Consistently with the previously observed decrease in testicular testosterone production, the genes and gene pathways involved in steroidogenesis and cholesterol homeostasisand were all down regulated . The effects of DBP on the expression of genes involved in cholesterol transport and steroidogenesis were dose-dependent, with significant reductions in mRNA levels of scavenger receptor B type 1 and 3β-hydroxysteroid dehydrogenase observed at doses of 0.1 and 1.0 mg/kg/d, respectively. Conversely, several genes regulating cell proliferation and survival were upregulated , which is consistent with the observed Leydig cell hyperplasia. Other targeted genes and gene pathways included α-inhibin, which is essential for normal Sertoli cell development and insulin signaling . Within the Wolffian duct, exposure to DBP from GDs 15 to 19 or 21 altered the expression of genes within the insulin-like growth factor pathway and other developmentally important signaling pathways as well as genes for extracellular matrix components . These findings suggest a model in which prenatal DBP exposure disrupts orchestrated molecular responses between epithelia, mesenchyme, and extracellular matrix, thereby altering Wolffian duct morphology. These alterations are likely to be secondary to decreased testosterone synthesis but could also be mediated more directly. Reduced testicular testosterone production and concentration have also been shown to occur in prepubertal rats . A comparison of different windows of exposure indicated that DEHP had differential effects during gestation, lactation, prepuberty and young adulthood,curing cannabis with decreasing effects observed with increasing age . Additionally, different durations of DEHP treatment were associated with either up- or down regulation of Leydig cell testosterone synthesis, whereas serum levels did not necessarily change in the same direction and apparently depended on the differential effects that various durations of DEHP exposure had on enzymes and hormones regulating testosterone synthesis and metabolism .
The proximate developmental toxicants of phthalates in rats and mice are believed to be their respective monoesters. After oral exposure, gut lipases and esterases hydrolyze phthalate esters into their more easily absorbable monoesters. Pronounced interspecies differences exist in lipase activity, with primates exhibiting much lower activity than rats and having correspondingly lower dose-normalized monoester levels . Consequently, a default risk assessment, consisting of the lowest observed adverse effect level multiplied by default factors of 10 each for interspecies and interindividual differences, was deemed inappropriate . A recent direct comparison confirmed that oral treatment with equal doses of DEHP per unit of body weight resulted in up to 7.5 times lower peak concentrations of MEHP in marmosets than in rats .However, a human volunteer who consumed an almost 50-foldlower dose of DEHP than the lowest dose used in the study of marmosets and rats had a similar Cmax of MEHP . Additionally, the dose-normalized area under the curve for this volunteer was at least 15 times higher than in the rats and almost 100 times higher than in the marmosets. Although this is only based on a single individual, it certainly does not suggest that human tissues are exposed to lower concentrations of MEHP than rats after the same dose of DEHP. It has been proposed that the unconjugated monoesters are the mediators of reproductive toxicity in rats because monoesters undergo little glucuronidation in these animals. Conversely, in humans, the majority of phthalate monoesters and even the secondary metabolites are present in urine in the form of glucuronides . In serum, the metabolites were reported to be mostly conjugated , but this is in marked contrast to the findings from a single human volunteer . Note that this volunteer had ingested a high dose of DEHP, and researchers recently showed that, at least in urine, free MEHP made up 3% of total MEHP at the 50th percentile concentration but made up almost 87% at the 95th percentile .
This correlation was not statistically significant for MEHP, but there was a linear increase in the percentage of free monoethyl phthalate , MBP, and monobenzyl phthalate in urine with increasing total forms. This could indicate that the difference between the findings in a single volunteer and those of the larger study resulted from the higher dose the volunteer ingested. However, it could also be a reflection of variability in phthalate metabolism, because substantial interindividual variation has been reported in the degree of conjugation . Notably, in the investigation of urinary phthalate monoester metabolites in a subsample of NHANES III, 5% of urine samples from 289 subjects had markedly elevated concentrations of unconjugated monoesters . In addition to glucuronidation, MEHP undergoes extensive oxidative metabolism in humans . Nanomolar concentrations of two of the oxidative metabolites of DEHP, 5-oxoMEHP and 5-OH-MEHP, were recently reported to inhibit DTH-induced androgen receptor activation in a stably transfected breast cancer cell line by 55 and 60%, respectively, whereas neither DEHP nor MEHP had a significant effect . This suggests that these metabolites may contribute to the anti-androgenic effects of this phthalate. In view of these findings, it is particularly concerning that women of childbearing age had significantly higher urinary concentrations of MBP than women in other age groups . However, other studies did not find a significant difference between women of reproductive age and younger or older females but confirmed that women of all ages had higher urinary concentrations of MBP, MEP, and MBzP compared with men . The detection of MEHP and DEHP has been reported in umbilical cord serum, suggesting that human exposure to these chemicals starts in utero . A correlation between detectable cord serum MEHP concentrations and lower gestational age, although not with birth weight or Apgar scores, was also suggested. However, the improbably high concentrations of DEHP and its monoester and the finding of higher DEHP than MEHP levels suggest that there may have been considerable contamination of the samples; therefore, the above findings should be considered with caution. Fisher et al. were the first to note the many similarities between the changes on the cellular and tissue level induced by exposure to DBP in utero and those observed in the testicular dysgenesis syndrome in humans.
This syndrome has its origin in abnormal fetal development of Sertoli and Leydig cells and includes cryptorchidism and hypospadias, testicular germ cell cancers, and disorders of sperm production. These disorders all constitute risk factors for each other, and their incidence is believed to be rising, but the evidence for each is conflicting, with the exception of testicular germ cell cancers . Additionally, there is no convincing evidence that if there is a true decline in male reproductive health, phthalates and/or other endocrine-disrupting chemicals are causally related to it. There are first indications that phthalate exposure is related to semen quality. In adult men, urinary MEP levels were found to be associated with DNA damage in sperm , whereas MEHP, MBzP, MBP, and monomethyl phthalate were not . There was an inverse and dose-dependent relation between urinary MBP concentrations and sperm motility and between MBzPand MBP levels and sperm concentration . None of the other phthalate metabolites detectable in at least 75% of the urine samples,cannabis dryer were significantly associated with sperm parameters. Changes in reproductive hormone levels were also observed, but several of them exhibited unexpected patterns and directions . For example, inhibin B is secreted by Sertoli cells, and because MBP disrupts Sertoli structure and function, it was surprising that inhibin B increased with higher MBP exposure, whereas follicle-stimulating hormone did not increase. Higher MBzP exposure was associated with a decrease in follicle-stimulating hormone, but there was no change in inhibin B levels. Note that the attempts to detect associations between phthalate exposure and semen or reproductive hormone parameters were based on single measurements of urinary phthalate metabolite levels. Because of the high withinsubject variability—particularly of MEHP levels —a single sample may not have accurately reflected average exposure to MEHP and other phthalate monoesters, and this may account for the failure to detect an association between them and semen quality. DEHP is hepatocarcinogenic in rats and mice , but the liver tumors arise from the ability of DEHP to act as peroxisome proliferators in rodents, a mechanism that is not believed to be relevant to humans. Accordingly, the IARC reclassified DEHP from “possible carcinogen to humans” to “non-classifiable as to its carcinogenicity to humans” . However, the US EPA classified DEHP as a probable human carcinogen. The decision by the IARC has been harshly criticized for allegedly not giving due consideration to all of the available scientific evidence, particularly experimental and epidemiological evidence suggesting that DEHP induces pancreatic tumors in rodents and possibly humans . A recent addition to that database is a chronic feeding study in Sprague–Dawley rats, in which exposure to DEHP at a dose of 300 mg/kg/d significantly increased the incidence not only of liver tumors but also that of testicular tumors . Although lower doses did not significantly increase the incidence of Leydig cell tumors, there was a significant trend for increasing neoplasias with increasing dose.The term pesticide includes herbicides, insecticides, fungicides, fumigants, rodenticides, and other chemicals designed to destroy or repel pests. According to the US EPA, their use exceeded 5 billion pounds worldwide and 1.2 billion pounds in the United States in 2000 and 2001. When chlorine/hypochlorites , wood preservatives, and specialty biocides were included, total usage in the United States alone was almost five billion pounds. At least 75% of this amount is used in agriculture, and home and garden use and commercial/industrial/government use almost equally share the remaining 20 to 25%. Between 80 and 90% of households have reported indoor use of pesticides .
Of particular concern, 70 and 85% of pregnant women from two New York City cohorts, respectively, reported the indoor use of pesticides during pregnancy , and 37% employed an exterminator . The use of organophosphate insecticides declined from approx 131 million pounds in 1980 to 73 million pounds in 2001, but its percentage among total insecticides increased from 58 to 70% in the same period. In 1999 and 2001, the two most commonly used OP insecticide active ingredients were malathion and chlorpyrifos, followed by diazinon and terbufos. Exposure to pesticides can occur via inhalation, dermal absorption, and ingestion. Pharmacokinetics studies in human volunteershave indicated that OPs are readily absorbed after oral administration and are quickly metabolized to more polar metabolites, which are then eliminated in urine with half-lives ranging from 2 h for orally administered diazinon to up to 27 h for chlorpyrifos . Limited absorption was observed from occluded dermal doses, and urinary elimination halflives were longer than after oral administration . Approximately 60% of diazinon and 70 to 93% of chlorpyrifos were recovered as urinary metabolites . Only 1 to 3% of the dose was recovered for any of the OP pesticides investigated after dermal application . Under the Food Quality Protection Act of 1996, an assessment is required for cumulative risks from food, water, and nonoccupational exposure resulting from all uses of OPs and should account for exposure to multiple pesticides that have a common mode of toxicological action and end point of toxicity. The Food Quality Protection Act further requires that infants and children are given particular attention because their higher food and fluid intake per body mass, different diets, and behavior put them at risk of higher exposure. Additionally, the immaturity of the detoxifying enzyme system in small infants and the extensive growth and development that young children undergo renders them more vulnerable to the potential hormonal/endocrine disrupting, neurotoxic, immunotoxic, and/or carcinogenic effects of OP pesticides and other environmental pollutants . Simulations incorporating measured transfer efficiencies of pesticides from surfaces to hands and food and observations of children’s activities during eating suggest that the frequent hand–food, hand–surface, and surface– food contacts have the potential to contribute 20 to 80% of the total dietary intake of pesticides in children younger than age 4 yr . After broadcast application of chlorpyrifos, air concentrations remained markedly higher in a child’s breathing zone than in the breathing zone of a sitting adult , even after ventilation . Even on the second day after application, the dose a child was estimated to absorb was 0.038 mg/ kg, vastly exceeding the current US EPA RfD for infants and children .