六種重金屬之浮萍毒性試驗

Toxicity tests of six heavy metals using two common duckweeds in Taiwan

"浮萍科（Lemnaceae）植物為分佈廣泛、生長快速、形態簡單且易培養之水生維管束漂浮植物，這些特點使其適用於水域或溼地之環境污染物監測。本研究選擇兩種臺灣常見浮萍科植物青萍（Lemna aequinctialis Welwitsch）及紫萍（Spirodela punctata（G. F. W. Meyer）Thompson），進行鎘（Cd）、鋁（Cr）、銅（Cu）、鎳（Ni）、鉛（Pb）及鋅（Zn）等六種重金屬之植物毒性試驗（phytotoxic test），包括建立試驗條件、觀察受害徵狀並計算4天及7天的50%生長抑制濃度（IC_（50），50% growth inhibitory concentration）評估兩種浮萍科植物對重金屬的敏感性。試驗結果顯示，重金屬對青萍之4天及7天的IC_（50）值分別為銅0.34、0.20 mg/L，鎘0.63、0. 23 mg/L，鉻2.99、2.00 mg.L，鎳1.24、0.98 mg/L，鋅30.1、20.0 mg/L;重金屬對紫萍之4天及7天的IC_（50）值分別為銅0.16、0.11 mg/L，鎘0.17、0.09 mg/L，鉻1.24、1.08mg/L ,鎳3.00、1.82mg/L，鋅20.4、12.2 mg/L;由於鉛於培養液中會出現沈澱的現象，因此鉛是以去離子水配製進行實驗，對青萍及紫萍4天的IC_（50）值分別為0.30、0.14 mg/L。重金屬對浮萍葉狀體（fronds）造成的為害徵狀類型包括葉狀體黃化、白化、組織壞死、變形、葉狀體分離及失去浮性等，浮萍根部受重金屬影響會出現生長受抑制或斷裂的現象。根據IC_（50）值，重金屬對青萍的植物毒性依序為銅＞鎘＞鎳＞鉻＞鋅；重金屬對紫萍的植物毒性為銅為銅≈鎘＞鉻＞鎳＞鋅。由青萍及紫萍對不同重金屬毒性反應之高低及所呈現之受害徵狀，顯示本土浮萍科植物具有應用為放流水及工業廢水中重金屬監測指標之潛力。"

"Duckweeds (family Lemnaceae) are widely distributed, floating vascular plants. Their small size, structural simplicity, rapid reproductive rate, and ease of culture have allowed them to be used as test species when monitoring aquatic and wetIand pollution. In this study, Lemna aequinoctialis Welwitsch and Spirodela punctata (G. F. W. Meyer) Thompson, two common duckweed species in Taiwan, were used in a phytotoxic assessment of six heavy metals: cadmium (Cd), chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), and lead (Pb). To evaluate the duckweeds' response to heavy metals, static renewal toxicity tests were performed, and frond number was used to calculate IC_(50) (50% inhibitory concentration) values after 4 d and 7 d of exposure. The IC_(50) values for L. aequinoctialis at days 4 and 7 were, respectively, 0.34 and 0.20 mg/L for Cu, 0.63 and 0.23 mg/L for Cd, 2.99 and 2.00 mg/L for Cr, 1.24 and 0.98 mg/L for Ni, and 30.1 and 20.0 mg/L for Zn. The IC_(50) values for S. punctata at days 4 and 7 were, respectively, 0.16 and 0.11 mg/L for Cu, 0.17 and 0.09 mg/L for Cd, 1.24 and 1.08 mg/L for Cr 3.00 and 1.82 mg/L for Ni, and 20.4 and 12.2 mgIL for Zn. Because Pb in the culture medium will precipitate, Pb was prepared in deionized water. The 4 d Pb IC_(50) values for L. aequinoctialis and S. punctata in deionized water were 0.30 and 0.14 mg/L, respectively. The symptoms of toxic injury included chlorosis, whitening, necrosis, deformation, colony breakup, and loss of buoyancy. In addition, some metals resulted in growth inhibition or destruction of duckweed roots. Based on the ICso values, the toxicity to L.aequinoctialis was Cu ＞ Cd ＞ Ni ＞ Cr ＞ Zn and the toxicity to S. punctata was Cu ≈ Cd ＞ Cl' ＞ Ni ＞ Zn. The results suggest that L. aequinoctialis and S. punctata are suitable as bio-indi cators when monitoring effluent and industrial wastewater and are useful for studying the phytotoxic effects of heavy metals."