Biology Reference
In-Depth Information
biochemical processes [metallothionein (MT) or stress protein induction, enhanced activi-
ties of biotransformation enzymes, antioxidative defenses, etc.] involved in the ability of
organisms to cope with the presence of contaminants such as metals, polycyclic aromatic
hydrocarbons (PAHs), polychlorobiphenyls (PCBs), etc. in their medium.
In addition to the intrinsic relative sensitivity characteristic of different species to a con-
taminant (see Chapter 7), it is well established that within the same species, populations
chronically exposed to chemical contaminants in their medium are often more able to
cope with chemical stress than “naïve” individuals originating from cleaner sites. The
best known examples include bacterial resistance to antibiotics, the tolerance of terrestrial
plants to metals (Frérot et al. in Amiard-Triquet et al. 2011), and the resistance of insects to
pesticides (Ghanim and Ishaaya in Amiard-Triquet et al. 2011).
Tolerance appears primarily as beneficial for environmental conservation because it con-
tributes to the protection of biodiversity, thus allowing normal functioning of ecosystems.
However, some mechanisms involved in tolerance can have less positive consequences in
the longer term, such as the production of carcinogenic metabolites during the biotrans-
formation of organic pollutants, the reduced performance of some resistant genotypes, or
the energy cost of being tolerant. Lastly, in polluted ecosystems, tolerance may be respon-
sible for high body burdens of toxicants in certain prey species with a subsequent risk of
trophic transfer or biomagnification in food webs. Thus, it is necessary to assess carefully
the health and ecological consequences of tolerance.
3.2 Tolerance to Chemical Stress in Chronically Exposed Populations
Species either tolerant or susceptible to pollution have been recognized in numerous taxo-
nomic groups (Chapter 7). In this section, we will focus on data about the relative sus-
ceptibility of populations originating from natural environments that are comparatively
contaminated or as clean as practically possible (reference sites). Results obtained with
experimental populations exposed in the laboratory over several generations will also
be taken into account. Tolerance appears as a widespread phenomenon, particularly well
documented for metals (Table 3.1), but a number of studies have also reported tolerance to
organic contaminants (Table 3.2).
A relationship between the origin of phytoplankton strains and their tolerance to met-
als originating from mining activities (Cu or Zn), industrial effluents, and PCBs has been
established, whereas several laboratories have developed resistant strains by exposing
them to sublethal doses of other organic contaminants (Cosper et al. 1987 and literature
cited therein; Takamura et al. 1989).
In the freshwater crustacean Daphnia magna , tolerance was induced over successive gen-
erations exposed in the laboratory to different metals (Bossuyt and Janssen 2004b and
literature cited therein), whereas Ceriodaphnia dubia reared in a metal-depleted medium
showed an abnormal sensitivity to metals (Muyssen and Janssen 2002). As soon as the
second generation of daphnia was obtained from herbicide (molinate)-exposed parents,
longevity was increased and reproduction improved (Sánchez et al. 2004). Ethyl parathion
also induced a certain tolerance (Barata et al. 2001). On the contrary, exposure over sev-
eral generations to another insecticide (diazinon) induced an increased susceptibility;
young daphnia obtained from parents exposed to an acaricide (tetradifon) or an indus-
trial effluent showed an increased susceptibility to these contaminants (in Sánchez et al.
Search WWH ::




Custom Search