State of Science :: Commentaries
Another Perspective on Heavy Metals and "Rusted Roots"
Author(s): Dr. Brian Baker
Organic Materials Review Institute (OMRI)
As a subject interviewed by the cited article's author, I emphasized that although organic was not immune to heavy metal contamination, the problem faced by organic farmers paled by comparison with conventional agriculture. Farmers who are not organic can and do use all fertilizers and soil amendments used by organic farmers. In addition, non-organic farms apply sewage sludge and industrial by-products prohibited in organic farming.
I also pointed out that rather than denying there was a problem, the organic community was dealing with it. McWilliams didn't mention any of that.
The National Organic Program's National List prohibits natural arsenic and lead. It is OMRI's opinion that it is illegal to apply fertilizers that are heavily contaminated with these toxic elements to land certified organic under the NOP. Even though it is not on the National List as a prohibited element, OMRI also considered high levels of cadmium in fertilizers to be unacceptable based on a general prohibition of heavy metals in the soils section. We prepared a study of the problem in 2005.
Patty Martin, mayor of Quincy, Washington has been deeply involved with this issue for some time. Martin was mayor of the Quincy when local dairy farmers in the area began bringing in an industrial toxic waste that was marketed as a 'zinc' fertilizer and applied it to their hayfields. Yes, it had zinc--enough to qualify as a micronutrient. The problem was that it had cadmium as well. Some batches had more cadmium than zinc. Wasn't any law against it.
The cadmium started killing their cows--cadmium causes kidney and other organ failure at low doses. At higher rates it killed stands of alfalfa and practically made it impossible to grow all but a few weeds. I have yet to meet a dairy farmer who wants to do that. The losses were devastating to Quincy's economy.
After that was exposed by Seattle Times report Duff Wilson in a series of articles published in July 1997, Washington State passed a law limiting heavy metals in fertilizers. After a lengthy consultation with experts and the public, we found it was the most appropriate to apply to organic standards, and recommended that the NOSB, NOP, and certifiers consider it as guidance. OMRI adopted the WSDA standard,with minor modification as what we think the limit should be for organic farmers. Anything above that, it is our opinion that a farmer who applies a fertilizer with heavy metal levels above that should not have that land certified as organic.
It wasn't strict enough for Mayor Martin, but in response to her valid criticism, we published a second, stricter threshold based on average background levels where we issue a warning. You probably won't get into trouble if you apply fertilizers that has these elements at above the background level, but application will cause those levels to slowly trend upwards. Also, soils with higher than average background levels will be more likely to cause problems.
Of course, heavy metal contamination is not a simple function of amount or loading. Soil pH, cation exchange capacity, and nutrient levels also are factors in determining plant uptake.
Dairy farmers should also be aware that heavy metals can make their way into mineral pre-mixes. There have been a few incidents where pre-mix manufacturers have used industrial waste as an ingredient and did not have a quality program that kept the contaminant levels feed grade.
These are problems all farmers face. People have higher expectations of organic farmers.