The complexities associated with predicting the consequences at the ‘organism level’ of variations of specific antioxidant defences have been recently overcome by the ability to quantify an index of specific biological resistance to various kinds of ROS.

The total oxyradical scavenging capacity (TOSC) assay has been used in three species of scallops for quantifying their ability to neutralize peroxyl (ROO^√) and hydroxyl (√OH) radicals and peroxynitrite (HOONO). Adamussium colbecki and Chlamys islandicus represent key organisms for monitoring Antarctic and Arctic regions while Pecten jacobaeus was chosen for a comparison with a related temperate species. TOSC values for ROO√ were significantly higher in A. colbecki indicating this species as the most efficient scavenger of ROO√. Mediterranean scallops had the lowest TOSC for ROO^√. A. colbecki also exhibited the highest scavenging capacity for √OH with values more than 2-fold greater than for C. islandicus and P. jacobaeus. TOSC for HOONO was lower for all scallops as compared to those for ROO√ or √OH. TOSC for microsomes was not significantly different among the species for any ROS studied, and the percentage contribution to the specific TOSC for the various oxidants of microsomes of all scallops accounted for 1–3% of the total TOSC of the post-mitochondrial fraction. The specific TOSC of scallop microsomes for √OH was approximately ten times lower than that for ROO√ or HOONO.

The higher basal capability of the Antarctic scallop to neutralize different reactive oxygen species is discussed in terms of a possible adaptation to this extreme environment and TOSC is validated as a quantifiable measure of susceptibility to oxidative stress in marine organisms.