Biomarkers of exposure to pesticides in humans

Abstract: Almost every human is exposed to pesticides, in work environments, by domestic use and via diet, drinking water and personal products. Current research expresses concern that low dose exposure over time can lead to adverse health effects. It is therefore important to biomonitor exposure to pesticides in different groups, especially vulnerable groups such as pregnant women. However, there is a general lack of validated bioanalytical methods in order to generate reliable biomonitoring data for the quantification of exposure biomarkers to pesticides. The present thesis describes efforts directed at addressing this shortage.Three new high throughput LC-MS/MS (liquid chromatography coupled with tandem mass spectrometry) methods were developed and validated for the quantification of the exposure biomarkers for ethylenebisdithiocarbamates (EBDCs): ethylenethiourea (ETU); thiabendazole (TBZ): 5-hydroxythiabendazole (5-OH-TBZ) and pyrimethanil (PYR): 4-hydroxypyrimethanil (OH-PYR). Human experimental studies, where two volunteers were orally and dermally exposed,were conducted to confirm that these three biomarkers are metabolites of their parent compounds. For ETU, however, only dermal exposure was studied. In these studies, also basic pharmacokinetics were determined. In an epidemiological cohort study of 445 pregnant women living close to banana plantations in Costa Rica, the LC-MS/MS method for ETU and a modified version of the combined methods for 5-OH-TBZ and OH-PYR were applied to assess exposure to EBDCs, TBZ, PYR and chlorpyrifos, pesticides used on the plantations. Commonly used pyrethroids and 2,4-dichlorophenoxyacetic acid were also assessed. Exposure to TBZ and PYR had not been studied earlier in pregnant women or other human populations. The LC-MS/MS methods were selective and had excellent sensitivity; the limit of detection was ≤0.2 ng/mL. The precision and accuracy were also excellent; the coefficient of variation was ≤15%. In all the experimental studies, the exposure biomarkers ETU, 5-OH-TBZ and OH-PYR were excreted in urine as conjugates. In the dermal exposure experiments, the urinary elimination half-life (t½) was a few days for ETU and hours for 5-OH-TBZ and OH-PYR. In the oral exposure experiments, the t½ was a few hours both for 5-OH-TBZ and OH-PYR. The exposure biomarkers of TBZ and PYR were determined in hundreds of samples from a general Swedish population; half of them had levels of 5-OH-TBZ and of OH-PYR above the limit of detection. In 909 urine samples repeatedly collected from the 445 pregnant women, ETU was detected in 100%, 5-OH-TBZ in 65% and OH-PYR in 87% of the samples. The concentrations of ETU seem comparable to levels in Italian agricultural workers. Further, the other pesticide exposure biomarkers were detected in almost all the samples. The pregnant women working at the banana plantations were significantly more exposed to TBZ and EBDCs than the nonworking pregnant women in the cohort and, in addition, the exposure to chlorpyrifos was slightly higher among the working women.In conclusion, the developed LC-MS/MS methods can be used in biomonitoring of EBDCs, TBZ and PYR in large exposure studies of general populations. The metabolites ETU, 5-OH-TBZ and OH-PYR were confirmed to be reliable urinaryexposure biomarkers after dermal and oral exposure. Hydrolysis to release the analyte from the conjugate in urine is essential in the LC-MS/MS methods. Some new pharmacokinetic information on ETU, TBZ and PYR were obtained from exposure experiments in two volunteers. Because of the short t½ of the biomarkers, repeated sampling is recommended in exposure assessments. The exposure to pesticides in pregnant women in Costa Rica is of great concern.