Introduction - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 1

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Introducti on
Claude Amiard-Triquet and Jean-Claude Amiard
CONTENTS
References ....................................................................................................................................... 11
Anthropogenic activities are responsible for the environmental input of many classes of
chemicals through industrial sources, domestic and urban effluents, and diffuse sources
linked to agriculture. The main categories of contaminants include both organic [petro-
leum hydrocarbons, polychlorobiphenyls (PCBs), pesticides, etc.] and inorganic (metals
and nonmetallic elements) compounds. These compounds were studied as soon as eco-
toxicology appeared as a specific branch of environmental studies, whereas emerging con-
taminants have become a topic of concern more recently, even though some of them have
been present in the environment for years. Emerging contaminants include pharmaceuti-
cal and care products, alkylphenols, brominated flame retardants, perfluorinated organic
compounds, and nanoparticles.
Depending on their physical characteristics, three main categories may be distinguished
among chemical wastes: solids, liquids, and gases. Each category corresponds to one of
the compartments of our physical environment: lithosphere, hydrosphere, atmosphere.
However, it is impossible to describe chemicals entering our environment as continental,
aquatic, or atmospheric contaminants since many exchanges occur between these com-
partments. Whatever the point of entrance of a given substance into the environment, an
important fraction may be carried over what may be a significant distance as a result of
water and air circulation. As a consequence, even polar environments are not spared, and
in a charismatic species such as the polar bear, increasing levels of persistent organic pol-
lutants are well documented, with possible ecotoxicological effects at the population level
(Letcher et al. 2010).
Even if contaminants are distributed on a worldwide scale, dilution in air or water masses
increases with distance from the contamination source. This contamination gradient is the
primary factor controlling contaminant uptake into organisms (Figure 1.1). Environmental
conditions influence the transformation of many chemicals through chelation, hydrolysis,
photodegradation, biodegradation, etc. However, some degradation products of contami-
nants are not less toxic than the initial molecule, sometimes being even more noxious.
Many toxicants are able to cross biological membranes but these membranes and associ-
ated structures can act as barriers to contaminant entry (Figure 1.1). For instance, metal
speciation and therefore dissolved metal bioavailability may be modified through ligand
secretion into the external medium or by precipitation of dissolved metals as microcrys-
tals of metal sulfides onto the cell surface. Secretion of exudates by a variety of organisms
(bacteria, plants, animals) can involve a great variety of compounds. Subtle changes in
the charge and types of reactive groups in such secretions can interfere markedly with
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