I’ve seen a lot of comments and questions regarding the safety and organic credentials of our compost after our soil was featured in the CNN/Great Big Story.
I am writing to respond in general regarding the ink, bio-accumulation of heavy metals, and toxicity. Unfortunately a lot of people are not provided the scientific literacy needed to understand the composting, organic chemistry, and the soil food web. I hope the following help!
Bio magnification is the process of greater and greater accumulation of stable elements (or compounds) that is increased while unchanged though each stage of the food web. The act of aerobic composting by its nature is used to destroy any VOC’s and other macro molecules, breaking such potentially harmful molecules down into non volatile constituent elements or simple compounds that are then used in natural biological processes. There are limits to such processes, for example we will not compost turf grasses or most ruminant manures due to the presence of herbicides used in turf management (e.g. clopyralid, 2-4d amine, isoxabine) which are not broken down by the bacterial composting process and therefore are increased in concentration. However, the vast majority of potentially harmful compounds are degraded into very simple elements and used by the various organism within the soil food web as well as plants. Even organic chemicals that are hydrocarbon based, take crude oil with its benzene rings, can be (with the right kind of composting and bacterial populations) converted into the basic building blocks of all life. Benzene itself is just carbon and hydrogen, two of the most critical elements to all life on earth. When it is in its C6H6 state, it is a carcinogen, then those carbon and hydrogen atoms are broken down, then can be used as needed.
The compost this is made from passes all US Composting Council Seal Of Testing Assurance. This looks at inert materials, heavy metal accumulation, disease causing bacteria, among standard agronomic, biochemical, and geo-technical markers. All metals are at very low concentrations, lower than background levels in many soils. All life uses every element (non man made) on the periodic table of elements, though most of us need such slight amounts and never have to go out of our way to actively get many of those elements. For example, this compost, per TMECC testing, shows arsenic at 1.54 mg/kg, EPA limit is 41 mg/kg (analysis method SW846-6010B 04.06-As . Now naturally occurring arsenic levels in soil have much to do with the parent material. For example in Ohio the naturally occurring levels of 2.0 to 45.0 ppm (EPA limit as expressed in ppm is 0.39) so the natural soils of the metal arsenic in Ohio is exponentially greater than occurs in this compost. Mercury, EPA limit is 17 mg/kg, the testing method can only pick-up 0.50 mg/kg or greater and so no Mercury could be seen in our soil as the results were below detectable concentrations. Lead, ours has 20.48 mg/kg with the EPA limit at 3000 mg/kg. Selenium 3.45 mg/kg with the EPA limit being 36 mg/kg. Hopefully these examples illustrate that our material is managed and tested to the highest levels to ensure that it is safe and healthy for ever organism that will come into contact with it. I am a conservationist and if I found evidence that any of my practices threatened our environmental health I would not take any part of it.
While the ink is a unique trade secret of the Federal Bank, proper testing ensures that no trace elements of the composted currency exist at levels harmful to the living creatures that live in (e.g. bacterial, archaea, protist, fungi, arthropod, nematodes), grow in, work with, or eat plants grown in this soil. The finished compost is actually tested and verified to meet US Composting Council Seal Of Approval requirements, which are exceedingly high. These test look less at agronomic/horticultural aspects of the soil (e.g. pH, nutrient availability, CEC, total OM, salts) and focus more on the presence of inert material (plastic, glass, metals), pathogens (coliform), and toxic metals (arsenic, cadmium, zinc, copper, mercury, molybdenum, lead, nickel, selenium). This material passed all well below EPA limits. The reality is that all living creatures likely require every non-synthetic element on the periodic table to some degree or another. Most of the ink components exist as polymers initially (though ink chemist prefer the term “resins”) then are broken into monomers that are no longer toxic or volatile. These are then used as building blocks of the true stars of the composting show, bacteria. Any trace materials left are are limits that would be found in most naturally occurring soils.
The compost is held at a thermophilic phase (roughly 106 to 250 degrees Fahrenheit though the material is not usually allowed to reach greater than 164 degrees for long and only a few times is allowed to reach temperatures of 182 degrees) for up to weeks at a time, repeatedly, during the composting process. At 120 degrees oomycetes are killed (water molds), at 148 degrees almost all pathenogenic fungi, bacteria, are killed and viruses denatured. Sadly that temperatures also kills nematodes and arthropods. At 160 degrees bacteria that cause plant diseases are killed as are soil insects. The soil is brought to 184 degrees for short periods to kill weed seeds that might be present. Temperature and proper management of moisture, oxygen, nutrient ratios, and composting organisms is a very intense, wonderfully diverse, and dedicated biological science! I hope that helped. Cheers!