Accumulation, responses and genotoxicity of trace elements in octopus vulgaris

Dissertação apresentada para obtenção do Grau de Doutor em Bioquímica pela Universidade Nova de Lisboa, Faculdade de Ciências e Tecnologia

Common octopus, Octopus vulgaris, is a sedentary cephalopod inhabiting coastal waters and thus susceptible to be exposed to local contamination. Octopuses were captured in three coastal areas with contrasting environmental contamination: Matosinhos, Cascais and Olhão. Levels of V, Cr, Fe, Co, Ni, Zn, Cu, As, Se, Cd, Hg and Pb were analysed in various tissues of octopus: digestive gland, gills, kidney, gonads, posterior salivary glands, branchial hearts, ink sac, stomach, skin, mantle and arm. The different metal concentrations in the eleven analysed tissues are apparently a consequence of the role of metals in metabolic functions (e.g. gonads, ink sac, kidney, gills and salivary glands), although non-essential elements in digestive gland, branchial hearths, kidney and ink sac may be linked to specific ligands or excretory/detoxification mechanisms. Metal levels found in octopus tissues (e.g. Cd, Pb and Hg) were in line with concentrations registered in the environment. Lead isotopic ratios in octopus digestive gland allowed separation of individuals according to environmental Pb sources (anthropogenic and natural). The consistent differences between organisms captured in the two areas (Matosinhos and Olhão) points that Pb isotopic signature provides a useful tool to distinguish octopus populations. Concentrations of Hg also responded to environmental availability and, for the first time, levels of MeHg were determined. Higher Hg, MeHg and Se concentrations were observed in digestive gland and MeHg (%) in mantle. Good relations were obtained between digestive gland and mantle for Hg and MeHg, suggesting an efficient transport from digestive gland and storage in mantle. Selenium seems to have a protective role against Hg assimilation. Demethylation processes may occur being more noticeable in organisms from the more contaminated area. When metals are accumulated, only a minor percentage is associated with organelles. However, levels in these sub-cellular fractions respond to the enhanced concentrations in the whole tissue. Moreover, it seems that the role of the elements in the cells, and consequently their association with the sub-cellular fraction, superimpose the response to availability. Within cytosolic fraction metals are associated either with low and high molecular weight proteins, being metallothioneins an important detoxification mechanism when levels, mainly Cd, exceeded a threshold value. Although different detoxification mechanisms were observed in octopus tissues, DNA damages were registered mainly in digestive gland. A good agreement was obtained with environmental availability, tissue function and cellturnover. Cadmium seems to be a strong strand breakage inducer. Octopus can be used as bioindicator.

Fundação para a Ciência e a Tecnologia, bolsa de doutoramento (SFRH/BD/37730/2007