The effect of acid precipitation on the leaching of copper, chromium and arsenic from timber treated with different CCA preservatives was studied in the presence of three types of soil under simulated field conditions. Pine sapwood, embedded in soil, was subjected to simulated rainfall at three different levels of acidity. The CCA preservative formulations tested were:- American Wood Preservers' Association (AWPA) type B; AWPA type C; and British Standard 4072 (1974) type 1. A preliminary test of leaching with simulated rain alone (i.e. no soil) was conducted. Significant quantities of copper (40%) were lost from wood treated with all three CCAs after leaching in "rainfall" at pH 3.0 . Copper was not leached from any treated wood at pH 5.6 . Arsenic was leached in appreciable amounts (20% from wood treated with the AWPA type B formulation at both pH 3.0 and pH 5.6 and, to a lesser extent (12%), from the BS 4072 type 1 treated wood but only at pH 3.0 . Chromium was not leached from any CCA treated wood at pH 5.6, with only the possible loss of a relatively low amount (6%) occuring at pH 3.0 from wood treated with the BS 4072 type 1 CCA. In the investigation with soil, "rainfall" acidity had no significant effect on the leaching of the metals from the CCA treated wood, as detected by soil leachate analysis. This was considered to be due to the natural buffering capacity of the soils. The type of soil did have a significant effect upon the quantities of elements retained in soil and appearing in the leachate. The concentration of arsenic in leachate was greatest from sandy soil with the AWPA type B CCA treated wood, clay and peat soils retained the greatest amount of arsenic with the same formulation. The concentrations of all three elements in soil and leachate reflected the different composition of the CCA formulations.

Download document (1.3 Mb)
free for the members of IRG. Available if purchased.

Purchase this document