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Organic Arsenicals

MSMA Registration Review
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Current as of April 2013

The organic arsenical pesticides consist of monosodium methanearsonate (MSMA), disodium methanearsonate (DSMA), calcium acid methanearsonate (CAMA), and cacodylic acid and its sodium salt. They are used or have been used as herbicides on cotton and other agricultural crops, in forestry, on residential and other lawns and turf, and in non-crop areas such as rights of way, drainage ditch banks, fence rows, and storage yards.

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Voluntary Cancellations and Amendments

EPA’s order, Organic Arsenicals; Product Cancellation Order and Amendments to Terminate Uses – FR Notice, September 30, 2009 terminates the last products containing DSMA, CAMA, and cacodylic acid and its sodium salt registered for use in the U.S. It terminates certain MSMA product registrations and amends others to phase out all uses except cotton. All uses of DSMA, CAMA, and cacodylic acid and its sodium salt, and all uses of MSMA except cotton, sod farms, golf courses, and highway rights-of-way, were canceled as of September 30, 2009. Use of MSMA on sod farms, golf courses, and highway rights-of-way was to have been prohibited after December 31, 2013. Because EPA has modified the 2009 Agreement in Principle with registrants to include a National Academy of Sciences review, presently these uses remain registered. See Organic Arsenicals; Amendments to Terminate Uses; Amendment to Existing Stocks Provisions – FR Notice, March 27, 2013.

The sod farm, golf course, and highway rights-of-way uses, in addition to the cotton use, will be considered during the registration review of MSMA that began in March 2013. For further details on these uses and related mitigation measures see MSMA Cotton Use is Eligible for Reregistration with Mitigation and All Other Uses will be Phased Out and Canceled.

Agreement in Principle

In January and February 2009, EPA reached agreement with the technical registrants of all existing organic arsenicals manufacturing-use products to eliminate, phase out, and modify certain uses.

The voluntary agreements steadily remove all organic arsenical pesticide product uses, except the use of MSMA on cotton, from the market and implement new restrictions to better protect drinking water resources. Phasing out these uses is expected to accelerate the transition to new, lower risk herbicides.

Under the agreements, many uses, including use on residential lawns, were canceled by the end of 2009, and mitigation measures to protect water resources are being implemented through revised product labeling.

For products used on cotton and products phased out after 2009, new use restrictions and mitigation measures have been added to increase protections to water resources.

The agreements also provided for scientific review of any new toxicity or benefits data prior to the final cancellation of major uses, if the data were provided by the date set forth in the agreements.

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Changes since the 2006 RED

In the Agency’s 2006 Reregistration Eligibility Decision (RED) for MSMA, DSMA, CAMA, and cacodylic acid and its sodium salt, EPA concluded that all uses of the organic arsenical herbicides were ineligible for reregistration. Following application, these pesticides convert over time to a more toxic form in soil, inorganic arsenic, and potentially contaminate drinking water through soil runoff.

Since MSMA is used on cotton, EPA also believed at that time that residues of inorganic arsenic could enter the human food supply through the meat and milk of animals fed cotton by-products (seeds, hulls, and gin by-products) that have been treated with MSMA. In completing the RED, EPA found that the aggregate dietary risks from exposure to inorganic arsenic in food and drinking water combined did not meet the reasonable certainty of no harm standard under the Federal Food, Drug, and Cosmetic Act (FFDCA).

In 2007 and 2008, stakeholders submitted to the Agency additional data on organic arsenicals that previously were not available. These data indicate that no residues of inorganic arsenic are likely to remain in the meat and milk of animals fed cotton by-products that have been grown in fields treated with MSMA, or in food crops that are rotated with cotton that has been treated with MSMA.

Cotton growers also have documented the increasing spread of Palmer amaranth or pigweed, a glyphosate-resistant weed that can significantly reduce cotton yields and could have a negative effect on conservation tillage efforts. Currently, no alternative herbicides to MSMA are registered on cotton to control this pest.

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MSMA Cotton Use is Eligible for Reregistration with Mitigation

In light of the new information, the agreements allow for the reregistration of MSMA use on cotton only, contingent on the development and acceptance of confirmatory data demonstrating that no residues of inorganic arsenic are likely to remain in the meat and milk of animals fed cotton by-products. These data were provided and are under review.

EPA also rescheduled the MSMA registration review to begin in March 2013. During this ongoing review, the risks and benefits of MSMA will be reevaluated considering any new toxicity information as well as the availability of new, lower-risk herbicides that should be entering the market.

The agreements require certain mitigation measures for MSMA use on cotton to protect water resources. Pre-plant cotton use has been deleted. The cotton use is limited to two post-emergent applications per year of two pounds active ingredient per acre each. Cotton growers also must maintain a 50-foot buffer zone around permanent water bodies.

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All Other Uses will be Phased Out and Canceled

All use of the organic arsenical herbicides, except MSMA use on cotton, will be canceled in two phases. In addition to products used on cotton, MSMA products with uses phasing out over several years will include new restrictions, summarized below, to protect water resources.
Phase 1 – Many existing uses were canceled as of September 30, 2009. These uses include among others: residential turf, forestry, non-bearing fruit and nuts, citrus (bearing and non-bearing), various grasses, and drainage ditch banks, certain rights-of-way, fence rows, storage yards and similar non-crop areas.
Phase 2 – MSMA use on golf courses, sod farms, and highway rights-of-way was to be canceled as of December 31, 2012, with use of existing stocks permitted through 2013. If any person submitted benefits information concerning these uses to EPA on or before December 31, 2011, EPA would review such information, along with peer review recommendations (see below), and could amend its position on the continued registration of these uses. EPA received and is considering benefits information regarding these three MSMA uses.

As discussed further below, peer review recommendations from the National Academy of Sciences (NAS) would inform EPA’s final decision regarding the use of MSMA on golf courses, sod farms, and highway rights-of-way. Because EPA did not provide a written determination by December 31, 2012, these three uses were not deleted at that time and will be extended until the Agency provides the required written determination.

The following new use restrictions currently apply.

For golf courses: For sod farms: For highway rights-of-way:

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Scientific Peer Review

The agreement also provides for scientific peer review related to the mode of action for cancer effects for inorganic arsenic prior to the final cancellation of MSMA use on golf courses, sod farms and highway rights-of-way. OPP was to seek concurrence from other EPA offices engaged in the regulation of inorganic arsenic to convene a joint review by the EPA Science Advisory Board (SAB) and the FIFRA Science Advisory Panel (SAP) in the first half of 2012.

In light of a Congressional directive to have the National Academy of Sciences (NAS) review the mode of action for carcinogenic effects by inorganic arsenic, EPA and the registrants have agreed to modify the agreement to include the NAS as a third potential peer review body, one of which must hold a public meeting on the mode of action before the cancellations can be finalized. EPA currently intends to undertake the peer review specified in the agreement by relying upon the NAS review. See EPA’s March 27, 2013, FR Notice. The Agency plans to consider recommendations of the NAS peer review and make a written determination as to whether the science has changed sufficiently to warrant continuation of any of the Phase 2 uses. Additional information on the NAS review of inorganic arsenic is available at: http://www8.nationalacademies.org/cp/projectview.aspx?key=49483

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How Organic Arsenical Herbicides Are Used

MSMA, DSMA, and CAMA are herbicides that are used or have been used for applications to cotton, bearing and non-bearing fruit and nut trees, commercial turf, golf courses, athletic fields, parks, and residential lawns, among other sites. MSMA, DSMA, and CAMA are selective, post-emergent herbicides that kill weeds without damaging grass and can be applied after weeds are visible.

Common trade names for MSMA, DSMA, or CAMA include Scotts Post Emergent Crabgrass Control, Gordon’s Crabgrass and Nutgrass Killer, and Ferti-Lome Crabgrass and Dallis Grass Killer.

Cacodylic acid is a defoliant used to edge and renovate lawns. Unlike MSMA, DSMA, and CAMA, cacodylic acid is non-selective, meaning that it kills weeds and surrounding grass. Common trade names for cacodylic acid include Scotts Spot Grass & Weed Control, Liquid Edger, and Liquid Fence & Grass Edger.

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Exposure through Drinking Water

For the cotton use and all uses being phased out, EPA is immediately requiring new restrictions that are designed to prevent exposure to inorganic arsenic in drinking water. These include limiting use in areas of particularly vulnerable ground water, implementing buffer zones around surface water bodies, limiting the number of applications, and restricting golf course use to spot treatment only.

For residential areas, it is important to follow label instructions and minimize runoff (e.g., do not apply to sidewalks and other impermeable surfaces; do not apply near storm drains or water bodies).

Exposure from Treated Residential Lawns

Short-term use of organic arsenical products used according to label directions does not present an imminent risk. The Agency’s primary concern is for these products to transform over time to the more toxic inorganic form of arsenic in soil and subsequently be transported to sources of drinking water. This issue is being addressed through new label restrictions. Because this transformation occurs beneath the soil surface, long-term residential exposure to inorganic arsenic in soil is unlikely. To further minimize potential exposure on lawns, keep children and pets off treated areas.

Safe Use and Disposal of Homeowner Products

It remains legal to purchase and use organic arsenical herbicides according to label directions and precautions. Use of these products according to label directions does not pose an imminent hazard. EPA has initiated action to address the potential for these chemicals to transform over time and contaminate sources of drinking water. Consumers who choose to use these products should take special care to always read and follow the label precautions and directions.

If you choose to discontinue use, contact your state or local hazardous waste disposal programs or your local solid waste collection service for information on proper disposal. See also Safe Disposal of Pesticides.

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Alternatives to Organic Arsenicals for Homeowner Use

The primary manner in which grass weeds such as crabgrass and dallisgrass can be effectively controlled is through the maintenance of a high quality turf. This includes developing healthy soil, using types of grass that thrive in your climate, and correcting thatch build-up. See additional information about Lawn and Garden pest control using integrated pest management and other environmentally friendly practices.

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