Human metabolism and urinary excretion of seven neonicotinoids and neonicotinoid-like compounds after controlled oral dosages

Abstract

Few human data on exposure and toxicity are available on neonicotinoids and neonicotinoid-like compounds (NNIs), an important group of insecticides worldwide. Specifically, exposure assessment of humans by biomonitoring remains a challenge due to the lack of appropriate biomarkers. We investigated the human metabolism and metabolite excretion in urine of acetamiprid (ACE), clothianidin (CLO), flupyradifurone (FLUP), imidacloprid (IMI), sulfoxaflor (SULF), thiacloprid (THIAC) and thiamethoxam (THIAM) after single oral dosages at the currently acceptable daily intake levels of the European Food Safety Authority. Consecutive post-dose urine samples were collected up to 48 h. Suspect screening of tentative metabolites was carried out by liquid chromatography–high-resolution mass spectrometry. Screening hits were identified based on their accurate mass, isotope signal masses and ratios, product ion spectra, and excretion kinetics. We found, with the exception of SULF, extensive metabolization of NNIs to specific metabolites which were excreted next to the parent compounds. Overall, 24 metabolites were detected with signal intensities indicative of high metabolic relevance. Phase-I metabolites were predominantly derived by mono-oxidation (such as hydroxy-FLUP, -IMI, and -THIAC) and by oxidative N-desalkylation (such as N-desdifluoroethyl-FLUP and N-desmethyl-ACE, -CLO and -THIAM). IMI-olefin, obtained by dehydration of hydroxylated IMI, was identified as a major metabolite of IMI. SULF was excreted unchanged in urine. Previously reported metabolites of NNIs such as 6-chloronicotinic acid or 2-chlorothiazole-4-carboxylic acid and their glycine derivatives were detected either at low signal intensities or not at all and seem less relevant for human biomonitoring. Our highly controlled approach provides specific insight into the human metabolism of NNIs and suggests suitable biomarkers for future exposure assessment at environmentally relevant exposures.

Insights into Free and Conjugated Forms of Neonicotinoid Insecticides in Human Serum and Their Association with Oxidative Stress

“…Limited studies have reported the serum concentrations of p-NEOs and m-NEOs in humans. ,− Our results on serum levels of NEOs agree with those monitored previously in whole blood samples (median Σ 11 NEOs: 7.75 ng/mL) and in periodontal blood samples (median Σ 9 NEOs: 6.87 ng/mL) collected from Guangzhou. , However, the median sum concentration of seven p-NEOs (including ACE, IMI, CLO, THD, and THM) in human serum samples collected from Wuxi city in China was 0.026 ng/mL, which is 2 orders of magnitude lower than that of Σp-NEOs_ total (median: 2.54 ng/mL) found in our study, mostly because our study used enzymatic hydrolysis while the other study did not. Therefore, our study highlights the significance of quantification of free and conjugated forms of NEOs.…”

“…In order to assess the differences in Phase I metabolic transformations of three p-NEOs (i.e., ACE, DIN, and IMI) selected in this study, a coefficient ( f i _I ) was used to elucidate the distribution of each metabolite ( N -dm-ACE _total , DIN-U _total , and 5-OH-IMI _total ) in relation to the total concentrations of p-NEO _total and m-NEO _total , calculated using the following eq : f i _ normalI = C 2 , j C 1 , i + C 2 , j where C 1, i (ng/mL) and C 2, j (ng/mL) are the individual serum concentrations of total form p-NEOs ( i : ACE, DIN, or IMI) and their corresponding total form m-NEOs ( j : N -dm-ACE, DIN-U, or 5-OH-IMI), respectively, for each sample. In vitro and in vivo studies identified Of-IMI as a less important metabolite of IMI. , Therefore, we excluded this m-NEO for the estimation of f IMI_I . Furthermore, the serum samples that contained undetectable concentrations (<LOQ) of m-NEOs _total or corresponding p-NEOs _total were also excluded from f i _I analysis.…”

“…In vitro and in vivo studies identified Of-IMI as a less important metabolite of IMI. 38,39 Therefore, we excluded this m-NEO for the estimation of f IMI_I . Furthermore, the serum samples that contained undetectable concentrations (<LOQ) of m-NEOs _total or corresponding p-NEOs _total were also excluded from f i_I analysis.…”

Quantitative Metabolism and Urinary Elimination Kinetics of Seven Neonicotinoids and Neonicotinoid-Like Compounds in Humans

“…Ethanol (≥99.8%) used for oral intake was purchased from Honeywell (Seelze, Germany). Chemicals and reagents have been described by us previously in detail on the suspect screening of NNI metabolites in urine 33 and their analyses in urine 34,35 with the exception of 6-(trifluoromethyl)nicotinoyl glycine (6-TMNA-gly), a potential metabolite of SULF. For this, 6-TMNA-gly and its stable isotope labeled analogue 13 C 2 , 15 N-6-TMNA-gly have been custom-synthesized (Dr. Vladimir Belov, Max Planck Institute for Biophysical Chemistry, Goẗtingen, Germany) and have been included in our study here.…”

Neonicotinoid Insecticides and Their Metabolites Can Pass through the Human Placenta Unimpeded

“…Furthermore, there were no significant correlations between IMI and of-IMI in either CS or MS. Unlike N -dm-ACE, of-IMI is a minor secondary metabolite of IMI; its presence in human matrices may be partly due to degradation of hydroxylated IMI (the main metabolite of IMI). , of-IMI in MS is derived from multiple sources, explaining the lack of a correlation with IMI.…”