TOXICOLOGICAL PROFILE FOR
 

4,4’-METHYLENEBIS(2-CHLOROANILINE) MBOCA
 

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
 

Public Health Service
 

Agency for Toxic Substances and Disease Registry
 

May 1994 
MBOCA ii 

DISCLAIMER 

The use of company or product name(s) is for identification only and does not imply endorsement 

by the Agency for Toxic Substances and Disease Registry. 
MBOCA iii 

UPDATE STATEMET 

Toxicological profiles are revised and republished as necessary, but no less than once every three 

years. For information regarding the update status of previously released profiles, contact ATSDR 

at: 

Agency for Toxic Substances and Disease Registry 

Division of Toxicology/Toxicology Information Branch 

1600 Clifton Road NE, E-29 

Atlanta, Georgia 30333 



3 

MBOCA	 vii 

CONTRIBUTORS 

CHEMICAL MANAGER(S)/AUTHOR(S): 

Penny Duerksen-Hughes, Ph.D.
 

ATSDR, Division of Toxicology, Atlanta, GA
 

Vera Brankovan, Ph.D.
 

Clement International Corporation
 

THE PROFILE HAS UNDERGONE THE FOLLOWING ATSDR INTERNAL REVIEWS: 

1.	 Green Border Review. Green Border Review assures the consistency with ATSDR policy. 

2.	 Health Effects Review. The Health Effects Review Committee examines the health effects 

chapter of each profile for consistency and accuracy in interpreting health effects and 

classifying end points. 

Minimal Risk Level Review. The Minimal Risk Level Workgroup considers issues relevant 

to substance-related minimal risk levels (MRLs), reviews the health effects database of each 

profile, and makes recommendations for derivation of MRLs. 

4.	 Quality Assurance Review. The Quality Assurance Branch assures that consistency across 

profiles is maintained, identifies any significant problems in format or content, and establishes 

that Guidance has been followed. 

MBOCA ix 

PEER REVIEW
 

A peer review panel was assembled for MBOCA. The panel consisted of the following members: 

1.	 Dr. W. Emmett Braselton, Jr., Professor of Pharmacology/Toxicology, Michigan State University, 

East Lansing, Michigan. 

2.	 Dr. Arthur Gregory, private consultant, Techto Enterprises, Sterling, Virginia. 

3.	 Dr. Fumio Matsumura, Assistant Director of Toxic Substances Program, Institute of Toxicology 

and Environmental Health, University of California, Davis, California. 

These experts collectively have knowledge of MBOCA’s physical and chemical properties, toxicokinetics, 

key health end points, mechanisms of action, human and animal exposure, and quantification of risk to 

humans. All reviewers were selected in conformity with the conditions for peer review specified in 

Section 104(i)(13) of the Comprehensive Environmental Response, Compensation, and Liability Act, as 

amended. 

Scientists from the Agency for Toxic Substances and Disease Registry (ATSDR) have reviewed the peer 

reviewers’ comments and determined which comments will be included in the profile. A listing of the 

peer reviewers’ comments not incorporated in the profile, with a brief explanation of the rationale for their 

exclusion, exists as part of the administrative record for this compound. A list of databases reviewed and 

a list of unpublished documents cited are also included in the administrative record. 

The citation of the peer review panel should not be understood to imply its approval of the profile’s final 

content. The responsibility for the content of this profile lies with the ATSDR. 









MBOCA 1 

1. PUBLIC HEALTH STATEMENT 

This Statement was prepared to give you information about 4,4’-methylenebis(2­

chloroaniline) (MBOCA) and to emphasize the human health effects that may result from 

exposure to it. The Environmental Protection Agency (EPA) has identified 1,350 hazardous 

waste sites as the most serious in the nation. These sites comprise the “National Priorities 

List” (NPL): Those sites which are targeted for long-term federal cleanup activities. 

MBOCA has been found in at least 4 of the sites on the NPL. However, the number of 

NPL sites evaluated for MBOCA is not known. As EPA evaluates more sites, the number 

of sites at which MBOCA is found may increase. This information is important because 

exposure to MBOCA may cause harmful health effects and because these sites are potential 

or actual sources of exposure to MBOCA. 

When a substance is released from a large area, such as an industrial plant, or from a 

container, such as a drum or bottle, it enters the environment. This release does not always 

lead to exposure. You can be exposed to a substance only when you come in contact with 

it. You may be exposed by breathing, eating, or drinking substances containing the 

substance or by skin contact with it. 

If you are exposed to a substance such as MBOCA, many factors will determine whether 

harmful health effects will occur and what the type and severity of those health effects will 

be. These factors include the dose (how much), the duration (how long), the route or 

pathway by which you are exposed (breathing, eating, drinking, or skin contact), the other 

chemicals to which you are exposed, and your individual characteristics, such as age, gender, 

nutritional status, family traits, life-style, and state of health. 

1.1 WHAT IS MBOCA? 

MBOCA is a synthetic chemical used in industry primarily to produce castable polyurethane 

parts. It also has a coating application in chemical reactions to “set” glues, plastics, and 

adhesives. Since plastics have many uses, MBOCA is used very widely. Other names for 

MBOCAinclude 4,4’-methylenebis(2-chloroaniline), bis amine, DACPM, MCA, methylenebis 

ortho chloroaniline, and MOCA. The name MBOCA comes from methylene bis ortho chloro 

aniline. Pure MBOCA is a colorless solid, but MBOCA is usually made and used as yellow, 

tan, or brown pellets. If MBOCA is heated above 205°C it may decompose. MBOCA has 

no odor or taste. Chapter 3 contains more information on the chemical and physical 

properties of MBOCA. Chapter 4 contains more information on its production and use. 

1.2 WHAT HAPPENS TO MBOCA WHEN IT ENTERS THE ENVIRONMENT? 

MBOCA may enter the ENVIRONMENT through disposal of solid waste from manufacturing 

plants that use MBOCA in castable polyurethane processing. MBOCA is not likely to 

evaporate from the soil or water into the air. However, it may enter the air as dust when 

it is made at production plants or during mixing and grinding operations at polyurethane 

plants. It may enter surface waters from the waste streams of these plants. Some of the 
MBOCA 2 

1. PUBLIC HEALTH STATEMENT 

MBOCA may be broken down by sunlight or by microscopic organisms. Chapter 4 contains 

more information on the production, use, and disposal of MBOCA, while Chapter 5 has 

information on the release of MBOCA to the environment. 

1.3 HOW MIGHT I BE EXPOSED TO MBOCA? 

Most exposure to MBOCA occurs in the workplace. If you work with MBOCA, you may 

breathe small particles of it in the air or get it on your skin if you brush against a surface 

covered by MBOCA dust. There are several ways to be exposed to MBOCA outside of the 

workplace. For example, you may be exposed to MBOCA if you live in an area where the 

soil is contaminated with MBOCA. You may also be exposed if you eat foods grown in soils 

that contain MBOCA. However, you are unlikely to drink water contaminated with 

MBOCA because it does not dissolve in water. Chapter 5 contains more information on the 

potential exposure of humans to MBOCA. 

1.4 HOW CAN MBOCA ENTER AND LEAVE MY BODY? 

MBOCA can enter your bloodstream if you breathe it in the air, eat it, or get it on your 

skin. Results of studies in humans and animals show that MBOCA can enter your body very 

quickly through the skin or lungs. Once MBOCA is in your body, most of it leaves your 

body quickly. MBOCA and its breakdown products leave the body through urine and feces. 

Results of studies in humans and animals show that most MBOCA leaves the body within 

a few days of exposure. The small amount of MBOCA that may remain in your body after 

you are exposed is likely to break down or leave your body at a slower rate. Chapter 2 

contains more information on how MBOCA can enter and leave the body. 

1.5 HOW CAN MBOCA AFFECT MY HEALTH? 

Studies of human exposure suggest that the small amounts of MBOCA usually found in the 

air or on surfaces in or near factories do not cause toxic effects. However, it is possible that 

acute exposure to a large amount of MBOCA, such as an industrial accident, may produce 

effects that we do not know very much about. Information on how MBOCA can affect your 

health is very limited, and we do not know if there are any other long-term human health 

effects of exposure to MBOCA. MBOCA is suspected of causing bladder cancer and is 

considered a probable human carcinogen. Information is being gathered to determine 

whether bladder cancer in humans may result from short-, medium-, or long-term exposures 

to MBOCA. We do not know if MBOCA causes birth defects in humans. Chapter 2 

contains more information on the human health effects of MBOCA. 

Studies in animals show that MBOCA can be harmful to the blood cells and livers of dogs 

and rats. MBOCA also causes lung, liver, breast, and bladder cancers. The Department of 

Health and Human Services, the International Agency for Research on Cancer, and EPA 

consider MBOCA to be a probable human carcinogen. 
 

MBOCA 3 

1. PUBLIC HEALTH STATEMENT 

1.6 IS THERE A MEDICAL TEST TO DETERMINE WHETHER I HAVE BEEN

 EXPOSED TO MBOCA? 

Your urine can be tested for MBOCA within a few hours of exposure. This test, however, 

will not detect MBOCA days after exposure has ceased. This test may not be readily 

available in your doctor’s office. Chapters 2 and 6 contain more information on testing for 

MBOCA in humans. 

1.7 WHAT RECOMMENDATIONS HAS THE FEDERAL GOVERNMENT MADE TO

 PROTECT HUMANHEALTH? 

The government has developed regulations and guidelines for handling MBOCA. They are 

designed to protect the public from the potential harmful health effects of this chemical. 

EPA has classified MBOCA as a hazardous waste that must meet specific disposal 

requirements. 

The Occupational Safety and Health Administration (OSHA) regulates MBOCA in the 

workplace. The maximum allowable amount of MBOCA in workroom air, assuming an 8-

hour workday and a 40-hour workweek, is 0.22 milligrams per cubic meter. However, the 

court has suspended such regulations for the present. Chapter 7 contains more information 

on international, national, and state regulations and guidelines for handling MBOCA in air, 

water, and other environments. 

1.8 WHERE CAN I GET MORE INFORMATION? 

If you have any more questions or concerns, please contact your community or state health 

or Environmental quality department or: 

Agency for Toxic Substances and Disease Registry 

Division of Toxicology 

1600 Clifton Road NE, E-29 

Atlanta, Georgia 30333 

(404) 639-6000 

This agency can also provide you with information on the location of occupational and 

Environmental health clinics. These clinics specialize in the identification, evaluation, and 

treatment of illness resulting from exposure to hazardous substances. 

MBOCA 5 

2. HEALTH EFFECTS 

2.1 INTRODUCTION 

The primary purpose of this chapter is to provide public health officials, physicians, toxicologists, and
 

other interested individuals and groups with an overall perspective of the toxicology of 4,4’­

methylene-bis(2-chloroaniline) (MBOCA). It contains descriptions and evaluations of toxicological
 

and epidemiological investigations and provides conclusions, where possible, on the relevance of
 

MBOCA toxicity to public health.
 

A glossary and list of acronyms, abbreviations, and symbols can be found at the end of this profile.
 

MBOCA is an aromatic diamine that is used as a curing agent for polyurethane and epoxy resins.
 

It has some of the general toxicity characteristics of aromatic amines. However, methemoglobinemia
 

and the resulting cyanosis, hallmark symptoms of exposure to aromatic amines, are reported with
 

much less frequency after exposure to MBOCA (Linch et al. 1971).
 

The majority of studies on MBOCA were undertaken to investigate its potential to cause cancer in
 

different animal species because MBOCA was suspected of being a human carcinogen. A large
 

number of studies focused on tumor incidence and did not investigate other toxic effects of MBOCA.
 

Another limitation of the animal studies is the information on acute toxicity. An acute effect of
 

MBOCA in the dog was marked methemoglobinemia after a single oral dose (Barnes 1964).
 

Information on intermediate and chronic exposure, however, indicates that MBOCA is carcinogenic
 

in animals.
 

2.2 DISCUSSION OF HEALTH EFFECTS BY ROUTE OF EXPOSURE 

To help public health professionals and others address the needs of persons living or working near 

hazardous waste sites, the information in this section is organized first by route of exposure ­

inhalation, oral, and dermal; and then by health effect -death, systemic, immunological, neurological, 

reproductive, developmental, genotoxic, and carcinogenic effects. These data are discussed in terms 

of three exposure periods -acute (14 days or less), intermediate (1.5-364 days), and chronic (36.5 days 

or more). 

Levels of significant exposure (LSE) for each route and duration are presented in Table 2-1 and 

illustrated in Figure (2-l). The points in the figure showing no-observable-adverse-effect levels 

(NOAELs) or lowest-observable-adverse-effect levels (LOAELs) reflect the actual doses (levels of 

exposure) used in the studies. LOAELs have been classified into “less serious” or “serious” effects. 

“Serious” effects are those that evoke failure in a biological system and can lead to morbidity or 

mortality (e.g., acute respiratory distress or death). “Less serious” effects are those that are not 

expected to cause significant dysfunction or death, or those whose significance to the organism is not 

entirely clear. ATSDR acknowledges that a considerable amount of judgment may be required in 

establishing whether an end point should be classified as a NOAEL, “less serious” LOAEL, or 

“serious” LOAEL, and that in some cases, there will be insufficient data to decide whether the effect 

is indicative of a significant dysfunction. However, the Agency has established guidelines and policies 

that are used to classify these end points, which can be found in Tables 2-1, 2-2, 2-3, and 2-4. 

ATSDR believes that there is sufficient merit in this approach to warrant an attempt at distinguishing 

between “less serious” and “serious” effects. The distinction between “less serious” and “serious” effects 
MBOCA 6 

2. HEALTH EFFECTS
 

is considered to be important because it helps the users of the profiles to identify levels of exposure 

at which major health effects start to appear. LOAELs or NOAELs should also help in determining 

whether or not the effects vary with dose and/or duration, and place into perspective the possible 

significance of these effects to human health. 

The significance of the exposure levels shown in the LSE tables and figures may differ depending on 

the user’s perspective. Public health officials and others concerned with taking appropriate actions 

to take at hazardous waste sites may want information on levels of exposure associated with more 

subtle effects in humans or animals (LOAELs) or exposure levels below which no adverse effects 

(NOAELs) have been observed. Estimates of levels posing minimal risk to humans (Minimal Risk 

Levels of MRLs) may be of interest to health professionals and citizens alike. 

Levels of exposure associated with carcinogenic effects (Cancer Effect Levels, CELs) of MBOCA 

are reported in Table 2-1 and Figure 2-1. Because cancer effects could occur at lower exposure 

levels, Figure 2-1 also shows a range for the upper bound of estimated excess risks, ranging from a 

risk of 1 in 10,000 to 1 in 10,000,000 (10m-4 to 10-7), as developed by EPA. 

Estimates of exposure levels posing minimal risk to humans (Minimal Risk Levels of MRLs) have 

been made for MBOCA. An MRL is defined as an estimate of daily human exposure to a substance 

that is likely to be without an appreciable risk of adverse effects (noncarcinogenic) over a specified 

duration of exposure. MRLs are derived when reliable and sufficient data exist to identify the target 

organ(s) of effect or the most sensitive health effect(s) for a specific duration within a given route 

of exposure. MRLs are based on noncancerous health effects only and do not consider carcinogenic 

effects. MRLs can be derived for acute, intermediate, and chronic duration exposures for inhalation 

and oral routes. Appropriate methodology does not exist to develop MRLs for dermal exposure. 

Although methods have been established to derive these levels (Barnes and Dourson 1988; EPA 

1989a), uncertainties are associated with these techniques. Furthermore, ATSDR acknowledges 

additional uncertainties inherent in the application of the procedures to derive less than lifetime 

MRLs. As an example, acute inhalation MRLs may not be protective for health effects that are 

delayed in development or are acquired following repeated acute insults, such as hypersensitivity 

reactions, asthma, or chronic bronchitis. As these kinds of health effects data become available and 

methods to assess levels of significant human exposure improve, these MRLs will be revised. 

A User’s Guide has been provided at the end of this profile (see Appendix A) to aid in the 

interpretation of the tables and figures for Levels of Significant Exposure ant the MRLs. 

2.2.1 Inhalation Exposure 

The studies presented in the section on inhalation exposure address occupational or accidental 

exposures. In occupational settings, dermal, inhalation and oral exposures often occur simultaneously. 

Therefore, many of the effects described in this section may be partially due to dermal or oral 

exposures to MBOCA. Exact levels of occupational and accidental exposures are not known. For 

this reason, the results in this section are not presented in table or figure form. 
 

MBOCA 7 

2. HEALTH EFFECTS 

2.2.1.1 Death 

No studies were located regarding death in humans or animals after inhalation exposure to MBOCA. 

A literature search did not reveal any human or animal studies that reported death due to MBOCA 

inhalation. 

2.2.1.2 Systemic Effects 

No studies were located regarding respiratory, cardiovascular, hematological, musculoskeletal, or 

hepatic effects in humans or animals after inhalation exposure to MBOCA. Other systemic effects 

observed following inhalation exposure are discussed below. 

Gastrointestinal Effects. Information on the gastrointestinal effects of MBOCA following 

inhalation exposure is extremely limited. In a case study of accidental occupational exposure, a 

worker complained of feeling ill in the stomach after he was sprayed in the face with molten MBOCA 

(Hosein and Van Roosmalen 1978). Some of the MBOCA entered his mouth. He was wearing 

overalls, gloves, and safety glasses, but no respirator or face shield. He washed his face and eyes 

immediately. no follow-up information was given about his condition. There was no information on 

the dose to which he was exposed. 

No studies were located regarding gastrointestinal effects in animals after inhalation exposure to 

MBOCA. 

Renal Effects. Five hours after a worker was accidentally sprayed in the face with molten MBOCA, 

his urine contained 220 mg/L of protein, indicating damage to the renal tubules (Hosein and Van 

Roosmalen 1978). However, 11 hours after the accident, there was only a trace of protein in the 

urine. Two urine specimens collected within 24 hours after the accident had low specific gravities, 

suggesting that damage to the renal tubules was transitory. The level of exposure was not reported. 

In a retrospective bladder cancer incidence study conducted with 532 workers exposed to MBOCA 

from 1968 to 1979 and 20 workers who were first employed in 1980 and 1981, 385 participated in a 

urine screening test (Ward et al. 1990). Exfoliative cytology revealed that the morning urine samples 

obtained from 21 workers contained atypical cells. no cytology readings were positive for cancer. 

Urine samples obtained from 16 workers were positive for heme (Ward et al. 1990). Almost 90% 

of the exposed workers were males, and the median duration of exposure was greater than 3 months. 

This study gathered information on a relatively large group of workers exposed solely to MBOCA 

(and not to benzidine and P-naphthylamine, which can confound exposures in other occupational 

settings) and because it alerted medical professionals to the limitations of follow-up procedures 

generally used after MBOCA exposure. In the course of screening, one participant who was negative 

for cytology and heme impairment was diagnosed with bladder cancer. Cystoscopy was introduced 

as a part of the follow-up procedure, and two additional low-grade papillary tumors of the bladder 

were detected. Data on MBOCA in urine from workers in companies belonging to the Polyurethane 

Manufacturers Association (PMA) confirmed the importance of biological monitoring (Lowry and 

Clapp 1992). The percentage of urine samples with <25 μg MBOCA/L increased from 77% in 1985 

to 86% in 1990. The percentage of urine samples with >5 μg MBOCA/L decreased from 12% in 

1985 to 8% in 1990. 

No studies were located regarding renal effects in animals after inhalation exposure to MBOCA. 
MBOCA 8 

2. HEALTH EFFECTS
 

Dermal/Ocular Effects. Very limited information is available regarding dermal/ocular effects after 

inhalation exposure to MBOCA. When a worker was accidentally sprayed with molten MBOCA, he 

experienced burning of the face and eyes shortly thereafter (Hosein and Van Roosmalen 1978). The 

worker was wearing gloves and safety glasses but no respirator or face shield, so the exposure may 

have occurred by ingestion or dermal absorption as well. The limitations of this study are: (1) no 

further follow-up information was provided on the worker’s condition; (2) the dose of MBOCA was 

not known; (3) exposure involved mixed routes; and (4) only one exposed individual was described. 

No studies were located regarding dermal/ocular effects in animals after inhalation exposure to 

MBOCA. 

No studies were located regarding the following health effects in humans or animals after inhalation 

exposure to MBOCA: 

2.2.1.3 Immunological Effects 

2.2.1.4 Neurological Effects 

2.2.1.5 Reproductive Effects 

2.2.1.6 Developmental Effects 

2.2.1.7 Genotoxic Effects 

No studies were located regarding genotoxic effects in humans after inhalation exposure to MBOCA. 

The sex-linked recessive lethal (SLRL) test in Drosophiki melunoguster was used to monitor the air 

in the vulcanizing, weighing, calendaring, and molding areas of a rubber plant (Donner et al. 1983). 

Male flies that were exposed in the molding area exhibited a small but significant increase (p<0.05) 

in SLRL genotoxicity. Exposure data were not provided, but high ambient exposures were expected 

to occur in the tested areas. Acute lethality to fruit flies in the molding area was 50%; sterility was 

not reported. Concomitant exposures to other chemicals may also have occurred. 

Other genotoxicity studies are discussed in Section 2.4. 

2.2.1.8 Cancer 

MBOCA is suspected of being a human carcinogen because its chemical structure is similar to a 

known human bladder carcinogen, benzidine, and to that of a potent animal carcinogen, 3,3’­

dichlorobenzidine (Osorio et al. 1990; Ward et al. 1990). A limited number of epidemiological studies were 

found that examined the incidence of cancer in workers exposed to MBOCA. Workers who were 

exposed to MBOCA for a median duration of employment of 3.2 months (between 1968 and 1981) 

were examined for bladder cancer (Ward et al. 1990). Of the 200 workers examined, 3 men were 

diagnosed with bladder tumors by cystoscopy: 1 with a papillary tumor, and 2 with low-grade papillary 

transitional cell tumors. Two of the men were less than 30 years old. The interval between the time 

of first exposure and diagnosis was 11.5 years; the latency period for most bladder carcinogens is 

about 20 years (Ward et al. 1990). Since bladder carcinoma in young men is very uncommon, this 

finding increases the concern that MBOCA may cause bladder tumors in humans. A limitation of 

this study is that there were no controls (there were no data on the incidence of bladder tumors 

diagnosed by cystoscopy in an unexposed population). The study did not provide statistical evidence 

for an association between bladder tumor incidence and MBOCA exposure in workers. The statistical 

significance of three cases of bladder tumors could not be evaluated. There is no information on the 
MBOCA 9 

2. HEALTH EFFECTS
 

daily amount of MBOCA to which workers were exposed, and a possibility exists of coexposure to 

other chemicals such as 4,4’-methylenedianiline, 4-chloro ortho-toluidine, aniline, and otiho-toluidine 

(Hogan 1993; Ward 1993). MBOCA may not be solely responsible for the observed carcinogenic 

effects. 

No studies were located regarding cancer in animals after inhalation exposure to MBOCA. 

2.2.2 Oral Exposure 

Very little information on acute oral toxicity of MBOCA in humans or animals is available. 

Information on the long-term health effects of MBOCA in humans is also limited. However, several 

chronic oral exposure studies in mice (Russfield et al. 1975), rats (Kommineni et al. 1979; Stula et 

al. 1975) and dogs (Stula et al. 1977) clearly demonstrate the carcinogenic potential of MBOCA in 

these species. These studies are discussed in Section 2.2.2.8. 

2.2.2.1 Death 

No studies were located regarding increased mortality in humans from any cause following exposure 

to MBOCA. 

Decreased lifespan has been noted in rats after chronic exposure to MBOCA (Kommineni et al. 

1979). Male Sprague-Dawley rats were fed a standard diet (with 27% protein) containing 0, 12.5, 25, 

or 50 mg/kg/day of MBOCA or a protein-deficient diet (with 8% protein) containing 0, 6.25, 12.5, 

or 25 mg/kg/day of MBOCA for 18 months. Decreased lifespan was observed in the rats fed 25 

mg/kg/day of MBOCA in either the standard or protein-deficient diet. Rats fed the standard diet 

containing the highest concentration of MBOCA, 50 mg/kg/day, also experienced a shortened lifespan. 

Similar decrease in lifespan was observed in Wistar II rats fed an average dose of 54 mg/kg/day of 

MBOCA for 500 days in a low-protein diet (Grundmann and Steinhoff 1970). The first death in 

females occurred on day 200 of treatment and in males on day 390 of treatment; the mean lifespan 

in control females was 535 days and in males 565 days. 

In another study, one of six female beagle dogs died after 3.4 years of oral administration of an 

average dose of 10 mg/kg/day of MBOCA (Stula et al. 1977). However, the report concludes that 

the death was not MBOCA-related, because the dog died from pyelonephritis. The report did not 

discuss any possible connection between MBOCA administration and pyelonephritis. no additional 

deaths were reported for the five remaining dogs that were part of the same 9-year study (Stula et 

al. 1977). 

The LOAEL value for death in rats for chronic exposure is reported in Table 2-1 and Figure 2-l. 

2.2.2.2 Systemic Effects 

No studies were located regarding cardiovascular or musculoskeletal effects in humans or animals 

after oral exposure to MBOCA. The systemic effects observed after oral exposure are discussed 

below. 

The highest NOAEL values and all LOAEL values from each reliable study for systemic effects in 

each species for chronic duration are presented in Table 2-1 and Figure 2-1. 
MBOCA 10
 

2. HEALTH EFFECTS
 

Respiratory Effects. no studies were located regarding respiratory effects in humans after oral 

exposure to MBOCA. 

Lung adenomatosis was found in rats fed 2.5 (low dose) or 50 (high dose) mg/kg/day of MBOCA for 

18 months. Three of 22 rats from the low-dose group and 4 of 19 from the high-dose group 

developed this preneoplastic condition (Russfield et al. 1975). Although this finding was not 

statistically significant, it is important because exposure to MBOCA induces preneoplastic lesions in 

the lungs. 

Gastrointestinal Effects. Extremely limited information is available regarding gastrointestinal 

effects of MBOCA after oral exposure. In a case study of an accidental occupational exposure, a 

worker complained of feeling ill in the stomach after his face was sprayed with molten MBOCA that 

also entered his mouth (Hosein and Van Roosmalen 1978). He wore overalls, gloves, and safety 

glasses but no respirator or face shield. He washed his face and eyes immediately after the exposure. 

no further information was given about his condition. As with other occupational exposure studies, 

there was no information on the dose to which he was exposed. Another limitation of this study is 

the possibility that some of the MBOCA was inhaled or dermally absorbed. 

No studies were located regarding gastrointestinal effects in animals following oral exposure to 

MBOCA. 

Hematological Effects. No studies were located regarding hematological effects in humans after 

oral exposure to MBOCA. 

No changes in hemoglobin, hematocrit, erythrocyte count, or mononuclear leukocyte count were 

noted in female beagle,dogs after 9 years of exposure to MBOCA. Dogs were fed MBOCA at a 

concentration of 10 mg/kg/day, 3 days/week, for the first 6 weeks of the study and then an average 

of 10 mg/kg/day, 5 days/week, for the remaining 9 years (Stula et al. 1977). The analyses were 

performed only twice a year, so the reported observations may not be meaningful. 

Hepatic Effects. No studies were located regarding hepatic effects in humans after oral exposure 

to MBOCA. 

While no information is available on acute or intermediate exposure, evidence of adverse hepatic 

effects was seen in rats and dogs after chronic exposure to MBOCA. Several adaptive changes 

occurred in the livers of rats fed 50 mg/kg/day of MBOCA for 2 years. These changes included 

hepatomegaly, fatty change, necrosis, fibrosis, and bile duct proliferation (Stula et al. 1975). Similar 

changes were seen in dogs fed 10 mg/kg/day of MBOCA 3 days/week for the first 6 weeks and then 

an average of 10 mg/kg/day, 5 days/week, for 9 years (Stula et al. 1977). Histopathology revealed 

nodular hepatic hyperplasia and disruption of liver architecture in three of six MBOCA-treated dogs 

but not in controls. Another indication of liver damage was a statistically significant increase in serum 

glutamic-pyruvic transaminase (SGPT) in MBOCA-treated dogs. The highest levels of SGPT 

occurred during the first 2 years and after 7.5-8 years of treatment (Stula et al. 1977). 

Based on the occurrence of hepatic effects in dogs exposed to MBOCA, a chronic-duration MRL of 

0.003 mg/kg/day has been calculated from the LOAEL of 10 mg/kg/day (Stula et al. 1977) as 

described in the footnote on Table 2-1. 

Renal Effects. There is very limited information regarding renal effects in humans after oral 
MBOCA 11
 

2. HEALTH EFFECTS
 

exposure to MBOCA. Five hours after an acute exposure to molten MBOCA, in which MBOCA 

was accidentally sprayed over the worker’s face and some entered his mouth, a urine sample from the 

exposed worker contained 220 mg/L of protein indicating an immediate, transient effect on tubular 

reabsorption of low molecular weight proteins (Hosein and Van Roosmalen 1978). However, 11 

hours after the accident, there was only a trace of protein in the urine of this worker. The urine 

specimens collected in the course of 24 hours after the accident had low specific gravity, indicating 

possible transient damage to the renal tubules and an attendant inability to concentrate urine. 

Dermal/Ocular Effects. There is very little information on dermal/ocular effects after oral exposure 

to MBOCA. In one occupational exposure study, a worker was accidentally sprayed with molten 

MBOCA, and some of the compound entered his mouth. The worker complained of burning face 

and eyes shortly after exposure (Hosein and Van Roosmalen 1978). At the time of the accident the 

worker was wearing gloves and safety glasses, but he had no respirator or face shield. It is therefore 

likely that exposure also occurred by inhalation and dermal absorption. This study is limited because 

only one exposed individual was described, and no further information was given regarding the 

worker’s condition, the dose of MBOCA, or the precise exposure route. 

No studies were located regarding dermal/ocular effects in animals after exposure to MBOCA. 

Other Systemic Effects. No studies were located regarding other systemic effects in humans after 

oral exposure to MBOCA. 

In rats fed 25 or 50 mg/kg/day of MBOCA-hydrochloride for 18 months, the average body weight was 

50 g and 100 g lower, respectively, than the body weight of controls at the end of the treatment 

period. The study does not provide the body weights for experimental animals at either dose level. 

During the first 20-25 weeks of the experiment, however, there was no difference in food 

consumption between MBOCA-treated animals and control animals (Russfield et al. 1975). The 

major limitation of this study is that data on weight changes are incomplete, which makes the 

interpretation difficult. 

2.2.2.3 Immunological Effects 

No studies were located regarding immunological effects in humans or animals after oral exposure 

to MBOCA. 

2.2.2.4 neurological Effects 

No studies were located regarding neurological effects in humans after oral exposure to MBOCA. 

Cystic hyperplasia of the pars intermedia of the anterior pituitary gland was found in one of five 

female beagle dogs after 8.3 years of treatment with an average dose of 10 mg/kg/day of MBOCA 

(Stula et .al. 1977). This change was not present in other treated dogs or in controls and was not 

considered to be treatment related. The dog also had a papillary transitional cell carcinoma of the 

urinary bladder. The limitations of this study are the lack of correlation between pituitary hyperplasia 

and transitional cell bladder carcinoma and the small number of animals used. 
 

MBOCA 12
 

2. HEALTH EFFECTS 

2.2.2.5 Reproductive Effects 

No studies were located regarding reproductive effects in humans or animals after oral exposure to 

MBOCA. 

2.2.2.6 Developmental Effects 

No studies were located regarding developmental effects in humans or animals after oral exposure 

to MBOCA. 

2.2.2.7 Genotoxic Effects 

No studies were located regarding genotoxic effects in humans after oral exposure to MBOCA. 

D. melanogaster larvae, heterozygous for visible wing mutations, were fed a medium made with a 

5-millimolar aqueous solution of MBOCA for 48 hours (Kugler-Steigmeier et al. 1989) to determine 

whether MBOCA exposure could induce recombinations and somatic mutations in fruit flies. The 

resulting adults exhibited a small but statistically significant increase in small single wing spots. Higher 

concentrations could not be tested because of MBOCA’s extremely limited solubility. Because the 

number of large single spots was not increased, the authors concluded that the somatic mutations 

occurred late in development. Similarly, the authors concluded, because of the absence of induced 

twin spots, that MBOCA did not exhibit strong recombinogenic activity. In an SLRL test, adult 

D. melanogaster were fed diets containing MBOCA at a concentration of 3.75 or 7.5millimoles for 

3 days (Vogel et al. 1981). A statistically significant increase in SLRL test values was observed at the 

7.5-millimolar concentration in one of two tests. The experiment was incomplete because mating was 

attempted only once after exposure; therefore, germ cells were sampled at only one stage of 

development. The method of feeding makes concomitant dermal exposure possible in both 

experiments. However, MBOCA is expected to be too non-polar to penetrate through the larval 

integument. 

Radioactive deoxyribonucleic acid (DNA) adducts were identified in rats administered 75 mg/kg of 

MBOCA labeled with 14C at the methylene carbon by gavage (Cheever et al. 1990). The highest 

level of radioactive adducts was found in the liver (49.11 μmol/mg DNA at 24 hours). Covalent 

binding to bladder and lymphocyte DNA was also observed (about 7 and 0.9 pmol/mg DNA, 

respectively, at 24 hours). In a separate experiment, in which rats were exposed to 1.4-30 mg/kg 

[ 14C-methylene]-MBOCA by gavage. Significant quantities of DNA adducts were found in the liver 

and lung, marginal amounts were found in the kidney, and no adducts were detected in the bladder 

(Kugler-Steigmeier et al. 1989). Enzymatic hydrolysis of the DNA showed that two DNA adducts 

were generated in the liver and two different adducts were found in the lung. Kugler-Steigmeier et 

al. (1989) did not observe significant binding to kidney or bladder DNA because the quantity of DNA 

isolated from these tissues was too small to measure the amount of covalently bound MBOCA to 

DNA in these tissues. The research results suggest that oral exposures to MBOCA induce vascular 

and liver neoplasms in mice (Russfield et al. 1975) lung and liver tumors in rats (Kommineni et al. 

1979; Russfield et al. 1975; Stula et al. 1975), and bladder tumors in dogs (Stula et al. 1977) as 

discussed in Section 2.2.2.8. 

Other genotoxicity studies are discussed in Section 2.4. 
MBOCA 13
 

2. HEALTH EFFECTS 

2.2.2.8 Cancer 

MBOCA is suspected of being a human carcinogen because its chemical structure is similar to that 

of a known human bladder carcinogen, benzidine, and to that of a potent animal carcinogen, 

3,3’-dichloro-benzidine (Osorio et al. 1990). 

One epidemiological study examined the incidence of cancer in workers exposed to MBOCA. 

Workers who were occupationally exposed to MBOCA for a median employment period of 

3.2 months (between 1968 and 1981) were examined for bladder tumors (Ward et al. 1990). 

Although the route of exposure was not specified in the report, the most likely exposure pathways 

were inhalation and dermal. The oral route cannot be excluded, however, since some of the inhaled 

dust to the lungs could be subsequently swallowed. Low-grade papillary transitional cell tumor of the 

urinary bladder was diagnosed by cystoscopy in 2 out of 200 examined workers, and 1 was diagnosed 

with a full-blown papillary bladder tumor. Two of the men were less than 30 years old. The interval 

between the time of first exposure and the initiation of the study averaged 11.5 years, while the 

latency period for most bladder carcinogens is about 20 years (Ward et al. 1990). Since bladder 

carcinoma in young men is very uncommon, this finding increases the concern that MBOCA has a 

potential for causing bladder cancer in humans. A limitation of this study is that there were no 

controls (there are no data on the incidence of bladder tumors diagnosed by cystoscopy in an 

asymptomatic nonexposed population). There was also no evidence for statistical associations 

regarding bladder tumor incidence in exposed workers. There is also no information on the daily 

dose of MBOCA to which the workers were exposed or about the route of exposure. Further 

investigations of this occupational exposure revealed the possibility of coexposure to other chemicals 

such as 4,4’-methylenedianiline, 4-chloro ortho-toluidine, aniline, and ortho-toluidine (Hogan 1993; 

Ward 1993). The dose and duration of exposure to these chemicals is not known. It is therefore 

difficult to estimate the exact contribution of MBOCA to the observed carcinogenic effects in the 

occupationally exposed workers. 

No studies were located on cancer in animals after acute or intermediate oral exposure to MBOCA. 

Several studies in rats, mice, and dogs reported finding a carcinogenic response after chronic exposure 

to MBOCA. Lungs, liver, breast, and urinary bladder were the main target organs for cancer in these 

species. 

A dose-dependent increase in lung tumors was observed in Sprague-Dawley rats fed 12.5, 25, or 

50 mg/kg/day of MBOCA for 18 months; the incidence of lung tumors was 23%, 37%, and 70%, 

respectively (Kommineni et al. 1979). A similar observation (presence of lung adenocarcinomas) was 

made in Charles River rats fed 50 mg/kg/day of MBOCA for 2 years (Stula et al. 1975). In another 

study, male Charles River CD-1 rats were fed 25 or 50 mg/kg/day of MBOCA for 18 months. The 

authors reported finding lung adenocarcinoma in 1/22 and 1/19 animals, respectively (Russfield et al. 

1975) although this finding was not statistically significant. In addition, 3 of 22 and 4 of 19 rats 

receiving 25 or 50 mg/kg/day of MBOCA, respectively, developed adenomatosis, which is a 

preneoplastic lesion (Russfield et al. 1975). A limitation of this study is the small number of animals 

on which the tumor incidence was based. All these studies were done with animals fed standardprotein 

diets. In contrast, the incidence of lung tumors in rats was lower if animals were fed 

MBOCA in a protein-deficient diet. In rats fed 6.25, 12, or 25 mg/kg/day of MBOCA in a lowprotein 

diet for 18 months, the incidences of lung tumors were 6%, 15%, and 26%, respectively, while 

no tumors were found in control animals (Kommineni et al 1979). These numbers are less than half 

of the incidences reported for comparable doses of MBOCA given to rats fed a standard diet. Similar 

observations were made in rats fed a higher dose of MBOCA (50 mg/kg/day for 2 years); the 
MBOCA 14
 

2. HEALTH EFFECTS
 

incidence of lung tumors in rats fed a protein-deficient diet was roughly one-half of that observed in 

rats fed a standard-protein diet (Stula et al. 1975). In Wistar II rats fed an average of 54 mg/kg/day 

of MBOCA in a low-protein diet for 500 days, 32% of males and 12% of females developed lung 

tumors (Grundmann and Steinhoff 1970). These results indicate that, in general, rats given MBOCA 

in a low-protein diet, have a decreased incidence of lung adenocarcinomas when compared to rats 

given MBOCA in a standard-protein diet. Some exceptions to this generalization occur. Species, 

strain, and gender may also play a role. 

MBOCA also induces liver tumors in rats. An increase in the incidence of hepatomas was found in 

Charles River CD rats fed 25 or 50 mg/kg/day of MBOCA in a standard-protein diet for 18 months; 

the incidences were 5% and 21%, respectively (not statistically significant) (Russfield et al. 1975) 

compared to 4% and 36% found in Sprague-Dawley rats fed the same diet and the same amount of 

MBOCA (Kommineni et al. 1979). Similar findings were made in random-bred female albino mice 

(derived from HaM/ICR mice in 1959) fed 130 or 260 mg/kg/day of MBOCA for 18 months and then 

observed for an additional 6 months while on a control diet. They had a significantly increased 

incidence of hepatomas, 43% in the 130-mg/kg/day group and 50% in the 260-mg/kg/day group 

(Russfield et al. 1975). The incidence of hepatomas in treated random-bred male albino mice 

(derived from HaM/ICR mice in 1959) was not significantly different from that in controls. These 

results indicate that in mice there is a gender difference regarding MBOCA-induced hepatomas; 

female mice are affected, and male mice are not affected. The effect of standard- and low-protein 

diets on the incidence of MBOCA-induced hepatocellular carcinomas was investigated in SpragueDawley and Charles River rats (Kommineni et al. 1979; Stula et al. 1975). The results are 

inconclusive. In Sprague-Dawley rats fed 12.5 or 25 mg/kg/day of MBOCA in a standard-protein diet 

for 18 months, the incidences of hepatocellular carcinomas were 3% and 4%, respectively; in rats fed 

the same amounts of MBOCA in a protein-deficient diet, the incidences were 0% and 18%, 

respectively (Kommineni et al. 1979). These results indicate that a protein-deficient diet did not 

reduce the MBOCA-induced incidence of hepatocellular carcinoma in Sprague-Dawley rats. When 

male Charles River rats were fed 50 mg/kg/day of MBOCA for 2 years, however, the incidences of 

hepatocellular carcinomas were 7% in rats fed a standard-protein diet and 52% in rats fed a lowprotein 

diet (Stula et al. 1975). This observation, that the protein-deficient diet accentuates the 

carcinogenic effects of MBOCA, was not seen in female rats that had 7% and 5% hepatocellular 

carcinomas when fed standard-protein and low-protein diets, respectively (Stula et al. 1975). 

However, in Wistar II rats fed an average dose of 54 mg/kg/day of MBOCA in a low-protein diet for 

500 days, liver cancer was present in 88% of males and 72% of females (Grundmann and Steinhoff 

1970). The results suggest that gender and strain of rats play a role in the effect of low-protein diet 

on MBOCA-induced incidence of hepatocellular carcinomas. Furthermore, the possible contrasting 

effects of a protein-deficient diet on MBOCA-induced lung and liver tumors suggests different 

induction mechanisms for the formation of these two tumors by MBOCA (Kommineni et al. 1979). 

Another target organ for MBOCA carcinogenesis is the urinary bladder. Six female beagle dogs were 

fed an average of 10 mg/kg/day of MBOCA for 9 years. One beagle died approximately 3.4 years of 

pyelonephritis unassociated with MBOCA exposure. Of the five surviving dogs, three developed 

papillary transitional cell carcinomas of the urinary bladder; and one dog had a combined urethral 

adenocarcinoma and transitional cell carcinoma (Stula et al. 1977). Despite the small number of 

animals used, this study demonstrates that ingestion of MBOCA over 9 years was associated with the 

appearance of carcinomas of the urinary bladder and urethra in dogs. 

A statistically significant increase of malignant mammary tumors was found in female Sprague-Dawley 

rats fed 50 mg/kg/day of MBOCA in a low-protein diet for 2 years (Stula et al. 1975). A similar 
MBOCA 15
 

2. HEALTH EFFECTS
 

finding was made in male rats fed 25 mg/kg/day of MBOCA in a low-protein diet for 18 months; the 

incidence of mammary tumors was 6% (Kommineni et al. 1979). When rats were fed a standard diet, 

the incidence of mammary adenocarcinoma was 28% at 50 mg/kg/day of MBOCA and 11% at 25 

mg/kg/day (Kommineni et al. 1979). Zymbal’s gland carcinomas were found in 12% of rats fed a lowprotein diet and in 7% of rats fed a standard-protein diet; both diets contained 25 mg/kg/day 

MBOCA (Kommineni et al. 1979). The results in rats fed MBOCA in low- and standard-protein 

diets indicate that there is a dose-related increase in the incidence of lung and mammary carcinomas, 

while the incidence of hepatocellular carcinoma is not dose related (Kommineni et al. 1979). 

Other tumor types were also found after chronic oral administration of MBOCA. The incidence of 

hemangiosarcomas was 4% and 8% in Sprague-Dawley rats fed 25 mg/kg/day of MBOCA in 

standardprotein or low-protein diets, respectively (Kommineni et al. 1979). In another study, vascular 

tumors (generally subcutaneous hemangiomas and hemangiosarcomas) were present in randomly bred male 

albino mice (derived from the HaM/ICR strain in 1959) fed 130 or 260 mg/kg/day of MBOCA for 

18 months; the incidences were 23% and 40%, respectively (Russfield et al. 1975). In female mice, 

vascular tumors (43% ) were present only in the group treated with the high dose of 260 mg/kg/day 

of MBOCA. 

The incidence of pituitary adenomas (including adenocarcinomas) in Sprague-Dawley rats fed a 

standard-protein diet was reduced, especially in animals treated with high doses of MBOCA 

(Kommineni et al 1979). Rats fed 12.5, 25, or 50 mg/kg/day of MBOCA for 18 months had 36%, 

25% (statistically significant), and 4% (statistically significant) incidences of pituitary adenomas, 

respectively. The incidence of pituitary adenomas in the control group was 42% (Kommineni et al. 

1979). A statistically significant decrease in pituitary tumors was also observed in female, but not 

male, ChR-CD rats (Charles River Cesarean Delivered, Sprague-Dawley origin, random-bred albino 

rats) fed a standard-protein diet with 50 mg/kg/day of MBOCA for 2 years (Stula et al. 1975). This 

decrease in incidence of pituitary tumors was not as consistent in Sprague-Dawley rats fed a lowprotein 

diet; the incidences were 16%, 12% (statistically significant), and 20% in animals fed 6.25, 

12.5, and 25 mg/kg/day, respectively, for 18 months (Kommineni et al. 1979). In the control group, 

the incidence of pituitary adenomas was 23%. neither the certainty of these findings nor the 

mechanism by which they could occur are known at the present time. 

The precise mechanism of chemical carcinogenesis is not known, but it is thought that in some 

instances it involves the formation of chemical adducts in the genetic material through covalent 

binding of nucleophilic sites by electrophilic parent compounds or their activated electrophilic 

metabolites (Cheever et al. 1991). Therefore, it seems that the capacity of MBOCA to form adducts 

with tissue DNA (Cheever et al. 1990) hemoglobin (Cheever et al. 1991; Sabbioni and neumann 

1990) and globin and serum albumin (Cheever et al. 1991) in rats may play a role in its toxicity and 

carcinogenicity. 

The lowest doses that produced tumors (CELs) are presented in Table 2-1 and plotted in Figure 2-l. 





MBOCA 21
 

2. HEALTH EFFECTS 

2.2.3 Dermal Exposure 

2.2.3.1 Death 

No studies were located regarding death in humans or animals after dermal exposure to MBOCA. 

2.2.3.2 Systemic Effects 

No studies were located regarding respiratory, cardiovascular, hematological, musculoskeletal, or 

hepatic effects in humans or animals after dermal exposure to MBOCA. The systemic effects 

observed after dermal exposure are discussed below. 

Gastrointestinal Effects. Extremely limited information is available regarding gastrointestinal 

effects of MBOCA after dermal exposure. In a case study of an accidental occupational exposure, 

a worker complained of feeling ill in the stomach after his face was sprayed with molten MBOCA 

that also entered his mouth (Hosein and Van Roosmalen 1978). He wore overalls, gloves, and safety 

glasses but no respirator or face shield. He washed his face and eyes immediately after the incident. 

no further information was given about his condition. As with other occupational exposure studies, 

there was no information on the dose to which he was exposed. Another limitation of this study is 

the likelihood that some of the MBOCA was inhaled or ingested. 

No information was located regarding gastrointestinal effects in animals after dermal exposure to 

MBOCA. 

Renal Effects. In a retrospective bladder cancer incidence study conducted among 532 workers 

exposed to MBOCA from 1968 to 1979 and 20 workers who were first employed in 1980 and 1981, 

385 participated in the urine screening test (Ward et al. 1990). Exfoliative cytology revealed that 21 

urine samples contained atypical cells. no cytology readings were positive for cancer. Sixteen urine 

samples were positive for heme (Ward et al. 1990). Almost 90% of the exposed workers were males, 

and the median duration of exposure was 3.2 months. This study is important because it gathered 

information on a relatively large group of workers exposed to MBOCA and alerted medical 

professionals to the limitations of follow-up procedures used after MBOCA exposure. In the course 

of the screening, one of the participants who had negative cytology and was negative for the presence 

of heme in the urine was diagnosed with a tumor of the urinary bladder. Because of this 

development, cystoscopy was introduced as a part of the follow-up procedure, and two additional lowgrade 

papillary tumors of the bladder were detected. The analysis of data on free urinary MBOCA 

from workers in companies of the PMA confirmed the importance of biological monitoring (Lowry 

and Clapp 1992). Cumulative results for 1985-1990 show an increase in percentage of urinary 

samples containing below 25 μg/L of MBOCA (from 77% in 1985 to 86% in 1990) and a decrease 

in percentage of samples with over 5 μg/L of MBOCA (from 12% in 1985 to 8% in 1990). These 

findings indicate that wearing protective clothing, using MBOCA in pellets not powder, monitoring 

indoor air for MBOCA, and other protective measures may play an important role in controlling 

occupational exposures. 

Five hours after an acute exposure in which a worker was accidentally sprayed in the face with molten 

MBOCA, a urine sample contained 220 mg/L of protein, indicating possible damage to renal tubules 

(Hossein and Van Roosmalen 1978). There was only a trace amount of protein in the urine of this 

worker 11 hours after the accident. The two urine specimens collected over the course of 24 hours 

after the accident had low specific gravity indicating possible transient damage to the renal tubules. 
MBOCA 22
 

2. HEALTH EFFECTS
 

No studies were located regarding renal effects in animals after dermal exposure to MBOCA. 

Dermal/Ocular Effects. Very limited information is available regarding dermal/ocular effects after 

dermal exposure to MBOCA. In a case study, one worker was accidentally sprayed in the face with 

molten MBOCA. Some of the compound entered his mouth. The worker complained of burning 

face and eyes shortly after exposure (Hossein and Van Roosmalen 1978). The worker was wearing 

gloves and safety glasses but no respirator or face shield. Therefore, it is likely that the exposure may 

have also occurred by inhalation or oral absorption. The limitations of this study are that no further 

information was provided regarding the worker’s condition, the dose of MBOCA, or the precise 

exposure route, and that only one exposed individual was described. In another case of accidental 

exposure to approximately 11.3 L of molten MBOCA, the worker described a burning sensation on 

his skin. He was sprayed over his chest, abdomen, and extremities (NIOSH 1986a; Osorio et al. 

1990). Some exposure by inhalation and ingestion was also likely in this case. 

No studies were located regarding dermal/ocular effects in animals after dermal exposure to MBOCA. 

No studies were located regarding the following health effects in humans or animals after dermal 

exposure to MBOCA: 

2.2.3.3 Immunological Effects 

2.2.3.4 Neurological Effects 

2.2.3.5 Reproductive Effects 

2.2.3.6 Developmental Effects 

2.2.3.7 Genotoxic Effects 

No studies were located regarding genotoxic effects in humans following dermal exposure to 

MBOCA. Radiolabeled MBOCA was applied to a 36-cm2

 shaved skin patch on the dorsal side of 

rats at a dose of 75 mg/kg. DNA adduct formation was determined for various tissues at intervals 

ranging from 1 to 29 days after exposure (Cheever et al. 1990). Throughout the study, less than 14% 

of the applied dose was absorbed. Adduct formation was about 100-fold less than after oral exposure 

to the same dose, but adducts were found in the same tissues with the same order of binding (liver 

> bladder > lymphocytes). This indicates that MBOCA was absorbed through the skin to react with 

DNA in target organs. Two studies of the genotoxicity of MBOCA in D. melanogaster also involved 

concomitant oral and dermal exposure and were discussed under oral exposure in Section 2.2.2.7. 

Other genotoxicity studies are discussed in Section 2.4. 

2.2.3.8 Cancer 

A limited number of epidemiological studies were located that examined the incidence of cancer in 

workers exposed to MBOCA. Workers who were exposed to MBOCA for a median employment 

period of 3.2 months (between 1968 and 1981) were examined for bladder tumors (Ward et al. 1990). 

After cystoscopy revealed a papillary cell tumor in one worker, a low-grade papillary transitional cell 

tumor of the urinary bladder was diagnosed by cystoscopy in 2 of the remaining 200 workers 

examined. Two of the men were less than 30 years old. The interval between the time of first 

exposure and the initiation of the study averaged 11.5 years, while the latency period for most bladder 

carcinogens is about 20 years (Ward et al. 1990). Since bladder tumors in young men are very 

uncommon, this finding increases the concern that MBOCA has a potential for causing bladder 
MBOCA 23
 

2. HEALTH EFFECTS
 

cancer in humans. A limitation of this study is that there were no controls (there are no data on the 

incidence of bladder tumors diagnosed by cystoscopy in an asymptomatic nonexposed population). 

The daily dose of MBOCA to which workers were exposed, was only estimated by assigning an 

exposure score of 0-20. Further investigation of this occupational exposure raised a possibility of 

coexposure to other chemicals such as 4’,4-methylenedianiline, 4-chloro o-toluidine, aniline, and otoluidine (Hogan 1993; Ward 1993). The dose and duration of exposure to these chemicals could 

only be estimated on the basis worker recollection. It is therefore difficult to estimate the exact 

contribution of MBOCA to carcinogenic effects observed in occupationally exposed workers. 

No studies were located regarding cancer in animals after dermal exposure to MBOCA. 

2. 3 TOXICOKINETICS 

Limited information is available regarding absorption of MBOCA. Following acute inhalatiomdermal 

exposure to very low concentrations of MBOCA, absorption appears to be rapid, based on the 

presence of MBOCA in the urine of occupationally exposed workers (Ichikawa et al. 1990). The 

urine of a worker accidentally exposed to molten MBOCA, contained 1,700 ppb of MBOCA 9 hours 

later indicating absorption and distribution following dermal and/or inhalation exposure (NIOSH 

1986a; Osorio et al. 1990). 

The distribution of MBOCA in laboratory animals is relatively uniform. In rats, the highest amount 

of MBOCA and its metabolites (total 14C-radioactivity) was found in the liver following an acute P.O. 

injection or intermediate, gavage, exposure (Cheever et al. 1991). The tissue distribution of 

radioactivity following the acute exposure, was as follows: liver > kidney > lung > spleen > urinary 

bladder > testes > brain > lymphocytes (Cheever et al. 1991). The highest concentration of 

radioactivity in dogs following acute dermal exposure to radiolabeled MBOCA was in the bile (Manis 

et al. 1984). Detectable concentrations were also found in the liver, kidney, and fat. These results 

suggest that the distribution of MBOCA is similar in rats and dogs following oral and dermal 

exposures. A distribution study in rats following a single intravenous exposure to MBOCA, further 

support to these observations (Tobes et al. 1983). 

MBOCA metabolism can proceed via several pathways: N-acetylation, N-hydroxylation, which may 

be followed by n-oxidation, and ring hydroxylation (see Figure 2-2). Some of these processes may 

be followed by conjugation. These are considered important pathways with regard to carcinogenicity 

(as cited in Cheever et al. 1991). Results of in vitro studies suggest that MBOCA rapidly penetrates 

the skin but is not metabolized in the process (Chin et al. 1983). 

After inhalation of low levels, excretion of MBOCA has been monitored by measuring the amount 

in urine. Excretion occurs rapidly during the first 48 hours (NIOSH 1986a). Following an accidental 

exposure to 11.34 L of molten MBOCA, 1,700 ppb of MBOCA was found in the worker’s urine four 

hours later (NIOSH 1986a; Osorio et al. 1990). This result suggests the rapid excretion of MBOCA 

after acute dermal and/or inhalation exposure. It is not clear, however, if urine is indeed the primary 

route of excretion in humans, since no information was presented on the amount of MBOCA 

contained in the feces. In rats that received a single oral dose of 10 mg/kg of radiolabeled MBOCA, 

60% of the radioactivity was found in the feces (Farmer et al. 1981; Groth et al. 1984). 

Little information is available on the kinetics of urinary MBOCA excretion in humans. One study 

found that 23 hours after an acute occupational exposure to MBOCA, 50% of this material was 

excreted in the urine (Osorio et al. 1990). However, other work (NIOSH 1986b) indicates that 

 

MBOCA 25
 

2. HEALTH EFFECTS
 

clearance may be much slower, especially at higher exposures. The duration of exposure may also 

be a factor. 

The precise mechanism of carcinogenicity for MBOCA is not completely understood. Some evidence 

suggests, however, that the ability to form adducts with tissue DNA (Cheever et al. 1990; Sabbioni 

and neumann 1990) hemoglobin (Cheever et al. 1988, 1990, 1991; Chen et al. 1991; Sabbioni and 

neumann 1990) and globin and serum albumin (Cheever et al. 1991) in rats following MBOCA 

exposure may play a role in its carcinogenicity. 

2.3.1 Absorption 

2.3.1.1 Inhalation Exposure 

Studies that directly measure absorption in humans following inhalation exposure to known 

concentrations of MBOCA were not located. However, absorption was indirectly estimated in five 

male factory workers by measuring urinary MBOCA levels over a 5-day period (Ichikawa et al. 1990). 

Personal air exposure levels were obtained by continuously monitoring the breathing zone of each 

worker for 6-7 hours every other day. The air MBOCA levels ranged from 0.0002 to 0.0089 mg/m3

. 

The results showed that the preshift and postshift urine MBOCA levels of the exposed workers, 

including the worker with the highest level of exposure, did not significantly differ. Forty-eight hours 

after the exposure, urinary MBOCA levels were still similar to preshift levels; the authors interpreted 

this finding as evidence that the biological half-life of urinary MBOCA is relatively long (Ichikawa 

et al. 1990). The amount of MBOCA measured in the urine was much higher than the amounts of 

inhaled MBOCA as estimated from personal exposure measurements. This observation suggests that 

a certain amount of MBOCA exposure occurs in the workplace by some additional route(s). The 

limitations of this study include the small sample size and the probability that dermal exposure 

occurred as well. 

In another study, 13 urine samples were collected from workers occupationally exposed to MBOCA 

on a Monday morning after 2 days away from work. The results showed that there was no detectable 

MBOCA in the urine of workers who had low MBOCA exposure(s) during the previous week. Only 

the urine from the worker with the highest MBOCA urine concentration (30 μg/L) the week before 

had detectable MBOCA. In most cases, this clearance of MBOCA after the weekend suggested that 

MBOCA had a relatively short retention time in the body (Clapp et al. 1991). As in the previous 

study, the exposure route(s) probably included inhalation and dermal. In another study of 

occupational exposure (combination of inhalation and dermal exposures), levels of MBOCA in the 

urine were determined in workers over a period of 22 months. The mean concentrations of MBOCA 

during that time ranged from 5.3 to 43.8 μg/L (NIOSH 1986b). Further analysis of the data revealed 

that urine samples with highest levels of MBOCA came from workers that are in direct daily contact 

with MBOCA, such as mixers and molders (NIOSH 1986b). One of the samples from a mixer was 

analyzed during the week (average urine MBOCA level was 29.9 μg/L) and after a 2-day weekend 

(average urine MBOCA level was 8.9 μg/L). This demonstrated that MBOCA was not cleared from 

the urine of a worker who had relatively high levels of MBOCA during the previous week (NIOSH 

1986b). The reasons for the different clearance rates observed in the studies described (Clapp et al. 

1991; Ichikawa et al. 1990; NIOSH 1986b) are not clear. Since relatively small numbers of workers 

were observed, the results may merely reflect individual differences. Alternatively, MBOCA may be 

excreted at different rates depending upon exposure conditions including both the rate and duration 

of exposure. This question needs further examination. 
MBOCA 26
 

2. HEALTH EFFECTS 

No studies were located regarding absorption in animals after inhalation exposure to MBOCA. 

2.3.1.2 Oral Exposure 

No studies were located regarding absorption in humans after oral exposure to MBOCA. 

Several studies in animals following oral MBOCA exposure, detected MBOCA or its metabolites in 

body tissues, urine, and feces (Cheever et al. 1988; Farmer et al. 1981; Groth et al. 1984). When 

rats were given a single oral dose of 14C-MBOCA by gavage, 16.5% of the dose was excreted in the 

urine within 72 hours, while 13.7% was retained in the tissues (Groth et al. 1984). These data 

indicate that some MBOCA is absorbed after oral exposure in animals. Approximately 60% remains 

unabsorbed in the feces (Groth et al. 1984). 

2.3.1.3 Dermal Exposure 

Studies that directly measure MBOCA absorption in humans following dermal exposure to known 

concentrations of this compound were not located. However, absorption was measured in five male 

factory workers by measuring urinary MBOCA levels over a 5-day period (Ichikawa et al. 1990). 

Personal air exposure levels were obtained by continuously monitoring the breathing zone of each 

worker for 6-7 hours every other day. The air levels of MBOCA ranged from 0.0002 to 0.0089 

mgim”. The results showed that the preshift and postshift urine MBOCA levels did not significantly 

differ among exposed workers. Forty-eight hours after the exposure, the urinary MBOCA levels were 

similar to preshift levels suggesting that the biological half-time of MBOCA is relatively long 

(Ichikawa et al. 1990). The amount of MBOCA measured in urine was much higher than the 

amount(s) of inhaled MBOCA. The authors concluded that occupational exposures occur by other 

routes in addition to inhalation (in this case dermal exposure) and are important contributors to total 

body burdens of MBOCA. The limitations of this study include the small sample size and the 

probability that dermal exposure had occurred as well. 

In another study, 13 urine samples were collected from workers occupationally exposed to MBOCA 

on a Monday morning after 2 days away from work. The results showed that there was no detectable 

MBOCA in samples that had low MBOCA levels during the past week. Only the sample that came 

from the worker who had the highest average MBOCA urine concentration (30 μg/L) the week 

before had detectable MBOCA (Clapp et al. 1991). These results suggest that the higher initial dose 

of MBOCA the longer it takes to be excreted. In another occupational study the exposure resulted 

from a combination of inhalation and dermal routes. The levels of MBOCA in the urine of exposed 

workers were determined over a period of 22 months. The mean concentrations of MBOCA ranged 

from 5.3 to 43.8 μg/L (NIOSH 1986b). A detailed data analysis revealed that the urine samples with 

the highest MBOCA levels were obtained from mixers and molders, i.e., workers that are in direct 

daily contact with MBOCA (NIOSH 1986b). Urinary measurements of MBOCA were obtained for 

one worker a mixer over a 5-day work week and over a 2-day weekend. The average urine MBOCA 

level during the week was approximately 30 μg/L; the level dropped to 8.9 μg/mL over the weekend. 

This finding suggests that MBOCA was not completely excreted via urine in a worker who had 

relatively high levels of MBOCA during the preceeding week (NIOSH 1986b). The reasons for the 

different clearance rates reported in the studies described (Clapp et al. 1991; Ichikawa et al. 1990; 

NIOSH 1986b) are unclear. It is possible that due to the small sample size the results may merely 

reflect individual differences. It is also possible that MBOCA may be removed at different rates 

depending on the length and rate of exposure. 
MBOCA 27
 

2. HEALTH EFFECTS
 

Differential absorption rates of 14C-MBOCA were investigated following dermal and intravenous 

exposures in beagle dogs (Manis et al. 1984). By comparing the levels of MBOCA excreted via the 

urinary and biliary systems, following percutaneous and intravenous (100% absorption) administration, 

the investigators calculated that, after 24 hours, only 2.4% of the applied MBOCA was absorbed 

through the skin. In another study in rats, 11.5-21.9% of MBOCA applied to the skin was calculated 

to have been absorbed within 72 hours of application (Groth et al. 1984). 

Using radiolabeled MBOCA and fresh human neonatal foreskin organ cultures, the absorption and 

penetration of MBOCA through a 7 mm x 7 mm area was evaluated over 4 hours (Chin et al. 1983). 

One hour after application, 46% of the radiolabeled MBOCA was detected on the skin and 0.5% was 

detected on the underlying membrane (the remaining radioactivity was unabsorbed and stayed on the 

coverglass). Four hours later, 61% was detected in the skin, 26% had passed through and was on 

the underlying membrane filter, while 12% remained unabsorbed. The absorption process was 

optimal at 37°C and decreased sharply at 0°C. These findings indicate that MBOCA penetrates the 

neonatal foreskin readily without being metabolized, and that the absorption process is temperature 

dependent (Chin et al. 1983). 

2.3.2 Distribution 

2.3.2.1 Inhalation Exposure 

No studies were located regarding distribution in humans or animals after inhalation exposure to 

MBOCA. 

2.3.2.2 Oral Exposure 

No studies were located regarding distribution in humans after oral exposure to MBOCA. 

Twenty-four hours after oral administration of 28 μmol/kg of radioactive [methylene-14C-]MBOCA 

to male Sprague-Dawley rats, the highest level of radioactivity was in the liver. The tissue distribution 

of total radiolabels (i.e., MBOCA plus its metabolites) was as follows: liver > kidney > lung > 

spleen > urinary bladder > testes > brain > lymphocytes (Cheever et al. 1991). In another study, 

the distribution in female Wistar rats 24 hours after gavage with radioactive MBOCA was similar: 

liver > intestine > lung > kidney > blood > stomach > spleen > uterus (Sabbioni and neumann 

1990). The remaining radioactivity was recovered in urine and feces. After 28 consecutive oral doses 

of radioactive MBOCA, the radioactivity accumulated more rapidly in the liver than in the blood 

(1,455 femtomoles/mg versus 122 femtomoles/mg tissue, respectively) (Cheever et al. 1991). The 

results show that, after either acute or intermediate oral administration, the highest amount of 

MBOCA and its metabolites accumulates in the liver. The results also show that after 28 doses, 

accumulation in the liver increased more than 100-fold. 

Similar findings in terms of liver accumulation were found in a study in which two female LAC:Porton 

rats were fed 10 mg/kg of 14C-MBOCA, and MBOCA’s distribution was measured 48 hours later 

(Farmer et al. 1981). Again, liver had the highest amount of radioactivity, followed by white fat, 

blood, and kidney. This study is limited because it used only two animals. In another acute study, 

radiolabeled MBOCA was administered by gavage to rats by gavage (Morton et al. 1988). Forty-eight 

hours later, 64-87% of the administered radioactivity was recovered in the urine and feces. Excretion 

occurred primarily in the first 24 hours with feces containing 1.5-3 times the radioactivity of the 
MBOCA 28
 

2. HEALTH EFFECTS 

urine. These results are consistent with previous reports that in rats MBOCA is extensively 

metabolized and rapidly excreted. 

2.3.2.3 Dermal Exposure 

Although no studies were located regarding distribution in humans after dermal exposure to MBOCA, 

it appears that it is rapidly eliminated from the body following dermal exposure. Nine hours after 

an accidental spill, the urine of a worker exposed to 11.34 L of molten MBOCA contained 1,700 ppb 

of the chemical (NIOSH 1986a; Osorio et al. 1990). The biological half-life of MBOCA in the 

human body based on the amount excreted into the urine was estimated to be 23 hours (Osorio et 

al. 1990). The authors assumed a one-compartment model and estimated that about 94% of the 

initial MBOCA would be eliminated within 4 days. They concluded that urinary excretion of 

MBOCA was rapid, a finding that is consistent with the observations made by Hosein and Roosmalen 

(1978). Although this study is limited because only one case was presented, it is important because 

it indirectly demonstrates that after dermal exposure of humans a large portion of MBOCA is 

distributed by the circulatory system to the kidneys (Osorio et al. 1990). 

In a study using beagle dogs dermally exposed to 0.4 mg of radioactive MBOCA/cm2

, no measurable 

radioactivity was detected in blood or plasma up to 24 hours later (Manis et al. 1984). The highest 

concentration of radioactivity 24 hours post-exposure was found in the bile. no unmetabolized 

MBOCA was present in the bile. Detectable concentrations of radioactivity were found in the liver, 

kidney, fat, and lung. Urinary excretion of unmetabolized MBOCA was a small but consistent 

fraction, 0.4-0.5%, of the total urinary radioactivity, and the authors concluded that this may be a 

useful index of acute exposure. These results support the hypothesis that dermal absorption is a 

viable entry for MBOCA. They also demonstrate that the circulatory system distributes MBOCA to 

the liver, kidneys, fat, and lungs. In this study, intravenously exposed animals were used as controls 

in order to obtain a 100% absorbed dose baseline for comparison with the pharmacokinetic data 

obtained for dermal exposure. 

2.3.2.4 Other Routes of Exposure 

One hour after a single intravenous dose of 0.49 mg/kg of radiolabeled MBOCA to rats, radioactivity 

was found in the tissues in the following order: small intestine > liver > fat tissue > lungs > kidneys 

> skin > adrenals (Tobes et al. 1983). Similar results in terms of liver accumulation were obtained 

in rats 48 hours after an intraperitoneal injection of 1 mg/kg of radioactive MBOCA (Farmer et al. 

1981). However, only l-2% of MBOCA and 95-97% of radiolabeled metabolites were found in the 

urine indicating rapid and extensive MBOCA metabolism in the rat. The finding that liver has the 

highest amount of radiolabel 24 hours after a single exposure is consistent with the findings from 

other intraperitoneal exposure studies (Cheever et al. 1991). Similar results were obtained in dogs 

after intravenous administration of MBOCA (Manis et al. 1984). 

2.3.3 Metabolism 
MBOCA 29
 

2. HEALTH EFFECTS 

2.3.3.1 Inhalation Exposure 

Analysis of 23 urine samples from workers occupationally exposed to MBOCA showed that all 

contained MBOCA, but only 10 of 23 contained N-acetyl MBOCA. The ratio of N-acetyl MBOCA 

to parent MBOCA ranged from 0.005 to 0.09 indicating that N-acetyl MBOCA is a relatively minor 

urine metabolite in humans (Cocker et al. 1988). Further analysis shows that the urine of MBOCAexposed 

workers also contains a major hydrolysis-labile metabolite, probably β-N-glucuronide (Cocker 

et al. 1990). This metabolite, upon hydrolysis, yields two to three times more MBOCA than the 

amount of parent compound present in urine after exposure to MBOCA. Another metabolite 

detected in the urine is a heat-labile conjugate of n-acetyl MBOCA (Cocker et al. 1990). In another 

study of occupational exposure, 35% of the MBOCA metabolites were excreted as conjugates in the 

urine (Osorio et al. 1990). 

No studies were located regarding metabolism in animals after inhalation exposure to MBOCA. 

2.3.3.2 Oral Exposure 

No studies were located regarding metabolism in humans after oral exposure to MBOCA. 

MBOCA is extensively metabolized in experimental animals (Morton et al. 1988), and its metabolism 

can follow several pathways: N-acetylation, N-hydroxylation/ N-oxidation, and ring hydroxylation. 

These are important pathways with respect to the carcinogenicity of MBOCA (Cheever et al. 1991). 

Some of these metabolic conversions can be followed by conjugation. Carcinogenicity probably 

involves activation and adduct formation by MBOCA. A scheme of MBOCA metabolism and 

excretion in animals is presented in Figure 2-2. The microsomal P-450 enzyme system is involved in 

n-hydroxylation of MBOCA, which is considered to be an activation step related to adduct formation 

(Morton et al. 1988). Microsomes from phenobarbital-treated rats had an increased rate of MBOCA 

hydroxylation (Morton et al. 1988). Such effects were not obtained after treatment with 

methylcholanthrene. These findings were confirmed using human liver microsomes and purified rat 

liver cytochrome P-450 monooxygenases showing that the activation of MBOCA is catalyzed by the 

phenobarbital-inducible enzymes (Butler et al. 1989). More recently, it was shown that much higher 

binding of MBOCA to hemoglobin occurred in phenobarbital-treated rats (Cheever et al. 1991). 

These results suggest that enzymatic induction by phenobarbital leads to increased capacity of 

MBOCA and/or its metabolites to covalently bind to proteins and probably to DNA. 

After acute intragastric exposure of male rats to radiolabeled MBOCA, the levels of MBOCA and 

its metabolites were determined in the urine. The level of MBOCA was higher when urine was 

treated with exogenous glucuronidase or sulfatase, indicating the presence of conjugates (Morton et 

al. 1988). The conjugates, which are highly polar, can be digested with a sulphatase-glucuronidase 

mixture leading to 30-50% of deconjugation. When glucuronidase alone was tested it had a small 

effect on conjugates (Farmer et al. 1981). These findings suggest that a large proportion of the 

conjugates consists of sulfates (Farmer et al. 1981). 

The metabolism of MBOCA was also investigated in vitro by incubating human and rat liver 

microsomes with 14C-MBOCA. The formation of metabolites was quantified using appropriate 

chemically synthesized standards (Morton et al. 1988). The rate of n-hydroxylation of MBOCA, an 

obligatory step in metabolic activation of aromatic amines, was higher in rat than in human 

microsomes (Morton et al. 1988). Rat liver microsomes were also found to be more efficient in ohydroxy-MBOCA formation when compared with human microsomes (see Figure 2-2). The same in 
MBOCA 30
 

2. HEALTH EFFECTS
 

vitro microsomal system was used to elucidate the role of hepatic cytochrome P-450 monooxygenases 

in metabolic oxidation and detoxification of MBOCA (Butler et al. 1989). The analysis of 22 human 

liver microsome preparations showed that there was variation in N-oxidation of MBOCA by different 

preparations, and analysis of metabolism catalyzed by different rat isozymes showed that the process 

was catalyzed by phenobarbital-inducible cytochrome P-450 species. Since MBOCA is considered a 

potential human carcinogen, this result indicates that individual profiles of cytochromes P-450 may 

be important determinants of an individual’s susceptibility to MBOCA carcinogenesis (Butler et al. 

1989). Hydroxylation by liver microsomes results in two major metabolites, n-hydroxy- and o-hydroxyMBOCA (Chen et al. 1989; Morton et al. 1988) ( see Figure 2-2). The formation of these two 

metabolites was evaluated using canine, guinea pig, and rat liver microsomes (Chen et al. 1989). 

These results indicate that there are species differences in the oxidation of MBOCA. The major 

metabolite in the guinea pig liver microsome system was N-hydroxy MBOCA, while dog microsomes 

oxidized MBOCA to the o-hydroxylated metabolite with significant amounts of hydroxylamine. In 

the rat liver microsome system, other polar metabolites were predominant, while there were fewer 

n- and o-hydroxylated MBOCA derivatives (Chen et al. 1989). 

2.3.3.3 Dermal Exposure 

MBOCA metabolites were investigated in urine samples from workers occupationally exposed to 

MBOCA (Cocker et al. 1988, 1990). Of 23 urine samples, small amounts of N-acetyl MBOCA were 

present in only 10 samples, even after heat treatment, while MBOCA was present in all of the 

samples (Cocker et al. 1988). A similar observation was made by Ducos et al. (1985) who found that 

the level of n-acetyl MBOCA in urine was less than 10% of the level of MBOCA recovered in urine 

of exposed workers. Skin absorption of MBOCA was considered an important factor in both these 

studies. In a further attempt to identify the heat-labile MBOCA urine metabolites, Cocker et al. 

(1990) compared them to the chemically synthesized glucuronide. The results indicate that the major 

heat-labile conjugate of MBOCA in the urine of exposed workers is probably the β-N-glucuronide 

of the unmetabolized compound. MBOCA glucuronide spontaneously decomposes at 37°C within 

24 hours to yield the unmetabolized MBOCA (Cocker et al. 1990). 

Studies in dogs (Manis et al. 1984) and rats (Groth et al. 1984) indicate that MBOCA is rapidly 

metabolized following dermal exposure to 14C-MBOCA and that urinary levels of unmetabolized 

MBOCA represents only a small fraction of the total (MBOCA plus metabolites) excreted in urine. 

Twenty-four hours after exposure, 1.3% of the dose applied to the skin of dogs was excreted in the 

urine as total radioactivity, of which only 0.005% represented unmetabolized MBOCA. Similarly, in 

rats after 72 hours, 2.54% of the amount applied to the skin was excreted in the urine as total 

radioactivity, while only 0.008% represented unmetabolized MBOCA. 

The major DNA adduct of MBOCA was identified by a combination of in vivo and in vitro studies 

(Silk et al. 1989). Male rats derived from a Wistar strain were exposed intraperitoneally to 

89 μmol/kg of radioactive MBOCA or 141 μmol/kg of acetyl-MBOCA. Twenty-four hours later, 

animals were sacrificed, and their liver DNA was extracted and analyzed for the amount of bound 

radioactivity and DNA adduct formation. Results showed that the cleavage of the bond between the 

methylene bridge and one aromatic nucleus of MBOCA resulted in the formation of 

N-(deoxyadenosine-8-yl)-4-amino-3-chlorobenzyl alcohol, the major in vivo adduct. Two other adducts 

were also formed but were not characterized. 
MBOCA 31
 

2. HEALTH EFFECTS 

2.3.4 Excretion 

2.3.4.1 Inhalation Exposure 

MBOCA has been analyzed and detected in the urine of exposed humans. nine hours after an 

accidental spill, the urine of a worker exposed to 11.34 L of molten MBOCA contained 1,700 ppb 

of MBOCA (NIOSH 1986a; Osorio et al. 1990). The biological half-life of MBOCA in the urine was 

estimated to be approximately 23 hours (Osorio et al. 1990). This was determined by measuring the 

levels of MBOCA in urine 2 weeks after exposure ceased. Assuming a one-compartment model, 

about 94% of the initial dose of MBOCA would be eliminated within 4 days. In another report, after 

an acute occupational exposure to molten MBOCA, a worker complained of burning eyes and face. 

Hot, liquid MBOCA was sprayed over his face and some entered his mouth (Hosein and Van 

Roosmalen 1978). The worker was monitored and his urine was analyzed for MBOCA over a 3-week 

period. Five hours after the spill, the level of MBOCA in the urine was 3.6 mg/L (3,600 ppb). 

MBOCA was rapidly excreted during the first 18 hours after exposure. Twenty-four hours after 

exposure, urine MBOCA level was down to 0.03 mg/L (30 ppb), and 3 weeks later it was below that 

level (Hosein and Van Roosmalen 1978). It was unclear from this study whether urine was the 

primary route of MBOCA excretion in humans following dermal exposure since no information was 

presented on the amount of MBOCA measured in feces. 

Analysis of urine samples from 34 exposed workers showed that the urine levels of MBOCA were 

proportional to the exposure levels. Workers exposed to the highest levels of MBOCA (MBOCA 

mixers) had the highest level of the compound in the urine (NIOSH 1986b). Ten out of 10 mixers 

had a urinary MBOCA level of >5 μg/L and 5 of 10 had >50 μg/L of MBOCA in their urine. Urine 

samples from workers in the molding department (intermediate exposure) had levels of MBOCA 

ranging Erom <5 to 50 μg/L. All trimmers and supervisors (the lowest exposure group) had no 

detectable levels of MBOCA in the urine. The body clearance of MBOCA was tested in 13 urine 

samples from workers who were absent from exposure for 48 hours. Only one of the 13 workers, an 

MBOCA mixer, had a detectable MBOCA urine level (average: 8.9 μg/L) (NIOSH 1986b). The 

level of MBOCA in the air was <3 μg/m3

 most of the time, and the results of the wipe test ranged 

from 0.035 to 53 μg. The limitations of this study are that precise exposure levels and the exact 

routes of exposure were not given and that there were too few data points for any general 

conclusions to be made. In another study on five male workers exposed to MBOCA for 3-27 years, 

MBOCA levels in preshift (before starting work) and postshift (after work) urine samples were not 

significantly different (Ichikawa et al. 1990). Also, the MBOCA urine levels 48 hours after exposure 

were similar to preshift levels. The study authors concluded that the biological half-time of urina 

MBOCA is relatively long. The breathing zone levels of MBOCA were 0.0002-0.089 mg/m3

. 

Limitations of this study include a small sample size and lack of controls. 

The MBOCA levels in urine have been used to assess occupational exposure of workers engaged in 

the manufacture of polyurethane elastomers (Thomas and Wilson 1984). The objective of the study 

was also to identify areas that could be improved in order to reduce the exposure. Between 12 and 

15 workers were followed over a 5-year period, and the exposure levels were reported as the monthly 

average amount of nmol MBOCA/mmol creatinine. The results of this biological monitoring program 

indicated that urine levels of MBOCA slowly but steadily decreased. Between July and September 

of 1978, the average level was 50 nmol MBOCA/mmol creatinine. Although the individual variations 

were present, by February 1980 the average level had fallen to 5 nmol MBOCA/mmol creatinine. 

Some of the measures that helped reduce the exposure to MBOCA were improved ventilation system, 

use of protective clothing, dry cleaning of clothing, improvement of the general hygiene in the factory, 
MBOCA 32
 

2. HEALTH EFFECTS
 

and special attention to workers with consistently high urinary MBOCA levels (Thomas and Wilson 

1984). 

N-acetyl MBOCA is a minor metabolite that was found in the urine of occupationally exposed 

workers (Cocker et al. 1988). Also present was a major labile metabolite, probably β-N-glucuronide 

(Cocker et al. 1990). After hydrolysis, this conjugate yields unmetabolized MBOCA. In an 

occupational exposure study of 122 workers from 19 different plants (one MBOCA manufacturer, 

18 MBOCA users) urine MBOCA levels were determined in 215 samples collected mainly at the end 

of the shift (Ducos and Gaudin 1983). The highest urine levels of MBOCA were found in workers 

from the manufacturing plant: the highest mean urinary MBOCA level among the 12 workers was 

600 μg/L or 450 μg/g relative to creatinine. This level was greatly reduced (to an average of 62 μg/g 

of creatinine) following manufacturing and processing modifications related to increased workers 

protection and good manufacturing practices. The levels of urinary MBOCA in workers of the other 

18 businesses varied greatly and were highest in workers who had the greatest contact with MBOCA. 

The individual urinary MBOCA levels ranged from undetectable to a maximum of 940 μg/L (510 μg/g 

of creatinine). However, if the values outside of the detection limits (l-1400 μ/L) are excluded from 

the calculation, the urinary MBOCA averages are low varying from 4 to 318 μg/L (2-174 μg/g of 

creatinine) (Ducos and Gaudin 1983). The results indicate that the urinary MBOCA levels greatly 

depended on the frequency of MBOCA use, the quantities used, the form of MBOCA (granules, 

solid, or in solution), methods of manufacturing, and from work practices in general. Individual 

factors also affect the excretion levels. The predominant metabolite in urine was monoacetylated 

MBOCA present at low concentration of <1/10 of the total. Another metabolite, N,N’-diacetyl 

MBOCA was also identified in one of the workers. This was an unexpected finding because of the 

poor water solubility of diacetyl MBOCA. The identification of diacetyl MBOCA is important 

because it is possible that from N,N’-diacetyl MBOCA, N-hydoxy-N,N’-diacetyl MBOCA can be 

formed, using benzidine metabolism as a model. N-hydoxy-N,N’diacetyl MBOCA is important 

because it can directly bind to nucleic acids. If the existence of N-hydoxy-N,N’-diacetyl MBOCA is 

confirmed it would provide a plausible biochemical basis for adduct formation that has been proposed 

as one of the mechanisms involved in carcinogenesis. 

One proposed mechanism of MBOCA excretion suggests that very little MBOCA is excreted into the 

bladder as the free amine since most of the MBOCA in the renal perfusate may be present in the 

form of the β-N-glucuronide conjugate (Cocker et al. 1990). Urine contains β-glucuronidase, and 

therefore, β-N-glucuronide may undergo some hydrolysis in the bladder. This is proposed as the 

source of free MBOCA in the urine. 

2.3.4.2 Oral Exposure 

No detailed studies were located regarding excretion in humans following oral MBOCA exposure. 

After an acute occupational exposure to molten MBOCA, one worker complained of burning eyes 

and face. Hot, liquid MBOCA was sprayed over his face and some entered his mouth (Hosein and 

Van Roosmalen 1978). The worker’s urine was monitored for MBOCA excretion over a 3-week 

period. MBOCA was found to be rapidly excreted during the first 18 hours following exposure, 

reaching a maximum concentration of 3.6 mg/L; 6 hours later, (24 hours post-exposure), the urine 

MBOCA level was down to 0.03 mg/L. At 3 weeks, only trace amounts of MBOCA were detected 

in urine (Hosein and Van Roosmalen 1978). 

A single oral dose of 10 mg/kg of radiolabeled MBOCA was administered to female LAC:Porton rats. 

Forty-eight hours later, the majority of the radioactivity was excreted in the feces (60%), while the 
MBOCA 33
 

2. HEALTH EFFECTS
 

liver retained the most radioactivity (2%) (Farmer et al. 1981). Similar observations were made in 

Sprague-Dawley rats given 12 mg/kg of radiolabeled MBOCA (Groth et al. 1984). When male 

Sprague-Dawley rats were exposed to a single oral dose of 50 mg/kg/day of MBOCA, urinary 

MBOCA excretion is maximal on the 1st day and steadily decreases up to day (Ducos and Gaudin 

1983). The quantity of free urinary MBOCA is very small, approximately 0.5 parts per 1,000. The 

most abundant MBOCA metabolite in urine was identified as a monoacetylated compound in 

comparison to the N-acetyl-4,4-methylenebis(2-chloroaniline) and N,N-diacetyl-4,4-methylenebis(2­

chloroaniline) forms (Ducos and Gaudin 1983). The biological half-life of MBOCA was 4.4 and 

16.7 days in rat liver and blood, respectively, after a single oral exposure to 75 mg/kg of 14C-MBOCA 

(Cheever et al. 1988). The biological half-lives of MBOCA in adducts with globin and DNA were 

14.3 and 11.1 days, respectively (Cheever et al. 1988). After chronic exposure to MBOCA (in either 

standard-protein or low-protein diets), urine of tumor-bearing rats contained a significantly higher 

level of MBOCA than urine from animals without tumors (Kommineni et al. 1979). 

2.3.4.3 Dermal Exposure 

Nine hours after an accidental spill, the urine of a worker exposed to 11.34 L of molten MBOCA 

contained 1,700 ppb of MBOCA (NIOSH 1986a; Osorio et al. 1990). The biological half-life of 

MBOCA in the urine was approximately 23 hours (Osorio et al. 1990). This was evaluated by 

monitoring the MBOCA urine levels for 2 weeks after exposure. Assuming a one-compartment 

model, about 94% of the initial dose of MBOCA would be eliminated within 4 days. In another 

report, after an acute occupational exposure to molten MBOCA, one worker complained of burning 

eyes and face. Hot, liquid MBOCA was sprayed over his face and some entered his mouth (Hosein 

and Van Roosmalen 1978). The worker was monitored and his urine analyzed for MBOCA over a 

j-week period. MBOCA was rapidly excreted within the first 18 hours following exposure, reaching 

a maximum concentration of 3.6 mg/L. Six hours later, (24 hours post-exposure), the MBOCA level 

in urine was down to 0.03 mg/L, dropping to trace amounts 3 weeks later (Hosein and Van 

Roosmalen 1978). In another report on occupational exposure, 340 analyses were performed on 

urine samples from 150 workers from 19 factories (Ducos and Gaudin 1983; Ducos et al. 1985). 

Samples were usually collected at the end of the shift. The levels of MBOCA ranged from 

undetectable (<0.5 μg/L) to 1,600 μg/L. The highest urine MBOCA levels were present in 12 

workers from a factory that handled crystallized MBOCA. In a similar study, pre- and post-work 

urine samples from 11 employees of a polyurethane manufacturing plant and 10 control subjects were 

evaluated for MBOCA and thioether levels (Edwards and Priestly 1992). There was no information 

on the levels of MBOCA that employees were exposed to, on the duration of exposure, or on the 

route. Based on the type of work, it is likely that the main route of exposure was dermal. The 

urinary output of thioether was evaluated because thioethers are metabolic end products of the 

pathway involving mercapturic acid. The thioethers, therefore, were thought to be potential, nonspecific, 

markers of exposure to electrophilic xenobiotics such as rubber monomers or petroleum. 

They have not been used as markers for MBOCA exposure. The urinary thioether levels were similar 

in pre- and post-work samples (p>0.05) and did not correlate with urinary MBOCA levels, indicating 

that they are not useful for estimating occupational MBOCA exposure. Although there were no 

significant differences in urinary MBOCA levels between the three groups of employees (supervisors, 

laboratory personnel, process workers), the results reflect the potential exposure levels. The median 

values of MBOCA in the post-work urine of process workers and supervisors were 9.33 and 1.05 

μmol mol-1 of creatinine, respectively. There was no MBOCA in the urine samples from 10 control 

workers. The small amount of urinary MBOCA in occupationally exposed workers suggests that 

other major metabolites, such as β-N-glucuronide conjugate (Cocker et al. 1990) may be present in 

the urine. From the results of all of the exposure studies it is not clear, however, if urine is the 
MBOCA 34
 

2. HEALTH EFFECTS 

primary excretion route in humans after dermal exposure to MBOCA since no information was 

provided regarding the amount of MBOCA in the feces. 

Male Sprague-Dawley rats were treated with a single dermal dose of 2.5 mg MBOCA or

14C-MBOCA; within 72 hours, 2.54% of the administered radioactive MBOCA was excreted as 14C, 

while only 0.008% was excreted as the parent compound (Groth et al. 1984). Similar results were 

obtained in dogs. Twenty-four hours after a single dermal application of 0.4 mg/kg of 14C-MBOCA 

to beagle dogs, the highest concentration of radioactivity was found in the bile (Manis et al. 1984). 

no unmetabolized MBOCA was present in the bile. The results support the hypothesis that dermal 

absorption is a viable mode of entry and that MBOCA is rapidly metabolized and excreted after it 

enters the body regardless of the route of entry. Urinary excretion of unmetabolized MBOCA was 

a small but consistent fraction, comprising 0.4-0.5% of the total urinary excretion of radioactivity 

(Manis et al. 1984). 

2.3.4.4 Other Routes of Exposure 

Feces and urine were major excretion routes in rats after acute exposure to radiolabeled MBOCA 

by stomach intubation (Morton et al. 1988) or intravenous injection (Tobes et al. 1983). At 48 hours 

after exposure to 44-58 mg/kg of radiolabeled MBOCA by intubation, 64-87% of radioactivity was 

recovered in the urine and feces (Morton et al. 1988). A similar observation was made in rats 48 

hours after a single intravenous dose of 0.51 mg/kg; feces contained 73% of the total cumulative dose 

of radiolabeled MBOCA (Tobes et al. 1983). These results indicate that total elimination of 14C 

following intubation or intravenous injection of 14C-MBOCA to rats was similar to that observed 

following oral dosing, which also occurred primarily in the feces (Farmer et al. 1981; Groth et al. 

1984). After a single intraperitoneal injection of 1,13, or 100 mg/kg of MBOCA, the compound was 

excreted most rapidly within the first 24 hours. Rats receiving the highest concentration of MBOCA 

produced three times more urine during the first 24 hours than did controls (Farmer et al. 1981). 

Studies with intravenous administration of MBOCA in the dog found that the major route of 

excretion was through the urine (Manis et al. 1984). Within 24 hours after intravenous injection of

14C-MBOCA, 46% of the dose had been excreted in the urine and 32% in the bile, accounting for 

78% of the total dose. This indicates that often substantial differences occur between species and 

that route of exposure determines the route of elimination of MBOCA. 

In an attempt to use thioether as a potential urinary indicator for MBOCA exposure, male Wistar 

rats were exposed intraperitoneally to 125 or 250 mg/kg/day of MBOCA in peanut oil (vehicle) daily 

for 5 days, while the control received peanut oil only (Edwards and Priestly 1992). Urine was 

collected for 24 hours prior to and following exposure. Urinary MBOCA levels were significantly 

higher in the treated groups compared to controls. There were no significant differences noted 

between the two experimental groups. As in the study with occupationally exposed workers, the 

urinary thioether levels were not affected by MBOCA treatment indicating that thioether was not a 

useful indicator for MBOCA exposure (Edwards and Priestly 1992). 

The in vivo formation of MBOCA-hemoglobin adducts was determined in blood samples of male 

Sprague-Dawley rats intravenously injected with 0.04, 0.2, or 1.0 μmol/kg of n-hydroxy-MBOCA 

(Chen et al. 1991). The injection of the lowest dose of N-hydroxy-MBOCA resulted in formation of 

0.9 ng/50 mg of MBOCA-hemoglobin adducts 24 hours after the injection. This level remained 

almost unchanged (0.8 ng/50 mg) 1 week after exposure indicating a relatively long half life of this 

adduct. A similar observation was made in guinea pigs injected subcutaneously with 4, 20, or 

100 mg/kg of MBOCA. Detectable levels of MBOCA-hemoglobin adducts were still present 
MBOCA 35
 

2. HEALTH EFFECTS
 

10 weeks after exposure to the lowest dose of MBOCA. In guinea pigs, the life span of MBOCAhemoglobin adducts was similar to that of red blood cells, 60-80 days. 

2.3.5 Mechanisms of Action 

The precise mechanism of action of MBOCA is not completely understood. However, the capacity 

of MBOCA to form adducts with hemoglobin (Cheever et al. 1988, 1990, 1991; Chen et al. 1991; 

Sabbioni and neumann 1990) tissue DNA (Cheever et al. 1990) and globin and serum albumin 

(Cheever et al. 1991) in rats may play a role in its carcinogenicity. The adduct formation is especially 

important in elucidating the carcinogenicity of MBOCA. Two metabolites were identified in the 

urine of one occupationally exposed worker: n-acetyl MBOCA and N,N’-diacetyl MBOCA (Ducos 

and Gaudin 1983). The finding of n,n’-diacetyl MBOCA was unexpected (because of its poor water 

solubility) and important. It can be assumed, using benzidine metabolism as a model, that from N,N’­

diacetyl MBOCA, N-hydroxy-N,N’-diacetyl MBOCA can be formed. N-hydroxy-N,N’-diacetyl 

MBOCA is important because it can directly bind to nucleic acids. Therefore, the confirmation of 

its existence would elucidate the biochemical basis for adduct formation. This finding is in agreement 

with a recently proposed mechanism for chemical carcinogenesis that may involve the formation of 

chemical adducts in DNA through covalent binding. This proposition was based on the fact that 

MBOCA produces DNA adducts in rat liver at levels characteristic of genotoxic carcinogens (KuglerSteigmeier et al. 1989). Since it is known that MBOCA can bind to rat liver DNA (Cheever et al. 

1990), and that liver is one of the primary target organs for development of tumors after exposure 

of rats to MBOCA (Kommineni et al. 1979; Russfield et al. 1973, it may be assumed that MBOCADNA 

adducts play a role in the development of tumors. The mechanism of hemoglobin adduct 

formation by N-oxidized MBOCA metabolites was recently investigated in viva and in vitro using 

human and rat hemoglobin (Chen et al. 1991). Male Sprague-Dawley rats were injected 

intraperitoneally with 0.5-50 mg/kg of MBOCA, and male English short hair guinea pigs were 

injected subcutaneously with 4-100 mg/kg of MBOCA. In the same study, treatment of rats with 

either phenobarbital or β-naphthaloflavone (BnF) resulted in induction of cytochrome P-450 as 

evidenced by increased enzymatic activity of two P-450 isozymes. This induction caused increased 

ortho-hydroxylation of MBOCA that was not statistically significant and resulted in the formation of 

various metabolites. Two of those MBOCA metabolites, n-hydroxy MBOCA and mononitrosoMBOCA, formed measurable amounts of adducts with both human and rat hemoglobin, while the 

amount of adducts formed by the parent compound itself was very small. This in vitro binding 

occurred in a dose-related manner and could be inhibited by cysteine and glutathione but not by 

oxidized glutathione or methionine (Chen et al. 1991). Therefore, the administration of MBOCA 

to rats resulted in a dose-related formation of hemoglobin adducts that were detectable 24 days after 

treatment. Similar observa tions were made in guinea pigs; the life span of MBOCA-hemoglobin 

adducts followed that of re cells in the guinea pig and was approximately 60-80 days. 

One of the major DNA adducts of MBOCA was identified by a combination of in vivo and in vitro 

studies (Silk et al. 1989). Male rat derived from a Wistar strain were injected intraperitoneally with 

89 μmol/kg of radioactive MBOCA or 141 μmol/kg of acetyl-MBOCA. Twenty-four hours later, 

animals were sacrificed, and their liver-DNA was extracted and analyzed for the amount of bound 

radioactivity and nature of adducts. Results,showed that the cleavage of the bond between the 

methylene bridge and one aromatic nucleus of MBOCA resulted in the formation of the major in vivo 

adduct N-(deoxyadenosine-8-yl)-4-amino-3-chlorobenzyl alcohol. Two other adducts also formed after 

intraperitoneal injection were not identified. In an attempt to further elucidate the DNA adduct 

formation, DNA was isolated from liver, lung, and kidney of 14C-MBOCA-treated Charles River CD 

rats and compared to in vitro N-hydoxy-MBOCA-treated rat DNA (Segerback and Kadlubar 1992). 
MBOCA 36
 

2. HEALTH EFFECTS
 

Rats were orally treated with 95 μmol/kg body weight of radiolabeled MBOCA and sacrificed 1, 3, 

7, and 21 days later. In both in vivo and in vitro experiments, two major peaks were identified 

containing two adducts: N-(deoxyadenosine-8-yl)-4-amino-3-chlorobenzyl alcohol and n­

(deoxyadenosine-S-yl)-4-amino-3-chlorotoluene. These two major peaks were present in both liver 

and kidney DNA samples. The results confirmed the existence of one adduct found in a similar study 

(Silk et al. 1989) and identified the second one. The study found that the binding of N-hydroxyMBOCA to DNA can be inhibited by ascorbic acid, glutathione, nitrosobenzene, and methyl viologen 

but not by nitromethane,p-nitrobenzylpyridine or methionine. The precise mechanism of single-ring 

MBOCA DNA adduct formation is still not completely understood because of the indication that 

there is an unstable intermediate formed prior to the formation of the two major identified DNA 

adducts and that single-ring MBOCA adducts were not readily detectable (Segerback and Kadlubar 

1992). 

There is some evidence that MBOCA itself may be a tumor promoter. MBOCA caused a statistically 

significant dose-dependent inhibition of gap-junctional cell communication (GJC) at doses ranging 

from 7.5 nmol/mL (noncytotoxic) to 15.5 nmol/mL (cytotoxic) (Kuslikis et al. 1991). Since GJC is 

important in controlling cell proliferation, and many known tumor promoters inhibit GJC, GJCinhibition 

assays have been proposed as short-term screens for promoters. 

2.4 RELEVANCE TO PUBLIC HEALTH 

Exposure to MBOCA contaminated soil or water at hazardous waste sites is possible via the oral or 

dermal routes. Inhalation and dermal exposure to this compound in air are less likely because 

MBOCA is not volatile. There is no information regarding the level that would be of concern to a 

population living in the vicinity. Occupational or accidental exposure may occur in industries using 

MBOCA as a curing agent in manufacturing processes. It is not known if MBOCA and/or its 

metabolites can be released from polyurethane (MBOCA is used as a curing agent for castable liquid 

polyurethane elastomers) (HSDB 1991; IARC 1974; Sax and Lewis 1987). 

Acute-duration exposure to high levels of MBOCA may cause eye and skin irritation in humans 

(Hosein and Van Roosmalen 1978). Intermediate and chronic exposures to MBOCA may lead to 

tumors of the urinary bladder. Of 200 occupationally exposed workers, 3 were found to have urinary 

bladder tumors (Ward et al. 1990). This finding is supported by results obtained in dogs (Stula et al. 

1977). Results in other animal species also show that MBOCA is a potential carcinogen and that 

other target organs include the lung, liver, breast, and Zymbal’s gland in rats (Kommineni et al. 1978; 

Russfield et al. 1975; Stula et al. 1975) and lung, liver, and vascular system in mice (Russfield et al. 

1975). It is not possible to estimate if these tumors would be of concern to humans since there is 

no information available. 

Limited information indicates that MBOCA is rapidly absorbed in humans and that the amount 

absorbed through skin and inhalation is in proportion to the dose (Chin et al. 1983; Cocker et al 

1988, 1990; Ichikawa et al. 1990; NIOSH 1986b). No information is available regarding distribution 

and rate of metabolism in humans. However, toxicokinetic data obtained in animals indicate that 

MBOCA is rapidly absorbed, distributed, and excreted within 24-48 hours (Farmer et al. 1981; Groth 

et al. 1984). The bioaccumulation of MBOCA is unlikely because of its rapid metabolism and urinary 

excretion. Of potential concern, however, is the fact that MBOCA readily forms adducts with body 

proteins and DNA. Studies in rats and guinea pigs suggest that MBOCA-hemoglobin adducts have 

a biological life similar to that of red blood cells and may remain in the body for many weeks. 
MBOCA 37
 

2. HEALTH EFFECTS
 

No information was located regarding reproductive or developmental effects in humans or animals. 

There is no information in humans regarding MBOCA retention or any delayed effects. Information 

on the effects of exposure to MBOCA in humans comes from case reports of accidentally or 

occupationally exposed workers in manufacturing facilities. In one such study, low-grade papillary 

tumors of the urinary bladder were observed in 3 out of 200 workers more than 8 years following 

occupational exposure to MBOCA (Ward et al. 1990). Studies in progress include assessing the 

incidence of bladder carcinomas in workers occupationally exposed to MBOCA and the role of 

adducts in MBOCA-induced carcinogenicity (see Section 2.93). Animal studies support the 

hypothesis that MBOCA and/or its metabolites have carcinogenic potential. MBOCA metabolites 

bound to DNA were found following oral (Cheever et al. 1990; Kugler-Steigmeier et al. 1989) or 

dermal (Cheever et al. 1990) exposures in rats. 

No studies were located regarding the genotoxicity of MBOCA in humans in vivo. Results from in 

vivo animal studies support the conclusion that MBOCA is a mutagen; mixed results from some assays 

can probably be attributed to incomplete testing. 

Minimal Risk Levels for MBOCA 

Inhalation MRL3 

No inhalation MRLs have been derived for any duration of exposure because of lack of data. 

Oral MRL8 

No acute-duration oral MRL has been derived because of lack of data. 

No intermediate-duration oral MRL has been derived because of lack of data. 

An MRL of 0.003 mg/kg/day has been derived for chronic-duration oral exposure to MBOCA. This 

is based on a LOAEL of 10 mg/kg/day for hepatic effects in dogs (Stula et al. 1977). 

Death. no increased mortality from any cause has been reported in humans who have been exposed 

to MBOCA. Decreased lifespan was observed in rats following chronic oral exposure to MBOCA 

(Kommineni et al. 1979). Data are insufficient to assess the effects that prolonged exposure to 

MBOCA may have on populations that are potentially at risk. 

Systemic Effects 

Respiratory Eflects. no data are available regarding adverse effects of MBOCA on the respiratory 

tract in humans. 

Lung adenomatosis, a preneoplastic lesion, was observed in rats following chronic oral exposure to 

25 or 50 mg/kg/day of MBOCA (Russfield et al. 1975). MBOCA may induce changes in the lungs 

that can progress to cancerous lesions. Since information on respiratory effects following exposure 

to MBOCA is limited, the impact of findings in animals on public health is difficult to assess. For 

more information, see the discussion of Cancer, below, in this section. 

Gastrointestinal Eficts. Extremely limited information is available regarding adverse gastrointestinal 
MBOCA 38
 

2. HEALTH EFFECTS
 

effects in humans after exposure to MBOCA. A worker complained of feeling ill in the stomach 

after being sprayed in the face with molten MBOCA (Hosein and Van Roosmalen 1978). No further 

information was given on his condition or the level of exposure. Evidence is insufficient to assess the 

relevance of this finding to public health. 

Hematological Eflcts. no information is available regarding adverse hematological effects in humans 

after exposure to MBOCA. 

However, no changes in hemoglobin, hematocrit, erythrocyte, or mononuclear leukocyte counts were 

observed in beagle dogs following 9 years of exposure to MBOCA (Stula et al. 1977). This study is 

of limited usefulness because blood analysis was done only twice a year, so that changes between 

analyses were probably not recorded. The significance of this finding with regard to human health 

cannot be assessed. 

Hepatic Eficts. no information was located in humans regarding adverse hepatic effects following 

exposure to MBOCA. 

Hepatic effects such as elevated liver enzyme levels, nodular hepatic hyperplasia, fatty changes, 

necrosis, fibrosis, and bile duct proliferation were observed in rats and dogs following chronic 

exposure to MBOCA (Stula et al. 1975, 1977). Chronic exposures to high levels of MBOCA at 

hazardous waste sites may induce similar adverse hepatic effects. 

Renal Effects. Following an acute exposure in which a worker was sprayed in the face with molten 

MBOCA, protein was detected in the urine within the first 5 hours after exposure, suggesting that 

damage to renal tubules occurred (Hosein and Van Roosmalen 1978). Damage to the renal tubules 

was also indicated by a decrease in specific gravity of the urine collected the next day. Although the 

amount of MBOCA to which the worker was exposed was not known, it may have been substantial, 

since the urine MBOCA level was 3.6 mg/L 5 and 11 hours after the incident. It is unknown whether 

exposure to these high levels would occur at hazardous waste sites. In another study, exfoliative 

cytology revealed that 21 out of 385 urine samples collected from workers exposed to MBOCA 

contained atypical cells in urine sediment (Ward et al. 1990). None of the cytology readings were 

positive for cancer. Sixteen out of the 385 urine samples were positive for heme (Ward et al. 1990). 

The median duration of employment was 3.2 months. Although this study is limited because it lacks 

information on exposure levels, it is important because it alerted the medical community to the 

inadequacies of the procedures normally used following MBOCA exposure. Since one of the 

participants (who had negative cytology and was negative for heme) was diagnosed with a low-grade 

papillary tumor of the bladder, cystoscopy was introduced as a part of the follow-up procedure for 

workers exposed to MBOCA, and two additional cases of bladder tumors were detected subsequently. 

Therefore, exposure to MBOCA at hazardous waste sites may cause renal damage that may lead to 

cancer. 

Studies on chronic exposure of dogs to MBOCA support the findings in humans (Stula et al. 1977). 

In dogs treated orally with an average of 10 mg/kg/day of MBOCA for 9 years, urine sediment 

cytology revealed dysplastic changes indicative of neoplasia of the genitourinary system. 

Dermal/Oculur Effects. Burning of the face and eyes developed shortly after a worker was accidentally 

sprayed with molten MBOCA (Hosein and Van Roosmalen 1978). He was wearing gloves and safety 

glasses but no respirator or face shield. A similar burning sensation was described by a worker who 

was also accidentally sprayed over his upper body and extremities with molten MBOCA (Osorio et 
MBOCA 39
 

2. HEALTH EFFECTS
 

al. 1990). The general population is not likely to be involved in such exposures at hazardous waste 

sites. However, in cases of occupational accidents, exposure to MBOCA may cause adverse 

dermaliocular effects. 

Immunological Effects. no studies were located in humans or animals regarding immunological 

effects following exposure to MBOCA. 

Neurological Effects. no studies were located regarding adverse neurological effects in humans 

after exposure to MBOCA by any route. 

Cystic hyperplasia of the pituitary gland was found in one out of six dogs after 8.3 years of MBOCA 

exposure (Stula et al. 1977). This change was considered to be unrelated to chronic MBOCA 

treatment. It is difficult to predict if analogous effects would occur in individuals or populations living 

near hazardous waste sites. 

Reproductive Effects. no studies were located regarding reproductive effects in humans or animals 

following exposure to MBOCA. 

Developmental Effects. no studies were located regarding developmental effects in humans or 

animals after exposure to MBOCA. 

Genotoxic Effects. no studies were located regarding the genotoxicity of MBOCA in humans in 

vivo. 

In vivo animal studies provide direct and indirect evidence that MBOCA is a mutagen; MBOCA 

metabolites were bound to DNA following oral (Cheever et al. 1990; Kugler-Steigmeier et al. 1989) 

or dermal (Cheever et al. 1990) exposure in rats. Small increases in the SLRL values were observed 

in D. melanogaster adults fed a 7.5millimolar MBOCA solution for 3 days (Vogel et al. 1981). 

MBOCA induced gene mutations at the thymidine kinase (TK) locus in mouse lymphoma cells 

(Caspary et al. 1988; Myhr and Caspary 1988). Unscheduled DNA synthesis (UDS) was induced in 

HeLa cells (Martin and McDermid 1981), in rat primary hepatocytes at >10 μmol (McQueen et al. 

1981; Mori et al. 1988; Williams et al. 1982) and in hamster (McQueen et al. 1981) and rabbit 

(McQueen and Williams 1987) hepatocytes. The concentration that tested positive in the mouse was 

50 μmol (McQueen et al. 1981). Sensitivity to MBOCA showed species-specific variations: rat > 

mouse > hamster > rabbit (McQueen et al. 1981, 1983). Because hepatocytes have their own 

metabolic activation systems, no exogenous metabolic activation is needed. In assays using attachment 

independence as an end point, MBOCA, at concentrations near the LC50, transformed baby hamster 

kidney (Daniel and Dehnel 1981; Styles 1981), rat embryo (Dunkel et al. 1981; Traul et al. 1981), and 

Balb/3T3 cells (Dunkel et al. 1981). Transformation assays have not been evaluated as thoroughly 

as some other genotoxicity assays. In an interlaboratory comparison, one laboratory found equivocal 

evidence that nonactivated MBOCA induced sister chromatid exchange in Chinese hamster ovary cells 

at a dose of 5.0 μg/mL. The response is considered equivocal because the dose-response curve was 

inconsistent. The result was not confirmed by the second laboratory. In the presence of S9 

activation, positive results were obtained by one laboratory at 50 μg/mL. The other laboratory 

observed the beginning of a dose-response curve, but the high-dose (30 μg/mL) results did not meet 

the testing laboratory’s criterion for a positive response. In a chromosome aberration assay testing 

activated and nonactivated concentrations up to 5 and 30 μg/mL, respectively, neither laboratory 

found a positive result (Galloway et al. 1985). Another study (Perry and Thomson 1981) found no 
MBOCA 40
 

2. HEALTH EFFECTS
 

evidence of sister chromatid exchange at up to cytotoxic doses (100 μg/mL), but no doses were tested 

in the probable sensitive range (>10 and <100 μg/mL). Thus, MBOCA is clastogenic in some 

systems but not others. 

In another study, MBOCA was classified as a clastogen on the basis of results from an in viva 

micronucleus bone marrow assay (Katz et al. 1981). Evaluations using a two-phase micronucleus 

assay and intraperitoneal dosing of B6C3F1 hybrid mice were incomplete, but the results suggested 

that MBOCA is an in viva clastogen at doses of >32 mg/kg ( Sa amone et al. 1981) or 50% of the 1 

LD50 (Katz et al. 1981). Results were inconclusive because of toxicity during the first phase of 

testing in which mice were dosed at 0 and 24 hours with 80% of the LD50 (51 mg/kg), and results 

were evaluated at 48 hours. In the second phase of testing, mice were dosed with 32 or 51 mg/kg 

and sampled 48 hours later, or in a separate test, dosed with 32 or 48 mg/kg and sampled 36 hours 

later. Results were negative at 32 mg/kg when sampled at 48 hours but positive at the same dose in 

a separate assay when sampled at 36 hours. Results were positive at the higher dose for both 

sampling times. Multiple sampling times were not performed in any assay (Salamone et al. 1981). 

In another study, results in the micronucleus test were negative at doses up to 50% of the LD50 (32 

mg/kg) using CD-1 mice (dosing was done intraperitoneally at 0 and 24 hours and sampling at 

30 hours) (Tsuchimoto and Matter 1981). Results from in viva testing are summarized in Table 2-2. 

There is some evidence that MBOCA itself may be a tumor promoter. MBOCA caused a statistically 

significant dose-dependent inhibition of gap-junctional cell communication (GJC) at doses ranging 

from 7.5 nmol/mL (noncytotoxic) to 15.5 nmol/mL (cytotoxic) (Kuslikis et al. 1991). Since GJC is 

important in controlling cell proliferation, and many known tumor promoters inhibit GJC, GJCinhibition 

assays have been proposed as short-term screens for promoters. 

There is some evidence that MBOCA itself may be a tumor promoter. MBOCA caused a statistically 

significant dose-dependent inhibition of gap-junctional communication (GJC) at doses ranging from 

7.5 nmol/mL (noncytotoxic) to 15.5 nmol/mL (cytotoxic) (Kuslikis et al. 1991). Since GJC is 

important in controlling cell proliferation, and known tumor promoters inhibit GJC, GJC-inhibition 

assays have been proposed as short-term screens for promoters. The use of GJC-inhibition assays 

in individuals living in the vicinity of hazardous waste sites would provide needed information for 

better understanding of potential control of the tumor initiation process. 

In vitro testing has provided clear and convincing evidence that MBOCA is mutagenic in the 

Salmonella typhimurium/mammalian microsome mutagenesis assay and that the mutagenic effect 

requires exogenous metabolic activation (Baker and Bonin 1981; Cocker et al. 1985; Dunkel et al. 

1984; MacDonald 1981; Martire et al. 1981; McCann et al. 1975; Messerly et al. 1987; Rao et al. 

1982). Although not all investigators used each tester strain, the general result is that MBOCA is 

mutagenic only in strains TA98 and TA100, at 250 μg/plate, with some inconsistency regarding strain 

TA98. MBOCA and its metabolites are not mutagenic in S. typhimurium strains TA1535, TA1537, 

or TA1538. This suggests that the mutagenic effect of MBOCA metabolites in some bacteria is 

dependent on the plasmid pKM101; strains TA98 and TA100 contain this plasmid, but strains 

TA1535, TA1537, and TA1538 do not (Ames et al. 1975). This hypothesis is supported by the finding 

that S9-activated MBOCA is mutagenic in Escherichia coli strain WP2uvrA only in the presence of 

the plasmid pKM101 (Matsushima et al. 1981). The plasmid carries genes involved in an “errorprone” 

DNA repair system that introduces mutations as it removes DNA damage (Walker 1984). S9 

derived from dog and human liver could activate MBOCA to a form mutagenic to strain TA100 but 

only in a protocol using a fluctuation assay (Cocker et al. 1985). These data are presented in Table 





MBOCA 46
 

2. HEALTH EFFECTS
 

Most of MBOCA’s mutagenic activity appears to be due to the N-hydroxy metabolite, which caused 

dose-dependent increases in mutations of S. typhimurium strains TA100 and TA98 in a pre-incubation 

assay using nonactivated doses of ≥5 μg/plate (Kuslikis et al. 1991). This metabolite is produced by 

several species, including dogs and humans (Butler et al. 1989; Chen et al. 1989; Morton et al. 1988). 

The mononitroso derivative appears to be direct-acting mutagen but is much less potent, causing a 

statistically significant revertant increase in the pre-incubation assay at the highest tested nontoxic 

dose (50 μg/plate). neither the o-hydroxy nor the dinitroso derivatives were direct-acting mutagens 

at up to 50 or 500 μg/plate, respectively. neither chemical was tested to cytotoxic levels (Kuslikis et 

al. 1991). N-acetylation is a deactivating step. neither n-acetyl nor N,N-diacetyl derivatives were 

mutagenic in S. typhimutium in the absence of activation (Hesbert et al. 1985). In the presence of 

S9 activation, the mutagenic activity of the acetylated derivatives is less than that of the parent 

compound (Cocker et al. 1986; Hesbert et al. 1985). 

DNA adducts have been found following oral (Cheever et al. 1990; Kugler-Steigmeier et al. 1989; 

Segerback and Kadlubar 1992) and dermal (Cheever et al. 1990) administration of radiolabeled 

MBOCA to rats, following the incubation of radiolabeled MBOCA with explants of dog and human 

bladder urothelium (transitional cell epithelium) (Stoner et al. 198) and incubation of rat DNA and 

radiolabeled N-hydroxy-MBOCA (Segerback and Kadlubar 1992). The level of binding increased 

with dose, but the increase was not linear. Considerable individual variation in binding levels, varying 

over at least a 10-fold range, was found in both dogs and humans. At least six adducts were found 

in dog bladder epithelium; four adducts were found in human bladder epithelium, three of which 

appeared to be the same as those found in dogs. DNA adduct formation in dog bladder tissue is of 

particular note, since MBOCA has been found to cause bladder tumors in dogs (Stula et al. 1977). 

The in vivo and in vitro studies identified two other major rat DNA MBOCA adducts, n­

(deoxyadenosin-8-yl)-4-amino-3-chlorobenzyl alcohol and N-(deoxyadenosin-8-yl)-4-amino-3 

chlortoluene (Segerback and Kadlubar 1992). The finding of DNA adducts in human bladder tissue 

suggests similar processes may occur in humans. 

Intraperitoneal injection into rats of ring-labeled MBOCA, or ring-labeled N-acetylated MBOCA, 

resulted in the generation of three DNA adducts (Silk et al. 1989). Two of these adducts were also 

produced by the in vitro reaction of the N-hydroxy derivative of MBOCA with rat liver slices. The 

major product of this reaction was also formed following incubation of DNA with n-hydroxy-4-amino3-chlorobenzyl alcohol, the compound resulting from cleavage of the methylene bridge of N-hydroxy 

MBOCA. While the single ring species appears to be an intermediate in the formation of the DNA 

adduct, it is not known whether N-hydroxylation or bridge cleavage occurs first in the formation of 

the reactive species. The DNA adduct was analytically identified as N-(deoxyadenosin-8-yl)-4-amino3-chlorobenzyl alcohol. 

Cancer. Since MBOCA has been suspected of being a human carcinogen, epidemiological studies 

have examined the incidence of cancer in workers exposed to MBOCA. Three out of 200 examined 

workers exposed to MBOCA for an average of 3.2 months were found to have low-grade papillary 

tumors of the urinary bladder (Ward et al. 1990). The latency period for most bladder cancers is 

about 20 years; therefore, the detection of bladder tumors in this study 11.5 years (mean latency 

period for the entire cohort) after first exposure to MBOCA provides suggestive evidence that 

MBOCA is a suspected human carcinogen. Two of the men affected with bladder tumors were less 

than 30 years old. Since it is known that the occurrence of bladder tumors in young men is very 

uncommon, this finding increases the concern that MBOCA has a potential for causing bladder 

tumors in humans. However, there was no evidence of recurrent bladder lesions in the above cases 

after the initial discovery. It is also difficult to estimate the biological and statistical significance of 
MBOCA 47
 

2. HEALTH EFFECTS
 

these bladder lesions because of the small sample size. One important outcome of this study is the 

introduction of cystoscopy as a part of the monitoring protocol for workers exposed to MBOCA. The 

limitation of the study is that there are no data on bladder cancer incidence diagnosed by cystoscopy 

in an asymptomatic nonexposed (control) population. The importance of biological monitoring 

programs was also evident in the occupational study/review of urinary free MBOCA levels in workers 

from PMA member companies (Lowry and Clapp 1992). The data have been collected for over 15 

years, and the study summarized them for 1985-1990. The analysis of 7,844 urine samples confirmed 

that after the introduction of biological monitoring it was possible to reduce the urinary MBOCA 

levels by using effective exposure control and protection in the workplace. The reduced percentage 

of samples containing >50 μg/L of MBOCA (from 12% in 1985 to 8% in 1990) and increased 

percentage of urine samples with <25 μg/mL (from 77% in 1985 to 86% in 1990) further supported 

the importance of biological urinary MBOCA monitoring. 

The probable carcinogenicity of MBOCA has been a concern for some time. In 1972, the British 

rubber industry imposed upon itself a ban on the use of MBOCA because it was a suspected human 

carcinogen (Parkes 1979). The initiation of a biological monitoring program that would examine 

exposure levels and help establish Environmental or other pertinent controls as preventive measures 

has also been suggested (Ward et al. 1986). This biomonitoring program would also maintain a 

system to follow the workers exposed to MBOCA in order to detect possible neoplastic changes and 

initiate treatment. 

Chronic exposure studies in animals support the findings in humans. The main target organs for 

cancer development were the urinary bladder, lungs, liver, and breasts. The urinary bladder was a 

target organ in beagle dogs fed MBOCA for 9 years; three of the five surviving dogs developed 

papillary transitional cell carcinoma of the urinary bladder; another dog had a combined urethral 

adenocarcinoma and transitional cell carcinoma (Stula et al. 1977). This study, in spite of the use of 

a small number of animals, shows that the ingestion of MBOCA over 9 years was associated with the 

incidence of carcinomas of the urinary bladder and urethra. Several other chronic exposure studies 

in rats demonstrate the ability of MBOCA to cause lung cancer (Kommineni et al. 1979; Stula et al. 

1975). A significant increase in the incidence of liver tumors after chronic exposure to MBOCA was 

found in rats (Kommineni et al. 1979; Russfield et al. 1975) and in female mice (Russfield et al. 

1975). The rats fed MBOCA for 2 years had an increased incidence of mammary adenocarcinomas 

(Kommineni et al. 1979). Other tumor types were also observed after chronic oral administration of 

MBOCA. The incidence of hemangiosarcomas was 8% in rats (Kommineni et al. 1979); vascular 

tumors were present in male random-bred albino mice (Russfield et al. 1975); and hemangiosarcomas 

were present in both male and female mice (Russfield et al. 1975). Tumor incidence was affected 

by gender in mice; no data regarding gender specificity are available for rats or dogs. 

The precise mechanism of action of MBOCA is not completely understood, but it is thought that in 

some instances it involves the formation of chemical adducts in the genetic material through covalent 

binding of nucleophilic sites by electrophilic compounds or activated metabolites (Cheever et al. 

1991). Therefore, it seems that the capacity of MBOCA to form adducts with tissue DNA (Cheever 

et al. 1990), hemoglobin (Cheever et al. 1990, 1991; Sabbioni and neumann 1990) and globin and 

serum albumin (Cheever et al. 1991) in rats may play a role in its toxicity and carcinogenicity. The 

adduct formation is especially important in elucidating the carcinogenicity of MBOCA. It was 

recently proposed that chemical carcinogenesis may involve the formation of chemical adducts in 

DNA through covalent binding based on the fact that MBOCA produces DNA adducts in rat liver 

at levels characteristic of genotoxic carcinogens (Kugler-Steigmeier et al. 1989). Since it is known 

that MBOCA can bind to rat liver DNA (Cheever et al. 1990) and that liver is one of the primary 
MBOCA 48
 

2. HEALTH EFFECTS
 

target organs for development of tumors after exposure of rats to MBOCA (Kommineni et al. 1979; 

Russfield et al. 1975), it may be assumed that MBOCA-DNA adducts play a role in the development 

of tumors. Further support for the carcinogenic potential of MBOCA comes from the study showing 

that MBOCA binds to DNA from human and dog urinary bladder tissue (Shivapurkar et al. 1987). 

The mouse skin assay was used in one study to evaluate the carcinogenicity of MBOCA in the 

presence of 12-o-tetradecanoylphorbol-U-acetate (TPA) as a tumor promoter (nesnow et al. 1985). 

SEnCAR mice were exposed to 0, 0.1, 1, 10, 100, or 200 mg of MBOCA and 1 week later to 2 μg 

of TPA biweekly for 26 weeks. No mouse skin papillomas were observed at any dose level, but the 

authors stressed that this finding was based on the limited dose levels tested in the study. There are 

several limitations to this study; it was not clear if TPA was administered to control animals, if 

MBOCA was applied to shaved skin, or if was the area was protected after treatment; in addition, 

no other parameters aside from tumor initiation were examined during the 26-week period. 

There is some evidence that MBOCA itself may be a tumor promoter. MBOCA caused a statistically 

significant dose-dependent inhibition of GJC at doses ranging from 7.5 nmol/mL (noncytotoxic) to 

15.5 nmol/mL (cytotoxic) under in vitro conditions (Kuslikis et al. 1991). Since GJC is important in 

controlling cell proliferation, and known tumor promoters inhibit GJC, GJC-inhibition assays have 

been proposed as short-term screens for promoters. The use of GJC-inhibition assays in individuals 

living in the vicinity of hazardous waste sites would provide needed information for better 

understanding of potential control of the tumor initiation process. 

2.5 BIOMARKERS OF EXPOSURE AND EFFECT 

Biomarkers are indicators of events in biologic systems. They have been classified as markers of 

exposure, markers of effect, and markers of susceptibility (NAS/NRC 1989). 

A biomarker of exposure is a xenobiotic substance or its metabolite(s), or the product of an 

interaction between a xenobiotic agent and some target molecule(s) or cell(s) that is measured within 

a compartment of an organism (NAS/NRC 1989). Preferred exposure biomarkers are either the 

substance proper or substance-specific metabolites in readily obtainable body fluid(s) or excreta. 

Several factors may confound the use and interpretation of exposure biomarkers: (1) the body 

burden of a substance may represent more than one exposure; (2) the substance being measured may 

be the metabolite of another substance (e.g., high levels of phenol in urine can result from exposure 

to several different aromatic compounds). Depending on the substance’s properties (e.g., biologic 

half-life), and exposure conditions (e.g., duration and route of exposure), the substance and 

metabolites may have left the body by the time samples are collected. Individuals exposed to 

hazardous substances that are commonly found in body tissues and fluids (e.g., essential mineral 

nutrients such as copper, zinc, and selenium) may be difficult to identify. Biomarkers of exposure to 

MBOCA are discussed in Section 2.5.1. 

Biomarkers of effect are defined as any measurable biochemical, physiologic, or other alteration 

within an organism that, depending on magnitude, can be recognized as an established or potential 

health impairment or disease (NAS/NRC 1989). Biochemical or cellular signs of tissue dysfunction 

and physiologic alterations are included within this definition. note that these markers are often not 

substance specific. Biomarkers of effect(s) may indicate potential health impairment(s) (e.g., DNA 

adducts). Biomarkers of effects caused by MBOCA are discussed in Section 2.5.2. 
MBOCA 49
 

2. HEALTH EFFECTS
 

A biomarker of susceptibility may indicate an inherent or acquired limitation of an organism’s ability 

to respond to the challenge of exposure to a specific xenobiotic substance. It can be either an 

intrinsic genetic characteristic, a preexisting disease that results in greater absorbed dose, a decrease 

in the biologically effective dose, or a target tissue response. If biomarkers of susceptibility exist, they 

are discussed in Section 2.7, Populations That Are Unusually Susceptible. 

2.5.1 Biomarkers Used to Identify or Quantify Exposure to MBOCA 

Exposure to MBOCA has commonly been determined by measuring levels of MBOCA or its 

metabolites in urine. no information on quantifiable dose threshold levels in humans was located. 

Since MBOCA is rapidly metabolized, its presence in urine indicates recent exposure. MBOCA is 

rapidly biodegraded and converted to its glucuronide conjugates. Since varying levels of 

β-glucuronidase are present in urine, it may be difficult to determine accurate levels of MBOCA in 

the urine. Following administration of radiolabeled MBOCA to rats (Farmer et al., 191; Groth et 

al., 1984) and dogs (Manis et al. 1984b), less than 2% and l%, respectively, of the radioactivity 

recovered in urine was unmetabolized MBOCA. The biologic half-life of MBOCA in blood following 

intravenous exposure was estimated to be 0.70 hours; the levels of MBOCA found in various organs 

24 hours after dermal exposure were relatively small (Manis et al. 1984). Measuring the metabolites 

of MBOCA, therefore, would be useful surrogate exposure biomarkers. 

Male and female CD rats treated with 44 or 58 mg/kg of radiolabeled MBOCA by gavage had 

o-glucuronide and o-sulfate MBOCA conjugates in urine; the mono-N-glucuronide was the major 

biliary metabolite 24 hours after treatment (Morton et al. 19SS). After a single oral dose of 75 mg/kg, 

MBOCA formed adducts with globin and liver DNA in Sprague-Dawley rats (Cheever et al. 1988). 

The half-lives for rat globin and liver DNA were estimated to be 14 and 11 days, respectively. An 

o-hydroxysulfate,identifiedas5-hydroxy-3,3’-dichloro-4,4’-diamino-diphenylmethane-5-sulfate,wasthe 

major metabolite found in dog urine. This metabolite also formed adducts with DNA in vitro in a 

time-dependent manner (Manis and Braselton 1984). Studies in rats and guinea pigs have 

demonstrated MBOCA adducts to hemoglobin (Chen et al. 1991; Sabboioni and newmann 1990), 

with a disappearance rate that approximates the life of a red blood cell. These study results suggest 

that MBOCA adducts may be useful biomarkers to monitor MBOCA exposure. 

The levels of MBOCA have not been determined in chronic animal studies. It is unknown if chronic 

sequestering and low-level release of MBOCA, resulting in steady state levels, occur. 

2.5.2 Biomarkers Used to Characterize Effects Caused by MBOCA 

The available information suggests that the bladder is a target organ for MBOCA-induced 

carcinogenesis. Medical surveillance of occupationally exposed workers, currently in progress, may 

help to ascertain the incidence of MBOCA-induced bladder cancer. Cystoscopy may help identify 

new biomarkers and characterize early preneoplastic changes in the bladder. 

The ability of MBOCA to covalently bind to body proteins has been less frequently used to estimate 

exposure to MBOCA. MBOCA is known to bind to globin (Cheever et al. 1991). Therefore 

measurement of MBOCA-globin adducts could be used to monitor MBOCA exposure since the halflife 

of MBOCA-globin adducts is greater than the half-life of MBOCA. Section 2.2 contains more 

detailed information on adverse effects of MBOCA. Additional information can be obtained from 

the CDC/ATSDR (CDC/ATSDR 1990) and Office of Technology Assessment (OTA 1990) reports 

listed in Chapter 8. 
MBOCA 50
 

2. HEALTH EFFECTS 

2.6 INTERACTIONS WITH OTHER CHEMICALS 

Limited information was located on the interactive effects of other chemicals on MBOCA toxicity. 

MBOCA metabolism is influenced by phenobarbital (Chen et al. 1991; Morton et al. 1988). In vivo 

treatment with phenobarbital induced cytochrome P-450 enzymes which resulted in a slight increase 

in MBOCA hydroxylation (Chen et al. 1991). Rats treated with phenobarbital had a 4-8-fold 

increased metabolic rate for MBOCA (Morton et al. 19%). Phenobarbital did not, however, affect 

adduct formation (Chen et al. 1991). In vivo treatment with P-naphthoflavone did increase the rate 

of MBOCA-hemoglobin adduct formation in rats treated subcutaneously with either 100 or 

500 mg/kg/day (Chen et al. 1991). MBOCA metabolism is NADPH-dependent. Moreover, MBOCA 

hydroxylation is inhibited by 2,4-dichloro-6-phenylphenoxyethylamine, an inhibitor of microsomal 

mixed function oxidases (Chen et al. 19S9). Cysteine and glutathione inhibit in vivo hemoglobin 

adduct formation by N-hydroxy-MBOCA and mononitroso-MBOCA (Chen et al. 1991). The most 

recent findings suggest that binding of N-hydroxy-MBOCA to DNA in rat tissues can be inhibited by 

ascorbic acid, glutathione, nitrosobenzene, and methyl viologen but not by nitromethane, pnitrobenzylpyridine, or methionine (Segerback and Kadlubar 1992). 

2.7 POPULATIONS THAT ARE UNUSUALLY SUSCEPTIBLE 

A susceptible population may have a heightened response to MBOCA compared with the general 

population. A population’s susceptibility may be determined by their genetic make-up, developmental 

stage, age, health and nutritional status (including dietary habits that may increase susceptibility, such 

as inconsistent diets or nutritional deficiencies), and substance exposure history (including smoking). 

These unique characteristics could result in a decreased ability to detoxify and excrete the xenobiotic 

material and metabolites (mainly hepatic, renal, and respiratory). We expect that the elderly, (with 

declining organ function), and infants and children with immature and developing organs, may be 

more susceptible to the effects of toxic substance exposure(s) than healthy adults. Populations at 

greater risk because of their atypically high exposures are discussed in Section 5.6, Populations With 

Potentially High Exposure. 

Differences in species sensitivity to MBOCA have been explored in vitro and in vivo studies. In 

one study examining the DNA adduct formation in human bladder explant cultures, there was a 

distinct difference in the sensitivity to MBOCA (Stoner et al. 198%). Results showed that some 

cultures had much higher levels of MBOCA binding to bladder epithelium than did others. These 

findings suggest that some individuals are likely to develop more damage from MBOCA exposure 

than others. This could be an important consideration in cases of occupational exposure to 

MBOCA. Another observation concerns the cytochrome P-450 family of enzymes. It is known that 

profiles of cytochromes P-450, enzymes that play an essential role in detoxification of MBOCA, vary 

from one individual to another (Butler et al. 1989). Consequently, the rates of MBOCA metabolism 

may vary significantly among the population because of these differences in individual profiles of 

cytochrome P-450. The ability of a person to acetylate may also be of importance since it is well 

established for benzidine that this ability is directly related to the genotoxicity and carcinogenicity of 

the compound. 

An indication of DNA adduct formation following acute exposure to MBOCA was found in 

autoradiographs of postlabeled liver DNA from exposed rats (Endo and Hara 1991). Compared to 

control, the relative adduct level (RAL) was considerably higher in experimental samples than 

controls. However, further studies are needed to identify these rat liver DNA adducts. In an attempt 

to elucidate the DNA adduct formation, DNA was isolated from liver, lung, and kidney of 14C­
MBOCA 51
 

2. HEALTH EFFECTS
 

MBOCA-treated rats and compared to in vitro N-hydoxy-MBOCA-treated rat DNA (Segcrback and 

Kaclluhar 1992). In both casts, two major peaks wcrc identified containing two adclucts: n­

(deoxyadenosinc-8-yl)-4-amino-3-chlorobenzyl alcohol and N-(deoxyadenosine-8-yl)-4-amino-3­

chlorotoluene. Although the study found that the binding of N-hydroxy-MBOCA to DNA can be 

inhibited by ascorbic acid, glutathione, nitrosobenzcne, and methyl viologen (but not by nitromethane. 

p-nitrobcnzylpyridine, or met hionine), the precise mechanism of single-ring MBOCA DNA adduct 

formation is not completely understood. Gluthatione (GSH) has also been shown to protect against 

hemoglobin adduct formation with oxidized MBOCA metabolites (Chen et al. 1991). Individuals with 

lowcrcd GSH levels brought about by oxidative stress or excessive exposure to GSH depleting 

xenobiotics (such as acetaminophen) could also be at increased risk following MBOCA exposure. 

More studies are needed to understand the mechanism and the intermediaries in the DNA adduct 

formation. In the cast of MBOCA, acetylation was not related to genotoxicity (McQueen et al. 

1983). In a study performed in rabbits, the genotoxic response to MBOCA varied considcrnbly; the 

net number of radioactive grains per nucleus in individual rabbits ranged from 0 to 13.7. 

Factors such as these may partially inlluence individual susceptibilities to MBOCA-induced 

carcinogcnicity. Other populations that may show increased sensitivity include very young children 

who have an immature hepatic detoxification system and individuals with impaired liver or kidney 

function. 

Workers in MBOCA manufacturing facilities have a higher risk because of their higher-level 

exposures to MBOCA. Worker exposure occurs primarily through inhalation and dermal contact. 

Other populations with higher risk are those that live near these facilities (if releases are not 

controlled) and family members of exposed workers (because contamination of the household occurs 

as a result of clothing) (Willams 1979). 

2.8 METHODS FOR REDUCING TOXIC EFFECTS 

This section will describe clinical practice and research concerning methods for reducing toxic effects 

of exposure to MBOCA. However, because some of the treatments discussed may be experimental 

and unproven, this section should not be used as a guide for treatment of exposure to MBOCA. 

When specific exposures have occurred, poison control centers and medical toxicologists should be 

consulted for medical advice. 

2.8.1 Reducing Peak Absorption Following Exposure 

No information has been located regarding specific treatment of humans or animals following 

exposure to MBOCA other than removal from the source of exposure. However, as in cases of most 

toxic exposures, supportive therapy dealing with symptoms is recommended. These supportive 

therapies include the monitoring of vital functions, as well as electrocardiographic monitoring, 

observation of vital signs, the intake and output of fluids, body temperature, and possibly pulmonary 

wedge pressure if indicated (HSDB 1991). Of special importance in minimizing absorption is the 

selection of protective clothing and gloves. The permeability of tight commercially available glove 

materials to methanolic solutions of aromatic amines was tested (Weeks and Dean 1977). The results 

indicate that there are considerable differences in the permeability of tested materials. Natural latex 

seemed to be most protective for 9.8 mg/mL MBOCA (1.0 weight percent) in methanol (Weeks and 

Dean 1977). The recommendation of how frequently the gloves should be changed will depend on 

the specific situation. The results of the study show that penetration of the glove material by the 

MBOCA solution was concentration dependent, and that highly concentrated MBOCA (9.8 mg/mL) 
MBOCA 52
 

2. HEALTH EFFECTS
 

penetrated the gloves within 2 hours, while MBOCA at a relatively low concentration did not 

penetrate for 35 hours (Weeks and Dean 1977). Biological monitoring of workers occupationally 

exposed to MBOCA is a preventive measure that can reduce potential toxic and carcinogenic effects. 

Among the other recommended procedures are monitoring MBOCA air levels and urinary MBOCA 

levels, doing wipe tests to check surface contamination that can potentially lead to skin exposure 

(Clapp et al. 1991; Lowry and Clapp 1992), and considering the performance of cystoscopy in exposed 

workers for early detection of bladder tumors (Mason and Volger 1990; Ward et al. 1990). 

Continued education of the work force about potential work hazards is also important (NIOSH 

1986b). 

2.8.2 Reducing Body Burden 

MBOCA is not retained by the body since the majority of the compound is excreted within 

24-48 hours after exposure (Hosein and Van Roosmalen 1978). The biological half-life of MBOCA 

in the urine was estimated at approximately 23 hours in a case of an accidental exposure (NIOSH 

1986a). The same study assumed a one-compartment excretion model that would take 4 days to 

eliminate about 94% of MBOCA from the body. Similar results were obtained in rats after a single 

dose of radioactive MBOCA; 64-87% of the radioactivity was recovered in the urine and feces within 

48 hours after exposure (Morton et al. 1988). It is not known if MBOCA metabolites are retained 

in the body and for how long. no information was located regarding reduction of body burden in 

humans or animals following exposure to MBOCA. 

Because phenobarbital induces the microsomal cytochrome P-450 enzyme system responsible for 

MBOCA hydroxylation (Chen et al. 1991), phenobarbital treatment might increase the breakdown 

of MBOCA and speed its removal from the body. However, because MBOCA’s metabolites are more 

toxic than the unmetabolized moiety, this intervention must be used with caution. Such treatment 

could also affect MBOCA adduct formation. While phenobarbital did not increase in. Go 

hemoglobin adduct formation in one study in rats (Chen et al. 1991), Cheever et al. (1991) found an 

increase in globin adduct formation (radioactivity) following phenobarbital induction. The major 

DNA adduct of MBOCA was identified in another study by a combination of in vivo and in vitro 

experiments (Silk et al 1989). Male rats derived from a Wistar strain were intraperitoneally exposed 

to either 89 μmol/kg of radioactive MBOCA or 141 μmol/kg of acetyl-MBOCA. Twenty-four hours 

later, animals were sacrificed and their liver DNA was extracted and analyzed for the amount of 

bound radioactivity and nature of adducts. Results showed that the cleavage of the bond between 

the methylene bridge and one aromatic nucleus of MBOCA resulted in the formation of the major 

in vivo adduct identified as N-(deoxyadenosine-8-yl)-4-amino-3-chlorobenzyl alcohol. Two other 

adducts also formed after intraperitoneal injection were not identified. These findings were 

confirmed and extended when DNA was isolated from liver, lung, and kidney of 14C-MBOCA-treated 

rats and compared to in vitro N-hydoxy-MBOCA-treated rat DNA, and two major adducts were 

identified: N-(deoxyadenosine-8-yl)-4-amino-3-chlorobenzyl alcohol and N-(deoxyadenosine-8-yl)-4­

amino-3-chlorotoluene (Segerback and Kadlubar 1992). Although the results showed that the adduct 

formation (binding of N-hydroxy-MBOCA to DNA) can be inhibited by ascorbic acid, glutathione, 

nitrosobenzene, and methyl viologen but not by nitromethane, P-nitrobenzylpyridine, or methionine, 

the precise mechanism of single-ring MBOCA DNA adduct formation is not completely understood. 

Therefore, more information on DNA adduct formation especially in human bladder, and possibly 

in liver, is needed since DNA adducts are considered to play a major role in MBOCA-induced 

carcinogenesis. 
MBOCA 53
 

2. HEALTH EFFECTS 

2.8.3 Interfering with the Mechanism of Action for Toxic Effects 

Existence of an antidote capable of reducing or alleviating MBOCA-induced toxicity has not been 

reported. Available information indicates that most harmful effects of MBOCA in humans come 

from its metabolites. Once the detailed mechanism of action of MBOCA is known, and more 

Information is gathered on the potential adduct inhibitors, it may be possible to interfere with DNA 

adduct formation and reduce the adverse effects. 

2.9 ADEQUACY OF THE DATABASE 

Section 104(i)(S) of CERCLA, as amended, directs the Administrator of ATSDR (in consultation 

with the Administrator of EPA and agencies and programs of the Public Health Service) to assess 

whether adequate information on the health effects of MBOCA is available. Where adequate 

information is not available, ATSDR, in conjunction with the national Toxicology Program (NTP), 

is required to assure the initiation of a program of research designed to determine the health effects 

(and techniques for developing methods to determine such health effects) of MBOCA. 

The following categories of possible data needs have been identified by a joint team of scientists from 

ATSDR, NTP, and EPA. They are defined as substance-specific informational needs that if met 

would reduce the uncertainties of human health assessment. This definition should not be interpreted 

to mean that all data needs discussed in this section must be filled. In the future, the identified data 

needs will be evaluated and prioritized, and a substance-specific research agenda will be proposed. 

2.9.1 Existing Information on Health Effects of MBOCA 

The existing data on health effects of inhalation, oral, and dermal exposure of humans and animals 

to MBOCA are summarized in Figure 2-3. The purpose of this figure is to illustrate the existing 

information concerning the health effects of MBOCA. Each dot in the figure indicates that one or 

more studies provide information associated with that particular effect. The dot does not imply 

anything about the quality of the study or studies. Gaps in this figure should not be interpreted as 

“data needs.” A data need, as defined in ATSDR’s Decision Guide for Identifying Substance-Specific 

Data needs Related to Toxicological Profiles (ATSDR 1989), is substance-specific information 

necessary to conduct comprehensive public health assessments. Generally, ATSDR defines a data 

gap more broadly as any substance-specific information missing from the scientific literature. 

With regard to human health effects of MBOCA, the few available studies were either case reports 

of acute occupational exposure or involved intermediate or chronic epidemiological studies. Acute 

exposures to MBOCA were by the inhalation, oral, or dermal routes, although in some studies it was 

difficult to clearly define the exposure route. Intermediate exposures were by either inhalation and/or 

dermal contact; no intermediate oral exposure studies were located. Chronic exposure in humans 

occurred by inhalation and/or dermal contact; no chronic oral studies were located. no information 

is available regarding immunological, neurologic, reproductive, developmental, or genotoxic effects 

in humans by any route of exposure. Studies on cancer incidence in humans after inhalation and/or 

dermal exposure to MBOCA were located. 

Virtually all of the data regarding the health effects of MBOCA in animals were obtained from 

studies in which MBOCA was administered orally. Extremely limited information is available 

regarding health effects in animals following inhalation or dermal exposure. 

MBOCA 55
 

2. HEALTH EFFECTS 

2.9.2 Identification of Data Needs 

Acute-Duration Exposure. Populations close to hazardous waste sites that contain MBOCA would 

be exposed to MBOCA for short periods of time, most likely be through the dermis, although 

inhalation and ingestion exposure(s) cannot be excluded. Limited information on acute exposure in 

humans comes from reports on accidental exposure by skin absorption and inhalation (Hosein and 

Van Roosmalen 1978). In this case, eyes and skin were affected since the worker was sprayed on the 

face with molten, liquid MBOCA. A small amount of protein in his urine indicated that the kidney 

was a target organ for MBOCA toxicity. Insufficient information was available to calculate an 

acuteduration MRL for MBOCA. 

No information was located regarding toxic effects in animals following acute exposure to MBOCA. 

Studies addressing toxic effects of MBOCA in animals after skin application and inhalation (since 

these are the most likely routes of exposure for human populations in the vicinity of hazardous waste 

sites) could provide needed information for estimation of possible acute toxicity of MBOCA in 

humans. 

Intermediate-Duration Exposure. Limited information is available in humans regarding toxic 

effects of MBOCA following intermediate exposure by inhalation and/or dermal contact, and no 

information was located regarding oral exposure. In one study, exposure most likely occurred as a 

result of combined inhalation and dermal exposures, and the exposure duration was averaged at 3.2 

months. The results showed that the urinary bladder is the major target organ in humans after 

intermediate-duration exposures to MBOCA. Papillary neoplasms (one carcinoma) of the urinary 

bladder were found in 3 out of 200 occupationally exposed workers (Ward et al. 1990). No studies 

of intermediate-duration exposure in animals were located to support this finding. However, results 

from chronic animal studies clearly support the findings in humans after intermediate exposure to 

MBOCA. Lung, liver, and mammary tumors were found in rats (Kommineni et al. 1979; Stula et al. 

1975). Hepatomas and vascular tumors were present in mice (Russfield et al. 1973, while transitional 

cell carcinoma of the urinary bladder was found in dogs (Stula et al. 1977) after chronic exposure to 

MBOCA. Insufficient information is available to calculate an intermediate-duration MRL for 

MBOCA. 

Animal studies examining the effects of intermediate-duration exposure to MBOCA via the inhalation 

and dermal routes are necessary to evaluate the likelihood of urinary bladder carcinoma in humans 

after intermediate exposure to MBOCA. 

Chronic-Duration Exposure and Cancer. Epidemiological studies in humans following chronic 

exposure to MBOCA are very limited. No information is available regarding toxic effects in humans 

following chronic exposure to MBOCA. 

One study of chronic occupational exposure in humans found low-grade papillary tumors of the 

urinary bladder in 3 out of 200 workers (Ward et al. 1990). This result suggests that the urinary 

bladder is the major target organ in terms of tumor incidence in humans following chronic exposure. 

This finding is supported by results obtained in dogs (Stula et al. 1977). Data in other animal species 

following oral exposure also support the finding that MBOCA is a potential carcinogen and show that 

other target organs include lungs, liver, breast, and Zymbal’s gland in rats (Kommineni et al. 1979; 

Russfield et al. 1975; Stula et al. 1975) and lungs, liver, and vascular system in mice (Russfield et al. 

1975). Although the animal data support those in humans following an occupational exposure (Ward 

et al. 1990) the report in humans is limited in that it is a case report without controls to allow the 
MBOCA 56
 

2. HEALTH EFFECTS
 

determination of a dose-response relationship and statistical significance of data. There was also 

potential of co-exposure to other chemicals. Further occupational exposure studies are needed to 

establish the carcinogenic potential of MBOCA in humans. 

Currently, there are several studies in progress sponsored by NIOSH that are investigating different 

aspects of human exposure to MBOCA (FEDRIP 1991; also Section 2.93). One of the studies is 

involves the worker population exposed to MBOCA between 1969 and 1979. The principal 

investigator is E.M. Ward, and the objective of the study is to see if the occurrence of cancer can be 

linked to exposure to MBOCA. The second study concerns biomonitoring for populations 

occupationally exposed to aromatic amines (of which MBOCA is one). F.B. Daniel is the principal 

investigator for this study entitled “Biomonitoring for Populations Occupations Exposed to Aromatic 

Amines.” Hemoglobin and DNA adduct formation by MBOCA will be analyzed in order to propose 

a methodology for monitoring workplace exposure. Also sponsored by NIOSH is a third study which 

involves on developing and evaluating biological monitoring methodologies for detecting the presence 

and uptake of MBOCA by urine. L.L. Lowry is the principal investigator for this project entitled 

“Biological Monitoring Methods Research and Evaluation.” This investigator will also evaluate the 

effectiveness in predicting worker uptake of MBOCA and two other compounds. The NTP also has 

a study in progress on “At-y1 Amine Adducts in Blood as Indicators of Exposure.” In this study, blood 

samples from 100 workers will be analyzed for hemoglobin o-toluidine adducts. MBOCA will be used 

to develop a high-performance liquid chromatography (HPLC) method for separation and isolation 

of mitochondrial or total aryl amine-DNA adducts. In addition, the in vitro activation of potential 

carcinogens will be studied, and a mathematical model for MBOCA distribution, metabolism, and 

adduct formation will be prepared. The overall objective of the project is to develop a more sensitive 

adduct isolation procedure to be used for biological monitoring. The contact person for this project 

is K. Cheever (NTP 1991a). A grant was awarded in September 1991 to the Michigan Department 

of Public Health to conduct an epidemiologic study under the title “Analytic Epidemiologic Study of 

MBOCA” (ATSDR 1991). The objective of the study is to determine if there is an association 

between exposure to MBOCA and occurrence of bladder cancer in workers, their family members, 

and residents who live near three NPL sites. Cystoscopy will be used in all cases with positive 

screening results. The information on all MBOCA-exposed members of the cohort will be maintained 

in a registry. A case-control study will be conducted to assess the association of MBOCA exposure 

and bladder cancer incidence. The contact person for this project is H. Humphrey from the Michigan 

Department of Public Health. Thus, there are sufficient on-going studies on biomonitoring of 

humans exposed to MBOCA. 

Genotoxicity. There is considerable evidence that MBOCA metabolites are mutagenic in 

S. typhinurium strains TA98 and TA100 (Cocker et al. 1985; MacDonald 1981; Matsushima et al. 

1981; Messerly et al. 1987; Kuslikis et al. 1991) and in mouse lymphoma cells (Caspary et al. 1988; 

Myhr and Caspary 1988) and induce UDS in HeLa cells (Martin and McDermid 1981) and in 

hepatocytes from rats (McQueen et al. 1981; Moriet al. 1988; Williams et al. 1982) mice, hamsters 

(McQueen et al. 1981), and rabbits (McQueen and Williams 1987). However, nonactivated MBOCA 

is not a mutagen. In vitro evidence indicates that human liver (Cocker et al. 1985) and bladder 

epithelium (Stoner et al. 1988) contain enzymes that can activate MBOCA to genotoxic derivatives. 

It is less clear whether MBOCA is a clastogen. Mixed results have been obtained in the in vivo 

micronucleus assay (Katz et al. 1981; Salamone et al. 1981; Tsuchimoto and Matter 1981) and in the 

in vitro assays for sister chromatid exchange (Galloway et al. 1985; Perry and Thomson 1981) while 

data regarding chromosome aberrations were negative (Galloway et al. 1985; Perry and Thomson 

1981). Micronucleus assays done with multiple sampling times, and in vivo and in vitro chromosome 

aberration assays performed near cytotoxic levels would be useful in assessing the clastogenic 
MBOCA 57
 

2. HEALTH EFFECTS
 

potential of MBOCA. MBOCA metabolites bind to DNA in rat (Cheever et al. 1990; KuglerSteigmeier et al. 1989), dog, and human (Stoner et al. 1988) bladder and liver tissues. Wide 

variations in the amount of material bound were observed in dog and human tissue explants (Stoner 

et al. 1988). Identifying the source of this variability might help in identifying sensitive populations. 

One study reported that MBOCA itself may be a promoter (Kuslikis et al. 1991); confirmation or 

negation of this result might be useful in evaluating the interactions of MBOCA with other chemicals. 

Reproductive Toxicity. No studies were found regarding reproductive effects in humans or animals 

following exposure to MBOCA by any route. Thus, studies examining the effects on reproduction 

by any route of exposure would be useful. 

Developmental Toxicity. No human or animal studies are available on developmental effects for 

any exposure route. Studies assessing postnatal survival after maternal exposure to MBOCA by all 

three routes would be very informative. 

Immunotoxicity. No information on immunotoxicity after exposure to MBOCA by any of the three 

routes is available in humans or animals. Studies in laboratory animals following acute inhalation, 

oral, and dermal exposure to MBOCA would help define possible effects on antibody production and 

cellular immunity. This information would be useful for determining sensitive populations. 

Neurotoxicity. No studies on neurotoxicity in humans following exposure to MBOCA were located. 

In one out of six female beagle dogs, cystic hyperplasia of the pars intermedia of the anterior pituitary 

gland was found after 8.3 years of treatment with MBOCA (Stula et al. 1977). Although this change 

was not present in any of the control dogs, it was not considered to be treatment related. Studies 

in animals following acute, intermediate, or chronic exposure to MBOCA by any route would be 

useful in establishing if the central nervous system is one of the target organs for MBOCA toxicity. 

These studies should include neurobehavioral screening tests such as a functional observation battery 

of tests, tests for motor activity, and schedule-controlled operant performance tests. neuropathology 

data from MBOCA-exposed animals would also be helpful. 

Epidemiological and Human Dosimetry Studies. Human studies on MBOCA consist of either 

case reports of accidental exposure or follow-up studies of workers previously exposed to MBOCA. 

Exposures in both cases are mainly inhalation and dermal. Since MBOCA is a potential human 

carcinogen, the follow-up studies focused on monitoring the possible development of bladder 

carcinomas in workers exposed to MBOCA (Ward et al. 1990). At the present time, there are three 

studies in progress sponsored by NIOSH that are investigating different aspects of MBOCA exposure 

in humans (FEDRIP 1991) ( see Section 2.93). One of the studies involves workers exposed to 

MBOCA; the second involves biomonitoring for populations occupationally exposed to aromatic 

amines (including MBOCA); and the third involves the development and evaluation of biological 

methodologies for monitoring the presence and uptake of MBOCA in urine. Thus, at the present 

time, there are sufficient studies on biomonitoring of humans exposed to MBOCA. 

Biomarkers of Exposure and Effect 

Exposure. Sensitive methods for evaluation of MBOCA in urine are available. Since MBOCA can 

bind to body proteins and DNA, the presence of MBOCA adducts is an indication of exposure. 

Although information on some MBOCA metabolites and adducts is available, the development of 

sensitive methods for their determination is needed. Further identification of those two classes of 
MBOCA 58
 

2. HEALTH EFFECTS
 

biomarkers in humans would be helpful in assessing MBOCA exposure levels in high-risk populations. 

Studies in rats showed that intraperitoneal injection of ring-labeled MBOCA, or ring-labeled 

n-acetylated MBOCA, resulted in the generation of three DNA adducts (Silk et al. 1989). These 

adducts were also produced by the in vitro reaction of the N-hydroxy derivative of MBOCA with rat 

liver slices. The major product of this reaction was also formed following incubation of DNA with 

N-hydroxy-6amino-3-chlorobenzyl alcohol, the compound resulting from cleavage of the methylene 

bridge of N-hydroxy MBOCA. While the single ring species appears to be an intermediate in the 

formation of the DNA adduct, it is not known whether N-hydroxylation or bridge cleavage occurs first 

in the formation of the reactive species. The DNA adduct was analytically identified as n­

(deoxyadenosin-8-yl)-4-amino-3-chlorobenzyl alcohol. Since MBOCA adducts can be used as 

biomarkers of exposure additional information regarding their characteristics such as half-life would 

be useful in estimating MBOCA exposures. 

Effect. The urinary bladder is a target organ for MBOCA-induced carcinogenicity (Ward et al. 1990). 

Retrospective biological monitoring using cystoscopy would help identify new biomarkers necessary 

to characterize the preneoplastic state of the urinary bladder. 

Absorption, Distribution, Metabolism, and Excretion. Quantitative data on the absorption of 

MBOCA in humans and animals following all routes of exposure are very limited. Human studies 

indicate that MBOCA is absorbed rapidly and that the amount absorbed is proportional to the dose 

for the inhalation (Cocker et al. 1988, 1990; Ichikawa et al. 1990; NIOSH 1986b) and/or dermal 

routes (Chin et al. 1983; NIOSH 1986b). Data on absorption rates for all three routes are needed. 

Additional quantitative absorption data in animals via all three routes would be useful because they 

could be used to estimate absorption in humans. 

No studies were located regarding distribution in humans following inhalation, oral, or dermal 

exposures to MBOCA. Animal kinetic studies (following intraperitoneal or intravenous exposure) 

in rats and dogs indicate that MBOCA is distributed in the blood to liver, bile, kidney, lung, and fat 

(Cheever et al. 1991; Farmer et al. 1981; Manis et al. 1984; Morton et al. 1988; Sabbioni and 

neumann 1990). It is not known if MBOCA reaches a steady state after repeated exposures. 

Additional inhalation and dermal exposure studies regarding distribution would be useful because of 

the potential for human exposure via those two routes. 

No information was located regarding metabolism in humans after oral exposure to MBOCA. 

Limited information is available regarding metabolism in humans following inhalation or dermal 

exposure (Cocker 1988, 1990; Ducos et al. 1985; Osorio et al. 1990) to MBOCA. Metabolism has 

been partially characterized in animals following oral exposure. In vitro studies investigating the 

capacity of MBOCA to form adducts characterized one of its metabolites, a product of cleavage 

between the methylene bridge and one of the aromatic nuclei, as a DNA adduct-forming metabolite, 

N-hydroxy-MBOCA (MBOCA-NHOH) (Silk et al. 1989). Several MBOCA metabolites were 

identified following N- and o-hydroxylation of MBOCA by the canine, guinea pig, and rat liver 

mixed-function oxidase systems (Chen et al. 1989). Because differences in metabolism may occur with 

differences in the route of exposure, more data on metabolism following inhalation and dermal 

exposures would be useful. Also needed is information on MBOCA metabolites in terms of their 

potential carcinogenic capacities. 

No human data were located regarding excretion following oral exposure to MBOCA. There is, 
MBOCA 59
 

2. HEALTH EFFECTS
 

however, limited information on excretion in humans after inhalation and/or dermal exposure showing 

that the metabolites (N-acetyl MBOCA, β-N-glucuronide of MBOCA) and very limited amounts of 

parent MBOCA are excreted in the urine (Cocker et al. 1988; Ichikawa et al. 1990; NIOSH 1986b). 

Studies in rats show that, after acute oral exposure to radioactive MBOCA, the majority of the label 

is in the feces (Farmer et al. 1981; Groth et al. 1984). More information is needed on excretion rate 

in animals after exposure to MBOCA via all three routes in order to establish which is the major 

route of excretion. 

Comparative Toxicokinetics. Studies using rats (Farmer et al 1981; Groth et al 1984; Morton et 

al 1988; Tobes et al 1983) and dogs (Manis et al 1984b) indicate that the kinetics of MBOCA do not 

differ significantly across species and that the differences are primarily quantitative. Since the kinetic 

data alone do not allow for the identification of target organs common to humans and animals, 

additional studies on the distribution and toxicity may allow for identification of similar target organs. 

Additional studies in dogs would be helpful since they are similar to humans in that they develop 

bladder cancer following exposure to MBOCA. No animal data on toxicokinetics were located 

regarding interspecies differences or sex-related differences. The limited amount of animal data as 

well as a relative lack of data across different routes of exposure indicate that it may be difficult to 

compare the kinetics of MBOCA in animals with that in humans. Additional studies using several 

species and all three exposure routes are needed in order to determine similarities and differences 

between humans and animals. 

Methods for Reducing Toxic Effects. Protocols need to be developed to abolish or alleviate 

adverse effects following exposure to MBOCA. As in most cases of toxic exposures, supportive 

therapy dealing with symptoms is recommended. Biological monitoring of workers occupationally 

exposed to MBOCA is a preventive measure that can reduce potential toxic and carcinogenic effects. 

Among the other recommended procedures are monitoring MBOCA air levels and urinary MBOCA 

levels, doing wipe tests to check surface contamination that can potentially lead to skin exposure 

(Clapp et al. 1991), and considering the performance of cystoscopy in exposed workers for early 

detection of bladder tumors (Mason and Volger 1990; Ward et al. 1990). Also important in 

minimizing absorption is the selection of protective clothing and gloves. The permeability of eight 

commercially available glove materials (with regard to methanolic solutions of aromatic amines) 

differed considerably, and the penetration of MBOCA was dependent on the concentration (Weeks 

and Dean 1977). Therefore, the recommendation for how frequently the gloves should be changed 

depends on the specific situation. Continued education of the work force about potential work 

hazards is also important (NIOSH 1986b). 

2.9.3 On-going Studies 

On-going studies regarding the health effects of MBOCA were reported in the Federal Research in 

Progress (FEDRIP 1991) database. The national Institute for Occupational Safety and Health 

(NIOSH) is the sponsoring institution of three studies involving MBOCA currently in progress. One 

project is entitled “Investigation of Workers Exposed to MBOCA” and the principal investigator is 

E.M. Ward from NIOSH. The main objective of this study is to see if the occurrence of cancer can 

be linked to exposure to MBOCA. To achieve this, the study will use biological markers (MBOCA 

in the urine and urinary bladder cytology) to develop more effective, sensitive, and specific early 

markers for occupationally related health conditions. F.B. Daniel from NIOSH is the principal 

investigator of the study on “Biomonitoring for Populations Occupations Exposed to Aromatic 

Amines.” The investigator will analyze hemoglobin and DNA adduct formation by MBOCA in order 

to propose a methodology for monitoring workplace exposure. L.L. Lowry from NIOSH is the 
MBOCA 60
 

2. HEALTH EFFECTS 

principal investigator of the project entitled “Biological Monitoring Methods Research and 

Evaluation.” This study will develop and evaluate biological monitoring methods in urine for their 

effectiveness in predicting worker uptake of MBOCA and two other compounds. The NTP has a 

study in progress on “Aryl Amine Adducts in Blood as Indicators of Exposure.” In this study, blood 

samples from 100 workers will be analyzed for hemoglobin o-toluidine adducts. MBOCA will be used 

to develop a high-performance liquid chromatography (HPLC) method for separation and isolation 

of mitochondrial or total aryl amine-DNA adducts. In addition, the in vivo activation of potential 

carcinogens will be studied, and a mathematical model for MBOCA distribution, metabolism, and 

adduct formation will be prepared. The overall objective of the project is to develop a more sensitive 

adduct isolation procedure to be used for biological monitoring. The contact person for this project 

is K. Cheever (NTP 1991a). A grant was awarded in September 1991 to the Michigan Department 

of Public Health to conduct an epidemiologic study under the title “Analytic Epidemiologic Study of 

MBOCA” (ATSDR 1991). The objective of the study is to determine if there is an association 

between exposure to MBOCA and occurrence of bladder cancer in workers, their family members, 

and residents who live near three NPL sites. The screening regimen includes urine dipstick selftesting 

(using Hemastix kits) and collection of specimens for cytology. Cystoscopy will be used in all 

cases with positive screening results. The information on all MBOCA-exposed members of the cohort 

will be maintained in a registry. A case-control study will be conducted to assess the association of 

MBOCA exposure and bladder cancer incidence. The contact person for this project is H. Humphrey 

from the Michigan Department of Public Health. 
MBOCA 61 

3. CHEMICAL AND PHYSICAL INFORMATION 

3.1 CHEMICAL IDENTITY 

Information regarding the chemical identity of MBOCA is located in Table 3-1. 

3.2 PHYSICAL AND CHEMICAL PROPERTIES 

Information regarding the physical and chemical properties of MBOCA is located in Table 3-2. 



MBOCA 65
 

4. PRODUCTION, IMPORT/EXPORT, USE, AND DISPOSAL 

4.1 PRODUCTION 

MBOCA is a man-made chemical and has not been found in nature (IARC 1974). It is produced 

commercially by reacting formaldehyde with o-chloraniline (HSDB 1991; IARC 1974). Pure MBOCA 

is a colorless crystalline solid (Smith and Woodward 1983). The technical grade of MBOCA that is 

available in the United States comes mainly from Japan in the form of tan/yellow fused prills or 

pastilles. The diamine purity is 99.8%, typically with 0.2% free o-chloroaniline (monomer). Isomers 

are produced as side reactions such as trimers and tetrameres-diamines with three- and four-ring 

structures joined by methylene groups. Isomers constitute up to 8-10% of MBOCA. The dimer 

makes up to 90-92% of the MBOCA produced today for coatings and cast polyurethanes. There is 

no commercial use for pure dimer MBOCA other than for laboratory work. 

MBOCA has been produced commercially in the United States for some time. The first reported 

production was in 1956 (IARC 1974). U.S. production of MBOCA was estimated to be 

3.3-5.5 million pounds in 1970 and 7.7 million pounds in 1972 (IARC 1974). In 1982, production 

of MBOCA in the United States was reported to have ceased (HSDB 1991). 

MBOCA has been manufactured in the United States by two companies E.I. Du Pont de nemours 

and Company (Deepwater, new Jersey) and Anderson Development Company (Adrian, Michigan). 

However, E.I. Du Pont de nemours and Company ceased MBOCA production in 1978, and 

Anderson Development Company ceased production in 1979. Presently, all MBOCA used in the 

United States is imported. As of 1985, there were at least four production sites in the United States 

that use imported MBOCA: Polyester Corporation (Southampton, new York), American Cyanamid 

Company (Bound Brook, new Jersey), E.I. Du Pont De nemours and Company (Deepwater, New 

Jersey), and Anderson Development Company (Adrian, Michigan) (OHM/TADS 1985). However, 

in 1992, Allchem Industries, Inc. (Gainesville, Florida), Maypro Industries, Inc. (Harrison, New York), 

and Miki Sangyo (USA), Inc. (New York, New York), were also reported to produce MBOCA for 

commercial sale (Van et al. 1992). 

Eighteen industrial sites (Table 4-l) were listed in the 1990 Toxics Release Inventory (TRI) as 

producers and/or users of MBOCA (TRI90 1991). However, since not all producers of MBOCA are 

required to report to TRI, the companies listed on the inventory cannot be considered the exclusive 

producers of MBOCA in the United States. This is not an exhaustive list. 

4.2 IMPORT/EXPORT 

In 1978, approximately 0.4 million pounds of MBOCA were imported into the United States (HSDB 

1991). The amount of MBOCA imported into the United States increased in 1983 to 1.51 million 

pounds. In 1991, approximately 2.0 million pounds of MBOCA were imported into the United States. 

The MBOCA was manufactured by two Japanese producers and a Taiwanese producer. 

4.3 USE 

The majority of MBOCA consumed in the United States has been used as a curing agent for 

isocyanate-containing polymers, and only about 1% is used in epoxy/epoxy-urethane resin blends 

MBOCA 67
 

4. PRODUCTION, IMPORT, USE, AND DISPOSAL
 

(IARC 1974). These cured polymers have many commercial and military uses. MBOCA was 

reported to be the most widely used agent for curing castable liquid polyurethane elastomers (HSDB 

1991; IARC 1974; Sax and Lewis 1987). Commercially, these MBOCA-cured polyurethanes have 

been used to produce shoe soles, rolls for postage stamp machines, cutting bars in plywood 

manufacturing, rolls and belt drives in cameras, computers, and reproducing equipment, and wheels 

and pulleys for escalators and elevators (NRC 1981). MBOCA has also been reported to be 

formulated with other aromatic diamines and sold under trade names as a curing agent (IARC 1974). 

MBOCA has also been used in the manufacture of gun mounts, jet engine turbine blades, radar 

systems, components in home appliances (HSDB 1991), and as a wiring patting and curing agent 

(Cowles 1978). Military applications of MBOCA-cured polyurethanes include ball seals on nuclear 

submarines, positioning strips in Poseidon missiles, and encapsulation of electric components (NRC 

1981). 

4.4 DISPOSAL 

Because MBOCA is defined as a “hazardous waste,” companies that generate wastes containing 100 

kg or more of MBOCA are required to conform with EPA regulations (EPA 1989; HSDB 1991). 

For more information on the regulations and guidelines that apply to MBOCA, see Chapter 7. 

No universal method exists for the disposal of carcinogenic compounds such as MBOCA (HSDB 

1991). Product residues and sorbent media containing MBOCA have been packaged in epoxy-lined 

drums and disposed of at EPA-approved sites (OHM/TADS 1985). Destruction via chemical reaction 

is another method that has been used to dispose of small amounts of MBOCA (HSDB 1991). This 

method, in which MBOCA is oxidized with potassium permanganate, is generally used for laboratory 

wastes containing small amounts of MBOCA. 

Incineration technologies have been investigated for the disposal of MBOCA. MBOCA has been 

considered a good candidate for rotary kiln incineration at a temperature range of 820-1,600°C, with 

residence times of seconds for liquids and gases and hours for solids (EPA 1981b; HSDB 1991). 

MBOCA is also listed as a good candidate for fluidized bed incineration at temperatures ranging from 

450°C to 980°C and residence times similar to those for rotary kiln incineration (EPA 1981). 

Disposal of MBOCA contained in waste waters using activated carbon adsorption has been studied 

(HSDB 1991). Saturated filters used to remove MBOCA from waste water via carbon absorption 

can subsequently be destroyed by rotary kiln or fluidized bed incineration (EPA 1979). 

Biodegradation treatment of MBOCA using continuous flow reactors that are designed to remove 

potential hazardous chemicals from water and waste water may be also useful in clean-up operations. 

Similarly, activated carbon processes and ozone oxidation provide effective disposal treatment (EPA 

1979). There is, however, no information on the availability of MBOCA residues from polyurethanes 

and other plastics. 

MBOCA 69
 

5. POTENTIAL FOR HUMAN EXPOSURE 

5.1 OVERVIEW 

MBOCA may be discharged to the ENVIRONMENT as a result of an uncontained, open cycle, 

manufacturing process. Such a discharge could constitute a release to the atmosphere as a fugitive 

dust or as a spill of MBOCA pellets or heated liquid MBOCA. Otherwise non-hazardous solid wastes 

may become contaminated by MBOCA in the manufacturing process thus, making such wastes 

hazardous. The dust can settle to soil or surface waters where it will be strongly adsorbed to the 

organic matter in the soil or water column; therefore, it is unlikely to contaminate groundwater. 

Microbial degradation is a potentially significant degradation process and may be quite rapid if 

appropriate organisms are present in the soil or water. In air or surface waters, MBOCA may 

undergo photooxidation by alkoxyradicals. 

Members of the general population are unlikely to be exposed to MBOCA unless they live in an area 

that has been contaminated. Workers in plants that manufacture or use MBOCA have the potential 

to be highly exposed by inhalation or dermal contact. 

MBOCA has been identified in at least 4 of the 1,350 NPL hazardous waste sites (HAZDAT 1993). 

However, the number of sites analyzed for MBOCA is not known. The frequency of these sites 

within the United States can be seen in Figure 5-1. 

5.2 RELEASES TO THE ENVIRONMENT 

5.2.1 Air 

MBOCA may be released to the atmosphere in the exhaust emissions of facilities that manufacture 

it or use as a curing agent in the manufacture of diisocyanate-based polymers (Keeslar 1986) (Table 

5-l). 

According to TR191 (1993) a total of 1,362 pounds of MBOCA was released to the atmosphere in 

1991, from manufacturing and processing facilities in the United States (see Table 5-l). The TRI 

data should be used with caution, however, since only certain types of facilities are required to report. 

5.2.2 Water 

Of the 1,362 pounds of MBOCA released to the ENVIRONMENT from TRI facilities in 1991, no 

discharges to surface waters were reported. One pound was reported to be transferred to a publicly 

owned treatment facility works (TR191 1993). The TRI data should be used with caution since only 

certain types of facilities are required to report. 

5.2.3 Soil 

Of the 1,362 pounds of MBOCA released to the atmosphere in 1991 from TRI facilities, no releases 

of MBOCA to land or through underground injection were reported. An additional 5,228 pounds 

were reported to have been transferred to off-site waste treatment, storage, and 


MBOCA 72
 

5. POTENTIAL FOR HUMAN EXPOSURE
 

disposal facilities (TRI91 1993). The TRI data should be used with caution since only certain types 

of facilities are required to report. 

5.3 ENVIRONMENTAL FATE 

5.3.1 Transport and Partitioning 

Volatilization of MBOCA from soil or surface waters is unlikely to be a major factor for 

Environmental fate because of its very low vapor pressure (1x10-5 mmHg at 25°C) (Keeslar 1986; 

NIOSH 1978b) and its strong adsorption to organic matter. 

MBOCA partitions to soil rather than water as a result of its relatively low solubility in water (13.9 

mg/L) and its amine groups, which have an affinity for soil organic matter. This binding is rapid and 

very tight and results in virtually no movement of MBOCA through soil (Voorman and Penner 

1986a). 

The partitioning of MBOCA in the soil affects the uptake of the compound by plants grown in 

contaminated soil and its subsequent ingestion by humans. MBOCA is bioaccumulated by food plants 

(e.g., carrots, orchard grass, beans, cabbage, beet, sorghum, cucumber), but movement of the 

compound within the plant is extremely limited. MBOCA applied to leaf surfaces resulted in 

adsorption to the leaf cuticle but no movement beyond the application site. Exposure of roots of 

bean, sorghum, and carrots to aqueous solutions of 5 mg/L of MBOCA for 8 days resulted in 

relatively high concentrations on the root surfaces of these plants (37 mg/kg, 2,000 mg/kg, and 

20 mg/kg, respectively), demonstrating bioconcentration at that site but limited translocation to plant 

shoots (1.7 mg/kg, 2-5 mg/kg, and virtually undetectable, respectively). MBOCA applied to soils at 

a concentration of 5 mg/kg again showed an uptake in the roots of cucumbers and beans (up to 17 

mg/kg MBOCA); the shoots of these plants contained less than 0.2 mg/kg. This limited translocation 

may be due to the low water solubility of MBOCA (Voorman and Penner 1986b). This may be of 

concern in cases of accidents (or even during routine operations) in which MBOCA is released to 

the air. 

5.3.2 Transformation and Degradation 

5.3.2.1 Air 

The photooxidation half-life of MBOCA in air is estimated to be between 0.290 and 2.90 hours based 

on reactions with hydroxyl radicals (Howard et al. 1991) suggesting that this may be a significant fate 

process. 

5.3.2.2 Water 

Studies examining the biodegradation of MBOCA, using activated sludge microorganisms, suggested 

that MBOCA was readily degraded (from 2.02 mg/L to 0.09 mg/L) in a continuous biological reactor 

within 24 hours, but not during a 7-day static incubation test (EPA 1979; Tabak et al. 1981). Other 

degradation processes were also effective in reducing the concentrations of MBOCA present in 

simulated waste water. Ozone oxidation reduced an initial concentration of 1.52 mg/L MBOCA to 

nondetectable levels within 5 minutes. Between 21 and 35 mg of carbon per liter, depending on the 

type of carbon, were required to reduce 1.0 mg/L MBOCA to 0.1 mg/L (EPA 1979). MBOCA was 

not susceptible to oxygen stripping (EPA 1979). 
MBOCA 73
 

5. POTENTIAL FOR HUMAN EXPOSURE
 

The estimated photooxidation half-life of MBOCA in surface water is between 1.3 and 72 days; while 

in groundwaters, MBOCA may have a half-life of 8 weeks to 1 year (Howard et al. 1991). The 

estimated hydrolysis half-life of MBOCA in water at 25°C and pH 7 is more than 800 years (EPA 

1988c). 

Studies of microbial degradation of MBOCA showed several biodegradation products, including 

nmonoacetyl MBOCA and N,N’-diacetyl MBOCA (Yoneyama and Matsumura 1984). 4,4’-Diamino3,3’-dichlorobenzophenone was produced from metabolic conversion of MBOCA by soil 

microorganisms (Voorman and Penner 1986a). 

5.3.2.3 Sediment and Soil 

Carbon dioxide production from soil samples treated with MBOCA was less than 1% of the total 

applied, suggesting that aromatic rings are resistant to microbial degradation and oxidation (Voorman 

and Penner 1986a). These investigators did detect a metabolite with the methylene carbon oxidized 

to a carbonyl. Microbial degradation of MBOCA has been shown to occur using Bacillus megatetium 

and nocardiopsis sp. isolated from soil. These microorganisms readily metabolize MBOCA with 39% 

and 24%, respectively, of the original concentration remaining after 3 hours of incubation. The major 

degradation pathways were: (1) acetylation of MBOCA to N-monoacetyl MBOCA and then to 

N,N’-diacetyl MBOCA, and (2) hydroxylation of N-monoacetyl MBOCA to N-hydroxy-N-acetyl 

MBOCA with the final metabolite being N-hydroxy-N,N’-diacetyl MBOCA (Yoneyama and 

Matsumura 1984). Also present was a metabolite with the methylene carbon oxidized to a carbonyl 

(Voorman and Penner 1986a). 

The estimated half-life of MBOCA in soil based on aerobic biodegradation may range between 1 and 

6 months (Howard et al. 1991). 

5.4 LEVELS MONITORED OR ESTIMATED IN THE ENVIRONMENT 

5.4.1 Air 

Monitoring of MBOCA dust and vapor in the ambient air of a production facility in 1969 showed that 

the maximum 8-hour average concentrations were 0.32 mg/m3

 and 0.25 mg/m3, respectively. 

Significant levels were detected only in areas adjacent to the pelletizing unit--although even these 

levels were only intermittently high. Skin absorption was the major source of exposure and could be 

effectively controlled with appropriate protective clothing and engineering controls (Linch et al. 

1971). 

Ambient air and personal air monitoring was conducted at a plastics factory where MBOCA was used 

in the production of urethane. The results obtained from 10 ambient air samples (6 in the general 

work area, 4 in the area where MBOCA was melted) indicated that MBOCA was not present in the 

general area above the level of detection (0.015 μg/filter), and was present in the air near the 

MBOCA melting pot at levels up to 92 μg/m3

. Personal air monitoring indicated that only those 

employed as mixers and molders were exposed to detectable levels of MBOCA, ranging from 0.06 

to 0.70 μg/m3

. Wipe samples of surfaces that workers were most likely to be exposed to contained 

low levels of MBOCA throughout. Surface wipe samples showed MBOCA contamination ranging 

from 0.1 μg/100 cm2 near the trimmers work table to 19.1 μg/100 cm2

 adjacent to the MBOCA 

melting pot. Surfaces that were rarely wiped clean, but were not near the melting pot (such as the 

tops of storage cabinets), contained an average of 4.7 μg/100 cm2

 (Clapp et al. 1991). MBOCA air 
MBOCA 74
 

5. POTENTIAL FOR HUMAN EXPOSURE 

levels were also evaluated in a polyurethane elastomer factory, and the air exposure levels ranged 

from 0.2 to 8.9 μg/m3

 (Ichikawa et al. 1990). MBOCA levels were measured at 0.001-0.042 mg/m3 

in the air of a factory producing rubber ski boots (Smith and Woodward 1983). 

MBOCA was present at only trace concentrations in air samples of dust taken 1.5 feet above ground 

level in a residential area known to be contaminated with MBOCA (Keeslar 1986). 

5.4.2 Water 

A specialty chemical manufacturing plant in Adrian, Michigan, that produced more than 1 million 

pounds per year of MBOCA during the late 1970s was found to have released significant quantities 

of it in its waste water discharges. Water sampling surveys found the following concentrations of 

MBOCA associated with the facility (Parris et al. 1980): 

Industrial lagoon sediment >1,600 ppm
 

Industrial lagoon effluent water 250 ppb
 

Industrial site deep well water 1.5 ppb
 

Surface runoff water from site 1 ppb
 

Sewage treatment plant, influent water <0.5 ppb
 

Sewage treatment plant, effluent water <0.5 ppb
 

Sewage treatment plant, activated sludge 18 ppm (estimated)
 

Raisin River water ≤0.1 ppb
 

Samples of well water from a residential area adjacent to the manufacturing plant, however, did not 

contain detectable levels of MBOCA, suggesting that groundwater contamination had not occurred 

(Keeslar 1986). 

5.4.3 Sediment and Soil 

Soil samples taken on the site of a manufacturing plant using MBOCA contained levels as high as 

1,146 ppm, while concentrations along public roads near the site ranged from 4.6 to 590 ppm (Keeslar 

1986). Soil from the yards of residences adjacent to the site (within a 1 kilometer radius) typically 

had 1.74 mg/kg MBOCA in the top 2 inches of soil and 0.02 mg/kg in the next 4 inches. 

5.4.4 Other Environmental Media 

No studies were located on the levels of MBOCA found in other Enviromental media. However, 

it has been shown that MBOCA binds to and penetrates the roots of plants grown in contaminated 

soil. Once in the plant, MBOCA stays very close to the root surface and is not distributed 

throughout the plant (Voorman and Penner 1986b). 

5.5 GENERAL POPULATION AND OCCUPATIONAL EXPOSURE 

MBOCA is commercially used as a curing agent for isocyanate polymers by specialty manufacturers 

of industrial and commercial polyurethane products (e.g., as gears, gaskets, sport boots, and roller 

skate wheels). The form of MBOCA to which workers could be exposed is likely to be either a liquid 

emulsion, dust, or solid pellets (NIOSH 1986b; Schulte et al. 1988). Occupational exposures may 

occur at several stages of polymer production, especially where prepolymers are mixed with molten 

curing agent before molding (Edwards and Priestly 1992). In most cases, dermal absorption is the 
MBOCA 75
 

5. POTENTIAL FOR HUMAN EXPOSURE
 

most important occupational exposure pathway (Edwards and Priestly 1992; Lowry and Clapp 1992). 

The national Occupational Health Survey estimated that 2,094 workers were potentially exposed to 

MBOCA in the workplace in 1980 (Schulte et al. 1988). 

A urinary monitoring program can determine aggregate worker exposure to MBOCA (Ward et al. 

1986). Workers in a plastics plant that mixed or molded urethane products containing MBOCA were 

found to have detectable levels of MBOCA in their urine. Concentrations for the mixers ranged 

from 5 to greater than 100 μg/L urine (average concentration, 61.9 μg/L), whereas concentrations for 

the molders were considerably lower, nondetectable to 50 μg/L urine (average concentration, 14.8 

μg/L). The greatest exposure route was inferred to be direct skin contact with MBOCA, despite the 

fact that the mixers wore gloves while transferring dry MBOCA, melting it, or dispensing the molten 

fluid (Clapp et al. 1991). 

After 2 days away from work, only 1 of 13 workers in the plastics plant had detectable levels of 

MBOCA in his urine. This worker also had the highest peak urinary MBOCA levels during the 

preceeding week (Clapp et al. 1991). Another investigation of workers in a polyurethane elastomer 

factory reported that preshift and postshift urinary levels were not significantly different in all exposed 

workers and that levels measured 48 hours after cessation of work were not always the lowest 

(Ichikawa et al. 1990). The difference may partially be explained by the actual levels of MBOCA in 

the workplace; workers that had MBOCA in the urine after 2 days away from work had the highest 

levels of the compound when last measured, suggesting that they were exposed to higher MBOCA 

levels than workers without any MBOCA in urine after the weekend. The reported findings may also 

reflect differences in metabolic rates between workers, or that different depots of MBOCA are 

excreted over different time frames from the body. 

Workers in a manufacturing plant using MBOCA had urine concentrations of MBOCA ranging from 

13 to 458 ppb (mean 145 ppb). Their immediate families were found to have had exposures to 

MBOCA also--urine levels of MBOCA ranged from 0 to 15 ppb (Keeslar 1986). These findings 

suggest that direct exposure to MBOCA itself in an occupational setting or at a hazardous waste site 

may not be necessary for exposure, and that people can also be exposed to MBOCA by contact with 

an MBOCA-exposed individual. Monitoring of workers at seven facilities in Australia that used 

MBOCA in the manufacture of polyurethane polymers showed that average MBOCA levels in the 

urine of the workers dropped from 29.6 to 10.4 mg/L within 8-9 months after the implementation 

of an exposure prevention program (Wan et al. 1989). Another study of 150 workers in 19 factories 

with industrial exposure to MBOCA showed that, at the end of the workshift, excretion levels ranged 

from less than 0.5 μg/L to 1,600 μg/L of MBOCA, with the highest average urine concentrations (600 

μg/L) in workers directly involved in MBOCA manufacture or use; urine MBOCA levels dropped 

after exposure controls were implemented in the plant (Ducos et al. 1985). Similar decreases in urine 

MBOCA concentrations were observed following improvements in ventilation and with the use of 

protective clothing by workers exposed to MBOCA (Thomas and Wilson 1984). 

Results of a voluntary biological monitoring program implemented by the PMA suggest that exposure 

to MBOCA among users of the compound decreased between 1985 to 1990. Following 

implementation of a number of engineering controls to limit exposure, including the use of closed 

transfer systems and the use of a fused, hardened MBOCA pellet, worker urine specimens containing 

less than 25 μg MBOCA/L increased from 77% to 86% of the total amount collected. Over this 

same time period, urine samples containing greater than 50 μg MBOCA/L decreased from 12% to 

8% of the total number of samples collected (Lowry and Clapp 1992). 
MBOCA 76
 

5. POTENTIAL FOR HUMAN EXPOSURE
 

Workers in shipyards where MBOCA is used as a potting and molding agent for wiring may also have 

potentially high exposures to MBOCA (Cowles 1978). 

Members of the general population may be exposed to MBOCA if they consume certain types of 

plants (e.g., root crops) grown in MBOCA-contaminated soil. MBOCA has been found to adhere 

to the leaves and roots of plants, and the compound is not removed by rinsing with water (Voorman 

and Penner 1986b). 

5.6 POPULATIONS WITH POTENTIALLY HIGH EXPOSURES 

Populations living near areas known to be contaminated with MBOCA can be considered to have 

high potentials for exposure. Although adults living in a contaminated area of Adrian, Michigan, did 

not have detectable levels of MBOCA in their urine, young children (all under the age of 6 years) 

from the area had urine concentrations of 0.3 to 1.0 ppb. The levels in children were believed to be 

a direct consequence of their frequent contact with contaminated soils. MBOCA was detected in the 

residences of this area, primarily on floors, carpeting, and vacuum cleaner bags; however, other 

household surfaces did not have significant concentrations of MBOCA (Keeslar 1986). 

5.7 ADEQUACY OF THE DATABASE 

Section 104(i)(5) of CERCLA, as amended, directs the Administrator of ATSDR (in consultation 

with the Administrator of EPA and agencies and programs of the Public Health Service) to assess 

whether adequate information on the health effects of MBOCA is available. Where adequate 

information is not available, ATSDR, in conjunction with the NTP, is required to assure the initiation 

of a program of research designed to determine the health effects (and techniques for developing 

methods to determine such health effects) of MBOCA. 

The following categories of possible data needs have been identified by a joint team of scientists from 

ATSDR, NTP, and EPA. They are defined as substance-specific informational needs that if met 

would reduce the uncertainties of human health assessment. This definition should not be interpreted 

to mean that all data needs discussed in this section must be filled. In the future, the identified data 

needs will be evaluated and prioritized, and a substance-specific research agenda will be proposed. 

5.7.1 Identification of Data needs 

Physical and Chemical Properties. The physical and chemical properties of MBOCA are 

sufficiently defined to allow assessments of the Environmental fate of the compound to be made (see 

Chapter 3 and Tables 3-1 and 3-2). no further information is needed. 

Production, Import/Export, Use, Release, and Disposal. Presently, conflicting information exists 

on the number of people that have been or are being exposed to MBOCA in the workplace; the 

numbers range from 114 (NOES 1992) to 2,094 (Schulte et al. 1988). The general population is not 

likely to be exposed to MBOCA. 

Information is unavailable on current or historical MBOCA production in the United States. 

MBOCA is only used in the workplace in 18 facilities in the United States (TR190 1992). 

Information on potential food contamination with MBOCA would also be useful in reducing risks 

associated with general population exposures. MBOCA may be released to the environment in waste 

waters or fugitive emissions from plants. Additional information is needed on atmospheric releases 
MBOCA 77
 

5. POTENTIAL FOR HUMAN EXPOSURE
 

of MBOCA from manufacturing facilities to assess the potential for general population exposure. 

At the present time, there is no information on the amounts of MBOCA disposed by different 

methods except for TRI data on the amounts released into different media (see Tables 5-1 and 5-2). 

Additional information on currently used disposal methods would allow the determination of their 

efficiency. Also needed is information on the availability of MBOCA residues from polyurethanes 

and other plastics. 

According to the Emergency Planning and Community Right-to-Know Act of 1986,42 U.S.C. Section 

11023, industries are required to submit chemical release and off-site transfer information to the 

EPA. The Toxics Release Inventory (TRI), which contains this information for 1990, became 

available in May of 1992. This database will be updated yearly and should provide a list of industrial 

production facilities and emissions. 

Environmental Fate. The fate of MBOCA in soil has been described (EPA 1979; Voorman and 

Penner 1986a; Yoneyama and Matsumura 1984), and some information is available on the spread and 

transport of MBOCA in surface waters (Parris et al. 1980). Additional data on the aquatic fate of 

MBOCA, its residence time in the water column, and its absorption to sediment or organic matter 

in the water would assist in assessing drinking water contamination. Information on the fate of 

MBOCA adsorbed to sediment would be useful in assessing uptake by aquatic organisms and reentry 

of MBOCA into the water column. Information on the half-life of MBOCA in the environment 

would also be useful for assessing the risk for human exposure. 

Bioavailability from Environmental Media. Available pharmacokinetic data suggest that MBOCA 

is absorbed by humans following dermal and inhalation exposures (Chin et al. 1983; Cocker et al. 

1988, 1990; Ichikawa et al. 1990; NIOSH 1986b). MBOCA has been measured in the urine of 

workers following dermal and/or inhalation exposures, suggesting rapid absorption and excretion. 

Information on the absorption of MBOCA by humans as a result of ingestion of contaminated water 

or food has not been found and would be useful in assessing the uptake of MBOCA from 

contaminated foods. Further information on the uptake of MBOCA by all three exposure routes, 

particularly the differentiation of dermal and inhalation exposure in workers, would be helpful in 

determining potential uptake of MBOCA as a result of exposure to contaminated air, water, or foods, 

or contact with contaminated surfaces. 

Food Chain Bioaccumulation. The bioconcentration factor of MBOCA has been estimated to be 

5.75 in aquatic organisms (HSDB 1991). In addition, it has been shown that MBOCA binds to and 

penetrates the roots of plants grown in contaminated soil and is not easily removed by rinsing. 

However, MBOCA stays very close to the root surface and is not distributed throughout the plant, 

and the roots bioaccumulate the chemical (Voorman and Penner 1986b). This information suggests 

that there is a potential for food chain bioaccumulation both from aquatic organisms and the root 

systems of terrestrial plants. Actual data on the potential for aquatic organisms to bioaccumulate 

MBOCA would be useful in determining potential food chain concentrations. 

Exposure Levels in Environmental Media. Some information exists on levels of MBOCA found 

in the workplace and the ENVIRONMENT around facilities that manufacture or use MBOCA (Keeslar 

1986; Parris et al. 1980). Further information on atmospheric levels of MBOCA in areas other than 

the workplace would be helpful for estimating general population exposure. 

Reliable monitoring data for the levels of MBOCA at hazardous waste sites are also needed. The 
MBOCA 78
 

5. POTENTIAL FOR HUMAN EXPOSURE 

information collected on levels of MBOCA in the ENVIRONMENT could be combined with the 

information on body burden to assess the potential risk of adverse health effects in populations living 

near hazardous waste sites. 

Exposure Levels in Humans. Certain population groups are known to have a higher risk of 

exposure to MBOCA than others. The highest exposures are found in workers at manufacturing 

facilities that use MBOCA in the production of polyurethane plastics (Clapp et al. 1991; Ichikawa 

et al. 1990; Schulte et al. 1988; Ward et al. 1987). The next highest levels are found in populations 

that live near facilities where uncontrolled MBOCA releases occur (Keeslar 1986). Specific 

information on where such releases occur, on the populations living near such facilities, and on the 

levels to which they may be exposed was not found. This information is needed to assess whether 

health studies on these populations need to be conducted. 

Exposure Registries. No exposure registries for MBOCA were located. This substance is not 

currently one of the compounds for which a subregistry has been established in the national 

Exposure Registry. The substance will be considered in the future when chemical selection is made 

for subregistries to be established. The information that is amassed in the national Exposure Registry 

facilitates the epidemiological research needed to assess adverse health outcomes that may be related 

to exposure to this substance. 

5.7.2 On-going Studies 

The NIOSH is conducting a long-term study of former MBOCA workers in Adrian, Michigan. The 

health of the workers will be followed for 10-15 years to help assess the risk of MBOCA as a 

potential human carcinogen (FEDRIP 1991; Keeslar 1986). 
MBOCA 79
 

6. ANALYTICAL METHODS
 

The purpose of this chapter is to describe the analytical methods that are available for detecting, 

and/or measuring, and/or monitoring MBOCA, its metabolites, and other biomarkers of exposure and 

effect to MBOCA. The intent is not to provide an exhaustive list of analytical methods. Rather, the 

intention is to identify well-established methods that are used as the standard methods of analysis. 

Many of the analytical methods used for enviromental samples are the methods approved by federal 

agencies and organizations such as EPA and the national Institute for Occupational Safety and 

Health (NIOSH). Other methods presented in this chapter are those that are approved by groups 

such as the Association of Official Analytical Chemists (AOAC) and the American Public Health 

Association (APHA). Additionally, analytical methods are included that modify previously used 

methods to obtain lower detection limits, and/or to improve accuracy and precision. 

6.1 BIOLOGICAL MATERIALS 

Very few biological materials have been analyzed for the presence of MBOCA or its metabolites. 

MBOCA and its metabolites have been measured in urine of exposed humans and experimental 

animals. Hemoglobin adducts have also been measured in the blood of exposed animals. The most 

frequently used techniques are gas chromatography (GC) with electron capture detection (ECD) and 

high-performance liquid chromatography (HPLC) with electrochemical detection (ED). Detailed 

methodologies from selected studies are presented in Table 6-1. 

Only a small amount of absorbed MBOCA is excreted in urine as MBOCA in animals, and probably 

in humans as well (see Section 2.3). The methods used to detect MBOCA in urine are somewhat 

limited since they commonly measure unmetabolized MBOCA--not its metabolic by-products. Some 

methods have been developed to directly measure major MBOCA metabolites in urine. Other 

analytical methods pretreat urine samples with acid, base and/or heat to release MBOCA from its 

various conjugates. Another approach is to analyze the longer-lived complexes, such as 

MBOCAhemoglobin adducts. The specific methods used are noted in the following text and in Table 6-1. 

Hemoglobin adducts of MBOCA and its metabolites have been detected in animals dosed with the 

chemical (Chen et al. 1991; Sabbioni and neumann 1990). The methods used were HPLC/ED, gas 

chromatography/mass spectrometry (GC/MS), and GC/ECD. Sample preparation for all three 

methods required hemoglobin to be isolated from the blood of the test animals and hydrolyzed to 

release the bound MBOCA. Insufficient data were provided to compare the different methods, but 

MBOCA was detected and quantified in the blood of dosed rats by all three methods. GC/MS in the 

negative chemical ionization mode, with a detection limit of 2 pg, appeared to be the most sensitive 

of the methods tested (Sabbioni and neumann 1990). 

Both GC and HPLC have been used to separate MBOCA and its metabolites from urine. Most 

recently, HPLC has become the method of choice to selectively detect MBOCA and its metabolites 

in urine. The most sensitive and specific detection methods for HPLC are ED (Ichikawa et al. 1990; 

NIOSH 1986b; Okayama et al. 1988; Trippel-Schulte et al. 1986; Vantulder et al. 1981) and 

photoconductivity detection (PCD) (Ducos et al. 1985). Of these, ED has been the most frequently 

used detection method. Ultraviolet detection (UV) has also been paired with HPLC (McKerrell et 

al. 1987; Angerer and Schaller 1985; Trippel-Schulte et al. 1986) but is less sensitive and less selective 

than either ED or PCD (Trippel-Schulte et al. 1986). 






MBOCA 86
 

6. ANALYTICAL METHODS
 

Although not the preferred method, GC may still be used to measure MBOCA and its metabolites 

in urine. Analysis of a heptafluorobutyryl derivative of MBOCA using GC/ECD has been frequently 

used (Gristwood et al. 1984; NIOSH 1984; Thomas and Wilson 1984), but GC/flame ionization 

detection (FID) has also been used to analyze a trifluoroacetyl derivative (Van Roosmalen et al. 

1979, 1981). The sensitivity of GC with either ECD or FID is in the low-ppb (μg/L) range, but the 

electron capture detector is more selective and gave higher recovery of analyte. GC and MS are 

frequently used to confirm the identity of isolated MBOCA compounds (Chen et al. 1991) and a 

method for quantifying the metabolite n-acetyl-MBOCA in urine using GCMS has been developed 

(Cocker et al. 1988). The sensitivity of this method is also in the low-ppb range. 

6.2 ENVIRONMENTAL SAMPLES 

As with biological materials, the two primary methods used to separate MBOCA from other 

compounds in Environmental samples are HPLC and GC. Most of the analytical methods found 

describe detection and measurement of MBOCA in air, the medium of primary interest for 

monitoring potential worker exposures in facilities manufacturing or using the chemical. Table 6-2 

presents details on selected analytical methods for determining MBOCA in Environmental samples. 

Air samples have been collected either in impingers containing a sorbent liquid (Ebell et al. 1980; 

nieminen et al. 1983; Skarping et al. 1985) or on solid sorbent cartridges (Ichikawa et al. 1990; James 

et al. 1985; Sawicki et al. 1975; Yasuda 1975). Air samples have also been collected on glass fiber 

filters designed to trap and stabilize MBOCA in both particulate and vapor form (NIOSH 1985, 

1986b; Purnell and Warwick 1981; Rappaport and Morales 1979). MBOCA is desorbed from the 

collection medium with an organic solvent. For GC analysis, the extract is usually reacted with a 

perfluoro fatty acid anhydride to make the corresponding MBOCA derivative that is then analyzed. 

The most commonly used detectors are FID, ECD, and thermionic nitrogen-specific detection (TSD, 

but TSD and ECD are preferred because of their increased sensitivity (sub- to low-ppb [pg/m-] 

range) and selectivity compared to FID (low-ppb range) (Ichikawa et al. 1990; Sawicki et al. 1975; 

Skarping et al. 1985; Yasuda 1975). Sample preparation for HPLC generally requires only 

desorption from the collection medium prior to separation on the HPLC column. Two detection 

methods, UV and ED, have been paired with HPLC for the analysis of air samples containing 

MBOCA (James et al. 1985; nieminen et al. 1983; NIOSH 1986b; Purnell and Warwick 1980, 1981; 

Rappaport and Morales 1979). Of these, ED is clearly the most sensitive (ppt [rig/m”] compared to 

sub to low ppb for UV) and selective detection method, and HPLC/ED is the method recommended 

by NIOSH for the detection of low levels of MBOCA in air (NIOSH 1986b; Purnell and Warwick 

1980, 1981). Both the HPLC and GC methods gave high recoveries and precision making them 

reliable methods for determination of MBOCA in air samples. HPLC/UV and GC/FID can be used 

to determine MBOCA in incinerator effluents indicating that even highly contaminated air samples 

can be analyzed with these methods (James et al. 1985). While no specific information was located 

on the analysis of similar materials using the other methods, it is likely that they too can be used for 

highly complex samples. 

HPLC/ED can be used to measure MBOCA in surface water, groundwater, soil, and sludge and is 

the IARC-recommended method for these media (Rice and Kissinger 1981, 1982). Liquid samples 

require only filtering prior to concentration on a reverse-phase HPLC column and separation on an 

analytical column. Solid samples must be mixed with water and filtered prior to the concentration 

step. Sensitivity is in the low-ppt range and precision is excellent. no recovery data were reported. 

An alternative EPA-recommended method of determining MBOCA in waste water requires more 

extensive sample handling prior to analysis by GC/TSD (EPA 1981a). This method has a sensitivity 




MBOCA 91
 

6. ANALYTICAL METHODS
 

in the low-ppb range, but analyte recovery varies widely. Both methods are selective for MBOCA. 

MBOCA has been detected in laboratory wastes using HPLC/UV/ED (Barek et al. 1985). While ED 

was found to be more sensitive than UV for many chemicals in the wastes, it was comparable for 

detection of MBOCA. Either detector could be used to monitor the destruction of aromatic amines 

in laboratory wastes. no details on recovery or precision were provided. 

Surface wipe and hand monitoring samples taken from areas in a factory in which MBOCA was used 

were analyzed for the chemical using HPLCKJV and HPLC/ED (NIOSH 1986b). Because of its 

increased sensitivity, HPLC/ED was used for all samples containing low levels (≤2 μg/mL) of 

MBOCA and HPLC/UV was used to analyze those with higher levels. Recovery and precision were 

both high using these methods. 

6.3 ADEQUACY OF THE DATABASE 

Section 104(i)(5) of CERCLA, as amended, directs the Administrator of ATSDR (in consultation 

with the Administrator of EPA and agencies and programs of the Public Health Service) to assess 

whether adequate information on the health effects of MBOCA is available. Where adequate 

information is not available, ATSDR, in conjunction with the NTP, is required to assure the initiation 

of a program of research designed to determine the health effects (and techniques for developing 

methods to determine such health effects) of MBOCA. 

The following categories of possible data needs have been identified by a joint team of scientists from 

ATSDR, NTP, and EPA. They are defined as substance-specific informational needs that if met 

would reduce the uncertainties of human health assessment. This definition should not be interpreted 

to mean that all data needs discussed in this section must be filled. In the future, the identified data 

needs will be evaluated and prioritized, and a substance-specific research agenda will be proposed. 

6.3.1 Identification of Data needs 

Methods for Determining Biomarkers of Exposure and Effect. The measurement of MBOCA 

in urine has been used to monitor populations exposed occupationally to the chemical. The most 

frequently used methods are HPLC/ED and GC/ECD (Gristwood et al. 1984; Ichikawa et al. 1990; 

NIOSH 1984, 1986b; Okayama et al. 1988; Thomas and Wilson 1984; Trippel-Schulte et al. 1986; 

Vantulder et al. 1981). These methods are sensitive and have produced reliable results in several 

monitoring studies to estimate exposure of workers who have contact with MBOCA during 

manufacturing operations. 

There are no known adverse health effects associated with exposure to MBOCA other than its weak 

association with bladder cancer. While hemoglobin adduct formation has been demonstrated in 

exposed animals (Chen et al. 1991; Sabbioni and neumann 1990), the relevance of these adducts with 

bladder cancer or with other adverse health effects is not known. The methods that have been tested 

for measuring hemoglobin adducts include HPLC/ED, GC/ECD, and GCMS (Chen et al. 1991; 

Sabbioni and neumann 1990). The limited information on these methods suggests that they are 

sensitive and reliable. However, since there is no clear relationship between the presence of these 

adducts in blood and adverse health consequences, no additional methods development is 

recommended at this time. 

Methods for Determining Parent Compounds and Degradation Products in Environmental 

Media. numerous methods have been developed for the measurement of MBOCA in air (Ebell et 
MBOCA 92
 

6. ANALYTICAL METHODS
 

al. 1980; Ichikawa et al. 1990; nieminen et al. 1983; NIOSH 1986b; Purnell and Warwick 1980, 1981; 

Rappaport and Morales 1979; Sawicki et al. 1975). The most sensitive and reliable of these are GC 

with TSD or ECD and HPLC with ED (Ebell et al. 1980; Ichikawa et al. 1990; NIOSH 1986b; 

Purnell and Warwick 1980, 1981). These methods are useful for the measurement of low 

concentrations (ppt) of MBOCA in air, and no additional methods development is needed. 

HPLC/ED and GC/TSD can be used to determine the presence of MBOCA in water and soil (EPA 

1981a; Rice and Kissinger 1981, 1982), surface wipe and hand monitoring samples (NIOSH 1986b), 

and laboratory waste (Barek et al. 1985). While these methods are sensitive for measuring MBOCA 

in ENVIRONMENT media, they are of unknown reliability. Some additional data on the accuracy and 

precision of measurements in liquid and solid media would be useful. 

6.3.2 On-going Studies 

No on-going studies focused on analytical method development for MBOCA were located. However, 

several of the on-going studies on MBOCA (FEDRIP 1991) involve the development of methods to 

better identify MBOCA adducts, which should make the process of monitoring exposed individuals 

easier. NIOSH is the sponsoring institution of three studies involving MBOCA that are currently in 

progress. Two of the three studies involve the development of more sensitive methods to monitor 

and evaluate the effects following MBOCA exposure. F.B. Daniel from NIOSH is the principal 

investigator of the study on “Biomonitoring for Populations Occupations Exposed to Aromatic 

Amines.” The investigator will analyze hemoglobin and DNA adduct formation by MBOCA in order 

to propose a methodology for monitoring workplace exposure. For the second project, L.L. Lowry 

from NIOSH is the principal investigator of the study entitled “Biological Monitoring Methods 

Research and Evaluation.” This study involves the development and evaluation of biological 

monitoring methods in urine to determine their effectiveness in predicting worker exposure to 

MBOCA. 

The NTP has a study in progress on “Aryl Amine Adducts in Blood as Indicators of Exposure” (NTP 

1991a). In this study, blood samples from 100 workers will be analyzed for hemoglobin o-toluidine 

adducts. MBOCA will be used to develop an HPLC method for separation and isolation of 

mitochondrial or total aryl amine-DNA adducts. In addition, the in vitro activation of potential 

carcinogens will be studied, and a mathematical model for MBOCA distribution, metabolism, and 

adduct formation will be prepared. The overall objective of the project is to develop a more sensitive 

adduct isolation procedure to be used for biological monitoring. The contact person for this project 

is K. Cheever (NTP 1991a). 
MBOCA 93
 

7. REGULATIONS AND ADVISORIES
 

The international, national, and state regulations and guidelines regarding MBOCA in air, water, and 

other media are summarized in Table 7-1. 

ATSDR has derived one MRL value for MBOCA. A chronic-duration oral MRL of 0.003 mg/kg/day 

was derived for MBOCA based on its ability to cause hepatic effects in dogs (Stula et al. 1977). EPA 

has not assigned a reference dose or concentration for MBOCA. 

MBOCA is on the list of chemicals appearing in “Toxic Chemicals Subject to Section 313 of the 

Emergency Planning and Community Right-to-Know Act of 1986” (EPA 1988d, 1988e). 

MBOCA is designated as a hazardous substance (EPA 1985, 1989) and is subject to reporting and 

record-keeping requirements (EPA 1986, 1988f). 

The Department of Health and Human Services has determined that MBOCA may reasonably be 

Anticipated to be a carcinogen (NTP 1991b). 



______________________ 

MBOCA 97
 

8. REFERENCES
 

Acedo GN, Redei GP. 1982. Accuracy of the identification of carcinogens and noncarcinogens by 

arabidopsis. Arabidopsis Information Service (19):103-107. 

*ACGIH. 1990. Threshold limit values for chemical substances and physical agents and biological 

exposure indices for 1990-1991. American Conference of Governmental Industrial Hygienists. 

Cincinnati, OH. 

*Ames BN, McCann J, Yamasaki E. 1975. Methods for detecting carcinogens and mutagens with 

the Salmonella/mammalian-microsome mutagenicity test. Mutation Res 31:347-363. 

Anderson D, Styles JA. 1978. An evaluation of 6-short-term tests for detecting organic chemical 

carcinogens: Appendix 2. The bacterial mutation test. Br J Cancer 37:924-930. 

*Angerer J, Schaller KH. 1985. Analyses of hazardous substances in biological materials. Germany: 

VCH Verlagsgesellschaft mbH, 1:17-30. 

Ashby J, Paton D, Callander RD. 1988. Potent mutagenicity to salmonella of equimolar mixture of 

52 chemicals used in five collaborative studies. Mutagenesis 3(4):345-348. 

*ATSDR. 1989. Decision guide for identifying substance-specific data needs related to toxicological 

profiles. Agency for Toxic Substances and Disease Registry. Atlanta, GA. 

*ATSDR. 1991. Agency for Toxic Substances and Disease Registry Annual report FY 1991. U. S. 

Department of Health and Human Services, Public Health Service, Agency for Toxic Substances and 

Disease Registry. Atlanta, GA. 

*Baker RS, Bonin AM. 1981. Study of 42 coded compounds with the Salmonella/mammalian 

microsome assay. In: deserres FJ, Ashby J, eds. Evaluation of short-term tests for carcinogens: 

Report of the International Collaborative Program. Prog Mutat Res 1:249-260. 

*Barek J, Pacakova V, Stulik K, et al. 1985. Monitoring of aromatic amines by HPLC with electrochemical 

detection: Comparison of methods for destruction of carcinogenic aromatic amines in 

laboratory wastes. Talanta 32(4):279-283. 

*Barnes DC, Dourson M. 1988. Reference dose (RfD): Description and use in health risk 

assessments. Regul Toxicol Pharmacol 8:471-486. 

*Barnes JR. 1964. Toxicity study on “MOCA” 4,4’-methylene-bis(2-chloroaniline). DuPont Haskell 

Lab Study no. MR-652. Sept. 10. 

Benigni R, Giulani A. 1985. Cluster analysis of short-term tests: A new methodological approach. 

Mutat Res 147(4):139-152. 

*Cited in text 
MBOCA 98
 

8. REFERENCES
 

Bertazzi PA. 1975. [Methylene-bis-o-chloroaniline (MBOCA): Anew chemical carcinogen.] Med 

Lav 66(2):81-84. (Italian) 

*Brooks TM, Dean BJ. 1981. Mutagenic activity of 42 coded compounds in the 

Salmonella/microsome assay with preincubation. In: deserres FJ, Ashby J, eds. Evaluation of shortterm 

tests for carcinogens: Report of the International Collaborative Program. Prog Mutat Res 

1:261-270. 

Brookes P, Preston RJ. 1981. Summary report on the performance of in vitro mammalia assays. In: 

Evaluation of short-term tests for carcinogens: Report of the International Collaborative Program. 

Prog Mutat Res 1:77-85. 

*Butler MA, Guengerich FP, Kadlubar FF. 1989. Metabolic oxidation of the carcinogens 4-aminobiphenyl 

and 4,4’-methylene-bis(2-chloroaniline) by human hepatic microsomes and by purified rat 

hepatic cytochrome P-450 monooxygenases. Cancer Res 49(1):25-31. 

Carpenter AV, Flanders WD, Frome EL, et al. 1988. Chemical exposures and central nervous 

system cancers: A case-control study among workers at two nuclear facilities. Am J Ind Med 

13(3):351-362. 

Cartwright RA. 1990. Bladder cancer screening in the UK. In: International Conference on Bladder 

Cancer Screening in High-Risk Groups, September 13-14, 1989. J Occup Med 32(9):878-880. 

*Caspary WJ, Daston DS, Myhr BC, et al. 1988. Evaluation of the L5178Y mouse lymphoma cell 

mutagenesis assay: Interlaboratory reproducibility and assessment. Environmental Molecular 

Mutagenesis 12 (suppl 13): 195-229. 

Casto BC. 1980. Detection of chemical carcinogens and mutagens in hamster cells by enhancement 

of adenovirus transformation. Adv Mod Environ Toxicol 1:241. 

*Casto BC. 1983. Comparison of the sensitivity of rodent and human cells to chemical carcinogens 

using viral transformation, DNA damage, and cytotoxicity assays. Basic Life Sci 24:429-449. 

*CDC/ATSDR. 1990. Biomarkers of organ damage or dysfunction for the renal, hepatobiliary and 

immune systems. Atlanta, GA: CDC/ATSDR Subcommittee on Biomarkers of Organ Damage and 

Dysfunction, Centers for Disease Control, Agency for Toxic Substances and Disease Registry. 

Summary Report, August 27, 1990. 

“Cheever KL, DeBord DG, Swearengin TF. 1991. 4,4’-Methylenebis(2-chloroaniline) (MOCA): The 

effect of multiple oral administration, route and phenobarbital induction on macromolecular adduct 

formation in the rat. Fundam Appl Toxicol 16(1):71-80. 

*Cheever KL, Richards DE, Weigel WW, et al. 1988. Macromolecular adduct formation by 

4,4’methylene-bis(2-chloroaniline) in adult male rat. Stand J Work Environ Health 14:57-59. 

*Cheever KL, Richards DE, Weigel WW, et al. 1990. 4,4’-Methylene-bis(2-chloraniline) (MOCA): 

Comparison of macromolecular adduct formation after oral or dermal administration in the rat. 

Fundam Appl Toxicol 14(2):273-28X 
MBOCA 99
 

8. REFERENCES
 

*Chen TH, Kuslikis BI, Braselton WE Jr. 1989. Hydroxylation of 4,4’-methylenebis(2-chloroaniline) 

by canine, guinea pig, and rat liver microsomes. Drug Metab Dispos 17(4):406-413. 

*Chen TH, Kuslikis BI, Braselton WE Jr. 1991. Unlabeled hemoglobin adducts of 4,4’­

methylenebis(2-chloroaniline) in rats and guinea pigs. Arch Toxicol 65(3):177-185. 

*Chin B, Tobes MC, Han SS. 1983. Absorption of 4,4’-methylenebis(2-chloroaniline) by human skin. 

Environ Res 32(1):167-178. 

*:CIS 1992. Chemical Information Systems, Inc. Baltimore, MD. 

*Clapp DE, Piacitelli GM, Zaebst DD, et al. 1991. Assessing exposure to 4,4’-methylenebis(2­

chloroaniline) (MBOCA) in the workplace. Appl Occup Environ Hyg 6(2):125-130. 

Cocker J, Wilson HK. 1989. Determination of 4,4’-methylenebis(2-chloroaniline) in urine: Letter. 

Clin Chem 35(3):506. 

*Cocker J, Boobis AR, Davis DS. 1986. Routes of activation of 4,4’-methylenebis(2-chloroaniline) 

and 4,4’-methylenedianiline to bacterial mutagens. In: International Conference on Practical in vitro 

Toxicology, Berkshire, England, September 18-20, 1985. Food Chem Toxicol 24(6-7):755-756. 

*Cocker J, Boobis AR, Davis DS. 1988. Determination of the n-acetyl metabolites of 4,4’-methylene 

dianiline and 4,4’-methylene-bis(2-chloroaniline) in urine. Biomed Env Mass Spec 17(3):161-167 

. 

*Cocker J, Boobis AR, Gibson JF, et al. 1985. The metabolic activation of 4,4’methylenebis(2­

chlorobenzeneamine) to a bacterial mutagen by hepatic postmitochondrial supernatant from human 

and other species. Environ Mutagen 7(4):501-509. 

*Cocker J, Boobis AR, Wilson HK, et al. 1990. Evidence that a beta-n-glucuronide of 4,4’­

methylene-bis(2-chloroaniline) (MBOCA) is a major urinary metabolite in man: Implications for 

biological monitoring. Br J Ind Med 47(3):154-161. 

Cocker J, Gristwood W, Wilson HK. 1986. Assessment of occupational exposure to 4,4’­

diaminodiphenylmethane (methylene dianiline) by gas chromatograph-mass spectrometry analysis of 

urine. Br J Ind Med 43(9):620-625. 

*Cowles SR. 1978. Cancer in the workplace--Pericicall Pott to the present. Milit Med 143(6):395­

400. 

*Daniel MR, Dehnel JM. 1981. Cell transformation test with baby hamster kidney cells. In: 

deserres FJ, Ashby J, eds. Evaluation of short-term tests for carcinogens: Report of the 

International Collaborative Program. Prog Mutat Res 1:626-637. 

Debord DG, Cheever KL, Swearengin RF. 1990. Alterations in histone phosphorylation in rat 

spleen cells after in vitro treatment with 4,4’-methylene-bis(2-chloroaniline) (MOCA). In: Society of 

Toxicology 29th Annual Meeting, Miami Beach, Florida, February 12-16, 1990. Washington, DC: 

Society of Toxicology, 417. 

De Serres FJ, Hoffmann GR. 1981. Summary report on the performance of yeast assays. In: 
MBOCA 100
 

8. REFERENCES
 

Evaluation of short-term tests for carcinogens: Report of the International Collaborative Program. 

Prog Mutat Res 1:68-76. 

DOE. 1979. MOCA permeation of protective clothing. Contract no. W-7405ENG-26. Washington, 

DC: U.S. Department of Energy. 

*Dormer M, Hytonen S, Sorsa M. 1983. Application of the sex-linked recessive lethal test in 

Drosophila melanogaster for monitoring the work ENVIRONMENT of a rubber factory. Hereditas 

99(1):7-10. 

*DUCOS P, Gaudin R. 1983. Methylene bis orthochloroaniline (“MOCA”). Evaluation of the 

occupational exposure in France. Cahiers de notes Documentaires 1X3:517-522. 

*DUCOS P , Maire C, Gaudin R. 1985. Assessment of occupational exposure to 4,4’­

methylenebis(2-chloroaniline) (MOCA) by a new sensitive method for biological monitoring. Int 

Arch Occup Environ Health 55(2):159-167. 

*Dunkel VC, Pienta RJ, Sivak A, et al. 1981. Comparative neoplastic transformation responses of 

Balb/3T3 cells, Syrian hamster embryo cells, and Rauscher murine leukemia virus-infected Fischer 344 

rat embryo cells to chemical carcinogens. J nat1 Cancer Inst 67(6):1303-1312. 

*Dunkel VC, Zeiger E, Brusick D, et al. 1984. Reproducibility of microbial mutagenicity assays: 

1. Tests with Salmonella typhimurium and Escherichia coli using a standardized protocol. Environ 

Mutagen G(supp1 2):1-254. 

*Ebell GF, Fleming DE, Genovese JH, et al. 1980. Simultaneous determination of 2,4- and 2,6­

diisocyanatotoluene (TDI) and 3,3’-dichloro-4,4’-diaminodiphenylmethane (MOCA) in air. Ann 

Occup Hyg 23(2):185-188. 

*Edwards JW, Priestly BG. 1992. Biological and biological-effect monitoring of workers exposed to 

4,4’- methylene-bis(2-chloroaniline). Hum Exp Toxicol 11(3):229-236. 

*Endo Y, Hara I. 1991. DNA-adduct detection in rats administered with 4,4’-methylenedianiline or 

4,4’-methylenebis(2-chloroaniline). J Ind Health 33430-431. 

*EPA. 1979. Treatability of carcinogenic and other hazardous organic compounds. Contract no. 

CI-68-03-2559. Cincinnati, OH: U.S. Environmental Protection Agency, Office of Research and 

Development. Document no. 600/2-79-097. 

*EPA. 1981a. Development of analytical test procedures for organic pollutants in wastewater ­

application to pesticides. Contract no. 68-03-2711. Cincinnati, OH: U.S Environmental Protection 

Agency, Industrial Environmental Research Laboratory, Office of Research and Development. EPA 

600/4-81-017. Document no. PB82-182507. 

*EPA. 1981b. Engineering handbook for hazardous waste incineration. Contract no. 68-3-3025. 

Cincinnati, OH: U.S. Environmental Protection Agency, Office of Environmental Engineering and 

Technology. Document no. PB81-248163. 

EPA. 1984. Data acquisition for Environmental transport and fate screening for compound of 
MBOCA 101
 

8. REFERENCES
 

interest to the office of emergency and remedial response. Contract no. 68-03-2981. Athens, GA: 

U.S. Environmental Protection Agency, Office of Health and Environmental Assessment. Document no. 

PB84-245281. 

*EPA. 1985. List of hazardous substances and reportable quantities. U.S. Environmental Protection 

Agency. Code of Federal Regulations. 40 CFR 302.4. 

*EPA. 1986. 4,4’-Methylenebis (2-chloroaniline): Final reporting and record keeping requirements. 

U.S. Environmental Protection Agency. Federal Register 51(75):13220-13224. 

EPA. 1987a. Effects of 4,4’-methylene-(2-chloroaniline) and benzotrichloride in humans and/or 

animal tissues. Cooperative agreement no. CR-812121. Research Triangle Park, nC: U.S. 

Environmental Protection Agency, Health Effects Research Laboratory. Document no. PB88­

117882. 

EPA. 1987b. Letter from NIOSH to USEPA forwarding more information on workers exposed to 

4,4’-methylenebis(2-chloroaniline) and diagnosed as having a bladder tumor (5/29/87). Washington, 

DC. U.S. Environmental Protection Agency. EPA no. FYI-OTS-0687-0552. 

EPA. 1987c. Toxic air pollutant/source crosswalk - a screening tool for locating possible sources 

emitting toxic air pollutants. Washington, DC: U.S. Environmental Protection Agency, Office of Air 

Quality Planning and Standards. 

*EPA. 1988a. Hazardous waste management system: Identification and listing of hazardous waste. 

U.S. Environmental Protection Agency. Code of Federal Regulations. 40 CFR 261. 

*EPA. 1988b. Hazardous waste management system: Identification and listing of hazardous waste. 

U.S. Environmental Protection Agency. Federal Register 53(78): 13382-13393. 

*EPA. 1988~. Measurement of hydrolysis rate constants for evaluation of hazardous waste land 

disposal. Volume 3: Data on 70 chemicals. Athens, GA: U.S. Environmentall Protection Agency, 

Office of Research and Development. EPA/600/3-88028, document no. PB88-234042. 

*EPA. 1988d. Toxic chemical release reporting: Community right-to-know. U.S. Environmental 

Protection Agency. Code of Federal Regulations. 40 CFR 372. 

*EPA. 1988e. Toxic chemical release reporting: Community right-to-know. U.S. Environmental 

Protection Agency. Federal Register 53(30):4500-4554. 

*EPA. 1988f. TSCA comprehensive assessment information rule: Reporting and recordkeeping 

requirements. U.S. Environmental Protection Agency. Code of Federal Regulations. 40 CFR 704. 

*EPA. 1989. List of hazardous substances and reportable quantities. U.S. Environmental Protection 

Agency. Federal Register 54(155):33426-X3484. 

*EPA. 1990a. Interim methods for development of inhalation reference doses. Research Triangle 

Park, nC. U.S. Environmental Protection Agency. EPA/600/8-90/066A. 

*EPA. 1990b. Health and Environmental effects document for 4,4’-methylenebis(2-chloroaniline). 
MBOCA 102
 

8. REFERENCES 

Cincinnati, OH. U.S. Environmental Protection Agency, Office of Solid Waste and Emergency 

Responses. EPA 600/x-85/371. 

*EPA. 1991a. Land disposal restrictions. U.S. Environmental Protection Agency. Code of Federal 

Regulations. 40 CFR 268. 

*’EPA. 1991b. Land disposal restrictions. U.S. Environmental Protection Agency. Federal Register 

56(21):3876-3928. 

*Farmer PB, Rickard J, Robertson S. 1981. The metabolism and distribution of 4,4’-methylenebis(2­

chloroaniline) (MBOCA) in rats. J Appl Toxicol 1(6):317-322. 

*FEDRIP. 1991. Federal Research in Progress. Dialog Information Service, Inc.. December 1991. 

Fielder RJ, Dale EA, Smith AM, et al. 1983. Trimellitic anhydride (TMA); 4,4’-methylenebis-(2­

chloroaniline) (MBOCA): n-nitrosodiethanolamine (nDELA). London, England: H.M. Stationery 

Office. 

Fishbein L. 1984. Aromatic amines. In: The handbook of environmental chemistry: Anthropogenic 

substances. Berlin, Germany: Springer-Verlag, 3:1-40. 

*Galloway SM, Bloom AD, Resnick M, et al. 1985. Development of a standard protocol for in vitro 

cytogenetic testing with Chinese hamster ovary cells: Comparison of results for 22 compounds in two 

laboratories. Environ Mutagen 21-51. 

*Garner RC, Welch A, Pickering C. 1981. Mutagenic activity of 42 coded compounds in the 

Salmonella/microsome assay. In: deserres FJ, Ashby J, eds. Evaluation of short-term tests for 

carcinogens: Report of the International Collaborative Program. Prog Mutat Res 1:280-284. 

*Gatehouse D. 1981. Mutagenic activity of 42 coded compounds in the “microtiter” fluctuation test. 

In: deserres FJ, Ashby J, eds. Evaluation of short-term tests for carcinogens: Report of the 

International Collaborative Program. Prog Mutat Res 1376-386. 

*GISO. 1985. General Industry Safety Orders: California Title 8, Section 5215:886-890; effective 

July 1985. 

Goutet P. 1981. 4,4’-Methylenebis(2-chloroaniline): Toxicological hazards and exposure at work. 

Cahiers de notes Documentaires 104387-393. 

Graul RJ, Stanley RL. 1982. Specific gravity adjustment of urine analysis results. Am Ind Hyg Assoc 

J 43(11):86X 

*Gristwood W, Robertson SM, Wilson HK. 1984. The determination of 4,4’-methylenebis(2­

chloroaniline) in urine by electron capture gas chromatography. J Anal Toxicol 8(3):101-105. 

*Groth DH, Weigel WW, Tolos WP, et al. 1984. 4,4’-Methylene-bis-ortho-chloroaniline (MBOCA): 

Absorption and excretion after skin application and gavage. Environ Res 34(1):38-54. 

*Grundmann E, Steinhoff D. 1970. Liver and lung tumors in rats from 3,3’-dichloro-4,4’­
MBOCA 103
 

8. REFERENCES 

diaminodiphenyl-methane. Z Krebsforschung 74:28-39. 

Haworth S, Lawlor T, Mortelmans K, et al. 1983. Salmonella mutagenicity test results for 250 

chemicals. Environ Mutagen 5(Suppl):3-142. 

*HAZDAT. 1993. Agency for Toxic Substances and Disease Registry (ATSDR), Atlanta, GA. 

February 13, 1992. 

Hendry WF, Blandy JP, Glashan RW, et al. 1988. Occupational bladder cancer: A guide for 

clinicians. Br J of Urology 61(3):183-191. 

Henning HF. 1974. Precautions in the use of methylene-bis-o-chloroaniline (MBOCA). Ann Occup 

Hyg 17(2):137-142. 

Henschler D. 1983. Methods of determination of harmful industrial substances. Volume 2: Analyses 

of biological matter. Germany: Verlag Chemie, 7th Supplement. 

Henschler D. 1987. Risk assessment and evaluation of chemical carcinogens present and future 

strategies. J Cancer Res Clin Oncol 1X3(1):1-7. 

*Hesbert A, Bottin MC, DeCeaurriz J. 1985. Mutagenicity of 4,4’-methylenebis(2-chloroaniline) 

“MOCA” and its n-acetyl derivatives in S. typhimutium. Int Arch Occup Environ Health 55(2):169­

174. 

Hogan TJ. 1993. Case study “Carcinogens”: The MBOCA TLV example. Am Ind Hyg Assoc J 

54(S):458-460. 

*Hosein HR, Van Roosmalen PB. 1978. Acute exposure to methylene-bis-ortho chloroaniline 

(MOCA). Am Ind Hyg Assoc J 39(6):496-497. 

*Howard PH, Boethling RS, Jarvis WF, et al. 1991. Handbook of Environmental degradation rates. 

Chelsea, MI: Lewis Publishers, 348-349. 

*HSDB. 1991. 4,4’-Methylenebis(2-chloraniline). Hazardous Substances Data Bank. national 

Library of Medicine, national Toxicology Information Program, Bethesda, MD. October 17, 1991. 

*Hubbard SA, Green MHL, Bridges BA, et al. 1981. Fluctuation test with S9 and hepatocyte 

activation. In: deSerres FJ, Ashby J, eds. Evaluation of short-term tests for carcinogens: Report of 

the International Collaborative Program. Prog Mutat Res 1361-370. 

*IARC. 1974. IARC monographs on the evaluation of the carcinogenic risk of chemicals to man: 

Some aromatic amines, hydrazine and related substances, n-nitroso compounds and miscellaneous 

alkylating agents. Vol. 4:65-71. Lyon, France: World Health Organization, International Agency for 

Research on Cancer. 

*IARC. 1987. IARC monographs on the evaluation of the carcinogenic risk to man: Summary table. 

Supp. 7:66. Lyon, France: World Health Organization, International Agency for Research on 

Cancer. 
MBOCA 104
 

8. REFERENCES 

IARC. 1990. IARC scientific publications, no. 100. Cancer: causes, occurrence and control 

100:129-130. Lyon, France: World Health Organization, International Agency for Research on 

Cancer. 

*Ichikawa Y, Yoshida M, Okayama A, et al. 1990. Biological monitoring for workers exposed to 

4,4’-methylenebis(2-chloroaniline). Am Ind Hyg Assoc J 51(1):5-7. 

*Ichinotsubo D, Mower H, Mandel M. 1981a. Mutagen testing of a series of paired compounds with 

the Ames Salmonella testing system. In: deserres FJ, Ashby J, eds. Evaluation of short-term tests 

for carcinogens: Report of the International Collaborative Program. Prog Mutat Res 1:298-301. 

*Ichinotsubo D, Mower H, Mandel H. 1981b. Testing of a series of paired compounds (carcinogen 

and noncarcinogenic structural analog) by DNA repair-deficient E. coli strains. In: deSerres FJ, 

Ashby J, eds. Evaluation of short-term tests for carcinogens: Report of the International 

Collaborative Program. Prog Mutat Res 1:195-198. 

Igaku S. 1991. [DNA-adduct detection in rats administered with 4,4’-methylenedianiline or 

4’4-methylene bis(2-chloraniline).] Endo, Yoko: Hara, Ichiro (Department of Public Health, Kansai 

Med. Univ., Moriguchi 570) 33(5):430-431. (Japanese) 

*Jagannath DR, Vultaggio DM, Brusick DJ. 1981. Genetic activity of 42 coded compounds in the 

mitotic gene conversion assay using Saccharomyces cerevisiae strain D4. In: deserres FJ, Ashby J, 

eds. Evaluation of short-term tests for carcinogens: Report of the International Collaborative 

Program. Prog Mutat Res 1:456-467. 

*James RH, Adams RE, Finkel JM, et al. 1985. Evaluation of analytical methods for the 

determination of POHC in combustion products. J Air Pollut Control Assoc 35(9):959-969. 

Jedrzejczak K, Gaind VS. 1992. Determination of 4,4’-methylenebis(2-chloroaniline) in urine using 

capillary gas chromatography and negative ion chemical ionization mass spectrometry. Analyst 

117:1417-1420. 

Johnson LD. 1985. Air pollution - “toxic” or “hazardous” air pollutants. International Congress 

Symposium Series - R Society of Medicine 82:15-23. 

*Kada T. 1981. The DNA-damaging activity of 42 coded compounds in the Ret-assay. In: deserres 

FJ, Ashby J, eds. Evaluation of short-term tests for carcinogens: Report of the International 

Collaborative Program. Prog Mutat Res 1:175-182. 

Kada T, Green M, Mandel M, et al. 1981. Summary report on the performance of bacterial repair, 

phage induction, degranulation, and nuclear enlargement assay. In: deserres FJ, Ashby J, eds. 

Evaluation of short-term tests for carcinogens: Report of the International Collaborative Program. 

Prog Mutat Res 1:33-48. 

Kadlubar FF. 1987. Metabolism and DNA binding of carcinogenic aromatic amines. IS1 Atlas Sci 

Pharmacol 1(2):129-132. 

Kadlubar FF, Culp SJ, Turesky RJ, et al. 1990. Biochemical mechanisms of DNA adduct formation 

in human tissues by carcinogenic aromatic amines. In: 15th International Cancer Congress, Hamburg, 
MBOCA 105
 

8. REFERENCES 

Germany, August 16-22, 1990. J Cancer Res Clin Oncol llG(Supp1, part 2):1062. 

Karstadt M, Bobal R. 1982. Availability of epidemiologic data on humans exposed to animal 

carcinogens: 2. Chemical uses and production volume. Teratogenesis Carcinog Mutagen 2(2):1.51-168. 

Karstadt M, Bobal R, Selikoff IJ. 1981. A survey of availability of epidemiologic data on humans 

exposed to animal carcinogens. In: Peto R, Schneiderman M, eds. Banbury report, volume 9. 

Quantification of Occupational Cancer Meeting, March 29-April 2, 1981. Cold Spring Harbor, nY: 

Cold Spring Harbor Laboratory, 0(0):223-246. 

*Kassinova GV, Kovaltsova SV, Marfin SV, et al. 1981. Activity of 40 coded compounds in 

differential inhibition and mitotic crossing-over assays in yeast. In: deserres FJ, Ashby J, eds. 

Evaluation of short-term tests for carcinogens: Report of the International Collaborative Program. 

Prog Mutat Res 1:434-455. 

*Katz M, Heddle JA, Salamone MF. 1981. Mutagenic activity of polycyclic aromatic hydrocarbons 

and other Environmental pollutants. In: Dennis AJ, ed. Chemical analytical and biological fate: 

Polynuclear aromatic hydrocarbons, 5th International Symp. Columbus, OH: Battelle Press, 519-528. 

*Keeslar FL. 1986. The removal and control of methylene-bis orthochloroaniline in residential and 

industrial areas of Adrian, Michigan. In: Ludwigson J, ed. Proceedings of the 1986 Conference on 

Hazardous Material Spills, Preparedness, Prevention Control, and Cleanup of Releases, St. Louis, MO, 

May 5-8, 1986. Rockville, MD: Government Institute Inc., 93-97. 

*Kommineni C, Groth DH, Frockt IJ, et al. 1979. Determination of the tumorigenic potential of 

methylene-bis-orthochloroaniline. J Environ Pathol Toxicol 2(5):149-171. 

*Kugler-Stegmeier ME, Friederich U, Graf U, et al. 1989. Genotoxicity of aniline derivatives in 

various short-term tests. Mutat Res 211(2):279-289. 

Kuslikis BI. 1989. Metabolic activation in the rat, dog, guinea pig and human of the suspect 

carcinogen 4,4’-methylenebis(2-chloroaniline). Diss Abstr Int 50(3):825-B. 

*Kuslikis BI, Tosko JE, Braselton WE Jr. 1991. Mutagenicity and effect on gap-junctional 

intercellular communication of 4,4’-methylenebis(2-chloroaniline) and its oxidized metabolites. 

Mutagenesis 6(1):19-24. 

Lichtenberg JJ, Longbottom JE, Bellar TA. 1987. Analytical methods for the determination of 

volatile nonpolar organic chemicals in water and water related environments. In: Suffet IH, 

Malaiyandi M, eds. Advances in chemistry series 214, organic pollutants in water: Sampling, analysis, 

and toxicity testing. 188th Meeting of the American Chemical Society, Philadelphia, PA, August 29­

31, 1984. Washington, D-C.: American Chemical Society, 63-82. 

Linch AL. 1974. Biological monitoring for industrial exposure to cyanogenic aromatic nitro and 

amino compounds. Am Ind Hyg Assoc J 35:426-432. 
MBOCA 106
 

8. REFERENCES
 

*Linch AL, O’Connor GB, Barnes JR, et al. 1971. Methylene-bis-ortho-chloroaniline (MOCA): 

Evaluation of hazards and exposure control. Am Ind Hyg Assoc J 32(12):802-819. 

Locke J. 1986. Fixing exposure limits for toxic chemicals in the UK - some case studies. Sci Total 

Environ 51:237-260. 

*Lowry LK, Clapp DE. 1992. Urinary 4,4’-methylenebis(2-chloroaniline)(MBOCA): A case for 

biological monitoring. Appl Occup Environ Hyg 7:593-598. 

*MacDonald DJ. 1981. Salmonella/microsome tests on 42 coded chemicals. In: deSerres FJ, Ashby 

J, eds. Evaluation of short-term tests for carcinogens: Report of the International Collaborative 

Program. Prog Mutat Res 1:285-297. 

Manis MO, Braselton WE. 1982. Enzymatic and chromatographic characterization of the major 

urinary metabolite of 4,4’-methylenebis-2-chloroaniline in dogs. In: 66th Annual Meeting of the 

Federation of American Societies for Experimental Biology, new Orleans, LA, April 15-23, 1982. 

Fed Proc 41(5):Abstract 7646. 

Manis MO, Braselton WE. 1983. Protein binding and structure identification of the major urinary 

metabolite of 4,4’-methylenebis-2-chloroaniline in dogs. In: 67th Annual Meeting of the Federation 

of American Societies for Experimental Biology, Chicago, IL, April 10-15, 1983. Fed Proc 

42(3):Abstract 354. 

*Manis MO, Braselton WE. 1984. Structure elucidation and in vitro reactivity of the major 

metabolite of 4,4’-methylenebis(2-chloroaniline) (MBOCA) in canine urine. Fundam Appl Toxicol 

4(6):1000-1008. 

Manis MO, Braselton WE. 1986. Metabolism of 4,4’-methylenebis(2-chloroaniline) by canine liver 

and kidney slices. Drug Metab Dispos 14(2):166-174. 

*Manis MO, Williams DE, McCormack KM, et al. 1984. Percutaneous absorption, disposition, and 

excretion of 4,4’-methylenebis(2-chloroaniline) in dogs. Environ Res 33(1):234-245. 

*Martin Cn, McDermid AC. 1981. Testing of 42 coded compounds for their ability to induce 

unscheduled DNA repair synthesis in HeLa cells. In: deSerres FJ, Ashby J, eds. Evaluation of shortterm 

tests for carcinogens: Report of the International Collaborative Program. Prog Mutat Res 

1:533-537. 

*Martire G, Vricella G, Perfumo Am, et al. 1981. Evaluation of the mutagenic activity of coded 

compounds in the Salmonella test. In: deSerres FJ, Ashby J, eds. Evaluation of short-term tests for 

carcinogens: Report of the International Collaborative Program. Prog Mutat Res 1:271-279. 

*Mason TJ, Vogler WJ. 1990. Bladder cancer screening at the DuPont Chambers Works: A new 

initiative. J Occup Med 32(9):874-877. 

*Matsushima T, Takamoto Y, Shirai A, et al. 1981. Reverse mutation test on 42 coded compounds 

with the E. coli WP2 system. In: deSerres FJ, Ashby J, eds. Evaluation of short-term tests for 

carcinogens: Report of the International Collaborative Program. Prog Mutat Res 1:387-395. 
MBOCA 107
 

8. REFERENCES 

*McCann J, Choi E, Yamasaki E, et al. 1975. Detection of carcinogens as mutagens in the
 

Salmonella/microsome test: Assay of 300 chemicals. Proc nat1 Acad Sci 72:5135-5139.
 

*McKerrell PJ, Saunders GA, Geyer R. 1987. Determination of 4,4’-methylenebis(2-chloroaniline)
 

in urine by high-performance liquid chromatography. J Chromatog 408399-401.
 

McQueen CA, Williams GM. 1982. Cytotoxicity of xenobiotics in adult rat hepatocytes in primary
 

culture. Fundam Appl Toxicol 2(3):139-144.
 

*McQueen CA, Williams GM. 1987. The hepatocyte primary culture/DNA repair test using
 

hepatocytes from several species. Cell Biology and Toxicology 3(2):209-218.
 

McQueen CA, Williams GM. 1990. Review of the genotoxicity and carcinogenicity of 4,4’­

methylene-dianiline and 4,4’-methylene-bis-2-chloroaniline. Mutat Res 239(2):133-142.
 

*McQueen CA, MasLansky CJ, Crescenzi SB, et al. 1981. The genotoxicity of 4,4’-methylenebis-2­

chloroaniline in rat, mouse and hamster hepatocytes. Toxicol Appl Pharmacol 58(2):231-235.
 

*McQueen CA, Maslansky CJ, Williams GM. 1983. Role of the acetylation polymorphism in
 

determining susceptibility of cultured rabbit hepatocytes to DNA damage by aromatic amines. Cancer
 

Res 43(7): 3120-3123.
 

*Mehta RD, Von Borstel RC. 1981. Mutagenic activity of 42 encoded compounds in the haploid
 

yeast reversion assay, strain XV185-14C. In: deserres FJ, Ashby J, eds. Evaluation of short-term
 

tests for carcinogens: Report of the International Collaborative Program. Prog Mutat Res 1:414-423.
 

*Messerly EA, Fekete JE, Wade DR, et al. 1987. Structure-mutagenicity relationships of benzidine
 

analogues. Environ Mol Mutagen 10(3):263-274.
 

Mitchell AD, Myhr BC, Rudd CJ, et al. 1988. Evaluation of the L5178Y mouse lymphoma cell
 

mutagenesis assay: Methods used and chemicals evaluated. Environ Mol Mutagen 12(Suppl 13):1-18.
 

Morales R, Rappaport SM, Hermes RE. 1979. Air sampling and analytical procedures for benzidine,
 

3,3’-dichlorobenzidine and their salts. Am Ind Hyg Assoc J 40(11):970-978.
 

Mori H, Tanaka T, niwa K, et al. 1989. Induction of altered hepatocellular foci of hamster for a
 

I possible short-term assay for carcinogens. Res Commun Chem Pathol Pharmacol 63(3):451-454.
 

:“Mori H, Yoshimi n, Sugie S, et al. 1988. Genotoxicity of epoxy resin hardeners in the hepatocyte
 

primary culture/DNA repair test. Mutat Res 204(4):683-688.
 

Morton KC, King CM, Vaught JB, et al. 1983. Prostaglandin H synthase-mediated reaction of
 

carcinogenic arylamines with tRnA and homopolyribonucleotides. Biochem Biophy Res Commun
 

111(1):96-103.
 

*Morton KC, Lee M-S, Siedlik P, et al. 1988. Metabolism of 4,4’-methylenebis-2-chloroaniline
 

(MOCA) by rats in tiivo and formation of n-hydroxy MOCA by rat and human liver microsomes.
 

Carcinogenesis 9(5):731-739.
 
MBOCA 108
 

8. REFERENCES
 

*Myhr BC, Caspary WJ. 1988. Evaluation of the L5178Y mouse lymphoma cell mutagenesis assay: 

Intralaboratory results for sixty-three coded chemicals tested at Litton Bionetics, Inc. Environ Mol 

Mutagen 12(Suppl 13):103-194. 

*Nagao M, Takahashi Y. 1981. Mutagenic activity of 42 coded compounds in the 

Salmonella/microsome assay. In: deserres FJ, Ashby J, eds. Evaluation of short-term tests for 

carcinogens: Report of the International Collaborative Program. Prog Mutat Res 1302-313. 

Nakamura S, Oda Y, Oki I, et al. 1986. A simple test system (Umu test) for the detection of 

Environmental mutagens: 5. Further evaluation of the Umu test as a primary screening for 

carcinogens. Mutat Res 164:275. 

*NAS/NRC. 1989. Biologic markers in reproductive toxicology. national Academy of 

Sciences/national Research Council. Washington, DC: national Academy Press, 15-35. 

*NATICH. 1992. Data base report on state, local, and EPA air toxics activities. national Air Toxics 

Information Clearinghouse. Washington, DC: U.S. Environmental Protection Agency, Office of Air 

Quality Planning and Standards. March 12, 1992. 

*Nesnow S, Triplett LL, Slaga TJ, et al. 1985. Carcinogenesis: A comprehensive survey. Volume 

8. In: Mass MJ, Kaufman DG, Siegfried JM, eds. Cancer of the respiratory tract: Predisposing 

factors. new York, nY: Raven Press, 257-277. 

*Niemenen EH, Saarinen LH, Laakso JR. 1983. Simultaneous determination of aromatic isocyanates 

and some carcinogenic amines in the work atmosphere by reversed-phase high-performance liquid 

chromatography. J Liq Chromatogr 6(3):453-469. 

NIOSH. 1973. Hazard review of 4,4’-methylene-bis(2-chloroaniline). Rockville, MD: national 

Institute for Occupational Safety and Health. Document no. PB87-210837. 

NIOSH. 1977. 104-Week carcinogenicity study in male rats 4,4’-methylene-bis(2-chloroaniline) 

(MOCA). Cincinnati, OH: national Institute for Occupational Safety and Health. Document no. 

PB83-239475. 

NIOSH. 1978a. Health hazard evaluation determination. Report no. 77-125-547, Amphenol Cadre, 

Longmont, Colorado. Cincinnati, OH: national Institute for Occupational Safety and Health, Health 

Hazard and Technical Assistance Branch. Document no. PB81-143794. 

*NIOSH. 1978b. Special hazard review with control recommendations for 4,4’-methylenebis(2­

chloroaniline). U. S. Department of Health, Education and Welfare, national Institute for 

Occupational Safety and Health. Publication no. 78-188. 

*NIOSH. 1984. 1985 Supplement to NIOSH manual of analytical methods. 3rd edition. Cincinnati, 

OH: Division of Physical Sciences and Engineering, national Institute for Occupational Safety and 

Health, Department of Health and Human Services. Publication no. 84-100. 

*NIOSH. 1985. Health hazard evaluation report HETA 84-508-1626, Steinmetz and Sons, Moscow, 

Pennsylvania. Cincinnati, OH: national Institute for Occupational Safety and Health, Hazard 

Evaluations and Technical Assistance Branch. Document no. PB86-191830. 
MBOCA 109
 

8. REFERENCES
 

*NIOSH 1986a. Health hazards evaluation report HETA 85-407-1692, Parkway Products, Inc.. 

Contract no. HETA 85-407-1692. Cincinnati, OH: national Institute for Occupational Safety and 

Health, U.S. Department of Health and Humans Services. Document no. PB87-108023. 

*NIOSH. 1986b. Industrial hygiene survey report, Parkway Products, Inc., Cincinnati, OH. Contract 

no. IWS-144.13. Cincinnati, OH: national Institute for Occupational Safety and Health, Department 

of Heaith and Human Services. Document no. PB87-222360. 

*NOES. 1992. national Occupational Exposure Survey (1981-1983). Cincinnati, OH: U.S. 

Department of Health and Human Services, national Institute for Occupational Safety and Health, 

Division of Surveillance, Hazard Evaluations, and Field Studies (Unpublished provisional data as of 

7/l/90). 

*NRC. 1981. Aromatic Amines: An assessment of the biological and Environmental effects. 

Washington, DC: national Academy Press, p. 19, 168-197. 

*NTP. 1991a. national Toxicology Program: Fiscal Year 1991 Annual Plan, Atlanta, GA: national 

Toxicology Program, 72-73. 

*NTP. 1991b. national Toxicology Program: Sixth annual report on carcinogens: 1991 Summary. 

Atlanta, GA. national Toxicology Program. 

*OHM/TADS. 1985. 4,4’-Methylenebis(2-chloraniline). Oil and Hazardous Materials/Technical 

Assistance Data System. Baltimore, MD: Chemical Information Systems, Inc. December 1985. 

*Okayama A, Ichikawa Y, Yoshida M, et al. 1988. Determination of 4,4’-methylenebis(2­

chloroaniline) in urine by liquid chromatography with ion-paired solid-phase extraction and 

electrochemical detection. Clin Chem 34(10):2122-2125. 

*OSHA. 1987. Access to employee exposure and medical records. Occupational Safety and Health 

Administration. Code of Federal Regulations. 29 CFR 1910.20. 

*OSHA. 1988. Access to employee exposure and medical records. Occupational Safety and Health 

Administration. Federal Register 53(189): 30163-30164. 

*OSHA. 1989a. Toxic and hazardous substances. Occupational Safety and Health Administration. 

Code of Federal Regulations. 29 CFR 1910.1000. 

*OSHA. 1989b. Toxic and hazardous substances. Part 1910. Occupational Safety and Health 

Administration. Federal Register 54(12): 2920-2960. 

*Osorio AM, Clapp D, Ward E, et al. 1990. Biological monitoring of a worker acutely exposed to 

MBOCA. Am J Ind Med 18 (5): 577-589. 

*OTA. 1990. neurotoxicity: Identifying and controlling poisons of the nervous system. Washington, 

DC: Office of Technology Assessment, U.S. Congress. OTA-BA-436. April 1990. 
MBOCA 110
 

8. REFERENCES
 

*Parkes HG. 1976. The epidemiology of the aromatic amine cancers. In: Searle CE, ed. Chemical 

carcinogens. Washington, D.C.: American Chemical Society, American Chemical Society Monograph, 

173. 

*Parkes HG. 1979. The identification and control of occupational bladder cancer. IARC Sci Pub1 

25:462-480. 

*Parris GE, Diachenko GW, Entz RC, et al. 1980. Waterborne methylene bis-2-chloroaniline and 

2-chloroaniline contamination around Adrian, Michigan. Bull Environ Contam Toxicol 24(4):497-503. 

*Parry JM, Sharp DC. 1981. Induction of mitotic aneuploidy in the yeast strain D6 by 42 coded 

compounds. In: deserres FJ, Ashby J, eds. Evaluation of short-term tests for carcinogens: Report 

of the International Collaborative Program. Prog Mutat Res 1:468-480. 

Pereira MA. 1985. Mouse liver tumor data assessment of carcinogenic activity. In: An International 

Symposium on Advances in Health Risk Assessment for Systemic Toxicants and Chemical Mixtures. 

Toxicol Ind Health 1(4):311-334. 

*Perry PE, Thomson EJ. 1981. Evaluation of the sister chromatid exchange method in mammalian 

cells as a screening system for carcinogens. In: deSerres FJ, Ashby J, eds. Evaluation of short-term 

tests for carcinogens: Report of the International Collaborative Program. Prog Mutat Res 1:560-569. 

Piegorsch WW, Hoe1 DG. 1988. Exploring relationships between mutagenic and carcinogenic 

potencies. Mutat Res 196(2):161-176. 

Purchase IFH, Longstaff E, Ashby J, et al. 1978. Mutagenicity studies. Br J Cancer 37:873. 

*“Purnell CJ, Warwick CJ. 1980. Application of electrochemical detection to the measurement of 

4,4’-methylenebis(2-chloroaniline) and 2-chloroaniline concentrations in air by high-performance liquid 

chromatography. Analyst 105(1254):861-867. 

*Purnell CJ, Warwick CJ. 1981. Method 3 - analysis of 3,3’-dichloro-4,4’-diaminodiphenyl methane 

(MOCA) and 2-chloroaniline in air. In: Egan H, ed. Environmental carcinogens: Selected methods 

of analysis. Vol. 4: Some aromatic amines and azo dyes in the general and industrial Environment. 

Lyon, France: World Health Organization, International Agency for Research on Cancer. IARC 

scientific publication no. 40, 133-140. 

*Rae TK, Dorsey GF, Allen BE, et al. 1982. Mutagenicity of 4,4’-methylenedianiline derivatives in 

the Salmonella histidine reversion assay. Arch Toxicol 49(3-4):185-190. 

*Rappaport SM, Morales R. 1979. Air-sampling and analytical method for 4,4’-methylenebis 

(2-chloroaniline). Anal Chem 51(1):19-23. 

*Rice JR, Kissinger PT. 1981. Method for determination of benzidine, 3,3’-dimethoxybenzidine, 4­

aminobiphenyl, 3,3’-dichlorobenzidine, and 4,4’-methylene-bis(2-chloroaniline) (MOCA) in soil 

samples’ surface water and groundwater by liquid chromatography with electrochemical detection. 

In: Egan H, Fishbein L, Castegnaro M, et al. eds. Environmental carcinogens: Selected methods of 

analysis. Volume 4: Some aromatic amines and azo dyes in the general and industrial environment. 

Lyon, France: World Health Organization, International Agency for Research on Cancer, 141-151. 
MBOCA 111
 

8. REFERENCES
 

*Rice JR, Kissinger PT. 1982. Liquid chromatography with precolumn sample preconcentration and 

electrochemical detection: Determination of aromatic amines in Environmental samples. Environ Sci 

Technol 16(5):263-268. 

Richold M, Jones E. 1981. Mutagenic activity of 42 coded compounds in the salmonella/microsome 

assay. In: deserres FJ, Ashby J, eds. Evaluation of short-term tests for carcinogens: Report of the 

International Collaborative Program. Prog Mutat Res 1314-322. 

Ringen K. 1988. Regulate 4,4’-methylene-bis(2-chloroaniline). Am J Ind Med 14(3):255-256. 

*Rosenkranz HS, Hyman J, Leifer 2. 1981. DNA polymerase deficient assay. In: deserres FJ, 

Ashby J, eds. Evaluation of short-term tests for carcinogens: Report of the International 

Collaborative Program. Prog Mutat Res 1:210-218. 

Rosenkranz HS, Ennever FK, Dimayuga M, et al. 1990. Significant differences in the structural basis 

of the induction of sister chromatid exchanges and chromosomal aberrations in Chinese hamster ovary 

cells. Environ Mol Mutagen 16(3):149-177. 

*Rowland I, Severn B. 1981. Mutagenicity of carcinogens and noncarcinogens in the Salmonella/ 

microsome test. In: deserres FJ, Ashby J, eds. Evaluation of short-term tests for carcinogens: 

Report of the International Collaborative Program. Prog Mutat Res 1:323-332. 

*Russfield AB, Hornburger F, Boger E, et al. 1975. The carcinogenic effect of 4,4’-methylene-bis-(2­

chloroaniline) in mice and rats. Toxicol Appl Pharmacol 31(1):47-54. 

*Sabbioni G, neumann HG. 1990. Quantification of hemoglobin binding of 4,4’-methylenebis (2­

chloroaniline) (MOCA) in rats. Arch Toxicol 64(6):451-458. 

Salamone MF. 1981. Toxicity of carcinogens and noncarcinogenic analogues. In: deserres FJ, Ashby 

J, eds. Evaluation of short-term tests for carcinogens: Report of the International Collaborative 

Program. Prog Mutat Res 1:682-685. 

*Salamone MF, Heddle JA, Katz M. 1981. Mutagenic activity of 41 compounds in the in vivo 

micronucleus assay. In: deserres FJ, Ashby J, eds. Evaluation of short-term tests for carcinogens: 

Report of the International Collaborative Program. Prog Mutat Res 1:686-697. 

Savage RE, Weigel WW, Krieg EF. 1992. Induction of ornithine decarboxylase activity by 4,4’­

methylenebis(2-chloroaniline) in the rat. Cancer Lett 62:63-68. 

*Sawicki E, Belsky T, Friedel RA, et al. 1975. 3,3’-Dichloro-4,4’-diaminodiphenylmethane (MOCA) 

in air analytical method. Health Lab Sci 12(4):415-418. 

*Sax nI, Lewis RJ. 1987. Hawley’s condensed chemical dictionary. 11th ed. new York, nY: Van 

nostrand Reinhold Company, 767. 

Schmitt CR, Cagle GW. 1975. Sulfamic acid cleaning solution for 4,4’-methylene-bisorthochloroaniline 

(MOCA). Am Ind Hyg Assoc J 36(3):181-186. 

*Schulte PA. 1990. Screening for bladder cancer in high-risk groups: Delineation of the problem. 
MBOCA 112
 

8. REFERENCES 

J Occup Med 32(9):789-792. 

*Schulte PA, Ward E, Boeniger M, et al. 1988. Occupational exposure to n-substituted aryl 

compounds. In: King CM, Roman0 LJ, Schuetzle D, et al. eds. Carcinogenic and mutagenic 

responses to aromatic amines and nitroarenes. new York, nY: Elsevier, 23-35. 

*Searle CE, ed. 1984. Chemical carcinogens: Second edition, revised and expanded. ACS 

Monograph 182. Washington, DC: American Chemical Society, 1:283-284. 

*Segerback D, Kadlubar FF. 1992. Characterization of 4,4’-methylenebis(2-chloroaniline)-DNA 

adducts formed in vi~io and in vitro. Carcinogenesis 13:1587-1592. 

*Sharp DC, Parry JM. 1981. Induction of mitotic gene conversion by 41 coded compounds using 

the yeast culture JDl. In: deSerres FJ, Ashby J, eds. Evaluation of short-term tests for carcinogens: 

Report of the International Collaborative Program. Prog Mutat Res 1:491-501. 

*Shivapurkar n, Lehman TA, Schut HA, et al. 1987. DNA binding of 4,4’-methylenebis(2­

chloroaniline) (MOCA) in explant cultures of human and dog bladder. Cancer Lett 38(1-2):41-48. 

*Silk nA, Lay JO Jr, Martin Cn. 1989. Covalent binding of 4,4’-methylenebis-2-chloroaniline) to 

rat liver DNA in vivo and of its N-hydroxylated derivative to DNA in vitro. Biochem Pharmacol 

X3(2):279-287. 

*Simmon VF, Shepherd CF. 1981. Mutagenic activity of 42 coded compounds in the 

Salmonella/microsome assay. In: deserres FJ, Ashby J, eds. Evaluation of short-term tests for 

carcinogens: Report of the International Collaborative Program. Prog Mutat Res 133-342. 

*Skarping G, Renman L, Sangoe C, et al. 1985. Capillary gas chromatographic method for the 

determination of complex mixture of isocyanates and amines. J Chromatogr 346:191-204. 

Skarping G, Renman L, Smith BE. 1983. Trace analysis of amines and isocyanates using glass 

capillary gas chromatography and selective detection: I. Determination of aromatic amines as 

perfluoro fatty acid amides using electron-capture detection. J Chromatogr 267(2):315-327. 

*Skopek TR, Andon BM, Kaden DA, et al. 1981. Mutagenic activity of 42 coded compounds using 

8-azaguanine resistance as a genetic marker in Salmonella typhimurium. In: deSerres FJ, Ashby J, 

eds. Evaluation of short-term tests for carcinogens: Report of the International Collaborative Program. 

Prog Mutat Res 1371-375.] 

*Smith AM, Woodward Kn. 1983. 4,4’-Methylene bis-(2-chloroaniline)(MBOCA). Toxic Rev 8, 

Part 2:1-19. 

Smyth WF, Smyth MR. 1987. Electrochemical analysis of organic pollutants. Pure & Appl Chem 

59(2):245-256. 

Spiegelhalder B. 1983. Carcinogens in the workroom air in the rubber industry. Stand J of Work 

Environ Health 9(Suppl 2):15-26. 
MBOCA 113
 

8. REFERENCES
 

Steinhoff D, Grundmann E. 1969. Carcinogenic effect of 3,3’-dichloro-4,4’-diaminophemylmethane 

in rats. naturwissenschaften 56(4):215-216. 

Steinhoff D, Grundmann E. 1971. Cancerogenic effect of 3,3’dichloro-4,4’-diaminodiphenylmethane 

in rats. naturwissenschaften 58(11):578 

Stewart PA, Lee JS, Marano DE, et al. 1991. Retrospective cohort mortality study of workers at 

an aircraft maintenance facility: II. Exposures and their assessment. Br J Ind Med 48(8):531-537. 

Stoner GD. 1988. Metabolism of 4,4’-methylene-bis(2-chloroaniline) in explant cultures of human 

and dog bladder and dog liver cell cultures. In: Proceeding of the Fourth nCI/EPA/NIOSH 

Collaborative Workshop: Progress on Joint Environmental and Occupational Cancer Studies, April 

22-23, 1986. Rockville, MD: national Institutes of Health. Publication no. 88-2960, 343-350. 

Stoner GD, Shivapurkar nM, Schut HAJ, et al. 1987. Metabolism of 4,4’-methylenebis-2­

chloroaniline in explant cultures of human and dog bladder and dog liver cell cultures. In: 

Symposium on Predictive Toxicology Held at the 16th Conference on Environmental Toxicology. 

Toxicology 47(1-2):205. 

*Stoner GD, Shivapurkar nM, Schut HAJ, et al. 1988. DNA binding and adduct formation of 4,4’­

methylene-bis(2-chloroaniline) (MOCA) in explant cultures of human and dog bladder. In: King CM, 

Roman0 LJ, and Schultzle D, eds. Carcinogenic and mutagenic responses to aromatic amines and 

nitroarines. New York, NY: Elsevier, 237-240. 

*Stula EF, Sherman H, Zapp JA Jr, et al. 1975. Experimental neoplasia in rats from oral 

administrationof3,3’-dichlorobenzidine,4,4’-methylene-bis(2-chloroaniline), and4,4’-methylene-bis(2­

methylaniline). Toxicol Appl Pharmacol 31:159-176. 

*Stula EF, Barnes JR, Sherman H, et al. 1977. Urinary bladder tumors in dogs from 4,4’-methylenebis( 

2-chloroaniline) (MOCA). J Environ Pathol Toxicol l(l):3 l-50. 

*Styles JA. 1981. Activity of 42 coded compounds in the BHK-21 cell transformation test. In: 

deserres FJ, Ashby J, eds. Evaluation of short-term tests for carcinogens: Report of the 

International Collaborative Program. Prog Mutat Res 1:638-646. 

*Tabak HH, Quave SA, Mashni CI, et al. 1981. Biodegradability studies for predicting the 

Environmental fate of organic priority pollutants. In: Test protocols for Environmental fate and 

movement of toxicants. Proceedings of a Symposium of the Association of Official Analytical 

Chemists 94th Annual Meeting, Washington, D.C., October 21,198O. Arlington, VA: AOAC, 267-327. 

Tang C. 1990. [Rapid determination of 4,4’-methylenebis-(2-chloroaniline) by TLC during elastomer 

synthesis.] Sepu 8(6):389-391. (Chinese) 

*Thomas JD, Wilson HK. 1984. Biological monitoring of workers exposed to 4,4’-methylenebis (2­

chloroaniline) (MBOCA). Br J Ind Med 41(4):547-551. 

*Thomson JA. 1981. Mutagenic activity of 42 coded compounds in the lambda induction assay. In: 

deserres FJ, Ashby J, eds. Evaluation of short-term tests for carcinogens: Report of the 

International Collaborative Program. Prog Mutat Res 1:224-235. 
MBOCA 114
 

8. REFERENCES
 

*Tobes MC Brown LE, Chin B, et al. 1983. Kinetics of tissue distribution and elimination of 4,4’­

methylenebis-(2-chloroaniline) in rats. Toxicol Lett 17(1-2):69-76. 

Tosato ML, Cesareo D, Passerini L, et al. 1988. PLS assessment of the performance of short-term 

tests for carcinogens. J Chemometrics 2(3):171-187. 

*Traul KA, Takayama K, Kachevsky V, et al. 1981. A rapid in vitro assay for carcinogenicity of 

chemical substances in mammalian cells utilizing an attachment-independence endpoint: 2. Assay 

validation. J Appl Toxicol 1(3):190-195. 

*TRI90. 1992. Toxic Chemical Release Inventory. National Library of Medicine, national 

Toxicology Information Program, Bethesda, MD. 

*Trippel-Schulte P, Zeiske J, Kettrup A. 1986. Trace analysis of selected benzidine and 

diaminodiphenylmethane derivates in urine by means of liquid chromatography using precolumn sample 

preconcentration, UV and electrochemical detection. Chromatographia 22(1-6)138-146. 

*Trueman RW. 1981. Activity of 42 coded compounds in the Salmonella reverse mutation test. In: 

deserres FJ, Ashby J, eds. Evaluation of short-term tests for carcinogens: Report of the 

International Collaborative Program. Prog Mutat Res 1:343-350. 

*Tsuchimoto T, Matter BE. 1981. Activity of coded compounds in the micronucleus test. In: 

deserres FJ, Ashby J, eds. Evaluation of short-term tests for carcinogens: Report of the 

International Collaborative Program. Prog Mutat Res 1:705-711. 

*Tweats DJ. 1981. Activity of 42 coded compounds in a differential killing test using Escherichia 

coli strains WP2, WP67 (uvrA polA), and CM871 (uvrA 1exA recA). In: deserres FJ, Ashby J, eds. 

Evaluation of short-term tests for carcinogens: Report of the International Collaborative Program. 

Prog Mutat Res 1:199-209. 

Uziel M, Munro nB, Katz DS, et al. 1992. DNA adduct formation by 12 chemicals with populations 

potentially suitable for molecular epidemiological studies. Mutat Res 27735-90. 

*Van H Deyrup CA, Kavaler AR, et al., eds. 1992. OPD chemical buyers directory. 79th ed. new 

York, nY: Schell Publishing Company, Inc., 13, 27-28, 575. 

*Van Roosmalen PB, Klein AL, Drummond I. 1979. An improved method for determination of 4,4’­

methylenebis-(2-chloroaniline) (MOCA) in urine. Am Ind Hyg Assoc J 40(1):66-69. 

*Van Roosmalen PB, Klein Al, Drummond I. 1981. Method 8 - determination of 3,3’-dichloro4,4’diaminodiphenylmethane (MOCA) in urine, In: Egan H, ed. Environmental carcinogens: 

Selected methods of analysis. Vol 4: Some aromatic amines and azo dyes in the general and 

industrial environment. Lyon, France: International Agency for Research on Cancer, IARC scientific 

publications no. 40, 183-191. 

*Vantulder PJM, Howard CC, Riggin RM. 1981. High performance liquid chromatographic 

determination of aromatic amines in body fluid and commercial dyes. In: Choudhary G, ed. Chemical 

hazards in the workplace: Measurement and control. Washington, DC: ACS Symposium Series 

149:413-427. 
MBOCA 115
 

8. REFERENCES
 

*Venitt S, Crofton-Sleigh C. 1981. Mutagenicity of 42 coded compounds in a bacterial assay using 

Escherichia coli and Salmonella typhimurium. In: deserres FJ, Ashby J, eds. Evaluation of shortterm 

tests for carcinogens: Report of the International Collaborative Program. Prog Mutat Res 

1351-360. 

*Vogel E, Blijleven WG, Kortselius MJ, et al. 1981. Mutagenic activity of 17 coded compounds in 

the sex-linked recessive lethal test in Drosophila melanogaster. In: deserres FJ, Ashby J. eds. 

Evaluation of short-term tests for carcinogens: Report of the International Collaborative Program. 

Prog Mutat Res 1:660-665. 

*Voorman R, Penner D. 1986a. Fate of MBOCA (4,4’-methylene-bis(2-chloroaniline)) in soil. Arch 

Environ Contam Toxicol 15(5):595-602. 

*Voorman R, Penner D. 1986b. Plant uptake of MBOCA (4,4’-methylenebis-(2-chloroaniline)). 

Arch Environ Contam Toxicol 15(5):589-59X 

*WAC. 1988. Control of hazardous pollutants. Wisconsin Administrative Code. Chapter nR 455. 

Department of natural Resources, Madison, WI, 446-4 - 446-16. 

*Walker CG. 1984. Mutagenesis and inducible responses to deoxyribonucleic acid damage in 

Escherichia coli. Microbial Rev 48(1):60-9X 

Wallace DMA. 1988. Occupational urothelial cancer. Br J of Urology 61(3):175-182. 

*Wan KC, Dare BR, Street nR. 1989. Biomedical surveillance of workers exposed to 4,4’­

methylene-bis-(2-chloroaniline) (MBOCA) in Perth, Western Australia. J R Sot Health 109(5):159­

165. 

*Ward E, Clapp D, Tolos W, et al. 1986. Efficacy of urinary monitoring for 4,4’-methylenebis-(2­

chloroaniline). J Occup Med 28(8):637-642. 

*Ward E, Smith AB, Halperin W. 1987. 4,4’-Methylenebis(2-chloroaniline): An unregulated 

carcinogen. Am J Ind Med 12(5):537-549. 

Ward E, Halperin W, Thun M, et al. 1988. Bladder tumors in two young males occupationally 

exposed to MBOCA. Am J Ind Med 14(3):267-272. 

*Ward E, Halperin W, Thun M, et al. 1990. Screening workers exposed to 4,4’-methylenebis-(2­

chloroaniline) for bladder cancer by cystoscopy. In: International Conference on Bladder Cancer 

Screening in High-Risk Groups, September 13-14, 1989. J Occup Med 32(9):865-868. 

*Ward E. 1993. Response to “Case study ‘Carcinogenesis’: The MBOCA TLV example”. Am Ind 

Hyg Assoc J 54(8):461-46X 

*Weeks RW Jr, Dean BJ. 1977. Permeation of methanolic aromatic amine solutions through 

commercially available glove materials. J Am Ind Hyg Assoc 38(12):721-725. 

Weigel WW, Savage RE Jr. 1990. Induction of ornithine decarboxylase activity of 4,4’-methylenebis( 

Zchloroaniline) (MOCA) in the rat. In: Society of Toxicology 29th Annual Meeting, Miami 
MBOCA 116
 

8. REFERENCES 

Beach, FL, February 12-16, 1990. Washington, D.C.: Society of Toxicology, 760.
 

Williams DE. 1979. Progress report on the analysis and control of exposure to 4,4’methylene bis (2
 

chloroaniline. Lansing, MI: Michigan Department of Public Health, Division of Occupational Health,
 

Division of Environmental Epidemiology.
 

*Williams GM, Laspia MF, Dunkel VC. 1982. Reliability of the hepatocyte primary culture/DNA
 

repair test in testing of coded carcinogens and noncarcinogens. Mutat Res 97(5):359-370.
 

Wilson JD. 1978. Review of in vitro systems with potential for use in teratogenicity screening. J
 

Environ Pathol Toxicol 2(1):149.
 

Wu K, Leslie CL, Stacy nH. 1989. Effects of mutagenic and non-mutagenic aniline derivatives on
 

rat liver drug-metabolizing enzymes. Xenobiotica 19(11):1275-1283.
 

*Yasuda SK. 1975. Determination of 3,3’-dichloro-4,4’-diaminodiphenylmethane in air. J
 

Chromatogr 104(2):283-290.
 

*Yoneyama K, Matsumura F. 1984. Microbial metabolism of 4,4’-methylenebis(2-chloroaniline).
 

Arch Environ Contam Toxicol 13(4):501-507.
 

*Yoshikura H, Matsushima T. 1981. MLV test (integration enhancement test) of 42 coded
 

compounds in mouse kidney cells. In: deserres FJ, Ashby J, eds. Evaluation of short-term tests for
 

carcinogens: Report of the International Collaborative Program. Prog Mutat Res 1:647-650.
 

Yun C, Shimada T, Guengerich FP, et al. 1991. Purification and characterization of human liver
 

microsomal cytochrome P-450 2A6. Mol Pharmacol 40(5):679-685.
 

Yun CH, Shimada T, Guengerich FP. 1992. Contributions of human liver cytochrome P450 enzymes
 

to the n-oxidation of 4,4’-methylene-bis(2-chloroaniline). Carcinogenesis 13:217-222.
 

Zimmermann FK, Scheel I. 1981. Induction of mitotic gene conversion in strain D7 of
 

saccharomyces cerevisiae by 42 coded chemicals. In: deserres FJ, Ashby J, eds. Evaluation of shortterm
 

tests for carcinogens: Report of the International Collaborative Program. Prog Mutat Res
 

1:481-490.
 
MBOCA 117
 

9. GLOSSARY
 

Acute Exposure - Exposure to a chemical for a duration of 14 days or less, as specified in the 

Toxicological Profiles. 

Adsorption Coefficient (Koc) - The ratio of the amount of a chemical adsorbed per unit weight of 

organic carbon in the soil or sediment to the concentration of the chemical in solution at equilibrium. 

Adsorption Ratio (Kd) - The amount of a chemical adsorbed by a sediment or soil (i.e., the solid 

phase) divided by the amount of chemical in the solution phase, which is in equilibrium with the solid 

phase, at a fixed solid/solution ratio. It is generally expressed in micrograms of chemical absorbed 

per gram of soil or sediment. 

Bioconcentration Factor (BCF) - The quotient of the concentration of a chemical in aquatic 

organisms at a specific time or during a discrete time period of exposure divided by the concentration 

in the surrounding water at the same time or during the same period. 

Cancer Effect Level (CEL) - The lowest dose of chemical in a study, or group of studies, that 

produces significant increases in the incidence of cancer (or tumors) between the exposed population 

and its appropriate control. 

Carcinogen - A chemical capable of inducing cancer. 

Ceiling Value - A concentration of a substance that should not be exceeded, even instantaneously. 

Chronic Exposure - Exposure to a chemical for 365 days or more, as specified in the Toxicological 

Profiles. 

Developmental Toxicity - The occurrence of adverse effects on the developing organism that may 

result from exposure to a chemical prior to conception (either parent), during prenatal development, 

or postnatally to the time of sexual maturation. Adverse developmental effects may be detected at 

any point in the life span of the organism. 

Embryotoxicity and Fetotoxicity - Any toxic effect on the conceptus as a result of prenatal exposure 

to a chemical; the distinguishing feature between the two terms is the stage of development during 

which the insult occurred. The terms, as used here, include malformations and variations, altered 

growth, and in utero death. 

EPA Health Advisory - An estimate of acceptable drinking water levels for a chemical substance 

based on health effects information. A health advisory is not a legally enforceable federal standard, 

but serves as technical guidance to assist federal, state, and local officials. 

Immediately Dangerous to Life or Health (IDLH) - The maximum Environmental concentration of 

a contaminant from which one could escape within 30 min without any escape-impairing symptoms 

or irreversible health effects. 

Intermediate Exposure - Exposure to a chemical for a duration of 15364 days, as specified in the 

Toxicological Profiles. 
MBOCA 118
 

9. GLOSSARY
 

Immunologic Toxicity - The occurrence of adverse effects on the immune system that may result 

from exposure to Environmental agents such as chemicals. 

In vitro - Isolated from the living organism and artificially maintained, as in a test tube. 

In vivo - Occurring within the living organism. 

Lethal Concentration(LO) (LCLO) - The lowest concentration of a chemical in air which has been 

reported to have caused death in humans or animals. 

Lethal Concentration(50) (LC50) - A calculated concentration of a chemical in air to which exposure 

for a specific length of time is expected to cause death in 50% of a defined experimental animal 

population. 

Lethal Dose(LO) (LDLO) - The lowest dose of a chemical introduced by a route other than 

inhalation that is expected to have caused death in humans or animals. 

Lethal Dose(50) (LD50) - The dose of a chemical which has been calculated to cause death in 50% 

of a defined experimental animal population. 

Lethal Timet(5O) (LT50) - A calculated period of time within which a specific concentration of a 

chemical is expected to cause death in 50% of a defined experimental animal population. 

Lowest-Observed-Adverse-Effect Level (LOAEL) - The lowest dose of chemical in a study, or group 

of studies, that produces statistically or biologically significant increases in frequency or severity of 

adverse effects between the exposed population and its appropriate control. 

Malformations - Permanent structural changes that may adversely affect survival, development, or 

function. 

Minimal Risk Level - An estimate of daily human exposure to a dose of a chemical that is likely 

to be without an appreciable risk of adverse noncancerous effects over a specified duration of 

exposure. 

Mutagen - A substance that causes mutations. A mutation is a change in the genetic material in 

a body cell. Mutations can lead to birth defects, miscarriages, or cancer. 

Neurotoxicity - The occurrence of adverse effects on the nervous system following exposure to 

chemical. 

No-Observed-Adverse-Effect Level (NOAEL) - The dose of chemical at which there were no 

statistically or biologically significant increases in frequency or severity of adverse effects seen 

between the exposed population and its appropriate control. Effects may be produced at this dose, 

but they are not considered to be adverse. 

Octanol-Water Partition Coefficient (Kow) - The equilibrium ratio of the concentrations of a 

chemical in n-octanol and water, in dilute solution. 

Permissible Exposure Limit (PEL) - An allowable exposure level in workplace air averaged over 
MBOCA 119
 

9. GLOSSARY 

an 8-hour shift. 

q1* - The upper-bound estimate of the low-dose slope of the dose-response curve as determined
 

by the multistage procedure. The ql* can be used to calculate an estimate of carcinogenic potency,
 

the incremental excess cancer risk per unit of exposure (usually μg/L for water, mg/kg/day for food,
 

and μg/m” for air).
 

Reference Dose (RfD) - An estimate (with uncertainty spanning perhaps an order of magnitude) of
 

the daily exposure of the human population to a potential hazard that is likely to be without risk of
 

deleterious effects during a lifetime. The RfD is operationally derived from the NOAEL (from
 

animal and human studies) by a consistent application of uncertainty factors that reflect various types
 

of data used to estimate RfDs and an additional modifying factor, which is based on a professional
 

judgment of the entire database on the chemical. The RfDs are not applicable to nonthreshold
 

effects such as cancer.
 

Reportable Quantity (RQ) - The quantity of a hazardous substance that is considered reportable
 

under CERCLA. Reportable quantities are (1) 1 pound or greater or (2) for selected substances,
 

an amount established by regulation either under CERCLA or under Sect. 311 of the Clean Water
 

Act. Quantities are measured over a 24-hour period.
 

Reproductive Toxicity - The occurrence of adverse effects on the reproductive system that may
 

result from exposure to a chemical. The toxicity may be directed to the reproductive organs and/or
 

the related endocrine system. The manifestation of such toxicity may be noted as alterations in sexual
 

behavior, fertility, pregnancy outcomes, or modifications in other functions that are dependent on the
 

integrity of this system.
 

Short-Term Exposure Limit (STEL) - The maximum concentration to which workers can be
 

exposed for up to 15 min continually. no more than four excursions are allowed per day, and there
 

must be at least 60 min between exposure periods. The daily TLV-TWA may not be exceeded.
 

Target Organ Toxicity - This term covers a broad range of adverse effects on target organs or
 

physiological systems (e.g., renal, cardiovascular) extending from those arising through a single limited
 

exposure to those assumed over a lifetime of exposure to a chemical.
 

Teratogen - A chemical that causes structural defects that affect the development of an organism.
 

Threshold Limit Value (TLV) - A concentration of a substance to which most workers can be
 

exposed without adverse effect. The TLV may be expressed as a TWA, as a STEL, or as a CL.
 

Time-Weighted Average (TWA) - An allowable exposure concentration averaged over a normal 8­

hour workday or 40-hour workweek.
 

.
 

TOXIC Dose (TD,,) - A calculated dose of a chemical, introduced by a route other than inhalation,
 

which is expected to cause a specific toxic effect in 50% of a defined experimental animal population.
 

Uncertainty Factor (UF) - A factor used in operationally deriving the RfD from experimental data.
 

UFs are intended to account for (1) the variation in sensitivity among the members of the human
 

population, (2) the uncertainty in extrapolating animal data to the case of human, (3) the uncertainty
 

in extrapolating from data obtained in a study that is of less than lifetime exposure, and (4) the
 
MBOCA 120 

9. GLOSSARY 

uncertainty in using LOAEL data rather than NOAEL data. Usually each of these factors is set 

equal to 10.