Robert Knight: Canaries in a coal mine


Published: Sunday, March 31, 2013 at 6:01 a.m.
Last Modified: Wednesday, March 27, 2013 at 11:35 p.m.

In "Region at Risk," The Gainesville Sun spotlighted the high rates of fatal cancers in rural areas of north Florida. The conclusions of local cancer experts appear to be that rural residents do not receive adequate medical care needed to detect and treat cancers early.

In a companion article, The Sun cites studies in North Carolina and Iowa that found that exposure to agricultural pesticides is a possible factor in increased prostate cancer in males, melanoma in farmer's spouses and ovarian cancer risk in female pesticide applicators. But the professors interviewed for The Sun's story did not think that pesticides are likely to be the missing link to increased cancer risk in rural north Florida. In summary, this article pointed to rural poverty and increased tobacco use as possible correlates with higher local cancer death rates.

The President's Cancer Panel Report (2010) takes a much harder look at the effects of exposure to environmental contaminants and the incidence of cancer among farmers, their families and migrant farm workers. These people "are at highest risk from agricultural exposures" both on the job and in their daily lives. In rural north Florida, this population is almost totally dependent on private self-supply wells that draw groundwater from below the lands that are intensively farmed.

While The Sun article appears to conclude that pesticides are not elevated in groundwater in our area, there is one environmental contaminant that is clearly elevated in these drinking water wells — namely nitrate nitrogen derived from fertilizers, animal wastes and septic tanks.

Background nitrate nitrogen concentrations throughout areas where the Floridan Aquifer underlies protected lands (for example, the Ocala National Forest) are less than 0.05 parts per million (ppm or mg/L). County-wide average nitrate concentrations in Union County are over 0.54 ppm, more than 10 times higher than the baseline aquifer levels.

The average value in Suwannee County wells is 0.56 ppm, Gilchrist County's average is 0.41 ppm, and the average in Alachua County is 0.41 ppm, eight times higher than the background.

About 40 percent of the wells sampled in Gilchrist County had nitrate concentrations above 1 ppm, more than 20 times the baseline. Fanning Springs on the Suwannee River in Levy County has an average nitrate concentration above 5 ppm, or more than 100 times the background, and peak concentrations close to 10 ppm. Test wells in Suwannee and Lafayette counties associated with row crops frequently have nitrate concentrations above 30 ppm (600 times the baseline), and a few wells have been recorded at concentrations greater than 100 ppm (2,000 times the background level).

The President's Cancer Panel Report states that the "most likely known mechanism for human cancer related to nitrate is the body's formation of N-nitroso compounds (NOC), which have been shown to cause tumors at multiple organ sites in every animal species tested." The report goes on to say: "In humans, NOCs are suspected brain and central nervous system carcinogens" and that in an Iowa study, older women drinking water with elevated nitrate concentrations had increased risk for bladder cancers.

The authors conclude that nitrate in drinking water at concentrations less than 10 ppm (the "safe" human drinking water standard) could be carcinogenic and that further research is warranted, especially since groundwater nitrate concentrations in many agricultural areas continue to increase.

The Florida Department of Environmental Protection and the U.S. Environmental Protection Agency have found that nitrate concentrations between 0.2 and 0.4 ppm cause a kind of "ecological cancer" in natural springs by promoting a proliferation of nuisance algae. However, the state's nitrate standard in groundwater continues to be 10 ppm, a value that has resulted in the wholesale loss of desirable submerged aquatic vegetation in a growing number of Florida's springs. To date there has not been any publicized effort to look for a relationship between human consumption of groundwater contaminated by nitrate in Florida and the risk of increased cancer.

It has often been stated that springs are a window into our aquifer and are also like canaries in a coal mine. Perhaps those analogies are even truer than most people think.

If you see celebrated nature photographer John Moran's springs before-and-after photos at the Florida Museum of Natural History, you may conclude that the "cancerous" algal proliferation impairing our springs may be a fair warning of the unseen dangers to humans resulting from drinking polluted groundwater. With the documented increased risk of cancer deaths in north Florida's most rural counties, it is critical that state and federal epidemiologists look for a link between elevated nitrate concentrations in our groundwater and these high cancer rates.

Robert Knight, Ph.D., is director of the private, nonprofit Howard T. Odum Florida Springs Institute in Gainesville and holds a master of science in public health degree from the University of North Carolina.

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