Use of pharmacokinetic modeling to design studies for pathway-specific exposure model evaluation

Determination of organochlorine pesticides in human umbilical cord and association with orofacial clefts in offspring

Studies based on questionnaires suggested that maternal exposure to pesticides increases the risk for orofacial clefts (OFCs). However, whether organochlorine pesticides (OCPs) exposure in vivo affects the occurrence of OFCs remains unclear. The aims of this study are to investigate the association of OCP exposure with the risk of OFCs by examining the concentrations of OCPs in human umbilical cords, and investigate the potential dietary sources of OCPs in umbilical cord tissues. A case-control study consisting of 89 OFC cases and 129 nonmalformed controls with available tissues of umbilical cord was conducted. Concentrations of twenty specific OCPs were determined in the umbilical cord by gas chromatograph-mass spectrometry, and seven OCPs with detection rate larger than 50% were included in analyses. The individual effect and joint effect of multiple OCPs in umbilical cords on the risk for OFCs were investigated using multivariate logistic models and Bayesian Kernel Machine Regression (BKMR). No difference was found in the median levels of ΣOCPs between cases (1.04 ng/g) and controls (1.03 ng/g). No significant associations were observed between levels of OCPs in umbilical cords and risk for OFCs in either multivariate logistic models or BKMR models. Maternal consumptions of beans or bean products were positively correlated with levels of β-hexachlorocyclohexane, heptachlor epoxide, p,p'-DDE, and ∑OCPs in umbilical cord, respectively. In conclusion, we didn't find the association between in utero exposure to OCPs and the risk for OFCs. Maternal consumptions of beans or bean products may be a source of OCPs exposure.

Dietary intakes of pesticides based on community duplicate diet samples

The calculation of dietary intake of selected pesticides was accomplished using food samples collected from individual representatives of a defined demographic community using a community duplicate diet approach. A community of nine participants was identified in Apopka, FL from which intake assessments of organophosphate (OP) and pyrethroid pesticides were made. From these nine participants, sixty-seven individual samples were collected and subsequently analyzed by gas chromatography/mass spectrometry. Measured concentrations were used to estimate dietary intakes for individuals and for the community. Individual intakes of total OP and pyrethroid pesticides ranged from 6.7 to 996 ng and 1.2 to 16,000 ng, respectively. The community intake was 256 ng for OPs and 3430 ng for pyrethroid pesticides. The most commonly detected pesticide was permethrin, but the highest overall intake was of bifenthrin followed by esfenvalerate. These data indicate that the community in Apopka, FL, as represented by the nine individuals, was potentially exposed to both OP and pyrethroid pesticides at levels consistent with a dietary model and other field studies in which standard duplicate diet samples were collected. Higher levels of pyrethroid pesticides were measured than OPs, which is consistent with decreased usage of OPs. The diversity of pyrethroid pesticides detected in food samples was greater than expected. Continually changing pesticide usage patterns need to be considered when determining analytes of interest for large scale epidemiology studies. The Community Duplicate Diet Methodology is a tool for researchers to meet emerging exposure measurement needs that will lead to more accurate assessments of intake which may enhance decisions for chemical regulation. Successfully determining the intake of pesticides through the dietary route will allow for accurate assessments of pesticide exposures to a community of individuals, thereby significantly enhancing the research benefit realized from epidemiological exposure studies.

Review of pesticide urinary biomarker measurements from selected US EPA children's observational exposure studies

Children are exposed to a wide variety of pesticides originating from both outdoor and indoor sources. Several studies were conducted or funded by the EPA over the past decade to investigate children’s exposure to organophosphate and pyrethroid pesticides and the factors that impact their exposures. Urinary metabolite concentration measurements from these studies are consolidated here to identify trends, spatial and temporal patterns, and areas where further research is required. Namely, concentrations of the metabolites of chlorpyrifos (3,5,6-trichloro-2-pyridinol or TCPy), diazinon (2-isopropyl-6-methyl-4-pyrimidinol or IMP), and permethrin (3-phenoxybenzoic acid or 3-PBA) are presented. Information on the kinetic parameters describing absorption and elimination in humans is also presented to aid in interpretation. Metabolite concentrations varied more dramatically across studies for 3-PBA and IMP than for TCPy, with TCPy concentrations about an order of magnitude higher than the 3-PBA concentrations. Temporal variability was high for all metabolites with urinary 3-PBA concentrations slightly more consistent over time than the TCPy concentrations. Urinary biomarker levels provided only limited evidence of applications. The observed relationships between urinary metabolite levels and estimates of pesticide intake may be affected by differences in the contribution of each exposure route to total intake, which may vary with exposure intensity and across individuals.

Pesticides on household surfaces may influence dietary intake of children

The physical and chemical environment influences children's exposures to pesticides in and around the home. Children's activities, which increase their potential for exposure especially during eating, have been captured in the Children's Dietary Intake Model (CDIM). In addition to the chemical exposure associated with the food itself, this model incorporates excess dietary exposures due to handling of food during consumption. To stochastically evaluate CDIM, distributions of measured, and in some cases estimated, model factors were determined from measurements of permethrin, chlorpyrifos, and diazinon derived from assembled databases and laboratory experiments. Using the distributions of these factors, Monte Carlo simulations were performed to obtain distributions of total dietary intake of pesticides. To target the sources of pesticide contamination that were influencing total dietary intake, each factor was evaluated. We found pesticide surface concentration to be highly influential. By excluding surface concentration, we were also able to determine the influence of the other factors based on the F-statistic. Transfer efficiencies, followed by pesticide residue in consumed foods and amount of food consumed, were the next most influential factors within the model. With these distributions for model inputs, CDIM has the potential to more accurately predict total dietary intake of a contaminant by a child.

Influences on transfer of selected synthetic pyrethroids from treated Formica to foods

Children's unstructured eating habits and activities may lead to excess dietary exposures not traditionally measured by the US Environmental Protection Agency. Influence of these activities on transfer of pesticides from treated Formica to foods was studied. The objective was to perform simulation experiments using four foods (bread, apple slices, bologna, and sugar cookies) exposed to treated Formica after varied time intervals between surface contamination and contact (1, 6, and 24 h) and frequency of contact with and without recontamination. Pesticides investigated included permethrin, bifenthrin, cyfluthrin, cypermethrin, and deltamethrin. Data will be used as input parameters for transfer efficiencies (TEs) within the Children's Dietary Intake Model (CDIM), which predicts total dietary exposure of a child. Pesticide transfer from surfaces to bologna and apples was more efficient than to bread and cookies. For the bread and cookies, all pyrethroids had a TE that ranged from below detectible levels to ≤ 4%. A combined average of 32-64% and 19-43% was transferred to bologna and apples, respectively, for the three contact times for all pyrethroids. The TEs of the varied time intervals indicated that increased time between contamination and contact showed little difference for bologna, bread, and cookies, but a significant difference for apples. As long as pesticide levels are measureable on surfaces in children's eating environment, it can be concluded that transfer of pesticides to foods will take place. Foods' characteristics had an important function in the transfer of pesticides when multiple contacts occurred. Regardless of recontamination, pesticides were efficiently transferred from the treated surface to bologna. The bologna did not reach a saturation point during the contacts. Pesticides were also efficiently transferred to apples, but reached a maximum TE during the second contact. The distribution of activity factors within CDIM needs to reflect the differences in the characteristics of the foods.

Development of an analytical scheme for the determination of pyrethroid pesticides in composite diet samples

Analysis of an individual's total daily food intake may be used to determine aggregate dietary ingestion of given compounds. However, the resulting composite sample represents a complex mixture, and measurement of such can often prove to be difficult. In this work, an analytical scheme was developed for the determination of 12 select pyrethroid pesticides in dietary samples. In the first phase of the study, several cleanup steps were investigated for their effectiveness in removing interferences in samples with a range of fat content (1-10%). Food samples were homogenized in the laboratory, and preparatory techniques were evaluated through recoveries from fortified samples. The selected final procedure consisted of a lyophilization step prior to sample extraction. A sequential 2-fold cleanup procedure of the extract included diatomaceous earth for removal of lipid components followed with a combination of deactivated alumina and C(18) for the simultaneous removal of polar and nonpolar interferences. Recoveries from fortified composite diet samples (10 microg kg(-1)) ranged from 50.2 to 147%. In the second phase of this work, three instrumental techniques [gas chromatography-microelectron capture detection (GC-microECD), GC-quadrupole mass spectrometry (GC-quadrupole-MS), and GC-ion trap-MS/MS] were compared for greatest sensitivity. GC-quadrupole-MS operated in selective ion monitoring (SIM) mode proved to be most sensitive, yielding method detection limits of approximately 1 microg kg(-1). The developed extraction/instrumental scheme was applied to samples collected in an exposure measurement field study. The samples were fortified and analyte recoveries were acceptable (75.9-125%); however, compounds coextracted from the food matrix prevented quantitation of four of the pyrethroid analytes in two of the samples considered.

Surface-to-food pesticide transfer as a function of moisture and fat content

Transfer of pesticides from household surfaces to foods may result in excess dietary exposure in children (i.e., beyond that inherent in foods due to agricultural application). In this study, transfer was evaluated as a function of the moisture and fat content of various foods. Surfaces chosen for investigation were those commonly found in homes and included Formica, ceramic tile, plastic, carpet, and upholstery fabric. Each surface type was sprayed with an aqueous emulsion of organophosphates, fipronil, and synthetic pyrethroids. In the first phase of the study, multiple foods (apples, watermelon, wheat crackers, graham crackers, white bread, flour tortillas, bologna, fat-free bologna, sugar cookies, ham, Fruit Roll-ups, pancakes, and processed American cheese) were categorized with respect to moisture and fat content. All were evaluated for potential removal of applied pesticides from a Formica surface. In the second phase of the study, representative foods from each classification were investigated for their potential for pesticide transfer with an additional four surfaces: ceramic tile, plastic, upholstery, and carpet. Moisture content, not fat, was found to be a determining factor in most transfers. For nearly all surfaces, more efficient transfer occurred with increased hardness (Formica and ceramic tile). Comparatively, the polymer composition of the plastic delivered overall lower transfer efficiencies, presumably due to an attraction between it and the organic pesticides of interest.

In silico prediction of clinical efficacy

Drug development is a high risk and costly process, and the ability to predict clinical efficacy in silico (in a computer) can save the pharmaceutical industry time and resources. Additionally, such an approach will result in more targeted, personalized therapies. To date, a number of in silico strategies have been developed to provide better information about the human response to novel therapies earlier in the drug development process. Some of the most prominent include physiological modeling of disease and disease processes, analytical tools for population pharmacodynamics, tools for the analysis of genomic expression data, Monte Carlo simulation technologies, and predictive biosimulation. These strategies are likely to contribute significantly to reducing the failure rate of drugs entering clinical trials.