February 15, 2012

TOXICOLOGY AND 

MEDICAL 

Cynthia Graham, PhD

Huntsman
2

Objectives 

Toxicology 

• To discuss the importance of physical-chemical 

properties

• To provide an overview of new toxicology data for 

diisocyanates,

• To provide additional sources for information. 

Medical 

• To explain how exposure relates to development of 

symptoms 

• To explain medical surveillance recommendations. 
TOXICOLOGY
4

Major Factors Affecting 

Diisocyanate Toxicity Testing 

Physical and Chemical Properties

Hydrophobic

• Promotes a non-homogeneous reaction favoring formation of 

polyurea

Electrophilic

• Reactivity prefers nucleophiles containing –NH and –SH over –OH 

groups

• Thus reactions with endogenous macromolecules preferred over 

hydrolysis

Vapor & Aerosol

• Chemical reactivity of diisocyanates results in principally nasals 

lesions with vapor and pulmonary lesions with aerosols in 

experimental animals
5

Particle Size is Important 

Aerodynamic Diameter [μm]

0 20 40 60 80 100 120 140 160 180 200

0.2

0.4

0.6

0.8

1.0

1.2

• Respirable MDI particles are difficult to generate 

• The black curve is a laboratory generated atmosphere 

used in a LC50 study. The red curve reflects workplace 

spray particles
6

Major Factors Affecting 

Diisocyanate Toxicity Testing 

Consideration of these factors is critical for

• Designing toxicology studies

• Interpreting toxicology data

• Using the resulting data for Risk Assessments
7

Diisocyanates Have a Substantial 

Toxicity Database 

• Acute Oral, Dermal and Inhalation Toxicity

• Irritation 

• Eye, skin, sensory (RD50)

• Sensitization

• Skin and Respiratory

• Repeated Dose Toxicity

• Reproductive Toxicity

• Developmental Toxicity

• Mutagenicity 

• Carcinogenicity

• Absorption and Metabolism

(See Appendix for more details)
8

New Information 

• Threshold of Respiratory Sensitization

• Biochemistry and Biomonitoring

• TDI Carcinogenicity
9

Threshold of Respiratory 

Sensitization 

• BN rat model (MDI)

• 5-day inhalation (induction) exposure (various Conc. X Time)

• four 30-min inhalation challenges to 40 mg MDI/m3 on target days 20, 

25, 50, and 65.

• Exposure aerosols size (MMAD 1.5-1.9~m, GSD 1.6-1.9).

• Endpoints

• BAL-neutrophils and

• physiological measurements - changes in breathing patterns 

delayed in onset

• 2

nd protocol had 4th challenge at a dose escalation

• Elicitation threshold of 5 mg MDI-aerosol/m3 at a 30 min 

challenge duration

• Short high-level exposure patterns appear to bear a higher 

sensitizing potency than equal „Conc. x Time‟ products at 

longer exposure periods

Reference: Pauluhn J and Poole A. 2011 
10

Biochemistry & Biomonitoring

Mechanism of transfer of TDI from air to serum albumin

• Wisnewski, AV, JM Hettick and PD Siegel. Toluene diisocyanate 

reactivity with glutathione across a vapor/liquid interface and 

subsequent transcarbamoylation of human albumin. Chem. Res. 

Toxicol. (2011) 24: 1686-1693.

TDI-albumin adducts based on TDI-peptide analysis

• Hettick, JM and PD Siegel. Determination of the toluene diisocyanate 

binding sites on human serum albumin by tandem mass spectrometry. 

Anal. Biochem. (2011) 414(2): 232-238.

TDI-albumin adducts based on TDI-amino acid analysis

• Sabbioni, G., Q. Gu and LR Vanimireddy. Determination of isocyanate 

specific albumin-adducts in workers exposed to toluene diisocyanates. 

Biomarkers (2012) [Epub ahead of print]
11

TDI Carcinogenicity

• NTP / IARC cancer classifications - Based on oral (gavage) exposure to 

TDI (80/20)  rodent tumors, except male mice (NTP, 1986).

• Comparable tumor responses seen after oral (feed) exposure to 2,4-

TDA  rodent tumors, except male mice (NTP, 1979)

• Statistical analysis of TDI and TDA tumors reported by NTP 

consistent with 5% of TDI dose being converted to TDA prior to 

and/or post-dosing (Sielken et al., 2012)

• Atypical formation of TDA in NTP TDI study is chemically and biologically 

plausible due to flawed TDI handling (allowed TDI conversion to TDA) 

and exposure protocol (stomach acid)

• Contention that TDA is not formed under typical exposures (in presence of 

macromolecules at neutral pH) is consistent with:

• Inhalation of TDI at MTD (0.15 ppm)  no rodent tumors (Loeser, 1983)

• Inhalation of TDI (2 ppm)  no free TDA in rats (Timchalk et al., 1994)

• Occupational TDI exposures  no human cancers or free TDA in urine/blood 
12

For More Information 

• Pauluhn J and Poole A. 2011. Brown Norway rat asthma model 

of diphenylmethane-4,4'-diisocyanate (MDI): Determination of 

the elicitation threshold concentration of after inhalation 

sensitization. Toxicology. 281:15-24

• Sielken R., 2012. Statistical comparison of carcinogenic effects 

and dose-response relationships in rats and mice for 2,4-

toluenediamine to those ascribed to toluene diisocyanate. Hum. 

Ecol. Risk. Assess. (in press).

• MDI & TDI: Safety, Health and the Environment. A Source Book 

and Practical Guide. Eds. D.C. Allport, D. S. Gilbert and S. M. 

Otterside, Published by John Wiley & Sons, Ltd., 2003. 

• www.polyurethane.org

• Center for the Polyurethanes Industry

• http://dii.americanchemistry.com

• American Chemistry Council Diisocyanates Panel
MEDICAL 
14

Medical - Overview 

• To explain how exposure relates to 

development of symptoms 

• To explain medical surveillance 

recommendations
15

Possible Adverse Health Effects 

Possible Effects on Respiratory System:

• Occupational Asthma 

o Sensitization may occur after a single, extreme overexposure or 

repeated overexposure 

o Symptoms may not appear at initial exposure, but after several 

weeks and a subsequent exposure 

• Upper Respiratory Tract Irritant (MDI, TDI) 

o Irritating effects are generally associated with spills and/or 

process upset conditions

• Hypersensitivity Pneumonitis (HP)

o Low prevalence with diisocyanates (Vandenplas O, et al. 1993)

• Reactive Airways Dysfunction Syndrome (RADS)

o After an acute, single exposure to a high level of an irritant
16

Possible Adverse Health Effects 

Occupational Asthma Prevalence

• Diisocyanates are listed among the most common suspected causal 

agents in population-based occupational surveillance systems.

• “ISO and N-ISO claims declined from the previous period, especially for ISO, perhaps because of effective surveillance 

programs.” 

(Buyantseva L, Tarlo SM, et al. 2011)

• Incidence rates range from 0 to 1.5% per year with a cumulative incidence of 4% after 5 years, according to one study. 

• Increased incidence found in the first 2 years of employment and with certain job activities

• Risk declines with decrease in exposure
17

Prognosis for DiisocyanateSensitized Subjects 

Good outcome and prognosis when:

• Diagnosed early

• Complete removal from further exposure

• Improvement or complete recovery is seen in 50-80% of those

subjects removed from exposure

Prognosis is poor when subjects are not removed from

the exposure setting.

• Symptoms usually persist and can become worse

• Permanent lung damage may occur

• Asthma deaths have been reported
18

Worker Medical Surveillance 

Purpose:

• To establish a baseline prior to diisocyanate exposure.

• To evaluate employees for upper or lower respiratory

irritation or sensitization, and contact dermatitis.

• To ascertain whether any conditions have been caused

by, or will be aggravated by, diisocyanate exposure.

• Check for Non-Specific Bronchial Hyperreactivity (NSBR)

• May be important risk factor for symptom

development, can result in misclassification of 

occupational asthma

• Asthmatics may have increased symptoms and 

clinical findings with diisocyanate exposure. 
19

Worker Medical Surveillance 

Suggested Frequency

• Pre-placement screening

• Annual periodic examinations

• Return to work examinations

• Absence due to cardiac or respiratory illness

• Following accidental exposure to diisocyanates

• When diisocyanate workers experience recurrent

respiratory symptoms (which may be work related)
20

Diagnosis of Occupational Asthma 

Important to diagnose early and accurately to prevent chronic

disability

Diagnosis can usually be made by use of the following:

• History and physical,

• Measurement of serial Peak Expiratory Flow Rate (PEFR), 

with and without exposure,

• Measurement of serial, shift-related spirometry, preferably

performed concurrently with PEFR monitoring, and

• Methacholine challenge.

• Specific Bronchial Inhalation Challenge 

– Gold Standard

– Not widely available
21

DII-NIOSH TDI Research Study 

• Joint research effort between ACC DII Panel and NIOSH, also have 

union representation 

• Study Focus: Potential risk of asthma associated with occupational 

exposure to TDI at US manufacturing plants 

• All eligible TDI production workers were asked to participate 

• Study addresses three discrete areas: 

• Medical monitoring of workers identified as working with 

diisocyanates, 

• Exposure assessment to characterize jobs and specific tasks with 

regard to their risk for exposure to TDI, and 

• Medical assessment of asthma
22

Current Status 

• Two plants remain in the study including Bayer Baytown and BASF 

Geismar

• A redesign of the study was implemented in Q2 2011 to utilize 

web-based technology to improve data collection

• Data collection will continue until June 2012 for a five-year 

research study 

• Data analysis plan in development 

• Study could provide additional information for medical diagnosis 

guidelines

• Target is to publish findings in an appropriate peer-reviewed 

journal 
23

ACOEM* Respiratory Practices 

Guidelines 

• Previous guidelines directed toward Injury 

care

• Update to address diagnosis of airway 

disorders (asthma) and parenchymal 

(pneumoconioses) 

• Objectives 

– Improve Consistency

– Reduce Variability

– Follow Hierarchy of Evidence

– Improve Effectiveness

*American College of Occupational and Environmental Medicine
24

Dimension of Evidence Based 

Guidelines in Occupational Asthma

• Diagnosis and testing

• Work Relatedness

• Treatment

• Disability Management and Return to Work

– Intended to ensure that to the greatest 

extent possible, medical decisions, are based 

on and consistent with good evidence of 

effectiveness and benefit.
25

Resources 

• Vandenplas O, et al. 1993. Occupational asthma and extrinsic 

alveolitis due to isocyanates: current status and perspectives.

B J Ind. Med. 50:213-228

• Buyantseva L, Tarlo SM, et al. 2011. Reduction in Diisocyanate and 

Non-Diisocyanate Sensitizer-Induced Occupational Asthma in Ontario. 

JOEM.

• Bernstein, D.I. 1998. A Guide for the Primary Care Physician in 

Evaluating Diisocyanate 

• Bernstein, D.I. & Jolly, A. 1999. Current diagnostic methods for 

diisocyanate induced occupational asthma. Am J Ind Med. 36:459-468. 

• Klees, J.E. & Ott, M.G. 1999. Diisocyanates in Polyurethane Plastics 

Applications. Occup Med. 14 (4): 1-18. 

• National Institute for Occupational Safety and Health (NIOSH). 1996. 

NIOSH Alert: Request for assistance in preventing asthma and death 

from diisocyanate exposure. DHHS (NIOSH) Publication No. 96-111. 
APPENDIX 
TOXICOLOGY 
28

Acute Toxicity 

Test 

substance

Oral LD50

(mg/kg bw)

Dermal LD50

(mg/kg bw)

Inhalation 

LC50 (mg/m3)

Inhalation 

RD50 (mg/m3)

rats rabbits Rats (4 hr) mice

4,4’-MDI 2240 (1 hr)

PMDI >15,800 >7900 490 32 (4 hrs)

TDI 80:20 4130 >10,000 101 2.8 (4 hrs)

2,4-TDI 5800 69 1.4 (3 hrs)

2,6-TDI 4130 1.9 (3 hrs)

1) The lower the number, the higher the toxicity

2) Diisocyanates more toxic via inhalation; 

3) Differential toxicity of monomer vs. polyisocyanate
29

Irritation and Sensitization 

Test Substance Irritation 

(eye or skin)

Sensitization

(Skin & respiratory)

MDI mild to moderate positive

PMDI mild to moderate positive

TDI Moderate to severe positive
30

Repeated Inhalation Exposures 

Portal-of-Entry Toxicity 

MDI PMDI

Exposure 

scenario

17 hrs/day

5days/week

3 months

6 hrs/day

5days/week

1-2 years

Levels

(mg/m3)

0, 0.3, 1.0, 3.0 0, 0.2, 1.0, 6.0

Species rats rats

Histo-pathology Nasal and pulmonary 

tissue lesions 

(12-20 month data 

unavailable)

Nasal and pulmonary 

tissue lesions

NOAEL 0.3 mg/m3 0.2 mg/m3

NOAEL : No observed adverse effect level
31

Reproductive Toxicity 

• No damage to the reproductive organs was found with 

nearly lifetime inhalation exposure of rats to TDI 

• 2-generation inhalation study with 80/20 TDI

– No TDI-related effects were seen in any reproductive 

parameters (tested up to 300 ppb)

– MDI is expected to have similar effects as TDI
32

Developmental Toxicity 

• Studies designed to assess toxicity to the developing 

fetus including teratogenesis (malformations)

• Developmental toxicity studies (inhalation exposures) 

have been conducted with MDI, PMDI and TDI 

– No indication of toxicity to the developing fetus or to the newborn, in the absence of maternal toxicity

– No evidence of teratology

• Diisocyanates do not show a potential for 

developmental toxicity or teratogenicity
33

Carcinogenicity Studies 

TDI TDI MDI PMDI

Oral, in corn oil Inhalation 

vapor

Inhalation 

particulates

Inhalation 

particulates

rats & mice rats & mice rats (female) rats

(mg/kg bw)

0, 60, 120 (f r/m)†

0, 30, 60 (mr)

0, 120-140 (mm)

(mg/m3)

0, 0.4, 1.1

(mg/m3)

0, 0.2, 0.7, 2.0

(mg/m3)

0, 0.2, 1.0, 6.0

5 days/week

2 years

6 hr/day

2 years

17 hrs/day

20 months

6 hr/day

2 years

Increased tumors No tumor 

increase 

over 

controls

Tumors seen at 

high 

exposure 

levels

Tumors seen at 

high 

exposure 

levels

In all cases the Maximum Tolerated Dose (MTD) was achieved or exceeded

†

: f r/m: female rat/mouse; mr: male rat; mm: male mouse
34

Metabolism Study of MDI in Rats 

• Inhalation exposure to 3.67 mg/m3 14C-MDI for 6h

• Radioactivity distributed to all tissues

• Mainly excreted in feces, remainder in urine & bile; none 

via exhalation

• Major metabolic pathway following inhalation exposures

• Bioavailable fraction 

N-Acetylation and excretion via bile and urine

• Non-bioavailable fraction (lung surface, mouth, nares, skin)

Polyurea excreted via feces

• No MDA found in urine, bile or feces 
35

MDI Classification in EU 

• The EU Member States published the 30th ATP, June 1, 2009. 

– Contained revised classification for MDI - Carcinogen Category 3 (limited 

evidence of a carcinogenic effect). 

– MDI remains labeled as Xn harmful; it was not be re-labeled as T toxic. 

• DSD Category 3 becomes Category 2 under the CLP Regulation. 

– This change is not a stricter classification (Suspected of causing cancer by 

inhalation)

• Carcinogenicity studies:

– High concentrations of specially prepared aerosols respirable: having an 

aerodynamic diameter of ≤ 10 μm

– The concentration required to cause tumors in the lungs of the test animals 

was 6mg/m3, which is more than 100-times the MAK-value (0.05mg/m3).

– Only a few of the animals showed the formation of benign (likely from 

recurrent tissue irritation/inflammation)

• Aerosols emerging under practical working conditions are not expected to 

cause an increased risk for lung cancer 

– supported by epidemiological studies. Health surveillance programs involving 

around 12,000 workers in the MDI processing industry did not show any 

increased risk of lung cancer.

ISOPA DOCUMENT
MEDICAL 
37

Possible Adverse Health Effects 

Possible Skin Effects

• Irritant - Irritant contact dermatitis (ICD)

• Sensitizer - Allergic contact dermatitis (ACD)

– Prevalence

• Handful of reports of ACD due to diisocyanates

• ICD is more common than ACD

• Dermal exposure may result in respiratory sensitization

• Animal studies suggestive

• Inconclusive in humans

Possible Eye Effects

• Irritation (MDI, TDI)

– Irritating effects generally associated with spills

and/or process upset conditions
38

Possible Adverse Health Effects 

Possible Effects on Respiratory system:

• Upper Respiratory tract irritant (MDI, TDI) 

– Nose, Throat, and Airways 

– Odor threshold is above TLV (Sense of smell is not protective)

– Irritating effects are generally associated with spills and/or process

upset conditions

• Hypersensitivity Pneumonitis (HP)

• Lung tissue disease which presents as flu-like symptoms, with or without xray changes

• Low prevalence with diisocyanates

– Good prognosis with steroid treatmentunless sensitization develops

• Reactive Airways Dysfunction Syndrome (RADS)

– after an acute, single exposure to a high level of an irritant

– Good prognosis with steroid treatmentunless sensitization develops
39

Possible Adverse Health Effects 

Possible Effects on Respiratory System:

• Occupational Asthma

– Clinical Presentation

• Coughing

• Wheezing

• Tightness of chest

– Symptoms are less severe on week-ends or after a 

vacation 

– Symptoms will not appear at initial exposure, but 

after several weeks and a subsequent exposure
40

Worker Medical Surveillance 

Pre-placement Screening

• Medical Evaluation

• Respiratory and dermal symptom questionnaire

• Medical history

• Respiratory function tests

• Spirometry (FEV1, FVC)

• Peak Expiratory Flow Rate (PEFR)

• Medically categorize and assess on a case-by-case basis
41

Worker Medical Surveillance 

Periodic Examination

• Medical Symptom Questionnaire

• Targeted to skin and respiratory tract symptoms

• Determine any significant findings or change in symptoms

• Inquire as to possible exposure to diisocyanates

• Spirometry

• Compare with previous exams

• Measurements provide a means to monitor any changes in 

airway obstruction.

• Further physician assessment with findings or symptoms

of reversible airways changes.
42

Diagnostic Algorithm –

The Timeline

Diagnosis

SBIC

Methacholine Challenge Test

PEFR away from work/exposure (2-3 Weeks)

PEFR at Work (2-3 Weeks)

Determine Fitness for Duty (2-4 Weeks)

History, PE and Spirometry (Compare to Baseline)

Positive Questionnaire Response or Clinical Encounter
43

Diagnosis of Occupational Asthma

Specific Bronchial Inhalation 

Challenge (SBIC)

• An excellent diagonistic tool, but:

– Potentially dangerous

(if not done properly)

– Not widely available

– Usually not necessary

– Potentially costly

Good History, Physical Exam, Preand Post-Shift Spirometry, PEFR 

are Generally Sufficient
44

Diagnosis of Occupational Asthma

Role of “Diisocyanate-specific Antibody” Tests

• No reliable correlation with clinical disease

• Great variability seen among investigators

– Non-standardized methodology

– Interval from exposure differences

– Non-antibody mediated mechanism

• Does not replace physiologic methods for the 

diagnosis of diisocyanate asthma.
45

Basis for Current ACGIH TLV

Lung Function Decrement

MDI

• Exposures below 5 ppb TWA are without effect on 

FEV1.

• Results are consistent with a lack of effect at < 3 ppb, 

but should be interpreted cautiously.
46

Basis for Current ACGIH TLV 

Lung Function Decrement

TDI

• Exposures below 5 ppb TWA are without effect on FEV1

• Diem Study: Definitive 5 year study on lung effects.

• Reported loss of lung function in “high” vs. “low” nonsmoker exposure group.

• Geismar TDI Respiratory Health Study (1967 - 1997)

• No relationship between asthma and cumulative exposure. 

• No lung function effects were seen after transfer out of the 

TDI unit among work-related asthma cases.
47

Epidemiology Studies 

Several cohort mortality studies in polyurethane

manufacturing

– 40-year cohort study of TDI polyurethane foam manufacturing in 

England and Wales: 

"unable to link isocyanate exposed employment with risks of lung

cancer or with risks of non-malignant diseases of the respiratory

system. Increased SMR for female lung cancer is most likely caused

by factors unrelated to the industry." Sorahan & Nichols. 2002. 

Occ. Environ. Med.

– 37-year cohort study of TDI polyurethane foam manufacturing in 

US: " ...no cancer death category showed a strong relation with

duration of employment. " Schnorr et al. 1996. Occ. Environ. Med.

– 29-year cohort study of TDI & MDI polyurethane foam

manufacturing in Sweden: 

“tentative associations...and excess risk...were not supported. 

Instead non-significant associations...were seen."

 Hagmar et al. 1993. Br. Jrnl Indus. Med.