Major malformations occur in about 1 to 3% of all human births, but the causes of most malformations are unknown. The known causes, about one third of the total, include genetic abnormalities (eg. Down’s syndrome), specific infectious diseases (eg. rubella), malnutrition, ionizing radiation, certain drugs (eg. thalidomide) and some occupational exposures such as lead.

Many researchers believe that occupational exposures account for less than 1% of birth defects. This is largely because few occupations or occupational exposures are specifically associated with increased frequencies of malformations or developmental problems. However, research in this area is extremely difficult because malformations are rare, reporting is sporadic, occupational relationships are seldom investigated, exposures are often complex, and studies are usually retrospective (occupational histories are gathered after birth, when there may be problems with bias and recall).

Very few workplace materials have been properly tested in laboratory animals. Animal testing for developmental toxicity is particularly difficult because different animal species may respond very differently to a material. Developmental effects may be targetted to the developing embryo, or may be part of a generalized toxic response of the pregnant animal.

As a rule of thumb, many researchers believe that any chemical, if given at a sufficient dose, at an appropriate time, will cause adverse developmental effects. This is the reason that the WHMIS criteria for Teratogenicity and Embryotoxicity specify that injury to the embryo or fetus must be observed at a concentration that has no effect on the pregnant female. This is also the reason for the familiar medical advice that pregnant women should avoid all unnecessary chemical exposures.

A recent study at the Hospital for Sick Children in Toronto investigated the risk of major fetal malformations among women with occupational exposure to organic solvents. The results are published in the Journal of the American Medical Association (JAMA, 1999; 281:1106-1109)

The study examined the occurrence of birth defects in the children of 125 women who had been exposed occupationally to organic solvents during the first trimester of pregnancy, which is the most sensitive period of fetal development. Information about exposures was obtained during pregnancy, before birth outcomes were known. This design minimizes the major flaw of most human studies, known as recall bias.

Major birth defects were seen in 13 children of mothers in the occupationally exposed group. The women’s occupations included factory workers, laboratory technicians, artists, chemists, carpenters, and funeral home employees. Furthermore, 12 of the 13 children were born to women who reported health symptoms related to solvent exposures during pregnancy. In contrast, only 1 child with a birth defect was born to a woman in the control group (no occupational exposure) – 125 women matched to the study group.

The main limitations of the study were its small size – only 125 occupationally exposed women and 13 children with birth defects – and the diverse exposures. It is not possible to link the cases to any particular solvents or occupations. Nor can one draw general conclusions about the reproductive hazards of solvents. Moreover, it would be expensive and impractical to conduct larger studies.

The organic solvents mentioned in the study are "aliphatic and aromatic hydrocarbons, phenols, trichloroethylene, xylene, vinyl chloride, acetone and related compounds". In animal studies two of the solvents — trichloroethylene and xylene, have caused toxic effects in the offspring at doses which were reported not to be toxic to the mothers.

The authors conclude that it is prudent to minimize women's exposure to organic solvents during pregnancy and that "symptomatic exposure appears to confer an unacceptable level of fetal exposure and should be avoided by appropriate protection and ventilation."

Organic solvents are commonly found in most workplaces. They are present as ingredients in paints, adhesives, cleaners, and many other products. Most common solvents readily evaporate into the air, and most occupational exposure occurs by breathing the vapours. Skin contact may also be a significant route of exposure, since some solvents are readily absorbed through the skin.

Exposure to organic solvents is best controlled by the following strategies:

• Substitute. Use products containing less hazardous ingredients. Some organic solvents are toxic, while others are practically non-toxic. Check the CHEMINFO database at CCOHS for detailed information.

• Use the smallest feasible amounts of solvents.

• Use products with lower percentages of organic solvents. Read the Material Safety Data Sheet (MSDS) for information on ingredients.

• Use organic solvents in well-ventilated areas. Enclosure or local exhaust ventilation are superior to general area (dilution) ventilation.

• Wear solvent-resistant gloves and protective clothing to help prevent skin contact. Protective materials may be penetrated or degraded by solvents. Check the MSDS or contact CCOHS to find out about the best materials for protection.

• Face masks, such as dust masks or surgical masks, do not protect against organic vapours. If exposure cannot be prevented in any other way, wear a respirator with a cartridge approved for organic solvent vapours.

The CHEMINFO database at CCOHS contains detailed profiles on 800 industrial chemicals, including many common organic solvents. Profiles include information on developmental and other hazards, measures for working safely with hazardous materials, recommended protective clothing and respiratory protection measures, and emergency measures in case of spills, leaks or fires. CHEMINFO can help you to evaluate the hazards of the products you are using, and to identify safer substitutes.