ASPCRO Sets Soil Sampling Thresholds

Six years. Long enough to have seen one president through office and get a good start on the next. Enough time to have sat through several rounds of Olympic Games. And just enough time to develop a regimen for soil sampling of termiticides. Six years may not, on the other hand, be quite long enough to prepare for the presidency, to become a master of discus-throwing, or to come up with a soil sampling standard that all can agree on.

The Association of Structural Pest Control Regulatory Officials (ASPCRO) completed its Guidance Document for soil samples in late September, a project that was initiated in 1989. Now each state can decide for itself whether soil sampling of termiticides is a useful enforcement tool and whether this approach to regulating PCOs will be widely used at the state level.

Some regulators feel ASPCRO's document just might provide the yardstick they have been looking for to determine if PCOs are making "by-the-label" applications. But some manufacturers have questions about soil sampling as a regulatory tool and are concerned that wide variations in soil samples might sometimes skew the results, causing good applications to be deemed failures, resulting in fines and other penalties to the PCO.

Jim Wright, regulatory supervisor for the South Carolina Department of Pesticide Regulation, has spent the last six years developing and conducting a study to see if soil sampling can be a fair yardstick. He's headed up ASPCRO's Soil Residue Committee since March of 1989, from which time the group has been involved in a study designed to evaluate by-the-label termite treatments.

In the committee's Guidance Document, states are provided with a suggested protocol for taking soil samples, and then are advised on how to evaluate them. Threshold levels for six brands of termiticides are provided which represent the minimum amounts of chemicals regulators should expect to find when sampling treated soil. Wright is optimistic about the document and its potential for use by the states. He says it a fair and accurate regulatory tool that can be used in any state that wants to sample soil for regulatory purposes as part of an evaluation of a termite treatment.

ASPCRO's Guidance Document now carries an NPCA "stamp of approval." In states where soil sampling is currently performed, such as Arizona, Georgia, and the Carolinas, regulators will need to decide whether adopting ASPCRO's guidelines will be useful. (The guidelines have already been implemented in South Carolina's regulatory code.) And in those states where soil sampling is only partially or not at all done, some legislation might have to be changed before the states can consider adopting it.

EARLY HISTORY. The Soil Residue Committee first presented the study concept to the entire ASPCRO membership at the 1989 annual meeting in Reno, Nev. The idea was born because, Wright said, ASPCRO agreed that regulators should be looking at soil residues as a part of compliance enforcement. In January 1990, Wright called a meeting of manufacturers, regulators and members from the scientific community to discuss how to study soil residues. Everyone present agreed that the work should be done. "Finally in February of 1991, we had an agreement on the table and as to how the study would be conducted," said Wright. "Then the manufacturers, over the next four or five months, committed fiscal resources."

The Soil Residue Committee, originally made up of Wright; Jim Harron, agriculture manager with the Georgia Department of Agriculture; Dr. Joe Mauldin, project leader for the U.S.D.A.-Forest Service; and Bob Russell, technical director of Arrow Exterminators, Atlanta, got to work on the actual study. (Mauldin retired in 1993 and was replaced by Dr. Brad Kard, principle entomologist and Dr. Skip McDaniel, principle chemist, both of the Forest Service.)

"I knew the first year was actually going to be spent negotiating with the manufacturers on the protocol itself," Wright recalls. The committee had decided on which states would participate, then the state regulators selected PCOs to locate the sites and perform the treatments.

Seven different termiticides from five major manufacturers were tested on 84 different sites in Indiana, Arizona, Georgia and Oklahoma. (Each chemical was used on three groups of seven structures.) Treatments on the structures were completed by the summer of 1992, and sampling was completed by the fall of 1993. Samples were taken prior to treatment, immediately after treatment, 30 days after treatment, 120 days after treatment, and one year after treatment. The next year was spent compiling and analyzing the data.

For the study, ASPCRO used a sampling method derived from a method that had been previously validated by the Forest Service. The Forest Service's sampling method, which had been tested at a 95% confidence level, called for the collection of four soil cores which would then be combined to form one composite sample. A subsample would then be drawn from the composite sample. ASPCRO required that each composite sample be comprised of eight soil cores, and that a minimum of two composite samples be taken.

In the field study, PCOs were supervised by regulatory officials who ensured that the treatments were done by the label. Because it was a field study, as opposed to a laboratory study, Wright feels the study is an accurate reflection of real-life conditions. "It was done by PCOs as they treated real homes with real termite problems or potential termite problems, much like they deal with every day." The PCOs also used their own equipment and their own employees to perform the treatments, Wright said.

MODIFICATIONS MADE. Wright first presented the committee's findings to the ASPCRO 1994 annual meeting in San Antonio and distributed a draft version of the Guidance Document in December 1994. The NPCA initially doubted the validity of the study because it had not been independently reviewed and because there appeared to be considerable variability in the sample data, suggesting that PCOs might be incorrectly penalized. In response, ASPCRO, with help from the NPCA, selected Dr. Brian Forschler, assistant professor of entomology at the University of Georgia, to perform an independent evaluation of the study.

Dr. Forschler reviewed the study and validated the statistical model that was used. He recommended that ASPCRO apply a single residue standard for each termiticide (see chart at right), based on the lowest number of parts per million that would be expected to be found 180 days after a by-the-label application. Dr. Forschler found that under the sampling method used by ASPCRO, none of the sites tested in the field study would have been considered a failure. ASPCRO's protocol, according to Dr. Forschler, "attempted to capture the variability inherent in the different soil types and climatic influences which could affect termiticide soil residue recovery."

ASPCRO incorporated Dr. Forschler's recommendations. Other modifications were recommending that states allow PCOs to observe collection of soil samples, and that a portion of each sample be made available to a private laboratory for independent analysis. After these changes, NPCA approved the guidance document. In a letter sent to all state regulators and state pest control agencies, the NPCA commended ASPCRO for its work and wrote that the protocol is reasonable as part of a well-balanced regulatory program.

"While it's not for every state, " said Bob Rosenberg, NPCA director of government affairs, of the document, "if some states do want to develop and follow a soil sampling program, they should follow the ASPCRO guidelines." For those states that do adopt the guidelines, the NPCA adds, soil sampling should be part of the comprehensive program, and not used as a stand-alone enforcement tool.

Wright points out that the threshold levels established by ASPCRO do not represent the parts per million required in the soil for an effective termiticide barrier. "This was not an efficacy study," said Wright. "All this study says is that if you treated by the label, this is what you should expect to find." Furthermore, Wright says, regarding soil sampling, it shouldn't matter to the PCO which product he is using. "The same confidence level applies to each of the different pesticide threshold levels." Wright also said PCOs shouldn't switch from one product to another just because one has a lower threshold level. The threshold level doesn't suggest anything in terms of how well the product is going to control termites or how long it's going to last, he said.

The threshold level assigned to each product is a function of what residue was found after a by-the-label treatment. Degradation of each chemical was also factored in mathematically, Wright said, using findings from a previous degradation study done by the U.S. Forest Service. Although Wright admits the committee found some differences in the data by state, he feels the threshold levels the committee has established are fair and appropriate because high and low results have been taken into account. "My professional opinion would be that the states that are doing sampling need to take a close look at adopting these guidelines and procedures," said Wright. For those states that are considering using soil sampling, Wright adds that the guidelines will provide a basis for implementing soil sampling into their existing regulatory program.

In Florida, for example, there are no minimum treatment standards for subterranean termite control for postconstruction applications. Regardless, Phillip Helseth, pest control administrator with the Florida Department of Agriculture, thinks soil sampling has some merit. "It's a possibility we may be able to use some of the ASPCRO guidance figures in our enforcement in our pretreatment law that requires label rates." He feels the ASPCRO research is credible, and that it is feasible but difficult to come up with a nationwide standard, and that other compliance checking methods should be used as well.

SOME CONCERNS. A few of the concerns of ASPCRO's soil sampling recommendations have come from the manufacturing side. Dr. Mark Coffelt, national technical services manager, AgrEvo Environmental Health, said he felt it was difficult to establish one standard for the U.S. because of the differences in soil types and environmental conditions. According to Dr. Coffelt, more research is needed to establish regional soil residue levels.

Wright says the areas tested do represent a wide spectrum of soil types. "What we tried to do is develop as much geographic diversity as we could in those four states," said Wright. "Geographically those states are representative of the areas that have the highest termite population pressures, and I feel like there is an adequate amount of geographic diversity in the soil types and climate, rainfall, temperature, everything considered, that would give us the necessary foundation to develop a national standard."

Jim Ballard, technical manager with FMC, is concerned with the variation that is typically seen in soil sampling, even when composite sampling methods are used. "The biggest problem with using soil sampling as a tool is extreme variation of results," said Ballard. He says the variation comes from sources that can't be controlled, such as soil type, environmental conditions, differences in how the samples are taken, homeowner disruption of the soil, and most importantly, the application itself. The variation in the parts per million readings become important, he adds, when it comes to comparing samples' ppms with the established threshold levels. The higher the parts per million number that a product must reach, Ballard says, the more variation gets in the way of all that. "When you are looking for smaller numbers, the variation doesn't hit you so bad," he said. Ballard also mentioned that not all of the termiticides on the market were included in the ASPCRO field tests, and some of the products used in the tests have changed their label use rates since they were tested by ASPCRO.

Michael Chambers, product development manager for DowElanco, feels that soil sampling can be part of a compliance check, but it shouldn't be the sole means of performing checks. He says that through all of the company's testing of its own products, soil sampling has often shown tremendous variation. "I guess our position all along has been that soil sampling is a good means to determine if our product, chlorpyrifos, is present in the soil, but the levels you find may not necessarily be directly correlated to what was applied."

"The other key thing," Chambers said, "is that our labels talk about applying termiticides to stop termites. We do not specify that you apply to provide so many parts per million in the soil."

Each state must eventually make a decision on its own about whether to follow ASPCRO's recommendations. After all, the guidance document is just that: a guide that can be used by the regulatory agency in each state, in whole, in part, or not at all.

Why did it take ASPCRO the better part of six years to come up with a soil sampling guidance document? Wright refers to the sheer magnitude of conducting a study in more than four states and involving literally hundreds of people. "ASPCRO was committed to taking all of the time necessary to ensure that their soil residue study was not hastily done," Wright said. "While not all pest control operators will agree on the regulatory process, I believe that the user community will have a better comfort level with the recently completed ASPCRO study once they understand what this says."

Lisa Josof is associate editor of Pest Control Technology magazine.