Environ. Sci. Technol. 2006, 40, 5276-5281
Phthalate Esters in Human Milk: Concentration Variations over a 6-Month Postpartum Time J I P I N G Z H U , * ,† S U S A N P . P H I L L I P S , ‡ YONG-LAI FENG,† AND XIAOFENG YANG† Chemistry Research Division, Health Canada AL: 0800C, EHC (Building 8), Tunney’s Pasture, Ottawa, Ontario, Canada K1A 0L2, and Departments of Family Medicine and Community Health and Epidemiology, Queen’s University, Kingston, Ontario, Canada K7L 5E9
The present study investigated the levels of phthalate esters in a total of 86 human milk samples collected among 21 breast-feeding mothers over a 6-month postpartum time. Di(2-ethylhexyl) phthalate (DEHP) was the predominant ester with the arithmetic mean value of 222 ng g-1 (range: 156-398 ng g-1, 95% confidence limit), followed by dibutyl phthalate (DBP), 0.87 (range: 0.62-1.2) ng g-1. Diethyl phthalate (DEP), with a mean of 0.31 ng g-1, was detected in only a small number of samples. Weak correlations between lipid content and levels of phthalate esters were observed. The levels of phthalate esters in human milk fluctuated over the 6-month period; this may indicate a need for multiple sample collection, to calculate average concentrations over the feeding period. Multiple sample collection would provide a better estimate of the exposure of breast-fed infants to phthalate in human milk. For infants relying on breast-feeding, the mean daily intake over the first 6-month period considering a 7 kg infant consuming 750 g of milk was estimated at 167 µg d-1 for DEHP and less than 1 µg d-1 for DBP and DEP. While the nutritional and social benefits of breast-feeding are well established, the potential transfer of phthalate esters from mothers to breast-fed infants should also be recognized.
Introduction Phthalates are among the most widely distributed pollutants in modern society. Extensive use of phthalate esters in both industrial processes and consumer products has resulted in the ubiquitous presence of these chemicals in the environment. They have been detected in various media, including food,1-5 water and soil,6-10 consumer products,11-14 medical devices,15 marine ecosystems,16 indoor air,17,18 and indoor dust.19,20 Some phthalate esters and their metabolites have also been detected in human urine21-25 and amniotic fluid26 samples. Phthalate esters have endocrine disrupting properties.27 Studies on rodents have shown that phthalate esters are estrogenic and exhibit adverse reproductive effects.28-31 Phthalate esters may have linked to premature breast development observed in young Puerto Rican girls as there was a statistically significant association between the two.32 * Corresponding author e-mail:
[email protected]. † Health Canada. ‡ Queen’s University. 5276
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 40, NO. 17, 2006
There was also an inverse linear association between phthalate metabolite levels in urine and observed mobility, concentration, and normal morphology of sperm in American men.33 Exposure of general populations to several phthalate esters including di(2-ethylhexyl) phthalate (DEHP) and dibutyl phthalate (DBP) has been estimated by the Canadian government based on the Canadian National Market Basket Survey and the Nutrition Canada Survey, both of which were conducted in the early 1990s.34 Recent data of phthalate monoesters in urine also provided phthalate esters daily intake estimations for the general population in North America and in Germany.35 In addition to the biomonitoring of urines, German researchers have measured DEHP and DBP in a limited number (ten36 and five37 donors) of human milk samples collected in two different regions in Germany respectively, through which regional differences in concentration levels were observed. There have been, however, no studies on the determination of phthalate esters in human milk conducted in North America, where populations may have different diets and life styles from the German population, resulting in potentially different exposure scenarios to phthalate esters. Human milk with its reasonably high lipid content is a readily accessible body fluid for measuring phthalate esters, as these contaminants are highly lipophilic. For example, the log Kow (octanol-water partition coefficient) value of DEHP is 7.73 at 25 °C.38 Exposure data of phthalate esters in human milk can provide not only human exposure data for the mothers,but also vital information on the transfer of these contaminants from mothers to their infants through lactation; the data may be extrapolated to general population exposure, as well. In this paper, we are reporting the first data set of phthalate esters in human milk in North America. In addition to obtaining baseline information on the levels of phthalate esters in human milk, the study was designed to meet the following two objectives: (1) to gain knowledge on the changes in concentration of phthalate esters over time, which may have different temporal patterns as do other persistent organic pollutants such as polychlorinated biphenyls (PCBs) and dichloro-diphenyl-trichloroethane and its metabolites (DDTs) and (2) to provide a more accurate time averaged estimation on the exposure of breast-fed infants whose diet is heavily, if not exclusively, dependent on milk from their mothers.
Materials and Methods Study Design and Sample Collection. Participants were solicited from a group of healthy women not taking medications and attending a breast-feeding class in the city of Kingston, Ontario, Canada in 2003-2004. Ethics approval was received from the Ethics Review Board for both organizations of the research team. Milk samples of approximately 45 mL were hand-expressed into the precleaned Teflon topped glass jars (Canadawide Scientific, Ottawa, Ontario, Canada) to avoid potential contamination through using plastic devices, frozen immediately, and kept at -20 °C until sample analysis. The mothers were asked to collect the hind milk so as not to interfere with infant nutrition. Milk samples were expressed at the end of 2 weeks, 1 month, 2 months, 4 months, and 6 months postpartum. Samples were analyzed within 12 months of collection. Prior to analysis, each jar was thawed in a 50 °C water bath and then well mixed with a Vortex device. Aliquots of milk were taken for lipid determination and phthalate ester analyses, respectively. 10.1021/es060356w CCC: $33.50
2006 American Chemical Society Published on Web 07/12/2006
TABLE 1. Levels (ng g-1 Milk) of Phthalate Esters in Breast Milk and Their Distributions (Percentiles) among Samples percentile distribution det. freq DEP DBP DEHP
15/86 85/86 86/86
DLa 0.21 0.12 1.2
GMc
median
0.14 0.51 109
