Total urinary BPA, including free and conjugated species, was detected at low parts-per-billion levels in premenstrual Egyptian girls, 21% of whom exhibited concentrations below the limit of detection at 0.40 ng/mL. Overall, the Egyptian cohort showed significantly lower urinary BPA concentrations compared to age- and sex-matched American girls from NHANES 2009-2010. Similar ranges of BPA concentrations compared to this Egyptian cohort have been reported in several international cohorts. Recent studies report that the median concentration of urinary BPA in 48 Japanese women was 1.2 ng/mL [33
], while the median BPA concentration of 60 pregnant Mexican women was 0.95 ng/mL [34
] and 100 pregnant women in the Netherlands was 1.2 ng/mL [35
]. Comparison of urinary BPA concentrations between countries may be confounded by the method of analysis, adjustment for urine dilution, timing of urine collection, as well as age, sex, and genetic differences [3
]. However, differences can also be attributed to country specific lifestyle practices including food storage and consumer product use. Therefore, characterizing dietary and behavioral habits may provide insight into the potential exposure pathways and contribution of BPA to human health.
Previous studies have described heterogeneity in disease rates in Egypt based on urban/rural status. Women residing in urban Gharbiah Province of Egypt were found to have a 2-4 times higher incidence rate of estrogen receptor positive breast cancer compared to their rural counterparts [29
]. Xenoestrogen exposure during critical windows of development has been proposed to be a likely explanation for increasing cancer incidences, especially in regards to breast cancer [22
]. In this pilot study, however, we did not identify differential exposure to BPA, estimated from the urinary concentrations of BPA, based on residential status in premenstrual Egyptian girls. Both average unadjusted and SG-adjusted BPA concentrations were in the low parts-per-billion range and did not significantly differ between the urban and rural cohorts. Instead, specific gravity differed between urban and rural girls, indicating an underlying variability in fluid consumption, individual health, and/or lifestyle factors within the two cohorts.
It is possible that these data represent cohort-specific xenoestrogen exposure in Egypt, as discrepancies in xenoestrogen exposures between urban and rural populations have previously been observed in several studies [42
]. Lower BPA levels were found in sediments in rural compared to urban Okinawa, Japan, suggesting higher BPA exposure from industrial wastes and less so from agricultural activities [44
]. Fu and colleagues traced BPA in atmospheric aerosols from urban, rural, marine, and polar regions around the world, and observed higher atmospheric BPA concentrations in urban regions especially in countries like India where open burning of plastic wastes are common practice [45
]. Additionally, the preference of urban populations near Alexandria, Egypt for diets high in meat and fat may expose residents to higher levels of synthetic estrogens reported in poultry and meat [46
These Egyptian girls, as with other populations around the world, are likely to have exposure to a complex mixture of xenobiotics. When we characterized exposure to phthalates within the same population, urban girls exhibited higher specific gravity adjusted urinary concentrations of several phthalate metabolites compared to rural residents, although these differences were not observed in unadjusted concentrations [47
]. Characterization of multiple chemical exposures is necessary to understand the impact of the environment on disease, given that a combination of several low level exposures may contribute to a larger xenobiotic body burden and subsequently influence disease incidence [48
As occupational exposures are unlikely in girls of this age group, the most likely route of exposure is dietary ingestion of BPA [9
]. Several studies show migration of BPA from PVC films in food packaging and cans into foodstuff especially at high temperatures [8
]. Epoxy resin containing BPA is widely used to coat metal products such as canned foods and bottle tops [54
]. In addition, some food and drink containers are composed of polycarbonate plastics [9
]. Therefore, in our study we asked participants about food storage behaviors, and analyzed canned food consumption and food storage in plastic containers as predictors of urinary BPA concentrations. We found a significantly positive association between food storage in plastic containers and BPA concentrations after adjusting for urinary specific gravity, age, BMI, and residential status. A parallel study within this population noted that food storage in plastic was significantly associated with higher urinary phthalate metabolite concentrations [47
], suggesting the use of both BPA-containing polycarbonate plastics as well as phthalate-containing PVC storage products by these Egyptian girls. Studies often report BPA exposure from canned food consumption to be relevant [55
]; however, our results do not indicate a direct significantly positive association between canned food use and urinary BPA. Interestingly, canned food use improved the association between urinary BPA concentrations and food storage in plastics, acting as a potential confounder. Irrespective of these food consumption and storage behavior associations, BPA concentrations within this Egyptian cohort were significantly lower compared to age- and sex-matched US NHANES data. Comparatively low urinary concentrations of BPA among Egyptian girls may be attributed to the limited use of BPA containing products like thermal paper, and medical equipment, as well as relatively low frequency of plastic food storage and canned food consumption.
Although spot urine samples reflect recent BPA exposure, multiple spot urine testing is recommended for future studies in order to account for temporal variation in exposure [31
]. Besides the small sample size and the collection of only one spot urine sample from each girl, a major limitation of this pilot study is the inclusion of only general behavioral questions. Instead, specific analyses of behavioral and dietary habits are required such as whether food stored in cans and plastics were heated or how many canned food or drink products were consumed. Characterization of the types of food stored and the frequency of use may also be necessary, given that Egyptian adults and children are exposed to different diets especially in rural Egypt [58
] and that certain foods are more likely to leach BPA from containers [59
To the best of our knowledge, this study is one of the first to assess food storage practices and urinary BPA concentrations in girls from a developing country. Many exposure assessment studies focus on developed countries; for example, a previous study found a median unadjusted BPA concentration of 1.8 ng/mL among 1,200 6-8 year old girls from three large US cities [60
]. Exploring environmental exposures such as BPA at vulnerable stages of development, including the peripubertal period, will be important for assessing potential risks to disease later in life in developing countries. Reports on the Egyptian food market indicate an increased demand for packaged and convenience foods, and the canned food industry is expected to grow rapidly with the reduction of fresh produce [61
]. According to the National Food Consumption Survey, an increasing number of Egyptian households reported consumption of ready-made foods and carbonated soft drinks, and substantial differences in food consumption patterns were observed between urban and rural households over several decades [62
]. Given the expected expansion of the Egyptian economy, communities must be cognizant of the potential increase in various environmental exposures and consider appropriate actions to prevent potential adverse health outcomes in the future.