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.
Six lignins were used to obtain granular controlled release matrix
formulations of the herbicide
2,4-D (2,4-dichlorophenoxyacetic acid). The water insoluble
lignins were sourced from sugar cane
(Saccharum
officinarum) bagasse and
Eucalyptus sp. and Pinus sp. woods. Each
lignin was
characterized by its functional groups and molecular weight
distributions. The formulations were
prepared by melting the 2,4-D and mixing in the lignins individually
and then granulating (to 0.7−1.0 mm) the glassy matrix. Release rates determined in static water
were correlated to a diffusion-controlled mechanism according to the square root of time.
Principal component regression of the
slopes of these lines showed that these depend inversely on the
molecular weight and the total and
aliphatic hydroxyls of the lignins. For the other functional
groups (aromatic hydroxyls, methoxyls,
and carbonyls), the higher their contents, the higher the diffusion and
release rates.
Keywords: Controlled-release; 2,4-D; lignin; chemical structure;
release rates
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