Environ. Sci. Technol. 2008, 42, 8971–8977
Dietary Predictors of Perfluorinated Chemicals: A Study from the Danish National Birth Cohort T H O R H A L L U R I . H A L L D O R S S O N , * ,† C H U N Y U A N F E I , ‡ J Ø R N O L S E N , ‡,§ L O R E N L I P W O R T H , |,⊥ J O S E P H K . M C L A U G H L I N , |,⊥ A N D S J U R D U R F . O L S E N †,# Maternal Nutrition Group, Department of Epidemiology Research, Statens Serum Institut, Arillerivej 5, building 305, 2300 Copenhagen, Denmark, Department of Epidemiology, School of Public Health, University of California at Los Angeles, Box 951772, Los Angeles, California 90095, Institute of Public Health, University of Aarhus, Høegh-Guldbergsgade 6A, 8000 Aarhus C, Denmark, International Epidemiology Institute, 1455 Research Boulevard, Suite 550, Rockville, Maryland 20850, Vanderbilt University Medical Center and VanderbiltsIngram Cancer Center, 691 Preston Building, Nashville, Tennessee 37232, and Department of Nutrition, Harvard School of Public Health, 677 Huntington Avenue, Boston, Massachusetts 02115
Received July 10, 2008. Revised manuscript received October 4, 2008. Accepted October 6, 2008.
This study investigated the association between dietary variables and plasma levels of perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) among 1076 pregnant women. Diet was assessed at midpregnancy by a foodfrequency questionnaire. Mean first trimester plasma PFOS and PFOA levels were 35.1 and 5.6 ng/mL, respectively. PFOS levels were positively associated (p < 0.05) with intake of red meat, animal fats, and snacks (e.g., popcorn, potato chips), whereasintakeofvegetablesandpoultrywasinverselyassociated. The adjusted mean differences between the 75th and 25th intake percentiles were 4.3 ng/mL [95% CI: 2.1, 6.5] for red meat, 3.4 ng/mL [95% CI: 1.2, 5.6] for animal fats, and 2.0 ng/mL [95% CI: 0.3, 3.6] for snacks. Similar but weaker associations were observed for PFOA. Furthermore, a comparison between women reporting low (e25th percentile) red meat and high (g75th percentile) vegetable intake and women reporting low vegetable and high red meat intake resulted in differences in plasma PFOS and PFOA concentrations equal to 31% and 18% of mean levels, respectively. Studies quantifying levels of perfluorinated compounds in food have suggested that diet could be an important route of human exposure. The observed associations in our study between dietary variables and maternal exposure further support that conclusion.
* Corresponding author e-mail:
[email protected]; phone: +45 32 68 83 63; fax: +45 32 68 31 65. † Statens Serum Institut. ‡ University of California at Los Angeles. § University of Aarhus. | International Epidemiology Institute. ⊥ Vanderbilt University Medical Center and VanderbiltsIngram Cancer Center. # Harvard School of Public Health. 10.1021/es801907r CCC: $40.75
Published on Web 11/05/2008
2008 American Chemical Society
Introduction Perfluorinated chemicals (PFCs) are a class of manmade fluorinated organic compounds first produced on a large scale in the early 1950s (1). They have been used extensively in various commercial applications including polymer production, food packaging, textile coatings, lubricants, surfactants, and fire-fighting foams. Of these compounds, perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) have been widely detected in humans and wildlife (2, 3). These compounds have either been produced synthetically or formed by degradation from other PFCs (4, 5). In humans, low elimination rates have been observed for PFOS and PFOA, with reported elimination half-lives of 5 and 4 years, respectively (6). The combination of a fluorinated alkyl chain that is sparingly soluble in most media and a hydrophilic functional group makes their bioaccumulation behavior quite different from that of other persistent pollutants such as polychlorinated biphenyls. Although global emissions and production were reduced considerably between 1999 and 2004 (1), PFCs are likely to be of continued public health interest because of their persistent nature and potential adverse health effects in humans (4, 7-9). Different sources and pathways of human exposure to PFCs are currently not well understood (10). Drinking water has been shown to be an important route of exposure in the case of local contamination (10) and exposure through air inhalation has also been suggested (7). Studies from Spain (11), Canada (12, 13), Germany (14), and the U.K. (15) have suggested that diet also contributes to exposure in the general population. Although the main food items identified in these studies have varied, intakes of red meat, fish, dairy, eggs, and potatoes have been reported as potential sources of exposure. Indirect exposure through food packaging material has also been suggested (13). Based on the analysis of selected food items, the contribution from diet has been estimated as high as 60% of total exposure (12). However, information on the relative contributions of different food groups with respect to exposure is still quite limited, and in background exposed populations, a direct correlation between individual foods or food groups and exposure measured in blood has, to our knowledge, not been reported. The aim of this study was to investigate the association between intake of various food groups and PFOS and PFOA in plasma among 1076 women from the Danish National Birth Cohort.
Materials and Methods Study Population. The Danish National Birth Cohort (DNBC) includes data on 91827 pregnant women recruited between 1996 and 2002. Recruitment took place at about week 8 of gestation during the first prenatal visit to the general practitioner. The recruitment process relied on the participation of approximately 50% of all general practitioners in Denmark. During the study period, an estimated 30% of all deliveries in Denmark were recruited into the cohort (16). Information on maternal lifestyle and health was collected through four computer-assisted telephone interviews conducted at approximately weeks 12 and 30 of gestation and months 6 and 18 postpartum, in addition to a food-frequency questionnaire (FFQ) filled out in midpregnancy. The FFQ, telephone interview questionnaires, and information on ethics approval are publicly available in English (www. bsmb.dk). Maternal blood samples were collected during two routine visits to the general practitioner at approximately weeks 8 VOL. 42, NO. 23, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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and 24 of gestation, and cord blood was collected by the midwife attending the child birth. Each blood sample was sent for processing and storage by regular mail. Blood samples were thus transported at normal temperatures for up to 48 h, although most samples arrived within 28 h. Upon arrival, the blood was centrifuged, and the plasma was stored at -30 °C. Selection of Study Participants. Women who were eligible for selection were those who gave birth to a single live-born infant without reported congenital malformation (n ) 87752), had provided the first blood sample at about week 8 of gestation (n ) 80678), and responded to all four telephone interviews (n ) 43045). Based on these criteria, 1400 women were randomly selected for exposure assessment on the first blood sample. Of these women, 1102 had provided the second blood sample taken at about week 24 of gestation, and of those, 200 women were randomly selected for exposure assessment on the second blood sample. The proportion of women returning the FFQ was approximately 75%, which reduced the number of women available for this study to 1076 and 154 with respect to the first and second blood samples, respectively. Dietary Assessment. Information on diet was obtained from the FFQ (17), which has been validated for use in pregnancy in relation to a series of nutritional factors (18). The questionnaire was mailed to the women in week 25 of gestation and collected information on 360 food items, covering intakes for the previous four weeks. Individual food items were quantified into grams per day using assumptions on standard portion sizes (19), and related food items were aggregated into food groups. In our analysis, we included 14 different food groups reflecting intakes of vegetables, fruits, potatoes, poultry, fish, red meat (beef, pork, lamb, and organ meat), milk, cheese, egg, animal fats (butter, margarine with g80% animal fat, lard), vegetable fat (including margarine with e20% animal fat), cereals (bread, rice, pasta, etc.), snacks (potato crisps, peanuts, popcorn), and sweets (cakes, pastry, cookies, chocolates, candy). These food groups combined contributed to 93% of the total energy intake in our study population. To reduce the number of comparisons, potentially resulting in false positive associations, food groups with small intake variation or a high proportion of women with no intake, such as alcoholic beverages, soy products, and dressings were not included in our analyses. Exposure Assessment. Concentrations of PFOS and PFOA in plasma were measured using high-performance liquid chromatography/tandem mass spectrometry at the 3 M Toxicology Laboratory. The HPLC system used was from Shimadzu (Shimadzu Scientific Instruments, Inc., Columbia, MD) and consisted of two model LC-20AD pumps, an SILHTc integrated autosampler, and a controller unit with a model CTO-20AD oven for column temperature control. The autosampler was interfaced to a model API 5000 triple-stage quadrupole mass spectrometer purchased through Sciex Applied Biosystems (Foster City, CA). The HPLC column used was an ACE brand, base-deactivated 5-µm column purchased from MAC MOD analytical (Chads Ford, PA). The column was a 100 × 2.1 mm i.d. column used with a betasil, C-18, 5-µm (10 × 2.1 mm i.d.) analytical guard column purchased from Thermo-Fisher (San Jose, CA). Stable labeled analogs of PFOS (18O2 PFOS) and PFOA (13C2 PFOA) were used in all extracted procedures. For all samples (100 µL of maternal plasma), solid phase extraction wasperformedusingWaters(Milford,MA)Oasisshydrophiliclipophilic balance 3.0-mL cartridges. The maternal plasma concentrations were evaluated using standard curves based on extracted spiked calf serum. The use of calf serum for the standard curve matrix has been shown to be appropriate for quantification of plasma samples (20). The lower limit of 8972
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quantification (LLOQ) for the method was 1.0 ng/mL for each PFOS and PFOA. In our analysis, PFOS was measured above LLOQ in all samples, whereas PFOA was below LLOQ in only two samples, to which a value equal to half-the LLOQ was assigned. A more detailed description of the analytical method used can be found elsewhere (20). For quality control, a single lot of newborn calf serum was analyzed together with the samples to ensure the accuracy and reliability of the data. Two levels of spiked calf serum controls were extracted using 30 individual solid-phase extractions to establish within-run means and standard deviations for each separate level of control. The two levels of spike used were at 15 and 44 ng/mL for PFOA and 10 and 30 ng/mL for PFOS. The coefficients of variation for betweenrun control values (n ) 110) were 3.5% and 3.2%, respectively, for PFOA and 2.8% and 2.5%, respectively, for PFOS. As a further quality-control measure, 100 blind maternal plasma samples were selected for repeated analysis. Strong correlations were observed between the original and repeated analysis (R2 ) 0.993 for PFOS and R2 ) 0.987 for PFOA). Statistical Analysis. We used linear regression to investigate the association between PFOS or PFOA and diet. PFOS measurements were normally distributed, whereas the distribution for PFOA was slightly skewed; however, similar results were observed for untransformed and log-transformed PFOA levels. As a measure of association, we used the linear regression coefficient where the dietary variable was entered as a continuous term. As a measure of effect size, we used the dichotomous comparison between the 75th and 25th percentiles in the intake distribution. The association for each food group was tested in both univariate and covariateadjusted analyses using a Student t test for continuous variables and an F-test (Type III) for categorical variables. Because of skewed distributions for some of the food groups, percentiles were used to describe food group intakes, and nonparametric tests were used to test for associations between different food groups. For primary analysis, we used the first blood sample taken at about week 8 of gestation (n ) 1076). To check the stability of those results, we used the second blood sample taken at about week 24 of gestation (n ) 154). For covariate adjustment, we identified a priori and included parity (0, 1, 2, g3), smoking (nonsmoking, occasional smoking, daily smoking), maternal age (continuous), prepregnancy body mass index (continuous), and socio-occupational status (high, medium, low, student). Maternal age, prepregnancy body mass index, and parity were included as they have previously been reported to be predictors of diet (21) and plasma PFC levels (8). Smoking and socio-occupational status were included as these factors reflect behavioral patterns that might be associated with both diet and sources of PFC exposures. The category ”occasional smoking” refers to women who either quit smoking during pregnancy or smoked regularly, although less than daily. For sociooccupational status, women with a higher education (4 years beyond secondary-school education) or in managementlevel jobs were classified as “high”. Women with midlevel training and skilled workers were classified as “middle”, and unskilled workers and unemployed were classified as “low”.
Results Mean levels of PFOS and PFOA in maternal plasma according to characteristics of study participants are shown in Table 1. The associations of PFOS and PFOA with these maternal characteristics have been presented elsewhere (8). The average age at delivery was 29 years, and 46% of the women were giving birth to their first baby. The proportion of women reporting to be nonsmokers was 77%. The mean (standard deviation) concentrations of PFOS and PFOA were 35.1 (12.5) ng/mL and 5.6 (2.6) ng/mL,
TABLE 1. Characteristics of Study Participants with Respect to Mean PFOS and PFOA Levels (n = 1076) mean (standard deviation) plasma levels (ng/mL) % PFOS PFOA age at delivery (years)
