[Product Update] The Return of DDVP

If your product sales representative were to tell you he had a new product for you to consider that incorporates DDVP as its active ingredient, what would be your first reaction?

… No way, that’s a banned chemical!

… Sure, tell me about it, I’m glad to see we have some options again.

… Huh? I’ve never used that before.

DDVP, or dichlorvos, has been under special review with the Environmental Protection Agency (EPA) for the last 20 years, and in that time, has often come close to being banned. The EPA review was based primarily on concerns for cancer, cholinesterase inhibition and liver effects in humans and animals. Although some uses have been retained, such as fogging of food warehouses and resin strips, the chemical fell into such disfavor that some believed it to have been taken completely off the market. Various misconceptions ran rampant about the chemical, and many younger technicians have never had dichlorvos products as an option at all.

In fact, as consultant Harry Katz told PCT magazine, the newest editions of the Mallis Handbook of Pest Control and NPMA Field Guide to Structural Pests do not even mention dichlorvos. Rather, you have to go back to the 7th edition of Mallis (1990) to find a reference, and even this provides only a few paragraphs on the chemical and its uses.

So what is DDVP and why all the fuss? DDVP is a very volatile organophosphate, evaporating quickly but with acute toxicity and quick knockdown. Acting as a cholinesterase inhibitor on insects that it contacts, DDVP affects the nervous system of the target pest, blocking the enzyme required for proper nerve functioning. These very same characteristics are also what make DDVP such an effective pesticide — and the object of so much controversy.

DDVP: A LOOK BACK. “The product has had an interesting history,” said Richard Kramer, president of Innovative Pest Management, Brookeville, Md.

In brief: In 1995 EPA determined that exposure to DDVP from registered uses posed a carcinogenic risk of concern as well as risks of concern for cholinesterase inhibition. Since then, however,

• EPA determined the liver effects endpoint was no longer of regulatory concern.
• With the availability of additional data, EPA changed its assessment of some DDVP-associated risks and modified the terms and conditions of DDVP registrations accordingly.
• During the recent reregistration process, EPA conducted an intensive, public review of DDVP registrations conforming to Federal Insecticide, Fungicide and Rodenticide Act  (FIFRA) standards and resolved remaining concerns of cancer and cholinesterase effects.

Accordingly, EPA has revised its assessment of DDVP. Based on the Reregistration Eligibility Decision (RED), requested label amendments and voluntary cancellation of certain uses by the registrant, EPA has determined that the risks that were the basis of the Special Review are no longer of concern.

Thus, on Dec. 21, 2007, following notice of and a comment period for termination of the review, EPA issued its final determination to terminate special review of DDVP. According to the decision, “The Agency received no substantive comments in response to the proposal (for review) and EPA is announcing its final determination to terminate the Special Review of DDVP.”

“I’m surprised it has actually survived,” Kramer said. “Most of the organophosphates are gone for residual applications.”

RE-ISSUANCE OF DDVP. With the ruling, AMVAC Chemical Corporation, DDVP’s manufacturer, is beginning issuance of new DDVP products, with the reintroduction of resin strips this spring, and reformulated aerosols and liquids to follow. AMVAC was the primary advocate of the chemical during the EPA review. “Over the last 19 years and 11 months we addressed each and every one of their concerns,” said AMVAC Commercial Manager Jeff Alvis, “Everything (EPA) asked us to remove or limit on the label has been done.”

Among the completely discontinued uses are large strip use in living spaces (areas with human exposure of four hours or more per day), cat and dog collars, dry baits and some liquid formulation uses.

Resin strips were one of the uses that remained on the market throughout the review, however new registration requirements do mandate some changes to the strips and their labeling. While all uses have been retained, Alvis said, “EPA has now forced us to separate those uses out for exposure reasons.” Large strips now only can be used in areas where human exposure is limited to less than four hours per day, while the small strips can be used in residences and living areas that are inhabited 24 hours a day.

Even with the required changes, DDVP’s new technical label, issued in September 2007, is quite broad, Alvis said, “making it very useful in IPM.” The key benefits of the chemical, he explained, are:

• it has high volatility, so it evaporates quickly without leaving a residual;
• it has quick knockdown for a variety of pests;
• there is very little to no recorded insect resistance;
• it has no environmental persistence, rather it breaks down very rapidly;
• it is one of very few organophosphates available today;
• it is or will be available in three end-use formulations — resin strips, aerosol foggers and liquids, adding to its versatility

However, don’t expect to see AMVAC’s aerosols or liquids on the market quite yet. Not only do the products need to be relabeled, they need to be reformulated to fit new EPA requirements for inert ingredients as well as the active. The previous inert ingredients were flammable, had low flash points and could stain siding and carpets, so they have to be brought up to date, Alvis explained. “It’s like a brand new development of a product.”

Pest management professionals can expect to see a gradual roll-out of DDVP products over the next two to three years, with aerosols probably at least two years in the future.

ORGANOPHOSPHATES. DDVP is one of the few organophosphates available to pest management professionals today. Most have gradually been taken off the market, even though, “as a group, they were very, very effective insecticides,” said Gary Bennett, professor of entomology and director of Purdue University’s Center for Urban and Industrial Pest Management. And while the removal of these chemicals and EPA’s Special Review of DDVP attest to the general concerns over the pesticide, “if used properly, safely, according to the label, they really were of very little danger to anyone or anything.”

This is not to say that they were always used in the safest manner, however. In the “old days,” Bennett said, time-release units were often put over entry/exit doors in fast food restaurants, which sprayed DDVP to eliminate flying insects coming in. The problem was that this was often being sprayed right where food was being served, and that every person who walked in the door got a breath of the volatile chemical.

Some of these uses should probably have never been on the market, he said, and as a result, they led to a lot of pressure on DDVP and other organophosphates. And with that pressure, people moved away from the product and its various uses. “So now we have to work harder and, of course, charge for it,” he said.

YESTERDAY AND TODAY. Katz used DDVP quite extensively in the past and is glad to see it making a comeback, he said. “It was such a useful product; we used it for many purposes,” he said. “I don’t think there’s anything quite as good.” DDVP is particularly useful when mixed with a residual, Katz said, adding that “residuals kill too slowly for some people, but mix it with a little DDVP, it will give more action.”

Presto-X-Company has never stopped using DDVP, said Presto-X Vice President Jerry Keown. With its headquarters in Omaha, Neb., and service centers throughout the Midwest, the company uses the pesticide in the fogging of warehouses, such as flour mills and other grain-processing facilities. “It’s a fine product,” Keown said. “We use it quite a bit. We’ve been using it for the last 20 years.” In fact, he added, Presto-X Technical Manager Earl Hallberg testified on behalf of the product in the EPA reviews.

To some degree, Keown said, DDVP is looked at as a replacement for methyl bromide. Although it is not a fumigant, and as such does not have the penetration of a fumigant, it works well for spot treating and fogging. Applied with a fogger, DDVP fills the volume of air fairly equally so it has fairly even distribution, he said. “We find it isn’t going to penetrate like a true gas will, but it gives some penetration.” Because of this, it is critical that the customer clean very well to eliminate pest food and harborage. “It goes hand in hand with good sanitation,” Keown added.

BED BUGS. Kramer said he is looking forward to the re-issuance of an aerosol product registered for apartment use. “If I can use it in bedrooms,” he said, “I’m optimistic that this will help us knock bed bugs on their can.” As a volatile product somewhere between a fumigant and an insecticide, it could get into areas where bed bugs usually hide and provide quick knockdown — which is what the customer wants, he explained. “I think there’s some real potential there if the label is right.”

Kramer said he sees such value in this product because he knows of no resistance issues in any insects as has been documented in bed bugs with pyrethroids; there are not many chemicals or tools on the market for bed bugs as there are for most other pests; and “bed bugs are very difficult to control. They’re not one-shot deals,” he said. “So it gives us another tool that we don’t have to worry about resistance issues with.”

AMVAC does expect DDVP to be registered for bed bug control, Alvis said, adding that several products will be registered for the pest over the next two to three years, including Nuvan ProStrips, for which testing is ongoing and looks promising. Although bed bugs will not be on the first registration, out this spring, he added, they will follow soon after.

INDUSTRY REACTION. “I, personally, would like to have a lot of the organophosphates back out there,” Bennett said, “because we then wouldn’t be struggling with some of the pests we’re dealing with — like bed bugs.” Not only are many of today’s products slower acting, it takes more product to get the job done, and the product is less effective so it has to be applied in closer proximity to the target pest. “Nowadays it’s a real challenge to take care of the target pest — at least quickly,” he said. “And you’re putting more (active ingredient) out and you’re having to go back more frequently, so there’s sort of a trade off.”

Kramer said his company is satisfied with the products it currently uses for bed bug control, but he was excited to see that the products were to be reissued; that there is “something new on the horizon.” Although he does not expect to use DDVP for much else, Kramer said he could see some added value if the product were labeled for crack and crevice commercial use in restaurants. Because of its volatility, it could be particularly useful for severe cockroach infestations, he said. “That’s the real neat thing about it. (Pests) don’t necessarily have to touch it, they can inhale it.”

The key element of DDVP’s value, he said, will be the sites for which the product is labeled. He is less concerned about the specific pests on the label, because as long as there are no other restrictions, most states don’t require that the target pest be on the label, he said. “If only cockroaches are on the label I can still treat for bed bugs with the contingency that I believe it can control them.”

But the real key to DDVP’s value and efficacy is its proper use, Bennett said. “If the products are used the right way, they can be very effective with minimal negative effects or negative repercussions,” he added.

The author is a frequent contributor to PCT.

For documents related to EPA’s reregistration of DDVP, visit www.epa.gov/pesticides/reregistration/ddvp.

DDVP Facts
Proper name: Dichlorvos (2,2-dichlorovinyl dimethyl phosphate)

Class: Organophosphate

Mode of action: A cholinesterase inhibitor, DDVP affects the nervous system of the target pest, blocking the enzyme required for proper nerve functioning.

Manufacture: Dichlorvos is a synthetic organic chemical used as an insecticide. It does not occur naturally in the environment, but is manufactured by industry through a reaction between the chemicals chloral and trimethyl phosphate or through the heating of trichlorfon. Pure dichlorvos is a dense colorless liquid with a sweetish smell that evaporates easily into the air and dissolves slightly in water. 

Uses: The main uses of dichlorvos are for insect control in food storage areas, greenhouses and barns, and for parasite control in livestock. It is also used for indoor insect management and controlling parasites in pets. It is generally not used on outdoor crops.

Formulations:
Resin Strips — the first formulation to be re-introduced (available spring 2008), the strips are offered in large and small sizes. Because the size of the strip impacts the amount of chemical exposure, the size also determines the approved use, thus the two are separately labeled.

Small strips (5.25g, 10.5g, 16g) can be used in residences around the clock and are approved for use in areas such as closets, wardrobes, cupboards, storage units, trash dumpsters, garbage cans, catch basins and electrical boxes.

Large strips (65g, 80g) only can be used in areas where there is human exposure for less than four hours per day. Approved use areas include attics, garages, crawlspaces and sheds. Large strips also can be used in cabins and mobile homes if they are unoccupied for four months after the strip is placed.

Aerosols — While registration of aerosols is a bit further down the road, approval has been granted for a residential, non-total release can of less than 0.5 percent DDVP and a commercial-use, total release, greater than 0.5 percent DDVP can.

Foggers — Having never been taken off the market, fogging of food storage areas, warehouses, and food-processing facilities will continue to be approved, following all label specifications.

Liquids — To be available as a dilutable or ready-to-spray product, the liquids have commercial and agriculture approved uses, with most of the previous DDVP uses retained except: hand-held foggers in warehouses, greenhouses and mushroom houses; lawn, turf and ornamental uses; total-release foggers; and crack and crevice uses.

Safety: As with any pesticide, safe use is dependent on complete reading and following of all label directions, but basic guidelines include:

Resin Strips — When working with bare strips, protective gloves should always be worn. AMVAC is also marketing the strips with an optional protective cage to provide additional safety for pest management professionals.

Aerosols and Foggers — Because of the variety of uses, safety precautions with this formulation are dependent on the application, and may include anything from protective gloves and mask to a complete clearing and securing of the room for total-release products.

Liquids — Because of the variety of uses, safety precautions will be based on the specifications of the end-use label, which has not yet been developed for the newly approved uses.

DDVP Timeline

1988 February
EPA places dichlorvos (DDVP) into Special Review because of concerns for cancer, cholinesterase inhibition and liver effects

1995 September
EPA issues a Draft Notice to cancel DDVP registrations

1996 August
Food Quality Protection Act enacted

2001
EPA formally declines to use data from DDVP human tests

2004
DDVP enters National Academy of Sciences Review

2006 February
Human Studies Review Board set up for DDVP

2006 April
DDVP passes Human Studies Review Board review

2006 July
DDVP Interim Re-registration Eligibility Decision (IRED) issued;
Organophosphate Cumulative Risk Assessment issued, saying, “the pesticides that were covered by the IREDs that were pending the results of the OP cumulative assessment…are indeed eligible for re-registration.”

2007 September 
DDVP technical labels issued by EPA; DDVP Special Review Termination proposed/opened for comments. EPA said, “EPA has determined that the risks that were the basis of the Special Review are no longer of concern and, therefore, the agency is proposing to terminate the Special Review of DDVP.”

2007 October
Comments close on ending DDVP’s Special Review

2007 December
EPA Final Determination to Terminate Special Review; DDVP Re-registration Eligibility Decision (RED) issued. EPA said, “The Agency received no substantive comments in response to the proposal and EPA is announcing its final determination to terminate the Special Review of DDVP.”

2008 Spring
AMVAC plans to introduce Nuvan ProStrips, resin strips with DDVP