TCE was detected in the breast milk for 7 of 20 (35%) women residing in Nogales, AZ. All of the women were Latina and half had an infant <3 months in age. The majority of households had an annual income <$40,000. The level of TCE in breast milk was associated with the concentration of TCE in household bathing and laundry water and was more likely to be detected in the milk of mothers whose infant had a BMI <14. Although perhaps not generalizable to other populations, this exploratory study provides, to the authors’ knowledge, the first quantified values of TCE in breast milk, filling a key data gap in TCE risk assessment (3
), and allowing for examination of factors that may be associated with TCE in breast milk.
A previous study that assessed TCE in breast milk, reported that TCE was detected in all breast milk samples analyzed (12
). However, no quantified levels of TCE in breast milk or the LOD were provided. It is not clear if the results of the current study are different because of decreased detection frequency due to a higher LOD then the previous study or if fewer women in the current study population were exposed to TCE given that ambient levels of TCE in outdoor air have decreased substantially since the 1980s (1
Other studies have reported concentration of other VOCs in breast milk (30
). Kim et al. analyzed breast milk samples from Baltimore and North Carolina for chloroform, benzene, toluene and methyl tert-butyl ether, with a LOD of 0.01–0.02 µg/L (30
). Fabietti et al. analyzed breast milk for benzene and toluene in Italy with a LOD of 0.01 µg /kg milk (31
). The LOD for both of these studies is substantially lower than the LOD for TCE in the current study. These studies used head-space solid phase microextraction or “purge and trap”, while liquid-liquid extraction was used for the current study. Using one of these other methods may lower the LOD for TCE in breast milk in future studies. Given the large variability in milk concentration among VOC compounds in the other studies it is not clear how relevant these concentrations are to the concentration of TCE in the current study. However, the values measured in the current study are within the same order of magnitude of what was determined in previous studies.
Depending upon milk consumption rates, potential TCE intake via this pathway could exceed the US EPA RfD. However, potential TCE intake from breast milk consumption differed substantially when calculated using self-reported consumption versus consumption rates from the US EPA (28
). The mother with the highest TCE concentration only reported feeding her infant 2–3 times per day for less than 10 minutes at a time. However, using milk consumption rates from C-S EFH, the estimated dose was 3–5 times higher than that estimated with her self-reported rate. The mother with the highest breastfeeding consumption reported feeding her infant more than 7 times per day for 31–45 minutes per session corresponding to an approximate consumption rate of 2400 mL/day (590 mL/kg/day) in a 1–2 month old infant. This is 3 times the upper limit in the CS-EFH (28
). Better estimates of milk consumption rates in infants are needed to better characterize their risk of exposure from this pathway.
In the current study, a few factors were associated with increased TCE in breast milk and should be further examined to target future interventions. Concentration of TCE in breast milk was significantly correlated with concentration of TCE in water used for bathing and laundry, but not with water used for cooking or drinking. These results suggest that primary exposure to TCE may occur during these activities. Over 10 times more water is typically used in households for bathing and laundry than for cooking or drinking (32
). TCE exposure via inhalation from bathing with contaminated water may be 6–80 fold the exposure from ingesting 2 L of the same water (33
). Infants’ higher respiratory rates, greater surface area to body-weight ratio, and more permeable skin may make them particularly vulnerable to these exposures (34
). More assessments are needed to quantify these exposures and ensure that regulatory limits of TCE in water account adequately for exposures via multiple routes.
The field technician did not report the source of water used for washing breasts. It is likely that the mothers used their typical bathing water. This could be a potential source of sample contamination. However, it is unlikely that residual TCE on the breast would result in a measurable TCE concentration in 100 mL of breast milk. Residual TCE on the breast from washing would also be another significant potential source of exposure to the infant. Depending upon established scope, future studies should consider supplying laboratory grade water for washing the breasts.
TCE is the 3rd
most frequently detected contaminant above the MCL (4
), and approximately 9–34% of the drinking water supplies in the US have some TCE contamination (1
). Depending upon use, between 68–89% of the water samples in the current study exceeded the MCL for TCE (). The analytical method, which is not a US EPA Standard method, was selected from the peer-reviewed literature because of equipment availability. It is not clear if this method may have resulted in higher measured concentrations that should not be compared to the MCL. The significant correlation between TCE concentration in the water and breast milk samples indicates that the relative concentrations in these two matrices are probably correct; however the absolute median value of TCE in the water samples may be higher than reported from other analytical techniques. However, given that the water samples were collected with headspace these reported TCE concentrations in water may represent the lowest probable concentrations. Nevertheless, the strong correlation between TCE content in breast milk and bathing/laundry water, should be considered in developing interventions to reduce exposures to the mother and ultimately the infant.
Mothers who had TCE detected in their milk were 9.6 times more likely to have never lived outside of Nogales. This finding, along with the unusually high rates of SLE and multiple myeloma in this community (20
), highlights the need for further studies in this region, as well as in other geographic regions for comparison.
TCE is characterized by its ability to accumulate in fat tissues (35
). Although levels can decrease quickly following acute exposures, there may be insufficient time for levels to reach baseline following chronic exposures and saturation may be reached over time (36
). Breasts have higher concentration of lipophilic solvents than blood or other fatty tissues because of increased blood flow and recirculation of secretions in the duct system, even in non-lactating breasts (37
). Typically, the majority of depuration of exogenous substances occurs during the first two months of lactation (38
). It has been hypothesized that this might explain lower rates of breast cancer among women with cumulative lactation of at least three months (37
). Findings in the current study provide some insight into TCE toxicokinetics that should be better characterized in future studies.
TCE was detected in both samples from only one of the mothers who provided multiple samples. There was a relative percent difference of 102% and 93% for the volumetric and fat-adjusted TCE concentrations, respectively. There was also a 158% relative percent difference in fat composition between the samples. Studies have documented that lipid content of breast milk is highly variable between women, but also in multiple samples from the same woman and is related to duration of feeding, time post-partum, feeding intervals, hind vs. foremilk and left vs. right breast (38
). The current study supports the notion that variability in fat composition as well as in exposure may contribute to high variability of lipophilic chemical levels in breast milk (38
). Future studies should consider collecting multiple samples from each woman.
Other studies have demonstrated that concentration of environmental chemicals in breast milk decreases as the mother’s body burden is reduced (38
). Women with an infant with a BMI <14 were 5.2 times more likely to have TCE detected in their breast milk. The infant with the lowest BMI was breastfed by the mother with the highest concentration of TCE in her milk who reported the lowest daily breastfeeding duration, suggesting that she may have not depleted her body burden.
Although not many of the infant, mother or household characteristics were significantly associated with detection of TCE in breast milk, this small exploratory study probably had too little power to assess these risk factors. Additional studies should be performed with greater power to identify important risk factors for detection of TCE in breast milk, that allow for multivariate analyses so that these exposures can be reduced.
To the knowledge of the study authors, this is the first study to report quantified values of TCE in breast milk. Depending upon infant milk consumption patterns, based upon the values reported TCE intake could exceed the US EPA RfD. In this exploratory study there is a significant correlation between the concentration of TCE in breast milk and in bathing and laundry water. These results warrant replication in larger and more in depth studies. Future analyses with a lower LOD should be performed both in Nogales and other communities to obtain a better understanding of the levels of TCE in breast milk and associated risk factors so that intervention strategies can be developed to reduce exposures to nursing mothers and their children.