Single And Joint Ecotoxicity Of Novel Insecticides And Three Heavy Metals To Non-target Soil Invertebrates Folsomia Candida

Insecticides are extensively used in agriculture to control pests,being effective against soil fauna.Springtail(collembola)is considered as an important bioindicator of the soil ecosystem.Many insecticides are under examination for their harsh impact on collembolans.Naturally,it is difficult to find the single chemical in a soil sample.It often exists in combination with other chemicals.Heavy metal(HM)is one of the notorious immobilizes inorganic pollutant that stays in the soil for quite long time.Risk assessments based on individual insecticides tend to underestimate the effects associated with the toxic action of mixtures.In the present study,we evaluated the toxicities of single and binary combinations of novel insecticides and HMs against a springtail,Folsomia Candida willem,which is widely distributing in agricultural soils of China.(1)Individual acute and chronic toxicities of six insecticides(emamectin benzoate,spinetoram,indoxacarb,chlorantraniliprole,flubendiamide and cyantraniliprole,)were determined against F.candida.Results showed that emamectin benzoate had the highest acute toxicity to springtails with the 14 days(d)LC50 value of 36.09 mg/kg.The following insecticides chlorantraniliprole and cyantraniliprole,whose 14 d LC50 values were 40.41 mg/kg and 54.15 mg/kg.The lower 14 d LC50 values(208.09?705.20 mg/kg)were found for flubendiamide,spinetoram and indoxacarb.For reproductive 28 d chronic toxicity,spinetoram and cyantraniliprole(EC50=0.12 mg/kg and 0.48 mg/kg)showed higher toxicity to F.candida juveniles than emamectin benzoate,flubendiamide and chlorantraniliprole(EC50=3.00-6.90 mg/kg),while indoxacarb showed the least effective to springtail juveniles(EC50=227.70 mg/kg).(2)According to our preliminary experiments and other researches,three insecticides(thiaeloprid,imidacloprid and cyantraniliprole)with high toxicity and three HMs[cadmium(Cd),Nickel(Ni)and Zinc(Zn)]were choose for joint toxicity researches.Results of acute toxicity showed that thiacloprid,imidacloprid and cyantraniliprole were extremely higher toxic to springtails(LC50=1.68 mg/kg,3.70 mg/kg and 31.55 mg/kg)than Cd,Zn and Ni(LC50=28661 mg/kg,15825 mg/kg and 85466 mg/kg).Results from the binary toxicity of insecticides and HMs showed surprising outcomes.After calculating co-toxicity coefficient(CTC)values,most of binary combinations showed synergistic effects,with CTC values more than 120,two of which having great synergistic effects(Nickel + Cyantraniliprole and Cadmium +Cyantraniliprole;CTC= 1629.31 and 3987.65,respectively).Our data of the binary combinations suggested that a potential risk of contaminants between insecticides and HMs may exist.However,more studies of combined toxicities should be further conducted in lab and in field to confirm and identify the synergistic pattern found in this study.Our results would help us to better understand ecotoxicity response of novel insecticides and their mixture with HMs.This research opens a new way,to detect a response of insecticides in the availability of different types of polluted and non-polluted soil with the help of soil bioindicator.