Not Only Toxic but Repellent: What Can Organisms’ Responses Tell Us about Contamination and What Are the Ecological Consequences When They Flee from an Environment?

Abstract

The ability of aquatic organisms to sense the surrounding environment chemically and interpret such signals correctly is crucial for their ecological niche and survival. Although it is an oversimplification of the ecological interactions, we could consider that a significant part of the decisions taken by organisms are, to some extent, chemically driven. Accordingly, chemical contamination might interfere in the way organisms behave and interact with the environment. Just as any environmental factor, contamination can make a habitat less attractive or even unsuitable to accommodate life, conditioning to some degree the decision of organisms to stay in, or move from, an ecosystem. If we consider that contamination is not always spatially homogeneous and that many organisms can avoid it, the ability of contaminants to repel organisms should also be of concern. Thus, in this critical review, we have discussed the dual role of contamination: toxicity (disruption of the physiological and behavioral homeostasis) vs. repellency (contamination-driven changes in spatial distribution/habitat selection). The discussion is centered on methodologies (forced exposure against non-forced multi-compartmented exposure systems) and conceptual improvements (individual stress due to the toxic effects caused by a continuous exposure against contamination-driven spatial distribution). Finally, we propose an approach in which Stress and Landscape Ecology could be integrated with each other to improve our understanding of the threat contaminants represent to aquatic ecosystems.

Assessment of Advanced Oxidation Processes Using Zebrafish in a Non-Forced Exposure System: A Proof of Concept

“…Secondly, the use of an approach based on repellence, instead of toxicity, provides a novel view of the risks that contaminants can present for organisms and ecosystems [21,65,66]. This approach makes clear that the loss of biodiversity caused by the discharges of the effluents is not exclusively attributed to the toxicity and consequent death of organisms, but also the repellence of the chemical present triggering an avoidance response in many populations [21,65,67]. The results of the current study showed that the discharge of effluents into a river has the potential to trigger an avoidance response, which could bring about serious consequences for the ecosystems.…”

“…Although the conventional approach of measuring physicochemical parameters allows valuable information about the quality of water to be obtained, they likely do not provide a "big picture" of the impacts and/or implications on the environment of a discharged effluent. Therefore, such results should be combined with alternative ecotoxicological tests to reach broader interpretations [20,21]. The use of non-forced exposition systems, with well-known indicator organisms (e.g., zebrafish) for the assessment of water treatment methods, could be an innovative approach to complement traditional measurements.…”

Could Contamination Avoidance Be an Endpoint That Protects the Environment? An Overview on How Species Respond to Copper, Glyphosate, and Silver Nanoparticles

“…However, new methods using non-forced, multi-compartmented linear exposure systems (linear 1-D system by Lopes et al [14] and 2-D HeMHAS by Araújo et al [15]) have been developed recently. The main benefit of the multi-compartmentalization exposure systems is the possibility of determining the concentrations of a contaminant in each zone (compartment) through which the organisms can move freely, providing an idea of the potential repellence or attractiveness of the contaminants [14,16,17]. It is important to bear in mind that this approach should be seen as a complementary tool to the classical forced exposure approach, as the non-forced approach provides information about how contamination could affect the spatial distribution of the organisms, but not about the toxic effects [17,18].…”

“…The main benefit of the multi-compartmentalization exposure systems is the possibility of determining the concentrations of a contaminant in each zone (compartment) through which the organisms can move freely, providing an idea of the potential repellence or attractiveness of the contaminants [14,16,17]. It is important to bear in mind that this approach should be seen as a complementary tool to the classical forced exposure approach, as the non-forced approach provides information about how contamination could affect the spatial distribution of the organisms, but not about the toxic effects [17,18]. Thus, the concept of toxicity at the individual level is replaced by the effects on the dynamics of dispersion (spatial avoidance) and habitat selection, from a landscape (connected habitats) perspective [19][20][21].…”

“…Although this exposure approach has increased in ecotoxicological studies (see reviews by Araújo et al [23] and Moreira-Santos et al [24]), information about the real potential of contaminants to trigger avoidance in organisms and to change their habitat selection patterns is very limited. In addition, it is not clear whether toxicity and repellency are comparable in terms of sensitivity [17].…”