Proposal for a revised Reference Concentration (RfC) for manganese based on recent epidemiological studies

In 1993, based on observations of subclinical neurological effects in workers, the United States Environmental Protection Agency (US EPA) published a Reference Concentration (RfC) of 0.05 μg/m³ for manganese (Mn). The geometric mean exposure concentration, 150 μg/m³ respirable Mn, was considered the lowest observable adverse effect level (LOAEL), and uncertainty factors (UFs) were applied to account for sensitive populations, database limitations, a LOAEL, subchronic exposure, and potential differences in toxicity of different forms of Mn. Based on a review of more recent literature, we propose two alternate Mn RfCs. Of 12 more recent occupational studies of eight cohorts with chronic exposure durations, examining subclinical neurobehavioral effects, predominantly on the motor system, three were considered appropriate for development of an RfC. All three studies yielded no observable adverse effect levels (NOAELs) of approximately 60 μg/m³ respirable Mn. Converting the occupational NOAEL to a human equivalent concentration (HEC) of 21 μg/m³ (for continuous exposure) and applying a UF of 10 to account for intraspecies variability yielded an RfC of 2 μg/m³. We also derived a similar RfC (7 μg/m³) using an Mn benchmark dose (BMD) as the point of departure. Overall confidence in both RfCs is medium.     

Derivation of a chronic reference dose and reference concentration for trimethylbenzenes and C9 aromatic hydrocarbon solvents

Trimethylbenzenes (TMBs) and C9 aromatic hydrocarbon solvents are structurally similar and have similar toxicity. Based on a review of the entire TMB and C9 aromatic hydrocarbon solvents toxicology database, oral and inhalation studies were identified to serve as the basis for a Reference dose (RfD) and Reference concentrations (RfC). The RfD and RfC were derived using standard USEPA methods and assumptions. The RfD was calculated to be 0.4 mg/kg/day using a 90-day oral study that resulted in a NOAEL of 600 mg/kg/day, based on a lack of adverse effects at the highest dose level (reversible effects such as increased serum phosphorus levels and liver and kidney weights), along with a total uncertainty factor of 1000. For the RfC, three studies were considered based on different study designs and toxicological endpoints, including neurotoxicity, systemic toxicity, and potential developmental and reproductive toxicity. For all three studies, as the calculated RfCs were consistent (3–4 mg/m³), the most conservative RfC, 3 mg/m³, was selected. The C9 aromatic hydrocarbon solvents referred to herein are based on chemistries assessed as part of the TSCA Section 4 Test Rule. These solvents contain primarily ethyl toluene and tri-methyl benzene isomers, but the specific compositions can vary based on feedstock and manufacturing process, thus, it is important to consider the composition of any specific solvent to assess similarity to that assessed in the TSCA Section 4 Test Rule program.     

Derivation of a chronic reference dose and reference concentration for trimethylbenzenes and C9 aromatic hydrocarbon solvents

Trimethylbenzenes (TMBs) and C9 aromatic hydrocarbon solvents are structurally similar and have similar toxicity. Based on a review of the entire TMB and C9 aromatic hydrocarbon solvents toxicology database, oral and inhalation studies were identified to serve as the basis for a Reference dose (RfD) and Reference concentrations (RfC). The RfD and RfC were derived using standard USEPA methods and assumptions. The RfD was calculated to be 0.4 mg/kg/day using a 90-day oral study that resulted in a NOAEL of 600 mg/kg/day, based on a lack of adverse effects at the highest dose level (reversible effects such as increased serum phosphorus levels and liver and kidney weights), along with a total uncertainty factor of 1000. For the RfC, three studies were considered based on different study designs and toxicological endpoints, including neurotoxicity, systemic toxicity, and potential developmental and reproductive toxicity. For all three studies, as the calculated RfCs were consistent (3–4 mg/m³), the most conservative RfC, 3 mg/m³, was selected. The C9 aromatic hydrocarbon solvents referred to herein are based on chemistries assessed as part of the TSCA Section 4 Test Rule. These solvents contain primarily ethyl toluene and tri-methyl benzene isomers, but the specific compositions can vary based on feedstock and manufacturing process, thus, it is important to consider the composition of any specific solvent to assess similarity to that assessed in the TSCA Section 4 Test Rule program.     

Cognitive impairment in an adult Mexican population non-occupationally exposed to manganese

We examined the association between non-occupational exposure to Mn and cognitive functions. The study was carried out in a mining district located in Hidalgo State, Mexico, with 288 adults. Air and blood Mn concentrations were determined, and neuropsychological tests were administered to explore cognitive functions and depression. Blood Mn mean was 9.5 ± 4.14 μg/L. A total of 73% of the study group were in contact with air Mn levels that surpassed the EPA recommended guideline level for non-occupational environments (0.05 μg/m³). Air Mn concentration was associated as a risk factor for attention impairment (OR = 1.75, 95% CI: 1.01–3.06). Blood Mn levels were not associated to any of the measured outcomes. The main finding of this study is the presence of attention impairments associated to high levels of air Mn exposure. These results confirm previous studies, in which cognitive impairment is reported for exposed population.     

Manganese in plasma: A promising biomarker of exposure to Mn in welders. A pilot study

Background

There is raising concern about the potential neurotoxic effects of manganese (Mn) inhalation exposure in welders. Because most of the airborne particles in welding fume are in the respirable fraction, their bioavailability is likely to be higher than for coarser dust exposure. No well-validated biomarker for Mn exposure is available.

Objectives

To investigate the interest of measuring Mn in plasma (Mn-P) and urine (Mn-U) as biomarkers of exposure in a group of 28 welders whose tasks were only welding-related.

Methods

Ambient air exposure to Mn (Mn-air) was determined by personal full-shift measurements on Monday and Tuesday. On the same days, blood and urine samples were collected before and after the shift.

Results

Mn-air varied from 1.3 to 729 μg/m³ (GM 27.7). For Mn-U 65% of the values in welders were below the LOQ (0.20 μg/L). Compared to controls, the welders’ Mn-P averaged 33% higher (1.5 vs 2.0 μg/L). In welders, the after-shift Mn-P values correlated well with Mn-air above 10 μg/m³. In spite of similar Mn-air exposure on Monday and Tuesday, the relationships between Mn-air and after-shift Mn-P strikingly differed on Tuesday in that the inflection in the relationship was less obvious and the slope of the regression line (Mn-P after-shift/log Mn-air) for a doubling of log Mn-air was 2.3 times lower than on Monday. On Monday (the first day of the workweek), a Mn-P value of 2 μg/L could distinguish Mn-air exposure above or below 20 μg/m³ with a sensitivity of 69% and a specificity of 82%.

Conclusions

This preliminary study indicates that Mn-P is a promising biomarker of current exposure to Mn in welders and lends biological plausibility to the intended change for the Mn TLV-TWA of 20 μg/m³ proposed by ACGIH for respirable Mn particulate.     

Correlations between Low Doses of Zearalenone,Its Carryover Factor and Estrogen Receptor Expression in Different Segments of the Intestines in Pre-Pubertal Gilts—A Study Protocol

Plant materials can be contaminated with Fusarium mycotoxins and their derivatives, whose toxic effects on humans and animals may remain subclinical. Zearalenone (ZEN), a low-molecular-weight compound, is produced by molds in crop plants as a secondary metabolite. The objective of this study will be to analyze the in vivo correlations between very low monotonic doses of ZEN (5, 10, and 15 μg ZEN/kg body weight—BW for 42 days) and the carryover of this mycotoxin and its selected metabolites from the intestinal contents to the intestinal walls, the mRNA expression of estrogen receptor alfa (ERα) and estrogen receptor beta (ERβ) genes, and the mRNA expression of genes modulating selected colon enzymes (CYP1A1 and GSTP1) in the intestinal mucosa of pre-pubertal gilts. An in vivo experiment will be performed on 60 clinically healthy animals with initial BW of 14.5 ± 2 kg. The gilts will be randomly divided into a control group (group C, n = 15) and three experimental groups (group ZEN5, group ZEN10, and group ZEN15; n = 15). Group ZEN5 will be administered per os 5 μg ZEN/kg BW (MABEL), group ZEN10—10 μg ZEN/kg BW (NOAEL), and group ZEN15—15 µg ZEN/kg BW (low LOAEL). In each group, five animals will be euthanized on analytical dates 1 (exposure day 7), 2 (exposure day 21), and 3 (exposure day 42). Samples for in vitro analyses will be collected from an intestinal segment resected from the following regions: the third (horizontal) part of the duodenum, jejunum, ileum, cecum, ascending colon, transverse colon, and descending colon. The experimental material will be collected under special conditions, and it will be transported to specialist laboratories where samples will be obtained for further analyses.     

Proposal for reference concentrations (RfC) for inhalation exposure to methanol

A tentative reference concentration (RfC) for methanol in ambient air, i.e. an exposure concentration below which adverse effects are not expected to occur, was derived from the analysis of the toxicological data available in the literature. Well-documented studies that correlate environmental levels of methanol with observed toxic effects have not been found in the literature, nor have any long-term epidemiological studies of chronic low-level occupational exposure been found. Assessment of RfC for acute inhalation exposure is based on a human study (n=26 subjects) with a 'tentative' NOAEL of 262 mg/m(3). The calculated RfC for 1 h exposure is 104.8 mg/m(3). The RfC is given a low confidence rating as there was only one methanol concentration used. A well designed study on monkeys served as the basis for the assessment of RfC for chronic inhalation exposure. In this study, 13.1 and 131 mg/m(3) were considered as NOAEL and LOAEL, respectively. The calculated RfC is 0.38 mg/m(3). The overall database is weak, lacking data on reproductive and developmental endpoints in human or non-human primates. Nevertheless, the RfC is given a medium confidence rating because of the strength of the principal study.     

Minimum tolerable exposure period and maximum threshold dietary intake of ochratoxin A for causing renal cancer in male Dark Agouti rats

In rats fed dietary ochratoxin A (5 ppm for 3, 6 or 9 months) no renal tumours occurred throughout natural life of the group treated for 3 months, during which the ochratoxin dose was 3 times that in the high dose group of the NTP study. Bilateral renal carcinoma occurred in one rat in the 6 month group. Four rats treated for 9 months developed unilateral renal carcinoma. Overall latency between ceasing toxin exposure and discovering tumours was 35–97 weeks. Experimental verification of a ‘no observable effect level’ was made for feed containing 400 ppb, equivalent to 7 μg ochratoxin A/day for Dark Agouti rats for up to 2 years, during which mean daily dose commenced at 50 μg/kg, but later for adults was in the range 30–20 μg/kg. This data doubles the daily in vivo threshold dose from the NTP study (15 μg/kg), and could influence human risk assessment. An at least 3 month threshold period for exposure to exceptionally high daily OTA intake (90 μg; 640–450 μg/kg) raises doubts over interpretation of experimental molecular data for OTA exposure at lower dose for up to 3 months in studies aimed at understanding carcinogenic mechanism.     

Alteration of pregnancy related hormones and fetal survival in F-344 rats exposed by inhalation to benzo(a)pyrene

The objective of this study was to evaluate the effect of subacute exposure to inhaled benzo(a)pyrene (BaP) on fetal survival and luteal maintenance using timed-pregnant Fisher 344 rats. Prior to assignment of pregnant rats to treatment and control groups, numbers of implantation sites were determined on gestation day (GD) 8 via midventral laparotomy. Subsequently, animals were assigned randomly to three treatment groups and two control groups. Treatment consisted of subacute exposure of rats via inhalation to BaP 25, 75, and 100 μg/m³, 4 h daily for 10 days (GD-11–20). Control animals were either sham exposed to carbon black (CB) to control for inert BaP carrier or remained unexposed (UNC). Blood samples were collected on days 15 and 17 of gestation via sinus orbital veini-puncture for plasma. Number of pups per litter was determined postpartum and fetal survival rate was expressed as a percentage of the corresponding implantation sites. Radioimmunoassays were used to determine plasma progesterone, estrogen, and prolactin (indirect measurement of decidual luteotropin) concentrations. Fetal survival among BaP-treated rats declined in a dose-dependent manner (25 μg/m³, 78.3% per litter; 75 μg/m³, 38.0% per litter; 100 μg/m³, 33.8% per litter; P<0.05) compared with CB (96.7% per litter) and UNC (98.9% per litter). Plasma progesterone, estrogen, and prolactin concentrations also declined as a result of subacute exposure of rats to BaP compared to controls. These data suggest that inhaled BaP compromised fetal survival and consequently luteotropic activity in the exposed animals.     

An alternative to the USEPA's proposed inhalation reference concentrations for hexavalent and trivalent chromium.

The passage of the Clean Air Act Amendment of 1990 reflects a growing public concern over human exposure to air toxics. The EPA is currently identifying inhalation reference concentrations (RfCs) to be used as risk criteria for determining whether existing or predicted ambient levels of chemicals are above acceptable concentrations. This paper evaluates the risk assessment methods used by the EPA to develop the recently proposed RfC (0.002 micrograms/m3) for both trivalent chromium [Cr(III)] and hexavalent chromium [Cr(VI)]. Based on our evaluation, these RfC values do not appear to have been developed in accordance with standard Agency procedures or classic toxicology methods for setting RfCs. In particular, the "key" study used by the EPA [E. Lindberg and G. Hedenstierna (1983) Arch. Environ. Health 38, 367-374] as the basis for their proposal is not appropriate because it examined only the effects of exposure to chromic acid mist [Cr(VI)], even though most environmental exposure is to Cr(VI) and Cr(III) as a dust. The health hazards of Cr(VI) as an acid mist are significantly different from those associated with Cr(VI) as a dust. Further, the EPA's key study did not evaluate exposure to Cr(III), the toxicity of which is significantly different from both particulate Cr(VI) and chromic acid mist. Finally, the uncertainty factors used to account for data gaps were unusually high, thus providing RfC values equal to or below most naturally occurring environmental levels and standard analytical limits of detection. In this paper, we propose alternative RfCs for Cr(VI) as chromic acid mist and for Cr(VI) as a dust. Based on the Lindberg and Hedenstierna study, we derived an RfC of approximately 0.12 micrograms/m3 for chromic acid mist. An RfC of 1.2 micrograms/m3 is recommended for particulate Cr(VI) based on animal studies that evaluate long-term inhalation exposure to Cr(VI) dust. Due to its low toxicity, an RfC for Cr(III) is not warranted.     

Human exposure to acrolein: Time-dependence and individual variation in eye irritation

The aim of the study was to examine the time dependence on sensory irritation detection following exposure to threshold levels of acrolein, in humans. The exposures occurred in an exposure chamber and the subjects were breathing fresh air through a mask that covered the nose and mouth. All participants participated in four exposure conditions, of which three consisted of a mixture of acrolein and heptane and one of only heptane. Exposure to acrolein at a concentration half of the TLV-C lead to sensory irritation. The perceived sensory irritation resulted in both increased detectability and sensory irritation after about 6.8 min of exposure in 58% of the participants. The study confirm the previously suggested LOAEL of about 0.34 mg/m³ for eye irritation due to acrolein exposure. The sensory irritation was still significant 10 min after exposure. These results have implications for risk assessment and limit setting in occupational hygiene.     

Characterisation of copper oxide nanoparticles for antimicrobial applications

Copper oxide (CuO) nanoparticles were characterised and investigated with respect to potential antimicrobial applications. It was found that nanoscaled CuO, generated by thermal plasma technology, contains traces of pure Cu and Cu₂O nanoparticles. Transmission electron microscopy (TEM) demonstrated particle sizes in the range 20–95 nm. TEM energy dispersive spectroscopy gave the ratio of copper to oxygen elements as 54.18% to 45.26%. The mean surface area was determined as 15.69 m²/g by Brunau–Emmet–Teller (BET) analysis. CuO nanoparticles in suspension showed activity against a range of bacterial pathogens, including meticillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli, with minimum bactericidal concentrations (MBCs) ranging from 100 μg/mL to 5000 μg/mL. The ability of CuO nanoparticles to reduce bacterial populations to zero was enhanced in the presence of sub-MBC concentrations of silver nanoparticles. Studies of CuO nanoparticles incorporated into polymers suggest release of ions may be required for optimum killing.     

Impurity profile study of lopinavir and validation of HPLC method for the determination of related substances in lopinavir drug substance

Several related substances (RS4–RS10) were detected in lopinavir drug substance at levels ranging from 0.03% to 0.1% by employing gradient RP-HPLC. The related substances were identified by LC–MS analysis. These related substances were isolated and characterized by Mass, ¹H NMR and FT-IR spectral data. The separation was achieved on a YMC Pack ODS-AQ (250 mm × 4.6 mm, 5 μm) column thermostated at 45 °C using 0.02 M KH₂PO₄ (pH 2.5): acetonitrile as a mobile phase in gradient elution mode. A PDA detector set at 210 nm was used for detection. The investigated validation elements showed the method has acceptable specificity, accuracy, linearity, precision, robustness and high sensitivity with detection limits and quantitation limits ranging from 0.028 μg/ml to 0.063 μg/ml and 0.084 μg/ml to 0.192 μg/ml respectively. The method can be used for routine quality control analysis and stability testing of lopinavir drug substance.     

The neurotoxic effects of heavy metal exposure on GABAergic nervous system in nematode Caenorhabditis elegans

The number of cell body or synapse made by Caenorhabditis elegans GABAergic neurons is constant during development. The neurotoxic effects of metal (Pb, Hg, Cu, Cd, Cr, and Mn) exposure on GABAergic motor neurons were investigated in C. elegans. Exposure to examined metals could not alter the position of GABA neurons, whereas exposure to high concentrations (75 μM and 200 μM) of metals caused noticeable axonal degeneration and neuronal loss in nerve cords, suggesting neurodegeneration will be induced by metal exposure to different degrees. In addition, exposure to Pb, Hg, Cu, and Cd at the low concentration (2.5 μM) could also induce obviously neuronal loss. Moreover, exposure to high concentrations (75 μM and/or 200 μM) of most of examined metals significantly reduced the relative size and fluorescent intensities of AVL, RMEs, and RIS neurons. Therefore, the neurodegeneration and abnormal structures may be formed in GABAergic motor neurons after metal exposure, and the endpoint of neuronal loss will be useful for the neurotoxicity assessment from trace metal exposure.     

Comparison of the impact of the Tobacco Heating System 2.2 and a cigarette on indoor air quality

The impact of the Tobacco Heating System 2.2 (THS 2.2) on indoor air quality was evaluated in an environmentally controlled room using ventilation conditions recommended for simulating “Office”, “Residential” and “Hospitality” environments and was compared with smoking a lit-end cigarette (Marlboro Gold) under identical experimental conditions. The concentrations of eighteen indoor air constituents (respirable suspended particles (RSP) < 2.5 μm in diameter), ultraviolet particulate matter (UVPM), fluorescent particulate matter (FPM), solanesol, 3-ethenylpyridine, nicotine, 1,3-butadiene, acrylonitrile, benzene, isoprene, toluene, acetaldehyde, acrolein, crotonaldehyde, formaldehyde, carbon monoxide, nitrogen oxide, and combined oxides of nitrogen) were measured. In simulations evaluating THS 2.2, the concentrations of most studied analytes did not exceed the background concentrations determined when non-smoking panelists were present in the environmentally controlled room under equivalent conditions. Only acetaldehyde and nicotine concentrations were increased above background concentrations in the “Office” (3.65 and 1.10 μg/m³), “Residential” (5.09 and 1.81 μg/m³) and “Hospitality” (1.40 and 0.66 μg/m³) simulations, respectively. Smoking Marlboro Gold resulted in greater increases in the concentrations of acetaldehyde (58.8, 83.8 and 33.1 μg/m³) and nicotine (34.7, 29.1 and 34.6 μg/m³) as well as all other measured indoor air constituents in the “Office”, “Residential” and “Hospitality” simulations, respectively.     

Association between occupational exposure to arsenic and neurological, respiratory and renal effects

Occupational exposure by inhalation in copper smelter is associated with several subclinical health phenomena. The respiratory tract is usually involved in the process of detoxication of inhaled noxious agents which, as arsenic, can act as inductors of oxidative stress (Lantz, R.C., Hays, A.M., 2006. Role of oxidative stress in arsenic-induced toxicity. Drug Metab. Rev. 38, 791-804). It is also known that irritating fumes affect distal bronchioles of non-ciliated, epithelial Clara cells, which secrete anti-inflammatory and immunosuppressive Clara cell protein (CC16) into the respiratory tract.The study group comprised 39 smelters employed at different workplaces in a copper foundry, matched for age and smoking habits with the control group (n = 16). Subjective neurological symptoms (SNS), visual evoked potentials (VEP), electroneurographic (EneG) and electroencephalographic (EEG) results were examined in the workers and the relationships between As concentration in the air (As-Air) and urine (As-U) were assessed. Effects of exposure were expressed in terms of biomarkers: CC16 as early pulmonary biomarker and β₂-microglobulin (β₂M) in urine and serum and retinol binding protein (RBP) as renal markers, measured by sensitive latex immunoassay.The concentrations of arsenic exceeded about two times the Threshold Limit Values (TLV) (0.01 mg/m³). The contents of lead did not exceed the TLV (0.05 mg/m³).Low CC16 levels in serum (12.1 μg/l) of workers with SNS and VEP symptoms and highest level As-U (x_a 39.0 μg/l) were noted earliest in relation to occupational time. Moreover, those effects were associated with increased levels of urinary and serum β₂M and urinary RBP.Results of our study suggested the initiative key role of oxidative stress in triggering the processes that eventually lead to the subclinical effects of arsenic on the nervous system.     

Developmental anomalies induced by a non-selective COX inhibitor (ibuprofen) in zebrafish (Danio rerio)

Effects of ibuprofen (a non-selective COX inhibitor) on the embryonic development, hatching success, larval growth, behavioral pattern and survival competence were studied in Danio rerio. Embryos at 2/4 celled stage were exposed to graded doses (0, 1, 5, 10, 50 and 100 μg/L distilled water) of ibuprofen in triplicate sets (n = 30). The experiment was repeated thrice. The results indicate that developing embryos tolerated lower (1 and 5 μg/L) doses of the drug readily but, exposure to higher doses (>10 μg/L) caused retarded development, decreased hatching rate and growth, cardiac anomalies, spinal curvature, pectoral fin malformation and behavioral alterations resulting in greater mortality of experimental embryos. This study suggests that, ibuprofen which is marketed as over-the-counter (OTC) drug is embryotoxic at least at higher (>10 μg/L) dose level to zebrafish embryos.     

Health assessment of phosgene: approaches for derivation of reference concentration

This paper describes the derivation of the chronic reference concentration (RfC) for human inhalation of phosgene that was recently added to the Environmental Protection Agency's (EPA) Integrated Risk Information System (IRIS) data base (U.S. EPA, 2005. Toxicological Review of Phosgene: In Support of Summary Information on the Integrated Risk Information System (IRIS). Available online at: ). The RfC is an estimate of daily phosgene exposure to the human population that is likely to be without appreciable risk of deleterious effects during a lifetime. [For this and other definitions relevant to EPA risk assessments refer to the glossary of terms in the US EPA IRIS website (http://www.epa.gov/IRIS).] Phosgene is a potential environmental pollutant that is primarily used as a catalyst in the polyurethane industry. It is a gas at room temperature, and in aqueous solution it rapidly hydrolyzes to CO2 and HCl. In the absence of chronic human health effects information and lifetime animal cancer bioassays, the RfC is based on two 12-week inhalation studies in F344 rats which measured immune response and pulmonary effects, respectively. The immune response study showed impaired clearance of bacteria that was administered into the lungs of rats immediately after exposure to phosgene at concentrations of 0.1, 0.2 and 0.5 ppm. It also showed that the immune response in uninfected rats was stimulated by phosgene exposure at all concentrations. The pulmonary effects study showed a progressive concentration-related thickening and inflammation in the bronchiolar regions of the lung that was mild at 0.1 ppm and severe at 1.0 ppm. An increase in collagen content, as observed with histological collagen stains, was observed at 0.2 ppm and above. Though there is considerable uncertainty associated with the species and exposure duration employed, this endpoint is considered an indication of chronic lung injury of potential relevance to humans. Three different approaches for RfC derivation were taken in analyzing these studies: (1) the traditional NOAEL/LOAEL method; (2) the benchmark dose (BMD); and (3) the categorical regression for the analysis of severity-graded pulmonary damage data using the recently revised USEPA CatReg software. The BMD approach was selected as the method of choice to determine the RfC for phosgene because it has several advantages compared to the NOAEL/LOAEL: (1) it is not restricted to the set of doses used in the experiments; (2) the result is not dependent on sample size; (3) it incorporates information on statistical uncertainty. The CatReg approach allowed the incorporation of data on the severity of the pathological lesions, and therefore it complemented the other approaches. The BMD approach could not be applied to the immune response data because it was not possible to define an adverse effect level for bacterial resistance. However, NOAEL/LOAEL values for immune responses were consistent with benchmark dose levels derived from lung pathology data and used in the derivation of the RfC. The preferred RfC method and derivation involved dividing the benchmark dose from the collagen staining data (0.03 mg/m3) by a composite uncertainty factor of 100: RfC=0.03/100=3E-4 mg/m3.     

Carry-Over of Zearalenone and Its Metabolites to Intestinal Tissues and the Expression of CYP1A1 and GSTπ1 in the Colon of Gilts before Puberty

The objective of this study was to evaluate whether low doses of zearalenone (ZEN) affect the carry-over of ZEN and its metabolites to intestinal tissues and the expression of CYP1A1 and GSTπ1 in the large intestine. Prepubertal gilts (with a BW of up to 14.5 kg) were exposed in group ZEN to daily ZEN5 doses of 5 μg/kg BW (n = 15); in group ZEN10, 10 μg/kg BW (n = 15); in group ZEN15, 15 μg/kg BW (n = 15); or were administered a placebo (group C, n = 15) throughout the experiment. After euthanasia, tissues were sampled on exposure days 7, 21, and 42 (D1, D2, and D3, respectively). The results confirmed that the administered ZEN doses (LOAEL, NOAEL, and MABEL) were appropriate to reliably assess the carry-over of ZEN. Based on the observations made during 42 days of exposure to pure ZEN, it can be hypothesized that all mycotoxins (ZEN, α-zearalenol, and β-zearalenol) contribute to a balance between intestinal cells and the expression of selected genes encoding enzymes that participate in biotransformation processes in the large intestine; modulate feminization processes in prepubertal gilts; and elicit flexible, adaptive responses of the macroorganism to mycotoxin exposure at the analyzed doses.     

Simultaneous determination of 3-chlorotyrosine and 3-nitrotyrosine in human plasma by direct analysis in real time–tandem mass spectrometry

A novel method for the simultaneous determination of 3-nitrotyrosine (NT) and 3-chlorotyrosine (CT) in human plasma has been developed based on direct analysis in real time–tandem mass spectrometry (DART–MS/MS). Analysis was performed in the positive ionization mode using multiple reaction monitoring (MRM) of the ion transitions at m/z 216.2/170.1 for CT, m/z 227.2/181.1 for NT and m/z 230.2/184.2 for the internal standard, d³-NT. The assay was linear in the ranges 0.5–100 μg/mL for CT and 4–100 μg/mL for NT with corresponding limits of detection of 0.2 and 2 μg/mL. Intra- and inter-day precisions and accuracies were respectively <15% and ±15%. Matrix effects were also evaluated. The method is potentially useful for high throughput analysis although sensitivity needs to be improved before it can be applied in clinical research.KEY WORDS: 3-Nitrotyrosine, 3-Chlorotyrosine, Determintion, DART–MS/MS, Human plasma