Aims: Mainly used for the detection of medical and illicit drugs, hair analysis is increasingly used for the assessment of human exposure to pollutants thanks to recent progresses in analytical techniques which allowed the detection of low levels of concentration. Although the relationship between chemicals intake and resulting concentration in hair remains incompletely elucidated, the transfer from blood to hair bulb is generally considered the main route of incorporation in hair. Mechanisms of absorption, distribution and metabolization into blood should modulate the transfer of chemicals depending on their toxicokinetic parameters, resulting in different "blood to hair concentration" ratios. The present work investigated the correlation between "blood and hair concentration" and "toxicokinetic parameters" of more than twenty pesticides from different chemical classes in animal models submitted to controlled exposure. Methods: Two animal experiments were performed on the same strain (Lister Hooded). The first one was conducted to observe the relationship between hair and blood concentration. Hence, rats were administered pesticides by gavage over a 90 days-period, 3 times per week, at 7 different levels plus one control group. Each level of exposure consisted of n=8 animals. Animals' hair was collected at the end of the experiment by shaving. The second one provided toxicokinetic parameters of pesticides into blood. Rats were administered pesticides by gavage of a single dose and blood was sampled at different times using a catheter in the caudal vein. Toxicokinetic was established with 20 different time points with a 12-repetition for each in order to reduce individual variability. After hair sample decontamination, pulverization and extraction, both parents and metabolites were analyzed by GC-MS/MS. Blood was immediately turned into plasma, and after extraction, the same compounds were analyzed also by GC-MS/MS. Results: The data obtained for all the investigated compounds demonstrated significant association between plasma and hair concentrations (P value of 2.97E-45 and Rpearson of 0.875), with the exception of 3 outliers. For all the target compounds, toxicokinetic parameters (such as Cmax, tmax, Cmin, elimination half-life, area under the curve) were investigated in order to understand the influence of these parameters on outlier's specific behavior. Conclusions: Our results support that the concentration of chemicals in hair depends on the respective concentration in plasma and suggest that for most pesticides, the transfer from blood to hair would not represent a limiting step in the incorporation. Results will however be analyzed more in detail in regard to compound toxicokinetic parameters.
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