Entire leaves left on soil surfaces were extracted separately to
determine their glyphosate and AMPA contents after 80 days (see
section 2.4. Incubation procedure). The total extractable 14C from
leaves was 10.4 ± 2.4% AR for washed GT leaves, 6.5 ± 0.4% AR for
non-washed GT leaves, while it was 5.8 ± 2.5% AR for washed non-
GT leaves, and 6.3 ± 7.0% AR for non-washed non-GT leaves. There
were no significant differences among all four treatments
(P > 0.05). These amounts are lower than those observed by
Rampoldi et al. (2011) for other species like maize and soybean,
however in the latter experiments crop residues were incubated in
the absence of soils. After 80 days, CaCl2 extracts only contained
AMPA, which is consistent with the degradation pattern of glyphosate
in GT oilseed rape (Nandula et al., 2007). However, NH4OH
extracts contained, in addition to AMPA, significant amounts of
glyphosate: from 0.8 ± 0.2% AR for washed non-GT leaves to
2.6 ± 0.2% AR for non-washed GT leaves. The absorption of glyphosate
in plant material therefore provided a protection against soil
degradation. The formation of soil NER from glyphosate in entire
leaves on soil surface ranged from 9.2 ± 2.5 to 10.5 ± 2.4% AR,
without any significant differences between washed and nonwashed
leaf samples (P > 0.05).