殺草劑對環境之影響

王一雄

國立台灣大學 農業化學系

           

殺草劑與生態環境之關係,以殺草劑在植物體中之吸收與代謝;殺草劑施用後在土壤環境中移動至河川等水體中之動態行為;殺草劑在水生生物體內之累積與釋放;以及殺草劑在農業模擬生態系中之傳送等四方面來探討。殺草劑在環境中之命運包括被土壤吸附、隨進入土壤之水移動、進行光化學分解、揮發至大氣中、被動植物吸收代謝及土壤微生物之代謝分解等。其進入生物體內之量受該環境中濃度之影響,在一定環境濃度下各生物均在短期間內在體內累積達到最高濃度,即使被持續保持在該環境中亦不致再提高其體內濃度,除非提高環境中殺草劑之濃度。在植物體內因僅有代謝作用,故殺草劑在植物體內之殘留較不易消失,動物由於兼有排泄與代謝之作用,而能很快的清除體內殺草劑。例如水生動物對於水中農藥之累積在3~5天內達最高濃度,將其移至清水,則體內濃度迅速減少,許多在3~5天內就沒有可檢出之殘留量,因動物有排泄作用,但在植物體內則只能代謝或移至老葉。在水中與在土壤中之微生物均可分解代謝環境中之殺草劑。但微生物的作用係進行礦化作用(mineralization)或併代謝作用(co-metabolism),對生態環境有影響,前者分解成無毒之二氧化碳,而後者則在體內代謝後成為未知毒性的有機產物。在體內累積及清除之快慢受生物體內脂肪含量之多少影響很大,由於食物鏈及生物濃縮之關係,脂溶性化合物之生物濃縮係數(bioconcentration factor, BCF)很大。

關鍵詞:環境因子、生態系、礦化作用、併代謝作用。

 

 

Environmental Impact by Herbicides

Wang Yei-Shung

Department of Agricultural ChemistryNational Taiwan University, Taipei, Taiwan

 

Abstract

Relationships between herbicide and ecological environment are considered in four aspects in this report, that are, absorption and metabolism of herbicides in  plants; the behavior of herbicides in soil and water after applied to soil environment; accumulation and release of herbicides in aquatic organisms; and transformation of herbicides in agricultural model ecosystem. Including soil absorption, movement in soil by water, photodecomposition, volatilize to air, and degradation by plants, animals and soil microorganisms will affect the fate of herbicide in environment. Environmental concentraion is a primary factor affect the amounts of herbicide residue in organisms. At one concentration level, organisms accumulate herbicides to a maximum residue within a short period, and then herbicide concentratin in organ- ism keep constant, no residues change is found unless the environmental herbicide concentraion level is changed. Dissipation rate of herbicides and their metabolites in animals is greater than that in plants, because in animals not only metabolism but excretion are presented. There are two actions that herbicide degradation by soil microogranisms, the one is mineralization, degraded to non-toxic inorganic matters such as carbon dioxide and water, and the other is co-metabolism, degraded to the toxicity-unknown organic products. The rate of accumulation and clearence of a herbicide in organisms is depended on the fat contents of organisms. More non-polar chemicals give higher bioconcentration factor (BCF).