Developmental toxic potential of di-n-propyl phthalate administered orally to rats

Plasticizer exposure in Germany from 1988 to 2022: Human biomonitoring data of 20 plasticizers from the German Environmental Specimen Bank

The German Environmental Specimen Bank (ESB) annually archives 24-h urine samples since the early 1980s. In this study, we analyzed 420 of these samples from the years 2014 to 2022 for metabolites of 18 phthalates and two substitutes. We merged the new data with the data from previous measurement campaigns to a combined dataset of 1825 samples covering a 35-year period from 1988 to 2022 to investigate time trends, calculate daily intakes and perform an anti-androgenic mixture risk assessment. With the extended set of 41 biomarkers, we are now able to monitor the exposure to all EU-labelled reprotoxic phthalates. Most phthalate exposures continued to decrease since first measurements in the 80s, with biggest drops for DnBP (96.6 %) and DEHP (90.9 %). DiNP and DiDP, seen on the rise in earlier campaigns, now declined. Exposures to the newly included, reprotoxic phthalates were generally negligible. Regarding mixture risk, 5 % of the highly exposed still exceeded the Hazard Index (HI) of 1 in 2009. In the current measurement campaign only three individuals (0.7 %) exceeded the HI of 1 (with exceedances still driven by DEHP and DnBP).In 2022, 20 % of the individuals still had an HI > 0.2, which we propose as a benchmark for interpreting phthalate mixture risk, considering concurrent exposures to other anti-androgens. Exposure to the substitutes DINCH and DEHTP continues to increase, with daily intakes of DEHTP exceeding those of DEHP since 2018. Compared with the United States (US) National Health and Nutrition Examination Survey (NHANES) phthalate exposures seem to align, except for DEHTP with up to ten times higher levels in the US. Human biomonitoring (HBM) is the ideal tool to capture actual mixture exposures per individual, integrating all external exposure sources and pathways, thus we will continue to use HBM in exposure and risk assessment of phthalates and other (anti-androgenic) chemicals.

Mono-n-hexyl phthalate: exposure estimation and assessment of health risks based on levels found in human urine samples

Mono-n-hexyl phthalate (MnHexP) is a primary metabolite of di-n-hexyl phthalate (DnHexP) and other mixed side-chain phthalates that was recently detected in urine samples from adults and children in Germany. DnHexP is classified as toxic for reproduction category 1B in Annex VI of Regulation (EC) 1272/2008 and listed in Annex XIV of the European chemical legislation REACH; thereby, its use requires an authorisation. Health-based guidance values for DnHexP are lacking and a full-scale risk assessment has not been carried out under REACH. The detection of MnHexP in urine samples raises questions about the sources of exposure and concerns of consumer safety. Here, we propose the calculation of a provisional oral tolerable daily intake value (TDI) of 63 µg/kg body weight/day for DnHexP and compare it to intake levels corresponding to levels of MnHexP found in urine. The resulting mean intake levels correspond to less than 0.2% of the TDI, and maximum levels to less than 5%. The TDI was derived by means of an approximate probabilistic analysis using the credible interval from benchmark dose modelling of published ex vivo data on reduced foetal testosterone production in rats. Thus, for the dose associated to a 20% reduction in testosterone production, a lower and upper credible interval of 14.9 and 30.0 mg/kg bw/day, respectively, was used. This is considered a conservative approach, since apical developmental endpoints (e.g. changed anogenital distance) were only observed at higher doses. In addition, we modelled various scenarios of the exposure to the precursor substance DnHexP from different consumer products, taking measured contamination levels into account, and estimated systemic exposure doses. Of the modelled scenarios including the application of sunscreen (as a lotion or pump spray), the use of lip balm, and the wearing of plastic sandals, and considering conservative assumptions, the use of DnHexP-contaminated sunscreen was highlighted as a major contributing factor. A hypothetical calculation using conservative assumptions for the latter resulted in a margin of safety in relation to the lower credible interval of 3267 and 1007 for adults and young children, respectively. Most importantly, it was found that only a fraction of the TDI is reached in all studied exposure scenarios. Thus, with regard to the reported DnHexP exposure, a health risk can be considered very unlikely.

Phthalate toxicity mechanisms: An update

Phthalates are one of the most widely used plasticizers in polymer products, and they are increasingly being exposed to people all over the world, generating health concerns. Phthalates are often used as excipients in controlled-release capsules and enteric coatings, and patients taking these drugs may be at risk. In both animals and human, phthalates are mainly responsible for testicular dysfunction, ovarian toxicity, reduction in steroidogenesis. In this regard, for a better understanding of the health concerns corresponding to phthalates and their metabolites, still more research is required. Significantly, multifarious forms of phthalates and their biomedical effects are need to be beneficial to investigate in the various tissues or organs. Based on these investigations, researchers can decipher their toxicity concerns and related mechanisms in the body after phthalate's exposure. This review summarizes the chemical interactions, mechanisms, and their biomedical applications of phthalates in animals and human.

Effects of bis(2-butoxyethyl) phthalate exposure in utero on the development of fetal Leydig cells in rats

Phthalates are plasticizers widely found in the environment. They are potential endocrine disruptors. Bis(2-butoxyethyl) phthalate (BBOP) is a unique phthalate that contains oxygen atoms in the carbon backbone. Little is known about its reproductive and developmental toxicity. The objective of this study was to determine the effect of BBOP on fetal Leydig cell development after in utero exposure to rats. Sprague Dawley pregnant dams were randomly allocated into 6 groups, and were gavaged with BBOP (0, 10, 100, 250, 500, and 1000 mg/kg body weight/day) from gestational day (GD) 14-21. Seven of the 8 dams in the 1000 mg/kg BBOP group died before giving birth. Twelve of the 20 dams in the 500 mg/kg BBOP group had whole litter loss. BBOP significantly reduced the body weight of dams and male offspring and serum testosterone level and anogenital distance of male fetus on GD 21 at 500 mg/kg. BBOP markedly increased fetal Leydig cell proliferation and number at 500 mg/kg while inducing their abnormal aggregation at 250 and 500 mg/kg. BBOP down-regulated the expression of Lhcgr, Scarb1, Star, Cyp11a1, Hsd3b1, Cyp17a1, Hsd17b3, Insl3, and Nr5a1 at various doses while up-regulating the expression of Sertoli cell gene Fshr and Sox9. The phosphorylation of AKT1, AKT2, and ERK1/2 was also markedly reduced by BBOP. In conclusion, BBOP in utero exposure can disrupt fetal Leydig cell development, possibly via the mechanism that may include inhibiting the phosphorylation of AKT1, AKT2, and ERK1/2.

Phthalate-Induced Fetal Leydig Cell Dysfunction Mediates Male Reproductive Tract Anomalies

Male fetal Leydig cells in the testis secrete androgen and insulin-like 3, determining the sexual differentiation. The abnormal development of fetal Leydig cells could lead to the reduction of androgen and insulin-like 3, thus causing the male reproductive tract anomalies in male neonates, including cryptorchidism and hypospadias. Environmental pollutants, such as phthalic acid esters (phthalates), can perturb the development and differentiated function of Leydig cells, thereby contributing to the reproductive toxicity in the male. Here, we review the epidemiological studies in humans and experimental investigations in rodents of various phthalates. Most of phthalates disturb the expression of various genes encoded for steroidogenesis-related proteins and insulin-like 3 in fetal Leydig cells and the dose-additive effects are exerted after exposure in a mixture.

The structure-activity relationship (SAR) for phthalate-mediated developmental and reproductive toxicity in males

Testicular dysgenesis syndrome includes the hypospadias, cryptorchidism and abnormal fetal testis in male neonate. This is possibly caused by the environmental phthalates, which down-regulate the expression of androgen synthetic genes and Insl3 or directly inhibits steroidogenic enzymes. There are distinct structure-activity relationships (SARs) for phthalate-mediated developmental and reproductive toxicity. Here, we review the SAR for phthalate-mediated testicular dysgenesis syndrome. Of phthalates of straight side chains, C5-C6 ones are the most potent, C4 or C7 are moderate, C3 is weakest, and C1-2 or C8-13 are ineffective. The branching and unsaturation of side chains increases the toxicity. The cycling of side chains does not increase the toxicity.

Degradation of Diallyl Phthalate (DAP) by Fenton Oxidation: Mechanistic and Kinetic Studies

In this work, the degradation and mineralization of Diallyl Phthalate (DAP) in water by Fenton oxidation was investigated. The effects of different experimental parameters including the initial pH, the hydrogen peroxide (H2O2) dose, the catalyst (Fe2+) dose, the iron source, and the DAP concentration on the rate and the yield of DAP degradation by Fenton oxidation were evaluated. DAP and its intermediates were quantified by high performance liquid chromatography (HPLC) analysis and the measurement of total organic carbon (TOC) during Fenton oxidation. The results obtained confirmed that hydroxyl radicals (HO•) generated from Fenton’s reaction were capable of completely eliminating DAP from water. Fenton oxidation of 100 mg/L DAP aqueous solution at pH = 3.2 required 1000 mg/L H2O2 and 50 mg/L Fe2+. Under these conditions, more than TOC removal exceeded 95% after 300 min Fenton oxidation. The competition kinetics method was used to determine an absolute rate constant of 7.26.109 M−1 s−1 for the reaction between DAP and HO• radicals. HPLC analysis showed that phthalic acid, 1,2-dihydroxybenzene, 1,2,4-trihydroxybenzene, maleic acid, formic acid and oxalic acid were the main intermediates formed during DAP degradation. Accordingly, a simple DAP degradation mechanism by the Fenton reaction was proposed. These promising results proved the potential of Fenton oxidation as a cost-effective method for the decontamination of wastewaters containing phthalates.

Plasticizer endocrine disruption: Highlighting developmental and reproductive effects in mammals and non-mammalian aquatic species

Due to their versatility, robustness, and low production costs, plastics are used in a wide variety of applications. Plasticizers are mixed with polymers to increase flexibility of plastics. However, plasticizers are not covalently bound to plastics, and thus leach from products into the environment. Several studies have reported that two common plasticizers, bisphenol A (BPA) and phthalates, induce adverse health effects in vertebrates; however few studies have addressed their toxicity to non-mammalian species. The aim of this review is to compare the effects of plasticizers in animals, with a focus on aquatic species. In summary, we identified three main chains of events that occur in animals exposed to BPA and phthalates. Firstly, plasticizers affect development by altering both the thyroid hormone and growth hormone axes. Secondly, these chemicals interfere with reproduction by decreasing cholesterol transport through the mitochondrial membrane, leading to reduced steroidogenesis. Lastly, exposure to plasticizers leads to the activation of peroxisome proliferator-activated receptors, the increase of fatty acid oxidation, and the reduction in the ability to cope with the augmented oxidative stress leading to reproductive organ malformations, reproductive defects, and decreased fertility.

Reproductive and developmental effects of phthalate diesters in females

Phthalate diesters, widely used in flexible plastics and consumer products, have become prevalent contaminants in the environment. Human exposure is ubiquitous and higher phthalate metabolite concentrations documented in patients using medications with phthalate-containing slow release capsules raises concerns for potential health effects. Furthermore, animal studies suggest that phthalate exposure can modulate circulating hormone concentrations and thus may be able to adversely affect reproductive physiology and the development of estrogen sensitive target tissues. Therefore, we conducted a systematic review of the epidemiological and experimental animal literature examining the relationship between phthalate exposure and adverse female reproductive health outcomes. The epidemiological literature is sparse for most outcomes studied and plagued by small sample size, methodological weaknesses, and thus fails to support a conclusion of an adverse effect of phthalate exposure. Despite a paucity of experimental animal studies for several phthalates, we conclude that there is sufficient evidence to suggest that phthalates are reproductive toxicants. However, we note that the concentrations needed to induce adverse health effects are high compared to the concentrations measured in contemporary human biomonitoring studies. We propose that the current patchwork of studies, potential for additive effects and evidence of adverse effects of phthalate exposure in subsequent generations and at lower concentrations than in the parental generation support the need for further study.

The influence of endocrine disruptors on growth and development of children

PURPOSE OF REVIEW

This review describes the most recent data about the effects of endocrine disrupting compounds (EDCs) on infant and early childhood growth and reproductive tract development as well as controversies in the field.

RECENT FINDINGS

EDCs are present in pregnant women, young children and adolescents. Whether the level of exposure contributes to disease is an ongoing debate. Epidemiological studies suggest associations between prenatal EDC exposure and disease outcome, but animal studies using controlled EDC exposure have varying results with underlying mechanisms largely unknown.

SUMMARY

Human exposure to EDCs is widespread; bisphenol A, phthalates and persistent organic pollutants are detectable in all age groups and geographical locations in the USA. Epidemiological and animal studies suggest that phthalates and bisphenol A have adverse effects on birth weight, promote development of childhood obesity and adversely affect male reproductive tract development. Differences in the interpretation of available studies underlie the disparate conclusions of scientific and regulatory body's panels on potential toxicological effects of EDCs at current levels of human exposure.