Exposure apportionment: ranking food items by their contribution to dietary exposure.

This paper identifies and ranks food items by estimating their contribution to the dietary exposure of the US population and 19 subpopulation groups. Contributions to dietary exposures to arsenic, cadmium, chromium, lead, nickel, benzene, chlorpyrifos, and diazinon are estimated using either the Dietary Exposure Potential Model (DEPM) approach, the National Human Exposure Assessment Survey Arizona (NHEXAS-AZ) approach or the combination of the two. The DEPM is a computer model that uses several national databases of food consumption and residue concentrations for estimating dietary. The DEPM approach ranks the contribution of food items to the total dietary exposure using two methods, the direct method that ranks contributions by population exposure magnitude and the weighted method that ranks by subpopulation exposure magnitude. The DEPM approach identifies highly exposed subpopulations and a relatively small number of food items contributing the most to dietary exposure. The NHEXAS-AZ approach uses the NHEXAS-AZ database containing food consumption data for each subject and chemical residues of a composite of food items consumed by each subject in 1 day during the sampling week. These data are then modeled to obtain estimates of dietary exposure to chemical residues. The third approach uses the NHEXAS-AZ consumption data with residue values from the national residue database. This approach also estimates percent contributions to exposure of each ranked food item for the Arizona population. Dietary exposures estimated using the three approaches are compared. The DEPM results indicate groups with highest dietary exposures include Nonnursing Infants, Children 1-6, Hispanic, Non-Hispanic White, Western, Northeast and Poverty 0-130%. The use of the Combined National Residue Database (CNRD) identifies 43 food items as primary contributors to total dietary exposure; they contribute a minimum of 68% of the total dietary exposure to each of the eight chemical residues. The percent contribution of ranked food items estimated using the NHEXAS samples is smaller than those obtained from the western US population via the DEPM. This indicates differences in consumption characteristics of the two groups with respect to the ranked food items. Six of 15 food items consumed by the NHEXAS-AZ subjects per day are ranked food items contributing between 56% and 70% of the estimated NHEXAS-AZ dietary exposure to each of the eight chemical residues. The difference between total dietary exposure estimates from the DEPM and NHEXAS-AZ approaches varies by chemical residue and is attributable to differences in sampling and analytical methods, and geographic areas represented by the data. Most metal exposures estimated using the NHEXAS consumption data with the CNRD have lower values than those estimated via the other approaches, possibly because the NHEXAS-AZ residue values are higher than the CNRD values. In addition, exposure estimates are seemingly affected by the difference in demographic characteristics and factors that affect types and amounts of food consumed. Efficient control strategies for reducing dietary exposure to chemical residues may be designed by focusing on the relatively small number of food items having similar ingredients that contribute substantively to the total ingestion exposure.

Children's exposure assessment: a review of factors influencing Children's exposure, and the data available to characterize and assess that exposure.

We review the factors influencing children's exposure to environmental contaminants and the data available to characterize and assess that exposure. Children's activity pattern data requirements are demonstrated in the context of the algorithms used to estimate exposure by inhalation, dermal contact, and ingestion. Currently, data on children's exposures and activities are insufficient to adequately assess multimedia exposures to environmental contaminants. As a result, regulators use a series of default assumptions and exposure factors when conducting exposure assessments. Data to reduce uncertainty in the assumptions and exposure estimates are needed to ensure chemicals are regulated appropriately to protect children's health. To improve the database, advancement in the following general areas of research is required: identification of appropriate age/developmental benchmarks for categorizing children in exposure assessment; development and improvement of methods for monitoring children's exposures and activities; collection of activity pattern data for children (especially young children) required to assess exposure by all routes; collection of data on concentrations of environmental contaminants, biomarkers, and transfer coefficients that can be used as inputs to aggregate exposure models.

Factors influencing total dietary exposures of young children.

A deterministic model was developed to identify the critical input parameters needed to assess dietary intakes of young children. The model was used as a framework for understanding the important factors in data collection and data analysis. Factors incorporated into the model included transfer efficiencies of pesticide from surfaces to food, transfer efficiencies of pesticide from surfaces to hands to food, and more accurate microactivity data related to contact frequency for the three variables of interest--hands, surfaces, and food. Results from range-finding measurements of transfer efficiencies using an aqueous pesticide solution of a mixture of malathion, diazinon, and chlorpyrifos sprayed on the surfaces indicate that a higher pesticide transfer occurred from hard surfaces to food (hardwood, plastic), with low transfer from soft surfaces (carpet, cloth). Six children, all less than 4 years old, were videotaped to obtain realistic contact frequency and times for the interaction of hands, surfaces, and foods during eating meals and snacks while in their homes or day care centers. The time range of eating events varied from about 2 to 55 min, with an average of about 20 min. The average number of contact frequencies between food and hands was 19 times for each eating event, with a range of 10-40. Contacts between the surface and hand were about the same as the food and hands. Contacts between foods and surfaces ranged from 0 to 32, but only five or less of the contacts per eating event were associated with surfaces other than eating utensil. The children's microactivity data collected during the eating events, together with the laboratory results from the transfer studies, were provided as input into a Monte Carlo simulation of the dietary ingestion model. Simulation results indicate that children's handling of the food could contribute 20-80% of the total dietary intake of pesticides. Dietary exposure due to residues in the food before handling accounted for 16% and 47%, respectively, of the total mean intake from simulations for a child's consumption of an apple or banana. These results indicated that transfer efficiencies for foods on various surfaces typically found in homes as well as children's hand contacts with the food and surfaces are important as determinants of dietary exposure.

Dietary exposure of children in lead-laden environments.

Children are the most susceptible population to lead exposure because of three interacting factors; they have more opportunity for contact with lead sources due to their activities, lead absorption occurs more readily in a child compared to an adult, and the child's development is more vulnerable to lead than adults. Low levels of lead in the blood have been shown to cause adverse health effects; the level of concern for children is currently 10 microg/dl. The contribution of dietary exposure of lead to increased blood lead levels (PbB) is not well characterized. This study was conducted to measure potential dietary lead intakes of children 2 to 3 years of age who live in homes contaminated with environmental lead. Objectives were to estimate lead intakes for children consuming food in contaminated environments, recognizing unstructured eating patterns and to investigate if correlations exist between daily dietary exposure and measured PbB. Dietary exposure was evaluated by collecting samples that were typical of the foods the young children ate in their homes. A 24-h duplicate of all foods plus sentinel foods, i.e., individual items used to represent foods contaminated during handling, were collected from 48 children. Ten homes were revisited to obtain information on the variation in daily dietary intakes. Drinking water was evaluated both as part of the segregated beverage sample composite and by itself. Additional information collected included lead concentrations from hand wipes, floor wipes, and venous blood, and questionnaire responses from the caregiver on activities potentially related to exposure. Activities and hygiene practices of the children and contamination of foods in their environment influences total dietary intake. Estimated mean dietary intakes of lead (29.2 microg Pb/day) were more than three times the measured 24-h duplicate-diet levels (8.37 microg Pb/day), which were almost six times higher than current national estimates (1.40 microg Pb/day). Statistically significant correlations were observed between floor wipes and foods contacting contaminated surfaces, hand wipes and foods contacting contaminated hands and surfaces, and hand wipes and floor wipes. This study indicates that the dietary pathway of exposure to lead is impacted by eating activities of children living in lead-contaminated environments and that analysis of foods themselves is not enough to determine excess dietary exposures that are occurring.

Population-based dietary intakes and tap water concentrations for selected elements in the EPA region V National Human Exposure Assessment Survey (NHEXAS).

A National Human Exposure Assessment Survey (NHEXAS) field study was performed in U.S. Environmental Protection Agency (EPA) Region V, providing population-based exposure distribution data for selected elements in several personal, environmental, and biological media. Population distributions are reported for the 11 elements that were measured in water and dietary samples. Dietary intakes and home tap water concentrations of lead, arsenic, and cadmium were further examined for intermedia associations, for differences between dietary exposure for adults and children, and to estimate the proportion of the population above health-based reference values (dietary) or regulatory action levels or maximum contaminant levels (water). Water lead and arsenic concentrations were significantly associated with dietary intake. Intake of all elements was higher from solid foods than from liquid foods (including drinking water). Dietary intakes of Pb, As, and Cd were greater than those calculated for intake from home tap water or inhalation on a microg/day basis. Median dietary intakes for the Region V population for Pb, As, and Cd were 0.10, 0.13, and 0.19 microg/kg bw/day, respectively. While Pb, As, and Cd concentrations in the foods consumed by 0 to 6-year-old children were similar to or lower than those for adults, dietary intakes calculated on a body weight basis were 1.5 to 2.5 times higher for young children. Intrapersonal intake differences accounted for most of the variance in short-term (daily) dietary intakes for Pb and As, while interpersonal differences accounted for more of the intake variance for Cd. Only small percentages of the population exceeded health-based intake reference values or concentrations equal to regulatory levels in water for Pb, As, and Cd.

Advances in dietary exposure research at the United States Environmental Protection Agency-National Exposure Research Laboratory.

The United States Environmental Protection Agency-National Exposure Research Laboratory's (USEPA-NERL) dietary exposure research program investigates the role of diet, including drinking water, as a potential pathway of human exposure to environmental contaminants. A primary program goal is to establish measurement methods for ingestion that are consistent with approaches used by the USEPA to measure inhalation and dermal exposures, and, hence, total exposure. Research has focused on developing and field-testing measurement methods for personal dietary monitoring, known as duplicate-diet methodology, and on the methods to support analyses of environmental contaminants in foods and beverages. Guidance for measuring personal dietary exposure has been developed for the researcher performing measurements in which there is an established or potential route of exposure to environmental contaminants from foods consumed. Useful information for other types of dietary exposure assessment can be found in existing food consumption and food residue databases. Several of the major food databases have been integrated into an exposure model that provides estimates of potential dietary exposure and identifies potentially highly exposed people for guidance in exposure monitoring. Another component of this research program explores priority, diet-related issues to identify and reduce exposures from foods and beverages. The methods of preparing mercury-contaminated fish by Native Americans and children exposed to lead-laden environments are currently under investigation. Other research is designed to improve our understanding of the process of excess food contamination and the reduction of dietary exposure. Additional research needs are summarized. An overview of the USEPA-NERL dietary exposure program is presented and research discussed in this paper is described in the following papers in this issue.

Testing duplicate diet sample collection methods for measuring personal dietary exposures to chemical contaminants.

Dietary ingestion may be a significant pathway of human exposure to many potentially toxic chemicals. The U.S. Environmental Protection Agency-National Human Exposure Laboratory has made the development of methods for measuring personal dietary exposures a high priority for its dietary exposure research program. Of particular interest was the testing of methods that could be applied in the general population as one component of multipathway exposure measurement studies. This paper describes a controlled pilot study that was conducted to evaluate procedures for collecting and processing duplicate diet samples. Nine adult and three child participants volunteered to provide dietary information for 28 days, and duplicate portions of all foods consumed daily for seven consecutive days. Sample collection procedures were evaluated for participant collection and segregation of solid and liquid foods, and for identification and separation of high-fat and low-fat foods. Methods for compositing and homogenizing mixed diet samples were tested. Food records and questionnaires were tested to document the collected food and to evaluate procedures for assessing dietary changes and collection bias. Participant time and monetary needs were evaluated along with the approach for training and providing support to study participants. Participants were able to collect 96% of the meals they consumed, even with 33% of the meals consumed away from home. Food consumed in social settings was the most difficult to collect, and participants were unable or unwilling to collect foods in some social settings. Noncollection of meals and food items increased after the third day of collection. Mixed diet samples were successfully homogenized, with 1%-11% mean relative standard deviations for moisture, fat, protein, and ash analysis in replicate sample aliquots. The laboratory-measured caloric content of collected foods was an average of 12% (range: -24% to 36%) lower than estimates of energy intake using a food diary and 16% lower than estimated energy expenditure values.

Dietary exposure from pesticide application on farms in the Agricultural Health Pilot Study.

As part of total human exposure measurements performed on six farms in Iowa and North Carolina during the Agricultural Health Pilot Study, a household duplicate diet, several locally grown foods, an applicator meal, a child duplicate diet, and drinking water samples were collected. The pilot study was designed to test refined and newly developed protocols and analytical methods for collection and analyses of dietary samples to evaluate dietary exposure to farmers and their families in the household associated with current and former applications of pesticides. The household duplicate diet protocol was generally effective as a first step in measuring potential exposures of household members. The analytical methods used were capable of measuring 29 of the 33 targeted Agricultural Health Pilot Study pesticides in dietary samples. Collections were made during a pesticide nonapplication and application monitoring period. Pesticides in the foods and beverages of the participants were quantified at sub-ppb to 30-ppb levels in both the Iowa and North Carolina farms. Increased levels (20 ppb) of the pesticide being applied during the monitoring period were found in the applicator's meal. Dieldrin was persistent in the foods consumed on one Iowa farm. No pesticides were found in drinking water samples. The results show potential dietary exposures exceeding expected values exist to the farmers and their families for several of the pesticides in this study, particularly to those being applied and to the persistent pesticides in the environment.

Development of a Dietary Exposure Potential Model for evaluating dietary exposure to chemical residues in food.

The Dietary Exposure Potential Model (DEPM) is a computer-based model developed for estimating dietary exposure to chemical residues in food. The DEPM is based on food consumption data from the 1987-1988 Nationwide Food Consumption Survey (NFCS) administered by the United States Department of Agriculture (USDA) and on residue data from government-sponsored monitoring programs. Foods reported in the NFCS were categorized into exposure core foods (ECFs). A computer program for DOS-based personal computers was developed to link consumption of the ECFs with residue values observed in the foods. The data files utilized by the DEPM were designed in dBASE IV with FoxPro for Windows applications programs for queries and reporting. The program calculates exposure estimates for categories of core foods, such as grain dishes, fruits, or vegetables; for individual core foods, such as wheat and apple combination dishes; and for individual foods, such as apples or carrots. The program, residue summary databases, and core food consumption database permit the analyst to evaluate potential exposure of several population groups to various chemicals via the diet. The DEPM is not intended for risk assessments, but is a suitable tool for identifying data gaps and establishing priorities for research, and for identifying potentially significant foods for human exposure monitoring.

Effects of commonly used cooking practices on total mercury concentration in fish and their impact on exposure assessments.

The effects of cooking practices commonly used by Native Americans on total mercury concentrations in fish were investigated. A preparation factor relating mercury concentrations in fish as prepared for consumption to mercury concentration data as measured in typical environmental monitoring programs was calculated. Preparation factors are needed to provide risk assessors with a more accurate estimate of the actual amount of mercury ingested through consumption of contaminated fish. Data on fish preparation and consumption practices of two communities of Chippewa residing on the shores of Lake Superior in northern Wisconsin were used to select practices for study. The most commonly consumed species, walleye and lake trout, were selected. Whitefish livers were also selected for study. Commonly used cooking techniques including panfrying, deep-frying, baking, boiling, and smoking were duplicated in the laboratory. Total mercury concentrations were determined in fish portions before and after cooking and in a portion representative of that analyzed in programs to assess water quality (skin-on fillets). Total mercury was determined by microwave digestion-cold vapor atomic absorption spectroscopy. Mercury concentrations (wet weight basis) in panfried, baked, and boiled walleye fillets and deep-fried and baked whitefish livers ranged from 1.1 to 1.5 times higher than in corresponding raw portions. In lake trout, mercury concentrations were 1.5 to 2.0 times higher in cooked portions than in the raw portion. However, total mercury levels were constant before and after cooking, indicating the concentration effect is caused by weight (moisture and fat) loss. The addition of lemon juice to potentially release mercury from its bound state and promote volatilization did not exert any measurable influence on mercury concentrations in cooked walleye. In some cases mercury concentrations were increased with increased cooking times due to further loss of moisture and fat. Preparation factors (defined as the ratio of mercury concentration in cooked fish to the mercury concentration in the environmental portion) ranged from 1.3 to 2.0. Results suggest that consideration be given to the use of preparation factors in risk assessments, exposure assessments, or issuance of fish advisories where mercury concentration in raw fish tissue are used in conjunction with cooked fish meal sizes.

Alternate iron transport pathway. Mobilferrin and integrin in K562 cells.

A transferrin-independent iron transport system in cells containing transferrin receptors was described previously by several investigators. Prior studies did not identify the proteins involved in this alternate iron transport pathway. Using a human-derived erythroleukemia tissue culture line, iron-binding proteins were isolated from cytosol and cell membranes. The cytosol protein was soluble in 60% ammonium sulfate, had a molecular mass similar to mobilferrin (56 kDa), and reacted with anti-mobilferrin antibodies. The water-insoluble radiolabeled protein was solubilized with Nonidet P-40 and immunoprecipitated with monoclonal antibody against beta 3 human integrin. Pulse-chase studies suggested sequential passage of iron to integrin, mobilferrin, and ferritin, respectively. Thus, the alternate iron transport pathway contained proteins similar to those observed in intestinal cells which did not possess transferrin receptors on their absorptive surface. The alternate iron transport pathway is only partially shared with zinc and cadmium. Mobilferrin bound zinc and iron competitively, but the two metals were not transported competitively into K562 cells. Immunoprecipitates of integrin containing radiozinc were obtained with a monoclonal antibody against beta 1 human integrin. This suggested iron and zinc may utilize different integrins to passage the cell membrane.

The effects of a liquid diet on initial and sustained, stimulated parotid salivary secretion and on parotid structure in the rat.

Adult male rats were maintained on a nutritionally adequate liquid diet, or laboratory chow and water (controls), for 7 days. They were then anaesthetized and parotid flow was recorded after isoprenaline or pilocarpine stimulation, each collected over two, timed sampling periods--an initial 5 min and a subsequent 15 min. The isoprenaline-induced flow rates in liquid diet rats were reduced to 45 and 30% of those in control rats for the first and subsequent samples respectively (p less than 0.02). After pilocarpine stimulation there were no significant differences in the first samples, but in the subsequent samples the flow rate in liquid diet rats was reduced to 54% of that in controls (p less than 0.001). The parotid gland weights were reduced by 35% in liquid diet rats compared to controls (p less than 0.05). On computerized planimetric analysis, parotids (from rats that had not been given secretagogues) had significantly smaller mean acinar areas, mean acinar profile perimeters and mean acinar transection diameters after liquid feeding (p less than 0.001). The findings support the notion that there is a functional reserve capacity available in atrophied glands to support the relatively fast flow that occurs on initial stimulation but which becomes exhausted during sustained stimulation. This exhaustion occurs more severely and more rapidly in the low-volume, protein-rich saliva elicited by sympathomimetic stimulation than in the high-volume, low-protein saliva formed in response to parasympathomimetic stimulation.

Functional and structural adaptation of the parotid gland to medium-term chronic ethanol exposure in the rat.

Male rats were maintained on a regimen of twice daily intragastric administration of ethanol or a calorifically equivalent sucrose solution for thirty days. A second control group received no intragastric solution and all groups received chow and water ad libitum. Parotid saliva elicited by pilocarpine was collected by unilateral duct cannulation. The parotid flow rate over the initial post-stimulatory five minute period was raised by 44% in ethanol-dosed rats and the salivary sodium concentration was also raised, in line with higher flow rate. There were no histopathological changes related to ethanol or sucrose dosing, but stereological analysis showed a 64% increase in the proportional volume of intralobular vascular tissue in ethanol-dosed rats. These quantified histological findings suggest that parotid intralobular haemodynamics may be altered after chronic ethanol-dosing and this may contribute to the hypersecretory response exhibited by the ethanol-dosed rats.

Establishing the Heat-Preservation Process For Aseptically-Packaged Low-Acid Food Containing Large Particulates, Sterilized in a Continuous Heat-Hold-Cool System 1.

"Aseptic" is the shorthand name for the food production system where product moves in continuous flow through a heat-hold-cool thermal process and is then filled into a sterile package. The package is sterilized, filled, and sealed in a sterile environment. Today, both acid and low-acid homogeneous liquid foods are produced by aseptic systems; low-acid foods that contain particulates in a liquid vehicle may be produced soon. The principles for establishing a heat preservation process for low-acid foods that contain particles larger than 5 mm in diameter and are to be sterilized continuously in a heat-hold-cool system are described. Only product sterilization, which is just one part of the aseptic system, is addressed. The term "heat-hold-cool" identifies the system used to achieve microbial control of the product.

Effects of acute ethanol administration on stimulated parotid secretion in the rat.

Young adult male rats previously never exposed to ethanol were given a single dose of 4 ml of 35% (v/v) ethanol in water by direct intragastric intubation (approximate weight related dose = 5.2 g/kg). Control rats were given distilled water in the same volume by the same route or were given no intragastric fluids. After administration of Valium-Hypnorm anesthesia, parotid salivary secretion was stimulated by subcutaneous pilocarpine HCI (10 mg/kg), and accurately timed samples were collected. No differences were recorded in the rate of salivary flow during the initial (5-min) high-flow phase of secretion, but during the subsequent 25-min phase of secretion the output in ethanol-treated rats was depressed by 60% compared to controls (p less than 0.01). Furthermore, electrolyte analyses of this saliva indicated that salivary ductal resorptive activity might be diminished in the presence of high blood ethanol. However, when rats were previously habitually exposed to ethanol at a twice daily dose of 4 ml of 35% (v/v) ethanol in water, the inhibitory action of acute ethanol administration was abolished. Moreover, in these rats there was significantly depressed [Na+] in both high-flow and low-flow saliva samples (p less than 0.01) with little change in [Na+] occurring at higher flow rates. This suggests the possibility of enhanced ductal resorption developing in rats exposed to long-term ethanol feeding.

Chloride handling by submandibular cells from young and old rats with and without duct ligation.

To examine the relation between structure and function in aging salivary glands, we have studied the duct-ligated submandibular gland of rats. Following 5-8 days ligation, glands from young (7-8 months) and old (21-23 months) rats exhibited approximately 90% loss in proportional volume of acinar cells. Most remaining epithelium was highly abnormal. No significant differences were detected in the ability of cells prepared from young and old animals, either control or ligated, to flux 36Cl-. Both basal uptake and muscarinic-cholinergic stimulated release were comparable.

The effects of chronic ethanol administration on stimulated parotid secretion in the rat.

Young adult male rats were maintained on a regimen of twice daily intragastric administration of 4 ml of 35% (v/v) ethanol in water (daily dose approximately 7.0 g/kg) or 4 ml of calorifically equivalent sucrose solution over approximately 100 days. A second control group received no intragastric solutions. Under Valium-Hypnorm anaesthesia, parotid saliva was collected by intra-oral duct cannulation following stimulation by pilocarpine (10 mg/kg, subcutaneously) or by isoprenaline (30 mg/kg s.c.). In the ethanol-dosed rats the initial parotid salivary flow rate was raised in comparison to control animals by 39% after pilocarpine stimulation and by 37% after isoprenaline stimulation. The protein concentration was significantly reduced in saliva from ethanol-dosed rats compared to control groups but the amylase activity per ml of saliva was not significantly different from control groups. After pilocarpine stimulation, the [K+] was significantly higher in ethanol-dosed rats than in controls, but the [Na+] was effectively lower (allowing for flow rate differences). The blood-ethanol level was zero at the time of collection of saliva, suggesting that the salivary differences are due to functional adaptation induced in acinar and ductal epithelia by prolonged repeated exposure to high doses of ethanol.