Studying Human Fertility and

Environmental Exposures

In their review of approaches to studying the

influence of environmental exposures on

human fecundity, Tingen et al. (2004) compared several ways of assessing fecundity.

Fecundity—the probability of pregnancy

in couples having regular intercourse without

contraception—can be assessed by applying

appropriate statistical approaches to time-topregnancy (TTP) data. Tingen et al. (2004)

provided a thorough presentation of the

detailed prospective approach to assess TTP.

We agree that advantages of this approach,

in which daily urine samples are collected,

include allowing the estimation of the daily

probability of pregnancy within a menstrual

cycle and studying the early survival of the

embryo; however, we have reservations about

the authors’ conclusion that the detailed

prospective approach should be seen as the

gold standard for studying the effects of environmental exposures on fecundity.

We believe that prospective TTP studies,

whether detailed or not, have one main limitation, which lies in the difficulty of defining

precisely the target population: These studies

are often based on the inclusion of couples

soon planning to attempt conception or to

stop using contraceptive methods. In our

opinion, this population is ill-defined and

lacks a sampling frame, which makes the estimation of participation rates difficult. Indeed,

many published detailed prospective TTP

studies had unreported or low participation

rates (Buck et al. 2004), opening the door for

selection biases. We also doubt that these

“super pregnancy planners,” who program

their pregnancy attempts months ahead, are

representative of the general population. For

example, detailed prospective TTP studies

have sometimes included couples with

higher-than-average educational level (Wilcox

et al. 1988) or those who use natural family

planning methods not widely used (Dunson

et al. 2002). These characteristics may be

associated with the probability of pregnancy

and with the environmental exposures of

interest, thus resulting in possible biases.

These limitations of the prospective

approach do not justify a preference for

retrospective studies. As pointed out by

Tingen et al. (2004), the exclusion of infertile couples in most retrospective studies is

indeed of particular concern; it reduces statistical power and leads to underestimation

of the effect of the environmental exposure

of interest (Slama et al. 2004).

The current duration approach, another

approach not mentioned by Tingen et al.

(2004), makes it possible to include infertile

couples without resorting to detailed prospective studies. The current duration approach

relies on the inclusion of couples currently

trying to conceive or who are having intercourse without contraception (Keiding et al.

2002; Olsen and Andersen 1999). The

recruited couples are asked how long they

have been having unprotected sexual intercourse. Follow-up of these couples is not

required (Keiding et al. 2002), but it is possible to obtain information on the occurrence

of a pregnancy. In this case, the approach is

based on principles from the case–cohort

design (Olsen and Andersen 1999).

In the current duration approach, data

on the frequency of sexual intercourse, the

duration of the menstrual cycle during the

attempt at pregnancy, and environmental

exposures can be collected with virtually no

recall bias. The collection of urine or other

biologic samples is possible, at least from the

date of inclusion; that is, some time after cessation of contraceptive use. The advantage of

the current duration approach is that the

inclusion criterion (currently having sexual

intercourse without contraception) is more

clear-cut than that of the prospective

approach. This approach thus has a clearly

defined sampling frame. We are currently testing this approach on a representative population of French women 18–45 years of age. 

The four approaches to assessing TTP

are based on different inclusion schemes.

The retrospective approach is based on the

inclusion of couples who already had a pregnancy; prospective approaches (detailed and

not) are most often based on the inclusion of

couples who will soon discontinue contraceptive use; and the current duration

approach is based on the inclusion of couples

currently trying to conceive. We believe that

none of these methods can currently be considered a gold standard. In particular, unlike

Tingen et al. (2004), we do not think that

the potential bias from the exclusion of pregnancies occurring during contraceptive use

(Baird et al. 1994) is specific to the retrospective approach, because prospective (and

current duration) studies seldom include

couples using contraceptive methods.

Instead, we believe that the existence of

new, alternative approaches should provoke

comparative studies, leaving room for debate

before conclusions are drawn about which

approach is preferable for a given purpose.

The authors declare they have no competing

financial interests.

Rémy Slama 

Béatrice Ducot

INSERM and INED

(French National Institute for Health and

Medical Research and the French National

Institute for Demographic Studies)

Unit 569

Le Kremlin-Bicêtre, France

E-mail: slama@vjf.inserm.fr

Niels Keiding

Department of Biostatistics

University of Copenhagen

Copenhagen, Denmark

Jean Bouyer

INSERM and INED

(French National Institute for Health and

Medical Research and the French National

Institute for Demographic Studies)

Unit 569

Le Kremlin-Bicêtre, France

REFERENCES

Baird DD, Weinberg CR, Schwingl P, Wilcox AJ. 1994.

Selection bias associated with contraceptive practice in

time-to-pregnancy studies. Ann NY Acad Sci 709:156–164. 

Buck GM, Lynch CD, Stanford JB, Sweeney AM, Schieve LA,

Rockett JC, et al. 2004. Prospective pregnancy study

designs for assessing reproductive and developmental

toxicants. Environ Health Perspect 112:79–86. 

Dunson DB, Colombo B, Baird DD. 2002. Changes with age in

the level and duration of fertility in the menstrual cycle.

Hum Reprod 17:1399–1403. 

Keiding N, Kvist K, Hartvig H, Tvede M, Juul S. 2002.

Estimating time to pregnancy from current durations in a

cross-sectional sample. Biostatistics 3:565–578. 

Olsen J, Andersen PK. 1999. We should monitor human

fecundity, but how? A suggestion for a new method that

may also be used to identify determinants of low fecundity. Epidemiology 10:419–421. 

Slama R, Jensen TK, Scheike T, Ducot B, Spira A, Keiding N.

2004. How would a decline in sperm concentration over

time influence the probability of pregnancy? Epidemiology

15:458–465.

Tingen C, Stanford JB, Dunson DB. 2004. Methodologic and

statistical approaches to studying human fertility and

environmental exposure. Environ Health Perspect

112:87–93. 

Wilcox AJ, Weinberg CR, O’Connor JF, Baird DD, Schlatterer JP,

Canfield RE, et al. 1988. Incidence of early loss of pregnancy. N Engl J Med 319:189–194.

Studying Human Fertility

We very much welcome the National

Children’s Study, which promises to raise

the study of factors affecting reproduction

and development to a new level. An impressive and exciting range of new methodologies

is being developed (Chapin and Buck 2004;

National Children’s Study 2004). 

However, we think it important to correct some of the inaccurate statements concerning the use of retrospective time to

pregnancy (TTP) made by Tingen et al.

(2004). We do not see prospective methods

and the retrospective approach as alternatives;

they are complementary, each having their

strengths and weaknesses. Unfortunately,

Tingen et al. presented a negative and distorted view of retrospective TTP studies,

describing things that are “often” or “typically” done but that do not represent current

best practice; then they used their description

to denigrate all such studies. Although it is

true that retrospective studies are subject to

multiple potential “bias in recruitment, recall,

and behavior or exposure trends” (Tingen

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Perspectives Correspondence
Correspondence

et al. 2004), careful sampling and questionnaire design and use of appropriate methods

of analysis can address most of these issues. 

Retrospective studies are not necessarily

pregnancy based. They can be conducted in

random population-based samples and frequently are cross-sectional or birth cohort

studies (Joffe 2000; Joffe and Li 1994;

Karmaus et al. 1999; Sallmén et al. 1995;

Schaumburg and Boldsen 1992; Schaumburg

and Olsen 1989; Thonneau et al. 1999),

thereby overcoming the problem that only

women who eventually conceived are

included. Even in pregnancy-based studies, if

there are concerns about differential prenatal

care (an issue in the United States but not in

western Europe, for example), recruitment

could be based on births rather than pregnancies, obviously with loss of nonbirth outcomes. If sampling is population based, it is

feasible to ascertain periods of unprotected

intercourse not leading to conception (generally stipulating a minimum duration such as

6 months); these attempts can be added to

the pregnancy-related TTP values to generate

the “time of unprotected intercourse”

(Karmaus et al. 1999). 

Tingen et al. (2004) presented simple

issues of questionnaire design negatively, but

these problems can be easily solved. For

example, if data are collected in relation to

the starting time instead of the conception

time (Weinberg et al. 1994), behavior

change does not lead to bias but only to

nondifferential loss of information. 

A central issue is planning bias, the

question being how to exclude accidental

(unplanned) pregnancies without bias

occurring if the exposure variable is associated with the degree of “plannedness.”

Retrospective studies can readily investigate

this by following the standard guidance to

collect full information for all pregnancies,

including all covariates, and carry out parallel

analyses with “unplanned pregnancy rate” as

outcome variable (Weinberg et al. 1994).

Prospective studies are unable to do this

because only planners are recruited. 

Tingen et al. (2004) stated that in TTP

studies, “women are asked to recount their

contraceptive and sexual history.” This is

incorrect; in TTP studies, women are not

asked for this detailed information because

it would be invasive and inaccurate. Instead,

women are simply asked how long it took to

conceive, a question that is acceptable and

that most can answer. The replies give an

accurate representation of the true TTP distribution (Baird et al. 1991; Joffe et al.

1993, 1995; Zielhuis et al. 1992), even with

recall of up to 20 years (Joffe et al. 1995).

Although digit preference (and other nondifferential misclassification) can occur, the

implication is that more respondents are

required than would be the case with perfect

information. Nevertheless, stable estimates

of the TTP distribution can be obtained

with approximately 200 values in each exposure group, or fewer in the case of ordered

categories such as successive 5-year periods

(Joffe 2000). 

We agree that a major limitation of

retrospective studies is that it is impossible to

obtain detailed, timed information on exposures and key biologic events such as ovulation, and difficult to ascertain certain

covariates such as frequency or timing of

intercourse. This is the key strength of the

prospective design. On the other hand, retrospective studies are representative because, as

already noted, sampling from the general

population is available and planning bias can

be handled. The questions are easily administered and answered, and the response rate is

high. Even response bias can be avoided by

nesting the TTP questions within a more

general population survey, thus decoupling

survey nonresponse from differential fertility

or other motivation that would convert low

response rates to response bias (Joffe 2000).

Selection bias remains a potential problem

for some retrospective designs but can be

handled by appropriate statistical analysis

allowing for truncation effects (Scheike and

Jensen 1997). 

Not only are prospective studies timeconsuming and costly, and therefore likely

to be rarely used, but they have important

methodologic drawbacks. For example, it is

impossible to distinguish the approximately

3% of couples who are sterile from those

who merely take a long time to conceive

(> 10% typically take > 12 months), unless

follow-up is extremely long. 

More seriously, prospective studies are

dominated by the lack of a sampling frame

(except in occupational studies) and by a

potent combination of planning bias and

response bias. They can include only couples

who deliberately plan and are willing to volunteer for onerous monitoring. This is

acceptable for internal comparisons (e.g.,

studying day-specific conception rates, each

subject being her own control) but raises

serious problems with external validity.

Tingen et al. (2004) referred to this only in

their Table 1—“Participants might be less

representative of target population”—but

not in the text; in contrast, Buck et al.

(2004) admitted that women who plan their

pregnancies may be systematically different

from those who do not, that this may

adversely affect external validity to a degree

which cannot be empirically evaluated, and

that the findings may not be generalizable to

all women. 

The authors declare they have no competing

financial interests.

Michael Joffe 

Jane Key 

Nicky Best 

Department of Epidemiology 

& Public Health 

Imperial College Faculty of Medicine 

London, United Kingdom

E-mail: m.joffe@imperial.ac.uk

Tina Kold Jensen

Institute of Public Health

Department of Environmental Medicine 

University of Southern Denmark

Odense, Denmark

REFERENCES

Baird DD, Weinberg CR, Rowland AS. 1991. Reporting errors in

time-to-pregnancy data collected with a short questionnaire. Am J Epidemiol 133:1282–1290. 

Buck GM, Lynch CD, Stanford JB, Sweeney AM, Schieve LA,

Rockett JC, et al. 2004. Prospective pregnancy study

designs for assessing reproductive and developmental

toxicants. Environ Health Perspect 112:79–86. 

Chapin RE, Buck GM. 2004. Our once-in-a-lifetime opportunity.

Environ Health Perspect 112:67–68. 

Joffe M. 2000. Time trends in biological fertility in Britain.

Lancet 355:1961–1965. 

Joffe M, Li Z. 1994. Male and female factors in fertility. Am J

Epidemiol 140:921–929. 

Joffe M, Villard L, Li Z, Plowman R, Vessey M. 1993. Longterm recall of time-to-pregnancy. Fertil Steril 60:99–104. 

Joffe M, Villard L, Li Z, Plowman R, Vessey M. 1995. A time to

pregnancy questionnaire designed for long term recall:

validity in Oxford, England. J Epidemiol Community Health

49:314–319. 

Karmaus W, Juul S, European Infertility and Subfecundity

Group. 1999. Infertility and subfecundity in populationbased samples from Denmark, Germany, Italy, Poland

and Spain. Eur J Public Health 9:229–235. 

National Children’s Study. 2004. National Children’s Study

Homepage. Available: http://nationalchildrensstudy.gov/

[accessed 20 March 2004]. 

Sallmén M, Lindbohm M-L, Kyyrönen P, Nykyri E, Anttila A,

Taskinen H, et al. 1995. Reduced fertility among women

exposed to organic solvents. Am J Ind Med 27:699–713. 

Schaumburg I, Boldsen JL. 1992. Waiting time to pregnancy

and pregnancy outcome among Danish workers in the

textile, clothing, and footwear industries. Scand J Soc

Med 20:110–114. 

Schaumburg I, Olsen J. 1989. Time to pregnancy among Danish

pharmacy assistants. Scand J Work Environ Health

15:222–226. 

Scheike T, Jensen T. 1997. A discrete survival model with

random effects: an application to time to pregnancy.

Biometrics 53:318–329.

Thonneau P, Abell A, Larsen SB, Bonde JP, Joffe M,

Clavert A, et al. 1999. Effects of pesticide exposure on

time to pregnancy: results of a multicenter study in

France and Denmark. ASCLEPIOS Study Group. Am J

Epidemiol 150:157–163. 

Tingen C, Stanford JB, Dunson DB. 2004. Methodologic and statistical approaches to studying human fertility and environmental exposure. Environ Health Perspect 112:87–93. 

Weinberg CR, Baird DD, Wilcox AJ. 1994. Sources of bias in

studies of time to pregnancy. Stat Med 13:671–681. 

Zielhuis GA, Hulscher MEJL, Florack EIM. 1992. Validity and

reliability of a questionnaire on fecundability. Int J

Epidemiol 21:1151–1156. 

Studying Human Fertility:

Response to Slama et al. and

Joffe et al.

Slama et al. provide valuable comments on

sampling frames to study fecundity, and we

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Correspondence

agree that the sampling frame is a major

methodologic problem in fecundity studies of

all designs. The current duration strategy of

enrolling couples currently attempting pregnancy is a promising approach, particularly

when couples are followed after enrollment

to obtain detailed prospective information.

Data from the menstrual cycles before enrollment can then be combined with detailed

data from cycles during the study period

using recently proposed statistical methods

(Dunson 2003).

However, it is important to note that this

innovative combination of retrospective and

prospective designs still does not address the

vexing problem of couples who do not have

a clearly defined pregnancy attempt.

Demographic surveys and qualitative

research reveal that many—perhaps most—

pregnancies are not exactly planned in the

sense of an exactly defined onset of intention

to become pregnant (Trussell et al. 1999).

Even the onset of sexual intercourse without

contraception may not always be easy to

define reliably, with periods of use interspersed with periods of nonuse. Ultimately, a

complete evaluation of this issue will need to

include couples using contraception, at least

at study enrollment. Some studies have done

this, at least for barrier contraceptives

(Eskenazi et al. 1995).

Joffe et al. comment on alternative retrospective designs that can be considered to

address the problem of a nonrepresentative

sample. We agree that prospective studies

are limited by the fact that individuals willing to participate may not be representative

of the general population (as in prospective

epidemiologic studies of other heath outcomes). However, many of Joffe et al.’s

comments on the prospective design are

unduly negative. For example, the stated

methodologic problem of it being “impossible to distinguish the approximately 3% of

couples who are sterile from those who

merely take a long time to conceive” is not

specific to the prospective design, but a general issue in distinguishing sterility from

infertility in the absence of known causes of

sterility (Dunson et al. 2004). 

The “best” design (if it exists) really

depends on the scientific questions of 

interest. Retrospective and population-based

studies have an important role in assessing

population fecundability in demographic

studies, in studying effective fecundability,

and in surveillance for possibly significant

environmental exposures. However, our

focus is on studies investigating the potentially complex and time-varying effects of

environmental exposures on biologic

fecundability. Intercourse timing relative to

ovulation has a critical role, not only in

determining the overall probability of 

conception in a menstrual cycle, and hence

time to pregnancy, but also in predicting

later outcomes, such as early pregnancy loss

(Wilcox et al. 1998). Confounding resulting

from differences in exposed and unexposed

individuals in their sexual behavior, including timing and frequency of intercourse, is a

major concern. There can be problems even

if the individuals have the same intercourse

frequency because there is substantial variability in the timing of ovulation (Wilcox

et al. 2000). In addition, prospective data on

mucus and hormones potentially provide

important information about biologic

mechanisms. 

For all of these reasons, we continue to

recommend that whenever possible, detailed

prospective data of the type that we have

outlined should be collected in epidemiologic studies of fecundity, as well as in studies

that seek to relate periconception exposures

to later reproductive and developmental outcomes. Daily sampling of urine (via samples

sent to the laboratory, or onsite with commercially available computerized devices) is

one way to achieve this, but not the only

one. We detailed other currently available

and feasible approaches in our article

(Tingen et al. 2004).

The authors declare they have no competing

financial interests.

Joseph B. Stanford

Health Research Center

Department of Family and 

Preventive Medicine

University of Utah

Salt Lake City, Utah

David B. Dunson

Candace Tingen

National Institute of Environmental

Health Sciences

National Institutes of Health

Department of Health and 

Human Services

Research Triangle Park, North Carolina

E-mail: dunson1@niehs.nih.gov

REFERENCES

Dunson DB. Incorporating heterogeneous intercourse records

into time to pregnancy models. 2003. Math Popul Studies

10:127–143.

Dunson DB, Baird DD, Colombo B. 2004. Increased infertility

with age in men and women. Obstet Gynecol 103:57–62.

Eskenazi B, Gold EB, Samuels SJ, Wight S, Lasley BL,

Hammond SK, et al. 1995. Prospective assessment of

fecundability of female semiconductor workers. Am J Ind

Med 28(6):817–831.

Tingen C, Stanford JB, Dunson DB. 2004. Methodologic and statistical approaches to studying human fertility and environmental exposure. Environ Health Perspect 112:87–93. 

Trussell J, Vaughan B, Stanford J. 1999. Are all contraceptive

failures unintended pregnancies? Evidence from the 1995

National Survey of Family Growth. Fam Plann Perspect

31(5):246–247, 260.

Wilcox AJ, Weinberg CR, Baird DD. 1998. Post-ovulatory ageing

of the human oocyte and embryo failure. Hum Reprod

13:394–397.

Wilcox AJ, Dunson D, Baird DD. 2000. The timing of the “fertile

window” in the menstrual cycle: day specific estimates

from a prospective study. Br Med J 321(7271):1259–1262.

The WTC Disaster and

Asbestos Regulations

Landrigan et al. (2004) reported on exposure

to asbestos as a result of events involving the

World Trade Center (WTC). Their results

are somewhat lower than that reported by

others (Lange 2004) for this unfortunate

event. I reported a single asbestos bulk sample at 40% asbestos (Lange 2004), although

Landrigan et al. suggested that most are in

the range of 1–3%. Because there was one

“high” bulk sample observed, it is likely that

numerous other locations had similar “elevated” asbestos levels. Airborne exposures

were also elevated for a considerable time

period after the event (Lange 2004). Although

measurements were reported as task-length

averages (TLA), it is likely that some personal samples (Lange 2004) exceeded the

U.S. Occupational Safety and Health

Administration permissible exposure limit

(PEL) of 0.1 fibers/cm3 well after the first

few days of the event. For example, during

1 January 2002–11 February 2002 in the west

area, the arithmetic mean exposure and an

upper reported value (0.500 fibers/cm3-TLA)

were above the PEL (Lange 2004). 

Landrigan et al. (2004) also reported

clearance samples as fibers per millimeter

squared, which likely should be in structures per millimeter squared. It should be

noted that this clearance standard has not

been shown to be health based, and structures per millimeter squared cannot be

equilibrated or converted to fibers per millimeter squared.

Even with evidence of higher exposure

levels, on the basis of reported data (Lange

2004), it is unlikely that exposure to

asbestos itself will result in any actual health

effects. This is because the asbestos was

mostly chrysotile (Landrigan et al. 2004)

and the duration of exposure for most

workers was short (Lange 2003). However,

as previously reported (Lange 2001, 2002,

2004), regulatory agencies ignored their

own regulations at the WTC, whereas

asbestos concentrations (bulk and air) for

other locations would probably trigger a

regulatory response and most likely a citation with a requirement of some action

plan. Thus, it appears that there are two

standards to be taken from the WTC, one

for agencies themselves and another for all

others. 

The author declares he has no competing

financial interests.
Correspondence

John H. Lange

Envirosafe Training and Consultants, Inc.

Pittsburgh, Pennsylvania

E-mail: john.pam.lange@worldnet.att.net

REFERENCES

Landrigran PJ, Lioy PJ, Thurston G, Berkowitz G, Chen LC,

Chillrud SN, et al. 2004. Health and environmental consequences of the World Trade Center Disaster. Environ

Health Perspect 112:731–739.

Lange JH. 2001. Has the World Trade Center tragedy established a new standard for asbestos? [Editorial]. Indoor

Built Environ 10:346–349.

Lange JH. 2002. How do you interpret regulations: through

science or agency rules? Toxicol Ind Health 18:107–108.

Lange JH. 2003. Cough and bronchial responses in fire-fighters

at the World Trade Center Site [Letter]. N Engl J Med

348:76–77.

Lange JH. 2004. Emergence of a new policy for asbestos: a

result of the World Trade Center tragedy. Indoor Built

Environ 13:21–34.

The WTC Disaster: Landrigan’s

Response

My colleagues and I thank Lange for his letter confirming our finding that asbestos was

present in settled dust as well as in airborne

samples obtained at Ground Zero, the site of

the World Trade Center, and for his having

agreed with us that this asbestos almost certainly represented an exposure hazard for

workers. The asbestos that was detected in

the dust at Ground Zero originated from

asbestos that had been sprayed onto the steel

skeleton of the Twin Towers as fireproofing

when the structure was being built. It was

well known that asbestos was applied in the

North Tower up to about the 40th story and

at other locations throughout the structure

before the practice of spraying on asbestos

was banned in New York City in the early

1970s (Nicholson et al. 1971; Reitze et al.

1972). Concentrations of asbestos in the dust

at Ground Zero were highly variable, and the

level in any particular sample reflects the

location of sampling and the composition of

the dust that happened to be in that area. We

agree with Lange’s view that workers likely

had intermittent exposures to asbestos that

would have arisen unpredictably when, for

example, they picked up a steel beam or

turned over rubble and liberated asbestos

fibers into the air. The asbestos hazard to

workers was magnified by the fact that the

U.S. Occupational Safety and Health

Administration (OSHA) failed to require

constant use of respirators at Ground Zero.

We disagree strongly with Lange’s statement that “it is unlikely that exposure to

asbestos itself will result in any actual health

effects.” Lange appears to base his assertion,

first, on the fact that most of the asbestos at

the World Trade Center was chrysotile

asbestos, and second, that duration of

exposure for most workers was brief.

Unfortunately neither of those factors conveys protection. We remain concerned that

there now exists a risk for mesothelioma

caused by occupational exposure to asbestos

for the brave men and women who worked

and volunteered at Ground Zero.

All types of asbestos fibers, chrysotile

included, have been shown in laboratory as

well as clinical studies to be capable of causing malignant mesothelioma (Nicholson

and Landrigan 1996). All types of asbestos

fibers, chrysotile included, have been

declared proven human carcinogens by

OSHA, the U.S. Environmental Protection

Agency, and the International Agency for

Research on Cancer. Pathologic studies have

found short chrysotile fibers, the predominant type of fiber in World Trade Center

dust, to be the predominant fiber in

mesothelioma tissue (Dodson et al. 1991;

LeBouffant et al. 1973; Suzuki and Yuen

2002). Moreover, mesothelioma has been

reported in persons with relatively low-dose,

nonoccupational exposure to asbestos of

brief duration (Anderson 1982; Camus et al.

1998; Magnani et al. 2001). The greatest

future risk of mesothelioma would appear to

exist among first responders who were covered by the cloud of dust on 11 September

2001 as well as in other workers employed

directly at Ground Zero and workers

employed in cleaning asbestos-laden dust

from contaminated buildings. Although we

agree with Lange that the number of

mesothelioma cases will probably not be

great, we think it quite misleading to state

that no risk exists.

The author declares he has no competing

financial interests.

Philip J. Landrigan

Mount Sinai School of Medicine

New York, New York

E-mail: phil.landrigan@mssm.edu

REFERENCES

Anderson HA 1982. Family contact exposure. In: Proceedings

of the World Symposium on Asbestos, 25–27 May 1982,

Montreal, Quebec, Canada. Montreal, Quebec,

Canada:Canadian Asbestos Information Centre, 349–362.

Camus M, Siemiatycki J, Meek B. 1998. Nonoccupational exposure to chrysotile asbestos and the risk of lung cancer.

N Engl J Med 338:1565–1571.

Dodson RF, Williams MG, Corn CJ, Brollo A, Bianchi C. 1991.

A comparison of asbestos burden in lung parenchma,

lymph nodes and plaques. Ann NY Acad Sci 643:53–60.

LeBouffant L, Martin JC, Durif W, Daniel H. 1973. Structure and

composition of pleural plaque. In: Biological Effects of

Asbestos. (Bogovski P, Gilson JC, Timbrell V, Wagner JC,

eds). IARC Sci Publ 8:249–257.

Magnani C, Dalmasso P, Biggeri A, Ivaldi C, Mirabelli D,

Terracini B. 2001. Increased risk of malignant mesothelioma of the pleura after residential or domestic exposure

to asbestos: a case–control study in Casale Monferrato,

Italy. Environ Health Perspect 109:915–919.

Nicholson WJ, Rohl AN, Ferrand EF. 1971. Asbestos air pollution in New York City. In: Proceedings of the Second

International Clean Air Congress (Englund HM, Beer WT,

eds). New York:Academic Press, 36–139.

Nicholson WJ, Landrigan PJ. 1996. Asbestos: a status report.

Curr Issues Public Health 2:118–123.

Reitze WB, Nicholson WJ, Holaday DA, Selikoff IJ. 1972.

Application of sprayed inorganic fiber containing

asbestos: occupational health hazards. Am Ind Hyg

Assoc J 33:178–191.

Suzuki Y, Yuen SR. 2002. Asbestos fibers contributing to the

induction of human malignant mesothelioma. Annals NY

Acad Sci 982:160–176.

Trichloroethylene and Cardiac

Malformations

In a report of cardiac malformations in rats

exposed to trichloroethylene (TCE) in drinking water, Johnson et al. (2003) used two

(1.5 and 1,100 ppm) of the four treatment

concentrations that they reported in a previous study (Dawson et al. 1993). To evaluate

consistency of results in this single laboratory

across the 10-year interval, we compared cardiac defects reported in 2003 by Johnson

et al. with those reported in 1993 by Dawson

et al. Data from the two papers are shown in

Table 1.

Dawson et al. (1993) did not report the

number of litters per group, so that correlation was not possible. Regardless, it would be

an astonishing coincidence for two studies to

produce exactly the same number of fetuses

in each group. Still more astonishing is the

identical number of “abnormal hearts.”

Nothing reported by Johnson et al. (2003)

gives notice that previously published data

are being reported again, but that seems to

be the inescapable conclusion. If this is a

republication of 1993 data, then there has

also been reclassification of “defects” with the

passage of time.

Another feature of the article by Johnson

et al. (2003) that attracted our attention was

the uncharacteristically large control group

(55 litters). One can surmise that in the earlier study (Dawson et al. 1993), each group

would have consisted of approximately

10 females, which is consistent with the size

of exposed groups (9–13) reported by

Johnson et al. Their control group, however,

was unprecedentedly large, both in the context of conventional study design and relative

to the other groups in this study. Johnson et

al. (2003) provided no rationale for designing

their study with a concurrent control five

times larger than the treatment groups, which

leads us to ask whether the control group

reported here is, in fact, a composite of controls from multiple, perhaps five, different

studies. The immediate impact of this large

control group is that the very cardiac “abnormalities” at the 1.5 ppm dose that did not

differ significantly from controls in 1993

become statistically significant in 2003.

Conventional developmental and reproductive toxicology assays in mice, rats, and

rabbits consistently fail to find adverse effects

Environmental Health Perspectives • VOLUME 112 | NUMBER 11 | August 2004 A 607
Correspondence

of TCE on fertility or embryonic development aside from embryo- or fetotoxicity

associated with maternal toxicity [Cosby and

Dukelow 1992; Dorfmueller et al. 1979;

Hardin et al. 1981; Healy et al. 1982;

Manson et al. 1984; National Toxicology

Program (NTP) 1985, 1986; Schwetz et al.

1975]. Johnson and Dawson, with their collaborators, are alone in reporting that TCE is

a “specific” cardiac teratogen (Dawson et al.

1990, 1993; Goldberg et al. 1992; Johnson

et al. 1998; Johnson et al. 2003; Loeber et al.

1988). We have always considered those

findings suspect, and our comparison of data

from the studies of Dawson et al. (1993) and

Johnson et al. (2003) serves only to intensify

our reservations. Studies from this group

have potential for important public health

and public policy implications, so it is particularly important for the scientific and regulatory communities to have confidence in the

conduct and reporting of those studies. 

We are also concerned that S.J. Goldberg,

one of the authors of the publications alleging

that TCE is a selective cardiac teratogen, has

been a plaintiff expert in TCE lawsuits and

failed to reveal that fact in his publications.

B.D.H. has had no consulting relationships

involving TCE. B.J.K. has provided testimony as

a defense expert in TCE litigation pertaining to

congenital malformations. R.L.B. has provided

testimony as a defense expert in TCE litigation

pertaining to congenital malformations of the

heart. 

Bryan D. Hardin

GlobalTox, Inc.

Hilton Head, South Carolina

E-mail: bhardin@globaltox.com

Bruce J. Kelman

GlobalTox, Inc.

Redmond, Washington

Robert L. Brent

Alfred I. DuPont Institute

Wilmington, Delaware

REFERENCES

Cosby NC, Dukelow WR. 1992. Toxicology of maternally

ingested trichloroethylene (TCE) on embryonal and fetal

development in mice and of TCE metabolites on in vitro

fertilization. Fundam Appl Toxicol 19(2):268–274.

Dawson BV, Johnson PD, Goldberg SJ, Ulreich JB. 1990.

Cardiac teratogenesis of trichloroethylene and dichloroethylene in a mammalian model. J Am Coll Cardiol

16(5):1304–1309.

Dawson BV, Johnson PD, Goldberg SJ, Ulreich JB. 1993. Cardiac

teratogenesis of halogenated hydrocarbon-contaminated

drinking water. J Am Coll Cardiol 21:1466–1472.

Dorfmueller MA, Henne SP, York RG, Bornschein RL,

Manson JM. 1979. Evaluation of teratogenicity and

behavioral toxicity with inhalation exposure of maternal

rats to trichloroethylene. Toxicology 14(2):153–166.

Goldberg SJ, Dawson BV, Johnson PD, Hoyme HE, Ulreich

JB. 1992. Cardiac teratogenicity of dichloroethylene in a

chick model. Pediatr Res 32(1):23–26.

Hardin BD, Bond GP, Sikov MR, Andrew FD, Beliles RP,

Niemeier RW. 1981. Testing of selected workplace chemicals for teratogenic potential. Scand J Work Environ

Health 7(suppl 4):66–75.

Healy TE, Poole TR, Hopper A. 1982. Rat fetal development and

maternal exposure to trichloroethylene 100 p.p.m. Br J

Anaesth 54(3):337–341.

Johnson PD, Dawson BV, Goldberg SJ. 1998. A review:

trichloroethylene metabolites: potential cardiac teratogens. Environ Health Perspect 106(suppl 4):995–999.

Johnson PD, Goldberg SJ, Mays MZ, Dawson BV. 2003.

Threshold of trichloroethylene contamination in maternal

drinking waters affecting fetal heart development in the

rat. Environ Health Perspect 111:289–292.

Loeber CP, Hendrix MJ, Diez De Pinos S, Goldberg SJ. 1988.

Trichloroethylene: a cardiac teratogen in developing

chick embryos. Pediatr Res 24(6):740–744.

Manson JM, Murphy M, Richdale N, Smith MK. 1984. Effects of

oral exposure to trichloroethylene on female reproductive

function. Toxicology 32(3):229–242.

NTP. 1985. Trichloroethylene (CAS # 79-01-6): Reproduction and

Fertility Assessment in CD-1 Mice When Administered in

the Feed. NTP Report RACB84113. Research Triangle Park,

NC:National Toxicology Program.

NTP. 1986. Trichloroethylene (CAS # 79-01-6): Reproduction

and Fertility Assessment in F344 Rats When Administered

in Feed. NTP Report RACB84112. Research Triangle Park,

NC:National Toxicology Program.

Schwetz BA, Leong KJ, Gehring PJ. 1975. The effect of maternally inhaled trichloroethylene, perchloroethylene,

methyl chloroform, and methylene chloride on embryonal

and fetal development in mice and rats. Toxicol Appl

Pharmacol 32(1):84–96.

Trichloroethylene: Johnson

et al.’s Response 

We share Hardin et al.’s belief that any

apparent conflict of interest should be

reported. We note that Brent provided testimony for the defense in TCE litigation,

notably for the same case in which Goldberg

(based on his extensive epidemiologic and

laboratory research on the effects of TCE)

acted as an expert witness for the plaintiff.

We did not report Goldberg’s experience

acting as an expert witness because the point

of expert witness is to provide unbiased, factual explanations of extant data. We believe

this does not constitute a conflict of interest;

we have included a caveat about extrapolating data to humans in our publications. To

our knowledge none of our data have been

used inappropriately.

The work published in 1993 (Dawson

et al.) and in 2003 (Johnson et al.) was actually performed during a much shorter period

of time. Many extraneous factors contributed

to the late publication of the 2003 paper.

Data from our previous work was included

in the more recent paper because we needed

“boundary values” between or below which

we were looking for a threshold or a critical

level. This was a long-term study, and it

would have been an inappropriate use of animals to repeat the earlier animal studies for

those groups. We should have stated more

clearly that we were using the groups already

studied to prevent repetition and to conserve

animal resources, as recommended by the

Animal Welfare Act (1990); however, we did

refer to our previous paper. Our 2003 publication contained new data as well as previously published data. We welcome this

opportunity to clarify our method.

Our alleged reclassification of defects in

our Table 2 (Johnson et al. 2003) merely

reflects careful reevaluation by the cardiologist and minor updates in terminology that

mirror current clinical usage to clarify the

nature of a defect (e.g., great vessel defect vs.

the more specific aortic hypoplasia; L-transposition vs. abnormal looping, etc.). There

are other minor numerical differences in the

tables (Table 2, Johnson et al. 2003, and

Tables 1 and 3, Dawson et al. 1993), not

remarked upon by Hardin et al., which

derive from the more extensive statistical

analysis in the later paper. In an apparent

typographic error, we failed to report a pulmonary valve defect for the 1.5 ppm TCE

in the 2003 paper. This should have been

included in Table 2; however, it would not

have changed the number of hearts with

defects. 

Again, because this was a long-term continuous project, we did use all of the controls

together in a cumulative manner. We used

the larger sample size with data collected

over a long period because it increases the

generalizeability of our data, demonstrating

clearly the background rate and the variability around rate estimates. Control values

A 608 VOLUME 112 | NUMBER 11 | August 2004 • Environmental Health Perspectives

Table 1. Cardiac malformations in rats exposed throughout pregnancy to drinking water containing 1.5 or

1,100 ppm TCE.

Cardiac abnormalitiesa TCE dose Heart malformationsb TCE dose

(Dawson et al. 1993) 1.5 ppm 1,100 ppm (Johnson et al. 2003) 1.5 ppm 1,100 ppm

L-Transposition (left chest) 1 0 Abnormal looping 2 0

Great vessel defect 1 0 Aortic hypoplasia 1 0

Pulmonary valve defect 1 0 Pulmonary artery hypoplasia 1 0

Atrial septal defect 4 7 Atrial septal defect 4 7

Ventricular septal defects Ventricular septal defects

Subaortic 2 1 Perimembranous (subaortic) 3 3

Muscular 1 4 Muscular 1 1

Endocardial cushion defect 0 1 Atrioventricular septal defect 0 1

Aortic valve defect 0 2 Aortic valve defect 0 2

No. with abnormal hearts 9 11 9 11

No. fetuses examined 181 105 181 105

aData from Dawson et al. (1993) Tables 1 and 3, Groups III and IV. bData from Johnson et al. (2003) Table 2; percentage

was converted to number.
Correspondence

were consistent throughout our studies. The

larger sample size did increase statistical

power somewhat in our most recent paper

(Johnson et al. 2003), again without inappropriate use of further valuable animal

resources. It should be noted that the

increase in statistical power is small compared to the increase generated by the effect

sizes and the increase in the number of dose

groups—data that can only be generated in a

long-term project.

Our statistical analysis was simple and

conventional. Hardin et al. are incorrect in

stating that the differences at the 1.5-ppm

dose were statistically significant in our

recent paper (Johnson et al. 2003). The

p-values were reported in Figures 1 and 2 of

our paper as 0.14 and 0.08, respectively, values not conventionally seen as statistically

significant. Different levels of statistical significance used in each of the studies for each

of the groups were carefully listed in the

tables and figures and explained in the text.

There are many references in the scientific literature about effects of halogenated

hydrocarbons on development. We included

only a few of these in our articles. We are a

multidisciplinary team and have studied

both TCE and its major metabolites, often

basing some of our work on the findings of

others in the field without duplicating the

work of others. We have consulted with

other prominent researchers in the field

from time to time in establishing our experimental design or in interpreting our results.

We have found only heart defects associated

with these compounds, despite looking for

other effects. This work has been consistent

with the original epidemiological studies on

which our laboratory work was based. We

have been funded by government and other

nonbiased agencies requiring competitive

grant application and accountability. We

have presented our results as peer-reviewed

published articles in excellent journals. Our

work has all been carried out at The

University of Arizona. A major strength of

our studies was microdissection of each

heart by investigators fully versed in the

pathology of congenital cardiac malformations as well as noncardiac anatomy.

We fully agree with Hardin et al. that

studies in this area “have potential for important health and public policy implications, so

it is particularly important for the scientific

and regulatory communities to have confidence in the conduct and reporting of those

studies.” We believe that our studies have

been rationally planned, are statistically and

scientifically sound, and are of value for this

purpose. We welcome this opportunity for

postpublication discussion of results.

The authors declare they have no competing

financial interests. 

Paula D. Johnson

University Animal Care 

The University of Arizona

Tucson, Arizona

E-mail: pauladj@email.arizona.edu

Brenda V. Dawson

University of Auckland 

Faculty of Medical and Health Sciences

Auckland, New Zealand

Stanley J. Goldberg

Congenital Cardiology

University Physicians

Tucson, Arizona

Mary Z. Mays

Department of Family and 

Community Medicine

University of Arizona Health Sciences Center

Tucson, Arizona

REFERENCES

Animal Welfare Act. 1990. 7USC2131–2159. 

Dawson BV, Johnson PD, Goldberg SJ, Ulreich JB. 1993.

Cardiac teratogenesis of halogenated hydrocarbon-contaminated drinking water. J Am Coll Cardiol 21:1466–1472.

Johnson PD, Goldberg SJ, Mays MZ, Dawson BV. 2003.

Threshold of trichloroethylene contamination in drinking

waters affecting fetal heart development in the rat.

Environ Health Perspect 111:289–292.

Editor’s note: EHP considers expert witness

testimony to be a competing financial interest.

Environmental Health Perspectives • VOLUME 112 | NUMBER 11 | August 2004 A 609