Fc. Michel et al., MICROBIAL-DEGRADATION AND HUMIFICATION OF THE LAWN CARE PESTICIDE 2,4-DICHLOROPHENOXYACETIC ACID DURING THE COMPOSTING OF YARD TRIMMINGS, Applied and environmental microbiology, 61(7), 1995, pp. 2566-2571
The fate of the widely used lawn care herbicide 2,4-dichlorophenoxyace
tic acid (2,4-D) during the composting of yard trimmings consisting of
primarily leaves and grass is an important unexplored question. In th
is study, we determined the extent of 2,4-D mineralization, incorporat
ion into humic matter, volatilization, and sorption during the compost
ing of yard trimmings. Yard trimmings (2:1 [wt/wt] leaves-grass) were
amended with C-14-ring-labeled 2,4-D (17 mg/kg of dry weight) and comp
osted in a temperature-controlled laboratory scale compost system. Dur
ing composting, thermophilic microbes were numerically dominant, reach
ing a maximum of 2 x 10(11)/g. At the end of composting, 46% of the or
ganic matter (OM) present in the yard trimmings was lost and the compo
st was stable, with an oxygen uptake rate of 0.09 mg of O-2 per g of O
M per h, and was well humified (humification index, 0.39). Mineralizat
ion of the OM temporally paralleled mineralization of 2,4-D. In the fi
nal compost, 47% of the added 2,4-D carbon was mineralized, about 23%
was complexed with high-molecular-weight humic acids, and about 20% wa
s not extractable (humin fraction). Less than 1% of the added C-14 was
present in water expressed from the finished compost, suggesting a lo
w potential for leaching of 2,4-D. Very little volatilization of 2,4-D
occurred during composting. It is of interest that our results indica
te active mineralization of 2,4-D at composting temperatures of 60 deg
rees C because microbial 2,4-D degradation at thermophilic temperature
s has not been previously documented.