![[logo] US EPA](http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}
Soil Fumigant Assessments; Background Document
Quick Resources
Updated November 6, 2007
Soil fumigants play a very important role in agriculture, but they also have the potential to pose safety concerns to bystanders and to workers who may be exposed to them in the air following applications. EPA is assessing risks and will develop risk management decisions for five soil fumigant pesticides: chloropicrin, dazomet, metam sodium, methyl bromide, and a new active ingredient, iodomethane. Risks of a sixth soil fumigant, 1,3-Dichloropropene (1,3-D or Telone), will be discussed for comparative purposes; its risk management decision was completed in 1998. EPA's goal in evaluating the soil fumigants is to ensure safety and maintain their benefits to agriculture.
On this page:
- Soil Fumigant Uses
- Soil Fumigant Pesticides
- Soil Fumigant Hazards
- Assessing Soil Fumigant Exposure
- Preliminary Soil Fumigant Risk Assessments
- Public Participation Process and How to Get Involved
- California Soil Fumigant Assessment and Status
EPA is evaluating these soil fumigants concurrently to ensure that its risk assessment approaches are consistent. The Agency ultimately will make informed risk management decisions based on a level playing field, considering how mitigation for one fumigant may affect the risks and benefits of the others. This review is part of the Agency's program to ensure that all pesticides meet current health and safety standards.
Soil Fumigant Uses
Soil fumigants are pesticides which, when injected or incorporated into soil, form a gas which permeates the soil and kills soil-borne pests, such as insects, microorganisms, weeds, and nematodes. After the fumigant dissipates from the soil in a few days to a couple of weeks, planting can take place. Fumigants are used on a wide range of annual and perennial crops. The largest amounts of soil fumigants as a group are used in growing potatoes, tomatoes, tobacco, carrots, strawberries, and peppers. These six crops account for about 75 percent of the approximately 132 million pounds of soil fumigants used annually in the U.S.
Why fumigants are used Soil fumigation can provide a number of benefits to both consumers and growers.
- Consumers benefit from having many more fresh fruits and vegetables available the year around.
- Growers are able to control a wide range of economically important soil-borne pests, so crop yields and quality are increased.
- Labor costs are often reduced, since harvesting a weed-free crop increases the efficiency of workers.
- Growers can allow a shorter time between crops, avoiding the need to rotate crops or let fields lie fallow for several years to reduce levels of nematodes or pathogens.
- Soil fumigation is also required for some quarantine uses and pre-shipment treatments, such as the production of certified pest-free plant propagation material.
General use trends While use of other soil fumigants has remained steady during the past 10 years, use of methyl bromide has been declining as a result of the Montreal Protocol. This international agreement required that methyl bromide use in the US be phased out by January 1, 2005, except for exempted uses. Continued use is allowed for quarantine and pre-shipment, and for critical and emergency uses. In response, many growers have changed to other soil fumigants or pest control practices.
Alternatives The soil fumigants are to some extent alternatives for each other. In some situations, non-chemical alternative methods can be used, but the conditions that would allow their use and effectiveness are limited. For example, solarization can be used in areas with ample sunlight. This method involves covering the field with black tarps so that the soil temperature increases and the top layer of soil is sterilized. However, this method is sunlight-dependent, takes a long time, and generally does not sterilize soil to a great enough depth.
Considerable research is underway to identify and evaluate alternatives
to the soil fumigants, especially methyl bromide. For additional information,
see the Methyl Bromide Alternatives Outreach web site, http://www.mbao.org.
Additional information For additional information on soil fumigant uses, application methods and equipment, and alternatives, see:
- Overview of the Use of Soil Fumigants (PDF) (31 pp, 1.1 MB, About PDF)
Soil Fumigant Pesticides
Although EPA is assessing the soil fumigants concurrently, these pesticides are undergoing separate regulatory reviews which will result in individual risk management decisions. Reregistration Eligibility Decisions (REDs) will be completed in 2008.
Pesticide, Docket #, |
Status and Schedule |
Major Use Sites |
Unique Features |
|---|---|---|---|
Chloropicrin Chlor-O-Pic |
Undergoing reregistration: |
Tobacco |
* 18th most commonly used pesticide in the US * Used both alone as a soil fumigant and in fumigant formulations to act as a chemical warning agent |
|
Dichloropropene (1,-3-D)
InLine |
RED completed Sept. 1998: * Phase 3 comment period on human health risk assessment closed fall 2005 * Phase 5 comment period on risk mitigation options closed fall 2007 |
Potatoes |
* 8th most commonly used pesticide in the US * Included in fumigants review for comparative purposes, and to provide more complete picture of soil fumigant uses, risks, and benefits |
Dazomet Basamid |
Undergoing reregistration: |
Ornamentals |
* The only soil fumigant applied as a dry granule and incorporated into soil. (Others are applied as liquids, some under pressure.) * When tilled into moist soil, quickly breaks down to MITC and other degradates |
| Iodomethane | * EPA approved a time-limited one-year registration of iodomethane in October 2007 with highly protective restrictions governing its use. The Agency will reevaluate this registration in 2008, concurrent with developing decisions on the other soil fumigant pesticides. |
Tomatoes |
* New pesticide active ingredient * Methyl bromide alternative |
|
Metam Sodium1
Metam CLR |
Undergoing reregistration: * Phase 3 comment period on human health risk assessment closed fall 2005 * Phase 5 comment period on risk mitigation options closed fall 2007 * RED scheduled in 2008 |
Potatoes |
* The most widely used soil fumigant in the US * 3rd most commonly used pesticide in the US by weight (in 2001) * When applied, quickly breaks down to MITC and other degradates |
|
Metam Potassium1 K-Pam HL |
Same as above. |
Lettuce |
* When applied, quickly breaks down to MITC and other degradates |
|
Methyl Bromide Brom-O-Gas |
Undergoing reregistration:
* Phase 3 comment period on human health risk assessment closed fall 2005 * Phase 5 comment period on commodity uses closed spring 2006 * RED for commodity uses issued summer 2006 * Phase 5 comment period on risk mitigation options for soil fumigant uses closed fall 2007 * RED for soil fumigant uses scheduled in 2008 |
Tomatoes |
* 7th most commonly used pesticide in the US by weight (in 2001) * Also occurs naturally in the environment. Soil fumigation and automobile exhaust are largest non-natural sources * Has tolerances for residues on food, for post-harvest commodity fumigation * Under Montreal Protocol, use in US phased out as of January 1, 2005, except exempted uses including quarantine and preshipment, and critical and emergency uses |
1 Metam sodium and metam potassium are listed here separately because they are active ingredients in different products and have different use patterns, although they are part of the same reregistration case. EPA's human health risk assessments for these chemicals are combined in one document.
Soil Fumigant Hazards
Each of the soil fumigant pesticides is different, but all have the potential to move off site following field applications, resulting in exposure to bystanders near treated areas and to people far away from treated areas through ambient air. Use of the soil fumigants also results in exposure to those handling the pesticides or working in treated fields. Acute inhalation exposures to bystanders and workers appear to present the greatest risk concern.
Assessing Soil Fumigant Exposure
In assessing soil fumigant exposures and potential risks to bystanders and workers, EPA considered incident data, field monitoring studies, and two types of models.
- Incidents Documented incidents have occurred from the use
of fumigants. Symptoms that people exhibited as described in incident
reports often are consistent with toxicological symptoms described in
the risk assessments.
- Field Monitoring EPA assessed exposures and potential risks
using actual field concentration measurements taken at specific times
and locations around treated fields. Considerable uncertainty is associated
with this method because it represents a snapshot in time and location,
accounting only for the climate conditions and concentrations on a particular
day, at a particular time.
- EPA Office of Air's ISCST3 (Industrial Source Complex) Model
The ISCST3 air dispersion model is routinely used by the Agency's
Office of Air for regulatory purposes. A steady-state Gaussian plume
model, ISCST3 can be used to assess pollutant concentrations from a
wide variety of sources. ISCST3 provides useful results because it allows
estimation of air concentrations based on changing factors such as application
rates, field sizes, downwind distances, wind and weather conditions,
and other factors. Using this model for the soil fumigants allows EPA
to predict off-site movement given fixed meteorological and other conditions.
- Distributional Models: PERFUM, FEMS and SOFEA The most refined
methods developed at this time, distributional models show distributions
of potential bystander exposures and thus more fully characterize the
range of possible risks resulting to bystanders around treated fields.
Three recently developed distributional models, PERFUM, FEMS and SOFEA,
each represent a potential evolution of EPA's current methodology for
calculating bystander exposure to soil fumigants. To ensure that the
best science is used in the soil fumigant risk assessments, EPA conducted
FIFRA Scientific Advisory Panel (SAP) meetings in August and September
2004 to review these models. SAP evaluated the three models and found
them to be scientifically sound. For additional information see SAP's
web site, http://www.epa.gov/scipoly/sap/2004/index.htm.
PERFUM (Probabilistic Exposure and Risk model for FUMigants). PERFUM was developed by the registrants of iodomethane. EPA selected the PERFUM model over the other distributional models because PERFUM provides the most resolution for the acute duration of exposure, which is the key concern for these soil fumigants. PERFUM calculates distances from the field where airborne concentrations meet a threshold of concern around the perimeter of the field. The calculations are based on 5 years' worth of meteorological data. For additional information on PERFUM and to obtain an executable program, see http://www.epa.gov/opphed01/models/fumigant/.
FEMS (Fumigant Exposure Modeling System). FEMS was developed by the registrants of metam sodium. FEMS provides information on the broader distribution of potential air concentrations. EPA has placed a recently received FEMS model assessment developed by the Metam Sodium Alliance in the public docket for comparison and discussion purposes.
SOFEA (Soil Fumigant Exposure Assessment System). SOFEA was developed by the registrants of 1,3-D or Telone. SOFEA provides distributions of air concentrations for longer duration exposures.
Preliminary Soil Fumigant Risk Assessments
The purpose of the human health risk assessments is to provide and characterize a range of potential risks to bystanders at varying distances from treated fields, as well as to people farther away from treated fields. The risk assessments also provide and characterize potential risks to those applying soil fumigants and working in treated fields. With better characterization of the range of potential risks, EPA can make more fully informed risk management decisions.
Methyl bromide is the only one of the four soil fumigants that results in residues in food, from the post-harvest fumigation use. Dietary risks from residues in food and drinking water were only assessed for methyl bromide, and were not of concern; EPA reassessed methyl bromide tolerances in summer 2006. No residues of methyl bromide in food or drinking water result from application of methyl bromide as a soil fumigant.
Additional information For additional information about EPA's assessments and characterization of bystander and worker risks, see Regulations.gov Docket ID EPA-HQ-OPP-2005-0168, the Technical Briefing presentation on EPA's Human Health Risk Assessment by Health Effects Division (HED), OPP/EPA, and EPA's Overviews and Risk Assessments for each of the soil fumigants.
California Soil Fumigant Reviews
The State of California also is assessing soil fumigants and developing
risk management plans. For additional information, see the California
Department of Pesticide Regulation's Fumigant Resource Center, at http://www.cdpr.ca.gov/docs/dprdocs/methbrom/mb_main.htm.