Removal of paclobutrazol from irrigation water using granular-activated carbon

A small-scale granular-activated carbon (GAC) system was evaluated for removal of the plant growth regulator paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)pentan-3-ol] from water. A solution with 50 A mu g L-1 of paclobutrazol was passed through canisters filled with 0.50-4.75 mm particle size (8 x 30 US mesh) granular-activated carbon at a flow rate of 6 L min(-1). Paclobutrazol solution was exposed to varying amounts of contact time with GAC by increasing the number of filters in series. Analysis of samples using liquid chromatography-mass spectrometry (LC-MS/MS) found that paclobutrazol concentration decreased by 90 and 99% with a contact time of 12 and 59 s, respectively. In bioassay tests, broccoli hypocotyls at 14 days were 104% longer and begonia dry mass was 36% greater when treated with solutions that had a contact time of 59 s compared with the 0 s of GAC exposure. With the highest GAC contact time, begonia dry mass was the same as for plants treated with a zero paclobutrazol solution. Bituminous coal and coconut shell GAC sources were equally effective in reducing paclobutrazol concentration based on broccoli hypocotyl length, and paclobutrazol concentration measured using gas chromatography-mass spectrometry (GC-MS). Removal of paclobutrazol was not affected by solution pH from 4.0 to 10.0.