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Transfer efficiencies of pesticides from household flooring surfaces to foods

Abstract

The transfer of pesticides from household surfaces to foods was measured to determine the degree of excess dietary exposure that occurs when children's foods contact contaminated surfaces prior to being eaten. Three household flooring surfaces (ceramic tile, hardwood, and carpet) were contaminated with an aqueous emulsion of commercially available pesticides (diazinon, heptachlor, malathion, chlorpyrifos, isofenphos, and cis- and trans-permethrin) frequently found in residential environments. A surface wipe method, as typically used in residential exposure studies, was used to measure the pesticides available on the surfaces as a basis for calculating transfer efficiency to the foods. Three foods (apple, bologna, and cheese) routinely handled by children before eating were placed on the contaminated surfaces and transfers of pesticides were measured after 10 min contact. Other contact durations (1 and 60 min) and applying additional contact force (1500 g) to the foods were evaluated for their impact on transferred pesticides. More pesticides transferred to the foods from the hard surfaces, that is, ceramic tile and hardwood flooring, than from carpet. Mean transfer efficiencies for all pesticides to the three foods ranged from 24% to 40% from ceramic tile and 15% to 29% from hardwood, as compared to mostly non-detectable transfers from carpet. Contact duration and applied force notably increased pesticide transfer. The mean transfer efficiency for the seven pesticides increased from around 1% at 1 min to 55– 83% when contact duration was increased to 60 min for the three foods contacting hardwood flooring. Mean transfer efficiency for 10-min contact increased from 15% to 70% when a 1500 g force was applied to bologna placed on hardwood flooring. Contamination of food occurs from contact with pesticide-laden surfaces, thus increasing the potential for excess dietary exposure of children.

Introduction

Pesticides are used in and around residences to kill or control pests, including weeds, insects, fungi, bacteria, and rodents (NRC, 1993). Application of pesticides in residential areas can pose a potential source of exposure, especially to children (Fenske et al., 1990; Gurunathan et al., 1998; Eskenazi et al., 1999). Pest control formulations sprayed indoors either directly adhere to, or are indirectly deposited on, furniture and surfaces in the home. Pesticides applied outdoors can be tracked inside and accumulate and linger on surfaces. Once indoors, pesticides are protected from environmental elements such as rain, sun, or microorganisms and are less likely to degrade (Simcox et al., 1995; Lewis et al., 1999). Thus, household surfaces and furnishings act as reservoirs for pesticides as well as other environmental contaminants (Bradman et al., 1997).

Children 1–4 years of age spend more than 20 h/day indoors (USEPA, 1997). During that time, normal activities of crawling and playing on the floor can result in exposure to contaminants (Lewis et al., 1994) through indirect ingestion routes associated with hand (or object)-to-mouth and surface-to-hand-to-mouth activities (Mukerjee, 1998). Also, and in addition to contaminants ingested directly with foods, there is the potential for excess dietary intake caused by food-to-surface-to-mouth or surface-to-hand-to-food activities (Melnyk et al., 2000). Therefore, exposure and risk assessments for children should focus on indoor environments (Silvers et al., 1994) and all potential pathways must be fully evaluated (NRC, 1993). The Food Quality Protection Act of 1996 requires such evaluations for pesticides registered in the United States.

Exposure of children to environmental contaminants is expected to vary from adults and in many cases can be higher (NRC, 1993; Bearer, 1995). Increased dietary exposures occur because children eat foods that have come into contact with the floor and other contaminated residential surfaces (Akland et al., 2000; Melnyk et al., 2000). Young children (1–6 years old) consume foods with their fingers as well as foods that have been picked up from the floor (NRC, 1993) and other contaminated surfaces. Their lack of basic hygiene patterns can contribute to higher dietary exposure (Freeman et al., 2001). The most commonly eaten finger-foods are apples, grain products (e.g., bread and crackers), cold cuts, cheese, and bananas (Freeman et al., 1997). Other differences in the behavior of children, especially in their interaction with the environment, that is, where they eat, time their food remains on a surface prior to ingestion, and amount of foods they eat from the surface, need to be assessed because these factors may have a profound effect on the magnitude of their dietary exposure.

Several studies have used videotaping to quantify children's behavior for specific activities (Zartarian et al., 1997; Reed, 1998; Akland et al., 2000). The frequency and duration of hand-to-surface and hand-to-food contacts, and time foods remain on surfaces prior to ingestion, are highly variable (Akland et al., 2000). Currently, such data on children's eating behaviors and their impact on excess dietary exposure caused by them are limited and total dietary exposures to pesticides cannot be fully assessed.

Historically, dietary exposure of an individual has been measured by duplicate-diet methods in which the individual prepares and collects duplicate portions of foods or meals eaten for a specified time (24–96 h) (Berry, 1997; Melnyk et al., 1997; Thomas et al., 1997; Cohen-Hubal et al., 2000). However, it is often difficult to collect duplicate-diet samples from a young child because they are less likely to consume food in a structured environment (Cohen-Hubal et al., 2000) and may instead sit on the floor or walk around while eating. Non-traditional exposure measurement techniques and exposure models are being refined for more accurate assessments of dietary exposures of children (Akland et al., 2000; Melnyk et al., 2000). A dietary exposure model proposed to estimate ingestion of pesticides by children (Akland et al., 2000) includes terms for both pesticides inherent to foods consumed and pesticides contaminating foods following transfer from surfaces to foods and hand to foods prior to consumption. Incorporated in the model are surface to food transfer coefficients for each of the latter terms. The magnitudes of these transfer coefficients have not been determined, but have been shown to be the most significant factor in estimating excess dietary exposures of young children (Melnyk et al., 2003).

This study was designed to measure the transfer of pesticides from common household flooring surfaces to foods as a first step in estimating the surface transfer coefficients needed to model a child's dietary intake of pesticides. An emphasis was placed on simulating conditions that occur with children in residential or day-care settings to better understand the measurements needed to improve assessments of children's dietary exposure in the context of aggregate exposure assessment. The foods chosen were common finger-foods that young children might ingest after contact with contaminated surfaces. The surfaces chosen were flooring materials often found in homes and day-care settings where pesticides are typically applied by spraying and would be potential sources of high contamination if foods were dropped before being eaten. The pesticides were chosen based on a combination of the following factors: (1) most frequently found in food samples from previous residential exposure studies (Berry et al., 1997, 2) high systemic toxicity or carcinogenic potential, (3) most often applied in 1998 in residential areas by pest control professionals, (4) applicability to a single analytical method, and (5) ones found in environmental samples from residential studies (Lewis et al., 1994; Bradman et al., 1997; Byrne et al., 1998).

The primary objective of this study was to evaluate transfer efficiency (TE) of pesticide contaminants available for transfer from various flooring surfaces to foods to determine the factors that have the most potential to impact dietary exposures of young children when foods are dropped on floors or similar surfaces before they are eaten. Pesticide transfer was determined after simulation of surface–food contact scenarios, including variable contact durations between foods and surfaces, and added forces on the foods contacting the surfaces, such as those occurring when children press on foods with their hands. Transfer efficiency was determined as the amount of pesticide transfer to a food after contact compared to the amount available on the surface, as measured by a surface wipe typical of those used to measure surface contamination in residential exposure studies.

Methods

The foods, flooring surfaces, and pesticides used in the transfer studies are shown in Table 1. The selection of dry and moist foods included red delicious apple slices, presliced packaged bologna, and American cheese slices. The flooring materials included low pile carpet, ceramic floor tile, and prefinished hardwood. Most of the pesticides were purchased from a local retail store and prepared as an emulsion in water following label instructions, as would a homeowner applicator preparing to spray. The pesticides used to contaminate the surfaces included diazinon, chlorpyrifos, malathion, and permethrin (cis and trans). Neat solutions of the pesticides heptachlor and isofenphos in methanol were included in the prepared mixture.

Table 1 Foods, flooring surfaces, and pesticides used for transfer efficiency measurements

Preparation of Samples

Food samples were purchased from a local grocery. When practical, multiple packages of a specific food item having the same lot number were purchased. Samples were prepared prior to contact with contaminated surfaces similar to how they might be given to a child to eat. Slices of cold bologna and cheese were taken directly from their packages. Apples were sliced to 1/16 in using a home-style food-slicing machine (Geka, West Germany) and seeds were removed. Hard surfaces (tile and hardwood) were cleaned with distilled water, dried and rinsed with 10 ml of acetone (Fisher, Fair Lawn, NJ) prior to use. No preparation was used for the carpet. The aqueous pesticide emulsion for contaminating surfaces was prepared daily and analyzed to verify pesticide concentrations. In order to achieve relatively similar concentrations of all active ingredients, 50 μl diazinon, 200 μl chlorpyrifos, and 25 μl malathion were pipetted from the store-bought supplies into a 100-ml volumetric flask and diluted to volume with reagent-grade water. This emulsion was verified to be stable for 6 h without significant change in concentration. A portion of this emulsion (500 μl) was pipetted along with 100 μl permethrins, 300 μl isofenphos, and 100 μl heptachlor into a separate volumetric flask and diluted to 50 ml. The final emulsion was stable for up to 4 h. Once applied to a surface, the pesticides ranged in concentration from 20 to 55 ng/cm2 (Table 1), which is compatible with the analytical instrumentation of the laboratory and also typical of levels, reported on indoor surfaces (43 ng/cm2; Gurunathan et al., 1998). Daily variations in individual pesticide concentrations occurred and were determined to be acceptable as long as the concentrations fell within the target concentration range for each pesticide (Table 1).

Transfer Experiments

Four replicates of a single surface type were arranged in a laminar flow hood (29 m/min) under the following conditions: 63±5% relative humidity (RH), 21±3°C, and room lighting only. To each replicate surface, 8 ml of the pesticide emulsion was applied to emulate spraying by a droplet-wise distribution technique using an eight-channel micropipettor (Finnpipette®, Labsystems, Franklin, MA). Approximately 20-μl-size drops were placed at 1-cm intervals to achieve uniform coverage across the entire surface. Contamination of replicate surfaces took place at 10–15 min intervals to allow experiments to occur after the same elapsed drying time. Replicate surfaces were fully dried as determined by visual observation after 2½ h±15 min, depending on RH. On high humidity days, testing was discontinued until RH conditions were met in the hood. Two of the dry replicate surfaces were used for food placement and two were wiped for surface residue determinations. Averages of the duplicate food and surface samples were used in TE calculations. Powder-free gloves and a clean work area were used to minimize interferences.

An isopropanol surface wipe method similar to those used previously to measure surface loading in residential exposure studies (Geno et al., 1996; Camann, 1998) was used to measure the pesticides available for transfer. Two, 3 cm × 3 cm × 12 ply sterile gauze pads (Dukal, Syosset, NY) were wetted with 10 ml isopropanol each (Fisher, Fair Lawn, NJ) and swiped six times horizontally then six times vertically with steady hand pressure across the entire surface. Two dry gauze pads using the same procedure followed wet wiping. The four gauze pads were combined for analysis.

The prepared food items were placed on the surfaces to fully cover as much of the surface as possible (approximately 50–60%) while leaving foods in whole slices. All foods were weighed prior to laying them onto the surface. Approximate weights of the bologna, apple, and cheese were 30, 15, and 20 g, respectively. Maximum coverage of the surface required two slices of bologna, four slices of cheese, and approximately nine slices of apple. The area covered by each food ranged from 208 to 260 cm2 and was recorded for each experiment in order to calculate a TE based on food contact area. Owing to the variability in apple sizes, the total area of apple slices covering each surface was determined as follows: (1) apple slices were weighed, (2) a circular section of known area was removed from an unused slice and weighed to determine the weight per unit area of the slice, and (3) the total contact area was calculated by dividing (1) by (2) and assuming a uniform apple density.

Contact Time and Applied Force

Each of the foods contacted each surface under standard conditions of 10 min contact duration with no additional contact force. Considering the high variability of potential contact times, 10 min was chosen as a realistic duration that a food could remain on a surface before being consumed by a child, although other durations (1 and 60 min) were tested to determine their influence. Hardwood flooring was the surface chosen for tests with varying contact duration and applied force. In order to demonstrate the effect of externally applied contact force to the foods, a weight (three clean, unused ceramic tiles weighing 1500 g) similar to that used in previously reported hand presses (Brouwer et al., 1999) was placed on top of each type of food for 1- and 10-min contact durations. After the designated contact conditions, the foods were removed from the surfaces and prepared for analysis.

Analysis of Samples

Figure 1 is a flow diagram depicting the details of the surface transfer measurement and sample analysis scheme. The procedures are briefly summarized as follows. After foods contacted surfaces under the specified conditions, they were removed from the surface and ground with equal parts by weight of hydromatrix (Varian, Harbor City, CA) to disperse the food for extraction using an automated accelerated solvent extractor (ASE-200, Dionex Corp., Sunnyvale, CA). Following extraction, the solvent (approximately 50 ml) containing pesticides required a two-step clean-up procedure (Rosenblum et al., 2001) using a 10-g alumina column (20 g for cheese). The resulting extract, with 50 μl of 4,4′-dibromobiphenyl (Chem Service, West Chester, PA) surrogate standard added, was concentrated to 0.5 ml on a Turbo Vap II evaporator (Zymark Corp., Hopkinton, MA) and solvent exchanged to ethyl acetate (Optima Grade, Fisher, Fair Lawn, NJ). After 25 μl of the 9,10-dichloroanthracene (DCA) (Aldrich Chemical Co., Milwaukee, WI) internal standard was added, analysis was by gas chromatography (GC) with an electron capture detector (ECD).

Figure 1
figure1

Flow diagram of transfer measurements and sample analysis scheme for pesticides on surfaces and foods.

The four combined gauze wipes with 50 μl surrogate standard were sonicated for 2 h, the solvent decanted into a Turbo Vap II vessel, and concentrated to 1 ml followed by a solvent exchange with ethyl acetate and addition of 25-μl internal standard. The ethyl acetate containing the pesticides was transferred after filtering through a 0.45 μm syringe tip filter (25 mm, PTFE, Gelman Laboratory, Acrodisk®, Fisher, Fair Lawn, NJ) into an autosampler vial for analysis by GC/ECD.

Gas Chromatography

The food and wipe samples were analyzed for the seven pesticides by capillary GC on a 0.32-mm (i.d.) × 30-m DB-5 fused silica column (J & W Scientific, Folsom, CA) with the ECD temperature at 300°C. The GC column temperature was programmed from 45°C to 300°C at 15°C/min with helium as a carrier gas.

Quantitative analyses were carried out using a six-point linear calibration curve and DCA as an internal standard. Calibration solutions containing all target pesticides at approximately equal concentrations (10 ng/μl) were diluted to concentration levels ranging from 0.1 to 2.5 ng/μl for instrument calibration. Pesticide standards (Absolute Standards, Inc., Hamden, CT) and surrogate and internal standards for calibration were prepared from certified solutions. An initial calibration curve was determined prior to the start of the study. During each day of analysis, a mid-level calibration standard of 0.5 ng/μl and a continuing calibration check standard of 1.0 ng/μl were analyzed after every 10 samples. Instrument calibration was considered acceptable if the concentrations for the check standard were within 25% of the initial calibration. The lowest calibration standard (0.1 ng/μl) was considered to be the method quantitation limit for each pesticide. Concentrations (ng/μl) acquired from GC/ECD analysis were converted to a food contact area basis (ng/cm2) for TE calculations.

Analysis of method blanks (foods and wipes) and spiked samples constituted 30% of the daily samples analyzed. Samples were spiked with 30 ng/g of each pesticide by direct addition to food samples and gauze wipes. Immediately after spiking, samples were extracted, cleaned up, and analyzed following the analysis scheme (Figure 1). Blanks of food samples were analyzed with every new lot or package of each food. Blank gauze wipes were analyzed with samples.

Surface Transfer Efficiency

Surface TEs for the foods contacting the surfaces were calculated as a percentage of the measured surface wipe concentration:

where Cf is the concentration of pesticide transferred to the food sample per unit contact area (ng/cm2) and Cs is the measured surface concentration (ng/cm2) determined from surface wiping. Transfer efficiencies defined in this manner were, therefore, specific for both contact duration and applied external force, as well as for specific foods, surfaces, and pesticides.

Results and discussion

Recovering Pesticides from Foods and Surfaces

Recoveries of pesticides from three to six spiked surface and food samples are summarized in Table 2. Mean recoveries of the organophosphate pesticides (diazinon, malathion, chlorpyrifos, and isofenphos) ranged from 78% to 105% and the organochlorine pesticide (heptachlor) ranged from 71% to 97%. The cis- and trans-permethrins were the lowest recovered, particularly from the high fat-containing foods, with a recovery range of 50–91%. Background levels of incurred pesticides were detected in some samples of each food type. Highest occurrences were diazinon and malathion in apples, ranging from 0.01 to 0.12 and 0.01 to 0.05 mg/kg, respectively, in about 50% of the samples. Food concentrations were corrected by subtracting background concentrations when detectable levels were found in blanks. Daily instrument verification using the calibration standards resulted in average relative standard deviations (RSD) within an acceptable range of less than 25%. Surrogate recoveries ranged from 66% to 120%.

Table 2 Mean pesticide recoveries (%) for spiked samples.

The pesticide emulsion was applied uniformly to the surfaces by pipette as small droplets because of space limitations and contamination and safety issues in the laboratory. After application, but before they were dried, the surfaces were similar in appearance to those that had been sprayed. Typically less than 50% of the applied pesticides were recovered from any surface by wiping (Table 3), with those from hard surfaces greatly exceeding carpet, and those from tile generally exceeding those from hardwood. Highest pesticide recoveries were from tile with diazinon (59%), chlorpyrifos (80%), and permethrins (52% cis; 53% trans) being the only pesticides recovered by wiping at greater than 50% of the applied concentrations. Lowest levels recovered from both tile and hardwood were heptachlor (7.2% and 5.6%, respectively). Despite high recoveries from spiked surface wipes, little heptachlor was recovered from surface wipes and therefore, little was available to transfer to food. This was possibly due to either volatilization and/or dissipation from the surface or reactivity with the surface itself. Traces of all pesticides were recovered by wiping the carpet, but were at 1% or lower of applied concentrations, and recoveries were highly variable. The carpet fibers may have absorbed the pesticides making them unremovable by the surface wipes. Similar results have been found for carpet with less than 1% of chlorpyrifos applied by broadcast application directly to carpet recovered by wiping (Lu and Fenske, 1998).

Table 3 Mean recoveries of pesticides applied to surfaces by surface wiping (%).

Pesticides Transferred from Surfaces to Foods

The concentrations of pesticides (ng/cm2) measured in each food based on the area contacting the three contaminated surfaces are summarized in Tables 4, 5 and 6. For all foods, as with surface wiping, the amount of heptachlor detected from surface transfer was near or below the quantitation limit (BQL). Low levels of heptachlor in foods also may be due to analytical limitations, but most likely because only low levels were available on surfaces for transfer (Table 3). Relatively low recoveries of the permethrins were also noted in foods, particularly for cheese, and possibly because of similar phenomena. Since pesticide recoveries from surfaces were highly variable, and, for some pesticides and surfaces, the standard deviation (SD) from multiple wipes was higher than anticipated, TE calculations (Eq. (1)) were based on average concentrations measured for duplicate foods and duplicate surface wipes within the daily, four-surface set.

Table 4 Pesticide concentrations in surface wipes and foods and mean transfer efficiencies (TE) after contact with contaminated ceramic tile.a
Table 5 Pesticide concentrations in surface wipes and foods and mean transfer efficiencies (%TE) after contact with hardwood flooring.a
Table 6 Pesticide concentrations in surface wipes and foods after contact with contaminated carpet.a

TE was determined for each pesticide, food, and surface combination. Mean TE and SD were also calculated for each food and for each pesticide, and a overall mean for all foods and pesticides was calculated for each surface (Tables 4 and 5). When a food sample had no measurable transfer of pesticides (BQL), zero was assumed in all subsequent calculations. If the surface residue from wiping could not be determined (i.e., non-quantifiable carpet wipes), the transfer could not be calculated, and these values were omitted (Table 6).

Table 4 summarizes pesticide concentrations for duplicate food samples after contact with the ceramic tile surface and concentrations wiped from duplicate tile surfaces. Agreement between duplicate samples is generally good, although SD for the mean TE is moderately high. Pesticides transferred to bologna and apple from tile generally exceeded 4 ng/cm2 for diazinon, malathion, chlorpyrifos, isofenphos, and the permethrins. For cheese, malathion was transferred most readily and was comparable to the other foods (average of 8.4 ng/cm2), but all other pesticide concentrations were less than 3.5 ng/cm2. Quantifiable levels of permethrins were not transferred to cheese from tile. Transfers of heptachlor to all foods were much lower (0.38–0.92 ng/cm2) as a result of lower levels available for transfer from the tile surface (0.86–2.5 ng/cm2), as previously discussed. Variations in concentrations of pesticides transferred are possibly attributable to one or more of the following factors: pesticide volatility and surface interactions, physical characteristics of foods (i.e., moisture and fat content), method of extraction and clean-up, degradation in the instrument injector port, or from combining all pesticides into a single mixture.

Pesticides transferred from hardwood flooring to the three foods are summarized in Table 5 and are generally similar to those from tile. Substantial variation in the mean TE for the three foods occurred among pesticides on both hard surfaces as evidenced by moderately high SD for all but bologna. Cheese TE had the highest relative SD for both hard surfaces. Diazinon, malathion, and isofenphos were most readily transferred from both hard surfaces to each food, with mean TE always exceeding 31%, to as high as 91% for malathion from tile (Table 4). The mean TE of all pesticides to each food was greater from tile than from hardwood (Tables 4 and 5), with cheese being the possible exception. TE for bologna and apple exceeded that for cheese for the tile surface, but that was not a consistent trend for hardwood. Notable differences when comparing the two hard surfaces occurred for malathion and isofenphos. Malathion TE was 91% from tile, but only 31% from hardwood. On the other hand, diazinon TE was 32% from tile and 59% from hardwood. Mean TE of the permethrins from hardwood was consistently low (averaging 5%). The overall mean TE values of all pesticides from hardwood to apple (23%) and cheese (29%) were similar, while that of bologna was lower (15%). The results support the general conclusion that the overall mean TE (average of means for seven pesticides to the three foods) was greater from tile (35%) than from hardwood (22%) the three foods tested.

The only pesticide transferred from carpet detected above analytical limits (Table 6) was malathion to cheese and apple (avg. 0.59 and 0.79 ng/cm2, respectively). None of the applied pesticides were transferred from carpet to bologna. Wipes of the carpet yielded pesticide concentrations less than 0.50 ng/cm2, and very near or below (BQL) the analytical quantitation limits. The low (0%), high (greater than 100%), and indeterminate (when wipes are BQL) TEs that would be calculated from these low values are, therefore, neither reliable nor meaningful values. Whereas the wipe procedure seems to be a logical choice, different methods may be needed to determine availability of pesticides on carpet as a basis for TE. This is particularly relevant if pesticides are particle bound, as opposed to sprayed residues.

Figure 2 graphically summarizes the mean TE (±SD) for all pesticides for the three foods and the two hard surfaces. Three conclusions are noted: (1) for two of the three foods (bologna and apple), pesticides transferred were highly dependent on the surface, (2) pesticides transferred to cheese were similar for the two surfaces, but were more variable, and (3) pesticides transferred from tile more readily than from hardwood. Water contents of apple, bologna, and cheese are 84%, 54%, and 39%, respectively (USDA, 1999) and may be relevant in explaining why transfers of pesticides are different. The foods of a sticky and/or moist nature (bologna and apple), in contrast to the drier cheese, did not appear to be a factor related to TE for these surfaces and pesticide application procedures. Similarly, both bologna and cheese contain fat, which also did not appear to be a dominant factor in the transfer of pesticides. In summary, under similar conditions of contact duration and without external applied force, there appears to be no dominant physical factor influencing TE for the hard surfaces and foods tested.

Figure 2
figure2

Mean transfer efficiency (%) ±1SD for all pesticides from hard surfaces to foods (10 min contact duration with no applied force).

Effect of Contact Duration

Contact durations of 1 and 60 min on hardwood flooring were used to determine if the length of time that foods remain in contact with a surface affects the transfer of pesticides (Table 7). After 1 min contact, few pesticides on bologna, cheese, and apple were detected above the quantitation limits. Only low levels for chlorpyrifos (0.60 ng/cm2 for one cheese sample and 0.66 ng/cm2 for one apple sample) and isofenphos (0.3 ng/cm2 for both cheese samples) were detected. However, after 60 min of contact, much more of each pesticide was transferred to each food, ranging from a low of 0.44 ng/cm2 (heptachlor to apple) to 23 ng/cm2 (malathion to bologna). The 1- and 60-min measurements also bracket the data for 10- min contact duration (Table 5). Mean TE for each pesticide increased from essentially zero for 1- min contact to at least 35% (trans-permethrin) for a 60-min contact. The overall mean TE after 1 min was less than 1%, increasing to 22% after 10-min (Table 5), and to 67% after 60-min contact duration.

Table 7 Effect of contact duration on the transfer of pesticides from hardwood flooring to foodsa

Effect of Contact Force

Applying a contact force of 1500 g to each food on hardwood flooring for 1 and 10 min was evaluated for its effect on transfers of pesticides (Table 8). After a 1 min contact, the applied force had caused a considerable increase in the transfer of all pesticides except heptachlor, again because of low heptachlor levels available on the surface, as previously discussed. Applying a force increased transfers after 1 min from non-detectable (Table 7) to detectable levels (Table 8) for four of the seven pesticides to bologna (chlorpyrifos, isofenphos, and cis- and trans-permethrin) and six of the seven pesticides to apple (diazinon, malathion, chlorpyrifos, isofenphos, and cis- and trans-permethrin). Applying force for 1 min to cheese resulted in insignificant, if any, additional transfer of pesticides, except for malathion. Overall TE of all pesticides from hardwood after 1-min contact increased with applied force, from 0% to 6% for bologna, from 1% to 2% for cheese, and from 1% to 6% for apple.

Table 8 Effect of applied contact force (1500 g) on the transfer of pesticides from hardwood flooring to foods.

The effect of applied force was even more dramatic as contact duration increased (Table 8). For each pesticide, mean TE to all foods increased from 1-to 10-min contact duration with applied contact force. Highest increases were found for diazinon (2–36%), malathion (4–63%), isofenphos (8–72%), and cis- and trans-permethrins (4–34% and 4–33%, respectively). Applying contact force for a 10-min duration increased TE for all pesticides from hardwood flooring to bologna from 15% (Table 5) to 70% (Table 8), to cheese from 29% to 38%, and to apple from 23% to 26%.

Figure 3 combines, graphically, the influence of both contact time and applied force on mean TE for all pesticides to the three foods for a visual illustration of the influence of these factors. Applying force had a similar effect as increased contact duration in increasing TE for all foods, although it was less dramatic for apple.

Figure 3
figure3

Mean transfer efficiency (%) ±1SD for all pesticides from hardwood to various foods with varying contact duration and with and without applied force (1500 g).

Conclusions

The primary purpose of this study was to determine the degree to which common pesticides transfer to foods upon contact with typical household flooring surfaces that have been contaminated by an aqueous emulsion of a variety of residential-use pesticides. It was found that, under certain defined laboratory conditions, pesticides transfer readily to foods that come into contact with contaminated hard flooring surfaces, similar to those found in homes or day-care facilities. Most significant were organophosphate pesticides, which were shown to transfer more readily than cis- and trans-permethrin or heptachlor. For aqueous applied pesticides, hard floors, as compared to soft carpet, were the more important surfaces for contaminating foods. Overall mean TE values for all pesticides and foods were 35% and 22% for the hard surfaces tested (ceramic tile and hardwood flooring, respectively). Carpet is probably not an important source of contamination to foods from aqueous applied pesticides because most concentrations measured were near the quantitation limits for the pesticides wiped from carpet or recovered from foods after contact with carpet. Both contact duration and applied contact force notably increased TE for the hard surfaces, thus demonstrating the need to include these variables when defining TE. Understanding and determining TE is the first step in assessing children's dietary exposure from handling and eating foods that have contacted surfaces. The TE measurements provided by this study will be used as input parameters for modeling children's total dietary intake (Akland et al., 2000; Melnyk et al., 2003).

The TE defined for this study was based on surface wiping because surface wipes are the current generally acceptable measure of surface contamination in residential exposure studies. It should be noted that pesticides applied to surfaces were not generally recovered at applied levels by wiping the surfaces. Therefore, an improved method for measuring pesticide residues on surfaces, a better understanding of pesticide dynamics after application to surfaces, or both, is needed for more accurate evaluations of pesticides available on surfaces. Once a standard surface measurement is defined, a standardized definition of TE should be defined.

Further investigations examining current-use pesticides that have been directly applied to surfaces for their potential to transfer to foods are underway, and are focused on both flooring and other hard surface materials, such as those used for counters and table-tops, as well as soft surfaces, such as table cloths and upholstered furniture. Activity patterns of eating behaviors for children, in particular the time foods remain on a surface prior to consumption, and the contact force applied to foods by the child's hand, need to be understood when evaluating exposures of children to pesticides.

This study is one of the first investigations of its type to provide data on pesticides transferred from surfaces to foods. As such, it had several factors worthy of mention that limit the use of the TE measurements. The experiments were conducted subject to several laboratory constraints, and residential environments will vary from these conditions. Additional research is warranted to confirm the pesticide transfers from surfaces to foods in residential settings and to expand the food/surface combinations so as to better understand the important transfer scenarios. Only one pesticide concentration was applied and its effect on TE is not known. Transfers of dust-laden or particle-bound pesticides, as opposed to pesticides applied in an aqueous emulsion, need to be evaluated for a complete assessment of TE from surfaces and their potential for increasing dietary exposures of young children.

Abbreviations

ASE:

accelerated solvent extraction

BQL:

below quantitation limit

DCA:

9,10-dichloroanthracene

ECD:

electron capture detector

GC:

gas chromatography

QA:

quality assurance

QC:

quality control

RH:

relative humidity

RSD:

relative standard deviation

TE:

transfer efficiency

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Acknowledgements

The U.S. Environmental Protection Agency through its Office of Research and Development collaborated in the research, described here under NERL 98-01 to the Postgraduate Research Participation Program at the National Exposure Research Laboratory administered by the Oak Ridge Institute for Science and Education, through an interagency agreement between the U.S. Department of Energy and the U.S. Environmental Protection Agency.

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Correspondence to Maurice R Berry.

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The U.S. Environmental Protection Agency through its Office of Research and Development funded and managed the research described in this paper. It has been reviewed in accordance with the Agency's peer and administrative review policies and approved for publication. Mention of trade names or commercial products does not constitute an endorsement or recommendation for use.

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Rohrer, C., Hieber, T., Melnyk, L. et al. Transfer efficiencies of pesticides from household flooring surfaces to foods. J Expo Sci Environ Epidemiol 13, 454–464 (2003). https://doi.org/10.1038/sj.jea.7500300

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Keywords

  • dietary exposure
  • pesticides
  • children
  • surface transfer
  • transfer efficiency
  • contact duration
  • contact force.

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