DDT在亚热带环境和农业生态的行为研究Ⅱ．DDT在水稻植株中的残留动态

￣（１４）Ｃ－ＤＤＴ示踪实验结果表明：地处广州亚热带地区的水稻，施用ＤＤＴ农药，在植株各器官中消失很快，整株总的ＤＤＴ的衰变常数是２９．４×１０￣（－２）／ｄ，半衰期（Ｔ＿（５０））为２３．６ｄ，残留量与施药时到收获期时间的长短和施药次数有关，实验证明：可溶态ＤＤＴ约占总残留量的７５％，约有２５％转化为结合态ＤＤＴ；水稻在收获前１５ｄ进行最后一次施用ＤＤＴ１０００ｍｇ／ｋｇ是安全的。

Rcsidue and Fate of DDT in Subtropical Paddy Rice

The Residue and fate of DDT in paddy rice of subtropical environment were studied byradionuclear tracing. The results obtained were as follows:Loss rate of DDT was rapidly underthe subtropical agroecosystem in Guangzhou, Using normal spray dosage in agroecosystem,DDTresidue in spikes of paddy rice is not over the trace standard( 7 mg/kg),The DDT residue was2. 1 mg/kg in rice bran,1.8 mg/kg in grain residue was 5. 8 mg/kg in rice bran,4.5 mg/kg ingrain of rice when applicated three times at tillering stage,booting stage and filling stage, It main-lv exists in stems and leaves.Therefore ,using normal spray dosage 1000 mg/kg DDT of 15 daysbefore harvesting stage in subtropical crops is safe.