Study On Stereoselective Toxicity And Accumulation Of Tau-fluvalinate

Tau-Fluvalinate(TFLV) has good prevention effect on bee mites, as the world’s first apiculture big country, therefore TFLV has been widely used in China. However, the non-standard or long-term use of TFLV may lead to its long-term accumulation and migration in the lipophilic beeswax and other bee products. This would affect the quality and safety of bee products, and harm the health of consumers. TFLV is a chiral pyrethroid acaricide, its two diastereoisomers would exhibit different toxicity for non-target environmental organisms and target insects, as well as different residual behaviors in bee products and organisms. Therefore, study on stereoselective toxicity and accumulation behaviors of TFLV isomers is of great significance to accurate and comprehensive risk assessment of TFLV.According to above description, this paper used chiral high-performance liquid chromatography to separate two stereoisomers of TFLV, and the effects of mobile phase and flow rate on resolution were investigated. The best preparative separation conditions was obtained with mobile phase of hexane/isopropanol(96/4, v/v) at flow rate of 2.5 mL/min(the resolution factor is 1.674). The results of online optical detection showed that the(+)-TFLV was firstly eluted, but its optical rotation signal is much higher than that of(-)-TFLV, indicating that TFLV is not a racemate. Subsequently, a large number of single stereoisomers were prepared and quantified. This provides the key pesticides for the following research on stereoselective behaviors.The results of acute toxicity test on zebrafish for 96 h showed that(+)-TFLV has the highest toxicity(LC50 is 2.5μg/L), and are 273.4 times of(-)-TFLV and 6.7 times of TFLV, respectively. According to “the standard on test for environmental safety evaluation of toxicity of chemical pesticide to fish”, TFLV and(+)-TFLV belong to the extreme toxic pesticides, and(-)-TFLV is a highly toxic pesticide.(+)-TFLV and TFLV showed similar 48-h acute toxicity for carmine spider mite and bean aphid Aphis, and were 20 times and 4-5 times of(-)-TFLV for carmine spider mite and bean aphid aphis, respectively.(+)-TFLV also exhibited the highest acute toxicity for housefly, then the corresponding relations between the absolute configurations and optical rotations of two stereoisomers were confirmed as(+)-(R, S)-TFLV and(-)-(R, R)-TFLV according to the literature. Thus, TFLV stereoisomers showed a great selective difference on toxicity for the target and non-target organisms.A GC-MS method was developed to analyze TFLV residue in zebrafish, and bioaccumulation test was achieved based on this. The results showed that two stereoisomers exhibited similar trend on their accumulation and elimination in zebrafish, when were tested in single isomer and mixture dosage at 2.5 g/L. However, the accumulation concentration when using TFLV and(R, R)-TFLV was 2 times higher than(R, S)-TFLV. The accumulation tended to be stable at 28 d, and reached the highest value of 1464.7 μg/kg at 40 d, indicating zebrafish has very strong enrichment ability for TFLV in water. At the same time, the elimination time from the highest accumulation concentration of TFLV in vivo of zebrafish to its 20% was 63 d. Although the(R, S)-TFLV and(R, R)-TFLV were separately used in test, both isomers were detected in fish with EF values of 0.481-0.504, suggested that the accumulation and elimination of TFLV in zebrafish were not stereoselective, may be derived from that two isomers in water would isomerize.A GC-ECD method was established to detect TFLV residue in the honeybee, and a test for application of TFLV in honeybee was achieved. The results of long-term monitoring showed that the accumulation concentration of TFLV was relative stable in the range of 0.379-0.471mg/kg, and EF values showed the accumulation was non-stereoselective. The accumulation concentrations of(R, S)- and(R, R)-TFLV in beeswax increased to 31.81mg/kg and 32.12mg/kg at 820 d in the group with normal application. TFLV would migrate from old comb to new comb because of replacement, and thus can reduce its residue in old comb. EF values of TFLV in all beeswax samples were in the range of 0.486-0.505, indicating non-stereoselective accumulation and migration, may be that these processes were physical deposition but not biological process with asymmetric effect. In addition, the EF values of TFLV in 93.5% of 31 positive samples from market had little difference with that of the mixture(EF=0.5), indicating that TFLV residues in the majority of honey samples didn’t show obvious stereoselectivity.