关键词: 氯硝柳胺乙醇胺盐, 氯硝柳胺, 螺灭杀, 高效液相色谱法, 水体, 降解

Abstract:

Objective To establish a sensitive and accurate analytical chemistry method as an alternative to biological tests for determination of degradation dynamics of a molluscicide, Luomiecide (50% wettable powder of niclosamide ethanolamine salt), in laboratory and in water bodies. Methods High performance liquid chromatography (HPLC) was performed using a C₁₈ column and a mobile phase of methanol-0.01 mol/L sodium acetate (87∶13) with the theoretical plate number ＞3000; a 100 μl, UV detection wavelength of 330 nm was chosen. Laboratory simulation of degradation was conducted, where vials of luomiecide solutions were placed in the sun for 6 times of sampling in 10 d; a parallel couple of samples were either directly filtered or solubilized with organic solvents, and measured. Another 6 samples were collected on the spot of molluscicidal application, treated and detected following the same procedures. Results The minimum detectable concentration by HPLC was 0.007 mg/L, the linear range 0.01-2.42 mg/L (r＝0.9999, n＝12) and the separation between main peaks and impurities ＞1.5. In laboratory simulation, the original drug concentration dropped rapidly within the first 3 d, with a decrease of 83% on day 10 compared with that on day 0, and the measured concentration on day 7 reduced to the minimum effective level. The bottoming flocculi were identified as niclosamide. As for on-site application, the measured concentration on day 2 was already lower than the minimum effective level, which might be due to the scarce representativeness of the used samples. Conclusion The laboratory study revealed that the decreasing molluscicidal effect of the agent in water with time was a result of the gradual degradation of the agent to niclosamide monomers in water, which again accumulated to form insoluble flocculi and led to concentration decrease, other than chemical degradation of niclosamide. Analytical chemistry methods were not applicable for on-site monitoring of large water bodies.

Key words: Niclosamide ethanolamine salt, Niclosamide, Luomiecide, High performance liquid chromatography, Water, Degradation