Gayanga Weerasekera

Measurement of dialkyl phosphate metabolites of organophosphorus pesticides in human urine using lyophilization with gas chromatography-tandem mass spectrometry and isotope dilution quantification.

Urinary dialkylphosphate (DAP) metabolites have been used to estimate human exposure to organophosphorus pesticides. We developed a method for quantifying the six DAP urinary metabolites of at least 28 organophosphorus pesticides using lyophilization and chemical derivatization followed by analysis using isotope-dilution gas chromatography–tandem mass spectrometry (GC–MS/MS). Urine samples were spiked with stable isotope analogues of the DAPs and the water was removed from the samples using a lyophilizer. The dried residue was dissolved in acetonitrile and diethyl ether, and the DAPs were chemically derivatized to their respective chloropropyl phosphate esters. The chloropropyl phosphate esters were concentrated, and analyzed using GC–MS/MS. The limits of detection of the method were in the low μg/l (parts per billion) to mid pg/ml range (parts per trillion) with coefficients of variation of 7–14%. The use of stable isotope analogues as internal standards for each of these metabolites allows for sample-specific adjustment for recovery and thus permits a high degree of accuracy and precision. Use of this method with approximately 1100 urine samples collected from pregnant women and children indicate that the low limits of detection allow this method to be used in general population studies.

The Presence of Dialkylphosphates in Fresh Fruit Juices: Implication For Organophosphorus Pesticide Exposure and Risk Assessments

This study was designed to determine whether dialkylphosphates (DAPs) are present in fresh fruit juices, as a result of organophosphorus (OP) pesticides degradation. Fresh conventional and organic fruit (apple and orange) juices were purchased from local grocery stores. DAPs were found in both conventional and organic juices, and the original levels were higher, for both apple and orange juices, in conventional than in organic juices. Additional DAPs were found in OP pesticide fortified juices after 72 h of storage at 4°C, suggesting a degradation of OP pesticides in juices. Overall, 12% and 36.2% of fortified azinphosmethyl, a dimethyl OP pesticide, and the combination of fortified diazinon and chlorpyrifos, both diethyl OP pesticides, were degraded to dimethyl and diethyl DAPs, respectively. Although the exact mechanism of the degradation is unknown, hydrolysis is likely the cause of OP pesticide degradation in juice. The presence of DAPs in fresh fruit juices clouds the validity of using urinary DAP measurements for estimating OP pesticide exposures in humans, particularly in children. The overestimated OP pesticide exposures based on urinary DAPs reported in other studies is likely due to the coexistence of preformed DAPs and DAPs resulting from OP pesticide exposures. Thus, before urinary DAP concentrations can be reliably used in exposure and risk assessment, the proportion of the concentration attributable to environmental DAP exposure, particularly through the diet, must be ascertained. In conclusion, urinary DAPs have many limitations when being used as biomarkers for OP pesticides in exposure and risk assessment, and caution should be exercised when interpreting DAPs results. This work was supported by the U.S. Environmental Protection Agency (EPA) through Science to Achieve Results (STAR) program (grant R829364). Its contents are solely the responsibility of the authors and do not necessarily represent the official view of the U.S. Environmental Protection Agency.

Urinary Concentrations of Dialkylphosphate Metabolites of Organophosphorus Pesticides: National Health and Nutrition Examination Survey 1999–2004

Organophosphorus (OP) insecticides were among the first pesticides that EPA reevaluated as part of the Food Quality Protection Act of 1996. Our goal was to assess exposure to OP insecticides in the U.S. general population over a six-year period. We analyzed 7,456 urine samples collected as part of three two-year cycles of the National Health and Nutrition Examination Survey (NHANES) from 1999–2004. We measured six dialkylphosphate metabolites of OP pesticides to assess OP pesticide exposure. In NHANES 2003–2004, dimethylthiophosphate was detected most frequently with median and 95th percentile concentrations of 2.03 and 35.3 μg/L, respectively. Adolescents were two to three times more likely to have diethylphosphate concentrations above the 95th percentile estimate of 15.5 μg/L than adults and senior adults. Conversely, for dimethyldithiophosphate, senior adults were 3.8 times and 1.8 times more likely to be above the 95th percentile than adults and adolescents, respectively, while adults were 2.1 times more likely to be above the 95th percentile than the adolescents. Our data indicate that the most vulnerable segments of our population—children and older adults—have higher exposures to OP pesticides than other population segments. However, according to DAP urinary metabolite data, exposures to OP pesticides have declined during the last six years at both the median and 95th percentile levels.

Outbreak of acute renal failure in Panama in 2006: a case-control study

OBJECTIVE In September 2006, a Panamanian physician reported an unusual number of patients with unexplained acute renal failure frequently accompanied by severe neurological dysfunction. Twelve (57%) of 21 patients had died of the illness. This paper describes the investigation into the cause of the illness and the source of the outbreak. METHODS Case-control and laboratory investigations were implemented. Case patients (with acute renal failure of unknown etiology and serum creatinine > 2 mg/dl) were individually matched to hospitalized controls for age (+/- 5 years), sex and admission date (< 2 days before the case patient). Questionnaire and biological data were collected. The main outcome measure was the odds of ingesting prescription cough syrup in cases and controls. FINDINGS Forty-two case patients and 140 control patients participated. The median age of cases was 68 years (range: 25-91 years); 64% were male. After controlling for pre-existing hypertension and renal disease and the use of angiotensin-converting enzyme inhibitors, a significant association was found between ingestion of prescription cough syrup and illness onset (adjusted odds ratio: 31.0, 95% confidence interval: 6.93-138). Laboratory analyses confirmed the presence of diethylene glycol (DEG) in biological samples from case patients, 8% DEG contamination in cough syrup samples and 22% contamination in the glycerin used to prepare the cough syrup. CONCLUSION The source of the outbreak was DEG-contaminated cough syrup. This investigation led to the recall of approximately 60 000 bottles of contaminated cough syrup, widespread screening of potentially exposed consumers and treatment of over 100 affected patients.

Quantification of dialkylphosphate metabolites of organophosphorus insecticides in human urine using 96-well plate sample preparation and high-performance liquid chromatography–electrospray ionization-tandem mass spectrometry☆

Organophosphorus (OP) pesticides kill by disrupting a targeted pests brain and nervous systems. But if humans and other animals are sufficiently exposed, OP pesticides can have the same effect on them. We developed a fast and accurate high-performance liquid chromatography-tandem mass spectrometry method for the quantitative measurement of the following six common dialkylphosphate (DAP) metabolites of organophosphorus insecticides: dimethylphosphate (DMP), dimethylthiophosphate (DMTP), dimethyldithiophosphate (DMDTP), diethylphosphate, (DEP), diethylthiophosphate (DETP), and diethyldithiophosphate (DEDTP). The general sample preparation included 96-well plate solid phase extraction using weak anion exchange cartridges. The analytical separation was performed by high-performance liquid chromatography with a HILIC column. Detection involved a triple quadrupole mass spectrometer with an ESI probe in negative ion mode using multiple reaction monitoring. Repeated analyses of urine samples spiked at 150, 90 and 32 ng/mL with the analytes gave relative standard deviations of less than 22%. The extraction efficiency ranged from 40% to 98%. The limits of detection were in the range of 0.04-1.5 ng/mL. The throughput is 1152 samples per week, effectively quadrupling our previous throughput. The method is safe, quick, and sensitive enough to be used in environmental and emergency biological monitoring of occupational and nonoccupational exposure to organophosphates.

Measurement of pyrethroid, organophosphorus, and carbamate insecticides in human plasma using isotope dilution gas chromatography-high resolution mass spectrometry.

We have developed a gas chromatography-high resolution mass spectrometry method for measuring pyrethroid, organophosphorus, carbamate and fipronil pesticides and the synergist piperonyl butoxide in human plasma. Plasma samples were extracted using solid phase extraction and were then concentrated for injection and analysis using isotope dilution gas chromatography-high resolution mass spectrometry. The limits of detection ranged from 10 to 158 pg/mL with relative recoveries at concentrations near the LODs (e.g., 25 or 250 pg/mL) ranging from 87% to 156% (9 of the 16 compounds were within ±15% of 100%). The extraction recoveries ranged from 20% to 98% and the overall method relative standard deviations were typically less than 20% with some exceptions. Analytical characteristics were determined at 25, 250, and 1000 pg/mL.

Organophosphorous pesticide breakdown products in house dust and children's urine

Human exposure to preformed dialkylphosphates (DAPs) in food or the environment may affect the reliability of DAP urinary metabolites as biomarkers of organophosphate (OP) pesticide exposure. We conducted a study to investigate the presence of DAPs in indoor residential environments and their association with childrens urinary DAP levels. We collected dust samples from homes in farmworker and urban communities (40 homes total, n=79 samples) and up to two urine samples from resident children ages 3–6 years. We measured six DAPs in all samples and eight DAP-devolving OP pesticides in a subset of dust samples (n=54). DAPs were detected in dust with diethylphosphate (DEP) being the most frequently detected (≥60%); detection frequencies for other DAPs were ≤50%. DEP dust concentrations did not significantly differ between communities, nor were concentrations significantly correlated with concentrations of chlorpyrifos and diazinon, the most frequently detected diethyl-OP pesticides (Spearman ρ=−0.41 to 0.38, P>0.05). Detection of DEP, chlorpyrifos, or diazinon, was not associated with DEP and/or DEP+diethylthiophosphate detection in urine (Kappa coefficients=−0.33 to 0.16). Finally, estimated non-dietary ingestion intake from DEP in dust was found to be ≤5% of the dose calculated from DEP levels in urine, suggesting that ingestion of dust is not a significant source of DAPs in urine if they are excreted unchanged.

COMMUNITY AERIAL MOSQUITO CONTROL AND NALED EXPOSURE

ABSTRACT In October 2004, the Florida Department of Health (FLDOH) and the Centers for Disease Control and Prevention (CDC) assessed human exposure to ultra-low volume (ULV) aerial application of naled. Teams administered activity questionnaires regarding pesticide exposure and obtained baseline urine samples to quantify prespray naled metabolite levels. Following the spray event, participants were asked to collect postspray urine specimens within 12 h of the spray event and at 8-h intervals for up to 40 h. Upon completion, a postspray activity questionnaire was administered to study participants. Two hundred five (87%) participants completed the study. The urine analysis showed that although 67% of prespray urine samples had detectable levels of a naled metabolite, the majority of postspray samples were below the limit of detection (40 h) following exposure, the number of samples with detectable levels exceeded 50%. There was a significant decrease in naled metabolites from prespray to postspray ( = .02), perhaps associated with a significant reduction (≤0.05) in some participants that may have resulted in pesticide exposure by means other than the mosquito control operations. These data suggest that aerial spraying of naled does not result in increased levels of naled in humans, provided the naled is used according to label instructions.

A mass spectrometry-based method to measure dialkylphosphate degradation products of organophosphorous insecticides in dust and orange juice

Dialkylphosphates (DAPs) are urinary metabolites and breakdown products of organophosphorous (OP) pesticides. Urinary DAPs are widely used to assess exposure to OP pesticides in epidemiologic studies. Recent evidence suggests that preformed DAPs are present in food and that they may also be present in other parts of the environment. Thus, DAP concentrations observed in urine may reflect a persons exposure to both parent OP pesticides and preformed DAPs in food and other environmental media. The presence of preformed DAPs in multiple media may indicate that previous studies have overestimated exposure to OP pesticides and that the use of urinary DAPs as biomarkers of exposure for OP pesticides may not accurately characterize exposure in non-acute settings. To establish the presence of DAPs in environmental and food media, we developed analytical methods to measure six DAPs in dust and orange juice. The limits of detection (LOD) for the dimethyl phosphates (dimethylphosphate (DMP), dimethylthiophosphate, and dimethyldithiophosphate) ranged from 2.8-9.9 ng g(-1) and 0.2-0.4 ng mL(-1) in dust and juice, respectively. The LODs for the diethyl phosphates (diethylphosphate (DEP), diethylthiophosphate, diethyldithiophosphate) ranged from 5.2-10.4 ng g(-1) and 0.5-3.0 ng mL(-1) in dust and juice, respectively. The extraction efficiencies for the analytes ranged from 23% to 91% and from 41% to 85% in dust and orange juice, respectively. DMP was detected in about half of the dust samples whereas DEP was detected in 80% of the dust samples tested. Other DAPs were less frequently detected in dust. Less than 3% of intact pesticide present in the matrices was converted to their respective DAPs during the pre-analytic and analytic process. Evaluation of the conversion of intact pesticides in the samples to DAPs will help us to better understand the contribution of preformed DAPs to urinary DAP concentrations.