Characterization Of Exposure Of General Population To Insecticide Fipronil And Its Metabolites Via Indoor Dust And Serum Samples

Fipronil（FP）is a phenylpyrazole insecticide that inhibitsγ-aminobutyric acid-gated chloride channels.Because FP has the advantages of no cross-resistance with traditional insecticides,high efficiency,and broad spectrum,it is widely used in agricultural,indoor sanitary,and veterinary settings for pest and parasite control.Following the widespread use of FP and its relatively long-lasting characteristics,FP and its metabolites（FPMs）are detectable in various environmental and biological samples.Thereby the potential risk of FPMs to the ecosystem and human health has gradually raised concern.Humans can be exposed to FPMs through ingestion of food,dust,and drinking water.Previous animal studies have shown that FPMs are not easily excreted from the body after absorption,as well as have neurotoxicity,reproductive,and developmental toxicity.But there is limited data available regarding human exposure to FPMs.Therefore,it is important to assess the level of human exposure to FPMs.No known data are available regarding the residual level and exposure risk of FPMs in indoor dust and human biological samples in China.In this study,we detected FPMs in indoor dust samples collected from Taiyuan,Wuhan,and Shenzhen in China to illustrate the spatiotemporal variations of the FPMs in indoor dust,and to estimate the daily intake of FPMs via the ingestion of indoor dust for various age groups.In addition,we detected FPMs in paired samples of blood（including serum,plasma,and blood cells）and urine samples from Wuhan population to reveal the characteristics of concentration profiles and clarify the internal exposure marker that can effectively evaluate human exposure to FPMs.FPMs were also determined in serum samples collected from four cities（including Wuhan,Huangshi,Nanjing,and Zhenjiang）to analyze the regional differences of general population exposure to FPMs in China.Part Ⅰ:Fipronil and its Metabolite in Indoor Dust:Spatiotemporal Variations and Human Exposure AssessmentObjective:We aimed to illustrate the residual level of FPMs in indoor dust in China and explore its spatiotemporal distribution characteristics.Meanwhile,to calculate the daily intake of FPMs via the ingestion of indoor dust for various age groups and assess the risk of human exposure.Methods:In this study,indoor dust samples（n=321）were collected from Taiyuan（in 2016,n=84）,Wuhan（in 2016[n=60]and 2018[n=106]）,and Shenzhen（in 2019,n=71）three cities between 2016 and 2019.Samples from both urban and rural areas were collected from Taiyuan and Wuhan to determine the urban-rural differences of FPMs in indoor dust;samples from Wuhan in different years were repeatedly collected to analyze the temporal trend of FPMs in indoor dust.Ultra-performance liquid chromatography-tandem mass spectrometry（UPLC-MS/MS）was used to detect the concentrations of FP and its four major metabolites（fipronil-sulfone,fipronil-sulfide,fipronil-desulfinyl,and fipronil-amide;abbreviated as FP-SFO,FP-SFI,FP-DES,and FP-AM）in the indoor dust samples.The additive mass concentration（ΣFPMs）represented the sum of the concentrations of FP and its four metabolites.The nonparametric test（Wilcoxon or Kruskal-Wallis test）was performed to determine the spatial and temporal distribution differences of FPMs’concentrations.The median and 95th percentile concentrations ofΣFPMs in indoor dust were used to represent the average and high exposure levels,respectively,and the daily intake of FPMs via the ingestion of indoor dust(EDI_dust)of four age groups of toddlers（3–<6 years）,children（6–<12 years）,teenagers（12–<18 years）,and adults（≥18 years）was calculated to assess the risk of human exposure for various age groups.Results:（1）In all indoor dust samples,the concentration ofΣFPMs for the dust samples ranged from not detected（ND）to 6.03μg/g（median:4.23 ng/g）.FP and FP-SFO were the major target analytes detected in the sample with detection frequency（DF）of81.9%and 81.3%,respectively,the DF of other metabolites was low（≤43.6%）.Compared the concentrations of FPMs in the indoor dust samples from the three study cities,the concentration ofΣFPMs in the samples from Shenzhen（20.9 ng/g）was significantly higher than that in Taiyuan（1.87 ng/g）and Wuhan（2.71 ng/g）was found.（2）Analyzed the urban-rural distribution of FPMs’concentrations in the samples from Taiyuan and Wuhan showed that the level ofΣFPMs in the dust samples collected in rural areas was significantly lower than that in urban areas（0.92 vs.7.19 ng/g;P<0.05）.Analyzed the temporal variation trend of FPMs’concentrations in Wuhan samples showed that there was no significant difference in the level ofΣFPMs between Wuhan2016（2.38 ng/g）and Wuhan 2018（2.84 ng/g）,but in the rural areas of Wuhan,compared with the rural areas of Wuhan 2016,the concentrations ofΣFPMs in the indoor dust samples collected in rural areas of Wuhan 2018 showed an significantly increasing trend（1.51 vs.0.87 ng/g;P<0.05）.（3）Assessed the daily intake of FPMs via the ingestion of indoor dust for various age groups,we found that the EDI_dust value of toddlers was the highest,and the EDI_dustvalue of each age group gradually decreased with age.Calculating the EDI_dust value with the 95th percentile concentration ofΣFPMs in the dust samples represented the high exposure level and compared it with the chronic reference dose of FP（c Rf D,0.2μg/kg-bw/d）to assess the risk of human exposure,the highest EDI_dust value（851 pg/kg-bw/d,toddlers group in Shenzhen）was approximately 235 times lower than the c Rf D of FP.Conclusions:We observed the spatial and temporal distribution differences of FPMs’concentrations in indoor dust.The daily intake of FPMs via the ingestion of indoor dust for toddlers were higher than that for adults and the EDI_dust value of each age group was lower than the c Rf D of FP.Future studies are needed to determine whether the residual levels of FPMs in indoor dust pose a risk to the health of sensitive population.Part Ⅱ:The Internal Exposure Level of Fipronil and its Metabolites in General Population:Assessment Risk of Human HealthObjective:To explore the characteristics of concentration profiles by detected FPMs in paired samples of human blood and urine,and clarify the internal exposure marker that can effectively evaluate human exposure to FPMs.Furthermore,to assess the internal exposure level and health risks of FPMs in general population in China.Methods:In this study,39 pairs of blood（including serum,plasma,and blood cells）and urine samples were collected from Wuhan in September 2020,as well as serum samples（n=226）were collected from Wuhan（n=57）,Huangshi（n=56）,Nanjing（n=56）,and Zhenjiang（n=57）of China in 2015.UPLC-MS/MS was used to measure the concentrations of FP and its four major metabolites（FP-SFO,FP-SFI,FP-DES,and FP-AM）in the samples.The additive mass concentration（ΣFPMs）represented the sum of the concentrations of FP and its four metabolites.Descriptive statistics were used to describe FPMs’concentrations in the urine,serum,plasma,and blood cells samples.Spearman correlation was performed to evaluate the correlations between FPMs’concentrations in paired blood matrices.We used the nonparametric test（Wilcoxon or Kruskal-Wallis test）to determine the regional,gender-related,and age-related differences of FPMs’concentrations.The median and 95th percentile concentrations ofΣFPMs in the serum samples from four cities were used to represent the average and high exposure levels,respectively,to assess the estimation of daily human intake(EDI_serum)ofΣFPMs.Results:（1）In the paired blood and urine samples from Wuhan,the median concentrations of FP-SFO in serum（0.17 ng/m L）and plasma（0.16 ng/m L）were higher than that in blood cells（0.03 ng/m L）and urine（ND）.The composition profiles of FPMs in serum,plasma,and blood cells were similar,and FP-SFO was the predominant metabolite with DF of 100%,and the median concentration was 0.17,0.16,and 0.03ng/m L,respectively.We found very strong positive correlations between different blood matrices for FP-SFO（r=0.94–0.97,P<0.05）.However,the DF of the major metabolite FP-SFO in the urine samples was only 10.3%.The DF and concentration of FP-DES in the serum and plasma samples were 97.4%（0.02 ng/m L）and 84.6%（0.02 ng/m L）,respectively,while the DF of blood cells and urine were below 18.0%.The DF of other target compounds in blood and urine samples were low（<5%）.（2）Compared the levels of FPMs in the serum samples from the four different cities,the highest median concentration ofΣFPMs in the serum samples was found in Nanjing（0.56 ng/m L）,followed by Wuhan（0.34 ng/m L）,Huangshi（0.10 ng/m L）,and Zhenjiang（0.08 ng/m L）.The statistical differences in the level ofΣFPMs between any two cities except for between Zhenjiang and Huangshi were observed（P<0.05）.（3）The estimation of daily human intake(EDI_serum)ofΣFPMs was assessed based on the median concentration ofΣFPMs in the serum samples,the EDI_serum ofΣFPMs from Nanjing（19.4 ng/kg-bw/d）was higher than that of Wuhan（11.8 ng/kg-bw/d）,Huangshi（3.47 ng/kg-bw/d）and Zhenjiang（2.77 ng/kg-bw/d）.Even calculated the EDI_serumvalue with the 95th percentile concentration ofΣFPMs in the serum samples represented the high exposure level,the highest EDI_serum value of the four cities（Nanjing,44.7 ng/kg-bw/d）was approximately five times lower than the c Rf D of FP（0.2μg/kg-bw/d）.Conclusions:Compared with blood cells and urine,FP-SFO in serum and plasma is more suitable as the internal exposure marker of human exposure to FPMs.We observed the regional difference of FPMs’concentrations in the serum samples.Although the EDI_serum value of FPMs was lower than the c Rf D of FP,FPMs have bioaccumulation effect and previous animal studies have shown that FPMs have neurological,reproductive and developmental toxicity,more attention needs to be paid to the potential health risks of human exposure to FPMs.