Is organic agriculture polluting our food with heavy metals?

News and commentary about environmental issues.
Sept. 8 2008 12:02 PM

Rusted Roots

Is organic agriculture polluting our food with heavy metals?

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Beyond the comparative impact of organic vs. conventional systems on the soil's heavy-metal concentration, there's the question of how easily these trace elements enter crops. Although the research here is also relatively thin, what has been done suggests that the problem of plant uptake is equally serious in both organic and conventional systems. For example, 14 percent to 28 percent of New Zealand's cattle (destined to be organic beef) were found to have kidney cadmium levels exceeding limits set by the New Zealand Department of Health because of a diet of plants grown in contaminated soil. Similarly, a 2007 study of Greek produce found that organic agriculture does not necessarily reduce the cadmium and lead levels in crops. As it turned out, "certified" organic cereals, leafy greens, pulses, and alcoholic beverages had slightly less heavy-metal contamination than conventional products, but "uncertified" organic products had "far larger concentrations" than conventional ones.

These findings might be preliminary and inconsistent, but pressure is mounting on the organic community to take action. Under rules set by the USDA's National Organic Program, responsibility has been left to the individual farmer to manage plants and animals in a way that does not contaminate crops with heavy metals. The question of how to monitor that responsibility, however, is complicated by the fact that there are as yet no federal limits on heavy-metal concentrations applicable to all fertilizers.

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Organic farmers thus work with broad suggestions rather than concrete federal regulations. They're routinely forewarned by organic watchdog groups such as the Organic Trade Association about dangerous levels of copper and arsenic in poultry manure. They're reminded of proper "nutrient management planning" and encouraged to experiment with the relationship between soil pH levels and rates of heavy-metal contamination. They're advised to test soil regularly for heavy metals and to adjust fertilizer combinations and relative nitrogen, phosphorous, and potassium levels in the soil when metal concentrations rise. A handful of states—California, Oregon, Washington, and Texas among them—have established loose legal guidelines. But the fact remains: The decentralized sprawl of information about fertilizers and heavy metals fosters a far-flung approach to the problem.

The Organic Materials Review Institute, a nonprofit organization that provides certifiers with an independent review of products intended for organic use, is working to change this situation by framing a standard of fertilizer use. OMRI officials have evaluated models from Canada, Washington state, and the Association of American Plant Food Control Officials. Initially, the organization established regulations that, according to Patty Martin, director of Safe Food and Fertilizer, would have been like "driving a hazardous waste truck into organic agriculture." After her 2006 testimony, however, OMRI revised its recommendations to include a somewhat more stringent set of limits on heavy metals in fertilizers.

No matter how they end up, OMRI's guidelines may ultimately come to naught. Scientists are currently documenting another cause of heavy-metal pollution in global agriculture. "Atmospheric deposition"—the transfer of pollutants from the air to the earth—has nothing to do with organic practices per se but is, rather, the result of industrial processes beyond the farmer's control. Farmers already know that fertilizers are not the sole source of heavy-metal contamination. They've inherited a landscape once pummeled with arsenic and lead insecticides. Heavy metals can leach from wooden fences treated with copper chromium arsenate and from lead paint on houses. But the idea that these contaminants can come directly from the air takes all this to a more bewildering level.

Mercury from tooth fillings incinerated with humans corpses and magnesium dust blown east from the Gobi Desert can now join heavy-metal residues wafting from smelting plants and arsenic from coal mines to contaminate soil. Needless to say, airborne contaminants don't land on conventional farms alone. As atmospheric deposition grows more widespread, the difference between organic and nonorganic farming will become ever smaller.

Fortunately, complete despair may still be avoided. Consider this: Plant biologists are working to genetically modify a fern plant that, when ashed and dusted on soil, is capable of sucking up zinc. The dust can then be gathered so the recovered zinc may be recycled and put to better use. Of course, in order for bioremedial technologies such as this to move forward, the dichotomy between organic and conventional agriculture will have to be collapsed, a sober view of organic agriculture will have to be adopted, and we'll have to read the banana leaves with greater skepticism.

James E. McWilliams is the author of Just Food: Where Locavores Get It Wrong and How We Can Truly Eat Responsibly and a professor of history at Texas State University.