Biomarkers in mussels from a copper site gradient (Visnes, Norway): An integrated biochemical, histochemical and histological study

Abstract

In the present work, mussels ( Mytilus edulis) were transplanted into a copper (Cu) gradient in Visnes (Norway) for a period of 3 weeks during November 2003. Sites 1 and 2 showed similar low levels of Cu, site 3 had intermediate Cu levels and site 4 was the most polluted with Cu as confirmed by AAS of digestive gland tissue. Values of lysosomal membrane labilization period were significantly lower at sites 3 and 4 compared to sites 1 and 2. The volume density and size of lysosomes was significantly decreased at site 4. The volume density of neutral lipids was also significantly lower at site 4 compared with the rest of sites. The volume density of lipofuscins showed significantly higher values at sites 2 and 3 compared to the reference site 1. Similar results were obtained regarding bioavailable metal levels measured by autometallography. All together, results are indicative of exocytosis of metal-containing lysosomes and lipofuscins to the digestive tubule lumen in mussels from site 4. In fact, autometallographic metal deposits were detected in digestive tubule lumen, brown cells and stomach in site 4 mussels. In agreement, there was a loss of digestive cells in mussels from site 4 (atrophy of the digestive epithelium) and cell type replacement (diminished volume density of digestive cells and increased volume density of basophilic cells). In conclusion, selected biomarkers indicated that mussels transplanted to sites closest to the Cu mine showed significant differences in metal accumulation pattern and in organization of the digestive gland tissue. Finally, female mussels closest to the Cu mine showed advanced gametogenesis with higher gonad index and vitellogenin-like protein levels than mussels at sites 1 and 2.