Exposure parameters necessary for delayed puberty and mammary gland development in Long–Evans rats exposed in utero to atrazine

Peripubertal exposure of atrazine cause decrease in exploratory activity, deficits in sociability and few alterations on brain monoaminergic systems of rats

Atrazine is a pesticide used to control weeds in both in pre- and post-emergence crops. The chronic exposure to atrazine can lead to severe damage in animals, especially in the endocrine and reproduction systems, leading to the inclusion of this pesticide into the endocrine disrupting chemicals group. Studies with rats showed that atrazine exposure during lactation in dams caused changes in the juvenile offspring, however; there is still limited information regarding the effects of atrazine during puberty. Thus, the aim of this study is to evaluate the effects of peripubertal exposure of atrazine in rats, assessing motor activity, social behavior and neurochemical alterations. Juvenile rats were treated with different doses of atrazine (0, 10, 30 or 100 mg/kg) by gavage from postnatal day 22 to 41. Behavioral tests were conducted for the evaluation of motor activity and social behavior, and neurochemical evaluation was done in order to assess monoamine levels. Atrazine caused behavioral alterations, evidenced by decrease in the exploratory activity (p values variation between 0.05 and 0.0001) and deficits in the social behavior of both male and females as adults (p values variation between 0.01 and 0.0001). As for the monoaminergic neurotransmission, atrazine led to very few alterations on the dopamine and serotonin systems that were limited to the females (p < 0.05). Altogether, the results suggests that peripubertal exposure of atrazine cause behavioral and neurochemical alterations. More studies need to be conducted to fully understand the differences in atrazine's effects and its use should be considered carefully.

Application of the Key Characteristics Framework to Identify Potential Breast Carcinogens Using Publicly Available in Vivo, in Vitro, and in Silico Data

BACKGROUND

Chemicals that induce mammary tumors in rodents or activate estrogen or progesterone signaling are likely to increase breast cancer (BC) risk. Identifying chemicals with these activities can prompt steps to protect human health.

OBJECTIVES

We compiled data on rodent tumors, endocrine activity, and genotoxicity to assess the key characteristics (KCs) of rodent mammary carcinogens (MCs), and to identify other chemicals that exhibit these effects and may therefore increase BC risk.

METHODS

Using authoritative databases, including International Agency for Research on Cancer (IARC) Monographs and the US Environmental Protection's (EPA) ToxCast, we selected chemicals that induce mammary tumors in rodents, stimulate estradiol or progesterone synthesis, or activate the estrogen receptor (ER) in vitro. We classified these chemicals by their genotoxicity and strength of endocrine activity and calculated the overrepresentation (enrichment) of these KCs among MCs. Finally, we evaluated whether these KCs predict whether a chemical is likely to induce mammary tumors.

RESULTS

We identified 279 MCs and an additional 642 chemicals that stimulate estrogen or progesterone signaling. MCs were significantly enriched for steroidogenicity, ER agonism, and genotoxicity, supporting the use of these KCs to predict whether a chemical is likely to induce rodent mammary tumors and, by inference, increase BC risk. More MCs were steroidogens than ER agonists, and many increased both estradiol and progesterone. Enrichment among MCs was greater for strong endocrine activity vs. weak or inactive, with a significant trend.

DISCUSSION

We identified hundreds of compounds that have biological activities that could increase BC risk and demonstrated that these activities are enriched among MCs. We argue that many of these should not be considered low hazard without investigating their ability to affect the breast, and chemicals with the strongest evidence can be targeted for exposure reduction. We describe ways to strengthen hazard identification, including improved assessments for mammary effects, developing assays for more KCs, and more comprehensive chemical testing. https://doi.org/10.1289/EHP13233.

Occurrence, fate, seasonal variability, and risk assessment of twelve triazine herbicides and eight related derivatives in source, treated, and tap water of Wuhan, Central China

Triazine herbicides have been widely used, are frequently detected in aqueous environments and soils, and can cause acute or chronic toxicity to living organisms. We collected source water samples (n = 20) originating from the Hanshui River and the Yangtze River of Wuhan section, treated water samples (n = 20), and tap water samples (n = 169) in Wuhan, Central China during 2019 for determination of twelve triazine herbicides and their eight derivatives (collectively defined as TZs) and characterizing their fate during water treatment. Eighteen of the twenty TZs were detected in the source water. Atrazine (ATZ) had the highest concentrations (median: 22.4 ng/L) in the source water samples while DACT had the highest concentrations (median: 31.4 ng/L) in the treated water. "Tryns" (ametryn, prometryn, simetryn, terbutryn) were efficiently removed by conventional water treatment, while other target analytes were not; interestingly, hydroxypropazine and prometon increased significantly accompanied by prometryn disappearance, which implicated potential transformation pathways. In addition, "tryns" might be transformed into "tons" (atraton, prometon, secbumeton, terbumeton) by ozonation. In the tap water samples, diaminochlorotriazine had the highest concentrations (median: 34.9 ng/L) among the target analytes, followed by ATZ (18.3 ng/L), hydroxyatrazine (5.17 ng/L), deethylatrazine (5.00 ng/L), hydroxypropazine (3.20 ng/L), deisopropylatrazine (2.05 ng/L), hydroxydesethylatrazine (1.68 ng/L), and others. The TZs had the highest cumulative concentration in July in the tap water samples (median: 89.7 ng/L). This study found that ozonation in combination with activated carbon was more efficient in removing triazine herbicides, although "tryns" could also be transformed during conventional treatment. Ecological risk assessment showed moderate risks posed by hydroxyterbuthylazine, prometryn, and simetryn; the Hanshui River had higher risks than the Yangtze River, and July had higher risks than February. Human exposure to the TZs via water ingestion was low compared to the reference doses. This study characterized the occurrence of some new emerging TZs in the source water, their fate during drinking water treatment, and their seasonal variability in the tap water.

Atrazine exposure induces necroptosis through the P450/ROS pathway and causes inflammation in the gill of common carp (Cyprinus carpioL.)

Atrazine (ATR) is used worldwide and has been confirmed be hazardous materials that harmful to the health of organisms. Since ATR was more persistent in the water, the specific damage caused by ATR to aquatic organisms should be concern. The role of P450/ROS has been proposed in many pathomechanisms. To explore whether P450/ROS mediated necroptosis and promote inflammatory response caused by ATR exposure, 120 common carp (Cyprinus carpio L.) were randomly divided into four groups which were exposed to 0 μg/L, 4 μg/L, 40 μg/L and 400 μg/L ATR respectively. The residual levels of ATR and its metabolites increased, signs of necrosis and inflammation were found in the gills of the ATR-treatment groups. The levels of ROS and cytochrome P450 content were increased, and P450 enzymes were activated. The expression levels of the core components of necroptosis (RIPK1, RIPK3 and MLKL) increased. Moreover, gene expression of inflammatory factors (TNF-α, NF-κB, iNOS, COX-2, IL-1β and PTGE) increased significantly in the ATR-spiked group. Our results suggested that ATR exposure triggered necroptosis through the P450/ROS pathway and causes inflammation of common carp gill. This study provides valuable clue about the mechanism by which ATR causes injury to common carp gill.

Histopathological, immunohistochemical, and molecular investigation of atrazine toxic effect on some organs of adult male albino rats with a screening of Acacia nilotica as a protective trial

Atrazine (ATZ) is a widely used herbicide; however, it has deleterious effects. The current study aimed to investigate the potential toxic effect of ATZ as a neuroendocrine disruptor on the cerebellum and thyroid gland and on the liver as a detoxifying organ. We examined the ability of ATZ to induce oxidative stress and subsequent apoptosis in these organs. Moreover, we investigated the potential protective effect of Acacia nilotica, because of its potent antioxidant activity. Thus, our study was carried out on 40 adult male albino rats that were divided equally into 4 groups (10 rats/each group). The first group received distilled water, while the second group received ATZ dissolved in corn oil at 200 mg/kg body weight/day by stomach gavage. The third group was treated orally by ATZ (200 mg/kg body weight/day) plus Acacia nilotica (400 mg/kg/day). Group IV received Acacia nilotica only at a dose (400 mg/kg/day). After successive 30 days of the experiment, blood and tissue samples were collected from all groups. Our findings revealed the ability of ATZ to induce toxic effects was observed microscopically in the form of degenerated neurons and vacuolated neuropil of the cerebellum, degenerated hepatocytes, and vacuolation of the follicular cells of the thyroid gland. Furthermore, ATZ significantly elevated AST, ALT, and ALP serum levels and TB concentration, while decreased GSH. DNA fragmentation% and activated caspase-3 expression significantly increased after ATZ exposure. Interestingly, Acacia nilotica administration was able to partially protect the examined organs against the toxic effect of ATZ exposure.

Killing two birds with one stone: Pregnancy is a sensitive window for endocrine effects on both the mother and the fetus

Pregnancy is a complex process requiring tremendous physiological changes in the mother in order to fulfill the needs of the growing fetus, and to give birth, expel the placenta and nurse the newborn. These physiological modifications are accompanied with psychological changes, as well as with variations in habits and behaviors. As a result, this period of life is considered as a sensitive window as impaired functional and physiological changes in the mother can have short- and long-term impacts on her health. In addition, dysregulation of the placenta and of mechanisms governing placentation have been linked to chronic diseases later-on in life for the fetus, in a concept known as the Developmental Origin of Health and Diseases (DOHaD). This concept stipulates that any change in the environment during the pre-conception and perinatal (in utero life and neonatal) period to puberty, can be "imprinted" in the organism, thereby impacting the health and risk of chronic diseases later in life. Pregnancy is a succession of events that is regulated, in large part, by hormones and growth factors. Therefore, small changes in hormonal balance can have important effects on both the mother and the developing fetus. An increasing number of studies demonstrate that exposure to endocrine disrupting compounds (EDCs) affect both the mother and the fetus giving rise to growing concerns surrounding these exposures. This review will give an overview of changes that happen during pregnancy with respect to the mother, the placenta, and the fetus, and of the current literature regarding the effects of EDCs during this specific sensitive window of exposure.

Chemical Effects on Breast Development, Function, and Cancer Risk: Existing Knowledge and New Opportunities

Population studies show worrisome trends towards earlier breast development, difficulty in breastfeeding, and increasing rates of breast cancer in young women. Multiple epidemiological studies have linked these outcomes with chemical exposures, and experimental studies have shown that many of these chemicals generate similar effects in rodents, often by disrupting hormonal regulation. These endocrine-disrupting chemicals (EDCs) can alter the progression of mammary gland (MG) development, impair the ability to nourish offspring via lactation, increase mammary tissue density, and increase the propensity to develop cancer. However, current toxicological approaches to measuring the effects of chemical exposures on the MG are often inadequate to detect these effects, impairing our ability to identify exposures harmful to the breast and limiting opportunities for prevention. This paper describes key adverse outcomes for the MG, including impaired lactation, altered pubertal development, altered morphology (such as increased mammographic density), and cancer. It also summarizes evidence from humans and rodent models for exposures associated with these effects. We also review current toxicological practices for evaluating MG effects, highlight limitations of current methods, summarize debates related to how effects are interpreted in risk assessment, and make recommendations to strengthen assessment approaches. Increasing the rigor of MG assessment would improve our ability to identify chemicals of concern, regulate those chemicals based on their effects, and prevent exposures and associated adverse health effects.

Endocrine disrupting chemicals and the mammary gland

Development of the mammary gland requires coordination of hormone signaling pathways including those mediated by estrogen, progesterone, androgen and prolactin receptors. These hormones play important roles at several distinct stages of life including embryonic/fetal development, puberty, pregnancy, lactation, and old age. This also makes the gland sensitive to perturbations from environmental agents including endocrine disrupting chemicals (EDCs). Although there is evidence from human populations of associations between EDCs and disruptions to breast development and lactation, these studies are often complicated by the timing of exposure assessments and the latency to develop breast diseases (e.g., years to decades). Rodents have been instrumental in providing insights-not only to the basic biology and endocrinology of the mammary gland, but to the effects of EDCs on this tissue at different stages of development. Studies, mostly but not exclusively, of estrogenic EDCs have shown that the mammary gland is a sensitive tissue, that exposures during perinatal development can produce abnormal mammary structures (e.g., alveolar buds, typically seen in pregnant females) in adulthood; that exposures during pregnancy can alter milk production; and that EDC exposures can enhance the response of the mammary tissue to hormones and chemical carcinogens. Other studies of persistent organic pollutants have shown that EDC exposures during critical windows of development can delay development of the gland, with lifelong consequences for the individual. Collectively, this work continues to support the conclusion that EDCs can harm the mammary gland, with effects that depend on the period of exposure and the period of evaluation.

Prenatal exposure to atrazine induces cryptorchidism and hypospadias in F1 male mouse offspring

The main objective of the present study was to determine whether prenatal exposure to atrazine could affect testicle descent and penile masculinization. Atrazine has been demonstrated with a variety of endocrine disrupting activities and reproductive toxicities. However, the effects of prenatal atrazine exposure on male offspring's genital malformation, such as hypospadias and cryptorchidism, remain poorly understood. In this study, pregnant ICR mice were gavaged from gestational day 12.5-16.5 with different doses of atrazine. Although no sign of systemic toxicity was observed in F1 male pups, prenatal exposure to 100 mg/kg/day atrazine affected penile morphology, urethral meatus position and descent of testis, and reduced anogenital distance and penile size in postnatal day 21 F1 male pups. The comparative study with an androgen receptor (AR) antagonist vinclozolin suggested that these effects of atrazine on male genital development may not be through antagonism of AR. The results also revealed that atrazine exposure significantly reduced maternal serum testosterone levels, decreased AR nuclear translocation, and altered the expression levels of developmental gene networks in developing penis of mice. Atrazine exposure also affected the expression of insulin-like 3 (Insl3) and steroidogenic gene expression in developing reproductive tract. Therefore, our data indicate that prenatal atrazine exposure can induce hypospadias in F1 mice, likely through disruption of testosterone production, decreasing genomic androgen action, and then altering expression of developmental genes during sexual differentiation. Our data also suggest that prenatal atrazine exposure can induce cryptorchidism in F1 mice, possibly through down regulation of Insl3.

Pharmacokinetic, behavioral, and brain activity effects of Δ9-tetrahydrocannabinol in adolescent male and female rats

Δ⁹-tetrahydrocannabinol (THC) is the intoxicating constituent of cannabis and is responsible for the drug's reinforcing effects. Retrospective human studies suggest that cannabis use during adolescence is linked to long-term negative psychological outcomes, but in such studies it is difficult to distinguish the effects of THC from those of coexisting factors. Therefore, translationally relevant animal models are required to properly investigate THC effects in adolescents. However, though the relevance of these studies depends upon human-relevant dosing, surprisingly little is known about THC pharmacology and its effects on behavior and brain activity in adolescent rodents-especially in females. Here, we conducted a systematic investigation of THC pharmacokinetics, metabolism and distribution in blood and brain, and of THC effects upon behavior and neural activity in adolescent Long Evans rats of both sexes. We administered THC during an early-middle adolescent window (postnatal days 27-45) in which the brain may be particularly sensitive to developmental perturbation by THC. We determined the pharmacokinetic profile of THC and its main first-pass metabolites (11-hydroxy-THC and 11-nor-9-carboxy-THC) in blood and brain following acute injection (0.5 or 5 mg/kg, intraperitoneal). We also evaluated THC effects on behavioral assays of anxiety, locomotion, and place conditioning, as well as c-Fos expression in 14 brain regions. Confirming previous work, we find marked sex differences in THC metabolism, including a female-specific elevation in the bioactive metabolite 11-hydroxy-THC. Furthermore, we find dose-dependent and sex-dependent effects on behavior, neural activity, and functional connectivity across multiple nodes of brain stress and reward networks. Our findings are relevant for interpreting results of rat adolescent THC exposure studies, and may lend new insights into how THC impacts the brain in a sex-dependent manner.

Plastic wastes: environmental hazard and instrument for wealth creation in Nigeria

Combating the menace of plastic waste pollution has become a global environmental challenge. Plastic pollution is capable of affecting land, waterways and oceans as a large percentage of marine and land creatures have died due to the fact that plastic is non-biodegradable and it causes hazards to soil. It also emits toxic gasses when exposed or heated up. It blocks drainage lines and fill up land space causing floods and erosion thereby causing deterioration of the Nigerian roads. Plastics wastes are also harmful to human health; they may contain harmful acids which may lead to death. Nigeria, which is the biggest oil exporting country in Africa, relies mainly on the proceeds of the oil trade for its GDP and based strategy in growing her economy. However, with the declination of oil prices and increase in plastic wastes, the world is tending towards energy and sustainable development. Therefore, an urgent need for recycling plastic wastes into a solution for wealth creation is fundamental in Nigeria. This paper therefore seeks to identify favorable methods for recycling plastic wastes in Nigeria as a tool for solution to diversification and implementation. Evidence based examples are illustrated in the article with viable solution recommended for implementation.

Impact of pesticide exposure on adipose tissue development and function

Obesity is a leading cause of morbidity, mortality and health care expenditure whose incidence is rapidly rising across the globe. Although the cause of the obesity epidemic is typically viewed as a product of an increased availability of high calorie foods and/or a reduction in physical activity, there is mounting evidence that exposure to synthetic chemicals in our environment may play an important role. Pesticides, are a class of chemicals whose widespread use has coincided with the global rise of obesity over the past two decades. Importantly, given their lipophilic nature many pesticides have been shown to accumulate with adipose tissue depots, suggesting they may be disrupting the function of white adipose tissue (WAT), brown adipose tissue (BAT) and beige adipose tissue to promote obesity and metabolic diseases such as type 2 diabetes. In this review, we discuss epidemiological evidence linking pesticide exposure with body mass index (BMI) and the incidence of diabetes. We then review preclinical studies in rodent models which have directly evaluated the effects of different classes of insecticides and herbicides on obesity and metabolic dysfunction. Lastly, we review studies conducted in adipose tissue cells lines and the purported mechanisms by which pesticides may induce alterations in adipose tissue function. The review of the literature reveals major gaps in our knowledge regarding human exposure to pesticides and our understanding of whether physiologically relevant concentrations promote obesity and elicit alterations in key signaling pathways vital for maintaining adipose tissue metabolism.

Relationship between agrochemical compounds and mammary gland development and breast cancer

The exposure to agrochemical pesticides has been associated with several chronic diseases, including different types of cancer and reproductive disorders. In addition, because agrochemical pesticides may act as endocrine disrupting chemicals (EDCs) during different windows of susceptibility, they can increase the risk of impairing the normal development of the mammary gland and/or of developing mammary lesions. Therefore, the aim of this review is to summarize how exposure to different agrochemical pesticides suspected of being EDCs can interfere with the normal development of the mammary gland and the possible association with breast cancer. It has been shown that the mammary glands of male and female rats and mice are susceptible to exposure to non-organochlorine (vinclozolin, atrazine, glyphosate, chlorpyrifos) and organochlorine (endosulfan, methoxychlor, hexachlorobenzene) pesticides. Some of the effects of these compounds in experimental models include increased or decreased mammary development, impaired cell proliferation and steroid receptor expression and signaling, increased malignant cellular transformation and tumor development and angiogenesis. Contradictory findings have been found as to whether there is a causal link between the exposure or the pesticide body burden and breast cancer in humans. However, an association has been observed between pesticides (especially organochlorine compounds) and specific subtypes of breast cancer. Further studies are needed in both humans and experimental models to understand how agrochemical pesticides can induce or promote changes in the development, differentiation and/or malignant transformation of the mammary gland.

Plastic Waste Environmental and Human Health Impacts

Plastics have become a vital asset for humanity. Plastics are known as synthetic materials produced from synthetic or semi-synthetic organic polymers derived from petro-based chemicals, able to displace traditional natural polymeric materials (wood, stone, ceramics, etc.). Plastics have malformed everyday life; usage is increasing, and annual production is likely to exceed 300 million tons by 2010. In this chapter, the authors blend current understanding of the benefits and concerns surrounding the use of plastics and look to future priorities, challenges, and opportunities. Plastics case serious environmental pollution such as soil pollution, water pollution, and air pollution. Application of proper rules and regulations for the production and use of plastics can reduce the toxic effects of plastics on human health and the environment.

Atrazine-induced toxicity in goat spermatozoa is alleviated to some extent by polyphenol-enriched feed

Atrazine (ATZ) is one of the most extensively used herbicides to control growth of broadleaf and grassy weeds in crops. ATZ and its metabolites have deleterious effect on sperm quality. ATZ is also known for its ability to induce oxidative stress. Pistacia lentiscus (PL) is an evergreen shrub, with a high content of polyphenols in leaf extracts, with a known anti-inflammatory and antioxidant properties. The protective effect of PL or its extracts against ATZ-induced damage have not been yet evaluated. We examined the harmful effects of atrazine (ATZ) exposure on male reproductive system, using goat (Capra hircus) model spermatozoa and the protective effects of PL and PL ethanolic extract (PLE). In in-vivo experiments, male goats were fed a standard ration or one supplemented with 15 mg ATZ/kg body weight daily, for 6 months. Exposure to ATZ impaired the spermatozoa's morphology, viability, mitochondrial membrane potential and cell lipid composition. These alterations may in turn lead to reduced fertilization competence of the exposed spermatozoa. In an ex-vivo experiment, spermatozoa from male goats fed a standard ration or one supplemented with PL or PLE for 90 days and then were exposed to 1 μM ATZ or 10 μM of its major metabolite diaminochlorotriazine (DACT) through in-vitro capacitation. Prefeeding with PL or PLE partially attenuated the harmful effects of ATZ and DACT. Dietary supplementation with polyphenol-enriched feed can protect, to a certain extent, spermatozoa in males exposed to environmental toxicants.

Acute in vitro exposure to environmentally relevant atrazine levels perturbs bovine preimplantation embryo metabolism and cell number

Atrazine is a widely used herbicide known to negatively alter endocrine systems and perturb metabolism. Preimplantation exposure to pesticides may adversely affect long-term health, however few studies examine the effect of environmental levels and whether specific periods of development are particularly sensitive. In this study, the effect of acute, preimplantation atrazine exposure (days 3.5-7.5 post-fertilization) at levels detected and deemed safe in drinking water (0.02 and 20 μg/L respectively) on in vitro bovine embryo development, quality, metabolism, and gene expression was investigated. Atrazine exposure had no effect on development or quality, but significantly reduced blastocyst total cell numbers, attributable to a decrease in trophectoderm cells. Notably, atrazine (20 μg/L) markedly increased carbohydrate metabolism. Therefore, short-term exposure to environmentally relevant atrazine concentrations perturbs bovine preimplantation embryo metabolism and cell number, highlighting a potential mechanism by which atrazine can mediate embryo viability and health.

Atrazine Contamination of Drinking Water and Adverse Birth Outcomes in Community Water Systems with Elevated Atrazine in Ohio, 2006⁻2008

Atrazine, a common water contaminant in the U.S., has been associated with adverse birth outcomes in previous studies. This study aimed to determine if atrazine concentrations in drinking water are associated with adverse birth outcomes including small for gestational age (SGA), term low birth weight (term LBW), very low birth weight (VLBW), preterm birth (PTB), and very preterm birth (VPTB). This study included 14,445 live singleton births from Ohio communities served by 22 water systems enrolled in the U.S. Environmental Protection Agency's Atrazine Monitoring Program between 2006 and 2008. Mean gestational and trimester-specific atrazine concentrations were calculated. Significantly increased odds of term LBW birth was associated with atrazine exposure over the entire gestational period (OR 1.27, 95% CI 1.10, 1.45), as well as the first (OR 1.20, 95% CI 1.08, 1.34) and second trimesters (OR 1.13, 95% CI 1.07, 1.20) of pregnancy. We observed no evidence of an association between atrazine exposure via drinking water and SGA, VLBW, PTB, or VPTB. Our results suggest that atrazine exposure is associated with reduced birth weight among term infants and that exposure to atrazine in drinking water in early and mid-pregnancy may be most critical for its toxic effects on the fetus.

Low dose bisphenol S or ethinyl estradiol exposures during the perinatal period alter female mouse mammary gland development

Throughout life, mammary tissue is strongly influenced by hormones. Scientists have hypothesized that synthetic chemicals with hormonal activities could disrupt mammary gland development and contribute to breast diseases and dysfunction. Bisphenol S (BPS) is an estrogenic compound used in many consumer products. In this study, CD-1 mice were exposed to BPS (2 or 200 μg/kg/day) during pregnancy and lactation. Mice exposed to 0.01 or 1 μg/kg/day ethinyl estradiol (EE2), a pharmaceutical estrogen, were also evaluated. Mammary glands from female offspring were collected prior to the onset of puberty, during puberty, and in early adulthood. Growth parameters, histopathology, cell proliferation and expression of hormone receptors were quantified. Our evaluations revealed age- and dose-specific effects of BPS that were different from the effects of EE2, and distinct from the effects of BPA that have been reported previously. These assessments suggest that individual xenoestrogens may have unique effects on this sensitive tissue.

Embryonic exposure to the widely-used herbicide atrazine disrupts meiosis and normal follicle formation in female mice

The widely-used herbicide atrazine (ATZ) is detected in ground and surface water in many countries. Several studies in animals have demonstrated that ATZ has endocrine-disrupting effects on male and female reproduction in many vertebrate species. In this study, we investigated the effects of ATZ exposure on meiosis, a key step in gametogenesis in mammals. The treatment was initiated before oocyte entry into meiosis, which occurs during the embryonic period in females. We found that embryonic exposure to ATZ increases the level of 8-oxo-guanine in the nucleus of meiotic cells, reflecting oxidative stress and affecting meiotic double-strand break repair, chromosome synapsis and crossover numbers. Finally, embryonic exposure to ATZ reduces the number of primordial follicles and increases the incidence of multi-oocyte follicles in adult mice. Our data demonstrate that embryonic exposure to ATZ disrupts prophase I of meiosis and affects normal follicle formation in female mice.

Differences in the Rate of in Situ Mammary Gland Development and Other Developmental Endpoints in Three Strains of Female Rat Commonly Used in Mammary Carcinogenesis Studies: Implications for Timing of Carcinogen Exposure

The potential of chemicals to alter susceptibility to mammary tumor formation is often assessed using a carcinogen-induced study design in various rat strains. The rate of mammary gland (MG) development must be considered so that the timing of carcinogen administration is impactful. In this study, in situ MG development was assessed in females of the Harlan Sprague-Dawley (Hsd:SD), Charles River Sprague-Dawley (Crl:SD), and Charles River Long-Evans (Crl:LE) rat strains at postnatal days 25, 33, and 45. Development was evaluated by physical assessment of growth parameters, developmental scoring, and quantitative morphometric analysis. Although body weight (BW) was consistently lower and day of vaginal opening (VO) occurred latest in female Hsd:SD rats, they exhibited accelerated pre- and peripubertal MG development compared to other strains. Glands of Crl:SD and Crl:LE rats exhibited significantly more terminal end buds (TEBs) and TEB/mm than Hsd:SD rats around the time of VO. These data suggest a considerable difference in the rate of MG development across commonly used strains, which is independent of BW and timing of VO. In mammary tumor induction studies employing these strains, administration of the carcinogen should be timed appropriately, based on strain, to specifically target the peak of TEB occurrence.

Identifying reference chemicals for thyroid bioactivity screening

Reference chemicals were selected based on thyroid bioactivity in 'Tier 1' screening assays used by the U.S. EPA's Endocrine Disruptor Screening Program. Active reference chemicals had significant effects on thyroid-responsive endpoints in the amphibian metamorphosis assay, and the male and female pubertal rat assays. In the absence of thyroid weight or histopathological effects, additional published studies providing mechanistic data on thyroid activity were required for active chemicals. Inactive reference chemicals had no significant effects on thyroid-responsive endpoints in Tier 1 assays, or in amphibian or rodent studies from several online databases. The 34 reference chemicals (29 active and five inactive) will be useful for performance-based validation of alternative, high throughput screening assays for thyroid bioactivity.

Atrazine induces endoplasmic reticulum stress-mediated apoptosis of T lymphocytes via the caspase-8-dependent pathway

Atrazine (ATR) is one of the most commonly applied broad-spectrum herbicides. Although ATR is well known to be a biologically hazardous molecule with potential toxicity in the immune system, the molecular mechanisms responsible for ATR-induced immunotoxicity remain unclear. In this study, we found that the immunotoxic properties of ATR were mediated through the induction of apoptotic changes in T lymphocytes. Mice exposed to ATR for 4 weeks exhibited a significant decrease in the number of spleen CD3(+) T lymphocytes, while CD19(+) B lymphocytes and nonlymphoid cells were unaffected. ATR exposure also led to inhibition of cell growth and induction of apoptosis in human Jurkat T-cells. Importantly, ATR triggered the activation of caspase-3 and the cleavage of caspase-8 and PARP, whereas it did not affect the release of cytochrome c from the mitochondria in Jurkat T-cells. In addition, ATR activated the unfolded protein response signaling pathway, as indicated by eIF2α phosphorylation and CHOP induction. Our results demonstrate that ATR elicited an immunotoxic effect by inducing ER stress-induced apoptosis in T-cells, therefore providing evidence for the molecular mechanism by which ATR induces dysregulation of the immune system. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 998-1008, 2016.

Ziracin-Induced Congenital Urogenital Malformations in Female Rats

Spontaneous hypospadias is seldom observed in rats in contrast to its occurrence in 1 out of 250 human births. Ziracin, an antibacterial of the everninomycin class under development for serious enterococcal, staphylococcal, and streptococcal infections, caused anomalies of the external genitalia in F1 female rats and decreased reproductive performance. To characterize the urogenital malformations and determine the period of sensitivity to the effects of Ziracin during development, pregnant rats (F0) were administered 60 mg/kg IV of Ziracin from GD6 to LD21, GD6 to 13, GD14 to the last day of gestation or LD0 to 21. Controls received saline or placebo from GD6 to LD21. Ziracin-induced changes occurred in F1 rats exposed from GD6 to LD21 and GD14 to the last day of gestation, indicating that the period of sensitivity to Ziracin was from GD 14 to the last day of gestation. The urogenital abnormalities consisted of cranial displacement of the urethral opening within the vagina from its normal location at the tip of the genital tubercle. When the urethrovaginal junction occurred at the distal third of the vagina, it created an urogenital cloaca. As a result, ascending infections were seen in the urinary and genital tract. No differences in survivability, body weight, and date of vaginal opening were observed in F1 females. The estrous cycles were slightly prolonged. The mating and fertility indices were decreased as a result of the urogenital anomalies. The mammary glands of pregnant F1 females were underdeveloped, thus F2 pups from affected F1 females had a decreased survival rate. Although the cause of these effects is not known, the findings are consistent with a potential hormonal mechanism.

EDC-2: The Endocrine Society's Second Scientific Statement on Endocrine-Disrupting Chemicals

The Endocrine Society's first Scientific Statement in 2009 provided a wake-up call to the scientific community about how environmental endocrine-disrupting chemicals (EDCs) affect health and disease. Five years later, a substantially larger body of literature has solidified our understanding of plausible mechanisms underlying EDC actions and how exposures in animals and humans-especially during development-may lay the foundations for disease later in life. At this point in history, we have much stronger knowledge about how EDCs alter gene-environment interactions via physiological, cellular, molecular, and epigenetic changes, thereby producing effects in exposed individuals as well as their descendants. Causal links between exposure and manifestation of disease are substantiated by experimental animal models and are consistent with correlative epidemiological data in humans. There are several caveats because differences in how experimental animal work is conducted can lead to difficulties in drawing broad conclusions, and we must continue to be cautious about inferring causality in humans. In this second Scientific Statement, we reviewed the literature on a subset of topics for which the translational evidence is strongest: 1) obesity and diabetes; 2) female reproduction; 3) male reproduction; 4) hormone-sensitive cancers in females; 5) prostate; 6) thyroid; and 7) neurodevelopment and neuroendocrine systems. Our inclusion criteria for studies were those conducted predominantly in the past 5 years deemed to be of high quality based on appropriate negative and positive control groups or populations, adequate sample size and experimental design, and mammalian animal studies with exposure levels in a range that was relevant to humans. We also focused on studies using the developmental origins of health and disease model. No report was excluded based on a positive or negative effect of the EDC exposure. The bulk of the results across the board strengthen the evidence for endocrine health-related actions of EDCs. Based on this much more complete understanding of the endocrine principles by which EDCs act, including nonmonotonic dose-responses, low-dose effects, and developmental vulnerability, these findings can be much better translated to human health. Armed with this information, researchers, physicians, and other healthcare providers can guide regulators and policymakers as they make responsible decisions.

Atrazine Exposure and Reproductive Dysfunction through the Hypothalamus-Pituitary-Gonadal (HPG) Axis

Endocrine disrupting chemicals (EDC) are exogenous agents that alter endogenous hormone signaling pathways. These chemicals target the neuroendocrine system which is composed of organs throughout the body that work alongside the central nervous system to regulate biological processes. Of primary importance is the hypothalamic-pituitary-gonadal (HPG) axis which is vital for maintaining proper reproductive function. Atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) is a pre-emergent herbicide used to prevent the growth of weeds on various crops. This herbicide is reported to widely contaminate potable water supplies everywhere it is applied. As such, the European Union banned the use of atrazine in 2004. Currently the United States Environmental Protection Agency regulates atrazine at 3 parts per billion (ppb; μg/L) in drinking water, while the World Health Organization recently changed their drinking water guideline to 100 ppb. Atrazine is implicated to be an EDC that alters reproductive dysfunction by targeting the HPG axis. However, questions remain as to the human health risks associated with atrazine exposure with studies reporting mixed results on the ability of atrazine to alter the HPG axis. In this review, the current findings for atrazine’s effects on the HPG axis are examined in mammalian, anuran, and fish models and in epidemiological studies.

Atrazine Triggers DNA Damage Response and Induces DNA Double-Strand Breaks in MCF-10A Cells

Atrazine, a pre-emergent herbicide in the chloro-s-triazine family, has been widely used in crop lands and often detected in agriculture watersheds, which is considered as a potential threat to human health. Although atrazine and its metabolites showed an elevated incidence of mammary tumors in female Sprague–Dawley (SD) rats, no molecular evidence was found relevant to its carcinogenesis in humans. This study aims to determine whether atrazine could induce the expression of DNA damage response-related proteins in normal human breast epithelial cells (MCF-10A) and to examine the cytotoxicity of atrazine at a molecular level. Our results indicate that a short-term exposure of MCF-10A to an environmentally-detectable concentration of atrazine (0.1 µg/mL) significantly increased the expression of tumor necrosis factor receptor-1 (TNFR1) and phosphorylated Rad17 in the cells. Atrazine treatment increased H2AX phosphorylation (γH2AX) and the formation of γH2AX foci in the nuclei of MCF-10A cells. Atrazine also sequentially elevated DNA damage checkpoint proteins of ATM- and RAD3-related (ATR), ATRIP and phospho-Chk1, suggesting that atrazine could induce DNA double-strand breaks and trigger the DNA damage response ATR-Chk1 pathway in MCF-10A cells. Further investigations are needed to determine whether atrazine-triggered DNA double-strand breaks and DNA damage response ATR-Chk1 pathway occur in vivo.

Failure of pesticides to alter migration of cancerous and non-cancerous breast cell lines in vitro

Organochlorine pesticides are routinely used in agricultural processes across the United States.

Atrazine affects phosphoprotein and protein expression in MCF-10A human breast epithelial cells

Atrazine, a member of the 2-chloro-s-triazine family of herbicides, is the most widely used pesticide in the world and often detected in agriculture watersheds. Although it was generally considered as an endocrine disruptor, posing a potential threat to human health, the molecular mechanisms of atrazine effects remain unclear. Using two-dimensional gel electrophoresis, we identified a panel of differentially expressed phosphoproteins and total proteins in human breast epithelial MCF-10A cells after being exposed to environmentally relevant concentrations of atrazine. Atrazine treatments for 6 h resulted in differential expression of 4 phosphoproteins and 8 total-proteins as compared to the control cells (>1.5-fold, p < 0.05). MALDI-TOF MS/MS analysis revealed that the differentially expressed proteins belong to various cellular compartments (nucleus, cytosol, membrane) and varied in function, including those regulating the stress response such as peroxiredoxin I, HSP70 and HSP27; structural proteins such as tropomyosin and profilin 1; and oncogenesis proteins such as ANP32A. Six of the 12 identified proteins were verified by quantitative PCR for their transcript levels. The most up-regulated phosphoprotein by atrazine treatment, ANP32A, was further analyzed for its expression, distribution and cellular localization using Western blot and immunocytochemical approaches. The results revealed that ANP32 expression after atrazine treatment increased dose and time dependently and was primarily located in the nucleus. This study may provide new evidence on the potential toxicity of atrazine in human cells.

Gestational and lactational exposure to atrazine via the drinking water causes specific behavioral deficits and selectively alters monoaminergic systems in C57BL/6 mouse dams, juvenile and adult offspring

Atrazine (ATR) is one of the most frequently detected pesticides in the U.S. water supply. This study aimed to investigate neurobehavioral and neurochemical effects of ATR in C57BL/6 mouse offspring and dams exposed to a relatively low (3 mg/l, estimated intake 1.4 mg/kg/day) concentration of ATR via the drinking water (DW) from gestational day 6 to postnatal day (PND) 23. Behavioral tests included open field, pole, grip strength, novel object recognition (NOR), forced swim, and marble burying tests. Maternal weight gain and offspring (PND21, 35, and 70) body or brain weights were not affected by ATR. However, ATR-treated dams exhibited decreased NOR performance and a trend toward hyperactivity. Juvenile offspring (PND35) from ATR-exposed dams were hyperactive (both sexes), spent less time swimming (males), and buried more marbles (females). In adult offspring (PND70), the only behavioral change was a sex-specific (females) decreased NOR performance by ATR. Neurochemically, a trend toward increased striatal dopamine (DA) in dams and a significant increase in juvenile offspring (both sexes) was observed. Additionally, ATR exposure decreased perirhinal cortex serotonin in the adult female offspring. These results suggest that perinatal DW exposure to ATR targets the nigrostriatal DA pathway in dams and, especially, juvenile offspring, alters dams' cognitive performance, induces sex-selective changes involving motor and emotional functions in juvenile offspring, and decreases cognitive ability of adult female offspring, with the latter possibly associated with altered perirhinal cortex serotonin homeostasis. Overall, ATR exposure during gestation and lactation may cause adverse nervous system effects to both offspring and dams.

Which exposure stage (gestation or lactation) is more vulnerable to atrazine toxicity? Studies on mouse dams and their pups

Either during gestation or lactation, the experimental mouse dams received one of the following treatments: (a) diet free of pesticide; (b) diet enriched with atrazine (ATZ); 31.0 μg kg⁻¹; (c) diet free of pesticide + oral vitamin E (α-tocopherol; 200 mg kg⁻¹ per mouse); and (d) diet enriched with ATZ (31.0 μg kg⁻¹) + oral vitamin E (200 mg kg⁻¹ per mouse). At the weaning, pups and dams were killed and selected organs and blood samples were collected for analyses. Compared with the control results, ATZ induced alteration in a number of biochemical and histopathological parameters either in the dams or their offspring. The ameliorative effect of vitamin E, based on estimating the “Ameliorative Index; AI” to malondialdehyde (MDA) and superoxide dismutase (SOD) ranged between 0.95 and 1.06 (≈1.0) for the dams and the pups either in gestational or lactational exposure routes. In general, the mouse pups were more vulnerable to ATZ toxicity than their mothers and exposure during gestation was suggested to be more effective than during lactation. The findings may support the need to further investigating the adverse effects of exposure to low doses of commonly used pesticides, especially during pregnancy and breast-feeding as well as effects on newborn child.

Multigeneration reproduction and male developmental toxicity studies on atrazine in rats

BACKGROUND

Reproductive toxicity of Atrazine (ATR) was evaluated in two rat multigenerational studies. Development of male reproductive parameters was evaluated in separate studies after prenatal or postnatal exposure.

METHODS

In multigenerational studies, rats received dietary concentrations of 0, 10, 50, 100 or 500 ppm ATR. In separate studies in female rats, ATR was administered by gavage at 0, 1, 5, 25 or 125 mg/kg/day during pregnancy (GD6–21) or lactation (LD2–21). Plasma testosterone concentration, testicular and epididymal weights, and sperm counts were measured in male offspring on PND70 and 170.

RESULTS

In the multigenerational studies, parental systemic toxicity occurred at 500 ppm (38.7 mg/kg/day), but reproductive endpoints were unaffected. In the prenatal study, maternal toxicity and embryo-fetal mortality occurred at 125 mg/kg/day. In male offspring, testosterone levels and sperm counts were unaffected, although the percentage of abnormal sperm increased at 125 mg/kg/day (PND 70) and 25 mg/kg/day (PND170). In the postnatal study, maternal toxicity and reduced body weights of male offspring occurred at 125 mg/kg/day. Additionally, reduced testicular (PND70, PND170) and epididymal (PND70) weights and increased numbers of abnormal sperm (PND70, PND170) were seen, but no changes in plasma testosterone or sperm counts.

CONCLUSIONS

Dietary administration of ATR did not affect rat reproduction up to a parentally toxic dose of 38.7 mg/kg/day. Some effects on male reproductive system development occurred after high dose, bolus administration to dams, but doses were much higher than expected under normal use conditions. Thus, oral RfDs for ATR would be protective for reproductive effects

Exposure to atrazine during gestation and lactation periods: toxicity effects on dopaminergic neurons in offspring by downregulation of Nurr1 and VMAT2

High atrazine (2-chloro-4-ethytlamino-6-isopropylamine-1,3,5-triazine; ATR) contents in the environment threaten the health conditions of organisms. We examined the effects of ATR exposure on Sprague-Dawley rats during gestation and on the dopaminergic neurons of offspring during lactation. Pregnant dams were orally treated with 0 mg/kg/day to 50 mg/kg/day of ATR from gestational day 5 to postnatal day 22. Afterward, neither offspring nor dams received ATR. Dopamine (DA) content was examined in striatum samples by HPLC-FL; the mRNA expressions of tyrosine hydroxylase (TH), orphan nuclear hormone (Nurr1), dopamine transporter (DAT), and vesicular monoamine transporter 2 (VMAT2) in the ventral midbrain samples were examined by fluorescence PCR when the offspring reached one year of age. After the pregnant rats were exposed to ATR, the DA concentrations and mRNA levels of Nurr1 were decreased in their offspring. Decreased Nurr1 levels were also accompanied by changes in the mRNA levels of VMAT2, which controls the transport and reuptake of DA.

Antioxidant attenuation of atrazine induced histopathological changes in testicular tissue of goat in vitro

During the present investigation the effect of α-tocopherol (100 μmolL^-1) in prevention of testicular toxicity induced by atrazine in goat Capra hircus have been analyzed. Vitamin E (α-tocopherol) at dose level 100 μmolL^-1 provides attenuation over the histopathological changes generated by pesticide atrazine (100 nmolml^-1). Small pieces (approximately 1mm³) of testicular tissue were divided into three groups (one control group + two experimental groups). Experimental group (A) was supplemented with 100 nmolml^-1 concentration of atrazine and experimental group (B) was supplemented with 100 nmolml^-1 atrazine and 100 μmolL^-1 concentrations of vitamin E (α-Tocopherol) and harvesting was carried out after 1, 4 and 8 hrs of exposure. Control was run along with all the experimental groups. In the experimental group (A) treated with atrazine at dose level 100 nmolml^-1, revealed histomorphological alterations in the seminiferous tubule. After one hour of exposure duration small vacuoles in cytoplasm of the Sertoli cells and spermatogonia were observed. Chromolysis at pycnosis were also noticed in the spermatogonia and spermatids. In the experimental group (B) exposed with atrazine and simultaneously supplemented with Vitamin E also showed degeneration but it was milder as compared with experimental group treated with atrazine without antioxidant. Atrazine exposure induced a decline in diameter of spermatocytes from 10.51 ± 0.2052 μm in control to 7.915 ± 0.2972, 7.5 ± 0.211 and 7.14 ± 0.225 μm after exposure of 1, 4 and 8 hrs respectively but in case of atrazine supplemented with vitamin E [experimental group (B)], there was less decline in cell diameter that was 8.5 ± 0.1865, 8.1 ± 0.1201 and 7.8 ± 0.2066μm after exposure of 1, 4 and 8 hrs respectively. The result demonstrated that vitamin E delays the degenerative changes induced by atrazine.

The epigenetic lorax: gene-environment interactions in human health

Over the last decade, we have witnessed an explosion of information on genetic factors underlying common human diseases and disorders. This 'human genomics' information revolution has occurred as a backdrop to a rapid increase in the rates of many human disorders and diseases. For example, obesity, Type 2 diabetes, asthma, autism spectrum disorder and attention deficit hyperactivity disorder have increased at rates that cannot be due to changes in the genetic structure of the population, and are difficult to ascribe to changes in diagnostic criteria or ascertainment. A likely cause of the increased incidence of these disorders is increased exposure to environmental factors that modify gene function. Many environmental factors that have epidemiological association with common human disorders are likely to exert their effects through epigenetic alterations. This general mechanism of gene-environment interaction poses special challenges for individuals, educators, scientists and public policy makers in defining, monitoring and mitigating exposures.

Atrazine-induced changes in the myocardial structure of peripubertal rats

The aim of the present study was to investigate the effect of atrazine (6-chloro-N(2)-ethyl-N(4)-isopropyl-1,3,5-triazine-2,4-diamine) on the left ventricle myocardium in juvenile/peripubertal male Wistar rats. Atrazine was administered orally at 50 or 200 mg/kg of body weight dose for 28 consecutive days. In order to assess possible structural alterations, tissue sections were examined histologically and then subjected to quantification analysis using stereological methods. The tissue specimens were routinely processed and stained with Mallory trichrome method in order to clearly distinguish muscle cells from the connective tissue components. A toluidine blue staining method was additionally used for the demonstration of mast cells. Statistically significant increase in length density and numerical density of capillaries were found at both the investigated doses of atrazine compared with the control. The increase in surface density and volume density of capillaries found at lower dosage of atrazine was significant in comparison with the control. The extensive mast cell degranulation was noted on the histological examination at both doses of the applied chemical. No significant changes were demonstrated for the stereological parameters of cardiomyocytes. Based on the available published data and the present results, it can be concluded that atrazine promoted angiogenesis in the rat myocardium, which might be partially mediated by mast cells.

Hormones and endocrine-disrupting chemicals: low-dose effects and nonmonotonic dose responses

For decades, studies of endocrine-disrupting chemicals (EDCs) have challenged traditional concepts in toxicology, in particular the dogma of "the dose makes the poison," because EDCs can have effects at low doses that are not predicted by effects at higher doses. Here, we review two major concepts in EDC studies: low dose and nonmonotonicity. Low-dose effects were defined by the National Toxicology Program as those that occur in the range of human exposures or effects observed at doses below those used for traditional toxicological studies. We review the mechanistic data for low-dose effects and use a weight-of-evidence approach to analyze five examples from the EDC literature. Additionally, we explore nonmonotonic dose-response curves, defined as a nonlinear relationship between dose and effect where the slope of the curve changes sign somewhere within the range of doses examined. We provide a detailed discussion of the mechanisms responsible for generating these phenomena, plus hundreds of examples from the cell culture, animal, and epidemiology literature. We illustrate that nonmonotonic responses and low-dose effects are remarkably common in studies of natural hormones and EDCs. Whether low doses of EDCs influence certain human disorders is no longer conjecture, because epidemiological studies show that environmental exposures to EDCs are associated with human diseases and disabilities. We conclude that when nonmonotonic dose-response curves occur, the effects of low doses cannot be predicted by the effects observed at high doses. Thus, fundamental changes in chemical testing and safety determination are needed to protect human health.

Atrazine-induced apoptosis of splenocytes in BALB/C mice

BACKGROUND

Atrazine (2-chloro-4-ethytlamino-6-isopropylamine-1,3,5-triazine; ATR), is the most commonly applied broad-spectrum herbicide in the world. Unintentional overspray of ATR poses an immune function health hazard. The biomolecular mechanisms responsible for ATR-induced immunotoxicity, however, are little understood. This study presents on our investigation into the apoptosis of splenocytes in mice exposed to ATR as we explore possible immunotoxic mechanisms.

METHODS

Oral doses of ATR were administered to BALB/C mice for 21 days. The histopathology, lymphocyte apoptosis and the expression of apoptosis-related proteins from the Fas/Fas ligand (FasL) apoptotic pathway were examined from spleen samples.

RESULTS

Mice administered ATR exhibited a significant decrease in spleen and thymus weight. Electron microscope histology of ultrathin sections of spleen revealed degenerative micromorphology indicative of apoptosis of splenocytes. Flow cytometry revealed that the percentage of apoptotic lymphocytes increased in a dose-dependent manner after ATR treatment. Western blots identified increased expression of Fas, FasL and active caspase-3 proteins in the treatment groups.

CONCLUSIONS

ATR is capable of inducing splenocytic apoptosis mediated by the Fas/FasL pathway in mice, which could be the potential mechanism underlying the immunotoxicity of ATR.

Perinatal environmental exposures affect mammary development, function, and cancer risk in adulthood

Puberty is an important transition that enables reproduction of mammalian species. Precocious puberty, specifically early thelarche (the appearance of breast "buds"), in girls of multiple ethnic backgrounds is a major health problem in the United States and other countries. The cause for a continued decrease in the age of breast development in girls is unknown, but environmental factors likely play a major role. Laboratory and epidemiological studies have identified several individual environmental factors that affect breast development, but further progress is needed. Current research needs include increased attention to and recording of prenatal and neonatal environmental exposures, testing of marketed chemicals for effects on the mammary gland, and understanding of the mammary gland-specific mechanisms that are altered by chemicals. Such research is required to halt the increasing trend toward puberty at earlier ages.

Demasculinization and feminization of male gonads by atrazine: consistent effects across vertebrate classes

Atrazine is the most commonly detected pesticide contaminant of ground water, surface water, and precipitation. Atrazine is also an endocrine disruptor that, among other effects, alters male reproductive tissues when animals are exposed during development. Here, we apply the nine so-called "Hill criteria" (Strength, Consistency, Specificity, Temporality, Biological Gradient, Plausibility, Coherence, Experiment, and Analogy) for establishing cause-effect relationships to examine the evidence for atrazine as an endocrine disruptor that demasculinizes and feminizes the gonads of male vertebrates. We present experimental evidence that the effects of atrazine on male development are consistent across all vertebrate classes examined and we present a state of the art summary of the mechanisms by which atrazine acts as an endocrine disruptor to produce these effects. Atrazine demasculinizes male gonads producing testicular lesions associated with reduced germ cell numbers in teleost fish, amphibians, reptiles, and mammals, and induces partial and/or complete feminization in fish, amphibians, and reptiles. These effects are strong (statistically significant), consistent across vertebrate classes, and specific. Reductions in androgen levels and the induction of estrogen synthesis - demonstrated in fish, amphibians, reptiles, and mammals - represent plausible and coherent mechanisms that explain these effects. Biological gradients are observed in several of the cited studies, although threshold doses and patterns vary among species. Given that the effects on the male gonads described in all of these experimental studies occurred only after atrazine exposure, temporality is also met here. Thus the case for atrazine as an endocrine disruptor that demasculinizes and feminizes male vertebrates meets all nine of the "Hill criteria".