(NH4)2SO4-extractable
NH4H2PO4-extractable
(NH4)2C2O4-extractable
(NH4)2C2O4/ascorbic acid-extractable
Residual As
H3PO4 HCl HCl/Na
dithionite
Neutral
phosphate
Original
(b)
0
20
40
60
80
100
H3PO4 HCl HCl/Na
dithionite
Neutral
phosphate
As extraction (%)
(a)
Fig. 1. Effect of different soil washing solutions on (a) arsenic (As) extraction and (b) chemical forms of residual As in the washed soils. H3PO4: 1 h washing with