I am not an organic food believer. Like the inimitable farmer in Omnivore’s Dilemma, I think eating locally is much more important than buying mass-produced organic produce grown in a different hemisphere with (for example) ecologically-toxic pyrethrins. So I’m quite open – even eager – for intelligent criticism of organic food, particularly of the “everything organic is healthy and happy” marketing. But this Slate article by James E. McWilliams wasn’t it.
Essentially, McWilliams claims that heavy metals from organic fertilizers (manure, bird guano, and so on) lead to a greater amount of metals in organic produce, and thus to a greater risk of health problems But it is written in a misleading way. For example:
George Kuepper, an agriculture specialist with the National Center for Appropriate Technology, observed in a 2003 report that composting manure actually concentrates the fertilizer’s metal content, which could lead to greater levels of the contaminants in organic soil.
Composting manure concentrates the metal content relative to raw manure, certainly. But the Kuepper report doesn’t say anything about the concentration of heavy metals in organically-farmed soils compared to that of conventionally-farmed soils. It just notes that contaminated source materials lead to contaminated compost, and suggests that farmers “inquire about the feeding practices at the source or have the material tested.” This is a problem of sloppy farmers, not organic farming.
But it gets worse. McWilliams does not seem to understand that twice as much of very little is still very little.
Recent studies have lent Kuepper’s concern tentative support. For example, in 2007, researchers conducted an analysis of wheat grown on various farms in Belgium; based on the results, they estimate that consumers of organically grown wheat take in more than twice as much lead, slightly more cadmium, and nearly equivalent levels of mercury as consumers of wheat grown on conventional farms.
When I went to the source, I found that “twice as much lead” was 0.28 ug lead per kg body weight for organic consumers, and 0.12 ug lead per kg body weight for conventional consumers. 0.28 is indeed more than twice as much as 0.12. However, according to that very same study, this is less than 10% of the Belgian tolerable daily intake (TDI) and is very unlikely to lead to health problems.
McWilliams also mentions a Greek study that found that:
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.
This probably has more to do with farms that are uncertified and unregulated than with organic farming methods. McWilliams’s very own source, the Kuepper report, explains why. In the United States, certified organic produce cannot be fertilized with, for example, arsenic-contaminated chicken bedding. Uncertified products are not similarly restricted.
I think it’s good to be reminded that organic agriculture is not the end-all be-all solution to perfect human and environmental health. But I think the McWilliams piece comes dangerously close to OMG POISON IN UR FOOD!!!! There is nothing inherent about organic farming that makes it more metal-filled than conventional farming, and no data to suggest that there is enough metal in organic food to harm your health.