Physiological responses to mercury in feral carp populations inhabiting the low Ebro River (NE Spain), a historically contaminated site

Abstract

The low Ebro River course (Northeast Spain) is historically affected by mercury pollution due to a chlor-alkali plant operating at the town of Flix for more than a century. River sediments analysed during the last 10 years showed high mercury levels in the river section starting just downstream the factory and spanning some 90km, down to the river delta. The possible environmental impact was studied by a combination of field and laboratory studies. Mercury concentrations in liver, kidney and muscle of feral carp (Cyprinus carpio) sampled downstream Flix were one to two orders of magnitude higher than those from carps sampled upstream Flix. Elevated levels of mercury in these samples associated with significant increases on the concentration of reduced glutathione (GSH) in liver and on mRNA expression of two metallothionein genes, MT1 and MT2, in kidney and, partially, in scales, but not in liver. Conversely, no biochemical evidence for oxidative stress or DNA damage was found in these tissues. Non-contaminated carps subjected to intraperitoneal mercury injection resulted in a 20-fold increase of MT1 and MT2 mRNA levels in carp kidney, with minimal changes in liver levels. Our data suggests the coordinate increase of metallothionein mRNA in kidney and of GSH in liver constitutes an excellent marker of exposure to sub-toxic mercury levels in carps. This study also demonstrates that apparently healthy fish populations may exceed the mercury contamination acceptable for human consumption.

Evaluation of environmental impact on natural populations of the Mediterranean killifish Aphanius fasciatus by quantitative RNA biomarkers

“…The transient effect of Cd (and other heavy metals) in liver MT transcript abundance has been observed in different systems (Gonzalez et al, 2005;Quirós et al, 2007b). In natural fish populations, metal chronic exposure usually results in elevated MT mRNA levels in kidney and other tissues, but not necessarily in the liver (Hayes et al, 2004;Navarro et al, 2009;Quirós et al, 2007b;Tom et al, 1999). This may well be the case for A. fasciatus, as we did not observe an increment of MT mRNA levels in the Cd chronically exposed Sfax fish population.…”

“…In this context, markers based on RNA quantification methods, such qRT-PCR, provide a suitable alternative, as they only require minute amounts of sample Rotchell and Ostrander, 2003;Valasek and Repa, 2005). These techniques have proved their usefulness for monitoring of different types of environmental pollutants, like estrogens (Barucca et al, 2006;Garcia-Reyero et al, 2004;George et al, 2004), metals (Cheung et al, 2004;Navarro et al, 2009;Tom et al, 2004), and organic substances (Eljarrat et al, 2008;Quirós et al, 2007a;Quirós et al, 2007b). It is clear that biomarkers based on mRNA levels only reflect the initial steps of a cascade of events linking environmental insults to ecological impact (van der Oost et al, 2003).…”

“…In this work, we develop mRNA markers for monitoring A. fasciatus exposure to different kinds of pollutants, using known DNA sequences from evolutionarily related species (mainly Cyprinodonts and Percomorphs). Genes used in this analysis included the main metal-responsive metallothionein (MT) gene (Cheung et al, 2004;Navarro et al, 2009;Schlenk et al, 1995;Tom et al, 2004;Van Cleef-Toedt et al, 2001), the egg-forming, liver-expressed vitellogenin (Vtg), a known marker for estrogens (Barucca et al, 2006;Denslow et al, 2001;Garcia-Reyero et al, 2004), the dioxin-like responsive Cytochrome P4501A (CYP1A, Chung-Davidson et al, 2004;Craft et al, 2001;Quirós et al, 2007a;Quirós et al, 2007b), the oxidative stress-related gene Superoxide dismutase (SOD, Cho et al, 2006;Gonzalez et al, 2006;Pandey et al, 2003), and the protein chaperone HSP70, which are involved in the processing of missfolded proteins due to different kinds of stress (Carnevali and Maradonna, 2003;Maradonna and Carnevali, 2007;Schroder et al, 2000;Varo et al, 2002). In addition, probes for two housekeeping genes (ß actin and the elongation translation factor EF1)…”

Metals as a cause of oxidative stress in fish: a review

“…The mRNA expression of two MT genes was noted by Navarro et al (2009) in the liver of feral carp Cyprinus carpio from a mercury-contaminated river. No biochemical evidence of oxidative damage associated with these changes was found in the tissue.…”

Impact of industries in the accumulation of radionuclides in the lower part of Ebro river (Catalonia, Spain)

“…There are several industrial activities concentrated in the vicinity of the river which have caused contamination problems in the basin, and for this reason the study of the presence of different kinds of pollutants in Ebro river water is an issue of great concern, to evaluate the water quality and also the effects on the delta wildlife (Loureiro et al, 2009;Navarro et al, 2009).…”