Environmental Engineering Reference
In-Depth Information
Arsenic Contamination After Wood
Impregnation: Speciation, Sorption
and Leaching
Emma Johansson, Kristine Ek, Malin Norin, and Ann-Margret Strömvall
Introduction
Arsenic (As) is a semi-metallic element, all forms are toxic and explain its use as a
wood impregnation agent component. In the past, wood impregnation plants had no
protection against dripping and leakage, resulting in a contaminated area around the
impregnation equipment. In Sweden, the most commonly used impregnation agents
containing arsenic are Boliden industry salt (BIS) and CCA fluids. BIS contains
zinc (Zn) and As, and CCA fluids contain chromium (Cr), copper (Cu) and As.
The most common CCA fluid is called Boliden K33. The As content of BIS is 18%,
while in Boliden K33 it is 24%
[1]
. Since 2004, only professionals are allowed to
use CCS-impregnated timber in Sweden. Several more environmentally friendly
impregnation agents have been introduced in recent years. Remediation of arsenic
contaminated sites will be common in the future and of the completed soil remediation
projects in Sweden in 2006, 15% were former wood impregnation sites
[2]
. Research
on suitable remediation techniques is in progress, and tests have demonstrated that
arsenic in contaminated soil can be stabilized by addition of iron oxides
[3]
.
In nature, arsenic is present in both inorganic and organic species. Inorganic
As generally occurs in arsenite/As(III) form as H
2
AsO
3
−
or HAsO
3
2−
or the form
arsenate/As(V) as H
3
AsO
4
0
or H
2
AsO
4
−
[4]
; the form depending on the redox
potential and pH value
[5]
. Both forms often occur together, since As is reduced and
oxidized rather slowly. As(V) is dominant in oxidizing environments and present as
HAsO
4
2−
in alkaline and as H
2
AsO
4
−
in acidic environments
[6]
. In reducing envi-
ronments, As(III) is dominant in the neutral form H
3
AsO
3
0
and only occurs in the
