Visible light-dependent degradation of long-chain alkenes in killed cells of Emiliania huxleyi and Nannochloropsis salina

Photosensitized degradation rates of phytoplanktonic n-alkenes under visibl e light exposure were determined in laboratory experiments. Killed cells of Emiliania huxleyi and Nannochloropsis salina were used as source of biogen ic alkenes. In E. huxleyi killed cells, minor C-31 and C-33 n-alkenes were strongly photodegraded, while the major C-37 and C-38 n-alkenes appeared pa rticularly recalcitrant towards photochemical processes. This particular ph otochemical recalcitrance has been attributed to the chemical structure and localization of these hydrocarbons in the cells. Most of the n-alkenes of N. salina were strongly photodegraded in killed cells. The photodegradation of phytoplanktonic alkenes showed apparent second-order kinetics with resp ect to light exposure, and the half-life doses obtained logically decrease with increasing number of double bonds in these compounds. These results st rongly suggest that significant amounts of phytoplanktonic n-alkenes must b e photodegraded in the euphotic zone of the oceans during senescence. (C) 2 001 Elsevier Science Ltd. All rights reserved.