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Paladin® in Florida - FAQ

Paladin® is an EPA registered soil fumigant with the active ingredient dimethyl disulfide (DMDS).  Paladin® was developed as an alternative to methyl bromide.   Methyl bromide, while odorless and effective, was phased out due to its ozone depletion potential.   The following information is provided to help answer questions about Paladin® and DMDS.

For more information about Paladin®, please contact arkema.usph-paladin@arkema.com.  Concerns about personal exposure incidents should be directed to the Paladin® Hotline at 1-800-286-4110.  We will update information on this page as necessary.

Questions related to Paladin® soil fumigant

1. What is Paladin®?

Paladin® is the registered trade name for the pre-plant soil fumigant products manufactured and formulated by Arkema.   The active ingredient in the Paladin® products is dimethyl disulfide (DMDS).  These products were brought to market to provide alternatives to methyl bromide (MeBr), which was banned by the Montreal Protocol International Treaty because of its ozone-depleting potential.    

The Paladin® products were first registered by the US EPA in 2010.   The approved applications include the control or suppression of weeds, soil-borne plant pathogens and nematodes in soils to be planted with vegetables (tomatoes, peppers, eggplants), cucurbit crops (cucumber, squash and melons), strawberries, blueberries, field-grown ornamentals, and forest nursery stock where plastic tarp is used for fumigation.   Products are available for drip and shank applications.

2. What is the toxicity?

EPA Registration of pesticides requires that extensive toxicological testing be performed to determine risks to workers, bystanders, and the environment.  The toxicity of a substance is dependent on the species tested, the exposure concentration, and the route of exposure such as consumption, inhalation, or dermal contact.   A summary of tests and results are available in the US EPA Pesticide Fact Sheet issued for DMDS July 9, 2010 (https://www3.epa.gov/pesticides/chem_search/reg_actions/pending/fs_PC-029088_09-Jul-10.pdf).   The results of these tests are used to establish the “levels of concern” for human exposure.   The EPA has set the level of concern for DMDS at 55 ppb based on the rat inhalation study where the No Adverse Effect Level (NOAEL) was determined to be 9000 ppb.  Given that the odor threshold for DMDS is 7 to 12 ppb (0.007 - 0.012 ppm), individuals near a treated field are likely to detect the odor of DMDS before it reaches a concentration at which it would begin to produce nasal irritation.

3. I could smell Paladin® near the strawberry fields – how concentrated was the Paladin® I was exposed to?

The concentration of exposure in air at a given moment and location continuously fluctuates with changes in temperature, humidity, and wind speed.   To better understand exposures outside the buffer zones, Arkema performed rigorous tests in Hillsborough County during the application season in August and September of 2014 to determine the concentration of Paladin® at the edges of the farm fields.  More than 500 readings were collected with concentration values between 0-1 ppb.   All recorded readings were below the US EPA 55 ppb level of concern.

4. I live near a strawberry farm and I have been experiencing long-term symptoms that do not go away.

Arkema is concerned about the wellbeing of the farming communities.  We, our distributors, and the certified applicators are required by law to strictly follow the application requirements on identified on the US EPA approved label.  In addition to the label requirements, part of our stewardship program includes on site assessment of application effectiveness and active air monitoring to confirm ambient concentrations. For example, during the 2014 growing season, air monitoring for the concentration of Paladin® at the edge of every field treated was conducted. The 500 air monitoring results of the 2014 season showed DMDS concentrations between 0-1 ppb.

The US EPA Pesticide Fact Sheet for Dimethyl Disulfide Issued June 2010 states:  “A literature review conducted by the registrant suggests that the mean odor threshold for DMDS is 7 to 12 ppb (0.007 - 0.012 ppm), which is approximately three orders of magnitude (1000x) below the concentration at which nasal irritation is observed in rodent inhalation studies. This suggests that individuals near a treated field are likely to detect the odor of DMDS before it reaches a concentration at which it would begin to produce nasal irritation.”  (https://www3.epa.gov/pesticides/chem_search/reg_actions/pending/fs_PC-029088_09-Jul-10.pdf )

It is important to determine  original cause of your illness and get the proper treatment.  If you are concerned about any long term symptoms you are experiencing, we suggest you visit a licensed physician.   The physician can obtain additional information by contacting the Paladin® Hotline at 1-800-286-4110.

5. Can the smell of Paladin® make me feel sick?

DMDS odor has been described as pungent garlic, propane, decaying fish, or decomposing materials.   In addition to the fumigated fields, investigations of odor complaints have resulted in findings of decomposing animals, swine farms, low tide wetlands, and other odor producing sources in proximity to the complaint.    The odor of DMDS is typically detected above 7 ppb.  As noted in the report titled “Hillsborough County Paladin Investigation, 2014” from the Florida Department of Health “Detecting an odor does not mean that harmful amounts of DMDS are being inhaled”.  

If you are experiencing symptoms of illness and are concerned, we encourage you to visit a licensed physician.   The physician can obtain additional information by contacting the Paladin® Hotline at 1-800-286-4110.  Arkema is actively working on application techniques and complementary tools to eliminate all off-site odor detection.

6. What are the pros and cons of Paladin®?

Paladin® was developed as a methyl bromide replacement.  Methyl bromide was banned by the Montreal Protocol due to its ozone depleting potential.  Paladin® helps local Florida farmers produce high quality food, at a cost that is competitive in the global market.  The low odor threshold of 7 ppb permits detection of the active ingredient DMDS below the EPA’s 55 ppb level of concern. Unfortunately, the down side is that the odor is considered unpleasant or offensive.

8. What about ground water contamination?

The US EPA has assessed the risk of ground water contamination from DMDS used as a pesticide, and based on environmental modeling, determined that, even in a worst-case assessment, the potential for ground water contamination is very low. The EPA estimates the maximum possible concentration of DMDS at 2 ppb or less. By comparison, garlic has 600 to 2000 ppb of DMDS, and fresh haddock (fish) has 1000 ppb.

References:

- Ejaz, S, Woong. LC, Ejaz, A, Extract of Garlic (Allium Sativum) in cancer chemoprevention, Experimental Oncology, 25 (2003) 93-97.

-Merritt, C, Qualitiative and Quantitative Aspects of Volatile Components in Irradiated Foods and Food Substances, Radiation Research Reviews, 3 (1972) 353-368.

http://nsrdec.natick.army.mil/LIBRARY/70-79/R72-75.pdf

- US EPA "Environmental Fate and Ecological Risk Assessment for the Proposed Registration of Dimethyl Disulfide (DMDS) for use on Tomatoes, Peppers, Eggplant, Cucumbers, Squash, Melons, Strawberries, Onions, Field Grown Ornamentals, and Forest Nursery Crops" pages 51-53.

9. Does DMDS accumulate in the environment?

DMDS does not persist or accumulate in the air, water, or soil. DMDS evaporates readily from soil and water. When released into the atmosphere, DMDS degrades rapidly with a half-life of about 1 hour. In surface water and in the presence of sunlight, the half-life of DMDS is 1.3 days. This data is consistent with the established behavior of biogenic sources of DMDS within the global sulfur cycle.

References:

- Definition of Half Life: http://en.wikipedia.org/wiki/Half-life

- Variability in Biogenic Sulfur Emissions from Florida Wetlands: http://pubs.acs.org/doi/abs/10.1021/bk-1989-0393.ch003

10. Does DMDS accumulate in people and pets?

DMDS does not bio-accumulate in organisms. DMDS is a product of mammalian metabolism and there are normal biochemical pathways, such as respiration, to eliminate it from the body.  DMDS is present in many foods including, but not limited to, broccoli, cheese, onions, and garlic.    Furthermore, food grade Dimethyl Disulfide (DMDS) is authorized for use as a food flavoring agent by the US Food and Drug Administration (FDA) and FAO/WHO Joint Expert Committee on Food Additives (JECFA) and by the European Food Safety Authority (EFSA).

References:

-21 CFR 172.515 Synthetic flavoring substances and adjuvants: http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?FR=172.515

-EFSA Journal (2010), Flavouring Group Evaluation 8, Revision 2, 8(11), 1408.

-TRS-896 JECFA 53/32, 2003

11. Why on the label does it say that a field with a buffer zone greater than 300 feet is not permitted within a 1/4 mile of a "Difficult to Evacuate Site" but the product can be used within 25 feet of my house?

Why on the label does it say that a field with a buffer zone greater than 300 feet is not permitted within a 1/4 mile of a "Difficult to Evacuate Site" (eg. state licensed daycare centers, nursing homes, assisted living facility, hospitals, in-patient clinics and prisons), but the product can be used within 25 feet of my house?

The EPA requires this language on the labels of all fumigants that have been registered, or re-registered in the past 5 years. A "Difficult to Evacuate" facility requires a larger buffer zone, because if there ever were an emergency situation that required action by a local first responder, a "Difficult to Evacuate" facility would have special provisions. This larger buffer zone was defined to address emergency issues, not normal product use concerns.  In fact, because bedded row application Paladin® requires at most a 250 foot buffer zone, the label always permits Paladin in bedded rows to be used with 1/8 of a mile restriction from a "Difficult to Evacuate Site".   All (100%) of Paladin® fields were inspected in 2014 and were in conformance with buffer zone requirements.

12. How was dimethyl disulfide developed?

Farmers who grew garlic, and then plowed the crop remains into their field noticed a distinct improvement in their next crop yield.  Research into the compounds that were released by garlic led to the discovery that one of these compounds, dimethyl disulfide (DMDS), was particularly effective at controlling plant parasitic nematodes.  This is what led to the development of DMDS as a new soil fumigant.

Dimethyl disulfide is found in crops of the Allium (garlic and onion) and Brassica (broccoli, radishes, kale, mustard, etc.) families.  It is also formed in some foods during the process of fermentation (cheese, wine, beer) and cooking (salmon, coffee).  It is present in milk as well.  Dimethyl disulfide is authorized for use as a (US FDA, Europe’s EFSA) food additive to impart a garlic odor and taste to foods.  While it is a food additive, the average person consumes far more dimethyl disulfide from natural food sources than from food additives.  People also produce dimethyl disulfide as a metabolism product.

13. Does residue from soil treatment work its way into the crops planted in that soil?

Pesticide residue studies were performed for food crops included on the product label.  No DMDS was observed over the limit of quantification (LOQ) for the approved crops.  A distinction between natural background levels of DMDS and crop levels from fumigated DMDS cannot be determined in crop residue studies.  Therefore, crop foods containing natural background levels of DMDS are excluded from Paladin® applications.  Such crops include onions garlic, radishes, cabbage, broccoli to name a few.

14. What is the purpose of the buffer zones?

Buffer zones are established by the US EPA to protect bystanders (people who are not actively working in the treated field but who live, work, or for other reasons are nearby, the treated field) from adverse health effects resulting from exposure to soil fumigants.

15. If 55 ppb is the level of concern for healthy people, what is the level of concern for other categories of people (such as those with compromised immune systems)?

The EPA has established a level of concern for dimethyl disulfide of 55 parts per billion (ppb) based on the potential for health effects to the entire bystander population, not just specific groups based on a NOAEL (no observed adverse effects level) of 9,000 ppb and a LOAEL (low observed adverse effects level) of 12,500 ppb in rats.  The observed adverse effect at 12,500 ppb is nasal irritation.  The EPA also established 55 ppb as the level of concern for farm workers involved in soil fumigation. 

16. If farm workers need to wear protective respirators when they can smell garlic, why are you saying it is not necessary for nearby residents to wear respirators if they can smell garlic?

Dimethyl disulfide has a low odor threshold; it can be detected at very low concentrations of between 7-12 ppb; even lower for some people.  Given that odor is detected well below the level where there is a potential for health effects, odor detection is a protective warning signal.  Farm workers involved in fumigation do not have the protection provided by the EPA’s buffer zones.   When odor is initially detected, workers are advised to wear respirators until monitoring is performed to verify the air concentration in the work zone is below the established level of concern of 55 ppb. With air monitoring, it is feasible that workers will not require respirators when odors are present.

17. If I can smell garlic, does that mean I am exposed to a high level of DMDS?

Because the odor of dimethyl disulfide can be sensed well below the EPA level of concern (LOC), odor detection is an acceptable warning signal.  Odor detection, however, does not mean exposure to levels exceeding the LOC of dimethyl disulfide.  The primary protective measure for those off-field is the EPA established buffer zones.  Since buffer zones are designed for protection from health effects, not odor perception, the fact that the odor of dimethyl disulfide can sometimes be detected outside the buffer zones is not surprising.

18. If nearby residents can smell garlic, does that mean there is a leak or tear in the Totally Impermeable Film covering the soil beds?

When dimethyl disulfide is applied, it is injected at least 8” deep into the soil and then the soil bed is covered with a plastic tarp.  The tarps used for Paladin® are a special construction call Totally Impermeable Film (TIF), which contain a barrier layer which holds dimethyl disulfide in the soil.  The use of the special tarp provides two benefits: first, it reduces the amount of dimethyl disulfide released into the atmosphere; second, it allows the farmer to obtain the same level of crop protection while using less dimethyl disulfide.  Both of these factors reduce emissions.

While the TIF effectively limits dimethyl disulfide release through the plastic tarp, some amount of dimethyl disulfide does diffuse through the soil around the tarps and can escape between the rows.  This is a small fraction.  Most of the dimethyl disulfide decomposes in the soil.

Because some dimethyl disulfide is released by diffusion through the soil, odor detection in the days immediately following an application is not necessarily a signal that a tarp is torn or leaking.  Applicators work to ensure that tarps are not damaged during or after a fumigant application and to ensure the application delivers the performance that is expected.

19. How do I know that the level of DMDS I smelled was below the acceptable 55 ppb threshold?

During the 2014 fumigation season in Hillsborough County Florida, Arkema personnel monitored volatile organic compound (VOC) concentrations around farm fields treated with Paladin®.  During this monitoring, 682 measurements were taken around 19 treated fields starting 7-August and ending 10-September.  Zero calibration was performed using ambient air away from fumigation sites or roads and then the air was monitored to measure all VOCs.  Ambient VOCs could include things like DMDS, 1,3-Dichloropropene, diesel or gas fumes.  While other compounds might have been present, all VOCs detected were assumed to be DMDS.  99% of all measurements were <15 ppb.  The average measurement was 0.4 ppb.  The Environmental Protection Commission (EPC) of Hillsborough County also sampled sites in the Plant City/Dover area during the 2014 fumigation season, primarily in response to odor complaints.  None of the EPC’s measurements detected dimethyl disulfide. (The EPC is able to detect DMDS at levels of 3 ppb and above.)

21. What is half life?

"Half-life" is the amount of time it takes for 50% of something to be eliminated.  Consider if you have 100 pounds of something, with a half life of 1 hour:

At time 0, you would have 100 pounds

After 1 hour, you would have 50 pounds

After 2 hours, you would have 25 pounds

After 3 hours, you would have 12.5 pounds

After 4 hours, you would have 6.25 pounds, etc.

22. The Safety Data Sheet for DMDS says measures to prevent significant cutaneous (skin) absorption may be required in addition to air sampling. What measures should neighbors be taking to avoid cutaneous absorption?

The "cutaneous" information referenced on the Safety Data Sheet is intended for those whose skin may come directly in contact with full strength undiluted (liquid) product. Unless you are applying the product or trespassing inside the buffer zone, neighbors are not at risk of being exposed cutaneously to Paladin®.  

23. Is Paladin® soil fumigant, based on DMDS (dimethyl disulfide) related to Malathion?

There is absolutely no connection.  DMDS (dimethyl disulfide), the active ingredient in Paladin® soil fumigant, is a di-sulfide with the molecular formula C2 H6 S2.  Malathion is an organophosphate with the molecular formula C10 H19 O6 PS2.  These are completely separate molecules, and completely separate products.  There has never been any Malathion in Paladin® soil fumigant.  Malathion is not DMDS.  Paladin® soil fumigant is not Malathion.

Florida Department of Agriculture & Consumer Services

The following questions are transcribed from the Florida Department of Agriculture & Consumer Services document “Frequently Asked Questions about Dimethyl Disulfide”, revised April 7, 2014:

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