Toxic hydrogen peroxide (H202] is photochemically generated in hyperoxic and normoxlc intertidal pools. Surprisingly high amounts of H202 penetrate the redoxcline, and are measurable in pore water in spite of the anoxic conditions prevailing there. Bioturbate macrofauna inhabiting these sediments encounters oxic conditions with peroxide in surface pools and anoxic conditions with peroxide in the sediment. We studied antioxidative properties in the polychaete Nereis diversicolor. Antioxidant enzyme activities of catalase and superoxide dismutase (SOD) showed annual variations correlated to the environmental peroxide concentrations. Epitokous specimens from April exhibited very high enzyme activities. Catalase was predominantly localised in the mitochondria and is inducible by peroxide incubation under experimental conditions. SOD activities were not inducible during oxic peroxide incubation. In contrast, SOD had higher activities when the worms were kept anoxically in the presence of hydrogen sulfide (100 pM) or hydrogen peroxide (5 PM). The radical stress the worms encountered during anoxic peroxide incubation was reflected by a highly increased lactate formation.Under oxic conditions 500 nM H202 decreased oxygen uptake of N. diversicolor by 38%. In epitokous N. diversicolor, this was accompanied by a conversion of heme to the green pigment biliverdin, a potent antioxidant. Billverdin was accumulated by the worms dunng oogenesis under natural conditions. Therefore its formation during spawning seems to be a response to increasing hydrogen peroxide concentrations in sediment pore water during spring. Biliverdin was not formed under anoxic conditions, because the conversion requires oxygen. Atokous worms lacked the ability to form biliverdin when exposed to peroxide.
Oysters, Crassostrea rhizophorae, were reciprocally transplanted to two different sites: a contaminated site in the Cotegipe Channel at Aratu Bay and an uncontaminated site at Cacha-Prego, inside and outside of Todos os Santos Bay (Brazil), respectively. Trace metal accumulation was measured after 0, 15, 30, and 60 days of exposure at the contaminated site. Oysters transplanted for 60 days from the clean to the contaminated site had accumulated cadmium and lead to similar concentrations as found in the native oysters. They had also accumulated copper and zinc, but to lower levels compared to native specimens. Elimination experiments were carried out by transplanting oysters in the reverse direction. After 30 days, concentrations of cadmium and lead had decreased to levels comparable to those in the native specimen, whereas concentrations of copper and zinc did not diminish. A second elimination experiment, bringing back to Cacha-Prego oysters that had been exposed 60 days at Cotegipe Channel, indicated stronger decreases of copper and lead, but no clear changes of cadmium and zinc concentrations. The accumulation experiment with C. rhizophorae is useful to estimate trace metal bioavailability and changes in concentrations as a function of time at the contaminated site. The different results of elimination experiments in the uncontaminated site suggest different degrees of trace metal fixation after long-term and short-term accumulation periods.
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