This is a proposal by a Subcommittee of the National Organic Standards Board (NOSB). Proposals are posted for public 

comment and then may be voted upon by the full Board. They are not final Board recommendations or NOP policy. 

Revised June 20 2013

National Organic Standards Board

Crops Subcommittee

Petitioned Material Proposal

Magnesium Oxide

August 6, 2013

*Revised February 26, 2014 - Minority opinion added

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 
This is a proposal by a Subcommittee of the National Organic Standards Board (NOSB). Proposals are posted for public 

comment and then may be voted upon by the full Board. They are not final Board recommendations or NOP policy. 

Revised June 20 2013

Subcommittee Action & Vote:

Classification Motion: 

Motion 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

Listing Motion: 

Motion to list Magnesium Oxide at §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

Minority position: During Subcommittee discussions in January and February 2014, a member

of the Crops Subcommittee made a motion for the following: To list Magnesium Oxide at

§205.601 with the following annotation: Until May 1, 2019 [or 5 years after the date it is first 

allowed]. The motion did not pass. The justification for the minority opinion is as follows: A 

synthetic material used in organic production, even if used in small quantities, must meet all of 

the OFPA criteria. Current consideration of the material has raised issues relating to 

environmental impacts and alternatives. (1) The review in 5 years must be performed with the 

same standard for allowing continued use as is used to approve use in the first place; (2) the 

need for liquid humates and hence MgO should be re-evaluated; (3) the possibility of using 

nonsynthetic acids in place of synthetic sulfuric acid must be re-evaluated.

Approved by Zea Sonnabend, Subcommittee Chair, to transmit to NOSB February 26, 

2014
This is a proposal by a Subcommittee of the National Organic Standards Board (NOSB). Proposals are posted for public 

comment and then may be voted upon by the full Board. They are not final Board recommendations or NOP policy. 

Revised June 20 2013

NOSB Evaluation Criteria for Substances Added To the National List: Crops

Category 1. Adverse impacts on humans or the environment? 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

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
This is a proposal by a Subcommittee of the National Organic Standards Board (NOSB). Proposals are posted for public 

comment and then may be voted upon by the full Board. They are not final Board recommendations or NOP policy. 

Revised June 20 2013

NOSB Evaluation Criteria for Substances Added To the National List: Crops 

Category 2. Is the Substance Essential for Organic Production? 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).

Category 3. Is the substance compatible with organic production practices? Magnesium Oxide

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
This is a proposal by a Subcommittee of the National Organic Standards Board (NOSB). Proposals are posted for public 

comment and then may be voted upon by the full Board. They are not final Board recommendations or NOP policy. 

Revised June 20 2013

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