Gustavo Emilio Santos-Medrano

Effect of coexposure to DDT and manganese on freshwater invertebrates: Pore water from contaminated rivers and laboratory studies

An environmental survey of several rivers of the southern Huasteca area of Mexico revealed high concentrations of manganese (Mn) and the presence of DDT in the sediments and pore water. Therefore, acute (48-h) toxicities of Mn and DDT were assessed both independently and as a combination on 24-h-old neonates of Daphnia magna Strauss and Lecane quadridentata Ehrenberg. Daphnia magna showed high sensitivity to both toxicants, whereas L. quadridentata was highly resistant to DDT and less susceptible to Mn. For D. magna, the Mn and DDT coexposure was significantly more toxic than any of the singly tested compounds. When D. magna was exposed to sediment pore water, no association was found between the Mn content in the samples and the observed toxicity. Preliminary particle analysis of pore water showed different compounds of Mn, which apparently were not in bioavailable form.

Analysis of the toxicity of glyphosate and Faena® using the freshwater invertebrates Daphnia magna and Lecane quadridentata

With the present contribution an evaluation of the toxicity of the pure herbicide glyphosate and its commercial formulation Faena® is reported using the cladoceran Daphnia magna Strauss and the rotifer Lecane quadridentata Ehrenberg. LC50, EC50, NOEC, and LOEC values for each toxicant and for both test organisms are obtained. Regarding acute toxicity, Faena was 11-fold more toxic to L. quadridentata than pure glyphosate and slightly more toxic to D. magna (1.7-fold). Inhibition of esterase activity in L. quadridentata by glyphosate was the most sensitive end-point; the EC50 was 1500-fold smaller than the LC50. The implications of these results and their comparison with established international and national limit values for glyphosate are discussed.

Determination of toxicity levels in the San Pedro River Watershed, Aguascalientes, Mexico.

A quantitative study of toxicity levels of the San Pedro River and its main tributaries around the city of Aguascalientes, Mexico was conducted. Our study determined individual CL50 values for each sampling point at 3 different times of the year corresponding to the main seasons of the year in terms of the hydrological cycle (dry, low rain and high rain season). Those LC50 values were used to calculate the acute. Toxicity Units (aTU) that allowed us to compare levels of toxicity along the San Pedro River and two of its main tributaries. The sample that showed highest toxicity was IPIVA. This is due to the large quantity of industrial discharges that receives. Its effluent was responsible for the largest contribution of toxicity to the San Pedro River over the three rounds of sampling of this study. Our study classified an important portion of the San Pedro River and two of its main tributaries in toxic, moderately toxic and lightly toxic. No portion of the river studied was free of toxicity, either acute or sublethal. This study demonstrated that in spite of the operation of several water treatment plants along the San Pedro River, for the most part, the water quality of the river is still unacceptable.

THE USE OF AQUATIC INVERTEBRATE TOXICITY TESTS AND INVERTEBRATE ENZYME BIOMARKERS TO ASSESS TOXICITY IN THE STATES OF AGUASCALIENTES AND JALISCO, MEXICO

This1 paper describes a series of techniques using several aquatic invertebrates as indicators of adverse effects in natural and man-made aquatic environments. The information obtained in these techniques allowed the monitoring of the municipal drinking water system of the city of Aguascalientes, Mexico and the detection of toxicity in streams suspected of dumping of agricultural and industrial discharges in the states of Aguascalientes and Jalisco, in Mexico.

Identification of acetylcholinesterase receptors in Rotifera

We have identified acetylcholinesterase (AChE) receptors in six freshwater rotifers. Using β-bungarotoxin labelled with fluoresceinisothiocyanate (FITC), muscarinic and nicotinic receptors were found in Brachionus quadridentatus (females and males), Lecane luna, Lecane quadridentata, Plationus patulus, and Rotaria neptunia. Using α-bungarotoxin-FITC, nicotinic receptors were identified in B. quadridentatus, Lecane bulla, L. luna, L. quadridentata, P. patulus and R. Neptunia. Concentrations as low as 1.5 nM of β-bungarotoxin, and 5 nM of α-bungarotoxin identified receptors in the digestive tract. Higher concentrations of both toxins identified additional receptors associated with the lorica. A preliminary analysis of fluorescence intensity in L. quadridentata showed that response to α-bungarotoxin increases with age from newborn to 48-h old, but not in older individuals, thus suggesting an increase in binding sites, and possibly in number of nicotinic receptors, during the first 48-h of life. Our study extends the number of rotifer species in which AChE receptors have been reported.

Life table demography of Asplanchna brightwellii Gosse, 1850 fed with five different prey items

We conducted life table experiments on the freshwater rotifer Asplanchna brightwellii to analyze its demography when fed with prey items from several taxonomic groups (cladocerans, protozoans, and rotifers) and under two different temperature regimes (20 and 25°C); the aim of the study was to determine the preferred prey for A. brightwellii in terms of fitness (evaluated as reproductive success) among five cladoceran, protozoan, and rotifer preys, and to test which temperature (20 or 25°C) is better for life table parameters of Asplanchna. Our analysis identified Brachionus calyciflorus as the preferred prey for A. brightwellii based on life table statistics, ingestion rate and electivity indices. The greatest values for net reproductive rate and intrinsic growth rate were achieved when A. brightwellii was fed B. calyciflorus. Greater reproductive values (Ro and r) were found at 25°C than at 20°C for A. brightwellii across the five prey species. We found significant differences in the ingestion rate and electivity index among zooplanktonic and benthic preys. The influence of temperature, the cost of predation, and how prey selection by A. brightwellii is influenced by: biomass, size, and swimming speed; they are discussed hoping to gain a better understanding of trophic transfers in zooplankton communities.

Rotifers as Models in Toxicity Screening of Chemicals and Environmental Samples

An important objective of aquatic ecotoxicology is to determine the effects of toxic com‐ pounds in organisms that play a central role in aquatic communities where rotifers have a large impact on several important ecological processes. The contribution of the rotifers to secondary production in many aquatic communities is substantial as they are often the larger fraction of zooplankton biomass at certain times of the year. In addition to the im‐ portance of their ecological roles in aquatic communities, the rotifers are attractive organ‐ isms for ecotoxicological studies by its short life cycles and rapid reproduction, their small size, and little volumes needed for culture and toxicity assays. The main end points used in ecotoxicological studies are mortality, reproduction, behavior, and biomarkers. Such parameters are included in international regulations from all over the world, where different species are used to evaluate the effect of environmental samples or chemical compounds. The high diversity of rotifers is an important issue because it can modify their relative susceptibility to toxicants. Thus, more studies are needed to know the rela‐ tions and mechanisms involved in clonal variation, sensitivity, and development, which can be all assessed by state-of-the-art procedures.

Using Amplified Fragment Length Polymorphisms (AFLP) to Study Genetic Variability in Several Freshwater Rotifer Species

We have used amplified fragment length polymorphisms (AFLP) to investigate the potential of this technique as a tool to measure genetic variability in eight species of freshwater rotifers: Brachionus calyciflorus, Lecane bulla, L. luna, L. quadridentata, Plationus patulus, Philodina acuticornis odiosa, Rotaria neptunia, and R. rotatoria. We used nine combinations of oligonucleotides. We observed a total of 806 amplified bands, 798 polymorphic and 8 monomorphic. The data were analyzed using cluster analysis with UPGMA, first within each set of oligonucleotide combination and finally using all nine combinations. Our best dendrogram clearly separated monogononts from digononts, and grouped the species of monogononts in the two genera. However, it grouped R. neptunia with P. acuticornis odiosa rather than with R. rotatoria. These results are discussed in view of recent works in the literature measuring genetic variability and discussing the phylogeny of the Rotifera.

Chapter 3:Rotifers as Models for Ecotoxicology and Genotoxicology

Rotifera is a group of pseudocoelomate aquatic invertebrates with great potential as model organisms for ecotoxicology and genotoxicology. This potential is based on their: (a) fast growth and reproduction, (b) ease of culture and maintenance, (c) cyst production, (d) alternation of asexual and sexual generations, among others. While the use of rotifers as models for ecotoxicology is well documented and more species, tests, and information are added every day, the potential use of rotifers for genotoxicology is still very limited. In this chapter the authors attempt to explain the state of the art regarding the use of rotifers as models for both eco- and geno-toxicology. To achieve this, the authors have implemented a complete search in the mainstream scientific literature describing types of studies, perspectives, and use of rotifers in both areas. In the case of genotoxicology an emphasis has been made to incorporate suggestions on the advantages that rotifers represent if used as model organisms for the different techniques and studies instead of the most traditionally used organisms. Among the main topics included in genotoxicity are: (a) aging, (b) horizontal gene transfers and gene conversion induced by chronic exposure, (c) detoxification mechanisms, (d) transgenerational effects, and (e) micro evolution as mechanisms of adaptation to toxic exposure.