Production of chloroform and other low molecular-weight halocarbons by some species of macroalgae

Abstract

The production of volatile low-molecular-weight halocarbons by macroalgae was investigated at a site on the west coast of Scotland. Levels of CH31, CH,Br,, CHBr,, CHBr,Cl, CHBrCl,, and CHC13 were elevated in beds of Laminaria digitata. Storage tests on 11 common species of brown, green, and red seaweeds indicated release of some or all of these compounds. Estimates of production rates were obtained from laboratory incubations and, where comparative data are available, are in the range of those previously reported. Measured rates of halomethane release varied with algal species and were inconsistent with halomethane formation by the release of HOBr to seawater and subsequent reaction with organic matter. The production of CHCl, was best explained by the presence of a chloroperoxidase enzyme. Laboratory experiments suggested that release rates can bc influenced by partial desiccation, light availability, tissue age, tissue wounding, and grazing. The release of CH31, CH,Br,, CHBr,, CHBr,Cl, and probably CHCl, by algae from within a rock pool was observed for the first time. Rates of in situ production were in broad agreement with laboratory studies. No production of Ccl, or of CHClCCl,, CCl,CCl,, or CH,CCl, was detected. In addition to CHBr,, macroalgae may be a significant source of CHCl, to the atmosphere. This study arises from an earlier investigation into the spatial and seasonal variations of low-molecular-weight (LMW) halocarbons in the southern North Sea (Nightingale 199 1). One of the main conclusions of the earlier study was that the main sources of bromoform (CHBr,), dibromochloromethane (CHBr,Cl), dichlorobromomethane (CHBrCl,), chloroform (CHCL,), and dibromomethane (CH,Br,) were in coastal areas. Moore and Tokarczyk (1993) reached the same conclusion during a study of halocarbons in the NW Atlantic, although measurements of CHC13 were not reported. In the North Sea, such a source could be biogenic, due, for example, to production by species of macroalgae that are widely distributed along the coast of the United Kingdom, or may be anthropogenic and formed via water chlorination (e.g. Carpenter and Smith 1978). Production of CH31 by macroalgae was first suggested by Lovelock (1975), who found a 1 ,OOO-fold elevation in concentration in Laminaria digitata beds off SW Ireland compared with open-ocean valucs. He observed no increase in inshore beds of fucoids, suggesting that production was species-dependent. Subsequently, elevated levels of CHBr,, CH,Br,, CHBr,Cl, and CH31 have been observed in seaweed beds (Dyrssen