainly induced to increase MT content.5.There was no significant difference in the enrichment concentration of Cd2+ and Pb2+ in the C.kiiensis larvae between Cd2+and Pb2+ treatments for 7 days,but the enrichment concentration of Pb2+ treatments for 14 days significantly increased The concentration of Cd2+,Pb2+in mixed ion treatment with different ratios of two heavy metals was different from that in single heavy metal ion treatment.The enrichment factors of Cd2+in C.kiiensis larvae and sediments were higher than those of Pb2+,which indicated that the enrichment capacity of Cd2+in C.kiiensis larvae and sediments was higher than that of Pb2+.Heavy metals Cd2+ and Cd2+ have acute?chronic toxicity and combined toxicity to C kiiensis larvae,and they have effects on pupation rate and emergence rate of C.kiiensis,and they also have obvious teratogenic effects on the mouthparts of C.kiiensis larvae.The Cd2+enrichment ability of C.kiiensis is higher than that of Pb2+.Antioxidant enzymes(CAT,SOD),detoxifying enzymes(GST,P450)and MT in C.kiiensis participated in the response to the stresses of heavy metal pollutants and showed time-dose effects,which could be used as one of the biochemical markers to evaluate Cd2+ and Pb2+ pollution.