Monitoring and risk assessment of hazardous chemicals in toy-slime and putty in the Netherlands.

In 2019, the Dutch Food and Consumer Product Safety Authority performed a market surveillance for toy-slime (23 samples) and putty (16 samples). For 35% of the toy-slimes and 13% of the putties, the migration of boron exceeded the European legal limit of 300 and 1200 mg/kg respectively. In 36% of the toy samples, methylisothiazolinone (MI) and chloromethylisothiazolinone (CMI) were detected in levels up to 25 and 38 mg/kg, respectively, much higher than the European legal limit for aqueous toys intended for children younger than three. 59% of the toys contained other preservatives such as 2-phenoxyethanol, p-hydroxybenzoic acid and parabens. In 2 toy-slimes and 2 putties N-nitrosodiethanolamine (NDELA) was found in amounts up to 2.3 mg/kg. A risk assessment was performed for boron and NDELA. The estimated exposure to boron did not exceed the health based guidance value. The estimated exposure to NDELA from 2 toy-slimes may pose a health risk. For 2 putties the estimated exposure to NDELA was somewhat lower, but health risks could not be excluded. The presence of isothiazolinones may lead to skin sensitisation. It is recommended to extend the legal limit for NDELA, MI and CMI in finger-paint and labelling requirements to other aqueous toys.

Probabilistic derivation of the interspecies assessment factor for skin sensitization.

An interspecies sensitization assessment factor (SAF) is used in the quantitative risk assessment (QRA) for skin sensitization when a murine-based NESIL (No Expected Sensitization Induction Level) is taken as point of departure. Several studies showed that, on average, the murine sensitization threshold is in good correspondence with that determined in humans. However, on an individual level, the murine and human sensitization thresholds may differ considerably. In this study, the interspecies SAF was quantified by using a probabilistic approach, to be able to take these cases into account. As expected, the geometric means of the probability distributions of murine and human sensitization threshold ratios were close to one, but taking the 95 th percentile of these distributions resulted in an interspecies SAF of 15. By using this value, one is sure that with 95% probability, the sensitization threshold determined in mice does not underestimate the human threshold. It can be concluded that a murine-based NESIL requires the use of an interspecies SAF (of 15) in the QRA for skin sensitization, to correct for the differences between mice and humans. This empirically derived interspecies SAF contributes to refinement of the risk assessment methodology.

Aggregate exposure approaches for parabens in personal care products: a case assessment for children between 0 and 3 years old.

In the risk assessment of chemical substances, aggregation of exposure to a substance from different sources via different pathways is not common practice. Focusing the exposure assessment on a substance from a single source can lead to a significant underestimation of the risk. To gain more insight on how to perform an aggregate exposure assessment, we applied a deterministic (tier 1) and a person-oriented probabilistic approach (tier 2) for exposure to the four most common parabens through personal care products in children between 0 and 3 years old. Following a deterministic approach, a worst-case exposure estimate is calculated for methyl-, ethyl-, propyl- and butylparaben. As an illustration for risk assessment, Margins of Exposure (MoE) are calculated. These are 991 and 4966 for methyl- and ethylparaben, and 8 and 10 for propyl- and butylparaben, respectively. In tier 2, more detailed information on product use has been obtained from a small survey on product use of consumers. A probabilistic exposure assessment is performed to estimate the variability and uncertainty of exposure in a population. Results show that the internal exposure for each paraben is below the level determined in tier 1. However, for propyl- and butylparaben, the percentile of the population with an exposure probability above the assumed "safe" MoE of 100, is 13% and 7%, respectively. In conclusion, a tier 1 approach can be performed using simple equations and default point estimates, and serves as a starting point for exposure and risk assessment. If refinement is warranted, the more data demanding person-oriented probabilistic approach should be used. This probabilistic approach results in a more realistic exposure estimate, including the uncertainty, and allows determining the main drivers of exposure. Furthermore, it allows to estimate the percentage of the population for which the exposure is likely to be above a specific value.

Retinoid status and responsiveness to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in mice lacking retinoid binding protein or retinoid receptor forms.

We have investigated the role of Vitamin A (retinoid) proteins in hepatic retinoid processing under normal conditions and during chemical stress induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a chemical known to interfere with retinoid turnover and metabolism. Three separate studies were performed in wildtype control mice and transgenic mice that lack one or more isoforms of retinoic acid receptors (RAR), retinoid X receptors (RXR), or intracellular retinoid-binding proteins (CRABP I, CRABP II, CRBP I). Body and organ weight development was monitored from 2 weeks of age to adult, and hepatic levels of retinyl esters, retinol, and retinoic acid were investigated. In addition, hepatic concentrations of 9-cis-4-oxo-13,14-dihydro-retinoic acid, a recently discovered retinoid metabolite that has proven sensitive to both TCDD exposure and Vitamin A status, were also determined. Mice absent in the three proteins CRBP I, CRABP I, and CRABP II (CI/CAI/CAII-/-) displayed significantly lower hepatic retinyl ester, retinol, and all-trans-retinoic acid levels compared to wildtype mice, whereas the liver concentrations of 9-cis-4-oxo-13,14-dihydro-retinoic acid was considerably higher. After treatment with TCDD, hepatic total retinoids were almost entirely depleted in the CI/CAI/CAII-/- mice, whereas wildtype mice and mice lacking CRABP I, and CRABP II (CAI/CAII-/-) retained approximately 60-70% of their Vitamin A content compared to controls at 28 days. RAR and RXR knockout mice responded similarly to wildtype mice with respect to TCDD-induced retinoid disruption, with the exception of RXRbeta-/- mice which showed no decrease in hepatic Vitamin A concentration, suggesting that the role of RXRbeta in TCDD-induced retinoid disruption should be further investigated. Overall, the abnormal retinoid profile in the triple knockout mice (CI/CAI/CAII-/-), but not double knockout (CAI/CAII-/-) mice, suggests that a loss of CRBP I may account for the difference in retinoid profile in CI/CAI/CAII-/- mice, and is likely to result in an increased susceptibility to hepatic retinoid depletion following dioxin exposure.

[Solvents for the removal of gutta-percha from root canals. 2. Side effects of chloroform, halothane and xylene]. / Oplosmiddelen ter verwijdering van guttapercha uit wortelkanalen 2. Nevenwerkingen van chloroform, halothaan en xyleen.

High concentrations of organic solvents have adverse effects on the health of professional workers. In endodontics, halothane, chloroform and xylene are used to dissolve gutta-percha from root canals. It is therefore questioned whether the use of these solvents could affect the health of patients or of the dental team. It seems warranted to conclude that the amounts and concentrations of chloroform, xylene and halothane such as used in endodontic retreatment, are low and therefore are safe. However, the dentist should be aware of possible hypersensitivity induced by previous application of halothane as a narcotic.

Potent inhibition of estrogen sulfotransferase by hydroxylated metabolites of polyhalogenated aromatic hydrocarbons reveals alternative mechanism for estrogenic activity of endocrine disrupters.

Polyhalogenated aromatic hydrocarbons (PHAHs), such as polychlorinated dibenzo-p-dioxins and dibenzofurans, polybrominated diphenylethers, and bisphenol A derivatives are persistent environmental pollutants, which are capable of interfering with reproductive and endocrine function in birds, fish, reptiles, and mammals. PHAHs exert estrogenic effects that may be mediated in part by their hydroxylated metabolites (PHAH-OHs), the mechanisms of which remain to be identified. PHAH-OHs show low affinity for the ER. Alternatively, they may exert their estrogenic effects by inhibiting E2 metabolism. As sulfation of E2 by estrogen sulfotransferase (SULT1E1) is an important pathway for E2 inactivation, inhibition of SULT1E1 may lead to an increased bioavailability of estrogens in tissues expressing this enzyme. Therefore, we studied the possible inhibition of human SULT1E1 by hydroxylated PHAH metabolites and the sulfation of the different compounds by SULT1E1. We found marked inhibition of SULT1E1 by various PHAH-OHs, in particular by compounds with two adjacent halogen substituents around the hydroxyl group that were effective at (sub)nanomolar concentrations. Depending on the structure, the inhibition is primarily competitive or noncompetitive. Most PHAH-OHs are also sulfated by SULT1E1. We also investigated the inhibitory effects of the various PHAH-OHs on E2 sulfation by human liver cytosol and found that the effects were strongly correlated with their inhibitions of recombinant SULT1E1 (r = 0.922). Based on these results, we hypothesize that hydroxylated PHAHs exert their estrogenic effects at least in part by inhibiting SULT1E1-catalyzed E2 sulfation.

Potent inhibition of estrogen sulfotransferase by hydroxylated PCB metabolites: a novel pathway explaining the estrogenic activity of PCBs.

Polychlorinated biphenyls (PCBs) are persistent environmental pollutants which exert a variety of toxic effects in animals, including disturbances of sexual development and reproductive function. The estrogenic effects of PCBs may be mediated in part by hydroxylated PCB metabolites (PCB-OHs), but the mechanisms by which they are brought about are not understood. PCBs as well as PCB-Hs show low affinities for both alpha and beta estrogen receptor isoforms. In the present study we demonstrate that various environmentally relevant PCB-OHs are extremely potent inhibitors of human estrogen sulfotransferase, strongly suggesting that they indirectly induce estrogenic activity by increasing estradiol bioavailability in target tissues.

Effects of pentachlorophenol and hydroxylated polychlorinated biphenyls on thyroid hormone conjugation in a rat and a human hepatoma cell line.

It was previously demonstrated in our laboratory that hydroxylated metabolites of polychlorinated biphenyls (PCB-OHs) inhibit the sulfation of iodothyronines in rat liver cytosol. In this study, the inhibition of 3,3'-diiodothyronine (T2) sulfation by pentachlorophenol (PCP) and PCB-OHs was investigated in hepatoma cell lines in relation to the cellular uptake of these compounds, providing a more appropriate model of the in vivo situation. The human HepG2 hepatoma cell line was shown to conjugate T2 almost exclusively by sulfation, glucuronidation being negligible. The rat FaO hepatoma cell line, on the other hand, produced 37% T2 sulfate and 63% T2 glucuronide. It was demonstrated that PCP inhibited T2 sulfation in both cell lines, although it was 10(3) times less potent in cells than in rat liver cytosol. Remarkably, 10 mumPCP inhibited the sulfation and glucuronidation of T2 by FaO cells to the same extent. Micromolar concentrations of 4-hydroxy-3,3',4',5-tetrachlorobiphenyl or 4-hydroxy-2',3,3',4',5-pentachlorobiphenyl hardly affected T2 conjugation in FaO cells, but both PCB-OHs reduced T2 sulfate formation in HepG2 cells. Inhibition of T2 sulfation was stronger using medium without foetal calf serum (FCS) than medium with 5% FCS. This was due to a lower uptake of inhibitor by the cells in the presence of serum, as demonstrated using radiolabelled PCP. In conclusion, this study confirms the inhibition of T2 sulfation by PCP and PCB-OHs previously observed in rat liver cytosol in a rat and a human hepatoma cell line. Thus, it seems reasonable to assume that iodothyronine sulfation is also inhibited by PCB metabolites and PCP in vivo.

In vitro inhibition of thyroid hormone sulfation by polychlorobiphenylols: isozyme specificity and inhibition kinetics.

It was recently demonstrated by our laboratory that hydroxylated metabolites of polychlorinated biphenyls (PCB-OHs) are inhibitors of thyroid hormone sulfation. In this study, a more detailed investigation on sulfotransferase isozyme specificity and the kinetics of inhibition was performed. Thyroid hormone sulfation was determined using 3,3'-diiodothyronine (T2) as a substrate, and various sources of sulfotransferase (SULT) enzyme were used; e.g., female and male rat liver cytosol, male brain cytosol and cytosolic preparations of V79 cells transfected with rat SULT1C1, and human SULT1A1 and human SULT1A3. The inhibition pattern and IC50 values were very similar for male and female rat liver and rSULT1C1 and hSULT1A1. PCB-OHs were not able to inhibit the T2 sulfotransferase activity using hSULT1A3. Metabolite 3-hydroxy-2,3',4,4',5-pentachlorobiphenyl did not inhibit T2 sulfotransferase activity in male brain cytosol, while it was a very potent inhibitor in male and female rat liver cytosol. IC50 values for the tested PCB-OHs were not different with either T2 or 3,3',5-triiodothyronine (T3) as substrate, supporting the hypothesis that T2 is the preferred iodothyronine substrate for the sulfotransferases catalyzing the sulfation of the active hormone T3. The Lineweaver-Burk plot obtained with rat liver cytosol and T2 suggested that the nature of the T2 sulfation inhibition by 4-hydroxy-2',3,3',4',5-pentachlorobiphenyl is competitive. Finally, it was demonstrated that tested hydroxylated polychlorinated dibenzo-p-dioxins and biphenyls were, albeit poorly, sulfated by sulfotransferases as measured by the production of 35S-labeled metabolites.

In vitro inhibition of thyroid hormone sulfation by hydroxylated metabolites of halogenated aromatic hydrocarbons.

Earlier studies in our laboratory showed that hydroxylated metabolites of polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs), and dibenzofurans (PCDFs) competitively inhibit thyroxine (T4) binding to transthyretin (TTR) and type I deiodinase (D1) activity. In this study, we investigated the possible inhibitory effects of hydroxylated metabolites of polyhalogenated aromatic hydrocarbons (PHAHs) on iodothyronine sulfotransferase activity. Rat liver cytosol was used as a source of sulfotransferase enzyme in an in vitro assay with 125I-labeled 3,3'-diiodothyronine (T2) as a model substrate. Increasing amounts of hydroxylated PCBs, PCDDs, or PCDFs or extracts from incubation mixtures of PHAHs and induced liver microsomes were added as potential inhibitors of T2 sulfotransferase activity. Hydroxylated metabolites of PCBs, PCDDs, and PCDFs were found to be potent inhibitors of T2 sulfotransferase activity in vitro with IC50 values in the low micromolar range (0.2-3.8 microM). The most potent inhibitor of T2 sulfotransferase activity in our experiments was the PCB metabolite 3-hydroxy-2,3',4, 4',5-pentachlorobiphenyl with an IC50 value of 0.2 microM. A hydroxyl group in the para or meta position appeared to be an important structural requirement for T2 sulfotransferase inhibition by PCB metabolites. Ortho hydroxy PCBs were much less potent, and none of the parent PHAHs was capable of inhibiting T2 sulfotransferase activity. In addition, the formation of T2 sulfotransferase-inhibiting metabolites of individual brominated diphenyl ethers and nitrofen as well as from some commercial PHAH mixtures (e.g., Bromkal, Clophen A50, and Aroclor 1254) was also demonstrated. These results indicate that hydroxylated PHAHs are potent inhibitors of thyroid hormone sulfation. Since thyroid hormone sulfation may play an important role in regulating free hormone levels in the fetus, and PCB metabolites are known to accumulate in fetal tissues after maternal exposure to PCBs, these observations may have implications for fetal thyroid hormone homeostasis and development.

Inhibition of thyroid hormone sulfation by hydroxylated metabolites of polychlorinated biphenyls.

In this study we investigated the possible inhibitory effects of hydroxylated metabolites of polychlorinated biphenyls (OH-PCBs) on iodothyronine sulfotransferase activity. The results indicate that OH-PCBs are potent inhibitors of this activity in vitro, with IC50 concentrations in the low micro molar range. Inhibition of sulfotransferase activity towards 3,3'-diiodothyronine (T2) was similar to that towards 3,3',5-triiodothyronine (T3) in this in vitro assay, therefore, T2 can be used as the model substrate for the active hormone T3. An important structural requirement for T2 sulfotransferase inhibition is a hydroxyl group on the para or meta position of the OH-PCBs. Since T3 is the active hormone, playing a very important role in somatic and brain development and since hydroxylated PCBs can accumulate in fetuses, inhibition of T3 sulfation could be a possible mechanism for the developmental neurotoxicity of PCBs.

Interactions of persistent environmental organohalogens with the thyroid hormone system: mechanisms and possible consequences for animal and human health.

Several classes of environmental contaminants have been claimed or suggested to possess endocrine-disrupting potency, which may result in reproductive problems and developmental disorders. In this paper the focus is on the multiple and interactive mechanisms of interference of persistent polyhalogenated aromatic hydrocarbons (PHAHs) and their metabolites with the thyroid hormone system. Evidence suggests that pure congeners or mixtures of PHAHs directly interfere with the thyroid gland; with thyroid hormone metabolizing enzymes, such as uridine-diphosphate-glucuronyl transferases (UGTs), iodothyronine deiodinases (IDs), and sulfotransferases (SULTs) in liver and brain; and with the plasma transport system of thyroid hormones in experimental animals and their offspring. Changes in thyroid hormone levels in conjunction with high PHAH exposure was also observed in captive as well as free ranging wildlife species and in humans. Maternal exposure to PHAHs during pregnancy resulted in a considerable fetal transfer of hydroxylated PHAHs, which are known to compete with thyroxine (T4) for plasma transthyretin (TTR) binding sites, and thus may be transported to the fetus with those carrier proteins that normally mediate the delivery of T4 to the fetus. Concomitant changes in thyroid hormone concentrations in plasma and in brain tissue were observed in fetal and neonatal stages of development, when sufficient thyroid hormone levels are essential for normal brain development. Alterations in structural and functional neurochemical parameters, such as glial fibrillary acidic protein (GFAP), synaptophysin, calcineurin, and serotonergic neurotransmitters, were observed in the same offspring up to postnatal day 90. In addition, some changes in locomotor and cognitive indices of behavior were observed in rat offspring, following in utero and lactational exposure to PHAHs. Alterations in thyroid hormone levels and subtle changes in neurobehavioral performance were also observed in human infants exposed in utero and through lactation to relatively high levels of PHAHs. Overall these studies indicate that persistent PHAHs can disrupt the thyroid hormone system at a multitude of interaction sites, which may have a profound impact on normal brain development in experimental animals, wildlife species, and human infants.

Modulating effects of thyroid state on the induction of biotransformation enzymes by 2,3,7,8-tetrachlorodibenzo-p-dioxin.

In this study we investigated to what extent the induction of detoxification enzymes by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is modulated by concomitant TCDD-induced changes in thyroid state. Euthyroid (Eu) male Sprague-Dawley rats, surgically thyroidectomized (Tx) rats and Tx rats receiving substitution doses of 3,3',5-triiodothyronine (Tx+T3) or thyroxine (Tx+T4) by osmotic minipumps were treated with a single ip injection of 10 µg TCDD/kg/bwt or with vehicle (corn oil). Three days after TCDD administration, rats were sacrificed and blood and livers were collected for analysis. Total hepatic cytochrome P450 (CYP) content was increased by ≈50% by TCDD in all groups but was not affected by thyroid state. In Eu rats, TCDD increased CYP1A1/1A2 activity 90-fold, CYP1A1 protein content 52-fold and CYP1A1 mRNA levels ≈5.8-fold. Similar findings were obtained in Tx, Tx+T3 and Tx+T4 rats except that TCDD-induced CYP1A1 activity was significantly decreased in Tx rats. NADPH cytochrome P450 reductase activity was not affected by TCDD but was decreased in Tx rats, which may explain the diminished TCDD-induced CYP1A1 activity in Tx rats. Hepatic p-nitrophenol UDP-glucuronyltransferase (UGT) activity was induced ≈4-fold by TCDD in Eu rats. Similar basal and TCDD-induced activities were observed in Tx+T3 and Tx+T4 rats, but TCDD-induced activities were significantly lower in Tx rats. TCDD did not have a significant effect on overall glutathione-S-transferase (GST) activity or hepatic GST 2-2, 3-3 or 4-4 protein levels but produced a marked increase in GST 1-1 protein levels. Thyroid state did not affect basal or TCDD-induced GST activity or subunit pattern. Iodothyronine sulfotransferase (ST) activity was not affected by TCDD treatment and was slightly but not significantly lower in Tx rats than in Eu, Tx+T3 and Tx+T4 rats. These results suggest that the changes in thyroid hormone levels associated with TCDD treatment have little modulating effects on the induction of hepatic detoxification enzymes in Sprague-Dawley rats exposed to this compound.

Extrathyroidal effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on thyroid hormone turnover in male Sprague-Dawley rats.

Treatment of rats with different polyhalogenated aromatic hydrocarbons strongly decreases plasma T4, with little or no decrease in plasma T3. The extrathyroidal effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on thyroid hormone turnover were studied by i.p. administration of a single dose of 10 microg TCDD/kg BW or vehicle (corn oil) to euthyroid (Eu) rats, thyroidectomized (Tx) rats, and Tx rats infused with 1 microg T4 (Tx+T4) or 0.4 microg T3 (Tx+T3)/100 g BW x day by osmotic minipumps. Tx rats showed decreased plasma T4 and T3 and increased plasma TSH levels, decreased hepatic type I deiodinase (D1) and malic enzyme activities, and increased brain type II deiodinase (D2) activities. All parameters were largely restored to Eu levels in Tx+T4 rats and, except for plasma T4 and brain D2 activity, in Tx+T3 rats, validating the thyroid hormone-replaced Tx rats as models to study the peripheral effects of TCDD. Three days after TCDD administration, plasma T4 and free T4 levels were significantly reduced in Eu and Tx+T4 rats, and plasma T3 was significantly reduced in Tx+T3, but not in Eu or Tx+T4 rats. Plasma TSH was not affected by TCDD in any group. Hepatic T4 UDP-glucuronyltransferase (UGT) activity was induced approximately 5-fold by TCDD, whereas T3 UGT activity was only increased by about 20% (P = NS) in the different groups. TCDD produced an insignificant decrease in liver D1 activity in Tx rats and an insignificant increase in brain D2 activity in Tx rats and hormone-replaced Tx rats. Hepatic malic enzyme activity was significantly increased by TCDD in all groups, except Tx rats. These results strongly suggest that the thyroid hormone-decreasing effects of TCDD are predominantly extrathyroidal and mediated by the marked induction of hepatic T4 UGT activity.

Chemical suppression of feeding in larval weakfish (Cynoscion regalis) by trochophores of the serpulid polychaeteHydroides dianthus.

We studied the effect of exudates from trochophore larvae of the polychaeteHydroides dianthus on feeding in larval weakfish (Cynoscion regalis). Laboratory prey consisted ofH. dianthus trochophores and/or comparably sized rotifers (Brachionus plicatilis). When experiments were conducted in filtered seawater, ingestion of rotifers was always greater than ingestion of trochophores. However, consumption of rotifers was depressed when water fromH. dianthus cultures (=trochophore water) was the experimental medium. The same effect was noted whether we added trochophore water from polychaete cultures that were two or five days postfertilization. However, no effect was noted when we used water from rotifer cultures. We concluded thatH. dianthus trochophores release a water-soluble compound that inhibits feeding in weakfish larvae.