本研究檢視汞污泥事件對台塑公司，及同產業的其他公司的股價行為有何影響?同時再就環保資訊揭露與環保處分金額兩層面，探討台塑汞污泥事件發生後的股價反應。由於台塑汞污泥事件歷經數年，故將觀察期區分為鐘觀察期 (事件前一日至事件後七日) 及長觀察期兩種，以市場模式被視塑膠產業各公司及產業投資組合的股價反應。另研究中採用迴歸分析檢視15家塑膠類股公司的環保資訊揭露多寡，與觀察期間股價反應間之關係。實證結果發現，台塑汞污泥事件發生當日，台塑公司本身及塑膠類股會產生負面的股價反應。在長觀察期方面，塑膠類股的股價反應並不明顯。本研究同時發現，公司事前持續於年報中揭露環保資訊內容者，在台塑汞污泥事件發生後，公司的股價會呈現負向的反應。

News of the illegal dumping of toxic industrial waste (nearly 3,000 tons of highly toxic mercury-tainted waste) near a Cambodian port of Sihanoukville by Taiwan's biggest conglomerate, the Formosa Plastics Group (FPG), was first surfaced in Taiwan's domestic press on December 16, 1998. Several tests of the waste were done by the independent parties produced a wide range of toxicity levels and determined that the waste materials were contaminated with high levels of mercury as well as a possible hazardous mixture of other metals. This study attempts to examine the relationship between the stock price behavior and the environmental disclosures on this environmental accident among plastics listed companies for which necessary data are available. This research adopts event study methodology and observes both short-window and long-window effects. The empirical results are: (1) For the short-window, both FPG and the plastic industry had negative stock price reaction upon the announcement of illegal dumping event; (2) For the long-window, the cumulative abnormal returns of plastics industry are positive but not significant statistically. (3) The consecutive environmental disclosures in the Annual Reports of plastics public companies had negative stock return on this environmental accident.