Transgenerational effects of Di (2-ethylhexyl) phthalate in the male CRL:CD(SD) rat: added value of assessing multiple offspring per litter

Man is not a big rat: concerns with traditional human risk assessment of phthalates based on their anti-androgenic effects observed in the rat foetus

Phthalates provide one of the most documented example evidencing how much we must be cautious when using the traditional paradigm based on extrapolation of experimental data from rodent studies for human health risk assessment of endocrine disruptors (EDs). Since foetal testis is known as one of the most sensitive targets of EDs, phthalate risk assessment is routinely based on the capacity of such compounds to decrease testosterone production by the testis or to impair masculinization in the rat during foetal life. In this paper, the well-established inhibiting effects of phthalates of the foetal Leydig cells function in the rat are briefly reviewed. Then, data obtained in humans and other species are carefully analysed. Already in January 2009, using the organotypic culture system named Fetal Testis Assay (FeTA) that we developed, we reported that phthalates might not affect testosterone production in human foetal testes. Several recent experimental studies using xenografts confirm the absence of detectable anti-androgenic effect of phthalates in the human foetal testes. Epidemiological studies led to contradictory results. Altogether, these findings suggest that phthalates effects on foetal Leydig cells are largely species-specific. Consequently, the phthalate threshold doses that disturb foetal steroidogenesis in rat testes and that are presently used to define the acceptable daily intake levels for human health protection must be questioned. This does not mean that phthalates are safe because these compounds have many deleterious effects upon germ cell development that may be common to the different studied species including human. More generally, the identification of common molecular, cellular or/and phenotypic targets in rat and human testes should precede the choice of the toxicological endpoint in rat to accurately assess the safety threshold of any ED in humans.

Concentration of di(2-ethylhexyl) phthalate (DEHP) in foods and its dietary exposure in China

Di(2-ethylhexyl) phthalate (DEHP) is a common plasticizer used in food contact materials that has been reported as an endocrine disruptor. In the present study, DEHP concentrations were analyzed in foods in order to determine dietary exposure among the Chinese population, including the general population (aged 2-100) and four age group, that is children aged 2-6, adolescent aged 7-12, young people aged 13-17 and adults aged 18 years old and above. 1704 food samples were collected during 2011-2012 and categorized into 12 food groups which covered major foods in China. Food consumption data were taken from China National Nutrient and Health Survey which was performed in 2002 and includes data from 68,959 subjects. Mean concentrations of DEHP were combined with individual food consumption data to estimate dietary exposure. It was found that DEHP levels in foods ranged from not detected to 3.41 mg/kg, with highest mean values in meat (0.23 mg/kg) and vegetable oils (0.21 mg/kg). Mean dietary intakes of DEHP in the general population, children, and adults were 2.34, 4.51, 2.03 μg/kg bw per day, respectively. The 97.5% intakes in these populations were 5.22, 8.43, 3.64 μg/kg bw per day, respectively. The main food sources of DEHP dietary intake were cereals (39.44%), drinking water (16.94%) and meat (15.81%) in children, and cereals (44.57%), meat (15.70%) and drinking water (12.28%) for adults. These findings suggested that dietary exposure to DEHP among Chinese population was lower than tolerable daily intake of DEHP and there are no health concerns based on generally accepted exposure limits.

Effects of di(n-butyl) and monobutyl phthalate on steroidogenesis pathways in the murine Leydig tumor cell line MLTC-1

Di(n-butyl) phthalate (DBP) and its active metabolite monobutyl phthalate (MBP) have been shown to disrupt reproductive organ growth. The objective of this study was to evaluate the effects of DBP/MBP on steroidogenesis in the murine Leydig tumor cell line MLTC-1 in vitro. MLTC-1 cells were incubated with various concentrations of DBP (100, 1, 0.01, and 0μmol/l in DMSO) and MBP (1000, 10, 0.1, and 0μmol/l in DMSO) for 24h. Testosterone secretion was stimulated at the lowest doses and inhibited at higher treatment doses of DBP and MBP. The mRNA levels of the side-chain cleavage enzyme (P450scc), cytochrome p450c17 (P450c17) and 3β-hydroxy-steroid dehydrogenase (3βHSD) were significantly reduced in the phthalate-exposed groups, whereas, the transcription and translation of insulin-like hormone 3 (INSL3) was affected by DBP and MBP. Alterations of the steroidogenic enzymes and INSL3 in MLTC-1 cells may be involved in the biphasic effects of DBP/MBP on androgen production.

Taiwan food scandal: the illegal use of phthalates as a clouding agent and their contribution to maternal exposure

In 2011 the Taiwan Food and Drug Administration reported that plasticizers di(2-ethylhexyl) phthalate (DEHP) and di-iso-nonyl phthalate (DiNP), endocrine disruptors, were illegally added to clouding agents used in foods and beverages. 965 products were found contaminated, of which 206 were exported to 22 countries. This study's purpose was to obtain English names for 28 contaminated products for which DEHP levels were reported, calculate estimated average daily intake (mg/kg/day) for a 50 kg woman consuming one portion, and compare to U.S. and E.U. guidelines for daily intake. We found that drinking just one bottle (500 ml) of sports drinks would result in an average DEHP intake of 0.14 mg/kg bw/day (range 0.091-0.341), which exceeds by several fold government guidelines (0.02-0.06 mg/kg bw/day). One (2 g) serving from 4/14 samples of contaminated dietary supplements exceeds the guideline of 0.02 mg/kg bw/day. In conclusion, consuming even one portion of tainted drinks and some powders would lead to daily intake of DEHP that greatly exceeds established safety guidelines, raising concerns about potential adverse effects, particularly reproductive tract development in the male fetus. Global distribution of DEHP-contaminated and other adulterated products should prompt governments to become proactive in food safety regulations and chemical testing.

Transgenerational effects of di-(2-ethylhexyl) phthalate on testicular germ cell associations and spermatogonial stem cells in mice

Recent evidence has linked human phthalate exposure to abnormal reproductive and hormonal effects. Phthalates are plasticizers that confer flexibility and transparency to plastics, but they readily contaminate the body and the environment. In this study, timed pregnant CD1 outbred mice were treated with di-(2-ethylhexyl) phthalate (DEHP) from Embryonic Day 7 (E7) to E14. The subsequent generation (F1) offspring were then bred to produce the F2, F3, and F4 offspring, without any further DEHP treatment. This exposure scheme disrupted testicular germ cell association and decreased sperm count and motility in F1 to F4 offspring. By spermatogonial transplantation techniques, the exposure scheme also disrupted spermatogonial stem cell (SSC) function of F3 offspring. The W/W(V) recipient testes transplanted with F3 offspring germ cells from the DEHP-treated group had a dramatically lower percentage of donor germ cell-derived spermatogenic recovery in seminiferous tubules when compared to the recipient testes transplanted with CD1 control germ cells. Further characterization showed that the major block of donor germ cell-derived spermatogenesis was before the appearance of undifferentiated spermatogonia. Interestingly, the testes transplanted with the F3 offspring germ cells from the DEHP-treated group, when regenerated, replicated testis morphology similar to that observed in the testes from the F1 to F3 offspring of the DEHP-treated group, suggesting that the germ cell disorganization phenotype originates from the stem cells of F3 offspring. In conclusion, embryonic exposure to DEHP was found to disrupt testicular germ cell organization and SSC function in a transgenerational manner.

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.

Chemical behavior of phthalates under abiotic conditions in landfills

The phthalates comprise a family of phthalic acid esters that are used primarily as plasticizers in polymeric materials to impart flexibility during the manufacturing process and to the end product. It is estimated that the annual worldwide production of phthalate esters exceeds five million tons. Plasticizers are one of the most prominent classes of chemicals, but unfortunately, they possess endocrine-disrupting chemical properties. As endocrine-disrupting chemicals, plasticizers have produced adverse developmental and reproductive effects in mammalian animal models.Phthalates are easily transported into the environment during manufacture, disposal,and leaching from plastic materials, because they are not covalently bound to the plastics of which they are a component. Because of their fugitive nature and widespread use, the phthalates are commonly detected in air, water, sediment/soil, and biota, including human tissue. Large amounts of phthalic acid esters are often leached from the plastics that are dumped at municipal landfills.Phthalate esters undergo chemical changes when released into the environment.The primary processes by which they are transformed include hydrolysis, photolysis,and biodegradation. It is noteworthy that all of these degradation processes are greatly influenced by the local physical and chemical conditions. Hence, in the present review, we have sought to ascertain from the literature how the phthalate esters undergo transformation when they are released into lower landfill layers.Within the upper landfill layers, biodegradation prevails as the major degradation mechanism by which the phthalates are dissipated. Generally, biodegradation pathways for the phthalates consist of primary biodegradation from phthalate diesters to phthalate monoesters, then to phthalic acid, and ultimately biodegradation of phthalic acid to form C02 and/or CH4• We have noted that the phthalate esters are also degraded through abiotic means,which proceeds via both hydrolysis and photolysis. Photodegradation generally involves reactions of the phthalates in the atmosphere with hydroxyl radicals. The hydrolysis of phthalate diesters produces the corresponding monoesters, which are subsequently converted to phthalic acid. Phthalic acid has been observed to accumulate within landfill zones where phthalate contamination exists.Hydrolysis is usually not an important fate process for phthalate esters in the environment, including in upper landfill layers. However, the conditions prevalent at lower landfill layers are generally suitable for phthalate transformation via hydrolysis.The conditions in this zone include high temperatures and pressures, presence of chemical catalysts, as well as wide pH fluctuations. Such conditions foster hydrolysis that may be either acid- or base-catalyzed by metal ions, anions, or organic materials catalysts. In addition, research indicates that the propensity for ongoing hydrolysis increases as landfill depth increases.We can be emphatic in asserting that hydrolysis of phthalate esters in lower landfill layers is the dominant process for transforming these esters; in contrast,biodegradation is the predominant process in the upper landfill layers.We recommend that future research be performed to expand the understanding of what influence each reaction condition (high temperature, presence of chemical catalysts, etc.) has on the rate of chemical transformation of the phthalates in lower landfill zones. We also recommend that the combined effects of all conditions on the rate of chemical transformation at lower landfill layers be assessed for the phthalates.Such research could be achieved under simulated conditions.

Effects of DEHP on endometrial receptivity and embryo implantation in pregnant mice

Di-(2-ethylhexyl)-phthalate (DEHP) is a ubiquitous environmental pollutant and endocrine disruptor (ED) that causes serious adverse effects on animal and human health. The harmful effects of DEHP on human reproduction are increasingly recognized, especially in women. However, it is not known how endometrial receptivity and embryo implantation, which play important roles in the establishment of pregnancy, are affected by DEHP. This study was aimed towards investigating the effects of DEHP on endometrial receptivity and embryo implantation in pregnant mice. The pregnant mice received DEHP at 0, 250, 500 and 1000 mg/kg/day from day 1 (D1) of gestation until sacrifice. Administration of DEHP led to compromised endometrial receptivity and decreased number of implantation sites. The mRNA and protein expression levels of ERα, PR and E-cadherin, but not those of HoxA10 and MMP-2, were up-regulated by DEHP in the mouse endometrium. The results further suggested that DEHP disrupts the MAPK and NF-κB signaling pathways. This was maybe one of paths which influenced the E-cadherin expression. In conclusion, DEHP reduced endometrial receptivity and impaired embryo implantation by influencing the expression of hormone receptors and E-cadherin. Therefore, determining the full extent of the hazards of DEHP to human reproduction will be vital to developing and implementing effective protective measures.

Di-(2-ethylhcxyl) phthalate reduces progesterone levels and induces apoptosis of ovarian granulosa cell in adult female ICR mice

Di-(2-ethylhexyl) phthalate (DEHP) as an environmental endocrine disruptor is a known reproductive toxicant and carcinogen. The purpose of this study was to evaluate the female reproductive toxicity of DEHP. Sixty ICR female mice were randomized into four groups dosed with 0, 125, 500, or 2 000 mg/kg DEHP by gavage for 16 weeks, 6 days/week. DEHP treatment prolonged duration of the estrous cycle in mice at 500 and 2000 mg/kg DEHP, but no significant effects on estrus phase of the cycle in each group were detected. Exposure to DEHP inhibited secretion of serum progesterone. DEHP arrested granulosa cells at G(0)/G(1) phases and increased proportion of apoptosis cells at 500 and 2000 mg/kg DEHP. There was no significant difference in P450arom mRNA expression among groups. Results demonstrate that DEHP can produce toxicity in female reproductive system.

Endocrine-disrupting chemicals and public health protection: a statement of principles from The Endocrine Society

An endocrine-disrupting chemical (EDC) is an exogenous chemical, or mixture of chemicals, that can interfere with any aspect of hormone action. The potential for deleterious effects of EDC must be considered relative to the regulation of hormone synthesis, secretion, and actions and the variability in regulation of these events across the life cycle. The developmental age at which EDC exposures occur is a critical consideration in understanding their effects. Because endocrine systems exhibit tissue-, cell-, and receptor-specific actions during the life cycle, EDC can produce complex, mosaic effects. This complexity causes difficulty when a static approach to toxicity through endocrine mechanisms driven by rigid guidelines is used to identify EDC and manage risk to human and wildlife populations. We propose that principles taken from fundamental endocrinology be employed to identify EDC and manage their risk to exposed populations. We emphasize the importance of developmental stage and, in particular, the realization that exposure to a presumptive "safe" dose of chemical may impact a life stage when there is normally no endogenous hormone exposure, thereby underscoring the potential for very low-dose EDC exposures to have potent and irreversible effects. Finally, with regard to the current program designed to detect putative EDC, namely, the Endocrine Disruptor Screening Program, we offer recommendations for strengthening this program through the incorporation of basic endocrine principles to promote further understanding of complex EDC effects, especially due to developmental exposures.

Reproductive effects in F1 adult females exposed in utero to moderate to high doses of mono-2-ethylhexylphthalate (MEHP)

Phthalates are widely used as plasticizers in everyday products. Yet, studies on the effects of phthalates on female reproductive health are limited. In this study, pregnant C57/Bl6 mice were exposed via oral gavage to corn oil, 100, 500, or 1000mg/kg MEHP from gestational days 17-19. Reproductive lifespan was decreased by one month in the highest F1 exposure group (9.8±0.4 versus 11.1±0.6 months in control F1 females). F1 females exhibited delayed estrous onset at the two higher exposures and prolonged estrus was observed in all MEHP-exposed females. Serum FSH and estradiol were significantly elevated at the highest exposure and altered mRNA expression was found for the steroidogenic genes LHCGR, aromatase, and StAR. At one year of age, mammary gland hyperplasia was observed in high dose MEHP-exposed females. In summary, late gestational exposure to MEHP leads to multiple latent reproductive effects throughout murine life resulting in premature ovarian senescence and mammary hyperplasia.

Assessing exposure to phthalates - the human biomonitoring approach

Some phthalates are developmental and reproductive toxicants in animals. Exposure to phthalates is considered to be potentially harmful to human health as well. Based on a comprehensive literature research, we present an overview of the sources of human phthalate exposure and results of exposure assessments with special focus on human biomonitoring data. Among the general population, there is widespread exposure to a number of phthalates. Foodstuff is the major source of phthalate exposure, particularly for the long-chain phthalates such as di(2-ethylhexyl) phthalate. For short-chain phthalates such as di-n-butyl-phthalate, additional pathways are of relevance. In general, children are exposed to higher phthalate doses than adults. Especially, high exposures can occur through some medications or medical devices. By comparing exposure data with existing limit values, one can also assess the risks associated with exposure to phthalates. Within the general population, some individuals exceed tolerable daily intake values for one or more phthalates. In high exposure groups, (intensive medical care, medications) tolerable daily intake transgressions can be substantial. Recent findings from animal studies suggest that a cumulative risk assessment for phthalates is warranted, and a cumulative exposure assessment to phthalates via human biomonitoring is a major step into this direction.

Dipentyl phthalate dosing during sexual differentiation disrupts fetal testis function and postnatal development of the male Sprague-Dawley rat with greater relative potency than other phthalates

Phthalate esters (PEs) constitute a large class of plasticizer compounds that are widely used for many consumer product applications. Ten or more members of the PE class of compounds are known to induce male fetal endocrine toxicity and postnatal reproductive malformations by disrupting androgen production during the sexual differentiation period of development. An early study conducted in the rat pubertal model suggested that dipentyl phthalate (DPeP) may be a more potent testicular toxicant than some more extensively studied phthalates. Regulatory agencies require dose-response and potency data to facilitate risk assessment; however, very little data are currently available for DPeP. The goal of this study was to establish a more comprehensive data set for DPeP, focusing on dose-response and potency information for fetal and postnatal male reproductive endpoints. We dosed pregnant rats on gestational day (GD) 17 or GD 14-18 and subsequently evaluated fetal testicular testosterone (T) production on GD 17.5 and GD 18, respectively. We also dosed pregnant rats on GD 8-18 and evaluated early postnatal endpoints in male offspring. Comparison of these data to data previously obtained under similar conditions for di (2-ethylhexyl) phthalate indicates that DPeP is approximately eightfold more potent in reducing fetal T production and two- to threefold more potent in inducing development of early postnatal male reproductive malformations. Additionally, fetal testicular T production was more sensitive to inhibitory effects of DPeP exposure than was gene expression of target genes involved in male reproductive development, supporting the use of this endpoint as a critical effect in the risk assessment process.

Reproductive and behavioral effects of diisononyl phthalate (DINP) in perinatally exposed rats

Diisononyl phthalate (DINP) is a plasticizer abundantly used in consumer products as a substitute for other plasticizers prohibited in certain products due to reproductive toxicity. As anti-androgenic effects of DINP are suspected, DINP effects on reproduction and sexually dimorphic behavior were studied. Pregnant Wistar rats were gavaged from gestation day 7 to postnatal day (PND) 17 with vehicle, 300, 600, 750 or 900 mg DINP/kg bw/day. In fetal testes histopathological effects typical of phthalates were observed. In male offspring, DINP caused increased nipple retention, reduced anogenital distance, reduced sperm motility and increased sperm count. DINP affected spatial learning as female offspring performed better than controls and similarly to control males in the Morris Water Maze, indicating masculinization of behavior in DINP exposed females. These results show that DINP causes anti-androgenic effects on reproductive development, though less potent than DEHP, DBP and BBP, and further safety evaluation of DINP appears warranted.

Perinatal exposure of rats to Bisphenol A affects fertility of male offspring--an overview

Endocrine disruptors (ED) induce both functional and behavioral reproductive abnormalities. Bisphenol A (BPA) is a known ED that leaches from polycarbonate plastics, as such human exposure is common. Maternal BPA exposure has been shown to have negative effects on the fertility of male offspring. Pregnant rats exposed perinatally to environmentally relevant doses of BPA gave birth to offspring with significantly impaired spermatogenesis and fertility. Perinatal exposure had deleterious effects on the male germ line which manifested as impairments in the fertility of F(1) male offspring and subsequent F(2) and F(3) generations. This overview is an attempt to summarize the currently available data in the literature with regards to perinatal BPA exposure and male fertility.

Pathway modeling of microarray data: a case study of pathway activity changes in the testis following in utero exposure to dibutyl phthalate (DBP)

Pathway activity level analysis, the approach pursued in this study, focuses on all genes that are known to be members of metabolic and signaling pathways as defined by the KEGG database. The pathway activity level analysis entails singular value decomposition (SVD) of the expression data of the genes constituting a given pathway. We explore an extension of the pathway activity methodology for application to time-course microarray data. We show that pathway analysis enhances our ability to detect biologically relevant changes in pathway activity using synthetic data. As a case study, we apply the pathway activity level formulation coupled with significance analysis to microarray data from two different rat testes exposed in utero to Dibutyl Phthalate (DBP). In utero DBP exposure in the rat results in developmental toxicity of a number of male reproductive organs, including the testes. One well-characterized mode of action for DBP and the male reproductive developmental effects is the repression of expression of genes involved in cholesterol transport, steroid biosynthesis and testosterone synthesis that lead to a decreased fetal testicular testosterone. Previous analyses of DBP testes microarray data focused on either individual gene expression changes or changes in the expression of specific genes that are hypothesized, or known, to be important in testicular development and testosterone synthesis. However, a pathway analysis may inform whether there are additional affected pathways that could inform additional modes of action linked to DBP developmental toxicity. We show that Pathway activity analysis may be considered for a more comprehensive analysis of microarray data.

Perinatal exposure to di-(2-ethylhexyl) phthalate leads to restricted growth and delayed lung maturation in newborn rats

BACKGROUND

Pregnant women and infants have significant exposures to the most commonly used plasticizer di-(2-ethylhexyl) phthalate (DEHP).

OBJECTIVES

This study was designed to evaluate the effects of DEHP exposure on growth and lung maturation in rats and determine if DEHP regulation of 11beta-hydroxysteroid dehydrogenase type 1 gene (Hsd11b1) expression in the lung tissue plays a role in its effects on lung maturation.

METHOD

Pregnant Sprague-Dawley rats were treated from gestational day 12 to postnatal day (PND) 21 with DEHP orally at dosages of 0, 10, 100 or 750 mg/kg/day, respectively (n=8 for each group). Two rat pups (one male and one female) from each litter were sacrificed at PND 1 and 21. Body weight was measured and the lung was processed for histology and calculation of lung interstitial tissue proportion as well as real-time PCR determination of the expressions of Hsd11b1, surfactant associated protein-A1 gene (Sftpa1) and B gene (Sftpb).

RESULTS

The perinatal DEHP exposure led to a dose dependent intrauterine and postnatal growth restriction (P<0.001). High dose DEHP (750 mg/kg/day) exposure led to decreased gas-exchange space as evidenced by increased lung interstitial tissue proportion (P<0.001), but did not cause significant changes in Hsd11b1, Sftpa1 or Sftpb gene expression in the rat lung at PND 1. The DEHP-induced change in lung histology remained significant at PND 21 with improvement despite continual exposure to DEHP.

CONCLUSION

Perinatal DEHP exposure leads to growth restriction and delayed lung maturation in newborn rats.

Determination of the di-(2-ethylhexyl) phthalate NOAEL for reproductive development in the rat: importance of the retention of extra animals to adulthood

Deriving No Observed Adverse Effect Level (NOAEL) or benchmark dose is important for risk assessment and can be influenced by study design considerations. In order to define the di-(2-ethylhexyl) phthalate (DEHP) dose-response curve for reproductive malformations, we retained more offspring to adulthood to improve detection of these malformations in the reproductive assessment by continuous breeding study design. Sprague-Dawley rats were given a dietary administration of 1.5 (control), 10, 30, 100, 300, 1000, 7500, and 10,000 ppm DEHP. Male pups were evaluated for gross reproductive tract malformations (RTMs) associated with the "phthalate syndrome." DEHP treatment had minimal effects on P0 males. There was a statistically significant increase in F1 and F2 total RTMs (testis, epididymides, seminal vesicle, and prostate) in the 7500-ppm dose group and F1 10,000-ppm dose group. The 10,000-ppm exposed F1 males did not produce an F2 generation. The NOAEL for F1 and F2 RTM combined data, because in utero exposures were similar, were 100 ppm (4.8 mg/kg/day), which was close to the 5% response benchmark dose lower confidence limit of 142 ppm. The utility of evaluating more pups per litter was examined by generating power curves from a Monte Carlo simulation. These curves indicate a substantial increase in detection rate when three males are evaluated per litter rather than one. A 10% effect across male pups would be detected 5% of the time if one pup per litter was evaluated, but these effects would be detected 66% of the time if three pups per litter were evaluated. Taken together, this study provides a well-defined dose response of DEHP-induced RTMs and demonstrates that retention of more adult F1 and F2 males per litter, animals that were already produced, increases the ability to detect RTMs and presumably other low-incidence phenomena.

Organic and inorganic mercury in neonatal rat brain after prenatal exposure to methylmercury and mercury vapor

BACKGROUND

Many populations are exposed to multiple species of mercury (Hg), predominantly organic Hg as methylmercury (MeHg) from fish, and inorganic Hg as Hg vapor from dental amalgams. Most of our knowledge of the neurotoxicity of Hg is based on research devoted to studying only one form at a time, mostly MeHg.

OBJECTIVES

In this study we investigated the effects of prenatal exposure to MeHg and Hg vapor on Hg concentrations in the brain of neonatal rats.

METHODS

Female Long-Evans hooded rats were exposed to MeHg (0, 3, 6, or 9 ppm as drinking solution), Hg vapor (0, 300, or 1,000 microg/m3 for 2 hr/day), or the combination of both, from 30 days before breeding through gestational day 18. On postnatal day 4, whole brains were taken from one male and one female from each of four litters in each treatment group to assess organic and inorganic Hg in the brain by cold vapor atomic absorption spectrometry.

RESULTS

Statistical analysis using linear mixed effects models showed that MeHg dose was the primary determinant of both organic and inorganic brain Hg levels. For both outcomes, we also found significant interactions between MeHg and Hg vapor exposure. These interactions were driven by the fact that among animals not exposed to MeHg, animals exposed to Hg vapor had significantly greater organic and inorganic brain Hg levels than did unexposed animals.

CONCLUSION

This interaction, heretofore not reported, suggests that coexposure to MeHg and Hg vapor at levels relevant to human exposure might elevate neurotoxic risks.