Abstract :
Behavior and fate of 14C-2,4-dichlorophenoxyacetic acid (2,4-D) was studied in a Malaysian rice model agroecosystem. This model agroecosystem that consists of ricefield soil obtained from the Muda rice granary area, rice crop (Oryza sativa var. indica cv. Telok Kecai) and stream water; was set-up in a lysimeter system in the radioactive glasshouse. Radioactivity of Carbon-14 labeled 2,4-D were analyzed in water, soil, weed and rice crop by using the Liquid Scintillation Counting (LSC) technique. The level of radioactivity was monitored in surface water until 74 days after application (DAA). Radioactivity in surface water declined very rapidly. At 1 DAA, 77.7 x 10-3% of the total applied radioactivity was measured in surface water, which declined to 8.9 x 10-3% at 4 DAA, 1.1 x 10-3% at 6 DAA, and 0.7 x 10-3% at 8 DAA. Radioactivity in surface water stabilized but fluctuated between 0.1 x 10-3% and 0.6 x 10-3% of the total applied radioactivity, from 11 DAA until 74 DAA. Under the tropical climate of Malaysia, the half-life of 2,4-D herbicide in ricefield water was less than 4 days. The order of importance of bioconcentration value was in weed > rice root > rice leaf. Means of bioconcentration values calculated were 51.30 + 11.65 in the rice leaf, 127.85 + 46.76 in the rice root, and 362.69 + 286.30 in weed plants. 2,4-dichlorophenoxyacetic acid herbicide was taken up by weed more than rice root and leaf at 74 DAA.
