Three or four years ago, public concern increased about the relationship between DDT and breast cancer. Several studies have been published on the topic, including those by Kreiger, et al and Wolff, et al. Dr. Hunter presented new evidence from the Nurses' Health Study. Measuring exposures to pesticides in humans is a difficult task, Dr. Hunter said. Questionnaires are inaccurate because people are almost never aware of which pesticides they have been exposed to, or in what amounts.
Blood samples provide a better measure, but are subject to detection limits.
The effects of pesticides on animals are understood to a greater degree. Several examples of this effect include male fish developing feminine characteristics, a decline in the penis size of alligators in the Everglades over the past decade, and thinning of egg shells in birds. Medical records have documented an increase in breast cancer since the second world war that is roughly correlated with the release of various pesticides to the environment. Others, including Bob Hoover of the National Cancer Institute, were not convinced, and believed the evidence did not rule out an association. Dr. Hunter reported new data from the Nurses' Health Study, a large ongoing cohort of female nurses, that confirms the results of previous null studies.