Potential effects of triclosan on spatial displacement and local population decline of the fish Poecilia reticulata using a non-forced system

Abstract

Triclosan (TCS) is an emerging contaminant of concern in environmental studies due to its potential adverse effects on fish behavior. Since avoidance has been shown to be a relevant behavioral endpoint, our aims were: (i) to determine if TCS is able to trigger an avoidance response in Poecilia reticulata; (ii) to predict the population immediate decline (PID) caused by TCS exposure, by integrating lethality and avoidance responses; and (iii) to verify the overestimation of risk when mortality is assessed under forced exposure. Fish were exposed to TCS in a forced exposure system, to assess mortality, and to a TCS gradient in a non-forced exposure (NFE) system. Two NFE scenarios were simulated: (#1) a spatially permanent gradient, including low and high concentrations; and (#2) a scenario with high concentrations, simulating a local discharge. The fish avoided TCS concentrations as low as 0.2 μg L (avoidance of 22%). The AC50 obtained from scenario #1 (8.04 μg L) was about 15 times more sensitive than that from scenario #2 (118.4 μg L). In general, up to the highest concentration tested (2000 μg L), the PID was determined by the avoidance. Mortality from the forced exposure was overestimated (48 h-LC50 of 1650 mg L), relative to the NFE. The reduced mortality in a non-forced environment does not imply a lower effect, because part of the population is expected to disappear by moving towards favorable environments. TCS is a potential environmental disturber, since at environmentally relevant concentrations (<2 μg L) it could cause a decline in the fish population.

Spatial avoidance as a response to contamination by aquatic organisms in nonforced, multicompartmented exposure systems: A complementary approach to the behavioral response

“…Later, Moreira‐Santos et al () improved that system to be used with small fish, and Rosa et al () proposed an alternative static system, with no pump, thus preventing any influence of water flow on the displacement of organisms. This recent alternative of a static linear system has been widely described in studies of contamination‐driven spatial avoidance (Araújo et al , , , 2016b, 2014c; Vasconcelos et al ; Silva et al , ). Compartments forming the linear system can be manually constructed from 2 plastic bottles glued at their cut‐off bases using white silicon and connected at the mouths to create a multicompartmented system, or else borosilicate glass can be used, as described by Silva et al ().…”

“…A laboratory study using the fish P . reticulata showed that an immediate population decline of approximately 40% might occur due to avoidance (with no influence from mortality) at environmentally relevant triclosan concentrations (<2 μg L −1 ; Silva et al ). By using either acute or chronic responses, the integration of both forced and nonforced approaches might improve our understanding of the population decline expected to occur when organisms are exposed to and are able to detect contamination.…”

Influence of interspecific interactions on avoidance response to contamination

“…This approach expands the concept of environmental disturbance beyond the traditional one based exclusively on the toxicity (and bioaccumulation) at the organism level. Evidence of contamination-driven spatial displacement (avoidance response) in non-forced exposure systems has been described for many organisms including fish (Moreira-Santos et al, 2008;Araújo et al, , 2018Silva et al, 2017Silva et al, , 2018, amphibians Vasconcelos et al, 2016), and invertebrate species (Lopes et al, 2004; exposed to different contaminants.…”

Effects of aquatic contaminants on the habitat selection and spatial distribution in fish: a complementary approach to traditional ecotoxicological tests

“…At the same time as it allows the passage of the fish, the reduced opening avoids diffusion between the compartments. The difference between both examples is that in the first one (figure 3-A) there is a renewal of the solution in each chamber through peristaltic pumps, while the second is static (Figure 3 Generally, in aquatic ecosystems, there is dispersion / dilution of the pollutants released (López-Doval et al, 2017), forming a gradient of contamination. That is, avoidance can be estimated in an environment simulating real environmental conditions Rosa et al, 2008;.…”

“…A second problem (besides concentrations) that contributes to the lack of realism in ecotoxicological studies arises when exposure to contaminants is simulated assuming a homogeneous distribution of the contamination. In aquatic systems, contaminants often disperse, forming a dilution gradient, so the induced stress tends to be negatively correlated with the distance from the source of the contamination (Araújo et al, 2016a;López-Doval et al, 2017). In the case of mobile organisms, their displacement to locations distant from the contamination source prevents continuous exposure to contaminants.…”