LAUSR

BACKGROUND Algal infestation in Korean lakes, rivers, and in agroecosystems is a catastrophic problem resulting in contaminated drinking and agricultural irrigation water. Developing allelochemical-based algicides has previously faced difficulties, including dosage requirements and chemical instability. Despite these challenges, these algicides have enormous potential for eco-friendly use. This study presents the efficient use of tannin derivatives as antialgal chemicals modeled on a tannin-rich stem extract of Rhus chinensis in a thermal processing application. RESULTS Tannic acids were the key component of algal necrosis in R. chinensis stem extract, and although heat extraction from the stem increased the crude extraction yield 1.8-fold, the procedure induced the conversion of tannic acids to gallic acid, resulting in lower antialgal activity. Gallotannin showed stronger antialgal activity (LD50 = 44.6 mg L-1 ) than gallic acid (LD50 = 99.2 mg L-1 ), and the nonheated extract exhibited 3.7-fold lower LD50 (0.66 g L-1 ) than the heated extract (LD50 = 2.45 g L-1 ), resulting in 2.6-fold higher content of gallotannin. CONCLUSION These results demonstrate heat treatment of R. chinensis stems during the extraction process is not beneficial to algal control because of the acceleration of thermal tannin degradation, despite it showing higher crude extract yields. Therefore, it is suggested extraction processes minimizing the loss of tannic acids should be the preferred methods used to develop tannin-based natural algicides for controlling algal infestation. This article is protected by copyright. All rights reserved.