Aquatic life criteria derivation and ecological risk assessment of DEET in China.

N,N-diethyl-meta-toluamide (DEET) is the most widely used active ingredient in commercial insect repellents. In addition to its adverse effects in insects, DEET can affect non-target organisms in surface water systems. Nevertheless, the aquatic life criteria of DEET are not available. This study conducted both acute and chronic toxicity tests on DEET in native Chinese aquatic species, and derived its criterion maximum concentration (CMC) and criterion continuous concentration (CCC). The determined CMC and CCC of DEET were 21.53 and 0.52 mg/L, respectively. The toxicity data indicated that DEET exposure posed a higher toxicity to some algae than other aquatic species. Compared with other insect repellents, DEET exposure posed a moderate toxicity to aquatic species. Therefore, the exposure concentration of DEET in Chinese surface water was collected to assess the potential ecological risk. The preliminary ecological risk assessment showed that DEET posed negligible risk to aquatic ecosystems in China. However, considering its toxic effects on the growth and reproduction to aquatic organisms, the ecological risk posed by DEET is worth further concern.

A pulsed pinhole atmospheric pressure interface for simplified mass spectrometry instrumentation with enhanced sensitivity.

RATIONALE: A proof-of-concept pulsed pinhole atmospheric pressure interface, namely PP-API, was developed and characterized for mass spectrometry instrumentation. METHODS: The PP-API was analyzed and optimized theoretically with respect to gas flow rate, opening force and dimensions. A PP-API interfaced mass spectrometry system was then constructed and tested. RESULTS: As a discontinuous pressure interface, the PP-API allows efficient ion transfer from atmosphere pressure ionization sources to ion traps directly. Both nano-ESI and APCI ionization sources have been successfully integrated with the PP-API interface for the detection of volatile, organic, peptide and polymer samples. The use of multiple ionization sources has also been demonstrated to enhance signal intensity, as well as avoid charge competitions in ionization sources. CONCLUSIONS: With simplified geometry and high ion transfer efficiency, this PP-API would enable miniaturized mass spectrometry systems with high sensitivity.

Assessment of groundwater pollution in Tokyo using PPCPs as sewage markers.

While the occurrence of pharmaceuticals and personal care products (PPCPs) in groundwater has typically been reported in bank filtration sites, irrigated fields, septic tanks, and sewage disposal practices, fewer studies have been conducted in highly urbanized areas, where infiltration of treated or untreated sewage is not supposed to be a source of groundwater recharge. Furthermore, little is known about the occurrence of various kinds of PPCPs in relation to microbial indicators in groundwater from different types of aquifers. Thus, we examined the city-wide occurrence of selected PPCPs (diethyltoluamide, crotamiton, ethenzamide, propyphenazone, carbamazepine, and caffeine) and E. coli in 50 groundwaters from unconfined aquifers (<30 m in depth) and confined aquifers (up to 500 m in depth) in Tokyo, where unintended groundwater contamination could take place due to decrepit sewer networks. PPCPs were detected in unconfined aquifers and springs (23/34 samples, 68%), and in confined aquifers (7/16 samples, 44%). Compared with published results for sewage influents, concentrations of PPCPs, excluding caffeine, were generally 1-2 orders of magnitude lower, while in some samples concentrations were quite comparable. The high occurrence rate of PPCPs, even in confined aquifers, indicated that such aquifers are not always protected from pollution by sewage near the land surface. Among the PPCPs analyzed, carbamazepine and crotamiton were most frequently detected, which would appear to be owing to their high persistence, combined with the high concentration of crotamiton in sewage. Crotamiton was detected in all four E. coli-positive groundwaters, and thus may potentially serve as a precautionary indicator of E. coli contamination. Using carbamazepine as a sewage marker, we estimated that 0.8%-1.7% of the dry-weather flow of sewage was leaking out into the unconfined aquifers.

[Contamination Characteristics and Ecological Risk Assessment of Pharmaceuticals and Personal Care Products (PPCPs) in the Third Drain of Ningxia].

To investigate the contamination characteristics and potential ecological risks of pharmaceuticals and personal care products (PPCPs) in the Third Drain of Ningxia, 14 PPCPs were detected and analyzed using solid-phase extraction coupled with ultra-high performance liquid chromatography-tandem mass spectrometry. The results showed that these 14 PPCPs were detected in the Third Drain and its confluent streams, with total concentrations of 117.74-1947.64 ng·L-1 and 63.94-4509.39 ng·L-1, respectively. Detection ratios of gemfibrozil (GEM), caffeine (CAF), avobenzone (BM-DBM), benzophenone-3 (BP-3), 3-(4-methylbenzylidene)-camphor (4-MBC), and diethyltoluamide (DEET) were 100% in the drain. The highest-concentration pharmaceutical was GEM (7.78-721.84 ng·L-1), followed by CAF (41.74-246.86 ng·L-1), and the highest-concentration personal care product was DEET (3.17-219.91 ng·L-1), followed by BP-3 (56.92-150.14 ng·L-1). Concentrations of PPCPs at different sampling points exhibited spatial differences. The total PPCPs concentration increased dramatically and reached a maximum value after flowing through Pingluo County, then showed a decreasing trend downstream. Correlation analysis showed that 4-MBC was significantly positively correlated with COD (P<0.01). IBU, XMTD, TCC, and TCS were significantly correlated with NH4+-N (P<0.05). DIC, BF, CBZ, and DEET were significantly correlated with TN (P<0.05). The results indicated that concentrations of PPCPs were closely related to water quality indexes. Risk assessment showed that DIC, IBU, GEM, CBZ, CAF, and BP-3 had high risks, whereas BM-DBM, TCC, and TCS had moderate risks.

Screening of pesticides and emerging contaminants in eighteen Greek lakes by using target and non-target HRMS approaches: Occurrence and ecological risk assessment.

Lakes, albeit ecosystems of vital importance, are insufficiently investigated with respect to the degradation of water quality due to the organic micropollutants load. As regards Greece, screening of lake waters is scarce and concerns a limited number of contaminants. However, understanding the occurrence of contaminants of emerging concern (CECs) and other micropollutants in lakes is essential to appraise their potential ecotoxicological effects. The aim of this study was to deploy a multiresidue screening approach based on liquid chromatography-high-resolution mass spectrometry (HRMS) to get a first snapshot for >470 target CECs, including pesticides, pharmaceuticals, personal care products (PPCPs), per- and polyfluoroalkyl substances (PFASs), as well as organophosphate flame retardants (OPFRs) in eighteen Greek lakes in Central, Northern and West Northern Greece. The omnipresent compounds were DEET (N,N-diethyl-meta-toluamide), caffeine and TCPP (tris (1-chloro-2-propyl) phosphate). Maximum concentrations varied among the different classes. DEET was detected at a maximum average concentration of >1000 ng/L in Lake Orestiada, while its mean concentration was estimated at 233 ng/L. The maximum total concentrations for pesticides, PPCPs, PFASs, and OPFRs were 5807, 2669, 33.1, and 1214 ng/L, respectively, indicating that Greek lakes are still threatened by the intense agricultural activity. Besides, HRMS enabled a non-target screening by exploiting the rich content of the full-scan raw data, allowing the 'discovery' of tentative candidates, such as surfactants, pharmaceuticals, and preservatives among others, without reference standards. The potential ecotoxicity was assessed by both the risk quotient method and ECOSAR (Ecological Structure Activity Relationships) revealing low risk for most of the compounds.

Removal of selected endocrine disrupting chemicals and personal care products in surface waters and secondary wastewater by ozonation.

This study investigated the removal of parabens, N,N-diethyl-m-toluamide (DEET), and phthalates by ozonation. The second-order rate constants for the reaction between selected compounds with ozone at pH 7 were of (2.2 +/-0.2) X 10(6) to (2.9 +/-0.3) X 10(6) M 1/s for parabens, (2.1+/- 0.3) to (3.9 +/-0.5) M-1/s for phthalates, and (5.2 +/-0.3) M-1/s for DEET. The rate constants for the reaction between selected compounds with hydroxyl radical ranged from (2.49 +/-0.06) x 10(9) to (8.5 +/-0.2) x 10(9) M-1/s. Ozonation of selected compounds in secondary wastewater and surface waters revealed that ozone dose of 1 and 3 mg/L yielded greater than 99% depletion of parabens and greater than 92% DEET and phthalates, respectively. In addition, parabens were found to transform almost exclusively through the reaction with ozone, while DEET and phthalates were transformed almost entirely by hydroxyl radicals (.OH).

DEET occurrence in wastewaters: Seasonal, spatial and diurnal variability - mismatches between consumption data and environmental detection.

DEET (N, N-diethyl-m-toluamide) is one of the most frequently detected trace organic contaminants (TOrC) in wastewaters and is used primarily as an insect repellent. It was introduced for use in the general public in 1957. It is ubiquitously present in the environment and DEET concentrations are usually among the highest reported for TOrCs. Due to recent concerns about possible analytical interferences in detection methods being reported, this study focused on possible artifacts caused by seasonal, spatial, and diurnal variations in wastewater influent concentration of DEET. We also compared usage data to observed wastewater concentrations of seven wastewater treatment plants (WWTPs) in four different regions in the US monitored from November 2014 to November 2016. Consumption data obtained reveal patterns of consumption according to climatic regions and season. During the summer DEET usage accounts for almost 60% of all usage during a year, while during the winter months DEET usage accounts for <5%. Concerning spatial distribution, while per capita consumption of DEET in Florida is three times higher than the one observed in Arizona (44 g vs 14 g), DEET concentrations in wastewater tend to be much higher in Arizona. Regardless of WWTPs or monitoring period, concentrations as high as 15,200 ng/L were observed during the month of October 2016. While DEET has a diurnal variation in the wastewater influent, with a maximum at 18:00, the diurnal variability is not enough to explain the great discrepancies between consumption of DEET versus occurrence in wastewaters. Although LC-MS/MS analysis of isobaric and structural mimics suggests some possibility of interferences, NMR spectroscopy analysis of environmental samples does not support the presence of such mimics in real samples.

Is there a risk associated with the insect repellent DEET (N,N-diethyl-m-toluamide) commonly found in aquatic environments?

DEET (N,N-diethyl-m-toluamide) is the active ingredient of most commercial insect repellents. This compound has commonly been detected in aquatic water samples from around the world indicating that DEET is both mobile and persistent, despite earlier assumptions that DEET was unlikely to enter aquatic ecosystems. DEET's registration category does not require an ecological risk assessment, thus information on the ecological toxicity of DEET is sparse. This paper reviews the presence of DEET in aqueous samples from around the world (e.g. drinking water, streams, open seawater, groundwater and treated effluent) with reported DEET concentrations ranging from 40-3000 ng L(-1). In addition, new DEET data collected from 36 sites in coastal waterways from eastern Australia (detections ranging from 8 to 1500 ng L(-1)) are examined. A summary of new and existing toxicity data are discussed with an emphasis on preparing a preliminary risk assessment for DEET in the aquatic environment. Collated information on DEET in the aquatic environment suggests risk to aquatic biota at observed environmental concentrations is minimal. However, the information available was not sufficient to conduct a full risk assessment due to data deficiencies in source characterisation, transport mechanisms, fate, and ecotoxicity studies. These risks warrant further investigation due to the high frequency that this organic contaminant is detected in aquatic environments around the world.

Magnetic Solid-Phase Extraction of N,N-Diethyl-m-Toluamide From Baby Toilet Water Prior to its HPLC-UV Detection.

Fe3O4@MIL-100 (MIL, Material Institut Lavoisier) core-shell magnetic microspheres were prepared and applied as the sorbent for the magnetic solid phase extraction (MSPE) of N,N-diethyl-m-toluamide (DEET) in baby toilet water for the first time. The synthesized magnetic metal-organic frameworks were characterized by transmission electron microscope, infrared spectroscopy and thermogravimetric analysis. The functionalized magnetic microparticles showed excellent dispersibility in aqueous solution. The MSPE conditions were investigated in detail. Under the optimized conditions, an MSPE-high performance liquid chromatography method for the determination of DEET was developed. The method was linear in the concentration range from 5 to 500 µg L-1 for DEET in baby toilet water and good linearity (r2 > 0.9998) was obtained for the calibration curve. The limit of detection was 1.5 µg L-1. Both the intra-day and inter-day precisions (relative standard deviations) were <3%.

Critical assessment of the ubiquitous occurrence and fate of the insect repellent N,N-diethyl-m-toluamide in water.

The insect repellent diethyltoluamide (DEET) is among the most frequently detected organic chemical contaminants in water across a wide range of geographies from around the world. These observations are raising critical questions and increasing concerns regarding potential environmental relevance, particularly when the emergence of severe neurological conditions attributed to the Zika virus has increased the use of insect repellents. After dermal application, DEET is washed from the skin when bathing and enters the municipal sewer system before discharge into the environment. Mainly measured by gas chromatography or liquid chromatography coupled to mass spectrometry (GC-MS or LC-MS), more than 200 peer-reviewed publications have already reported concentrations of DEET ranging ng/L to mg/L in several water matrices from North America, Europe, Asia, Oceania, and more recently Africa and South America. While conventional wastewater treatment technology has limited capacity of removal, advanced technologies are capable of better attenuation and could lower the environmental discharge of organic contaminants, including DEET. For instance, adsorption on activated carbon, desalinating membrane processes (nanofiltration and reverse osmosis), ozonation, and advanced oxidation processes can achieve 50% to essentially 100% DEET attenuation. Despite the abundant literature on the topic, the ubiquity of DEET in the environment still raises questions due to the apparent lack of obvious spatio-temporal trends in concentrations measured in surface water, which does not fit the expected usage pattern of insect repellents. Moreover, two recent studies showed discrepancies between the concentrations obtained by GC-MS and LC-MS analyses. While the occurrence of DEET in the environment is well established, the concentrations reported should be interpreted cautiously, considering the disparities in methodologies applied and occurrence patterns observed. Therefore, this manuscript provides a critical overview of the origin of DEET in the environment, the relevant analytical methods, the occurrence reported in peer-reviewed literature, and the attenuation efficacy of water treatment processes.

Determination of personal care products and hormones in leachate and groundwater from Polish MSW landfills by ultrasound-assisted emulsification microextraction and GC-MS.

Determination of the endocrine disrupting compounds (EDCs) in leachate and groundwater samples from the landfill sites is very important because of the proven harmful effects of these compounds on human and animal organisms. A method combining ultrasound-assisted emulsification microextraction (USAEME) and gas chromatography-mass spectrometry (GC-MS) was developed for simultaneous determination of seven personal care products (PCPs): methylparaben (MP), ethylparaben (EP), propylparaben (PP), buthylparaben (BP), benzophenone (BPh), 3-(4-methylbenzylidene)camphor (4-MBC), N,N-diethyltoluamide (DEET), and two hormones: estrone (E1) and ß-estradiol (E2) in landfill leachate and groundwater samples. The limit of detection (LOD)/limit of quantification (LOQ) values in landfill leachate and groundwater samples were in the range of 0.003-0.083/0.009-0.277 µg L(-1) and 0.001-0.015/0.002-0.049 µg L(-1), respectively. Quantitative recoveries and satisfactory precision were obtained. All studied compounds were found in the landfill leachates from Polish municipal solid waste (MSW) landfills; the concentrations were between 0.66 and 202.42 µg L(-1). The concentration of pollutants in groundwater samples was generally below 0.1 µg L(-1).

Simultaneous analysis of insect repellent DEET, sunscreen oxybenzone and five relevant metabolites by reversed-phase HPLC with UV detection: application to an in vivo study in a piglet model.

N,N-Diethyl-m-toluamide (DEET) and oxybenzone are two essential active ingredients in insect repellent and sunscreen preparations. We developed and validated a simple, sensitive, and selective HPLC assay to simultaneously measure DEET, oxybenzone and five primary metabolites of DEET and oxybenzone in biological samples including plasma, urine and skin strips. The compounds were separated on a reversed-phase C18 column using three-stage gradient steps with methanol and water. DEET and two relevant metabolites were detected at 254 nm, while oxybenzone and three relevant metabolites were detected at 289 nm. The limit of detection was 0.6 ng for DEET and 0.5 ng for oxybenzone, respectively. The developed method was further applied to analyze various biological samples from an in vivo animal study that evaluated concurrent use of commercially available insect repellent and sunscreen preparations.

Widespread detection of N,N-diethyl-m-toluamide in U.S. streams: comparison with concentrations of pesticides, personal care products, and other organic wastewater compounds.

One of the most frequently detected organic chemicals in a nationwide study concerning the effects of wastewater on stream water quality conducted in the year 2000 was the widely used insect repellant N,N-diethyl-m-toluamide (DEET). It was detected at levels of 0.02 microg/L or greater in 73% of the stream sites sampled, with the selection of sampling sites being biased toward streams thought to be subject to wastewater contamination (i.e., downstream from intense urbanization and livestock production). Although DEET frequently was detected at all sites, the median concentration was low (0.05 microg/L). The highest concentrations of DEET were found in streams from the urban areas (maximum concentration, 1.1 microg/L). The results of the present study suggest that the movement of DEET to streams through wastewater-treatment systems is an important mechanism that might lead to the exposure of aquatic organisms to this chemical.

Emerging contaminants in urban groundwater sources in Africa.

The occurrence of emerging organic contaminants within the aquatic environment in Africa is currently unknown. This study provides early insights by characterising a broad range of emerging organic contaminants (n > 1000) in groundwater sources in Kabwe, Zambia. Groundwater samples were obtained during both the dry and wet seasons from a selection of deep boreholes and shallow wells completed within the bedrock and overlying superficial aquifers, respectively. Groundwater sources were distributed across the city to encompass peri-urban, lower cost housing, higher cost housing, and industrial land uses. The insect repellent DEET was ubiquitous within groundwater at concentrations up to 1.8 µg/L. Other compounds (n = 26) were detected in less than 15% of the sources and included the bactericide triclosan (up to 0.03 µg/L), chlorination by-products - trihalomethanes (up to 50 µg/L), and the surfactant 2,4,7,9-tetramethyl-5-decyne-4,7-diol (up to 0.6 µg/L). Emerging contaminants were most prevalent in shallow wells sited in low cost housing areas. This is attributed to localised vulnerability associated with inadequate well protection, sanitation, and household waste disposal. The five-fold increase in median DEET concentration following the onset of the seasonal rains highlights that more mobile compounds can rapidly migrate from the surface to the aquifer suggesting the aquifer is more vulnerable than previously considered. Furthermore it suggests DEET is potentially useful as a wastewater tracer in Africa. There was a general absence of personal care products, life-style compounds, and pharmaceuticals which are commonly detected in the aquatic environment in the developed world. This perhaps reflects some degree of attenuation within the subsurface, but could also be a result of the current limited use of products containing emerging contaminants by locals due to unaffordability and unavailability. As development and population increases in Africa, it is likely a wider-range of emerging contaminants will be released into the environment.

Potential analytical interferences and seasonal variability in diethyltoluamide environmental monitoring programs.

N,N-diethyl-m-toluamide (DEET), the active component of many insect repellents, is among the most frequently detected compounds in aqueous environments with concentrations reported in the ng L(-1) to µg L(-1) range. However, DEET is often detected in blanks and reported concentrations differ significantly depending on the analytical technique employed. In addition, relatively sparse data are available regarding the seasonal variability of DEET concentrations in water and there are apparent inconsistencies with expected use patterns. Therefore, the present study investigates potential interferences affecting the detection and quantification of DEET then the geographical and seasonal variations of DEET concentrations. To examine potential analytical interferences, DEET was analyzed in five geographically-diverse wastewater effluents using both gas chromatography and liquid chromatography coupled to mass spectrometric detectors. At times, the concentrations quantified by the employed analytical methods varied significantly. Five compounds with similar molecular weights and structures as DEET were investigated as potential mimics and some were shown to induce an overestimation of DEET. Further experimentation suggested that the solvents used in sample preparation and HPLC analysis are another possible source of interference. Besides potential interferences, the seven-month weekly monitoring of DEET in the primary effluent of a wastewater treatment plant demonstrated a clear seasonal trend with decreasing concentration from summer to winter. These data collectively demonstrate that there are many challenges in the quantification of DEET in complex environmental samples and that co-occurrence of similarly structured substances present in the water sample and/or the solvents used for the analysis could induce analytical bias.

Pharmaceuticals and other anthropogenic tracers in surface water: a randomized survey of 50 Minnesota lakes.

Water from 50 randomly selected lakes across Minnesota, USA, was analyzed for pharmaceuticals, personal care products, hormones, and other commercial or industrial chemicals in conjunction with the US Environmental Protection Agency's 2012 National Lakes Assessment. Thirty-eight of the 125 chemicals analyzed were detected at least once, all at parts per trillion concentrations. The most widely detected was N,N-diethyl-m-toluamide, present in 48% of the lakes sampled. Amitriptyline, a widely used antidepressant, was found in 28% of the lakes. The endocrine active chemicals bisphenol A, androstenedione, and nonylphenol were found in 42%, 30%, and 10% of the lakes, respectively. Cocaine was found in 32% of the lakes, and its degradation product, benzoylecgonine, was detected at 28% of the locations. Carbadox, an antibiotic used solely in the production of swine, was also present in 28% of the lakes sampled. The means by which these and other chemicals were transported to several of the remote lakes is unclear but may involve atmospheric transport.

Safety of the insect repellent N,N-diethyl-M-toluamide (DEET) in pregnancy.

The safety of daily application of N, N-diethyl-m-toluamide (DEET) (1.7 g of DEET/day) in the second and third trimesters of pregnancy was assessed as part of a double-blind, randomized, therapeutic trial of insect repellents for the prevention of malaria in pregnancy (n = 897). No adverse neurologic, gastrointestinal, or dermatologic effects were observed for women who applied a median total dose of 214.2 g of DEET per pregnancy (range = 0-345.1 g). DEET crossed the placenta and was detected in 8% (95% confidence interval = 2.6-18.2) of cord blood samples from a randomly selected subgroup of DEET users (n = 50). No adverse effects on survival, growth, or development at birth, or at one year, were found. This is the first study to document the safety of DEET applied regularly in the second and third trimesters of pregnancy. The results suggest that the risk of DEET accumulating in the fetus is low and that DEET is safe to use in later pregnancy.

Reduction in skin permeation of N,N-diethyl-m-toluamide (DEET) by altering the skin/vehicle partition coefficient.

Reported adverse side effects after using N,N-diethyl-m-toluamide (DEET)-containing mosquito repellent products appear to be the result of significant absorption of DEET through human skin. The overall objective was to develop formulations of DEET with significantly reduced permeation using the basic principles and model of skin permeation based on Fick's laws of diffusion at steady state. Ternary phase diagrams of DEET with water and semipolar solvents, ethanol, PG and PEG 400, showed an increase in the aqueous solubility of DEET. This resulted in a linear decline in octanol/water PC with an increase in the concentration of the solvent. Permeation of DEET across human skin was studied from vehicles containing various amounts of PG and PEG 400 using an infinite dose technique and Franz diffusion cell. DEET's flux reduced with increasing PG concentration and the flux from 90% PG was 9.9+/-2.1 microg/cm(2) h, 6-fold lower than flux of pure DEET control, 63.2+/-24.5 microg/cm(2) h. Flux was reduced 6-fold from 60% PEG 400 solution, and permeation of DEET was totally prevented from 90% PEG 400 which was very viscous. However, a combination of 60% PEG 400 with 30% PG not only reduced permeation 9-fold but was suitable as a vehicle for formulation. The decrease in flux and permeability of DEET with increasing concentration of solvent appeared to be a direct result of decrease in skin/vehicle PC and octanol/water PC. This study clearly demonstrates that alternative formulations can be developed for DEET aimed at reduced permeation and toxicity unlike the current formulations some of which contain ethanol which has been shown to enhance permeation of DEET. A similar approach can be used for developing formulations of other industrial and occupational agents to prevent their skin permeation when a user may be exposed to them.

Determination of some insect repellents in cosmetic products by high-performance thin-layer chromatography.

A simple and reliable thin-layer chromatographic method for the determination of N,N-diethyl-m-toluamide (DEET) and dimethyl phthalate (DMP) in raw material and cosmetic products was developed and validated. A benzene-diethyl ether-cyclohexane (5:3:2, v/v/v) solvent system was used for quantitative evaluation of chromatograms. The chromatographic zones corresponding to the spots of DEET and DMP on the silica gel plates were scanned in the reflectance/absorbance mode at 230 nm. The method was found to be reproducible and convenient for the quantitative analysis of DEET and DMF in raw material and cosmetic products.

Analysis of N,N-diethyl-m-toluamide in porcine skin perfusates using solid-phase extraction disks and reversed-phase high-performance liquid chromatography.

N,N-Diethyl-m-toluamide (DEET) is frequently used as an insect repellent by military and civilian populations. Because dermal exposure has resulted in several cases of DEET toxicosis, there is a need to rapidly and reliably determine DEET concentrations in biological matrices. An improved method for the analysis of DEET was developed for determining transdermal diffusion of low levels of DEET following application to an in vitro porcine skin flow-through diffusion cell system. The technical improvement involved the use of disk solid-phase extraction (SPE) instead of packed-bed SPE. The disk SPE method required small volumes of preconditioning, wash, and elution solvent (0.5-1 ml) to extract DEET from perfusate samples containing bovine serum albumin (BSA). The limit of quantitation (LOQ) was estimated as 0.08 micro g/ml DEET and recoveries from BSA media samples spiked with DEET ranged from 90.1 to 117% with relative standard deviation (RSD) ranging from 2.0 to 13.1%. This method was used to analyze perfusate samples from skin (n=4) topically exposed to DEET-ethanol formulations. The data from these analyses determined that DEET permeability in porcine skin was 2.55 x 10(-5)+/-0.54 x 10(-5) cm/h.