The red alga Asparagopsis taxiformis\Falkenbergia hillebrandii–a possible source of trichloroethylene and perchloroethylene?

Trichloroethylene (C2HCl3) and perchloroethylene (C2Cl4) are widely used industrially as solvents, dry cleaning, and degreasing agents, and the annual release from such sources is estimated to be 200,000 tons for the former and 300,000 tons for the latter. In European waters typical background concentrations range from 0.01 to 5 ng L21, with higher levels in ground waters of some areas (Herbert et al. 1986). The environmental concentrations of both compounds have been subject to close regulatory scrutiny, and the maximum allowable concentrations in effluent have been based on the principle that these compounds are entirely anthropogenic in origin. Interestingly, McCulloch and Midgley (1996), using the best available estimates of the atmospheric lifetime and atmospheric concentrations of trichloroethylene (Koppmann et al. 1993), have found a large discrepancy between the observed concentrations of trichloroethylene in each hemisphere and the concentrations calculated from the estimated anthropogenic inputs. A total source strength of the order of 1.5 million tons per annum appears to be necessary to explain ambient concentrations of the compound in the atmosphere, an amount sevenfold higher than that calculated as emanating from anthropogenic sources. In this context, the report by Abrahamsson et al. (1995a) that both compounds are produced by a wide range of macroalgal species of both temperate and tropical origin assumes considerable significance. These workers also reported release of both chlorocarbons by the red microalga Porphyridium purpureum. In their investigation, Abrahamsson et al. (1995a) employed purge-and-trap techniques to concentrate volatiles and subsequently determined halocarbons by gas chromatography with electron capture detection, but no unequivocal chemical identification of the compounds was performed. Release rates from macroalgal species were mostly in the range of 0.020 to 7 ng g21 FW h21 for trichloroethylene and 0.0026 to 0.3 ng g21 FW h21 for perchloroethylene. However, two subtropical red algae Asparagopsis taxiformis (Delile) Trev. and Falkenbergia hillebrandii (Born.) Falkenb. displayed very much higher rates of trichloroethylene production, 36 and 3,400 ng g21 FW h21, respectively. Both algae also released significant amounts of perchloroethylene, with production reported at 0.0021 and 8.2 ng g21 FW h21, respectively. F. hillebrandii is now considered to be the tetrasporophyte phase in the life history of A. taxiformis so that the two species are actually conspecific (Dixon and Irvine 1977). However, the only other Asparagopsis species currently recognized, the cold water A. armata, has a Falkenbergia phase (F. rufolanosa), which is considered morphologically indistinguishable from F. hillebrandii, so some confusion has arisen in the literature as to the exact taxonomic identity of various Falkenbergia isolates collected. Indeed, recent investigations of Falkenbergia isolates collected from locations worldwide in which total DNA restriction fragment length polymorphism was probed using organellar DNA suggests that a third species of the genus may exist (Nı́ Chualáin 1997; Marshall et al. 1999). We have attempted to confirm the observations of Abrahamsson et al. (1995) on F. hillebrandii using gas chromatography/mass spectrometry to provide unequivocal chemical identification of halocarbons. We have determined rates of production of trichloroethylene and perchloroethylene by laboratory grown cultures of 12 isolates of Falkenbergia phases originating from warm and cold water locations throughout the world, including Gran Canaria, where Abrahamsson et al. (1995) collected the Falkenbergia sample that they examined. We also collected fresh samples of the alga from Gran Canaria and Ireland. Measurements have been conducted during exposure to both normal and high irradiances, as it is known that increased irradiance can stimulate production of volatile halocarbons by marine algae (Mtolera et al. 1996).