Isotopic composition of polyhalomethanes from marine macrophytes – systematic effects of the halogen substituents on isotopic composition

Abstract

Environmental context. Once released to the atmosphere, halocarbons are involved in key chemical reactions. Stable carbon isotope measurements of halocarbons can provide valuable information on their sources and fate in the atmosphere. Here, we report d 13 C values of 13 polyhalomethanes released from brown algae, which may provide a basis for inferring their sources and fate in future studies.Abstract. Halocarbons are important vectors of reactive halogens to the atmosphere, where the latter participate in several key chemical processes. An improved understanding of the biogeochemical controls of the production-destruction equilibrium on halocarbons is of vital importance to address potential future changes in their fluxes to the atmosphere. Carbon stable isotope ratios of halocarbons could provide valuable additional information on their sources and fate that cannot be derived from mixing ratios alone. We determined the d 13 C values of 13 polyhalomethanes from three brown algae species (Laminaria digitata, Fucus vesiculosus, Fucus serratus) and one seagrass species (Zostera noltii). The d 13 C values were determined in laboratory incubations under variable environmental conditions of light, water levels (to simulate tidal events) and addition of hydrogen peroxide (H 2 O 2 ). The d 13 C values of the polyhalomethanes ranged from À42.2 % (AE3.5 s.d.) for CHCl 3 to 6.9 % (AE4.5) for CHI 2 Br and showed a systematic effect of the halogen substituents that could empirically be described in terms of linear free energy relationships. We further observed an enrichment in the d 13 C of the polyhalomethanes with decreasing polyhalomethane yield that is attributed to the competing formation of halogenated ketones. Though variable, the isotopic composition of polyhalomethanes may provide useful additional information to discriminate between marine polyhalomethane sources.

Will Climate Change Influence Production and Environmental Pathways of Halogenated Natural Products?

“…Other sources of nHCs are microalgae and bacteria in sea ice ,, and frost flowers on sea ice . Production also occurs by reaction of dissolved organic matter (DOM) with oxidized halogen species at the air–ice interface and enzyme-mediated reactions with DOM in seawater. ,, Carbon isotopic composition has been suggested as a tool for discriminating nHCs produced by macroalgae, phytoplankton, and reactions of DOM …”

“…27,35,36 Carbon isotopic composition has been suggested as a tool for discriminating nHCs produced by macroalgae, phytoplankton, and reactions of DOM. 37 The nHCs produced by marine phytoplankton were reviewed and species grouped by tropical, subtropical, temperate, and polar zones. 17 The number of nHC compounds reported in a particular study varied from 1 to 11, which might be characteristic of the producing species or simply to the suite selected for analysis.…”

Foreword to the Special Issue on ‘Naturally Produced Organohalogens – Atmosphere and Soil’

“…Bahlmann et al [12] reported d 13 Cvalues of polyhalomethanes released from three brown algae species (Laminaria digitata, Fucus vesiculosus, F. serratus) and one seagrass species (Zostera noltii). d 13 C values for CHCl 3 and CHI 2 Br from laboratory incubations under variable light and water level conditions showed a systematic effect of the halogen substituents that could empirically be described in terms of linear free energy relationships (LFER) and may be used in future to discriminate between different marine sources.…”