(Beyond Pesticides, June 5, 2012)
A new study finds that children exposed to high levels of naphthalene, a common air pollutant and the active ingredient in mothballs, are at increased risk for chromosomal aberrations (CA’s) that have been associated with increased cancer risk in adults. These include chromosomal translocations, a potentially more harmful and long-lasting subtype of CAs, which are of special concern as they result in a portion of one chromosome being juxtaposed to a portion of another chromosome, potentially scrambling the genetic script. Researchers from the Columbia Center for Children’s Environmental Health (CCCEH) at the Mailman School of Public Health, Columbia University Medical Center, and the Centers for Disease Control and Prevention (CDC) published the findings in Cancer, Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research.
“Translocations can persist for years after exposure. Some accumulated damage will be repaired, but not everyone’s repair capacity is the same. Previous studies have suggested that chromosomal breaks can double an adult’s lifetime risk for cancer, though implications for children are unknown,” says first author Manuela A. Orjuela, MD, ScM, assistant professor of clinical environmental health sciences and pediatrics (oncology) at Columbia University Medical Center and a pediatric oncologist at NewYork-Presbyterian Morgan Stanley Children’s Hospital.
The researchers followed 113 children, age 5, who are part of a larger cohort study in New York City. They assessed the children’s exposure to naphthalene; a CDC laboratory measured levels of its metabolites 1- and 2-naphtholin urine samples. (Metabolites are products of the body’s metabolism, and can serve as a marker for the presence of a chemical.) Researchers also measured CAs in the children’s white blood cells using a technique called fluorescent in situ hybridization. Chromosomal aberrations were present in 30 children; of these, 11 had translocations. With every doubling of levels of 1- and 2-naphthol, translocations are 1.55 and 1.92 times more likely, respectively, to occur.
Naphthalene is classified as a possible carcinogen by the International Agency for Cancer Research. Inhalation of vapors is linked to nasal tumors in laboratory animals. It has also been associated with non-Hodgkin Lymphoma and blood disorders, including several types of anemia. Studies have shown reactions including acute hemolysis, jaundice and death in infants wrapped in blankets that had been stored with mothballs. German workers exposed to naphthalene were found to have a variety of cancers, including laryngeal, gastric, nasal, and colon cancer.
Naphthalene belongs to a class of air pollutants called polycyclic aromatic hydrocarbons (PAH). Prior research at the CCCEH has established a link between prenatal exposure to PAH and increased risk for childhood obesity, IQ deficits, and CAs. The new study is the first to present evidence in humans of CAs, including translocations, associated with exposure to one specific PAH, naphthalene‚ during childhood.
To obtain a better sense of the long-term consequences of naphthalene exposure, Dr. Orjuela and other CCCEH investigators are following some of the children in the study as they reach fourth grade. While they expect to see further translocations, they do not expect to see any signs of cancer in the white blood cells. “So far, the translocations seem to be random, and there has been no evidence of the specific translocations that are known to be associated with leukemia. This is entirely expected; leukemia is very rare.” Frederica Perera, DrPH, senior author on the paper, adds that, “The findings provide yet more evidence of the vulnerability of the young child to carcinogenic air pollutants.”
Apart from mothballs, crystalline naphthalene is used as a deodorizer for diaper pails and toilets. It is also used as an intermediate in the manufacture of a wide range of products, including phthalate plasticizers, resins, dyes, pharmaceuticals, insect repellents, and other products. Since naphthalene easily vaporizes, its gas has a variety of other fumigant uses, including use as an insecticidal soil fumigant.