Geographical variation and partition of metals in tissues of Octopus vulgaris along the Portuguese coast

Zinc, Cu, Cd, Pb and Hg were determined in mantle, arm and digestive gland of 59 individuals of Octopus vulgaris captured at six sites along the Portuguese coast. Metal concentrations in tissues did not vary significantly (P<0.05) with size/weight, sex or sexual stage. The abundance of metals in each analysed tissue was: Zn>Cu Cd>Pb>Hg. Concentrations in the digestive gland reached one (Pb, Hg) and two (Zn, Cu, Cd) orders of magnitude higher than those found in arm and mantle, which indicates that the digestive gland contains the major storage sites for these elements, acting as a detoxification organ. However, concentrations in the digestive gland showed contrasting geographic patterns: Zn, Pb, Cu and Hg were higher in the Southern stations, while Cd levels increased drastically in Northern stations. This increase is in line with the contrasting Cd distribution in coastal waters. The lack of relations between metal concentration in tissues and biological parameters facilitates the recognition of those spatial patterns. The geographical contrast of Cd is extended to the accumulation in mantle and arm. A possible explanation for these enhanced values is that threshold level for Cd accumulation in digestive gland was attained and detoxification processes eventually modified.