Living Downstream: A Scientist's Personal Investigation of Cancer and the Environment

Body burden refers to the total of chemical exposures in the body—and how and where chemicals enter the body. Steingraber compares this to the reading of seasonal growth rings on trees. Body burden measures cumulative exposure but requires extensive sampling and is best completed during autopsy or archived human tissues. Biomonitoring, which records the levels of contamination in humans through blood and urine, is effective because it doesn’t rely on questionnaires, surveys, interviews, or personal anecdotes. It’s the drug test of the ecological world. Its success depends on sampling a large enough representative population and sufficient time to detect trends. Biomonitoring of children with high levels of lead contamination from gasoline successfully led to the elimination of lead from gasoline in the 1970s. Eliminating smoke inhalation has also decreased toxins, though this has a long way to go.

In 1999, the Centers for Disease Control (CDC) examined a sampling of the US population. The results suggest that nearly all US residents have chemicals used in flame-retardant materials, which act like PCBs in their bodies, or similar chemicals that appear to be greater in children and women of reproductive age. The study suggested, however, that PCBs had declined and that persistent organic pollutants had declined in pregnant women as compared to 50 years earlier. This suggests that bans work to reduce exposure. Advances in chemistry have made detecting contaminations easier than a decade ago, and biomonitoring has become a popular method of examining contamination in highly prone areas. The drawback to biomonitoring is that it can’t tell us where contaminants came from or how they entered the body and is thus most meaningful when combined with other types of analysis.

While biology can tell us a lot about mitosis, or cell division and replication, cancer cells don’t follow a specific, traceable pattern. Cancer cells are known for their unlimited growth as well as their potential to be invasive and revert to an earlier stage of development. Cancer cells develop in several distinct ways, the most known of which is through incremental changes to chromosomal DNA. Encounters with carcinogens help genes control cell division.

Along with the sporadic behavior of developing cancer cells, tumors take significant time to develop, often requiring decades to grow. Additionally, tumor growth can slow down at any point during its development. Initiation is a term that molecular biologists assign to the starting stages (small structural alterations) of a cell’s DNA strands. After a cell is initiated, it is transformed, as carcinogenesis is complete. To show up as a symptom of malignant cancer, the transformed cell must pass undetected through the body’s immune system.

Recent studies suggest, however, that the transformation of a normal cell into a malignant, cancerous cell may not always be the result of physical injury to genes. Rather, other factors at work in the human body may initiate the transformation. This discovery may help explain why the amounts and location of exposure to toxic chemicals varies from person to person. One such factor is obesity, which interferes with the body’s insulin production. Biological markers can help reveal past exposure and future cancers that biomonitoring can’t. This growing awareness has increased interest in biological studies of cancer cells.