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Download fileRole of Free Radicals/Reactive Oxygen Species in MeHg Photodegradation: Importance of Utilizing Appropriate Scavengers
journal contribution
posted on 2017-03-07, 00:00 authored by Xiaoxiao Han, Yanbin Li, Dan Li, Chang LiuA variety
of free radicals (FR)/reactive oxygen species (ROS) have
been proposed to dominate methylmercury (MeHg) photodegradation, primarily
based on the results of FR/ROS scavenger addition experiments. However,
in addition to eliminating FR/ROS, the added scavengers may also affect
the experimental results by altering some water chemical properties,
resulting in a misleading assessment of the importance of FR/ROS.
In this study, 20 common FR/ROS scavengers were evaluated in terms
of their influence on light absorbance, pH, MeHg analysis, MeHg-dissolved
organic matter (DOM) complexation, and the scavenger-induced degradation
of MeHg. Only nine scavengers were identified to be appropriate for
investigating MeHg photodegradation. By utilizing these appropriate
scavengers, direct photodegradation of MeHg-DOM complexes was found
to be the major pathway of MeHg photodegradation in Laoshan Reservoir
water and Stone Old Beach seawater. In contrast, MeHg photodegradation
in Ink River water primarily occurs through both ·OH and 3DOM* mediated indirect pathways and direct photodegradation
of MeHg-DOM complexes. The diverse pathways of MeHg photodegradation
in the tested water may be due to differences in water chemical properties.
A severe overestimation of the role of FR/ROS was observed when several
improper but commonly used scavengers were adopted, highlighting the
necessity of utilizing appropriate scavengers.