Arsenic Contamination After Wood Impregnation: Speciation, Sorption and Leaching - Highway and Urban Environment - page 270

45

40

0,6

35

0,5

30

0,4

25 0,3

Soil A
Soil B
Soil C

0,2

20

0,1

15

0

10

As(III) DMA MMA

5

0

As(V) As(III) DMA MMA

Fig. 2 Concentrations of As species in mixed soil samples A-C

Batch Tests - Leaching Aerobic/Anaerobic Conditions

The results of the As species' leachability from soil stored in beakers; one being
stirred, one undisturbed and one containing an inert atmosphere, are compared in
Table 1 . The largest amount of leached As was found in the beaker with anaerobic
conditions. This may be explained by the fact that As is more easily dissolved in
reducing environments if bound as iron arsenate to the soil particles. In a reducing
environment, iron oxides dissolve and thus the As in iron arsenate likewise
dissolves and becomes more mobile [13] .
The largest part (~90%) of all As leached in the samples was arsenate, As (V),
which was expected due to the high concentrations in the soil. The lowest amount
of leached As was found in the strongly oxidized environment in the stirred beaker,
which causes As to bind to iron oxides.
Only total As concentrations were analyzed in the leaching tests because the
shaking procedure oxygenates the samples and thus changes the As speciation [6] .
Arsenic levels after 6 and 18 h of shaking are presented in Table 2 .
Soil B exhibited a higher degree of leaching compared to soils A and C, as
demonstrated by the lower Kd value. The reason for this may be that soils A and C
had a higher total content of Fe and Al, metals which can bind As [6] . The As
concentration in leachate from soils A and C decreased because complex binding
of As with Fe increases over time. This binding is faster than the leaching of
As into the water phase. On the other hand, in soil B, which had a lower Fe content,
the leaching was faster than the complex binding. The As concentration therefore
increased in leachate from soil B over time.
The K d value was high in all soils; 800 (soil A), 77 (soil B) and 1,300 (soil C)
times higher than the general K d value of As of 30 L/kg [15] . These values indicate