Chemical Analysis of Southern Pine Pole Stubs Sixty Months Following Treatment with a Methylisothiocyanate-Based Solid Fumigant Stick
D J Herdman, T Pope, R R Browning
Methylisothiocyanate-based fumigants have been commercially used in the United States for over 35 years to control internal decay in utility poles and other wooden structures with little technological advancement. The most recently commercialized methylisothiocyanate-based fumigant is chemically known as dazomet. Dazomet is a free-flowing powder or granule that decomposes in the presence of moisture within a utility pole to release methylisothiocyanate. As a means to accelerate the decomposition to methylisothiocyanate, a copper solution can be applied to dazomet during the time of fumigant application. Laboratory and field studies conducted as part of the Utility Pole Research Cooperative at Oregon State University have demonstrated the long-term efficacy of dazomet. Concerns with applicator safety, inefficient copper-dazomet interaction, accurate dosing and a high potential for accidental spills, has led OSU researchers to develop several solid forms of dazomet. While long-term field testing by the OSU-UPRC has generated positive results, the prototype forms of solid dazomet had little commercial value. Recently, a commercially viable solid-stick dazomet product was introduced to the remedial wood preservative market to prevent and arrest active decay within in-service wood utility poles. To demonstrate the long-term performance characteristics of this solid form of dazomet, a field study was established in January 2014 in southern pine utility pole sections. At the fourth inspection conducted 60 months following fumigant treatment, chemical assay borings were removed at various pole heights and depths and analyzed for concentrations of methylisothiocyanate using GCMS. The 60-month results showed the concentrations of methylisothiocyanate were greatest in the pole sections treated with the copper amended solid-stick dazomet. When compared to previous chemical assay results at 12, 32 and 46 months following fumigant treatment, the 60-month results showed a sharp increase in concentrations of methylisothiocyanate in the copper amended solid-stick dazomet treated pole sections. The granular dazomet showed a slight increase in methylisothiocyanate production, where the unamended solid-stick and copper amended granular dazomet showed little change from 46 to 60 months of exposure. When compared to a methylisothiocyanate threshold value for decay fungi proposed by Oregon State University, the chemical assay results at 60 months indicated all fumigant treatments are effectively protecting the zone of fumigant treatment (15.2 cm below to 15.2 cm above groundline) of southern pine pole sections. However, the greatest protection within and above the zone of treatment was provided by the copper amended solid-stick dazomet treatment. Future sampling and chemical analysis of the southern pine pole sections are planned to monitor long term efficacy of the fumigant treatments.
Keywords: methylisothiocyanate, solid dazomet stick, southern pine poles, field studies, efficacy