臺灣烏腳病疫區含砷地下水釋出因子及其生物復育

Abstract

飲用含砷地下水對人類健康所造成的危害已是全球性的議題。雖然地下水含砷在台灣很早就被發現，但影響砷釋放的因子以及如何降低砷汙染仍需探討。本研究中，我們討論農業行為裡肥料的使用(磷肥、銨肥)對砷釋出的影響，並從砷汙染地區篩選出一株具有三價砷氧化能力的菌株，探討其應用於砷的生物復育之潛力。實驗結果顯示，在厭氧環境下磷肥與銨肥皆會使砷自土壤中釋放到地下水。此外，添加磷肥與銨肥會加速鐵的釋出並改變微生物群相。As7325為自砷汙染地區篩選出來的細菌，屬於Pseudomonas屬，異營菌。As7325最適合生長的溫度為30oC，最適合生長的酸鹼值約為7。As7325對砷具有高抗性，可抵抗1 mM三價砷與高於100 mM五價砷。由砷的氧化實驗中發現，利用現地地下水在好氧環境條件下，As7325可以在一天內將30 μM (~ 2250 μg/L)三價砷全部氧化成五價砷。此外，經冷凍乾燥後的As7325可用來做為生物吸附劑；實驗結果顯示As7325能在六天內百分之百吸附6.67 μM (~ 500 μg/L)或13.33 μM (~ 1000 μg/L)的五價砷。以上結果皆顯示As7325在砷的生物復育上具有很大的應用潛力。

The contamination of groundwater with arsenic is a major concern to public health from local to international. Although arsenic groundwater problems in Taiwan had been noted for several years, the factors affecting arsenic release and technology to significantly reduce arsenic level still remain elucidated. In this study, we investigate the effect of agricultural behavior such as fertilizing (ammonium and phosphate) on arsenic mobilization, and isolate an arsenite-oxidizing bacterium As7325 to examine its potential for arsenic bioremediation. The results showed that under anaerobic condition, both phosphate and ammonium caused arsenic release from sediment to groundwater. In addition, the addition of phosphate and ammonium also enhanced the release of ferrous and changed the microbial communities. Bacterial strain As7325, which was isolated from the arsenic-contaminated site, belongs to the genus of Pseudomonas. Strain As7325 is a heterotroph. The optimal temperature for growth was 30oC and the pH was about 7. Strain As7325 could resist high concentration of arsenic with minimum inhibitory concentration at 1 mM for arsenite and over 100 mM for arsenate. Strain As7325 could completely oxidize 30 μM (~ 2250 μg/L) arsenite using in situ groundwater within 1 day under aerobic condition. In addition, lyophilized cell pellet of strain As7325 was used as a biosorbent and could adsorb 6.67 μM (~ 500 μg/L) and 13.33 μM (~ 1000 μg/L) arsenate near 100% at 6-day period. The results showed that strain As7325 has the potential for bioremediation of arsenic.