Lysosomal enlargement and lysosomal membrane destabilisation in mussel digestive cells measured by an integrative index

Lysosomal responses (enlargement and membrane destabilisation) in mussel digestive cells are well-known environmental stress biomarkers in pollution effects monitoring in marine ecosystems. Presently, in laboratory and field studies, both responses were measured separately (in terms of lysosomal volume density - Vv - and labilisation period -LP) and combined (lysosomal response index - LRI) in order to contribute to their understanding and to develop an index useful for decisions makers. LRI integrates Vv and LP, which are not necessarily dependent lysosomal responses. It is unbiased and more sensitive than Vv and LP alone and diminishes background due to confounding factors. LRI provides a simple numerical index (consensus reference = 0; critical threshold = 1) directly related to the pollution impact degree. Moreover, LRI can be represented in a way that allows the interpretation of lysosomal responses, which is useful for environmental scientists.     

Application of a battery of biomarkers in mussel digestive gland to assess long-term effects of the Prestige oil spill in Galicia and the Bay of Biscay: lysosomal responses

In order to assess the long-term lysosomal responses to the Prestige oil spill (POS), mussels, Mytilus galloprovincialis, were collected in 22 localities from Galicia and the Bay of Biscay (North Iberian peninsula) in July, and September 2003, April, July, and October 2004-2005 and April 2006. Lysosomal membrane stability (labilisation period, LP) and lysosomal structural changes (lysosomal volume density, Vv(L) and lysosomal surface-to-volume ratio, S/V(L)) were measured as general stress biomarkers. The most remarkable long-term effects after the POS were drastic changes in lysosomal size (lysosomal enlargement) and membrane stability (extremely low LP values) up to April-04. Later on, a recovery trend was envisaged all along the studied area after July-04, albeit membrane stability continued to be below 20 min throughout the studied period up to April-06, which indicates a "distress-to-moderate-stress" condition. Lysosomal Response Index (LRI) revealed that environmental stress was more marked in Galicia than in the Bay of Biscay, mainly in the first sampling year, although a "moderate-to-high-stress" condition persisted until July-05. Overall, although lysosomal size returned to reference values, membrane stability was not fully recovered indicating a stress situation throughout the studied period.