Three studies evaluated phthalate leaching from food packaging, the pathway by which phthalates affect uterine leiomyoma formation, and their mixture risks. Phthalates are commonly used in plastic packaging as plasticizers and have been associated with several human health outcomes such as lower semen quality, neurodevelopmental effects, childhood asthma, Type 2 diabetes, as well as breast and uterine cancer (FPF reported). In 2017, the EU REACH Committee recognized diisobutyl phthalate (DIBP, CAS 84-69-5), dibutyl phthalate (DBP, CAS 84-74-2), benzyl butyl phthalate (BBP, CAS 85-68-7), and phthalate di (2-ethylhexyl) phthalate (DEHP, CAS 117-81-7) as substances of very high concern (SVHCs) due to their endocrine disrupting properties for humans (FPF reported). Epidemiological studies have also observed an association between uterine leiomyoma and exposure to the endocrine-disrupting DEHP but the underlying mechanism has not yet been resolved.
Therefore, Takashi Iizuka from Northwestern University, Chicago, USA, and co-authors, assessed if the principal metabolite of DEHP mono(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) and other phthalate metabolites support the survival of uterine leiomyoma cells. Generally, in the body, phthalate diesters are rapidly metabolized to monoester metabolites which are often more bioactive than their parent compound.
In the article published on November 14, 2022, in the journal Proceedings of the National Academy of Sciences (PNAS), Iizuka and co-authors, described that they used data from the Midlife Women’s Health Study (MWHS, n = 712 patients) to investigate the association between individual urinary phthalate metabolite levels and their mixtures with leiomyoma diagnosis in women with or without that fibroid tumor. They also performed several assays to test the effect of phthalates on viability, cytotoxicity, and apoptosis of leiomyoma and myometrium cells, extracted the cells’ RNA for real-time quantitative polymerase chain reaction (PCR), extracted and quantified proteins, and measured tryptophane metabolite levels.
Iizuaka and co-authors found that urinary levels of MEHHP were most strongly associated with uterine leiomyoma diagnosis. MEHHP was also the compound that affected cell viability and apoptosis of primary leiomyoma and smooth muscle cells the most and at concentrations equivalent to those detected in the urine samples. The scientists further reported that “MEHHP promotes leiomyoma cell survival by activating the tryptophan-kynurenine-AHR pathway.” AHR stands for aryl hydrocarbon receptor and is a nuclear receptor whose function can be affected by endocrine-disrupting chemicals. The study showed that MEHHP resulted in the nuclear localization of AHR and led to an upregulation of two of the receptor’s targets, CYP1A1 and CYP1B1. Furthermore, MEHHP exposure increased the cellular levels of tryptophan and kynurenine and enhanced the expression of the tryptophan transporter and the enzyme which catalyzes the conversion of tryptophan to kynurenine. The latter binds to the AHR.
Iizuka and co-authors concluded that MEHHP exposure represents “a high-risk factor for leiomyoma growth” and that their findings “facilitate the development of novel intervention strategies for the treatment or prevention of disease.”
Uterine leiomyomas are gynecological benign tumors that affect almost 80% of women of reproductive age and which have estimated health costs of $5.9 to $34.4 billion in the United States. One-quarter of women affected by this tumor become symptomatic with excessive and uncontrolled uterine bleeding, anemia, miscarriages, infertility, and large abdominal tumors.
In a review published on November 15, 2022, in the journal Environmental Pollution, Yiyun Liu from Chongqing Medical University, China, and co-authors summarized the association between DEHP exposure and neurodevelopmental abnormalities and neurological diseases by reviewing human epidemiological and animal behavioral studies. The authors reported that DEHP exposure during critical periods of development increases “the risk of neurobehavioral abnormalities, depression, and autism spectrum disorders.” While they found effects to be sex dependent, they also pointed out that results on neurotoxicity were “inconsistent”. Therefore, Liu and co-authors recommended to perform further studies on populations and model organisms to derive more consistent results. According to the review, the main mechanisms for DEHP neurotoxicity are apoptosis and oxidative stress.
Phthalates were among the priority substances selected for advanced human biomonitoring under The European Human Biomonitoring Initiative (HBM4EU) which ran from December 2016 to early 2022 (FPF reported). In an article published on October 12, 2022, by the journal International Journal of Hygiene and Environmental Health, Rosa Lange from the German Environment Agency (UBA), Berlin, Germany, and co-authors from several European research institutions, evaluated the mixture risk of five phthalates within HBM4EU. The phthalates were selected due to their known reprotoxic properties and their co-occurrence in the European subpopulation and included DEHP, diisobutyl phthalate (DiBP, CAS 84-69-5), di-n-butyl phthalate (DnBP, CAS 84-74-2), diisobutyl phthalate (DiBP, CAS 84-69-5), diisononyl phthalate (DiNP, CAS 28553-12-0,), and butyl benzylphthalate (BBzP, CAS 85-68-7).
In the collection of harmonized and quality-controlled human biomonitoring data, Lange and co-authors included studies that were already completed and provided biobanked samples, that were already initiated before HBM4E, and such that had not yet started. A mixture risk assessment was performed by using the hazard index approach in which the risk quotients of individual substances are summed up. A hazard index <1 is considered to be of no concern.
The results indicated “that 17% of the European children and adolescents are at risk from concurrent exposure to five reprotoxic phthalates.” DnBP and DIBP were found to drive the most risk within the mixture. The authors further reported that if single substances had been evaluated, 63% of the risk from combined phthalate exposure would not have been noticed.
Based on these findings they see an “urgent need to incorporate mixture risk assessment into current regulatory practice at a regular basis.” The overall hazard index was 0.44 (geometric mean). However, if co-exposures to further anti-androgenic chemicals would be considered “substantial exceedances of 83% and 95% are observed.” To account for such other anti-androgenic chemicals, the authors proposed to use a precautionary factor. While there was no significant difference between age groups (children and adolescents) and sexes, hazard indexes varied with geographical region and the period of sampling. The eastern European region and the sampling period between 2014 and 2016 had the highest average hazard indices. Lange et al. highlighted “the need for follow-up investigations of human internal exposures of the European population to chemical mixtures by continuous human biomonitoring studies harmonised at EU level.”
In an article published on November 8, 2022, in the Journal of Food Safety, Minhao Wang and co-authors from Xi’an Jiaotong-Liverpool University, Suzhou, China, analyzed five phthalates contained in and migrating from polypropylene (PP) takeaway plastic boxes and coverings. After cutting the articles purchased from a Chinese E-shop, the scientists performed extraction experiments with n-hexane for 30 min ultrasonication and repeated this step three times. For migration experiments, they followed the National Standard of Phthalates Migration to Food Contact Materials (GB31604.30-2016) and used acetic acid (3%, 60 °C) and deionized water (60 and 80 °C) as food simulants. Concentrations of the phthalates DEHP, BBP, DBP, diethyl phthalate (DEP, CAS 84-66-2), and dimethyl phthalate (DMP, CAS 131-11-3) were analyzed by gas chromatography-mass spectrometry.
All five phthalates were detected in all samples in concentrations between 0.002 and 2.53 µg/g plastic with DEHP and DBP leaching at the highest levels into n-hexane and the other food simulants. Phthalate migration increased with higher temperatures. Furthermore, Wang et al. reported that the migration was dependent on the combination of phthalate type and food simulant. While DBP, BBP, and DEHP showed a higher migration into acetic acid, DMP and DEP preferably migrated into n-hexane.
The researchers also calculated if the dietary phthalate exposure would exceed the safe intake levels based on blackhead minnow 50% lethal concentration (LC50) and oral rat 50% lethal dose (LD50) and by using the Toxicity Estimation Software Tool (T.E.S.T) and Dietary Exposure Evaluation Model (D.E.E.M) developed by the US Environmental Protection Agency. Here, they concluded that “phthalate contents in dietary exposure did not surpass the concentration that could represent a risk to human health.” However, the authors pointed out that they only used articles from one brand and made of one polymer type and, consequently, they “may not fully represent all the takeaway packaging plastic boxes on the market.”
Opposed to the findings of Wang et al, a review published in 2021 examining 38 human health studies concluded that regulatory ‘safe’ limits for human exposure to phthalates may be set at levels not sufficiently protective of human health (FPF reported).
References
Iizuka, T. (2022). “Mono-(2-ethyl-5-hydroxyhexyl) phthalate promotes uterine leiomyoma cell survival through tryptophan-kynurenine-AHR pathway activation.” Proceedings of the National Academy of Sciences (PNAS). DOI: 10.1073/pnas.2208886119
Lange, R. (2022). “Cumulative risk assessment of five phthalates in European children and adolescents.” International Journal of Hygiene and Environmental Health. DOI: 10.1016/j.ijheh.2022.114052
Liu, Y. (2022). “An insight into sex-specific neurotoxicity and molecular mechanisms of DEHP: A critical review.” Environmental Pollution. DOI: 10.1016/j.envpol.2022.120673
Wang, M. (2022). “Migration analysis and health impact assessment of phthalates in takeaway food packaging materials.” Journal of Food Safety. DOI: 10.1111/jfs.13021
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Samuelson, K. (November 14, 2022). “Uterine fibroid growth activated by chemicals found in everyday products.” Northwestern
