Absorption Of Pesticides Research Articles

Importance of Physicochemical Properties for the Design of New Pesticides

The physicochemical properties of candidate compounds play important roles in the design of new pesticides. Pesticides must be absorbed by pests, be transported to the target site, and then interact with proteins. Hydrophobicity is very important for these processes. Log P, where P is the partition coefficient in the 1-octanol/water system, is commonly used as a hydrophobic descriptor and correlates with membrane permeation and transport. It was recently reported that permeability by the parallel artificial membrane permeation assay (PAMPA) could be used to predict human oral absorption of passively transported compounds. PAMPA, which is a rapid high-throughput screening system, may be useful to predict pesticide absorption because PAMPA permeability can be calculated using log P and other parameters. Electronic and structural properties as well as hydrophobicity are important factors for protein-ligand interaction. To show the importance of physicochemical properties, the classic QSAR and CoMFA of neonicotinoids and prediction of bioavailability of pesticides in terms of membrane permeability in comparison with drugs are described.

Repeated pesticide exposure among North Carolina migrant and seasonal farmworkers.

Limited data document the multiple and repeated pesticide absorption experienced by farmworkers in an agricultural season or their risk factors. Data were collected from 196 farmworkers four times at monthly intervals in 2007. Urine samples were tested for 12 pesticide urinary metabolites. Questionnaire data provided measures of exposure risks. Farmworkers had at least one detection for many pesticide urinary metabolites; for example, 84.2% had at least one detection for acephate, 88.8% for 3,5,6-trichloro-2-pyridinol. Most farmworkers had multiple detections for specific metabolites; for example, 64.8% had two or more detections for acephate, 64.8% for 3,5,6-trichloro-2-pyridinol, 79.1% for 3-phenoxybenzoic acid, and 86.7% for 2,4-dichlorophenoxyacetic acid. Housing type had a consistent significant association with metabolite detections. Farmworkers are exposed to multiple pesticides across an agricultural season, and they experience repeated exposures to the same pesticides. Reducing farmworker pesticide exposure and delineating the health outcomes of this exposure require more detailed data. Am. J. Ind. Med. 53:802-813, 2010. (c) 2010 Wiley-Liss, Inc.

In vitro dermal absorption of pyrethroid pesticides in human and rat skin

Dermal exposure to pyrethroid pesticides can occur during manufacture and application. This study examined the in vitro dermal absorption of pyrethroids using rat and human skin. Dermatomed skin from adult male Long Evans rats or human cadavers was mounted in flow-through diffusion cells, and radiolabeled bifenthrin, deltamethrin or cis-permethrin was applied in acetone to the skin. Fractions of receptor fluid were collected every 4 h. At 24 h, the skins were washed with soap and water to remove unabsorbed chemical. The skin was then solubilized. Two additional experiments were performed after washing the skin; the first was tape-stripping the skin and the second was the collection of receptor fluid for an additional 24 h. Receptor fluid, skin washes, tape strips and skin were analyzed for radioactivity. For rat skin, the wash removed 53–71% of the dose and 26–43% remained in the skin. The cumulative percentage of the dose at 24 h in the receptor fluid ranged from 1 to 5%. For human skin, the wash removed 71–83% of the dose and 14–25% remained in the skin. The cumulative percentage of the dose at 24 h in the receptor fluid was 1–2%. Tape-stripping removed 50–56% and 79–95% of the dose in rat and human skin, respectively, after the wash. From 24–48 h, 1–3% and about 1% of the dose diffused into the receptor fluid of rat and human skin, respectively. The pyrethroids bifenthrin, deltamethrin and cis-permethrin penetrated rat and human skin following dermal application in vitro. However, a skin wash removed 50% or more of the dose from rat and human skin. Rat skin was more permeable to the pyrethroids than human skin. Of the dose in skin, 50% or more was removed by tape-stripping, suggesting that permeation of pyrethroids into viable tissue could be impeded. The percentage of the dose absorbed into the receptor fluid was considerably less than the dose in rat and human skin. Therefore, consideration of the skin type used and fractions analyzed are important when using in vitro dermal absorption data for risk assessment.

Percutaneous absorption and exposure assessment of pesticides

Dermal exposure to a diverse range of chemicals may result from various uses. In order to assess exposure and estimate potential risks, accurate quantitative data on absorption are required. Various factors will influence the final results and interpretations of studies designed to assess the ability of compounds to penetrate the skin. This overview will discuss skin penetration by pesticides, emphasizing key parameters to be considered from the perspective of exposure assessment.

Near Real-Time Monitoring of Organophosphate Pesticides in the Aqueous-Phase Using SH-SAW Sensors Including Estimation-Based Signal Analysis

The sensor response times for the absorption of organophosphate pesticides (phosmet and parathion) from aqueous solution into partially selective coatings [poly(epichlorohydrin) (PECH) and polyurethane (PU)], are investigated using guided shear horizontal surface acoustic wave (SH-SAW) devices on LiTaO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> as the sensing platform. A study of the response time (absorption time constant) reveals that it is possible to decrease the sensor response time by increasing temperature and/or decreasing film thickness. However, these approaches reduced device sensitivity. A second approach involving nonlinear estimation-based sensor signal analysis is also investigated in an attempt to decrease the time required for identification and quantification without decreasing sensitivity. Specifically, the extended Kalman filter is employed for online analysis of the sensor data during the detection process. To achieve this, the sensor response was first represented by a state-space model which includes all relevant contributions to the polymer-coated device response. This allows for the steady-state sensor response and absorption time constant to be extracted online well before the steady-state is reached, thus reducing the time required for quantification. Extracting the absorption time, which is often unique to a class of analyte-coating pairs, will make it possible to improve analyte recognition in sensor array design.

Modelling the pesticide concentration in a rice field by a level IV fugacity model coupled with a dispersion-advection equation

The numerical simulation of a level IV fugacity model coupled to a dispersion-advection equation to simulate the environmental concentration of a pesticide in rice fields is presented. The model simulates the dynamic distribution of the pesticide in a compartmental system constituted by air, water, rice plants and bottom sediment together with saturated soil layers. The level IV fugacity model is given by a linear system of ordinary differential equations that considers the fugacities and, consequently, the concentrations of the pesticide in air, water, rice plants and bottom sediment. The dispersion-advection equation simulates the pesticide leaching in the saturated layers of the soil, considering the hydrodynamic dispersion, the pesticide degradation rate and the soil pesticide absorption in the saturated soil layer.

Проникнення пестицидів крізь шкіру з водних розчинів препаративних форм

Проникнення пестицидів крізь шкіру з водних розчинів препаративних форм

Potential impact of ABCB1 (p-glycoprotein) polymorphisms on avermectin toxicity in humans

Several members of the ATP binding cassette (ABC) transporter protein superfamily perform xenobiotic efflux functions in mammals, limiting gut absorption, mediating excretion, and controlling entry of a wide range of chemicals to sensitive compartments such as brain, testes and foetus. Perhaps the best characterised of these is p-glycoprotein (gene name ABCB1/MDR1), a barrier epithelia expressed protein with structurally diverse substrates, including the avermectin pesticides. In specific mouse and dog strains, ABCB1 mutations have been identified that result in loss of p-glycoprotein function in the blood brain barrier (BBB) and increased susceptibility to avermectin neurotoxicity. As yet no large rearrangements of the human ABCB1 gene analogous to those in the mouse and dog have been identified. However, numerous human ABCB1 single nucleotide polymorphisms (SNPs) have been identified, the allelic frequencies of which vary with ethnicity. There is no clear consensus on whether or not SNPs, or combinations of SNPs, reduce human p-glycoprotein functionality. However, recent in vivo human data indicate that the two commonest ABCB1 haplotypes both exhibit full BBB functionality. We discuss here the role of p-glycoprotein in limiting brain absorption of avermectin pesticides, as well as the potential impact of the reported functional effects and population frequencies of known ABCB1 polymorphisms on avermectin pesticide risk assessments.

Influence of formulation on the dermal absorption of pesticide actives at spray dilution concentrations

Influence of formulation on the dermal absorption of pesticide actives at spray dilution concentrations

A Physiologically Based Pharmacokinetic Model of Organophosphate Dermal Absorption

The rate and extent of dermal absorption are important in the analysis of risk from dermal exposure to toxic chemicals and for the development of topically applied drugs, barriers, insect repellents, and cosmetics. In vitro flow-through cells offer a convenient method for the study of dermal absorption that is relevant to the initial processes of dermal absorption. This study describes a physiologically based pharmacokinetic (PBPK) model developed to simulate the absorption of organophosphate pesticides, such as parathion, fenthion, and methyl parathion through porcine skin with flow-through cells. Parameters related to the structure of the stratum corneum and solvent evaporation rates were independently estimated. Three parameters were optimized based on experimental dermal absorption data, including solvent evaporation rate, diffusivity, and a mass transfer factor. Diffusion cell studies were conducted to validate the model under a variety of conditions, including different dose ranges (6.3-106.9 microg/cm2 for parathion; 0.8-23.6 microg/cm2 for fenthion; 1.6-39.3 microg/cm2 for methyl parathion), different solvents (ethanol, 2-propanol and acetone), different solvent volumes (5-120 microl for ethanol; 20-80 microl for 2-propanol and acetone), occlusion versus open to atmosphere dosing, and corneocyte removal by tape-stripping. The study demonstrated the utility of PBPK models for studying dermal absorption, which can be useful as explanatory and predictive tools that may be used for in silico hypotheses generation and limited hypotheses testing. The similarity between the overall shapes of the experimental and model-predicted flux/time curves and the successful simulation of altered system conditions for this series of small, lipophilic compounds indicated that the absorption processes that were described in the model successfully simulated important aspects of dermal absorption in flow-through cells. These data have direct relevance to topical organophosphate pesticide risk assessments.

Noninvasive Method for the Assessment of Dermal Uptake of Pesticides Using Attenuated Total Reflectance Infrared Spectroscopy

Dermal absorption of pesticides is a primary exposure route for agricultural workers, but is not well characterized. Current measurement techniques are either invasive, such as tape-stripping, or require extensive sample preparation or analysis time, such as urinary metabolite monitoring or wipe sampling followed by gas chromatography analysis. We present the application of a noninvasive, spectroscopic approach for the measurement of pesticide absorption into skin. Attenuated total reflectance infrared spectroscopy (ATR-IR) was used to monitor directly the absorption of two pesticides--captan and azinphos-methyl--in ten volunteers over 20 min under occlusive conditions. We found substantial variability in absorption across subjects. Our results were comparable to those measured by the more traditional method of wipe-sampling followed by extraction and gas chromatography analysis. Multivariate data analysis, in the form of multivariate curve resolution (MCR), is a novel addition to this type of experiment, yielding time-resolved information unachievable by standard methods. These data are potentially more informative than the monitoring of blood or urinary metabolites because they can be acquired in essentially real-time, allowing observations of pesticide absorption on a rapid timescale rather than over hours or days.

Thermal Stress and the Physiological Response to Environmental Toxicants

Most toxicological and pharmacological studies are performed in laboratory animals maintained under comfortable environmental conditions. Yet, the exposure to environmental toxicants as well as many drugs can occur under stressful environmental conditions during rest or while exercising. The intake and biological efficacy of many toxicants is exacerbated by exposure to heat stress, which can occur in several ways. The increase in pulmonary ventilation during exposure to hot environments results in an increase in the uptake of airborne toxicants. Furthermore, the transcutaneous absorption of pesticides on the skin as well as drugs delivered by skin patches is increased during heat stress because of the combined elevation in skin blood flow coupled with moist skin from sweat. The thermoregulatory response to toxicant exposure, such as hypothermia in relatively small rodents and fever in humans, also modulates the physiological response to most chemical agents. This paper endeavors to review the issue of environmental heat stress and exercise and how they influence thermoregulatory and related pathophysiological responses to environmental toxicants, as well as exposure to drugs.

Toxicity of a Mixture of 2,4-Dichlorophenoxyacetic Acid and Mono-soduim Methanearsonate to the Red Swamp Crawfish, Procambarus clarkii

2,4-dichlorophenoxyacetic acid and monosodium methanearsonate are often sold in commercial herbicide mixtures. Toxicity studies have been performed for each herbicide individually, but there is a dearth of information concerning the toxicity of these herbicides in a mixture. The following study examined the toxicity of a mixture of these two herbicides in the red swamp crawfish, Procambarus clarkii. 96-hour acute toxicity assays were performed to determine whether surfactant significantly altered the toxicity of these herbicides individually or in combination. Markings additive index was calculated to identify the interactions of the herbicide mixture. Surfactant was observed to significantly increase the toxicity of 2,4-dichlorophenoxyacetic acid and the toxicity of the herbicide mixture. The herbicide mixture alone displayed half the toxicity of the individual herbicides, but the mixture with surfactant was twice as toxic as the individual herbicides. The synergistic action of surfactant may be attributed to increased pesticide absorption across biological membranes. 2,4-dichlorophenoxyacetic acid and surfactant may also compromise gill function, increasing the sensitivity of the crawfish to herbicide toxicity. The antagonistic effects of the herbicide mixture in the absence of surfactant may be caused by competition of both herbicides for the same sites of activity.

Sunscreens containing physical UV blockers can increase transdermal absorption of pesticides.

People are encouraged to wear sunscreens because of their effectiveness at reducing the risk of skin cancer. The dermal penetration of the herbicide 2,4-D can be enhanced by commercial formulations containing chemical ultraviolet (UV) absorbers, the absorbers themselves and the insect repellent DEET. This work has been extended to determine whether commercially available sunscreens containing the physical UV absorbers titanium dioxide (TiO2) or zinc oxide (ZnO) enhance the transdermal absorption of pesticides. Hairless mouse skin was pretreated with either commercially available sunscreens or the UV absorbers themselves, dissolved in phenyl trimethicone. In vitro permeability studies were performed with the pesticides 2,4-D, paraquat, parathion or malathion. The data demonstrate that pretreatment with five of the nine sunscreens tested increased the transdermal absorption of 2,4-D (P<0.05). Transdermal studies using paraquat, parathion and malathion pretreated with a representative sunscreen all demonstrated significant penetration enhancement when compared to controls (P<0.05). Repeated 2,4-D and sunscreen applications resulted in either no change between pulses or an increase in absorption after the second pulse depending on the washing regimen. Examining penetration of individual UV absorbers formulated in phenyl trimethicone showed that that ZnO can impede 2,4-D penetration and TiO2 had no effect. Combining UV absorbers in the presence of trimethicone resulted in 'sunscreens' that could actually inhibit 2,4-D penetration. Inert ingredients therefore control the increased absorption seen in commercial sunscreen products and this enhancement can be eliminated by substituting phenyl trimethicone as the solvent. Sunscreen use must still be encouraged even with the undesirable side effect of increased penetration through the skin.

Uncertainty in measurements of dermal absorption of pesticides.

Dermal absorption experiments form an important component in the assessment of risk from exposure to pesticides and other substances. Much dermal absorption data is gathered in rat experiments carried out using a certain standard protocol. Uncertainties in these data arise from many sources and can be quite large. For example, measurements of the systemic absorption of hexaconazole differed by more than an order of magnitude within a single experiment. Two diniconazole studies produced quite different results, due to minor differences in protocol and in chemical formulation. Limits of detection can also prevent accurate measurement when the amounts absorbed are small. These examples illustrate the need for measuring and reporting uncertainties in estimates that are based on these data. The most direct way to estimate uncertainty is to compute the sample standard deviations of replicate measurements. By pooling these estimates across dose and duration groups for which they are similar, the number of degrees of freedom is increased, and more precise confidence intervals can be obtained. In particular, the ratio of upper to lower 95% confidence limits was reduced by as much as ten-fold for hexaconazole, seven-fold for uniconazole, and nearly four-fold for propiconazole.

Dermal absorption of pesticides in the rat.

The Office of Pesticide Programs (OPP) of the Environmental Protection Agency has developed a standard protocol for evaluating the dermal penetration of pesticides in the rat. This protocol was formalized in 1994 as a guideline for Dermal Absorption Studies of Pesticides. To date, in excess of 263 studies on the dermal absorption of over 160 pesticide chemicals have been submitted to OPP as part of the pesticide registration and risk assessment processes. The majority of these studies has been performed according to the OPP standard protocol in the rat. These studies constitute the largest database in existence on the dermal absorption of a wide variety of chemicals using a standard protocol. From this standard protocol it is possible to describe, quantitatively with dose and time, the entrance of a chemical into and penetration through the mammalian epidermis into the systemic circulation, its concentration in blood and in the body, and its excretion in urine and feces. This article describes the experimental design of the standard protocol and presents examples of the types of pesticides studied: pesticides that are neither volatile nor damage the skin (the most common type), volatile pesticides, and pesticides that damage the skin. Examples are selected to illustrate differences in the pattern of dermal uptake and subsequent absorption into the systemic compartment among and within the three classes.

Dermal Absorption of Pesticides in the Rat

Dermal Absorption of Pesticides in the Rat

Safety and Chemicals

AbstractChemical engineers need to be aware of the increasing concern over the safe use of chemicals, a duty of care, and a positive effort to reduce exposure to chemicals by both the general public and persons working in the occupational environment. Benzene inhalation from gasoline during automobile tank filling should be minimized in order to reduce the risk of leukaemia. Dermal absorption of pesticides and solvents can have adverse health effects. Captan, an old pesticide about to re‐appear, is examined as a potential human carcinogen. Persistent old organochlorines in meat can enter the human food chain. Organophosphate pesticides, 50 times more toxic than HCN, are detected in Australian beef and sheep samples. The best estimate of occupational mortality due to past chemical exposure is 2,300 people per year. Chemical engineers need the management vision to include safety and chemicals in the design and operation of plant, and in the pathways leading to inhalation, ingestion and absorption in humans.

Panorama epidemiológico de exposición a plaguicidas inhibidores de colinesterasa en 17 departamentos del país

Organophosphorates and carbamates are responsible for the greater part of the pesticide poisonings which are presented in the country. They are potent inhibitors of the acetylcholinesterase enzyme, causing serious acute work-related poisoning as well as long term effects. In 1982, faced by this problem, the Instituto Nacional de Salud (INS), through its Environrnental Health Laboratory (Laboratorio de Salud Ambientao created the epidemiological vigilance for organophosphorate and carbamate pesticides (Programa de Vigilancia Epidemiológica de Plaguicidas Organofosforados y Carbarnatos (VEO)), employing the Lovibond method to determine acetylcholinesterase (ACHE) as indicator, in order to detect cases of high pesticide absorption. From 1993 onwards, information from 17 of the countty's departments was ready, this being the data which was analysed. The total number of people who participated in the study during the years 1993 to 1995 was 41,899, al1 of whom had antecedents of exposure to organophosphorate or catbarnate pesticides 80% of the workers who participated in the study were male, the age-group rnost affected being 18 to 40 years old. The greatest prevalence of ACHE abnormality, according to economic activity, was for urban application and related to the jobs of mixer-sprayerwarehousing. In relation to the social security of the 23,917 workers, only 31.7% were found to be afiiliated to this type of entity. The data obtained allowed an epidemiological panorama to be established concerning poisoning by cholinesterase inhibitor pesticides, thus determining the population at greatest risk, which will lead to new research studies of this population.

Influence of inert ingredients in pesticide formulations on dermal absorption of carbaryl

SUMMARY Objectives To assess the influence of solvent plus various mixtures on percutaneous absorption and disposition of the carbamate insecticide, carbaryl (CA). Animals Skin was obtained from the dorsum of 14 female weanling specific-pathogen-free Yorkshire pigs. Procedure In this 8-hour in vitro flow-through diffusion study, porcine skin sections were dosed with 40 μg of CA/cm2 of surface area, different amounts of solvents (40 or 80% acetone or dimethyl sulfoxide [DMSO]), different amounts of a surfactant (0, 1, or 5% sodium lauryl sulfate [SLS]), an insect repellent (0 or 15% diethyl-m-toluamide [DEET]), an insecticide synergist (0 or 2% piperonyl butoxide [PB]), and a CA metabolite (40 μg/cm2 1-naphthol (1-NA]). Results In general, CA absorption was greater from acetone than from DMSO mixtures, and CA penetration into skin and stratum corneum was greater from DMSO at 8 hours. This is consistent with the flux-time profiles, which depicted initial peak flux within 2 to 3 hours for most acetone mixtures, but a slow increase in flux for DMSO mixtures. Irrespective of the solvent, increasing water content in pesticide dosing mixtures significantly increased CA absorption from SLS mixtures only. The SLS also enhanced CA absorption, especially at low solvent concentrations. The DEET significantly reduced CA absorption from acetone, but not from DMSO mixtures, and 1-NA enhanced CA absorption from acetone, but not from DMSO mixtures. Piperonyl butoxide significantly enhanced CA absorption from acetone and DMSO mixtures. However, addition of PB or PB plus SLS did not significantly increase CA flux above that observed from solvent plus surfactant mixtures. Conclusions Inert ingredients can modulate percutaneous absorption of toxicologically important pesticides and their effect or activity on CA disposition is dependent on solvent specificity and solvent concentration. Whereas SLS, PB, and 1-NA can enhance pesticide absorption, DEET can reduce absorption. (Am J Vet Res 1998;59:168–175)