The adso
rption of the insecticidal C
ry1Ab p
rotein of
Bacillus thuringiensis (
Bt) on Na-montmo
rillonite (M-Na) and soil clay f
ractions was studied. The aim of this study was not to find the adso
rption capacity of the soils f
rom the expe
rimental field site, whe
re
Bt co
rn (MON810) was cultivated, but
rathe
r to cha
racte
rize the adso
rption behavio
r of the C
ry1Ab p
rotein at concent
rations typically found at expe
rimental field sites. In kinetic expe
riments, the C
ry1Ab p
rotein adso
rbed
rapidly (<60 min) on M-Na. As the concent
ration of M-Na was va
ried and the added C
ry1Ab p
rotein concent
ration was kept constant (20 and 45 ng ml
−1), the adso
rption pe
r unit weight of C
ry1Ab p
rotein dec
reased with inc
reasing concent
rations of M-Na. Adso
rption of C
ry1Ab p
rotein on M-Na dec
reased as the pH value of the suspension inc
reased. All adso
rption isothe
rms could be desc
ribed mathematically by a linea
r reg
ression with the pa
ramete
r k, the dist
ribution coefficient, being the slope of the
reg
ression line. Although thei
r mine
ralogical composition was nea
rly identical, the soil clay f
ractions showed diffe
rent
k values. The diffe
rent
k values we
re co
rrelated with the physical and chemical p
rope
rties of the soil clay f
ractions, such as the o
rganic ca
rbon content, the specific exte
rnal su
rface a
rea, and the elect
rokinetic cha
rge of the exte
rnal su
rfaces of the clays, as well as with the exte
rnal su
rface cha
rge density. An inc
rease in the amount of soil o
rganic matte
r, as well as an inc
rease in the elect
rokinetic exte
rnal su
rface cha
rge of the soil clays, dec
reased the dist
ribution coefficient
k. An inc
rease of the specific exte
rnal su
rface a
reas of the soil clays
resulted in a highe
r dist
ribution coefficient
k.Less than 10%of adsorbed Cry1Ab protein was reversibly adsorbed on the soil clays and, thus, desorbed. The desorption efficiency of distilled water was higher than that of a solution of CaCl2 (2.25 mmol) and of dissolved organic carbon (50 mg C l−1).