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Glyphosate residue in rice and soil environment in central Taiwan area
Feng, Wamg Jane
本試驗之目的乃在建立嘉磷塞分析與萃取濃縮方法、嘉磷塞依國內推薦用量於台灣中部地區水稻栽培整地前及植前施用後，於一、二期作水稻各生育階段，分析植體中嘉磷塞之殘留量及水田土壤中嘉磷塞殘毒變化‚以了解在台灣氣候環境下殘留量是否受到光照及微生物影響。利用HPLC分析法可在0.495-9.92 nmole範圍內獲致直線回歸，偵測極限為0.5 nmol。在萃取方法上，水稻植體之水萃取液及田水經NaOH調整pH植後，以陰離子交換管柱可回收80%嘉磷塞。土壤中之嘉磷塞分別以水、甲醇、及NaOH萃取回收率為63.4, 0.5及22.2%，且隨著藥劑濃度增加水萃取比例增加。
在植體分析部分第一期作施用藥劑後1個月內植體殘毒快速降低，於水稻分蘗期植體內嘉磷塞僅殘留32.2%，進入開花期、子粒充實期及收穫期，於植體及食用部位子粒內未發現殘留。第二期作可能因栽培初期氣溫仍高殘留土中之嘉磷塞分解較第一期作快，於水稻幼苗期以後各時期取樣分析時發現均無嘉磷塞殘留。此外，分析中部地區五處水田於兩期作每月固定取樣田水分析，兩期作之田水水樣中嘉磷塞殘毒分別低於0.2 及0.1 ppm。
Experiments were conducted to establish the extraction and analysis techniques of glyphosate in rice plant, paddy water and soil, seasonal changes of glyphosate residue in rice (Oryza sativa L.) plant and paddy soil in central Taiwan, as well as the glyphosate degradation in paddy soil were investigated. The quantitation methods of glyphosate with high performance liquid chromatography (HPLC) was assessed for its efficiency to detect glyphosate residue. A linear regression in the range of 0.495 to 9.92 nmol glyphosate could be observed by HPLC coupled with peroxidation and o-phthalaldehyde (OPA)-derivatization of the sample eluent. Anion-exchange column could yield 80% recovery rate of glyphosate from water extract of rice plants and paddy water. Extraction of glyphosate from paddy soil by using water, methanol and NaOH sequentially showed 63.4, 0.5 and 22.2% recovery rates of glyphosate, respectively, and the proportion of water-extractable fraction was increased with glyphosate concentration. In this study, analysis of glyphosate in rice plants of first crop (spring crop) showed that glyphosate absorbed by rice plants decreased rapidly within one month, and further decreased to 32.2% at tillering stage; subsequently, no glyphosate residue could be detected in plants and grain part of rice. However, higher temperature and light intensity in the early growth stage of rice plants for second crop (fall crop), in comparison with first crop, might accelerate glyphosate dissipation in the soil environment. Thus no glyphosate was found to accumulate in rice plants throughout the whole cropping season in fall. In addition, field study showed that glyphosate residues in paddy water in two crop seasons were lower than 0.2 and 0.1 ppm, respectively, at five locations in central Taiwan. In greenhouse study, none of the glyphosate in distilled water degraded after 12 months regardless of lighting. However, glyphosate in soil solution ensealed with plastic bag dissipated with time independent of lighting condition, but glyphosate dissipation was accelerated by light under aeration. In addition, biodegradation of glyphosate by microbes in soil was obvious, especially in aerobic condition. Microbes responsible for glyphosate degradation will be isolated and identified further.
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