National Organic Standards Board

Crops Subcommittee

Petitioned Material Proposal

Carbon Dioxide

February 6, 2023

Summary of Petition: 

Carbon dioxide (CO2) was petitioned in 2020 to be added on the National List of Allowed and Prohibited 

Substances, for use as a plant or soil amendment at §205.601(j). The same petition requested the addition of

carbon dioxide at §205.601(a) of the National List for use as an algicide, disinfectant, and sanitizer, including

uses in irrigation systems, to acidify irrigation water. (The petition heavily focused on the use as an algicide, 

disinfectant and sanitizer in irrigation systems, and did not provide enough information about the material as a 

plant or soil amendment. Under “the intended use or current use of the substance” the petitioner stated “Carbon 

dioxide is used in a water pH adjustment process. Dissolved carbon dioxide in water makes carbonic acid, which 

reduces water pH, therefore increasing H+ concentration and neutralizing bicarbonates. Water pH adjustment is 

common practice in agriculture. Irrigation water sources are usually alkaline and with bicarbonates above the 

maximum desired levels for proper irrigation water quality.”

In 2022, the NOSB recommended the National Organic Program add carbon dioxide at §205.601(a) but 

requested a full-scope technical report (TR) to address the sections of the petition requesting the addition 

of carbon dioxide at §205.601(j), as a plant or soil amendment, before making a second recommendation). 

The 2023 Technical Report outlined the specific use of the petitioned material as an atmospheric adjustment in 

indoor production. In the report, we find that ambient air contains 350-450 ppm CO2, while the optimal 

concentration of CO2 for plant growth in a greenhouse environment is 800-1000 ppm (Poudel & Dunn, 2017; 

Thomson et al., 2022; Wang et al., 2022). As plants grow, they metabolize CO2 in the air of the greenhouse, 

depleting it to 100-250 ppm during peak CO2 consumption. Venting the greenhouses to allow more atmospheric 

CO2 in disrupts the controlled temperature. Ventilation alone cannot maintain constant CO2 concentrations 

within the greenhouse at a level comparable to that outside the greenhouse. Natural turnover of air by venting 

may help to moderate CO2 levels during warm months, but venting is usually not practical during colder periods or 

in colder regions, and supplementation is needed. 

Subcommittee Review: 

Because there was a lack of information in the petition about the importance or need for the substance to be 

listed as a crop or soil amendment, the Subcommittee has been hesitant to recommend its listing. The TR only 

listed its use as a plant or soil amendment in indoor production. The Subcommittee recognizes that this petition 

highlights the lack of clear standards pertaining to indoor and container production, and prevents the NOSB from 

fully evaluating petitions for substances used in this type of production. 

One member stated experience with the substance and its noticeable increase in production potential, while 

another questioned its necessity ;i.e., Is this material truly necessary to organic production or is it used as a 

booster like synthetic fertilizers or substance of high solubility . The Crops Subcommittee contacted organic 

greenhouse producers and found that CO2 was not needed nor supported for use. These producers were in the 

Southeast where average temperatures are warmer, and venting is less limited compared to colder climates. The 

Crops Subcommittee requested a greater explanation of the greenhouse gas effects of this material in its 

manufacture and use and how it ties to climate change.

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Category 1: Classification 

1. For CROP use: Is the substance ______ Non-synthetic or ___X___ Synthetic?

 Is the substance formulated or manufactured by a process that chemically changes a substance 

extracted from naturally occurring plant, animal, or mineral sources? [OFPA §6502(21)] If so, 

describe, using NOP 5033-1 as a guide. 

Carbon dioxide is the byproduct of many chemical and biological processes with fuel combustion and 

fermentation being the most prominent. The combustion of natural gas results in CO2 and water vapor

and CO2 may be produced as a by-product of carbohydrate fermentation by yeast in the production of 

ethanol or alcoholic beverages (TR, 2023). 

2. Reference to appropriate OFPA category: 

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; toxins derived from 

bacteria; pheromones, soaps, horticultural oils, fish emulsions, treated seed, vitamins and minerals; 

livestock parasiticides and medicines and production aids including netting, tree wraps and seals, 

insect traps, sticky barriers, row covers, and equipment cleansers; or (ii) is used in production and 

contains synthetic inert ingredients that are not classified by the Administrator of the 

Environmental Protection Agency as inerts of toxicological concern?

CO2 does not contain an active ingredient in any of the categories listed above. However, it is listed on 2004 

EPA List 4A and was not revoked under NOP 5008, Guidance: Reassessed Inert Ingredients. As an 

insecticide, “carbon dioxide is exempted from the requirement of a tolerance when used after harvest in 

modified atmospheresfor stored insect control on food commodities” per 40 CFR 180.1049 (TR, 2023).

Category 2: Adverse Impacts 

1. What is the potential for the substance to have detrimental chemical interactions with other 

materials used in organic farming systems? [§6518(m)(1)]

At normal temperatures, CO2 does not break down into simpler compounds, and it is not very

reactive. While unlikely to be an issue in organic crop production, CO2 can react with hydrogen 

gas to form carbon monoxide (CO). It can also react with ammonia to form ammonium 

carbamate, which when dehydrated then forms urea (TR, 2023). 

2. What is the toxicity and mode of action of the substance and of its breakdown products or any 

contaminants, and their persistence and areas of concentration in the environment? [§6518(m)(2)]

According to the TR, higher concentrations of CO2 can benefit plants, but soil composition, nutrient 

availability, plant species, and plant genetics all influence the response. The technical review 

referenced a study finding that plants in growth chambers showed symptoms of toxicity when 

subjected to 2000 ppm CO2. It can also be toxic to microorganisms, and animals at significantly elevated 

levels. No information that specifically indicated that carbonate (CO3

2-) or bicarbonate (HCO3-) ions, 

formed from the dissolution of CO2 in water, are toxic to plants. 

3. Describe the probability of environmental contamination during manufacture, use, misuse or 

disposal of such substance? [§6518(m)(3)]

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CO2 used in agriculture will largely be derived from fossil fuels, previously stored in the lithosphere, and 

will re-enter the carbon cycle temporarily persisting or concentrating in one of the three other major 

reservoirs: the terrestrial biosphere, the hydrosphere (oceanic reservoir), or atmosphere. Gaseous CO2

is relatively stable in the atmosphere. 

CO2 plays an essential role in soil pH and aquatic environments because of the carbonic-acid system. In 

contact with water, a proportion of CO2 dissolves until equilibrium is reached between CO2, bicarbonate 

(HCO3-), carbonate (CO3

2-), and carbonic acid (H2CO3). A greater proportion of CO2 shifts the equilibrium 

to the formation of carbonic acid resulting in lower pH (TR, 2023).

In the atmosphere, CO2 absorbs longwave radiation coming from the earth’s surface, causing 

warming known as “the greenhouse effect.” Greenhouses usually have a CO2-use efficiency of 

less than 60%, meaning that over 40% of the CO2 that is added is released into the atmosphere 

without being ever incorporated into plant biomass. 

4. Discuss the effect of the substance on human health. [§6517(c)(1)(A)(i); §6517(c)(2)(A)(i); 

§6518(m)(4)]. 

According to the TR, CO2 can be defined as a toxicant since it induces unconsciousness, respiratory 

failure, inflammation, and sensory impairment. Instances of CO2 poisoning are exceedingly rare events. 

The concentrations found in nature, in typical industrial settings, or used in greenhouses, are far lower 

than any of the concern levels listed above and are not a threat to human health. Adverse effects 

generally begin following exposure to 1% or greater CO2, while background atmospheric levels are 

approximately 0.04% and enriched greenhouse atmospheres are approximately 0.1%. Confined areas 

like mines, silos, or fermentation chambers, for example, may be environments where CO2

concentrations can surpass 1%, sometimes significantly. The current OSHA Permissible Exposure Limit 

(PEL) for 8-hour exposure to gaseous CO2 is 5,000 ppm, or 0.5%. 

5. Discuss any effects the substance may have on biological and chemical interactions in the 

agroecosystem, including the physiological effects of the substance on soil organisms (including the 

salt index and solubility of the soil), crops and livestock. [§6518(m)(5)] 

Lowering the pH to 6.0-6.8 can improve the bioavailability of some nutrients, such as iron, zinc, boron, 

and manganese. Cation availability can also increase due to increased weathering of parent material 

and minerals, therefore affecting soil chemistry. In wet environments or where large amounts of 

irrigation are used, these effects can leach these available cations (TR, 2023).

At low concentrations (up to about 1200 ppm), CO2 is generally safe and has low toxicity, and can have 

substantial beneficial effects to plants. However, at moderate concentrations (1200 ppm to several 

percent, depending on duration and tolerance of a given species, CO2 can cause toxic effects in plants 

and animals. At high levels (>~50%), it can be toxic to microorganisms as well. 

Decreasing water pH can increase the toxicity of copper for Arenicola marina, an aquatic segmented 

worm. 

6. Are there any adverse impacts on biodiversity? (§205.200) 

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Applying CO2 at higher than optimum levels could cause toxicity to a wide variety of organisms. This 

situation is unlikely, however, because it would also begin to exert negative growth effects on crops, thus 

defeating the purpose of its use.

Category 3: Alternatives/Compatibility

1. Are there alternatives to using the substance? Evaluate alternative practices as well as nonsynthetic and synthetic available materials. [§6518(m)(6)]

There is no substitute for gaseous CO2 in plant biology. It is an essential component of the 

photosynthesis process. 

It is possible to produce CO2 nonsynthetically using fermentation processes or extraction

from natural CO2 wells but the prevalence and availability of different CO2 production streams is difficult 

to define, is determined by regional industry and transport infrastructure, and by the nature of the 

commodified raw chemical material market because many streams may be combined. Previous written 

comments have indicated that inadequate infrastructure and costly transport restricts the source of

nonsynthetic carbon dioxide. The commentor also stated fermentation businesses were often using the 

CO2for carbonating fermented beverages. 

2. In balancing the responses to the criteria above, is the substance compatible with a system of

sustainable agriculture? [§6518(m)(7)]

CO2 can be used for agriculture without adding harm to the environment. Because it is a byproduct of

multiple manufacturing processes, the “production” of CO2 is occurring regardless of its use in organic

agriculture. If it weren’t used, it would be released into the atmosphere. Although its use does not reduce

emissions because the CO2 is only temporarily stored in the plant and then re-enters the carbon cycle, the

Crops subcommittee did have questions regarding the greater explanation of the overall greenhouse gas

effects of this material in its manufacturing and use, especially how it ties into climate change for this

particular petitioned usage. The Crops Subcommittee is not recommending adding Carbon Dioxide to the

National List due to it not being necessary for organic crop production."

Stakeholders Question:

How should NOSB evaluate necessity and compatibility with sustainable production for CO2without clear 

production standards for greenhouse and indoor production?

Classification Motion: 

Motion to classify carbon dioxide as synthetic. 

Motion by: Logan Petrey

Seconded by: Nate Lewis 

Yes: 6 No: 0 Abstain: 1 Recuse: 0 Absent: 2

National List Motion: 

Motion to add carbon dioxide at §205.601(j). 

Motion by: Logan Petrey

Seconded by: Nate Lewis 

Yes: 0 No: 6 Abstain: 1 Recuse: 0 Absent: 2

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