DEC letter addresses test results

One expert interpretation of soil sample results, albeit remote, is in.


At Town Supervisor Jim Dougherty’s request, Vincent Palmer, head of the Bureau of Pesticides for the state Department of Environmental Conservation, provided comments on the test results mid-day Wednesday. He emphasized that the private sampling effort has no affiliation with the state permitted 4-poster program.


“The reported detection of trace levels of permethrin in soil samples collected by other than trained professionals in the immediate vicinity of one 4-poster deer treatment device is not unexpected,” he wrote.


“Sample collection is not a trivial exercise, and is the weakest link in the chain of activities that comprise environmental sampling and analysis. It requires technical expertise in order to assign statistically supported limits of confidence to sample data. Contamination is a common source of error in environmental measurements owing to the fact that most environmental sampling and analytical applications offer numerous opportunities for sample contamination.”


Without detailed information on protocols, sample collection techniques and quality control measures, he could only comment on reported results, he wrote. He questioned the quality of the sampling, quoting from the lab report, which noted problems with sample holding times, temperatures and the qualifications of the sampler.


“The presence of permethrin at a reported depth of 18 inches below grade may be the result of cross-contamination that occurred during sample collection. If it is not … the dramatic reduction in concentration may represent the degradation process that takes place after permethrin is introduced to the environment. As the thousandths-fold decrease in concentration indicates, permethrin is being degraded as it moves in the soil column.”


He cited a multi-university database, EXTOXNET, on the fate of permethrin in the environment: “Permethrin is of low to moderate persistence in the soil environment, with reported half-lives of 30 to 38 days … Permethrin is tightly bound by soils, especially by organic matter. Very little leaching of permethrin has been reported. It is not very mobile in a wide range of soil types. Because permethrin binds very strongly to soil particles and is nearly insoluble in water, it is not expected to leach or to contaminate groundwater.”


Mr. Palmer commented on broadcast spraying, which “could be expected to result in the presence of permethrin on the surface of the entire treated area in concentrations ranging from 6 to 12 parts per million (ppm) … The amount of tick-killing pesticide” from the Island’s 60 4-posters “is significantly less than the amount delivered to the environment by alternative broadcast spraying…”


“Incidental deposition of trace amounts of permethrin in the immediate vicinity of a 4-poster is not unexpected.” Commercial pesticide applicators visit the stations twice a week, recharging rollers that hold a maximum load of 40 milliliters of tickicide, he wrote. “Given the degree of activity around these busy stations, it is inevitable that trace residues of permethrin would be present on the ground near these isolated treatment stations.”


He concluded, “This Department, Cornell University, Cornell Cooperative Extension of Suffolk County, and the many other professionals involved with this critically important public health and environmental quality research remain confident in the design of the study and the progress made thus far. At this phase of the study, we remain fully committed to seeing this research through to its conclusion.”