Biomonitoring and whole body cotton dosimetry to estimate potential human dermal exposure to semivolatile chemicals

Exposure Routes and Health Risks Associated with Pesticide Application

Pesticides play an important role in agricultural development. However, pesticide application can result in both acute and chronic human toxicities, and the adverse effects of pesticides on the environment and human health remain a serious problem. There is therefore a need to discuss the application methods for pesticides, the routes of pesticide exposure, and the health risks posed by pesticide application. The health problems related to pesticide application and exposure in developing countries are of particular concern. The purpose of this paper is to provide scientific information for policymakers in order to allow the development of proper pesticide application technics and methods to minimize pesticide exposure and the adverse health effects on both applicators and communities. Studies indicate that there are four main pesticide application methods, including hydraulic spraying, backpack spraying, basal trunk spraying, and aerial spraying. Pesticide application methods are mainly selected by considering the habits of target pests, the characteristics of target sites, and the properties of pesticides. Humans are directly exposed to pesticides in occupational, agricultural, and household activities and are indirectly exposed to pesticides via environmental media, including air, water, soil, and food. Human exposure to pesticides occurs mainly through dermal, oral, and respiratory routes. People who are directly and/or indirectly exposed to pesticides may contract acute toxicity effects and chronic diseases. Although no segment of the general population is completely protected against exposure to pesticides and their potentially serious health effects, a disproportionate burden is shouldered by people in developing countries. Both deterministic and probabilistic human health risk assessments have their advantages and disadvantages and both types of methods should be comprehensively implemented in research on exposure and human health risk assessment. Equipment for appropriate pesticide application is important for application efficiency to minimize the loss of spray solution as well as reduce pesticide residuals in the environment and adverse human health effects due to over-spraying and residues. Policymakers should implement various useful measures, such as integrated pest management (IPM) laws that prohibit the use of pesticides with high risks and the development of a national implementation plan (NIP) to reduce the adverse effects of pesticides on the environment and on human health.

Susceptibility to organophosphates pesticides and the development of infectious-contagious respiratory diseases

In this paper we develop an SIRS compartmental model to investigate the dynamic interplay between pesticide intoxication and the spread of infectious-contagious respiratory diseases. We are particularly interested in investigating three levels of genetic susceptibility to pesticide intoxication. The genotypic distribution of susceptibility to pesticide intoxication, is proposed and parameterized according to ethnic variation using real population data from published studies, and we assume that pesticide intoxication increases susceptibility to infection with a respiratory pathogen. We use mathematical models to illustrate the impact of this distribution on the spread of hypothetical respiratory disease in a population exposed to the organophosphate pesticide. In this context, we show how an initial basic reproductive number below the epidemic threshold of 1.0 could be enhanced to support epidemic outbreaks in agricultural populations that employ chlorpyrifos pesticides. We further illustrate our modeling framework to study the effect of ethnic group variation in Singapore (Malay, Indian and Chinese) using genetic distribution data from published studies.

Malathion dermal permeability in relation to dermal load: Assessment by physiologically based pharmacokinetic modeling of in vivo human data

Estimates of dermal permeability (K_p), obtained by fitting an updated human PBPK model for malathion to previously reported data on excreted urinary metabolites after 29 volunteers were dermally exposed to measured values of [¹⁴C]malathion dermal load (L), were used to examine the empirical relationship between K_p and L. The PBPK model was adapted from previously reported human biokinetic and PBPK models for malathion, fit to previously reported urinary excretion data after oral [¹⁴C]malathion intake by volunteers, and then augmented to incorporate a standard K_p approach to modeling dermal-uptake kinetics. Good to excellent PBPK-model fits were obtained to all of 29 sets of cumulative urinary metabolite-excretion data (ave. [±1 SD] R² = 0.953 [±0.064]). Contrary to the assumption that K_p and L are independent typically applied for dermally administered liquids or solutions, the 29 PBPK-based estimates of K_p obtained for malathion exhibit a strong positive association with the 2/3rds power of L (log-log Pearson correlation = 0.925, p = ∼0). Possible explanations of this observation involving physico-chemical characteristics and/or in vivo cutaneous effects of malathion are discussed. The PBPK model presented, and our observation that K_p estimates obtained by fitting this model to human experimental urinary-excretion data correlate well with L^2/3, allow more realistic assessments of absorbed and metabolized dose during or after a variety of scenarios involving actual or potential dermal or multi-route malathion exposures, including for pesticide workers or farmers who apply malathion to crops.

Postapplication Fipronil Exposure Following Use on Pets

Fipronil is a pyrazole acaricide and insecticide that may be used for insect, tick, lice, and mite control on pets. Residents' short-term and long-term postapplication exposures to fipronil, including secondary environmental exposures, were estimated using data from chemical-specific studies. Estimations of acute (24-h) absorbed doses for residents were based on U.S. Environmental Protection Agency (U.S. EPA) 2012 standard operating procedures (SOPs) for postapplication exposure. Chronic exposures were not estimated for residential use, as continuous, long-term application activities were unlikely to occur. Estimated acute postapplication absorbed doses were as high as 0.56 μg/kg-d for toddlers (1-2 yr) in households with treated pets based on current U.S. EPA SOPs. Acute toddler exposures estimated here were fivefold larger in comparison to adults. Secondary exposure from the household environment in which a treated pet lives that is not from contacting the pet, but from contacting the house interior to which pet residues were transferred, was estimated based on monitoring socks worn by pet owners. These secondary exposures were more than an order of magnitude lower than those estimated from contacting the pet and thus may be considered negligible.

Proteção da saúde de trabalhadores rurais: a necessidade de padronização das metodologias de quantificação da exposição dérmica a agrotóxicos

A quantificação da exposição dérmica a agrotóxicos, utilizada no processo de avaliação do risco à saúde de trabalhadores rurais, pode ser realizada usando-se diferentes metodologias, como patches ou corpo total. A existência de diversos métodos pode ser considerada uma limitação relacionada ao processo, já que podem não produzir resultados similares devido às diferenciações nos princípios envolvidos na coleta das amostras. Dessa maneira, realizou-se uma revisão crítica das principais metodologias utilizadas para a quantificação da exposição dérmica, com o objetivo de ressaltar a importância da discussão sobre o assunto e de evidenciar a necessidade de ações que contribuam para o estabelecimento de uma metodologia única para a quantificação da exposição dérmica de trabalhadores rurais. Entende-se que a harmonização das metodologias contribuirá para o alcance de condições mais seguras e saudáveis de trabalho, principalmente por possibilitar a obtenção de resultados mais confiáveis e, portanto, estabelecer, garantir e aprimorar o processo de prevenção de agravos à saúde do trabalhador.

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.

Concurrent 2,4-D and triclopyr biomonitoring of backpack applicators, mixer/loader and field supervisor in forestry

Two herbicides, 2,4-D and triclopyr esters (application ratio 1.6:1 acid equivalents) were applied as a tank mix by a crew of 8 backpack sprayer applicators, a mixer/loader, and a field supervisor. The crew was employed in a conifer release program in northern California during the summer of 2002. Biomonitoring (urine, 24 h) utilized 2,4-D and triclopyr (a.e.) as rapidly excreted exposure biomarkers. The absorbed dosages of 2,4-D and triclopyr were calculated based upon cotton whole body suits and biomonitoring. Dosages based upon accumulation of the herbicides on body suits averaged 42.6 μg (a.e.) 2,4-D/kg-d and 8.0 μg (a.e.) triclopyr/kg-d. Six consecutive days of concurrent urine collections showed that backpack applicators excreted an average of 11.0 μg (a.e.) 2,4-D/kg-d and 18.9 μg (a.e.) triclopyr/kg-d. Estimates based upon curve fitting were 17.1 and 29.3 μg (a.e.)/kg-d, respectively. Results suggest that passive dosimetry for 2,4-D consistently overestimated the dosage measured using biomonitoring by a factor of 2-3 fold, while for triclopyr, passive dosimetry underestimated the absorbed dose based on biomonitoring by a factor of 2-4 fold.

Potential exposure of children and adults to cypermethrin following use of indoor insecticide foggers

The magnitude and distribution of cypermethrin from total release, over-the-counter foggers was studied in a test room and in residences to facilitate evaluation of regulatory exposure algorithms and new human exposure assessments based upon urine biomonitoring. Surface residue (SR) was evenly distributed in a small test room (3.6 mciro g cypermethrin/cm(2)) where thorough mixing of the aerosol occurred. In a residence SR was significantly affected by room size and distance from the fogger. Air levels in the residence were as high as 30 mciro g cypermethrin/cm(3) after 4.5 h. The availability of surface residues was measured with an automated surface cotton cloth wipe and ethyl acetate extraction. Only 5% of the SR was available from nylon carpet. Tile, wood and linoleum resulted in 30, 10, and 10% of SR being available, respectively. These data are used to estimate cypermethrin exposure of children and adults for comparison with existing regulatory reference dosages and exposure assessments based upon biomonitoring.

Developing probability distributions for transfer efficiencies for dermal exposure

Many dermal exposure models use stochastic techniques to sample parameter distributions derived from experimental data to more accurately represent variability and uncertainty. Transfer efficiencies represent the fraction of a surface contaminant transferred from the surface to the skin during a contact event. Although an important parameter for assessing dermal exposure, examination of the literature confirms that no single study is large enough to provide a basis for a transfer efficiency distribution for use in stochastic dermal exposure models. It is therefore necessary to combine data sets from multiple studies to achieve the largest data set possible for distribution analysis. A literature review was conducted to identify publications reporting transfer efficiencies. Data sets were compared using the Kruskal-Wallis test to determine whether they arise from the same distribution. Combined data were evaluated for several theoretical distributions using the Kolmogorov-Smirnov and chi(2)-goodness-of-fit tests. Our literature review identified 35 studies comprising 25 different sampling methods, 25 chemicals, and 10 surface types. Distributions were developed for three different chemicals (chlorpyrifos, pyrethrin I, and piperonyl butoxide) on three different surface types (carpet, vinyl, and foil). Only the lognormal distribution was consistently accepted for each chemical and surface combination. Fitted distributions were significantly different (Kruskal-Wallis test; P<0.001) across chemicals and surface types. In future studies, increased effort should be placed on developing large studies, which more accurately represent transfer to human skin from surfaces, and on developing a normative transfer efficiency measure so that data from different methodologies can be compared.

Golfer exposure to chlorpyrifos and carbaryl following application to turfgrass

Exposure of golfers to pesticides following their application to turfgrass is of concern to regulators, turfgrass professionals, and consumers. Multipathway exposures were evaluated for golfers on turfgrass treated with chlorpyrifos and carbaryl. Air concentrations and transferable foliar residues (TFRs) were measured to assess potential respiratory and dermal exposures, respectively. At the same time, exposure to individuals simulating the play of golf was determined by dosimetry and urinary biomonitoring. Individual golfer exposure was determined in 76 rounds of golf following eight applications of chlorpyrifos and two applications of carbaryl. Estimated exposures to golfers following full course and full rate applications of chlorpyrifos and carbaryl were 19-68 times below current U.S. EPA acute reference dose (Rfd) values, indicating safe exposures under U.S. EPA hazard quotient criteria. Dermal exposure was determined to be the dominant exposure pathway to golfers, accounting for approximately 60% of the chlorpyrifos absorbed dose and 100% of the carbaryl absorbed dose. This study also provides a set of transfer factors (TFs) that may be used to determine dermal exposure of golfers to pesticides using transferable residue data.

Comparative evaluation of absorbed dose estimates derived from passive dosimetry measurements to those derived from biological monitoring: validation of exposure monitoring methodologies

Passive dosimetry (PD) methods for measuring and estimating exposure to agricultural workers (i.e., persons handling agricultural chemicals and working in treated crops) have been in use since the 1950s. A large number of studies were conducted in the 1950s through 1970s to characterize exposure. Since the 1980s quantitative dermal PD methods are used in conjunction with inhalation PD methods to measure whole-body exposure. These exposure or absorbed dose estimates are then compared to "no effect" exposure levels for hazards identified in toxicology studies, and have become the standard for risk assessment for regulatory agencies. The PD methods used have never been validated. Validation in the context of human exposure monitoring methods means that a method has been shown to measure accurately a delivered dose in humans. The most practical alternative to isolating parts of the body for validating recovery methods is to utilize field exposure studies in which concurrent or consecutive measurements of exposure and absorbed dose have been made with PD and biomonitoring in the same cohorts of individuals. This ensures that a direct comparison can be made between the two estimates of absorbed dose, one derived from PD and the other from biomonitoring. There are several studies available (published and proprietary) employing both of these approaches. Reports involving 14 concurrent or consecutive PD-biomonitoring studies were quantitatively evaluated with 18 different methods of application or reentry scenarios for eight different active ingredients for which measured human kinetics and dermal absorption data existed. This evaluation demonstrated that the total absorbed dose estimated using PD for important handler and reentry scenarios is generally similar to the measurements for those same scenarios made using human urinary biomonitoring methods. The statistical analysis of individual worker PD:biomonitoring ratios showed them to be significantly correlated in these studies. The PD techniques currently employed yield a reproducible, standard methodology that is valid and reliably quantifies exposure.

Sampling household surfaces for pesticide residues: comparison between a press sampler and solvent-moistened wipes

A modified Press Sampler was evaluated to determine the efficiency of pesticide transfer from household surfaces to collection disks as compared to wiping with a solvent-moistened gauze pad. Organophosphate (OP), pyrazole, and pyrethroid pesticides were applied to three hard flooring materials and carpet at two loading rates. Surfaces were dried and press sampled using C(18), 100% cotton or polyurethane foam (PUF) for either 2 or 10 min or wiped with isopropanol-moistened gauze pads. Transfer efficiencies (TE, %) were calculated as a fraction of surface loadings captured simultaneously on foil deposition coupons. The highest mean TEs (17-55%) for the Press Sampler were observed for OPs from hard surfaces to C(18), considering both contact times. Cotton and PUF transferred 6-27% and 5-30% of OPs, respectively. Corresponding mean TEs for pyrazole and pyrethroid pesticides were only 3% (C(18)), 2-3% (cotton) and 1-2% (PUF). Wipes of hard surfaces removed 84-97% of all pesticides while wipes of carpet removed 31-39%, much higher than transferred to any Press Sampler materials. The mean TEs suggested that the extent of pesticide residue transfer was affected by surface type, pesticide class, and sampling procedure. Wiping was more efficient than press sampling for pesticide surface residue measurements, particularly for loading rates typical of residences.

Risk assessment of human exposure to cypermethrin during treatment of mandarin fields

The potential dermal and respiratory exposure assessment and risk assessment for applicator were performed with cypermethrin EC. The pesticide was applied on a mandarin field using a power sprayer. Gloves were used for the hand exposure assessment, mask for face, and dermal patches for the other parts of the body. Personal air monitor equipped with a XAD-2 resin was used for the respiratory exposure assessment. During the application of cypermethrin in the field, the rate of potential dermal exposure ranged from 28.1 to 58.8 mg/h. The major exposure parts were upper-arms (22.1-24.6%) and legs (thigh and shin, 28.3-29.2%) for females and thigh (21.0-46.9%) and hand (14.9-19.3%) for males. Females were exposed more than males. No exposure was detected from the respiratory monitoring. For risk assessment, the potential dermal exposure (PDE), the absorbable quantity of exposure (AQE), and the margin of safety (MOS) were calculated. Among those four risk assessments, MOS was < 1 in only trial I, which indicated any possibility of risk. However, in the others, the possibility of risk was little. Moreover, the safe work time ranged from 3.61 h to 9.69 h.

Perspiration increased human pesticide absorption following surface contact during an indoor scripted activity program

Homeowners and professional applicators frequently use chemicals to control insect pests in urban environments. The identification and evaluation of determinants of human exposure are critical to conduct reliable and responsible human exposure assessments following indoor residential chemical applications. The effect of sweat on absorbed dose in humans was evaluated with human volunteers who participated in a structured activity program (SAP). Participants (n=20) performed a warm-up exercise to induce light sweating prior to an SAP on chlorpyrifos(cp)-treated nylon carpet. Absorbed daily dosages (ADDs) were calculated using urinary biomonitoring of trichloropyridinol. In two separate exposures, participation in the warm-up exercise prior to the exposure SAP resulted in an increased ADD of CP equivalents by approximately 50%. Measured ADDs averaged 2.8 (SAP 1) and 2.0 (SAP 2) microg CP equivalents/kg/day in volunteers who participated in the warm-up exercise. In participants who rested prior to the exposures, ADDs were significantly lower at 1.9 (SAP 1) and 1.3 (SAP 2) microg CP equivalents/kg/day. Perspiration may also be a determinant of exposure in active children and field workers. Measured ADDs were less than estimates of ADD made from environmental measurements including CP deposition, the California roller, and clothing dosimeters worn by participants.

Human exposure to indoor residential cyfluthrin residues during a structured activity program

Estimations of absorbed daily dosage (ADD) of chemicals following contact with treated surfaces may be required for risk assessment and risk management. Measurements of ADD based upon biomonitoring are a more reliable data than estimates of ADD from environmental measurements since they require fewer default assumptions. Study participants performed a structured activity program (SAP) 24-h after an application of Tempo((R)) 20 WP (cyfluthrin; 3-(2,2-dichloroethenyl)-2,2-dimethyl-cyclopropanecarboxylic acid cyano(4-fluoro-3-phenoxy-phenyl)-methyl ester) on a medium pile, plush nylon carpet. Measurements of total cyfluthrin residue and transferable cyfluthrin residue (cotton cloth and CDFA roller; personal sock and short dosimetry) were made at 3, 7, 12, 23, 47.5, and 407.5 h. Total cyfluthrin residue extracted from (Soxhlet extraction) carpet was 11.1+/-2.7 microg/cm(2) 1 h prior to the SAP. Transferable cyfluthrin residue obtained through analysis of cotton cloths rolled with a weighted 30-pound cylinder was 0.11 microg/cm(2). Cyfluthrin residues from socks and shorts were 0.74+/-0.23 and 0.15+/-0.03 microg/cm(2), respectively. Urine was collected at 12-h intervals during a 72-h period following the SAP and was analyzed for the cyfluthrin biomarker, 4-fluoro-3-phenoxybenzoic acid (FPBA). The mean cyfluthrin equivalents excreted were 8.4+/-5.7 microg/person (yielding an absorbed dosage of 0.10 microg/kg; n=7). The elimination half-life was 16+/-5 h. All predicted ADDs based upon environmental measurements overestimated the ADDs measured by urinary excretion.

Transmissible spongiform encephalopathies: a family of etiologically complex diseases--a review

The upsurge of 'mad cow disease' with its human implications has raised the problem of the etiological mechanisms and the similarities or differences underlying the family of transmissible spongiform encephalopathies. Structural properties of prions are reviewed in connection with their natural distribution and functions, factors of transmissibility and mechanisms of pathogenicity. Polymorphism is examined in relation to disease phenotype variants. The role of oxidative factors is emphasized, while raising complexity about the role of copper ions. Further investigation directions are suggested.