Adverse effects of microplastics and nanoplastics on the reproductive system: A comprehensive review of fertility and potential harmful interactions

New insights into the reproductive hazards posed by polystyrene nanoplastics

Reproductive toxicity from micro/nanoplastics (MNPLs) is an emerging concern requiring further investigation to close existing knowledge gaps. This study explores the reproductive toxicity of polystyrene nanoplastics (PSNPLs) using Drosophila as an in vivo model. Males and females were exposed to PSNPLs (100 and 500 µg/mL) for one/two weeks. Confocal and transmission electron microscopy revealed widespread distribution of PSNPLs across various tissues, including ovaries, testes, and gametes (ova and sperm). Structural damage, such as hole formation in the seminiferous tubules and ovarian atrophy, was observed following exposure. The physical presence of PSNPLs in reproductive organs disrupted reproductive outcomes, particularly in matings between exposed males and females. Key impairments included reduced fecundity, lower fertility, and a skewed sex ratio, especially after one week of exposure, with minimal effects after two weeks. Significant disruptions in the expression of reproductive and developmental genes were observed in both sexes, with males exhibiting greater sensitivity to PSNPLs, regardless of exposure concentration or duration. These findings provide critical insights into the reproductive toxicity of PSNPLs, underscoring both physical disruptions in reproductive tissues and molecular alterations. This highlights the potential for MNPLs to cause hidden reproductive damage and emphasizes the sex-dependent nature of these toxic effects.

Effects of phthalate exposure on human ovarian extracellular matrix composition: insights from a 3D spheroid model

Phthalates, widely used as plasticizers in consumer products, have become a significant public health concern due to their toxic effects on reproductive and endocrine systems. However, the specific mechanisms by which phthalates affect ovarian function remain poorly understood. To address this knowledge gap, we employed 3D spheroids derived from human ovarian stromal cells, which mimic the ovarian tissue. Since remodeling the ovarian extracellular matrix (ECM) is centrally involved in follicle growth, ovulation, and ovarian aging, we decided to study the impact of environmentally relevant phthalate mixtures (PM) on ECM components. Spheroids were generated from both reproductive-aged and menopausal ovarian tissues, then treated with PM for four days. Collagen deposition was assessed using picrosirius red staining, while immunofluorescence was used to evaluate the proliferation and deposition of collagen type VI, elastin, fibrillin-1, and elastin microfibril interfacer 1 (EMILIN-1). Our results revealed that PM exposure significantly increased collagen deposition (p < 0.0001) in spheroids from reproductive-aged ovaries, while reducing collagen VI levels (p < 0.05), potentially compromising the structural and functional integrity of the ovarian ECM. In contrast, spheroids from menopausal ovaries exhibited a decrease in EMILIN-1 (p < 0.05) and fibrillin-1 (p < 0.001), both crucial for maintaining tissue elasticity. These findings underscore the detrimental effects of phthalates on ovarian ECM across different age groups, with a particular emphasis on ECM elastisity. Additionally, this study highlights the utility of 3D spheroids as a reliable in vitro model for mechanistic research, drug screening and toxicology testing.

In-field degradation of polybutylene adipate-co-terephthalate (PBAT) films, microplastic formation, and impacts on soil health

Polybutylene adipate-co-terephthalate (PBAT) mulch films are potential alternatives to traditional polyethylene (PE) mulch films in agriculture. Here, we investigated the degradation rate and microplastic formation of PBAT films in an agricultural field and the impacts on soil health as well as maize yields. We compared two biodegradable films (PBAT clear film: BCF and PBAT black film: BBF) with two conventional films (PE clear film: PCF and PE black film: PBF) in a field experiment over three growing seasons. Biodegradable films consisted of >90% PBAT and 5% polylactic acid. After three years of mulching, more microplastics were detected for the BCF (1820 particles kg-1) and BBF (1560 particles kg-1) treatments than for PCF (840 particles kg-1) and PBF (747 particles kg-1). The majority (about 70%) of microplastics in BCF and BBF were <0.25 mm, while in PCF and PBF the fraction of microplastics <0.25 mm made up only 24-41%. Biodegradable films increased soil organic carbon, microbial biomass carbon, and nitrate nitrogen by 0.16-0.48 g kg-1, 5.5-33.8 mg kg-1, and 32.6-109.6 mg kg-1, respectively, compared to PE films. Yield was highest for BBF, exceeding that of non-film, PCF, PBF and BCF by 2550, 566, 960 and 367 kg ha-1, respectively. Overall, the biodegradable films had a positive impact on soil health and maize yields.

Developing a feasible fast-track testing method for developmental neurotoxicity studies: alternative model for risk assessment of micro- and nanoplastics

Micro- and nanoplastics (MNPs) are widespread environmental pollutants that pose significant health risks. They originate from industrial processes, consumer products, and environmental degradation, inducing oxidative stress through cellular dysfunctions such as membrane interaction, internalization, mitochondrial damage, inflammation, metal ion leaching, and impaired antioxidant defense. Despite increasing evidence of their toxicity-particularly developmental neurotoxicity (DNT) and mitochondrial impairment-our understanding remains limited due to the high costs of animal studies, which reduce the overall size of experimental data. This underscores the urgent need for alternative test methods that are cost-effective, rapid, and translational. This review examines new approach methodologies (NAMs) for DNT assessment, addressing the ethical, financial, and translational limitations of animal models. NAMs integrate three complementary non-animal models that enhance conventional testing. First, zebrafish models provide organismal insights into behavioral and neurodevelopmental outcomes at minimal cost. Second, neuronal organoids replicate human-specific neurodevelopmental processes in a 3D system, offering mechanistic insights. Lastly, human cell lines enable high-throughput screening, integrating findings from zebrafish and organoid studies. Establishing a new paradigm for DNT testing is crucial for faster and more efficient toxicity and risk assessments, ultimately protecting public health. Standardizing and gaining regulatory acceptance for NAMs will improve predictive accuracy and broaden their application in environmental toxicology. Advancing these methodologies is essential to addressing the risks of MNP exposure while promoting ethical and sustainable research practices.

Polystyrene microplastics impaired the function of leydig cells via GRP78/PERK/CHOP mediated endoplasmic reticulum stress in vivo and in vitro

The toxic effect of Polystyrene Microplastics (PS-MPs) on leydig cells were found in male mice, but the toxic mechanism was not clear. The PS-MPs exposure mice model and cell model were established in this study to explore the leydig cells toxic mechanism. In vivo study, the leydig cells toxicity in male mice was evaluated exposed to PS-MPs for 28 days. And found that the sperm density, mobility and testosterone (T) level decreased, and the sperm malformation rate and malondialdehyde level increased. PS-MPs exposure impaired the function of male reproduction. The results also showed that the levels of testosterone-producing proteins (StAR, P450scc,3β-HSD and CYP17A1) decreased, apoptosis signaling pathways (Bax/Bcl-2, Caspase-8 and Caspase-12) were activated and endoplasmic reticulum stress (GRP78/p-PERK/CHOP) occurred in male mice exposed to PS-MPs. In vitro study, TM3 cells (leydig cells) were treated with 50, 100 and 200 μg/mL of PS-MPs for 24 h. And we found that PS-MPs exposure reduced the cell viability and the level of T, increased reactive oxygen species (ROS) level in TM3 cells. PS-MPs exposure impaired the function of the leydig cells. Further testing revealed that PS-MPs could activate GRP78/p-PERK/CHOP pathway, aggrandized endoplasmic reticulum stress in the leydig cells, then increased apoptosis level, and induced testosterone synthase protein reduction. These could be reversed when exposed to ROS inhibitor or endoplasmic reticulum stress inhibitor. In conclusion, PS-MPs exposure induced the high level of ROS, activated the GRP78/p-PERK/CHOP signaling pathway, enhanced endoplasmic reticulum stress in leydig cells, then apoptosis level increased, which impaired the leydig cell function.

Using Insect Larvae and Their Microbiota for Plastic Degradation

Plastic pollution is one of the biggest current global threats to the environment given that petroleum-based plastic is recalcitrant and can stay in the environment for decades, even centuries, depending on the specific plastic type. Since less than 10% of all plastic made is recycled, and the other solutions (such as incineration or landfill storage) are pollutant methods, new, environmentally friendly solutions are needed. In this regard, the latest biotechnological discovery on this topic is the capability of insect larvae to use plastic polymers as carbon feedstock. This present review describes the most relevant information on the insect larvae capable of degrading plastic, mainly Galleria mellonella (Fabricius, 1798), Tenebrio molitor (Linnaeus, 1758), and Zophobas atratus (Fabricius, 1776), and also adds new information about other less commonly studied "plastivore" insects such as termites. This review covers the literature from the very first work describing plastic degradation by larvae published in 2014 all the way to the very latest research available (till June 2024), focusing on the identification of a wide variety of plastic-degrading microorganisms isolated from larvae guts and on the understanding of the potential molecular mechanisms present for degradation to take place. It also describes the latest discoveries, which include the identification of novel enzymes from waxworm saliva.

Impact of microplastics on female reproductive health: insights from animal and human experimental studies: a systematic review

OBJECTIVE

This systematic review aims to evaluate the impact of microplastics on female reproductive health by analyzing experimental studies.

METHOD

A comprehensive search was conducted in PubMed, Web of Science, and Scopus databases to identify experimental studies published between 2021 and 2023. Studies investigating the effects of microplastics on reproductive organs, hormone levels, fertility rates, and offspring development in female subjects were included. The quality of the studies was assessed using the Cochrane risk of bias tool.

RESULTS

A total of 15 studies met the inclusion criteria. The results indicate that exposure to microplastics significantly affects ovarian function, decreases fertility rates, and disrupts hormone levels in female subjects. Several studies also reported negative effects on embryo development and offsprings health. The quality of the studies varied, with some showing a high risk of bias.

CONCLUSION

The evidence from experimental studies suggests that microplastics have a detrimental effect on female reproductive health. However, the variation in study quality highlights the need for more rigorous research to confirm these results and better understand the underlying mechanisms.

Intestinal Barrier Damage and Growth Retardation Caused by Exposure to Polystyrene Nanoplastics Through Lactation Milk in Developing Mice

Microplastics, defined as plastic fragments smaller than 5 mm, degrade from larger pollutants, with nanoscale microplastic particles presenting significant biological interactions. This study investigates the toxic effects of polystyrene nanoplastics (PS-NPs) on juvenile mice, which were exposed through lactation milk and drinking water at concentrations of 0.01 mg/mL, 0.1 mg/mL, and 1 mg/mL. The results show that PS-NP exposure during lactation and juvenile periods caused delayed weight gain and impaired organ development, particularly in the liver and kidneys, without causing functional abnormalities or toxic injuries. The primary toxicity of PS-NPs was observed in the intestinal tract, including shortened villi, disrupted tight junctions, inhibited epithelial cell proliferation, and oxidative stress responses. These findings highlight the importance of evaluating the developmental toxicity of nanoplastics at environmentally relevant doses.

Advancements in Assays for Micro- and Nanoplastic Detection: Paving the Way for Biomonitoring and Exposomics Studies

Although plastic pollution and exposure to plastic-related compounds have received worldwide attention, health risks associated with micro- and nanoplastics (MNPs) are largely unknown. Emerging evidence suggests MNPs are present in human biofluids and tissue, including blood, breast milk, stool, lung tissue, and placenta; however, exposure assessment is limited and the extent of human exposure to MNPs is not well known. While there is a critical need to establish robust and scalable biomonitoring strategies to assess human exposure to MNPs and plastic-related chemicals, over 10,000 chemicals have been linked to plastic manufacturing with no existing standardized approaches to account for even a fraction of these exposures. This review provides an overview of the status of methods for measuring MNPs and associated plastic-related chemicals in humans, with a focus on approaches that could be adapted for population-wide biomonitoring and integration with biological response measures to develop hypotheses on potential health effects of plastic exposures. We also examine the exposure risks associated with the widespread use of chemical additives in plastics. Despite advancements in analytical techniques, there remains a pressing need for standardized measurement protocols and untargeted, high-throughput analysis methods to enable comprehensive MNP biomonitoring to identify key MNP exposures in human populations. This review aims to merge insights into the toxicological effects of MNPs and plastic additives with an evaluation of analytical challenges, advocating for enhanced research methods to fully assess, understand, and mitigate the public health implications of MNPs.

Wildfire Smoke: Health Effects, Mechanisms, and Mitigation

Wildfires are becoming more frequent and intense on a global scale, raising concerns about their acute and long-term effects on human health. We conducted a systematic review of the current epidemiological evidence on wildfire health risks and a meta-analysis to investigate the association between wildfire smoke exposure and various health outcomes. We discovered that wildfire smoke increases the risk of premature deaths and respiratory morbidity in the general population. Meta-analysis of cause-specific mortality and morbidity revealed that wildfire smoke had the strongest associations with cardiovascular mortality (RR: 1.018, 95% CI: 1.014-1.021), asthma hospitalization (RR: 1.054, 95% CI: 1.026-1.082), and asthma emergency department visits (RR: 1.117, 95% CI: 1.035-1.204) in the general population. Subgroup analyses of age found that adults and elderly adults were more susceptible to the cardiopulmonary effects of wildfire smoke. Next, we systematically addressed the toxicological mechanisms of wildfire smoke, including direct toxicity, oxidative stress, inflammatory reactions, immune dysregulation, genotoxicity and mutations, skin allergies, inflammation, and others. We discuss wildfire smoke risk mitigation strategies including public health interventions, regulatory measures, and personal actions. We conclude by highlighting current research limitations and future directions for wildfire research, such as elucidating the complex interactions of wildfire smoke components on human health, developing personalized risk assessment tools, and improving resilience and adaptation strategies to mitigate the health effects of wildfires in changing climate.

The porcine corpus luteum as a model for studying the effects of nanoplastics

Nanoplastics (NPs) affect fertility. We evaluated the effects of NPs treatment on luteal and endothelial cells. We examined crucial markers of growth and redox status. NPs treatment did not induce changes in ATP levels in luteal cells, while it increased (p< 0.05) their proliferation. In endothelial cells, no change in proliferation was detected, while an increase (p<0.05) in ATP levels was observed. The increase of reactive oxygen species, superoxide anion (p<0.05) and nitric oxide (p<0.001) was detected in both cell types, which also showed changes in superoxide dismutase enzyme activity as well as an increase of non-enzymatic antioxidant power (p<0.05). A decrease (p<0.05) in progesterone production as well as an increase of vascular endothelial growth factor A levels were detected (p<0.05). In addition, a dose-dependent accumulation of NPs in endothelial cells was shown, that likely occurred through adhesion and internalization. Results underline potential risk of NPs for corpus luteum functionality.

Microplastics in marine ecosystems: A comprehensive review of biological and ecological implications and its mitigation approach using nanotechnology for the sustainable environment

Microplastic contamination has rapidly become a serious environmental issue, threatening marine ecosystems and human health. This review aims to not only understand the distribution, impacts, and transfer mechanisms of microplastic contamination but also to explore potential solutions for mitigating its widespread impact. This review encompasses the categorisation, origins, and worldwide prevalence of microplastics and methodically navigates the complicated structure of microplastics. Understanding the sources of minute plastic particles infiltrating water bodies worldwide is critical for successful removal. The presence and accumulation of microplastics has far reaching negative impacts on various marine creatures, eventually extending its implications to human health. Microplastics are known to affect the metabolic activities and the survival of microbial communities, phytoplankton, zooplankton, and fauna present in marine environments. Moreover, these microplastics cause developmental abnormalities, endocrine disruption, and several metabolic disorders in humans. These microplastics accumulates in aquatic environments through trophic transfer mechanisms and biomagnification, thereby disrupting the delicate balance of these ecosystems. The review also addresses the tactics for minimising the widespread impact of microplastics by suggesting practical alternatives. These include increasing public awareness, fostering international cooperation, developing novel cleanup solutions, and encouraging the use of environment-friendly materials. In conclusion, this review examines the sources and prevalence of microplastic contamination in marine environment, its impacts on living organisms and ecosystems. It also proposes various sustainable strategies to mitigate the problem of microplastics pollution. Also, the current challenges associated with the mitigation of these pollutants have been discussed and addressing these challenges require immediate and collective action for restoring the balance in marine ecosystems.

The heart of plastic: utilizing the Drosophila model to investigate the effects of micro/nanoplastics on heart function

Microplastics (MPs) and nanoplastics (NPs) have increasingly been found in the environment. Until recently, most MPs/NPs toxicological research has been done in aquatic systems resulting in a gap in knowledge regarding terrestrial systems. Plastics have been shown to enter the circulatory system of humans, and can accumulate within organs, little is known about the effect this has on health. Heart disease is the leading cause of death globally, so it's critical to understand the possible impacts MPs/NPs have on the heart. The Drosophila model has been growing in popularity within the toxicology field, it allows for affordable and rapid research on the impacts of a variety of toxins, including plastics. Some research has examined toxicological effects of plastics on the fly, evaluating the effects on mortality, fecundity, development, and locomotion. However, no one has studied the effects on the Drosophila heart. We utilize the Drosophila model to identify the potential effects of oral exposure to polystyrene MPs (1 µm in diameter) and NPs (0.05 µm in diameter) particles on heart function. Flies were exposed to 1.4 × 1011 particles/d/kg of larvae for MPs and 1.2 × 1018 particles/d/kg of larvae for NPs from egg to pupal eclosion. Heart function was then analyzed utilizing semi-intact dissections and Semi-automatic Optic Heartbeat Analysis software (SOHA). Following exposure to MPs and NPs we see sexually dimorphic changes to heart size and function. This study highlights the importance of additional Drosophila MPs/NPs research to identify the molecular mechanisms behind these changes.

Beyond the food on your plate: Investigating sources of microplastic contamination in home kitchens

Given that a substantial amount of time is spent in kitchens preparing food, the kitchen equipment used may be relevant in determining the composition and amount of microplastics ending up on our dinner plate. While previous research has predominantly focused on foodstuffs as a source of microplastics, we emphasise that micro- and nanoplastics are ubiquitous and likely originate from diverse sources. To address the existing knowledge gap regarding additional sources contributing to microplastics on our dinner plates, this review investigates various kitchen processes, utensils and equipment (excluding single-use items and foodstuffs) to get a better understanding of potential microplastic sources within a home kitchen. Conducting a narrative literature review using terms related to kitchenware and kitchen-affiliated equipment and processes, this study underscores that the selection of preparation tools, storage, serving, cooking, and cleaning procedures in our kitchens may have a significant impact on microplastic exposure. Mechanical, physical, and chemical processes occurring during food preparation contribute to the release of microplastic particles, challenging the assumption that exposure to microplastics in food is solely tied to food products or packaging. This review highlights diverse sources of microplastics in home kitchens, posing concerns for food safety and human health.

Polystyrene nanoplastics induce apoptosis, autophagy, and steroidogenesis disruption in granulosa cells to reduce oocyte quality and fertility by inhibiting the PI3K/AKT pathway in female mice

BACKGROUND

Nanoplastics (NPs) are emerging pollutants that pose risks to living organisms. Recent findings have unveiled the reproductive harm caused by polystyrene nanoparticles (PS-NPs) in female animals, yet the intricate mechanism remains incompletely understood. Under this research, we investigated whether sustained exposure to PS-NPs at certain concentrations in vivo can enter oocytes through the zona pellucida or through other routes that affect female reproduction.

RESULTS

We show that PS-NPs disrupted ovarian functions and decreased oocyte quality, which may be a contributing factor to lower female fertility in mice. RNA sequencing of mouse ovaries illustrated that the PI3K-AKT signaling pathway emerged as the predominant environmental information processing pathway responding to PS-NPs. Western blotting results of ovaries in vivo and cells in vitro showed that PS-NPs deactivated PI3K-AKT signaling pathway by down-regulating the expression of PI3K and reducing AKT phosphorylation at the protein level, PI3K-AKT signaling pathway which was accompanied by the activation of autophagy and apoptosis and the disruption of steroidogenesis in granulosa cells. Since PS-NPs penetrate granulosa cells but not oocytes, we examined whether PS-NPs indirectly affect oocyte quality through granulosa cells using a granulosa cell-oocyte coculture system. Preincubation of granulosa cells with PS-NPs causes granulosa cell dysfunction, resulting in a decrease in the quality of the cocultured oocytes that can be reversed by the addition of 17β-estradiol.

CONCLUSIONS

This study provides findings on how PS-NPs impact ovarian function and include transcriptome sequencing analysis of ovarian tissue. The study demonstrates that PS-NPs impair oocyte quality by altering the functioning of ovarian granulosa cells. Therefore, it is necessary to focus on the research on the effects of PS-NPs on female reproduction and the related methods that may mitigate their toxicity.

Global prevalence of microplastics in tap water systems: Abundance, characteristics, drivers and knowledge gaps

Tap water is a main route for human direct exposure to microplastics (MPs). This study recompiled baseline data from 34 countries to assess the current status and drivers of MP contamination in global tap water systems (TWS). It was shown that MPs were detected in 87 % of 1148 samples, suggesting the widespread occurrence of MPs in TWS. The detected concentrations of MPs spanned seven orders of magnitude and followed the linearized log-normal distribution (MSE = 0.035, R2 = 0.965), with cumulative concentrations at 5th, 50th and 95th percentiles of 0.028, 4.491 and 728.105 items/L, respectively. The morphological characteristics were further investigated, indicating that particles smaller than 50 μm dominated in global TWS, with fragment, polyester and transparent as the most common shape, composition and color of MPs, respectively. Subsequently, the SHapley Additive exPlanations (SHAP) algorithm was implemented to quantify the importance of variables affecting the MP abundance in global TWS, showing that the lower particle size limit was the most important variables. Subgroup analysis revealed that the concentration of MPs counted at the size limit of 1 μm was >20 times higher than that above 1 μm. Ultimately, current knowledge gaps and future research needs were elucidated.

Prevalence and implications of microplastic contaminants in general human seminal fluid: A Raman spectroscopic study

Microplastics are ubiquitous environmental contaminants that have been detected in human semen from polluted areas, yet their prevalence and effects in the general population remain largely unexplored. To examine microplastic presence, abundance, polymer types, and associations with semen quality parameters in individuals without occupational exposures, this study was conducted by collecting semen samples from 40 participants undergoing premarital health assessments in Jinan, China. Raman microspectroscopy was employed to identify, quantify, and categorize microplastic polymers, sperm motility was assessed via computer-assisted analysis, and morphology was evaluated through Diff-Quik staining. Correlations between demographics, semen parameters, and microplastic content were examined by statistical analysis. We found that microplastics were detected in all semen samples, with 2 particles per sample (ranging from 0.72 to 7.02 μm). Eight distinct polymers were identified, with polystyrene (31 %) being most prevalent. Semen exposed to polystyrene demonstrated higher sperm progressive motility as compared to polyvinyl chloride exposure group (43.52 ± 14.21 % vs 19.04 ± 13.46 %). Sperm morphological abnormalities were observed but not significantly associated with specific plastic types. In conclusion, this study reveals microplastic contamination in semen from individuals without occupational exposure, with PS, PE, and PVC being the most prevalent and exhibiting differential correlations with sperm progressive motility, and highlight the need for further research into the potential reproductive impacts of microplastic exposure.

Gut microbiota and liver metabolomics reveal the potential mechanism of Lactobacillus rhamnosus GG modulating the liver toxicity caused by polystyrene microplastics in mice

Microplastics (MPs) are known to cause liver toxicity as they can spread through the food chain. Most researches on their toxicity have focused on individual organs, neglecting the crucial "gut-liver axis"-a bidirectional communication pathway between the gut and liver. Probiotics have shown promise in modulating the effects of environmental pollutants. In this study, we exposed mice to Lactobacillus rhamnosus GG (LGG, 100 mg/kg b.w./d) and/or polystyrene microplastics (PS-MPs, 5 mg/kg b.w./d) for 28 d via gavage to investigate how probiotics influence live toxicity through the gut-liver axis. Our results demonstrated that PS-MPs induced liver inflammation (increased IL-6 and TNF-α) and disrupted lipid metabolism. However, when combined with LGG, these effects were alleviated. LGG also improved colon health, rectifying ciliary defects and abnormal mucus secretion caused by PS-MPs. Furthermore, LGG improved gut microbiota dysbiosis induced by PS-MPs. Metabolomics and gene expression analysis (Cyp7a1 and Cyp7b1) indicated that LGG modulated bile acid metabolism. In summary, LGG appears to protect the liver by maintaining gut homeostasis, enhancing gut barrier integrity, and reducing the liver inflammation. These findings confirm the potential of LGG to modulate liver toxicity caused by PS-MPs through the gut-liver axis, offering insights into probiotics' application for environmental pollutant detoxification.

Imprinting and Reproductive Health: A Toxicological Perspective

This overview discusses the role of imprinting in the development of an organism, and how exposure to environmental chemicals during fetal development leads to the physiological and biochemical changes that can have adverse lifelong effects on the health of the offspring. There has been a recent upsurge in the use of chemical products in everyday life. These chemicals include industrial byproducts, pesticides, dietary supplements, and pharmaceutical products. They mimic the natural estrogens and bind to estradiol receptors. Consequently, they reduce the number of receptors available for ligand binding. This leads to a faulty signaling in the neuroendocrine system during the critical developmental process of 'imprinting'. Imprinting causes structural and organizational differentiation in male and female reproductive organs, sexual behavior, bone mineral density, and the metabolism of exogenous and endogenous chemical substances. Several studies conducted on animal models and epidemiological studies provide profound evidence that altered imprinting causes various developmental and reproductive abnormalities and other diseases in humans. Altered metabolism can be measured by various endpoints such as the profile of cytochrome P-450 enzymes (CYP450's), xenobiotic metabolite levels, and DNA adducts. The importance of imprinting in the potentiation or attenuation of toxic chemicals is discussed.