The scrap metal dealers in Wanli in Tainan want to extract the most valuable metals, so they wash the scrap in acid. "Low-value" copper is washed out with the acid, and flows into the neighboring Er-jen River, both of whose banks are planted with the hollow green veggie. "The content of copper in the convolvulus is very high," says Wang.
台南灣里廢五金業者為了取得貴重金屬，酸洗廢五金，「廉價」的重金屬銅也跟著被酸洗而出，流入鄰近的二仁溪，溪兩岸是空心菜園，「菜裡的銅含量很高」，王銀波說。