This article presents pollution indices in the following perspectives: in a biological (sensu lato) perspective applied to the ecological indicators; and in the framework of ecology applied to the protection and management of the environment. The quality of the environment could be monitored according to two complementary approaches: the detection of pollutants or any other materials naturally or artificially introduced in the environment; and the evaluation of the effects of these pollutants or materials on living organisms, even at the level of individuals or at higher levels, that is, populations and communities (Figure 1).

Traditionally, physical state and chemical state or their combinations are usually employed as testimony of the state of environment, mainly as the overall degree of pollution (or absence of pollution) of a more specific environment (water, air, soil, etc.). These categories of indicators are based upon the fact that environment quality is usually considered as the quality of state of resources in relation to human use. This anthropomorphic approach consists in measuring the environmental variables that could define, 'objectively', the characteristics of a supposed state of quality or of resources directly and profitably used by humans. It needs to be remembered that policies for management of land, fresh and marine waters tend to maintain minimum levels of acceptable quality permitting to protect the health of populations and their possibility to benefit or utilize their environment without major problems. This 'physical-chemical' approach only can ensure the quality of environment and the preservation of its resources over the short run, within the framework of given place, time, and aims. It is not able to take into account whether or not the quality of resources would meet fundamental needs of the environment as a whole. The interpretation of such a quality in terms of protection of environment should be integrated, providing that the use of resources and environment preserves effectively high levels of quality of life, not restricted to humans.

Figure 1 Use of ecological indicators at different levels of biological organization and scales of time. Prepared and drawn as inspired by different ecological approaches.

In recent decades this biological approach (the holistic ecological approach) has found acceptance. To attempt this goal, the 'biological indicators', organisms, could be utilized in monitoring programs of environment for various purposes:

1. deliver early warning of environmental problems;

2. identify the causal relations between the potential factors of alteration and resulting biological effects;

3. evaluate the overall state of stress of the environment through their different responses; and

4. evaluate the efficiency of restoration measures on the health of biological systems.

The transfer of fundamental ecological knowledge to applied ecology has always been the ambition of eco-logists. It demands simplification but rigor from the observation or explanation of an observed ecological fact to the conceptualization and its use as an ecological tool. To simplify, diversity indices, similarity indices, and bio-tic indices seem to be the most interesting and useful.

These approaches have their proponents and their detractors. In the early 1980s, a theoretical documented study on these indices was critical for the interest they presented in the characterization of the quality of ecosystems. The 'indicative organisms approach' was suspected to depend on the skill of operator, which is an expedite judgment, as to consider that biotic index is only an index of mortality of various organisms within a studied community. These criticisms have led to a mistrust in indices, at least in some scientific communities and among policy makers in some countries.

In spite of the expressed criticisms, the interest shown by scientists has not failed and has led to significant results. During the last decade, significant interest arose due to the more critical and more synthetic approaches based on biological observations. This has permitted scientists to grasp a complex reality that is difficult to model. Each species in a community behaves like an integrator of the more or less distant history of its environment. This is the reason that the indicator species and biotic indices correlate with it. It is widely different from the result apparently more rigorously expressed in chemical data, which are representative only of the time of samples. It has been pointed out that there is no a priori reason why any biological index should correlate with chemical data, as chemical changes are not mirrored uniformly by biological organisms or communities. It is necessary to recall the opinion that ''Benthic infauna clearly provide important quantitative, site-specific information that addresses the most common objectives of marine monitoring programs (...). That it is valuable for marine monitoring could be considered as relevant for any other monitoring programs on Earth, especially in running waters.''

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