Birth defects are defined as any physical or physiological abnormalities that exist at the time of birth.  Many birth defects can be attributed to chemicals present in the environment.

Birth defects can stem from either genetic causes or teratogenic substances, which can be environmental agents.  The latter can affect the fetus within the first three months of a pregnancy and can cause any number of deformities.

One example of such an environmental agent is methylmercury, a fungicide used for seed grain.  This, if accidentally ingested by a pregnant woman, can cause mental retardation as well as brain damage in the child.  Physically, damage could include abnormal palates, fingers, eyes, and hearts.  The chemical can affect the fetus throughout its development.

Another such hazardous chemical is polychlorinated biphenyl, which can cause skin pigmentation, low birth weight, and abnormal skin and nails in a fetus, upon ingestion on the part of the mother.  Mixtures of toxic chemicals can also be harmful, as can cigarette smoke, which is specifically associated with low birth weight in infants.  Radiation exposure, relating to everything from x-rays to nuclear accidents, is also thought to cause birth defects, including cleft palate, extra fingers, extra toes, extra nipples, fused fingers, heart defects, cerebral palsy, esophageal abnormalities, hip defects, and many more.

International Institute For Birth Defects