Marine Ecosystems under Toxic Pressure - Vulnerability of Coastal Ecosystems and Adaptation - page 11

1.3.1.1. General remarks on the modes of action
The contaminant's mode of action is determined by its chemical
structure [ESC 02, PAK 00, TRE 04]. Pollutants have been classified
into four categories, on the basis of their structure/activity ratios
(SARs) [HER 89]. The “inert” products (class I) and “slightly
reactive” products (class II) have a narcotic action: they react in a non-
selective manner with biological membranes, thus modifying their
structure and functioning. Their effect depends mainly on their
hydrophobia [VAN 92]. The “reactive” compounds (class III) and the
compounds “with a specific mode of action” (class IV) react
selectively or not at all with the cellular biomolecules. Once in the
cell, they are generally hydroxylated and eventually combined with
other molecules in order to be eliminated. However, the combinations
are sometimes more toxic than the initial substance.
For a family of contaminants with a given mode of action, the
cell's response depends on the presence and the abundance of the
product's targets and on its metabolic capacities, as well as on its
ability to repair damage [ESC 02]. These physiological properties
characterize species. For example, the active elimination of the
contaminant by cells calls upon different metabolic paths whose
biomolecules are unequally distributed between different species
[BAZ 97, CAL 83, IBR 98] or within the same species. Thus, a given
cell's membership of a taxonomic group determines its response to a
given product.
1.3.1.2. The cellular response: the means of identifying exposure to
contaminants before the event
The impact of pollutants on a subcellular level can lead to the
inhibition and/or triggering of diverse proteins and enzymes
implicated in the metabolism and the excretion of xenobiotics. These
detoxification mechanisms allow organisms to maintain themselves in
the fact of exposure to pollutants. Modulations of biotransformation
enzymes have, therefore, been the subject of a very large number of
investigations over the last 30 years, notably among fish [AND 92,
GOK 98, WHY 00]. Much effort has, in particular, been devoted to
the identification of biomarkers of detoxification, that is to say
proteins, or indeed enzymes, whose activity levels reveal the starting