Leonardo Zambotti-Villela

Metal cation toxicity in the alga Gracilaria domingensis as evaluated by the daily growth rates in synthetic seawater

Macroalgae of the genus Gracilaria have considerable economic importance as raw material for agar production and belong to an important group of organisms that are tolerant of high concentrations of metal. The median inhibitory concentration (IC50) values obtained by measuring the ratio of fresh mass variation (i.e., daily growth rates) of the red macroalga Gracilaria domingensis during a 48-h aquatic toxicity assay are reported here. The alga was exposed to 14 different metal cations as well as the molybdate anion in synthetic seawater. The actual concentrations of these ionic species (at IC50 values) and the proportion of free ions (aqueous complexes) were determined by inductively coupled plasma atomic emission spectroscopy and the Environmental Protection Agency-recommended software, MINTEQA2, respectively. Based on the free IC50 values (IC50F), the ions were ranked in terms of toxicity: Cd2+ ≫ Cu2+ ≫ Pb2+ ≫ Zn2+ ≫ Ni2+ > Co2+ > La3+ ≫ Mn2+ > Ca2+ ~ Li+ ≫ MoO42− ≫ Sr2+ > Mg2+ ≫ K+ > Na+. As a member of the first trophic level in the marine food chain, G. domingensis is an appropriate target organism both for the development of toxicological assays and as a bioindicator of marine degradation.

Toxic effect of metal cation binary mixtures to the seaweed Gracilaria domingensis (Gracilariales, Rhodophyta)

The macroalga Gracilaria domingensis is an important resource for the food, pharmaceutical, cosmetic, and biotechnology industries. G. domingensis is at a part of the food web foundation, providing nutrients and microelements to upper levels. As seaweed storage metals in the vacuoles, they are considered the main vectors to magnify these toxic elements. This work describes the evaluation of the toxicity of binary mixtures of available metal cations based on the growth rates of G. domingensis over a 48-h exposure. The interactive effects of each binary mixture were determined using a toxic unit (TU) concept that was the sum of the relative contribution of each toxicant and calculated using the ratio between the toxicant concentration and its endpoint. Mixtures of Cd(II)/Cu(II) and Zn(II)/Ca(II) demonstrated to be additive; Cu(II)/Zn(II), Cu(II)/Mg(II), Cu(II)/Ca(II), Zn(II)/Mg(II), and Ca(II)/Mg(II) mixtures were synergistic, and all interactions studied with Cd(II) were antagonistic. Hypotheses that explain the toxicity of binary mixtures at the molecular level are also suggested. These results represent the first effort to characterize the combined effect of available metal cations, based on the TU concept on seaweed in a total controlled medium. The results presented here are invaluable to the understanding of seaweed metal cation toxicity in the marine environment, the mechanism of toxicity action and how the tolerance of the organism.

PREDICTION OF MONO-, BI-, AND TRIVALENT METAL CATION RELATIVE TOXICITY TO THE SEAWEED GRACILARIA DOMINGENSIS (GRACILARIALES, RHODOPHYTA) IN SYNTHETIC SEAWATER

The present study reports a 48-h aquatic metal-toxicity assay based on daily growth rates of the red seaweed Gracilaria domingensis (Gracilariales, Rhodophyta) in synthetic seawater. The median inhibitory concentration (IC50) for each metal cation was experimentally determined, and the ratios of free ions (aqueous complex) were calculated by software minimization of the total equilibrium activity (MINTEQA2) to determine the free median inhibitory concentration (IC50F). A model for predicting the toxicity of 14 metal cations was developed using the generic function approximation algorithm (GFA) with log IC50F values as the dependent variables and the following properties as independent variables: ionic radius (r), atomic number (AN), electronegativity (Xm ), covalent index (Xm (2) r), first hydrolysis constant (|log KOH |), softness index (σp ), ion charge (Z), ionization potential (ΔIP), electrochemical potential (ΔEo ), atomic number divided by ionization potential (AN/ΔIP), and the cation polarizing power for Z(2) /r and Z/AR. The 3-term independent variables were predicted as the best-fit model (log IC50F: -23.64 + 5.59 Z/AR + 0.99 |log KOH | + 37.05 σp ; adjusted r(2) : 0.88; predicted r(2) : 0.68; Friedman lack-of-fit score: 1.6). This mathematical expression can be used to predict metal-biomolecule interactions, as well as the toxicity of mono-, bi-, and trivalent metal cations, which have not been experimentally tested in seaweed to date. Quantitative ion-character relationships allowed the authors to infer that the mechanism of toxicity might involve an interaction between metals and functional groups of biological species containing sulfur or oxygen.

Toxicological effects of metal-EDTA/NTA complex formation in a synthetic medium on the macroalga Gracilaria domingensis

Algae are appropriate target organisms both for the development of toxicological assays and as bioindicators of marine degradation by inorganic and organic compounds. In recent years, the compounds ethylenediaminetetraacetic (EDTA) and nitrilotriacetic (NTA) acids have been released from household and industrial processes and have been considered to be the major emerging contaminants in aquatic environments because they form higher, stable complexes with essential and unessential cations, lowering the bioavailabilities and toxicities of these metals. In the present work, the toxicity relationships of cadmium, copper, zinc, and lead, either free or available and after complexation by EDTA and NTA ions, were evaluated because these complexes may have contributed to the modification of cations toxicity under the experimental conditions. The assay is based on the daily growth rates of the red seaweed Gracilaria domingensis (Gracilariales, Rhodophyta) in synthetic seawater during a 48-h exposure. The ratios of free ions (aqueous complex) were calculated by software minimization of the total equilibrium activity (MINTEQA2). The toxicity of uncomplexed Cd, Cu, Zn, and Cu cations decreased with increasing EDTA ion concentrations because of the formation of metal complexes. The increasing NTA agents successfully mitigated the free-metal toxicity effects with the exception of that of Cu-NTA. The results suggest that there are relationships between toxicity for algae and free ions in solution.

Bioactive compounds against neglected diseases isolated from macroalgae: a review

To survive in a very competitive environment, marine macroalgae had to evolve defense strategies, resulting in an enormous diversity of compounds from different metabolic pathways. These secondary metabolites have been explored by the pharmaceutical industries in order to generate new drugs to treat several diseases. Recent publications in drug research from natural sources have indicated algae as an interesting choice to provide novel drugs to fulfill this gap. This review highlights algal metabolites that showed bioactivities suggesting their potential against neglected diseases. Drug discovery for neglected diseases has been overlooked by the Big Pharmas, mainly because they affect poor people, most of them living in developing countries. Moreover, this review shows the commercial application of the most explored chemicals from algae such as terpenes, phenols, quinones, macrolides, alkaloids, lipids, chromones, and other related metabolites and an overview regarding the status of green extraction technologies for seaweeds and their concepts.