臺灣地區過氧硝酸乙釀醋污染物對萵苣之影響

Abstract

台灣地區自1989年起已有本地種劍葉萵苣(Lactuca sativaL. cv. Sword Leaf)及圓葉萵苣(L. sativa L. cv. Round Leaf)不斷出現類似過氧硝酸乙醱醋(Peroxyacetyl nitrate，簡稱PAN）造成的下表面亮銅化(Bronzing)及銀白化(Silvering)病徵。經調查受害品種尚有盤萵苣(L. sativa L. cv. Pan Leaf)等。植物受害典型病徵一般在數小時或一天內開始呈現，且其分佈依不同葉齡及組織成熟度而呈特殊橫帶狀分佈致使幼葉之葉尖，剛成熟的上半葉，及已成熟的下半葉出現較多病徵。此些特殊病徵及其分佈特性經以人工產製之PAN氣體在光線充足的連續攪拌 薰氣箱(Continuously stirred tank Reactor)內對各種萵苣薰氣，結果皆能證實係因PAN所引起，而利用臭氧進行相同的處理則不能產生相同的病徵與病情。人工薰氣試驗亦能測出五種萵苣的敏感度大小分別是劍葉萵苣＞圓葉萵苣＞盤萵苣＞嫩莖萵苣＞皺葉萵苣，此與天然受害所見之敏感度十分一致。進一步以氣相層析儀配合電子捕捉檢知器測定大氣中之PAN濃度，並以氮氧化物分析儀加以校正，吾人可知台北市在台灣大學附近之PAN濃度最高可達27 ppb而其發生皆在晴天風小、空氣污濁之時，而在降雨日、陰天、風大之日皆不存在，污染日中PAN之高峰出現在每日中午時分，例如1992年6月共有6日污染較重，其中有3日造成劍葉萵苣的受害。劍葉萵苣及圓葉萵苣經證實可供做PAN污染之田間指標植物，利用此些指標植物不惟可供研判PAN發生為害頻率，亦可提供了解PAN真正的為害面積範圍。利用此些技術可證明目前在台北盆地約500平方公里，台中、彰化、南投約400平方公里及高雄、屏東約1,200平方公里的地區，皆屬目前PAN的為害區。相信目前三大地區的受害情況實與美國洛杉磯地區不相上下，而其原因可能與國內機車太多有關，欲求PAN之防制，自然也需環保署及國人的充分努力與配合。 Bronzing and silvering on lower leaf surfaces of Sword-leaved lettuce (Lactuca sativa L. cv. Sword Leaf) and Round-leaved lettuce (L. sativa L. cv. Round Leaf) were first found in Taipei area in 1989. Later these peroxyacetyl nitrate (PAN)-type symptoms were also found in Taichung and Kaohsiung areas and on more lettuce cultivars, such as Pan-leaved lettuce. Usually the typical symptoms developed within one day after a heavily polluted sunny day with still wind. They were restricted to the tip portion of young leaf, midsection portion of newly developed leaf, and sometimes to the base portion of mature leaf. Same symptoms and similar distribution type can be simulated from a fumigation test with lettuce plants using man-made peroxyacetyl nitrate at phytotoxic concentrations in continuously stirred tank reactors (CSTRs) in greenhouse. While these symptoms were completely different to those exhibited in an ozone fumigation test using the same experimental device. Results from fumigation test also showed that among five cultivars or varieties of lettuce, the sensitivity to PAN was Sword Leaf > Round Leaf > Pan Leaf > Celtuce > Crisp Leaf. The similar order can also be figured out after a heavily polluted day in the greenhouse having these cultivars or varieties planted in together. Measurement of the PAN in the Taipei atmosphere near National Taiwan University showed that in smogy noon time it might reach as high as 27 ppb, but it was undetectable in those days with rainy, cloudy, or windy weather. In the whole month of June, 1992, there were 6 days showing high concentrations of PAN near the noon time, but only 3 of them accompanied with lettuce injury in next morning in the greenhouse. It was, therefore, possible to use Sword-leaved lettuce or Round-leaved lettuce as PAN bioindicator to investigate the occurrence and severity of PAN injury in other parts of Taiwam Data in the past 3 years showed that PAN ia at present affecting the area of about 500 square km in Taipei, 400 square km in Taichung, and 1,200 square km in Kaohsiung. The severe PAN pollution seemed to be highly correlated with the high number of motorcycle here in Taiwan, and is a big challange for Taiwan EPA and Taiwan people at present and in the future.