Phthalate exposure in Thai children and adolescents

We included data from both boys and girls, who had a mean age of 9.4 ± 3.64 (range 2.83 – 17.10) y. Most children were aged 6–11 y (Table 1). Sociodemographic characteristics (Table 1) showed no significant associations with phthalate metabolites (data not shown). MMP was detected in about a third and MBP was detected in almost all urine specimens. The mean concentration of urinary MMP was 1303.94 ng/mL, and that of MBP was 563.82 ng/mL. The median Cr-adjusted concentration of MMP was 0 mg/g Cr and of MBP was 252 μg/g Cr (Table 2). In boys, the median (IQR) concentrations of adjusted MMP was 0 (0, 533) μg/g Cr and MBP 211.4 (75.9, 426.8) μg/g Cr. In girls, the adjusted concentrations of MMP was 0 (0, 1054.4) μg/g Cr and MBP was 193.8 (6.2, 579.1) μg/g Cr.

Table 1

Sociodemographic characteristics of the study population (N = 221)

Table 2

Detection rate of phthalate metabolites

No correlation was observed between urinary phthalate metabolites and age, gender, family income, parental education, secondhand smoke, media exposure times per day, BMI, waist circumference, waist-to-height ratio, or waist-to-hip ratio (data not shown). Other variables, including canned food consumption, canned beverage consumption, use of plastic containers for food, bottled water, use of microwave to heat plastic food containers, junk food consumption, bottled milk consumption, and exposure to plastic toys, were also not found to be associated with urinary phthalate metabolite levels (data not shown).

Higher Tanner stage was significantly associated with lower urinary Cr-adjusted MBP levels (Table 3). Compared with children not exposed to either paints or floor cleaning liquids, urinary concentrations of MMP and MBP were significantly higher in children exposed to paints, and urinary concentrations of MMP were significantly higher in children exposed to floor cleaning liquid products (Table 4).

Table 3

Beta coefficient of Cr-adjusted urinary MMP and MBP concentrations (μg/g of Cr) according to Tanner stage adjusted by sex

Table 4

Phthalate metabolite values expressed as mean ± SD and median (IQR) (μg/g of Creatinine) by source of exposure

To our knowledge, this is the first report in Thailand to study urinary phthalate metabolite levels in Thai children and adolescents. Exposure to phthalates may be associated with adverse health outcomes, especially in children. In the present study, we measured MMP and MBP, which are phthalate metabolites, and Cr levels in morning spot urine samples from Thai children and adolescents. The detection rates of MMP and MBP were 28.5% and 88.6%, with median concentrations of 0 and 252 μg/g Cr, respectively. When compared with other studies from Asia (Table 5), we found a lower detection rate of MMP; we also noted a lower median concentration level of urinary Cr-adjusted MMP concentration, compared with a study from China (0 and 12.2 μg/g Cr, respectively). For MBP, we found a lower detection rate, but a higher median urinary Cr-adjusted MBP level than found by the study from China (252 and 74 μg/g of Cr, respectively) [31]. Median concentration of MBP from the present study was higher than concentrations reported from studies in Spain (252 and 30.2 μg/g Cr) [32] and the USA (252 and 19.8 μg/g Cr) [33] (Table 5). DBP, the parent compound of MBP, was restricted from children’s products in the USA (Consumer Product Safety Improvement Act in 2008) and the European Union (EU) (Registration, Evaluation, Authorisation and Restriction of Chemicals 2005), and this may be the reason why urinary phthalate levels found by studies in the USA and Europe were lower for levels of MBP compared with those reported in our present study. Other factors that may be responsible for these differences include age and age-dependent metabolism, age group of participants, differences in food intake, variations in personal care product use patterns, and variations in levels of phthalates in food packaging and personal care products by country. Other sources of phthalates, such as medical products (blood bags and administration of intravenous solutions) [8], outdoor and indoor dust [34], building materials such as vinyl floors and wall paper [35], and PVC flooring were not explored in this study. Moreover, only 2 phthalate metabolites were investigated and 1 method of urinary phthalate metabolite analysis was used in the present study.

Table 5

Literature review of studies of urinary phthalate metabolite levels

We found lower urinary Cr-adjusted MBP concentrations to be associated with advanced Tanner stage, but similar concentrations of MMP were found in advanced Tanner stage (Table 3). Urinary Cr-adjusted MBP concentration was higher in younger children than in older children. This finding was similar to that reported in a previous study, in which the level of DBP metabolites (the parent compound of MBP) was higher in the younger group than in the older group [38]. In younger children, hand-to-mouth behaviors and higher body surface area per weight were the factors that were found to cause greater exposure to phthalate sources in the environment. However, and after adjusting for sex (data not shown), urinary Cr-adjusted MBP level was negatively associated with Tanner stage.

Significant association was observed between urinary Cr-adjusted MMP level and exposure to floor cleaning liquid and paint, and between urinary Cr-adjusted MBP level and exposure to paint (Table 4). No previous study has reported these associations. One possible explanation is that there may be substantial differences in the formulations of floor cleaning liquid and paint used in Thailand. Conversely, certain phthalates that are known to be often present in various personal care products were not observed in the present study population. DBP (whose main metabolite is MBP) is often present in deodorants, perfumes [39], and food wrapping materials, and DMP (whose main metabolite is MMP) is often found in deodorants, shampoos, and hair styling formulations these were not found to be associated with phthalate metabolite concentrations. This may be the result of the small number of participants who use these products or to recall bias on the report prepared by parents describing their child’s exposure history. No relationship was found between toothpaste use and phthalate metabolite concentrations, and 97.6% of participants reported using toothpaste. It may be that these products do not contain phthalates or that we did not measure the metabolites of the phthalate that is contained in the products.

Our results are not consistent with the increase in urinary phthalate concentrations that were observed when an increased number of products were used (data not shown), as was reported in other studies in adults [40] and infants [41].

The present study has some recognized limitations. First, although the size of the study population was relatively small, we were still able to demonstrate significant correlation between phthalates and some parameters. Second, only 2 low-molecular-weight phthalate metabolites were measured in this study. If we had investigated additional phthalate metabolites, it is possible that other significant associations may have been identified. Third, Tanner staging was not performed by medical personnel. Fourth, it is possible that measurements of urine concentrations of phthalate metabolites may have been better if we had collected urine repeatedly. However, a study by Teitelbaum et al. [42] reported that a single spot urine sample sufficiently represented exposure over a 6 mo period to warrant its use as an exposure estimate in epidemiological studies. Finally, the children included in this study reside in metropolitan Bangkok—a major metropolis. As such, our findings may not be generalizable to all other areas of Thailand. Future studies in Thailand should include a larger sample size, more phthalate metabolites, and the use of a questionnaire with improved specificity for detecting the amount and frequency of product used.

This is the first study to investigate and report urinary phthalate metabolite levels in Thai children and adolescents. Rates of detection of MMP and MBP were lower in this study compared with the rates reported in other studies conducted in Asia, Europe, and the USA, but the urinary Cr-adjusted MBP levels in Thai children and adolescents were higher compared with the same in other studies. Exposure to paints and floor cleaning products was associated with increasing urinary Cr-adjusted MMP levels. Early Tanner stage and exposure to paints were associated with higher urinary Cr-adjusted MBP levels.