“People who use pesticides are farmers, and they can actually tell you what they used,” said Aaron Blair, PhD, a study co-author and scientist emeritus in the Division of Cancer Epidemiology and Statistics at the NCI.

Multiple myeloma risk did not increase with longer self-reported exposure, though the risk was always greater than for those who were unexposed. The disease risk was greater for men with shorter exposure times for 2 of the 3 pesticides. Researchers observed a dose-response for DDT:

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Years of exposure

Odds ratio (OR) (95% CI)

Captan (Ptrend  = 0.13)

≤ 7 years

3.14 (1.30 to 7.58)

> 7 years

1.27 (0.49 to 3.31)

Carbaryl (Ptrend = 0.01)

≤ 6 years

2.69 (1.41 to 5.13)

> 6 years

1.76 (0.87 to 3.58)

DDT (Ptrend = 0.02)

≤ 9 years

1.48 (0.93 to 2.35)

> 9 years

1.56 (1.01 to 2.41)

Greater total lifetime exposure did not translate to higher risk for captan and carbaryl:

Cumulative exposure (lifetime days)

OR (95% CI)

Captan (Ptrend = 0.01)

≤ 17.5

3.52 (1.32 to 9.34)

> 17.5

2.29 (0.81 to 6.43)

Carbaryl (Ptrend = 0.01)

≤ 10

3.18 (1.40 to 7.23)

> 10

2.44 (1.05 to 5.64)

DDT (Ptrend = 0.04)

≤ 22

1.51 (0.74 to 3.09)

> 22

1.92 (0.95 to 3.88)

“For known carcinogens, we expect that as the exposure goes up, so does the risk. That’s true for lung cancer and cigarettes, for example. The more cigarettes you smoke, the greater the risk for lung cancer,” Dr Blair said.

“If you don’t see that monotonic relationship, a couple things come to mind. One, maybe this is just chance. Two, it could be a metabolic effect that changes at a certain level of exposure. At this stage, thinking about multiple myeloma and pesticides, we don’t know what it is. This is a relatively early stage of generating complex, high-quality data to look at multiple myeloma and pesticide exposure.”

The authors note a protective effect associated with immune system conditions. Allergies (OR = 0.48; 95% CI, 0.36 to 0.63), hay fever (OR = 0.58; 95% CI, 0.37 to 0.89), and rheumatoid arthritis (OR = 0.23; 95% CI, 0.14 to 0.40) were each associated with reduced risk for multiple myeloma. Allergies to specific foods (OR = 0.58; 95% CI, 0.39 to 0.87) and drugs (OR = 0.47; 95% CI, 0.33 to 0.67) also seemed to provide a protective effect.

This study reflects an analysis of research done 30 years ago involving men who may have been exposed to pesticides as far back as the 1960s. Although DDT has been banned in the United States since 1972 and in Canada since 1985, the chemical remains in use in other countries. Studies from the late 1990s and early 2000s found DDT in dust and soil in the United States.2,3

“We don’t have any measure of intensity of exposure. We really don’t know how long the farmers used the pesticides or whether they used protective equipment,” he said. “At this point, we don’t know enough to comment on a safe level [of pesticide use] or where a threshold would be. When you see evidence like this, that there’s an association with a pesticide, we need to be very careful in how we use [that pesticide].”

Correction: an earlier draft of this article incorrectly quoted Dr John Spinelli as saying “We looked at a number of different pesticides, including insecticides, herbicides, and fungicides. We saw a link between only 33 different types of pesticides and multiple myeloma.” The number of types of pesticides is 3, not 33.

References

  1. Presutti R, Harris SA, Kachuri L, Spinelli JJ, Pahwa M, Blair A, et al. Pesticide exposures and the risk of multiple myeloma in men: an analysis of the North American Pooled Project (NAPP) [published online ahead of print June 4, 2016]. Int J Cancer. doi: 10.1002/ijc.30218.
  2. Bradman MA, Harnly ME, Draper W, Seidel S, Teran S, Wakeham D, et al. Pesticide exposures to children from California’s Central Valley: results of a pilot study. J Expo Anal Environ Epidemiol. 1997;7(2):217–234.
  3. Butte W, Heinzow B. Pollutants in house dust as indicators of indoor contamination. Rev Environ Contam Toxicol. 2002;175:1–46.

Topics:

Hematologic Cancers Multiple Myeloma