Ecotoxicity in the Reconquista River, province of Buenos Aires, Argentina: a preliminary study

Differential sensitivity of aquatic life stages of Pelophylax perezi to an acidic metal-contaminated effluent

Acid mine drainage (AMD) involves complex mixtures of metals and hydrogen ions that can be highly toxic to the biota. Assessing the effects of AMD to aquatic stages of amphibians is key, as this group constitutes the vertebrate class with the highest proportion of species considered as threatened. Thus, the present work aimed at assessing the sensitivity of two aquatic life stages of the green frog Pelophylax perezi to an AMD originated from a cupric-pyrite mine. Embryos (Gosner stages 10-11) and tadpoles (Gosner stages 20-21) of P. perezi were exposed, for 96 h, to six AMD dilutions (1.39% to 7.5%). Endpoints involving responses at different levels of biological organization were monitored: mortality, malformations, hatching rates, body length and growth rate, enzymatic activity related with detoxification metabolism (glutathione S-transferase), and histopathologies (anatomical structures of the digestive, respiratory, and excretory systems). Embryos presented high mortality and malformation rates at AMD levels equal or above 5.36%, as well as premature hatching at 1.95% of AMD or higher. A significant reduction in body length and growth rate occurred in embryos and tadpoles exposed to 1.95% or higher levels of AMD, respectively. At the histological level, several abnormalities were observed for AMD-exposed tadpoles in a variety of tissues. One of the most noticeable histological changes occurred in the intestine that exhibited papillary epithelial hyperplasia along with a yellowish content and was more pronounced in tadpoles exposed to higher AMD levels. FEmbryos were more sensitive to lethal levels of AMD than tadpoles, suggesting embryos as a useful model life stage when performing amphibian risk assessment of mine drainage. Furthermore, AMD was highly toxic for P. perezi aquatic life stages since levels as low as 1.95% induced lethal effects. These results emphasize the importance of implementing efficient remediation methodologies for AMD, given its high toxicity.

Acclimation to low level exposure of copper in Bufo arenarum embryos: linkage of effects to tissue residues

The acclimation possibilities to copper in Bufo arenarum embryos was evaluated by means of three different low level copper exposure conditions during 14 days. By the end of the acclimation period the copper content in control embryos was 1.04 +/- 0.09 microg g(-1) (wet weight) while in all the acclimated embryos a reduction of about 25% of copper was found. Thus copper content could be considered as a biomarker of low level exposure conditions. Batches of 10 embryos (by triplicate) from each acclimation condition were challenged with three different toxic concentrations of copper. As a general pattern, the acclimation protocol to copper exerted a transient beneficial effect on the survival of the Bufo arenarum embryos. The acclimation phenomenon could be related to the selection of pollution tolerant organisms within an adaptive process and therefore the persistence of information within an ecological system following a toxicological stressor.

Evoecotoxicology: environmental changes and life features development during the evolutionary process-the record of the past at developmental stages of living organisms

For most of evolutionary history, scientific understanding of the environment and life forms is extremely limited. In this commentary I discuss the hypothesis that ontogenetic features of living organisms can be considered biomarkers of coevolution between organisms and physicochemical agents during Earth's history. I provide a new vision of evolution based on correlations between metabolic features and stage-dependent susceptibility of organisms to physicochemical agents with well-known environmental signatures. Thus, developmental features potentially reflect environmental changes during evolution. From this perspective, early multicellular life forms would have flourished in the anoxic Earth more than 2 billion years ago, which is at least 1.2 billion years in advance of available fossil evidence. The remarkable transition to aerobic metabolism in gastrula-stage embryos potentially reflects evolution toward tridermic organisms by 2 billion years ago. Noteworthy changes in embryonic resistance to physicochemical agents at different developmental stages that can be observed in living organisms potentially reflect the influence of environmental stress conditions during different periods of evolutionary history. Evoecotoxicology, as a multidisciplinary and transdisciplinary approach, can enhance our understanding of evolution, including the phylogenetic significance of differences in susceptibility/resistance to physicochemical agents in different organisms.