How are cod in a seawater inlet in Bergen, Norway, affected by environmental pollutants?

New research shows that environmental pollutants in Store Lungegårdsvann in Bergen affect gene expression involved in detoxification mechanisms and hormone balance in Atlantic cod. The research is part of the National Institute of Nutrition and Seafood Research' (NIFES) work to identify effects of environmental pollutants on fish health and seafood safety.

NIFES has studied the expression of genes in cod from the Store Lungegårdsvann, a seawater recipient in Bergen defined as relatively polluted, with considerable amounts of organic environmental pollutants present in the sediments. The cod from this location was compared with cod from the outer Hardanger Fjord, which is not considered to be a polluted area. The genes examined code for proteins known to respond to environmental pollutants often found in sewage and surface drainage water in urban areas. The project is part of ongoing research to determine how environmental pollutants affect fish health and seafood safety.

"The findings show that cod in the Store Lungegårdsvann are exposed to organic pollutants, and that they affect the expression of genes that are important for the detoxification mechanisms of the cod. In comparison to cod from the outer Hardanger Fjord, the CYP1A gene was up-regulated in male fish from the Store Lungegårdsvann, whereas it was down-regulated in the female cod. This also indicates that there are gender-specific differences in the regulation of CYP1A", says researcher Pål A. Olsvik in the Seafood Safety Programme at NIFES in Bergen.

The CYP1A gene is used as a biomarker for many organic environmental pollutants, including PCB and dioxin-like PCB, and plays an important role in the detoxification processes of animals. A biomarker is a change in a biological response that can be related to exposure to, or toxic effect of, an environmental chemical or chemicals.

"Studies from 2007 have shown that livers of cod obtained from Store Lungegårdsvann contain high levels of both PCB and dioxin-like PCB", says Olsvik.

Disturbed hormone balance?

Two out of five male fish caught in Store Lungegårdsvann showed considerable up-regulation of the three genes vitellogenin A (VtgA), VtgB and zona radiata 2 (ZP2) in the liver. These genes code for female egg yolk and egg shell proteins, commonly used as biomarkers for environmental estrogens in male fish.

This indicates that the male cod are affected by environmental estrogens. The estrogen inhibiting effect that has been found may be due to organic pollutants in the sediments and discharges from the sewage system. Store Lungegårdsvann is not a closed system, but has an opening into an adjoining fjord. As it is natural for the cod to move in and out of Store Lungegårdsvann, we can expect them to be affected to varying degrees. This may explain why elevated levels of these trancripts were only found only in two out of five males.

Estrogen inhibitors are substances which mimic natural estrogen in the body. Substances which mimic the body's natural hormones, and which can have the same effect, are called hormone inhibitors or hormone-disturbing substances.

Based on the scientific article:

Are Atlantic Cod in Store Lungegårdsvann, a Seawater Recipient in Bergen, Affected by Environmental Contaminants? A qRT-PCR Survey, by ål A. Olsvik1, Kai K. Lie1, Anders Goksøyr, Torbjørn Midtun, Sylvia Frantzen, and Amund Maage, published in Journal of Toxicology and Environmental Health, 72(3-4),140-54.

Collaborating partners: The University of Bergen, Norway.

What is meant by gene expression?

All cells in the body have a cell nucleus which contains DNA. The DNA contains genetic sequences which define the structure of different proteins with different functions. For a protein to be created, the DNA must undergo a process whereby the genetic sequences are transcribed to mRNA, which is transported out of the cell nucleus. The term "gene expression" means the amount of mRNA in a cell or a tissue at a given time. When mRNA is transported from the cell nucleus the transcription unit is translated to a protein. When we say that a gene is up-regulated, more of a specific mRNA that codes for a protein is produced. More of this protein will be produced, such as an intake protein, a transport protein or an enzyme. This, in turn, can affect processes in the cell and otherwise in the body.