119th General Meeting of the KCS

Type Poster Presentation
Area 환경에너지
Room No. 포스터발표장
Time 4월 20일 (목요일) 11:00~12:30
Code ENVR.P-512
Subject The photodemethylation of methylmercury in seawater: the influence of dissolved organic matter
Authors 김지희, 한승희*
GIST 환경공학과, Korea
Abstract The methylmercury (MeHg) photodemethylation (PD) with dissolved organic matter (DOM) can occur via two potential pathways in seawater: PD by photochemically produced reactive intermediates (PPRIs; 1O2, ³DOM*, e-aq, ·OH) and direct PD of MeHg-DOM complexes. We investigated the mechanisms of DOM mediation by measuring photodemethylation rate constants (kpd) in artificial seawater under UV-A (365 nm), in the absence/presence of Suwannee River Humic Acid/Fulvic Acid (SRHA, SRFA), Pony Lake Fulvic Acid (PLFA). A predominance of MeHg-SRHA species increased the kpd by 2-5 times that of MeHgCl. The kpd for SRHA was 0.010 h-1, and it decreased to 0.0057 h-1 (∙OH quencher) and 0.026 h-1 (1O2 quencher). In similar, the kpd was 0.016 h-1 for PLFA, and it decreased to 0.0125 h-1 (∙OH quencher) and 0.0085 h-1 (1O2 quencher). These results imply that microbial FA has higher photosensitization effects than terrestrial HA, and 1O2 is more important than ∙OH. Additional experiments with model compounds showed that the PD rate was higher by an order of magnitude in the presence of aromatic thiols (thiosalicylic acid, TA, 0.37 h-1) than aromatic carboxyls (salicylic acid, SA, 0.010 h-1) or nonaromatic thiols (glutathione, GT, 0.019 h-1). It was interesting to find that the kpd were lower in ∙OH quencher (0.0066 h-1 for GT, 0.0055 h-1 for SA) than with the 1O2 quencher (0.012 h-1 for GT, 0.0074 h-1 for SA) for nonaromatic thiols and aromatic carboxyls. The kpd for aromatic thiols were similar for both quenchers (0.45 h-1 for 1O2 quencher, 0.40 h-1 for ∙OH quencher) and these values were comparable to those determined without quenchers, implying that the role of PPRIs is not significant. Overall, direct PD of MeHg-DOM complexes via intramolecular charge transfer is suggested as a major mechanism for aromatic thiol, while PD by PPRIs is suggested for natural HA/FA. Further studies are necessary to identify effects of 3DOM* by using 3DOM* quencher.
E-mail wlgml21@gist.ac.kr