Reproductive wrongs

Dr. Koren is associated with the Motherrisk Program in the Department of Pharmacology and Toxicology at the Hospital for Sick Children in Toronto. He and his colleagues have been looking at the role of commonly used industrial solvents in producing birth defects among pregnant workers for a number of years.

The babies born to mothers who were exposed but who did not exhibit symptoms had no deficits; but all of the babies born to exposed and symptomatic mothers were colour blind. The exposed infants also had worse visual acuity than the control group of non exposed children. That, he said, is "very concerning to us" as it indicates that the development of the brain in the fetus may be adversely affected by exposure to solvents.

Organic solvents are a class of compounds that are useful in industry because of their ability to dissolve fats, oils, resins, rubber and plastic. They are extensively used for all sorts of applications ranging from spray painting to laboratory work. They were first developed in the latter half of the 19th Century from the coal tar industry, but chlorinated solvents came into being in the 1920s. Their introduction led to the first reports of toxicity among workers and among people living near industry.

Solvents are grouped into two categories — aliphatics, which exist in a chain form; and aromatic compounds, which are in a six carbon ring form. The aromatic compounds get their name from the fact that they have a pleasant odour. They are the ingredient that glue sniffers crave and include such chemicals as toluene, xylene, coal-tar naptha, styrene and benzene. They are used extensively in printing, fibreglass-reinforced products, manufacture of coatings, consumer products, glues and veneers (see sidebar for examples of some of the solvents, and their uses and health effects). Exposures are often to a number of different solvents.

Problems with cause and effect

Dr. Koren's work is part of a growing trend in research around the world that is beginning to implicate organic solvents, not just in birth defects but in reduced fertility. Until recently many scientists believed that these fertility and birth defects were only problems in cases of substance abuse. In the case of toluene, one of many organic solvents, the Canadian Centre for Occupational Health and Safety suggests that infertility and defects are risks only when there is abuse rather than normal controlled occupational exposure. Toluene is the active ingredient in glue that gives glue sniffers a high and causes all of the damage.

Determining cause and effect in occupational exposure to solvents, however, is difficult. The Hamilton office of the Occupational Health Clinics for Ontario Workers (OHCOW) recently released the results of a survey of 22 workers sent to them by the Canadian Union of Public Employees. These workers had all been employed as road and arena painters for a number of years by the Hamilton traffic department. They all had symptoms such as neurological and psychological complaints that could have been produced by the solvents they were exposed to in paint.

Paul Sampara, an occupational hygienist with OHCOW, says that the workers in question were subjected to a very detailed questionnaire and interview with an occupational health physician. He says that ten of them probably were displaying symptoms associated with exposure to the toluene in paint thinner and that their exposure took place over a long period of time. It is difficult, he adds, to "tease out" the specific cause of these particular symptoms or to determine the exact levels that these workers were exposed to.

Dr. Ulrike Luderer of the University of California at Irvine says that "as most epidemiological studies of occupational exposures necessarily study workers with mixed exposures, it is more difficult to say which specific solvents may cause these problems." She goes on to say that "there is a significant amount of epidemiological data linking occupational solvent exposure in general to miscarriages and more recent studies suggesting that solvent-exposed workers may have lower fertility."

Abuse of chemicals or very high exposures are much more obvious when it comes to determining effect. The subtle effects of long term, low levels of occupational exposure are much more difficult to determine. Dr. Georgianne Arnold, a pediatrician at the University of Rochester School of Medicine, has looked at the effects of toluene abuse (glue sniffing) on the developing fetus and concluded that toluene does cause damage.

What effect a small dose over time would have on a pregnant woman, she tells COS, is really not clear. There is more evidence of an increase in birth defects and, she adds, there is "enough evidence in the literature to suspect that care should be taken." She recommends that women "should exercise caution." Sloppy and careless safety in the workplace might increase the risk of birth defects.

Dr. Luderer's research did attempt to look at exposure to small amounts of toluene. She gave both men and women filtered air to breathe for three hours at a time. Some of the subjects breathed pure air, and others had air with 50 ppm of toluene added in. This level is well below the allowable limit for safe toluene exposure. Even with this very low level, she did find subtle effects on hormone secretions for both sexes when they inhaled the toluene air. She says that "with higher levels of exposure, one might see larger effects on reproductive hormones that could adversely affect fertility." A recently published (1999) study conducted in Germany on men and women working in the printing industry found that low daily exposures to toluene seems to be associated with reduced fecundity in women. The authors, from the NORDIG Institute for Health Research and Prevention in Hamburg noted that organic solvents could affect hormonal regulation and that they increase early fetal loss.

An evaluation of reproductive potential for 50 men working on aircraft maintenance at a U.S. airbase who were regularly exposed to a wide variety of solvents was carried out by Dr. Grace Lemasters of the University of Cincinnati. The men working in the paint shop, she found, had a significant decline of 19.5 percent in the motility of their sperm although other values remained in the normal range.

A Danish study that looked at the effect of styrene exposure on semen quality in reinforced plastics workers found a statistically significant decline in sperm density. It dropped from 63.5 to 46.0 million sperm/ml. There was no decline in sperm density in the non exposed control group. The total sperm count was almost halved from an initial 175 million sperm/ejaculate for those exposed to styrene.

A study in Singapore of women employed in the manufacture of audio speakers and who were exposed to high levels of toluene found that they had a much higher rate of spontaneous abortions than their non-exposed co-workers and other women in the community who were not exposed. The rate of miscarriage for the exposed group was 12.6/100 pregnancies compared to 2/100 for others working in the factory and 4/100 for those in the community.

The Canadian study

One of the largest and most comprehensive studies to date was conducted by Dr. Koren and his colleagues at the Hospital for Sick Children and published last year in the Journal of the American Medical Association. The study evaluated 125 women who were occupationally exposed to a variety of organic solvents between 1987 and 1995. Each woman was matched to a control who had not been exposed on a variety of criteria such as age, smoking and drinking status.

The occupations represented by these women were: factory worker (manufacturing, cosmetics, tooling, automotive and paint manufacturing), lab technician, artist, printer, chemist, painter, office worker, car cleaner, veterinary technician, orthotist, funeral home worker, carpenter, and social worker. Seventy-five of these women reported that they temporarily did experience symptoms of exposure, which included eye irritations, respiratory irritations, headaches and difficulty breathing.

Thirteen of the exposed women had malformations compared to only one in the non exposed group. Twelve of the women with malformed infants reported having symptoms from their exposure to the solvents while the presence of symptoms couldn't be determined for the thirteenth mother. More of these exposed women had suffered previous miscarriages than did those who were not exposed (46.2 percent vs 19.2 percent).

Dr. Koren and the others interviewed for this article all emphasize that women should minimize their exposure to organic solvents if pregnant or if attempting to become pregnant. Dr. Koren further emphasizes that proper ventilation and protective clothing are essential.

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