Nutrient level, microbial activity, and alachlor transformation in aerobic aquatic systems.
Alachlor (2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide) is a moderately toxic herbicide that is frequently found in agriculturally impacted surface waters. To assess primary mechanism(s) that affect its fate in aquatic systems, two field experiments were performed using large mesocosms (n=39) and smaller microcosms with and without microbial inhibitors (n=16). The mesocosm experiment tested the effect of fertility conditions on alachlor fate, assessing alachlor disappearance over time under oligotrophic (total phosphorus (TP) <12 microg/L) through hypereutrophic (TP>80 microg/L) water conditions. Whereas, the microcosm experiment assessed alachlor fate in the presence of microbial inhibitors that selectively blocked eubacterial (chloroamphenicol, streptomycin, and penicillin combined), eukaryotic (cycloheximide), and universal (all inhibitors) microbial activity. First-order alachlor transformation rate coefficients ranged from 0.006 to 0.042 day(-1) when microbial inhibitors were not present (half-lives from 16 to 122 days) with the highest rates occurring in hypereutrophic waters. Statistics indicated that mean TP, and universal and eubacterial small sub-unit rRNA level most closely correlated with transformation rate. Further, the inhibitor study indicated that alachlor transformation was biotic (>90%), but that high transformation rates only occurred when eubacterial and eukaryotic domains were both metabolically active. Our results confirm that alachlor transformation is primarily biotic; however, efficient biotransformation only occurs when both major microbial domains in aerobic systems are active.
Department of Civil and Environmental Engineering, University of Kansas, 4002 Learned Hall, 66045, Lawrence, KS, USA
Charles W
CW
Knapp
David W
DW
Graham
Gina
G
Berardesco
Frank
F
deNoyelles
Ben J
BJ
Cutak
Cynthia K
CK
Larive
D000081:Acetamides / Q000378:metabolism*; D001420:Bacteria, Aerobic / Q000235:genetics / Q000502:physiology; D001711:Biotransformation; D017753:Ecosystem; D004784:Environmental Monitoring; D005068:Eutrophication; D006540:Herbicides / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000032:analysis; D014871:Water Microbiology
D000081:Acetamides; D006540:Herbicides; D012335:RNA, Ribosomal; C000188:alachlor