Degradation of n‐Butylaminocyclohexyl phosphonic Acid di‐n‐Butylester (Buminafos) in Aqueous Medium.In aqueous medium, breakdown of Buminafos (1) is connected with total loss of its herbicidal activity. The phosphorus‐carbon bond is cleaved and n‐butylcyclohexylidene amine (3), cyclohexanone (5), phosphoric acid mono‐n‐butyl ester (4) (partly as n‐butylamine salt), and 1‐aminocyclohexyl phosphonic acid di‐n‐butylester (8) were found as degradation products of carbon‐14 labeled Buminafos. Identification was performed by MS, GC/MS,1H‐ and31P‐n.m.r. spectroscopy, by detection of phosphorus, and by