Method for the determination of dialkyl phosphates in urine by strong anion exchange disk extraction and in-vial derivatization

A state-of-the-science review of analytical methods for urinary dialkylphosphate metabolites in the assessment of exposure to organophosphate pesticides: From 2000 to 2022

The general population and workers are exposed to organophosphate insecticides, one of the leading chemical classes of pesticides used in rural and urban areas. This paper aims to conduct an integrative review of the most used analytical methods for identifying and quantifying dialkylphosphate-which are metabolites of organophosphate insecticides-in the urine of exposed workers, discussing their advantages, limitations and applicability. Searches utilized the PubMed, the Scientific Electronic Library Online and the Brazilian Digital Library of Theses and Dissertations databases between 2000 and 2021. Twenty-five studies were selected. The extraction methods most used were liquid-liquid extraction (LLE) (36%) and solid-phase extraction (SPE) (36%), with the SPE being more economical in terms of time and amount of solvents needed, and presenting the best percentage of recovery of analytes, when compared with LLE. Nineteen studies (76%) used the gas chromatography method of separation, and among these, 12 records (63%) indicated mass spectrometry used as a detection technology (analyzer). Studies demonstrate that dialkylphosphates are sensitive and representative exposure biomarkers for environmental and occupational organophosphate exposure.

A revised method for determination of dialkylphosphate levels in human urine by solid-phase extraction and liquid chromatography with tandem mass spectrometry: application to human urine samples from Japanese children

OBJECTIVES

Biological monitoring of organophosphorus insecticide (OP) metabolites, specifically dialkylphosphates (DAP) in urine, plays a key role in low-level exposure assessment of OP in individuals. The aims of this study are to develop a simple and sensitive method for determining four urinary DAPs using high-performance liquid chromatography with tandem mass spectrometry (LC-MS/MS), and to assess the concentration range of urinary DAP in Japanese children.

METHODS

Deuterium-labeled DAPs were used as internal standards. Urinary dimethylphosphate (DMP) and diethylphosphate (DEP), which passed through the solid-phase extraction (SPE) column, and dimethylthiophosphate (DMTP) and diethylthiophosphate (DETP), which were extracted from a SPE column using 2.5 % NH3 water including 50 % acetonitrile, were prepared for separation analysis. The samples were then injected into LC-MS/MS. The optimized method was applied to spot urine samples from 3-year-old children (109 males and 116 females) living in Aichi Prefecture in Japan.

RESULTS

Results from the validation study demonstrated good within- and between-run precisions (<10.7 %) with low detection limits (0.4 for DMP and DMTP, 0.2 for DEP and 0.1 μg/L for DETP). The geometric mean values and detection rates of the urinary DAPs in Japanese children were 14.4 μg/L and 100 % for DMP, 5.3 μg/L and 98 % for DMTP, 5.5 μg/L and 99 % for DEP, and 0.6 μg/L and 80 % for DETP, respectively.

CONCLUSIONS

The present high-throughput method is simple and reliable, and can thereby further contribute to development of an exposure assessment of OP. The present study is the first to reveal the DAP concentrations in young Japanese children.

Distribution of dimethoate in the body after a fatal organophosphate intoxication

Many organophosphate pesticides (OPs) such as dimethoate are used to eradicate household pests, and those occurring in agriculture and forestry sectors. Combinations of two or more different insecticides have been manufactured to increase their effectiveness. A case of death is presented as suspected organophosphates intoxication. Autopsy was unremarkable except for grayish fluid in the stomach, with garlicky odor. A systematic toxicological analysis on post-mortem specimens revealed high concentrations of dimethoate in blood 38 microg/mL, urine 0.47 microg/mL, brain 2.2 microg/g, myocardial muscle 7.6 microg/g, liver 4.6 microg/g, lung 7.6 microg/g, skeletal muscle 21 microg/g, kidney 55 microg/g and gall bladder 31 microg/g. Blood alcohol was 2.85 g/L, cyclohexanone and cyclohexanol were also detected in the blood but not quantified. The cause of death was determined as organophosphate intoxication.

Improved analysis of dialkylphosphates in urine using strong anion exchange disk extraction and in-vial derivatization

Determination of dialkylphosphates (DAPs) in urine is useful for assessing human exposure to organophosphates (OPs). An improved method for the determination of four DAPs based on a strong anion exchange (SAX) disk extraction and in-vial derivatization was presented in this study. The matrix effect of urine components such as chloride ion and phosphate ion by using a SAX disk to extract DAPs in urine analysis was carefully evaluated. It was observed that the chloride ion mainly affected the extraction of diethylphosphate (DEP), dimethylthiophosphate (DMTP), and diethylthiophosphate (DETP) in urine. The addition of silver hydroxide could significantly improve the extraction efficiencies of these three DAPs, but it decreases the extraction efficiencies of dimethyldithiophosphate (DMDTP) and diethyldithiophosphate (DEDTP). The LOD of this method for DMTP, DETP, DMDTP, and DEDTP are 5, 5, 11, and 5 microg/L, respectively. A pretreatment strategy for the determination of DMTP, DMDTP, DETP, and DEDTP in urine was proposed which can provide reliable and prompt determination of routine urine analysis.

A survey of laboratory and statistical issues related to farmworker exposure studies

Developing internally valid, and perhaps generalizable, farmworker exposure studies is a complex process that involves many statistical and laboratory considerations. Statistics are an integral component of each study beginning with the design stage and continuing to the final data analysis and interpretation. Similarly, data quality plays a significant role in the overall value of the study. Data quality can be derived from several experimental parameters including statistical design of the study and quality of environmental and biological analytical measurements. We discuss statistical and analytic issues that should be addressed in every farmworker study. These issues include study design and sample size determination, analytical methods and quality control and assurance, treatment of missing data or data below the method's limits of detection, and post-hoc analyses of data from multiple studies. Key words: analytical methodology, biomarkers, laboratory, limit of detection, omics, quality control, sample size, statistics.

Simultaneous determination of urinary dialkylphosphate metabolites of organophosphorus pesticides using gas chromatography–mass spectrometry

In this study, we developed a safe and sensitive method for the simultaneous determination of urinary dialkylphosphates (DAPs), metabolites of organophosphorus insecticides (OPs), including dimethylphosphate (DMP), diethylphosphate (DEP), dimethylthiophosphate (DMTP), and diethylthiophosphate (DETP), using a pentafluorobenzylbromide (PFBBr) derivatization and gas chromatography-mass spectrometry (GC-MS). Several parameters were investigated: pH on evaporation, reaction temperature and time for the derivatization, the use of an antioxidant for preventing oxidation, and a clean-up step. The pH was set at 6, adjusted with K2CO3, and the reaction temperature and time of derivatization were 80 degrees C and 30 min, respectively. Sodium disulfite was chosen as an antioxidant. The clean-up step was performed with a Florisil/PSE mini-column to remove the unreacted PFBBr and sample matrix. This established procedure markedly shortened the sample preparation time to only about 3 h, and completely inhibited the unwanted oxidization of dialkylthiophosphates. The limits of determination (LOD) were approximately 0.3 microg/L for DMP, and 0.1 microg/L for DEP, DMTP, and DETP in 5 mL of human urine. Within-series and between-day imprecision for the present method using pooled urine spiked with DAPs was less than 20.6% in the calibration range of 1-300 microg/L, and the mean recovery was 56.7-60.5% for DMP, 78.5-82.7% for DEP, 88.3-103.9% for DMTP, and 84.2-92.4% for DETP. This method detected geometric mean values of the urinary DAPs in Japanese with and without occupational exposure to OPs, 16.6 or 27.4 for DMP, 1.0 or 0.7 for DEP, 1.3 or 2.3 for DMTP, and 1.0 or 1.1 microg/L for DETP, respectively. The present method, which does not require special equipment except for GC-MS, is quick, safe, and sensitive enough to be adopted in routine biological monitoring of non-occupational as well as occupational exposure to OPs.

Determination of chlorpyrifos metabolites in human urine by reversed-phase/weak anion exchange liquid chromatography–electrospray ionisation–tandem mass spectrometry

A liquid chromatography-electrospray ionisation-tandem mass spectrometry (LC-ESI-MS/MS) method for the quantification of major chlorpyrifos (CP) metabolites, i.e. diethyl thiophosphate (DETP), diethyl phosphate (DEP), and 3,5,6-trichloro-2-pyridinol (TCP), in human urine was developed. Simultaneous separation of the parent compound and its primary biotransformation products was achieved within 20 min in gradient elution mode employing a mixed-mode reversed-phase/weak anion exchange (RP/WAX) separation principle. The analytical method was developed for a toxicokinetic study of an acute poisoning incidence with a CP containing pesticide formulation. An initial mass spectrometric screening performed with unprocessed urine samples revealed that CP is not excreted unchanged by the kidney. Hence, the quantitative assay was validated for DETP (quantifier transition: m/z 169-->95, qualifier transition: m/z 169-->141), DEP (m/z 153-->79, 153-->125), and TCP (m/z 196-->35, 198-->35) taking dibutyl phosphate (DBP) (m/z 209-->79, 209-->153) as internal standard. Clean-up of urine samples prior to LC-ESI-MS/MS analysis was carried out by a liquid-liquid extraction step with a mixture of ethylacetate and acetonitrile (70:30; v/v). Linearity was observed between 0.25 and 75 mgL(-1), and the signal-to-noise ratio at 0.25 mgL(-1) was better than six for the individual analytes. Recoveries, precision, and accuracies were all adequate across the validated range of 1-75 mgL(-1) for the present toxicological case study.

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 degrees 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.