National Organic Standards Board

Crops Subcommittee

Petitioned Material Checklist

Magnesium Oxide

August 6, 2013

Summary of Proposed Action:

 

Magnesium Oxide (MgO) has been petitioned for use under §205.601 Synthetic substances allowed for 

use in organic crop production. Specifically, the petition states “Magnesium oxide is intended to be used to 

control the viscosity of a clay suspension agent to prevent settling of materials suspended in water or other 

liquids.” The petitioner indicates they wish to use MgO for the application of finely ground humates, but the 

petition is written more broadly: “The substance is intended to be used in combination with other organic 

inputs applied as a liquid foliar on a wide variety of different agricultural, vegetable, fruit, and horticultural 

crops.”

The petitioner indicates they would use MgO at a very low level: at 0.074% of the humate suspension 

being applied, which would equate to 0.0007 to 0.0014 pounds of MgO applied per acre.

Magnesium oxide occurs as the mineral magnesia, and in its hydrated form – magnesium hydroxide -- is 

the naturally occurring mineral periclase. Magnesium oxide appears to be a fairly benign compound that 

has a wide range of uses, including as an antacid and laxative (milk of magnesia), and in lots of industrial 

processes such as in producing cement, abrasive materials and furnace linings. 

There are several manufacturing processes used to produce MgO. It is commonly made from sea water 

or salt brines, but can also be made by heating MgCO3 limestone to drive off CO2 and produce MgO. (To 

produce MgO from sea water or salt brine uses the following procedure: The raw materials are lime and 

salt water -- either sea water or brine from salty wells. The lime is heated to produce calcium oxide. Fresh 

water is then added to the calcium oxide to produce calcium hydroxide. Sea water or salt brine from a well 

-- treated with a small amount of sulfuric or hydrochloric acid -- is then added to the calcium hydroxide, 

causing the magnesium chloride in the salt water to react with calcium hydroxide to produce magnesium 

hydroxide and calcium chloride. The magnesium hydroxide is then heated to produce magnesium oxide.)

The MgO manufactured using sea water or salt brine (and some acid) produces a purer and more refined 

form of MgO than that produced by heating magnesium carbonate limestone, and so is preferred by the 

petitioner. 

Evaluation Criteria (see attached checklist for criteria in each category)

 Criteria Satisfied? 

1. Impact on Humans and Environment ☒ Yes ☐ No ☐ N/A 

2. Essential & Availability Criteria ☒ Yes ☐ No ☐ N/A

3. Compatibility & Consistency ☒ Yes ☐ No ☐ N/A 

Subcommittee Action & Vote: 

Classification Motion: Move to classify Magnesium Oxide as petitioned as synthetic. 

Motion by: Francis Thicke 

Seconded by: Colehour Bondera 

Yes: 8 No: 0 Absent: 0 Abstain: 0 Recuse: 0 

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Listing Motion: Move to list Magnesium Oxide to §205.601 with the following annotation: For use only 

to control the viscosity of a clay suspension agent for humates.”

Motion by: Francis Thicke 

Seconded by: Zea Sonnabend 

Yes: 8 No: 0 Absent: 0 Abstain: 0 Recuse: 0 

 Basis for annotation: ☒ To meet criteria above ☐ Other regulatory criteria ☐ Citation 

Notes: 

 Approved by Jay Feldman, Subcommittee Chair, to transmit to NOSB August 6, 2013

NOSB Evaluation Criteria for Substances Added To the National List

Crops 

Category 1. Adverse impacts on humans or the environment? Substance: Magnesium Oxide

Question Yes No N/A Comments/Documentation (TAP; 

petition; regulatory agency; other)

1. Is there a probability of environmental 

contamination during, use or misuse? 

[§6518(m)(3)]

X

2. Is there a probability of environmental 

contamination during, manufacture or 

disposal? [§6518(m)(3)]

X 

When MgO is produced using sea water 

or salt brine, a small amount of acid is 

used to lower the pH of the salt solution 

to prevent the formation of carbonates.

When MgO is produced using

magnesium carbonate limestone, carbon 

dioxide is released into the atmosphere.

Additional carbon dioxide is produced 

through the burning of fossil fuels used to 

achieve the high heat required to 

decompose the limestone.

3. Does the substance contain inerts 

classified by EPA as ‘inerts of 

toxicological concern’? [§6517 

(c)(1)(B)(ii)]

X 

4. Is there potential for detrimental chemical 

interaction with other materials used in 

organic farming systems?

[§6518(m)(1)]

X 

5. Is there a toxic or other adverse action of 

the material or its breakdown products?

[§6518(m)(2)]

X 

6. Is there persistence or concentration of 

the material or breakdown products in 

the environment? [§6518(m)(2)]

X

7. Would the use of the substance be 

harmful to human health or the 

environment? [§6517 (c)(1)(A)(i); §6517 

(c)(2)(A)(i); §6518(m)(4)]

X

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8. Are there adverse biological and 

chemical interactions in the agroecosystem, including biodiversity? 

[§6518(m)(5)]

X 

9. Are there detrimental physiological 

effects on soil organisms, crops, or 

livestock? [§6518(m)(5)]

X 

NOSB Evaluation Criteria for Substances Added To the National List

Crops 

Category 2. Is the Substance Essential for Organic Production? Substance: Magnesium Oxide

Question Yes No N/A Comments/Documentation (TAP; 

petition; regulatory agency; other)

1. Is the substance agricultural? [§6502(1)] X

2. Is the substance formulated or 

manufactured by a chemical process? 

[§6502(21)]

X 

3. Is the substance formulated or 

manufactured by a process that 

chemically changes a substance 

extracted from naturally occurring plant, 

animal, or mineral sources? 

[§6502(21)]

X 

4. Is the substance created by naturally 

occurring biological processes? 

[§6502(21)]

X 

5. Is there a natural source of the 

substance? [§ 205.600(b)(1)] X

.

6. Is there an organic substitute? 

[§205.600(b)(1)] X

7. Is there a wholly natural substitute 

product?

[§6517(c)(1)(A)(ii)]

X

8. Are there any alternative substances? 

[§6518(m)(6)]

X None that have the desired functional 

properties, according to the petitioner.

9. Are there other practices that would 

make the substance unnecessary? 

[§6518(m)(6)] 

X MgO is not absolutely essential for the 

materials application it is petitioned for, 

but it makes application easier, and 

perhaps safer for the person applying the 

materials (reduces dust).

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NOSB Evaluation Criteria for Substances Added To the National List

Crops 

Category 3. Is the substance compatible with organic production practices? Substance: MgO 

Question Yes No N/A Comments/Documentation (TAP; 

petition; regulatory agency; other)

1. Is the substance consistent with organic 

farming and handling? 

[§6517(c)(1)(A)(iii); 6517(c)(2)(A)(ii)]

X 

2. Is the substance compatible with a 

system of sustainable agriculture? 

[§6518(m)(7)]

X 

3. If used in livestock feed or pet food, Is 

the nutritional quality of the food 

maintained with the substance? 

[§205.600(b)(3)]

X 

4. If used in livestock feed or pet food, Is 

the primary use as a preservative? 

[§205.600(b)(4)]

X 

5. If used in livestock feed or pet food, Is 

the primary use to recreate or improve 

flavors, colors, textures, or nutritive value 

lost in processing (except when required 

by law)? [§205.600(b)(4)]

X 

6. Is the substance used in production, and 

does it contain an active synthetic 

ingredient in the following categories:

[§6517(c)(1)(B)(i)]; 

copper and sulfur compounds

X 

toxins derived from bacteria X

pheromones, soaps, horticultural oils, 

fish emulsions, treated seed, vitamins 

and minerals

X 

livestock parasiticides and medicines X

production aids including netting, tree 

wraps and seals, insect traps, sticky 

barriers, row covers, and equipment 

cleansers

X

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