Soil dehydrogenase activity adjacent to remedially treated timber, weathered in a physical field model

Three physical field models were constructed to assess the effects on soil of a chromated fluoride wood preservative treatment used at the groundline of creosoted electricity distribution poles. One model contained an untreated aged creosoted pole section in sandy loam soil, the second contained a remedially treated aged creosoted pole section in sandy loam soil and the third a similarly treated section in sand-amended sandy loam soil. The models were subjected to the equivalent of 6 months simulated rainfall exposure, and soil samples recovered from each model soilbed were used for the determination of soil dehydrogenase activity, fluoride and total chromium concentrations. Soil dehydrogenase activity was measured on both rye meal-supplemented and unsupplemented soil samples. Irrespective of supplementation, significant reductions in dehydrogenase activity were associated with increased soil concentrations of leached preservative constituents which were found within 5 cm of the treated pole sections. These reductions were enhanced by the lower organic matter content of the sand-amended soil. Supplementation with rye meal resulted in raised levels of dehydrogenase activity in all soil samples, which highlighted the negative effects of preservative soil contamination on microbial activity.