CONICET | Buscador de Institutos y Recursos Humanos

The most important source for H202 formation are photochemical reactions between dissolved organic carbon (DOC) and ultraviolet radiation (RUV, 280-400 nm), particularly RUVB (280-320 nm). High H2O2 concentrations produce deleterious effects to organisms via oxidative damage, with cellular membranes and photosynthetic pigments being key targets. The objective of this study was to evaluate how the effect of the increases in RUVB, resulting from the decrease of the stratospheric ozone on the Beagle Channel, modify DOC photochemistry. The oxidative stress on phytoplankton was determined by exposure of cells to different H2O2 concentrations and natural solar radiation. All the experiments were carried out in the Beagle Channel (Ushuaia, 54º 52'S, 68º 18'W). Water samples were filtered through 0.4 um filters to eliminate phytoplankton and bacterioplankton cells. Two treatments were analyzed using four-replicate samples for each one: water exposed to RUV > 280 nm and to RUV> 320 nm as control. To evaluate the possible oxidative stress on phytoplankton the oxidation of 2´7´-diclorofluorescein diacetate was measured. Three phytoplankton communities were exposed to natural solar radiation at 0 (control), 20, 30, 40 and 60 uM H2O2. A positive regression was observed (P <0.05, r2= 0.89) in the production of H2O2 when exposing the seawater to RUV > 280 nm. In contrast, no significant regression (P> 0.05) was observed after exposure of the water to RUV > 320 nm. The different phytoplankton communities did not show significant oxidative damage due to H2O2 exposure at any of the concentratrions used. Conclusions DOC concentration in Beagle was of between 1000 and 2000 ug/l. The threshold RUVB dose producing H2O2 was 20 kJ/m2 The H2O2 concentrations generated by RUVB on DOC have not produced an oxidative stress in any of the phytoplankton communities studied.

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