Biological monitoring as a valid tool to assess occupational exposure to mixtures of 2,4-:2,6-toluene diisocyanate

BACKGROUND AND OBJECTIVES

Despite its advantages over environmental monitoring, biological monitoring of exposure to 2,4-:2,6-toluene diisocyanate (TDI) mixtures is still underused. The present study was designed in order to evaluate the feasibility and reliability of biological monitoring in a factory producing polyurethane foam blocks.

METHODS

Airborne TDI isomers were sampled by both static and personal pumps and determined by HPLC with fluorimetric detection. Specific metabolites 2,4- and 2,6-toluenediamine (TDA) were determined by gas chromatography-mass spectrometry on hydrolysed urine samples collected from 16 workers at the beginning of the workweek and both before (BS) and at the end (ES) of the 4th workday. Additional samples were collected at the end of the 1st half-shift and at the beginning of the 2nd half-shift in 5 workers.

RESULTS

In the foam production shop, TDI values were on average about 20 microg/m3, with higher levels in the 2nd half-shift and peak levels in workers operating along the polymerization tunnel. Average TDI levels were significantly correlated with ES TDA concentrations (p < 0.0001). TDA showed a fast urinary elimination phase leading to progressively higher TDA levels either during the shift (5 workers) and at the end-of-shift. A slower elimination phase with a weekly accumulation was demonstrated by values at the beginning of the workweek (higher than in unexposed subjects) and by their elevation in subsequent BS samples.

CONCLUSIONS

The study demonstrates the feasibility and reliability of biological monitoring in workers exposed to 2,4-:2, 6-TDI mixtures. This approach can provide information about both the daily and weekly exposure levels.

Urinary excretion of toluene diisocyanates in rats following dermal exposure

Toluene diisocyanates (TDI) are commonly used in polyurethane (PU)-related products. TDIs have been documented as the leading cause of occupational asthma. Skin exposure to TDI in the workplace is common. However, no studies in the literature have investigated the exact biomarker concentration profile for skin TDI absorption through any in vivo animal studies. In this study a rat model was used to evaluate the TDI skin absorption to explore the dose-response pattern and to determine the kinetic characteristics of urinary toluene diamine (U-TDA) during skin exposure. TDIs were topically exposed on the dorsum of rat skin at 0.2%, 1% and 5%. Consecutive urine samples were collected for 6 days and U-TDA were analysed using GC/ECD. It was demonstrated in this rat study that absorption of 2,4- and 2,6-TDI through skin contact is possible. A clear dose-dependent skin absorption relationship for 2,4- and 2,6-TDI was demonstrated by the AUC, Cmax findings and accumulative amounts (r > or = 0.968). U-TDA concentration profiles in 6-day consecutive urine samples fit well in the first-order kinetics, although higher order kinetics could not be excluded for the high dose. The apparent half-lives for excretory urinary TDA were about 20 h consistent at various skin exposures. It is concluded that skin absorption of TDI was confirmed in a rat model and a clear dose-dependent skin absorption relationship for 2,4- and 2,6-TDI was demonstrated. Excretory U-TDA concentrations in 6-day consecutive urine samples via skin exposure reveal the first-order kinetics and the half-lives were about 20 h.

Increased levels of IgG to cytokeratin 19 in sera of patients with toluene diisocyanate-induced asthma

BACKGROUND

Inhaled isocyanate binds with cytokeratin (CK) of the epithelial cells, which could induce immune responses.

OBJECTIVE

To elucidate the possible existence of an isocyanate-induced, asthma-associated autoantigen from the bronchial epithelial cells, which may be associated with toluene diisocyanate (TDI)-induced asthma development.

METHODS

We cultured bronchial epithelial cells with incubation of TDI-human serum albumin (HSA) conjugate. Gene expression profiles of cultured epithelial cells were analyzed using a microarray technique. CK19 protein expression within the epithelial cells was confirmed by IgG immunoblot using monoclonal antibody to CK19. Serum IgG to CK19 and specific IgG and IgE antibodies to TDI-HSA conjugate were detected by enzyme-linked immunosorbent assay in 68 TDI asthma patients (group 1) and compared with 40 allergic asthma patients (group 2) and 80 unexposed healthy controls (group 3).

RESULTS

After TDI exposure, increased expression of CK19 and CK14 genes from the culture bronchial epithelial cells was noted using microarray analysis. IgG immunoblot analysis confirmed increased expression of CK19 after the TDI exposure. The levels of serum IgG to CK19 were significantly higher in the TDI asthma group than in groups 2 and 3 (P=.008). The prevalence of IgG to CK19 was significantly higher in group 1 (38.2%) than group 2 (22.5%) or group 3 (1.3%) (P=.008). Significant associations were noted between IgG to CK19 and specific IgG to TDI-HSA conjugate and transglutaminase (P=.02) but not with specific IgE to TDI-HSA conjugate.

CONCLUSION

We suggest that TDI exposure can augment CK19 expression from the bronchial epithelial cell, which may involve immune responses as an autoantigen to induce airway inflammation in TDI-induced asthma.

LC-MS determination of urinary toluenediamine in workers exposed to toluenediisocyanate

To improve the biological monitoring method for 2,6- and 2,4-toluenediisocyanate (TDI) exposure, we developed a simple and rapid method for analysis of the corresponding urinary metabolites, 2,6- and 2,4-toluenediamine (TDA) using liquid chromatograph-mass spectrometry (LC-MS). One ml of urine was hydrolyzed at 100 degrees C for 1.5 h with H(2)SO(4). Alkalinized hydrolysate was extracted with dichloromethane (DCM) and analyzed by atmospheric pressure chemical ionization (APCI) LC-MS, in positive-ion mode. The mass spectra of TDA isomers showed the protonated molecule [M+H](+), at m/z 123 as the base peak. Calibration curves of 2,6-TDA were linear up to 400 microg/l. TDA isomers in urine of exposed workers as determined by LC-MS correlated well with those obtained by gas chromatography-mass spectrometry. 2,6- and 2,4-TDA were not detected in non-exposed subjects, whereas exposed workers showed urinary levels up to 250 and 63 microg/l, respectively.

Carcinogenic risk of toluene diisocyanate and 4,4'-methylenediphenyl diisocyanate: epidemiological and experimental evidence

Diisocyanates are highly reactive compounds widely used, for example, in the production of polyurethane foams, elastomers, paints, and adhesives. The high chemical reactivity of these compounds is also reflected in their toxicity: diisocyanates are one of the most important causes of occupational asthma but also other adverse effects, such as irritation and toxic reactions, have been described in exposed subjects. One of the open questions is whether occupational isocyanate exposure is a carcinogenic hazard. The few epidemiological studies available have been based on young cohorts and short follow-up and are not conclusive. Toluene diisocyanate (TDI) has been classified as carcinogenic in animals on the basis of gavage administration studies, but no conclusions are available on inhalation exposure. For 4,4'-methylene diphenyldiisocyanate (MDI) there is suggestive evidence for carcinogenicity in rats. The possible carcinogenic mechanism of TDI and MDI is not clear. Both chemicals have been positive in a number of short-term tests inducing gene mutations and chromosomal damage. The reactive form could be either the diisocyanate itself or may derive from the metabolic activation of the aromatic diamine derivatives formed by hydrolysis. TDI and MDI react with DNA in vivo and in vitro. However, the structure of the adducts has not been identified. Especially from the in vivo experiment it is not known if the adducts are a product from the reaction with the isocyanate or the corresponding amine. In conclusion, both TDI and MDI are highly reactive chemicals that bind to DNA and are probably genotoxic. The alleged animal carcinogenicity of TDI and MDI would suggest that occupational exposure to these compounds is a carcinogenic risk. The few epidemiological studies available have not, however, been able to clarify if TDI and MDI are occupational carcinogens.

[Gas chromatography in detection of toluene diisocyanate in biological medium]

The authors suggested a method of gas chromatography for detection of toluylene diisocyanate (TDI) in biologic material: liver, lungs, spleen, brain, kidney. The method includes TDI extraction from tissues by solvent, subsequent concentration and the extract chromatography by a device with electron capture detector. The method was tested in white rats.

Toluene diisocyanate colocalizes with tubulin on cilia of differentiated human airway epithelial cells

Toluene diisocyanate (TDI), a highly reactive industrial chemical with widespread use in the manufacture of polyurethane and plastics, is the leading cause of occupational asthma associated with chemical exposure. We report the effects of TDI vapor (20, 100, 500, 1000 ppb) in vitro on differentiated human bronchial epithelial cells. Increased mucus was observed by electron microscopy at all TDI concentrations. Cytotoxicity, as evidenced by cell pyknosis and DNA fragmentation, was detected following a 30-min exposure to TDI concentrations of 100 ppb or higher. At 1000 ppb, transepithelial resistance was lost. Using confocal microscopy and double staining, TDI was found colocalized with ciliary tubulin in cultures that had been exposed to 20 and 100 ppb. These findings are the first to identify TDI binding to human pulmonary epithelial cells and indicate extensive binding to the cilia of differentiated epithelial cells. The in vivo implications of these findings include decreased ciliary movement and longer retention of TDI and hence increased exposure. Altered cytoskeletal-derived signal transduction may be a consequence of tubulin involvement. The effects of such changes on respiratory sensitization remain to be explored.

The importance of the diluent for airway transport of toluene diisocyanate following intranasal dosing of mice

Uncertainty of the transport of reactive chemicals to the lung is a major concern when using intranasal dosing of animals. In a preliminary study using mice, intranasal instillation of the dyes methylene blue (in water) and Sudan black B (in 1:4 ethyl acetate:olive oil), indicated that the following conditions were necessary to achieve transport to the lung: (1) aqueous diluent, (2) light anesthesia prior to dosing, (3) holding the animal in a supine position during chemical application, and (4) maintaining the animal in the same position postdosing. Using these conditions, we investigated the distribution of toluene diisocyanate (TDI), a major industrial asthmogen, to the lung following intranasal administration. Female C57BL/6 mice received 20 microl of 1% TDI in ethyl acetate:olive oil (1:4). Group 1 received a single application on day 1; group 2, single applications on 2 consecutive days; group 3, single applications on 4 consecutive days; and group 4, a single application of the vehicle on 2 consecutive days. All mice were necropsied 24 h after the final application. The nasal passages, upper pharynx, trachea, lungs, and olfactory bulbs of each animal were examined with hematoxylin-eosin and immunohistochemical staining, the latter using a rabbit anti-TDI antiserum. Histopathology revealed desquamation of ciliated epithelial cells as well as inflammatory cell debris in the nasal cavity and upper pharynx of animals in groups 1-3. The intensity of these changes was dependent on the number of applications. No inflammation was observed in the trachea, lungs, or olfactory bulbs in any of the groups. Immunohistochemical examination revealed positive staining for the TDI moiety in epithelial cells of the nasal cavity and upper pharynx in animals of groups 1-3. No staining was observed in the trachea, lungs, or olfactory bulbs of any animal. These results suggest that TDI, when dissolved in olive oil:ethyl acetate and applied intranasally, does not reach the trachea and/or lower airways.

Toxicokinetics of 2,4- and 2,6-toluenediamine in hydrolysed urine and plasma after occupational exposure to 2,4- and 2,6- toluene diisocyanate

OBJECTIVES

To assess the toxicokinetics of 2,4- and 2,6- toluenediisocyanate (TDI) in chronically exposed subjects.

METHODS

Blood and urine, from 11 workers at two flexible foam polyurethane production plants, were sampled. By gas chromatography-mass spectrometry (GC-MS) 2,4- and 2,6-toluene diamine (TDA) were measured as pentafluoropropionic anhydride (PFPA) derivatives after acidic hydrolysis of plasma (P-TDA, ng/ml) and urine (U-TDA, microgram/h).

RESULTS

In one of the plants the P-2,4-TDA concentrations were 0.4-1 ng/ml before a four to five week holiday and 0.2-0.5 ng/ml afterwards. The corresponding values for P-2,6-TDA were 2-6 and 0.5-2 ng/ml respectively. In the other plant the P-2,4-TDA concentrations were 2-23 ng/ml before the holiday and 0.5-6 ng/ml afterwards and the P-2,6-TDA concentrations were 7-24 ng/ml before and 3-6 ng/ml afterwards. The P-2,4-TDA concentrations were 2-24 ng/ml before a 12 day holiday, and 1-14 ng/ml afterwards. The corresponding values for P-2,6-TDA were 12-29 and 8-17 ng/ml, respectively. The urinary elimination rates (U-TDA, microgram/h) for 2,4-TDA before the holiday were 0.04-0.54 and 0.02-0.18 microgram/h afterwards. The corresponding values for 2,6-TDA were 0.18-0.76 microgram/h before and 0.09-0.27 microgram/h after the holiday. The half life in urine ranged between 5.8 and 11 days for 2,4- and 2,6-TDA. The differences in exposure were reflected by the P-TDA concentrations. The mean half life in plasma was 21 (range 14-34) days for 2,4-TDA and 21 (16-26) days for 2,6-TDA. The TDI air concentrations varied between 0.4 and 4 micrograms/m3 in one plant and in the other between 10 and 120 micrograms/m3.

CONCLUSIONS

The half life in plasma of chronically exposed workers for 2,4-and 2,6-TDA was twice as long as for volunteers with short term exposure. An indication of a two phase elimination pattern in urine was found. The first phase was related to the more recent exposure and the second, much slower one was probably related to release of TDA in urine from TDI adducts in the body.

Analysis of the reactivity of [14C]toluene diisocyanate (TDI) in an isolated, perfused lung model

An isolated, perfused, guinea pig lung model was used to investigate the molecular events which occur when a 14C-labeled TDI vapor reaches the airways. Exposure concentrations of 0.2 and 0.7 ppm were tested. Perfusate composition included: Krebs Ringer buffer only, as well as buffer containing either guinea pig serum albumin, human serum albumin, or diluted guinea pig plasma. Radioactivity was detected in the perfusate within minutes of exposure, and following a delay, increased linearly. The rate of uptake was dependent on TDI concentration and the composition of the perfusate. Biochemical characterization of the state of the 14C-labeled material in the perfusate was performed. The distribution between low and high molecular weight reaction products was determined by molecular sieve fractionation and varied as a function of perfusate composition but no variability was observed as a function of time during the 45 min of exposure. An increase in nucleophile concentration in the perfusate was associated with both a higher percentage of conjugated products (from 15% with buffer only to 45% with diluted guinea pig plasma) and an increase in the rate of TDX uptake (from 0.5 microns Eq/min with buffer alone to 0.1 micrograms Eq/min with diluted GPSA as perfusate at 0.7 ppm). GC-MS analysis of the samples for free TDA, before and after acid hydrolysis, showed that the low molecular weight product(s), which represented from 55-85% of the circulating radioactivity, was composed of hydrolyzable and non-hydrolyzable conjugates and metabolites with approximately 4% of the label associated with free TDA. Although the distribution between high and low molecular weight species varies, this result is analogous to the findings from in vivo studies and suggests that the isolated, perfused lung (IVPL) system may be a useful tool in investigating the molecular mechanisms of isocyanate-induced disease and metabolic activity of the lung.

Toluene diisocyanate: an assessment of carcinogenic risk following oral and inhalation exposure

Although respiratory sensitization and pulmonary irritation have been the subject of particular studies with toluene diisocyanate (TDI), in recent years the potential carcinogenicity of TDI has been a reason for concern and speculation. This has arisen from the expectation that following exposure to TDI the chemical would hydrolyze at aqueous tissue surfaces to give rise to toluene diamine (TDA), a mutagen and rodent carcinogen. The chemistry of TDI suggests that the reaction with biological NH2 groups such as those on proteins, and polymerization to oligoureas, will compete with the hydrolysis reaction. This has been shown with results of in vitro studies where conjugation to protein occurs without detectable formation of TDA when protein solutions in saline are exposed to TDI vapor. Lower pH levels leading to high protonation of biological NH2 groups facilitate hydrolysis of TDI to TDA and subsequent formation of polyureas. These observations are consistent with comparative toxicokinetic studies in rats, which demonstrate significant levels of TDA following oral dosing with TDI--due to the acidic environment in the stomach--but not after inhalation. These results provide an explanation for the tumors observed in rodents after oral dosing of TDI in corn oil, but not after inhalation. Inhalation is the relevant route of human exposure for TDI and the toxicokinetics of TDI exposure at occupational exposure limits have been studied. These data provide a means by which quantitative estimates of the risk of carcinogenicity possibly resulting from the intermediate formation of TDA during TDI exposure can be obtained. Several calculations have been made, all of which lead to the conclusion that TDI exposure by inhalation at the recommended occupational limits will not give rise to significant carcinogenic risk.

Distribution and reactivity of inhaled 14C-labeled toluene diisocyanate (TDI) in rats

Inhalation exposure to toluene diisocyanate (TDI) can result in a variety of airway diseases. Concern has been expressed that a putative carcinogenic potential of TDI exists as a result of the formation of toluenediamine (TDA) by hydrolysis of the isocyanate in the body. Results from long-term bioassays (TDI inhalation versus gavage in rats and mice) are contradictory and discrepancies do exist concerning the interpretation of adverse effects. This study was performed to analyze the distribution and reactivity of radioactively-labeled TDI using vapor exposure in a rat model system. Rats were exposed to 14C-TDI vapors at concentrations ranging from 0.026 to 0.821 ppm for 4 h. All tissues examined showed detectable quantities of radioactivity, with the airways, gastrointestinal system and blood having the highest levels which increased with exposure concentration. The concentration of radioactivity in the bloodstream after exposure was linear with respect to dose. The majority (74-87%) of the label associated with the blood was recovered in the plasma, and of this, 97-100% of the 14C existed in the form of biomolecular conjugates. Analysis of stomach contents shows that the majority of the label is also associated with high (> 10 kDa) molecular weight species. While a larger percentage (28%) of the label is found in the low molecular weight fraction relative to blood, this low molecular weight labeled material represents at least eight different components. Thus, over the vapor exposure concentrations and time tested, it appears that conjugation is the predominant reaction and that free TDA is not a primary in vivo reaction product under the conditions tested.

Route-dependent comparative metabolism of [14C]toluene 2,4-diisocyanate and [14C]toluene 2,4-diamine in Fischer 344 rats

This study was initiated to evaluate the pharmacokinetics/metabolism of 14C-labeled toluene 2,4-diisocyanate (2,4-[14C]-TDI) following oral and inhalation exposure in the rat. For comparison, the pharmacokinetics/metabolism of toluene 2,4-diamine (2,4-[14C]TDA) was also evaluated. Groups of 3 or 4 male rats were given either a single 60 mg/kg oral dose of 2,4-[14C]-TDI or were exposed to 2,4-[14C]TDI vapors at a target concentration of 2 ppm for a 4-hr period. Additional groups of male rats were given single 3 or 60 mg/kg oral doses or a single 3 mg/kg intravenous (iv) dose of 2,4-[14C]TDA. All rats were euthanized by 48 hr postexposure. Following oral administration of 2,4-[14C]TDI, > 93% of the administered radioactivity was recovered in the urine, feces, cage wash, and tissues. Approximately 8% of the oral dose was excreted in the urine while 81% was eliminated in the feces. It is estimated that during inhalation exposure, essentially all of the inhaled 2,4-[14C]TDI was retained by the animal. At 48 hr post-inhalation exposure approximately 15 and 47% of the recovered radioactivity was in the urine and feces, respectively. Following oral or inhalation exposure to 2,4-[14C]TDI, no radioactivity was eliminated as either expired 14C organics or 14CO2. Comparison of the 2,4-[14C]TDI inhalation group with the oral 2,4-[14C]TDI and 2,4-[14C]TDA treatment groups indicated that a larger percentage of the inhaled radioactivity was in the tissues/carcass (34% vs 2-4%) and the excretion of radioactivity into the urine was slower (t1/2 = 20 hr vs 5-8 hr) following TDI inhalation. The total amount of free+acetylated TDA metabolites detected in the urine specimens (0-12 hr) following oral and inhalation exposure to 2,4-[14C]TDI was 15 and 0.26 microgram eq 2,4-TDA, respectively. No free 2,4-TDA was detected in the urine specimen from the inhalation group. In comparison, 638 and 20 micrograms eq 2,4-TDA was detected in the urine specimen after oral administration of 60 and 3 mg/kg 2,4-[14C]TDA, respectively. Following 2,4-[14C]TDI inhalation and oral exposure approximately 90 and 65% of the quantitated urinary metabolites existed as acid-labile conjugates, respectively. In contrast, only 16-39% of the quantitated urinary metabolites existed as acid-labile conjugates following oral administration of 2,4-[14C]TDA. Inhalation exposure to 2,4-TDI primarily results in the formation of acid-labile conjugates with little or no 2,4-TDA being formed.(ABSTRACT TRUNCATED AT 400 WORDS)

Biological monitoring of occupational exposure to toluene diisocyanate

The study validated the use of urinary toluene diamine (TDA) in postshift samples as an indicator of preceding 8-h exposure to toluene diisocyanate (TDI). Nine workers exposed in TDI-based polyurethane foam production were studied. Their exposure levels varied in 8-h time-averaged samples from 9.5 to 94 micrograms/m3. The urinary TDA concentrations varied from 6.5 to 31.7 micrograms/g creatinine and they were linearly related to the atmospheric TDI levels. Approximately 20% of TDI is metabolized to diamines but their specificity is remarkable to the extent that by analysis for the 2,4- and 2,6-diamino isomers an idea of the percutaneous absorption may be had.

Biological monitoring of isocyanates and related amines. IV. 2,4- and 2,6-toluenediamine in hydrolysed plasma and urine after test-chamber exposure of humans to 2,4- and 2,6-toluene diisocyanate

Two men were exposed to toluene diisocyanate (TDI) atmospheres at three different air concentrations (ca. 25, 50 and 70 micrograms/m3). The TDI atmospheres were generated by a gas-phase permeation method, and the exposures were performed in an 8-m3 stainless-steel test chamber. The effective exposure period was 4 h. The isomeric composition of the air in the test chamber was 30% 2,4-TDI and 70% 2,6-TDI. The concentration of TDI in air of the test chamber was determined by an HPLC method using the 9-(N-methyl-amino-methyl)-anthracene reagent and by a continuous-monitoring filter-tape instrument. Following the hydrolysis of plasma and urine, the related amines, 2,4-toluenediamine (2,4-TDA) and 2,6-toluenediamine (2,6-TDA), were determined as pentafluoropropionic anhydride (PFPA) derivatives by capillary gas chromatography using selected ion monitoring (SIM) in the electron-impact mode. In plasma, 2,4- and 2,6-TDA showed a rapid-phase elimination half-time of ca. 2-5 h, and that for the slow phase was greater than 6 days. A connection was observed between concentrations of 2,4- and 2,6-TDI in air and the levels of 2,4- and 2,6-TDA in plasma. The cumulated amount of 2,4-TDA excreted in the urine over 24 h was ca. 15%-19% of the estimated inhaled dose of 2,4-TDI, and that of 2,6-TDA was ca. 17%-23% of the inhaled dose of 2,6-TDI. A connection was found between the cumulated (24-h) urinary excretion of 2,4- and 2,6-TDA and the air concentration of 2,4- and 2,6-TDI in the test chamber.(ABSTRACT TRUNCATED AT 250 WORDS)

Detoxification of an aliphatic amine by N-acetylation: experimental and clinical studies

Incubation of serum serpin (alpha-1-antitrypsin) with 5 mM 1,6-diaminohexane causes significant loss of heterozygotic inhibitor activity. While serpin genes have several alleles, the enzyme complex that acetylates the amine to render it suitable for excretion has primarily two phenotype populations, i.e. slow and fast N-acetylators. This study shows that diacetyl-1,6-diaminohexane does not cause in vitro loss of serpin activity, and that all regional cases (eleven in all) referred to us during one year with a diagnosis of occupational organic diisocyanate asthma were slow acetylators except one who presented a marginally fast reaction type.

Biological monitoring of isocyanates and related amines. III. Test chamber exposure of humans to toluene diisocyanate

Five men were exposed to toluene diisocyanate (TDI) atmospheres for 7.5 h. The TDI atmospheres were generated by a gas-phase permeation method, and the exposures were performed in an 8-m3 stainless-steel test chamber. The mean air concentration of TDI was ca. 40 micrograms/m3, which corresponds to the threshold limit value (TLV) of Sweden. The inhaled doses of 2,4- and 2,6-TDI were ca. 120 micrograms. TDI in the test chamber air was determined by an HPLC method using the 9-(N-methylaminomethyl)-anthracene reagent and by a continuous-monitoring filter-tape instrument. After hydrolysis of plasma and urine, the related amines, 2,4- and 2,6-toluenediamine 2,4-, and 2,6-TDA), were determined as pentafluoropropionic anhydride (PFPA) derivatives by capillary gas-chromatography using selected ion monitoring (SIM) in the electron-impact mode. The urinary elimination of the TDAs showed a possible biphasic pattern, with rapid first phases for 2,4-TDA (mean t1/2 for the concentration in urine, 1.9 h) and for 2,6-TDA (mean t1/2 for the concentration in urine, 1.6 h). The cumulative amount of 2,4-TDA excreted in urine within 28 h ranged from 8% to 14% of the estimated dose of 2,4-TDI, and the cumulative amount of 2,6-TDA in urine ranged from 14% to 18% of the 2,6-TDI dose. The average urinary level of 2,4-TDA was 5 micrograms/l in the 6 to 8-h sample (range 2.8-9.6 micrograms/l), and the corresponding value for 2,6-TDA was 8.6 micrograms/l (range, 5.6-16.6 micrograms/l). Biological monitoring of exposure to 2,4- and 2,6-TDI by analysis of 2,4- and 2,6-TDA in urine is feasible.

Uptake and distribution of 14C during and following inhalation exposure to radioactive toluene diisocyanate

Inhalation of toluene diisocyanate (TDI) results in toxic responses ranging from pulmonary irritation to immunological sensitization. The use of radioactively labeled isocyanate has made it possible to follow the initial uptake of the compound into the bloodstream independent of the final fate of the isocyanate. This study shows that the rate of uptake into the blood is linear during exposure to concentrations ranging from 0.00005 to 0.146 ppm and that the uptake continues to increase slightly postexposure. It also demonstrates that the radioactivity clears from the bloodstream to a level corresponding to approximately a 100 nM concentration of tolyl group after 72 hr and persists at a nanomolar level even 2 weeks following the exposure. This is similar to the response previously reported by this group for radioactively labeled methyl isocyanate. The initial rate of 14C uptake is also a linear function of the concentration of TDI when expressed either as concentration (ppm) or as concentration multiplied by duration of exposure (ppm.hr). This is discussed in comparison with the toxic responses as a function of both ppm and ppm.hr. Finally, the inclusion of the data on methyl isocyanate indicates that the uptake into arterial blood is a function of exposure concentration, independent of isocyanate structure.