S. Vonwirenlehr et al., MINERALIZATION OF [C-14] GLYPHOSATE AND ITS PLANT-ASSOCIATED RESIDUESIN ARABLE SOILS ORIGINATING FROM DIFFERENT FARMING SYSTEMS, Pesticide science, 51(4), 1997, pp. 436-442
The biomineralization of [C-14]glyphosate, both in the free state and
as C-14-residues associated with soybean cell-wall material, was studi
ed in soil samples from four different agricultural fanning systems. A
fter 26 days, [C-14]carbon dioxide production from free glyphosate acc
ounted for 34-51% of the applied radiocarbon, and 45-55% was recovered
from plant-associated residues. For three soils, the cumulative [C-14
]carbon dioxide production from free glyphosate was positively correla
ted with soil microbial biomass, determined by substrate-induced heat
output measurement and by total adenylate content. The fourth soil, or
iginating from a former hop plantation, and containing high concentrat
ions of copper from long-term fungicide applications, did not fit this
correlation but showed a significantly higher [C-14]carbon dioxide pr
oduction per unit of microbial biomass. Although the cumulative [C-14]
carbon dioxide production from plant-associated C-14-residues after 26
days was as high as from the free compound, it was not correlated wit
h the soil microbial biomass. This indicates that the biodegradation o
f plant-associated herbicide residues, in contrast to that of the free
compound, involves different degradation processes. These encompass e
ither additional steps to degrade the plant matrix, presumably perform
ed by different soil organisms, or fewer degradation steps since the p
lant-associated herbicide residues are likely to consist mainly of eas
ily degradable metabolites. Moreover, the bioavailability of plant-ass
ociated pesticide residues seems to be dominated by the type and stren
gth of their fixation in the plant matrix.