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Y. Ruiz et al.
products of the abnormal cells, that because of their colour, are named by several
authors “brown cells” (Cheng 1984; Zaroogian et al. 1989). However, haemocyte
proliferation may becoming uncontrolled and malignant, resulting in what has
been described as disseminated haemocitary neoplasia (Yevich and Barszcz 1976;
Twomey and Mulcahy 1988; Peters et al. 1994).
A feature associated in vertebrates with malignancy of tumours is the desmoplastic reaction. This reaction is considered a diagnostic of metastasis and involves
the formation of fibrous tissue around tumour, forming a more or less dense stroma.
Fibrosis is generated by collagen production by myofibroblasts from the interstitial
tissue and is activated by growth factors released by tumour cells (Walker 2001;
Hauptmann et al. 2003). In this work, like in others molluscs (Yevich and Barszcz
1976; Peters et al. 1994; Alonso et al. 2001), we found evidences of a desmoplastic
reaction associated with both the germinal and haemocitary neoplasias described.
Like other authors we observed certain seasonality in gonadal neoplasia prevalence related to reproductive status (Hesselman et al. 1988; Elston et al. 1992;
Ford et al. 1997; Alonso et al. 2001). However most of these authors cite a higher
prevalence in females (Yevich and Barszcz 1976; Hesselman et al. 1988; Gardner
et al. 1991; Bert et al. 1993; Barber 2004), whereas in this work it was higher in
males, as is also described by other authors (Pekkarinen 1993; Alonso et al. 2001;
Darriba et al. 2006; Carella et al. 2009).
Several authors have reported an increase of neoplastic pathologies in bivalves
related to the increase of environmental pollution (Thiriot-Qui´ evreux and Wolowicz
2001; Smolarz et al. 2005; Wolowicz et al. 2005). Other authors have shown
histological alterations caused by exposure to specific chemicals in controlled
laboratory conditions (Snedeker 2001; Huertas Pe˜ na 2005; Wolowicz et al. 2005).
However, in the natural environment, the establishment of cause-effect relationship
is not easy. In this work, the multivariate analysis carried out shows a significant
correlation between levels of mutagenic PAH’s, dioxin-like PCB’s and certain trace
metals in tissues and neoplastic disease development in the gonad of Mytilus, as
well as the lethal effects at high concentrations of these persistent chemicals.
Conclusions
We discovered a significant correlation between levels of persistent pollutants
accumulated in tissues and neoplastic disease development in the gonad (mantle
tissue) of Mytilus galloprovincialis, as shown by histopathological changes in this
tissue. The persistent chemicals measured in mussel tissues included mutagenic
PAH’s and dioxin-like PCB’s. Other studies (Au et al. 2003; Aarab et al. 2004;
Sch¨ afer and K¨ ohler 2009) have suggested that persistent chemicals, such as these,
may result in decreased fertility in invertebrates. Our results suggest that further
experimental studies are warranted to establish cause-effect relationships between
exposure to persistent chemicals and the reproductive capacity of cultured mussels.
Y. Ruiz et al.
products of the abnormal cells, that because of their colour, are named by several
authors “brown cells” (Cheng 1984; Zaroogian et al. 1989). However, haemocyte
proliferation may becoming uncontrolled and malignant, resulting in what has
been described as disseminated haemocitary neoplasia (Yevich and Barszcz 1976;
Twomey and Mulcahy 1988; Peters et al. 1994).
A feature associated in vertebrates with malignancy of tumours is the desmoplastic reaction. This reaction is considered a diagnostic of metastasis and involves
the formation of fibrous tissue around tumour, forming a more or less dense stroma.
Fibrosis is generated by collagen production by myofibroblasts from the interstitial
tissue and is activated by growth factors released by tumour cells (Walker 2001;
Hauptmann et al. 2003). In this work, like in others molluscs (Yevich and Barszcz
1976; Peters et al. 1994; Alonso et al. 2001), we found evidences of a desmoplastic
reaction associated with both the germinal and haemocitary neoplasias described.
Like other authors we observed certain seasonality in gonadal neoplasia prevalence related to reproductive status (Hesselman et al. 1988; Elston et al. 1992;
Ford et al. 1997; Alonso et al. 2001). However most of these authors cite a higher
prevalence in females (Yevich and Barszcz 1976; Hesselman et al. 1988; Gardner
et al. 1991; Bert et al. 1993; Barber 2004), whereas in this work it was higher in
males, as is also described by other authors (Pekkarinen 1993; Alonso et al. 2001;
Darriba et al. 2006; Carella et al. 2009).
Several authors have reported an increase of neoplastic pathologies in bivalves
related to the increase of environmental pollution (Thiriot-Qui´ evreux and Wolowicz
2001; Smolarz et al. 2005; Wolowicz et al. 2005). Other authors have shown
histological alterations caused by exposure to specific chemicals in controlled
laboratory conditions (Snedeker 2001; Huertas Pe˜ na 2005; Wolowicz et al. 2005).
However, in the natural environment, the establishment of cause-effect relationship
is not easy. In this work, the multivariate analysis carried out shows a significant
correlation between levels of mutagenic PAH’s, dioxin-like PCB’s and certain trace
metals in tissues and neoplastic disease development in the gonad of Mytilus, as
well as the lethal effects at high concentrations of these persistent chemicals.
Conclusions
We discovered a significant correlation between levels of persistent pollutants
accumulated in tissues and neoplastic disease development in the gonad (mantle
tissue) of Mytilus galloprovincialis, as shown by histopathological changes in this
tissue. The persistent chemicals measured in mussel tissues included mutagenic
PAH’s and dioxin-like PCB’s. Other studies (Au et al. 2003; Aarab et al. 2004;
Sch¨ afer and K¨ ohler 2009) have suggested that persistent chemicals, such as these,
may result in decreased fertility in invertebrates. Our results suggest that further
experimental studies are warranted to establish cause-effect relationships between
exposure to persistent chemicals and the reproductive capacity of cultured mussels.