Direct photolysis rates and transformation pathways of the lampricides TFM and niclosamide in simulated sunlight

Environmental Science & Technology
By: , and 

Links

Abstract

The lampricides 3-trifluoromethyl-4-nitrophenol (TFM) and 2′,5-dichloro-4′-nitrosalicylanilide (niclosamide) are directly added to many tributaries of the Great Lakes that harbor the invasive parasitic sea lamprey. Despite their long history of use, the fate of lampricides is not well understood. This study evaluates the rate and pathway of direct photodegradation of both lampricides under simulated sunlight. The estimated half-lives of TFM range from 16.6 ± 0.2 h (pH 9) to 32.9 ± 1.0 h (pH 6), while the half-lives of niclosamide range from 8.88 ± 0.52 days (pH 6) to 382 ± 83 days (pH 9) assuming continuous irradiation over a water depth of 55 cm. Both compounds degrade to form a series of aromatic intermediates, simple organic acids, ring cleavage products, and inorganic ions. Experimental data were used to construct a kinetic model which demonstrates that the aromatic products of TFM undergo rapid photolysis and emphasizes that niclosamide degradation is the rate-limiting step to dehalogenation and mineralization of the lampricide. This study demonstrates that TFM photodegradation is likely to occur on the time scale of lampricide applications (2–5 days), while niclosamide, the less selective lampricide, will undergo minimal direct photodegradation during its passage to the Great Lakes.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Direct photolysis rates and transformation pathways of the lampricides TFM and niclosamide in simulated sunlight
Series title Environmental Science & Technology
DOI 10.1021/acs.est.6b02607
Volume 50
Issue 18
Year Published 2016
Language English
Publisher ACS Publications
Contributing office(s) Upper Midwest Environmental Sciences Center
Description 9 p.
First page 9998
Last page 10006