INVESTIGATION OF CARCINOGENIC PESTICIDE-ASSOCIATED N-NITROSO COMPOUNDS IN HUMAN SERUM AND URINE IN PRINCE EDWARD ISLAND

Abstract

N-nitroso compounds form during acid-catalyzed reactions between certain nitrogen-containing compounds and nitrite. Approximately 90% of over 300 N–nitroso compounds have shown evidence of carcinogenicity. Pesticide-associated N-nitroso compounds (PANNs) may form endogenously from nitrosatable pesticide residues in food or water and may be detected in serum and urine. The objectives of this doctoral dissertation were to (i) develop analytical methods using ultra-high pressure liquid chromatography (UHPLC) high-resolution accurate mass (HRAM) orbital ion trap mass spectrometry (MS) for measuring 10 PANN precursors in serum and urine; (ii) investigate PANN formation in water by combining nitrosatable analytes with nitrite under environmentally-relevant conditions; and (iii) analyze serum and urine from a sample population in Prince Edward Island, the province with the highest pesticide-use intensity, and an urban control population (Halifax, Nova Scotia) for target analytes and PANNs. Three sample preparation methods were evaluated for extraction of target analytes from biomatrices. Deproteinization by methanol resulted in excessive ion enhancement of some analytes and complete loss of others. Solid-phase extraction showed less ion enhancement than did deproteinization; however, analyte loss remained an issue. The Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) approach resulted in a novel method for extraction of target analytes with mean initial recoveries in serum ranging between 74 and 120% (% relative standard deviation, RSD <12) and 96% to 116% (%RSD 10) in urine. To assess PANN formation, nine nitrosatable precursors were individually reacted at environmentally-relevant concentrations with sodium nitrite and hydrochloric acid in water. Ethylenethiourea (ETU) produced carcinogenic N-nitrosoethylenethiourea (N-ETU) in several experiments and at initial ETU concentrations as low as 7.5 µg L-1. Finally, serum and urine from 64 healthy individuals in PEI and NS were analyzed for 10 PANN precursors. ETU and 3,5,6-trichloro-2-pyridinol were detected in serum while atrazine and ETU were detected in urine with no significant differences in detection frequency in either biomatrix between provinces. Six and 10 PANNs were tentatively identified in serum and urine, respectively, in both provinces. Based on these findings, endogenous N-ETU formation may be a concern for individuals exposed to ETU and PANNs may be utilized as biomarkers of pesticide exposure.