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    ABSTRACT: Using the marine rotifer Brachionus plicatilis acute toxicity tests, we estimated the toxicity of Corexit 9500A(®), propylene glycol, and Macondo oil. Ratios of 1:10, 1:50 and 1:130 for Corexit 9500A(®):Macondo oil mixture represent: maximum exposure concentrations, recommended ratios for deploying Corexit (1:10-1:50), 1:130 the actual dispersant:oil ratio used in the Deep Water Horizon spill. Corexit 9500A(®) and oil are similar in their toxicity. However, when Corexit 9500A(®) and oil are mixed, toxicity to B. manjavacas increases up to 52-fold. Extrapolating these results to the oil released by the Macondo well, suggests underestimation of increased toxicity from Corexit application. We found small differences in sensitivity among species of the B. plicatilis species complex, likely reflecting phylogenetic similarity. Just 2.6% of the water-accommodated fraction of oil inhibited rotifer cyst hatching by 50%, an ecologically significant result because rotifer cyst in sediments are critical resources for the recolonization of populations each Spring.
    Environmental Pollution 11/2012; 173C:5-10.
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    ABSTRACT: Wastewater discharges into freshwater bodies represent a serious ecological problem worldwide. In underdeveloped and developing countries wastewater treatment plants (WTP) only count with basic treatment, leading to the pollution of important aquatic reservoirs causing critical situations. In the present work, a one year evaluation of toxicity and main physical and chemical parameters of one of the major WTP of the state of Aguascalientes was conducted fortnightly, and to assess treatment alternatives for this WTP we tested: a) three white rot fungi (WRF), b) a photo-electrochemical process, c) ion-exchangers resins and activated carbon. The 3 WRF exhibited high COD removal from influents (72 - 95 %) but only Phanerochaete chrysosporium reached significant toxicity removals (70 and 55 %, for an influent and an effluent, respectively). Treatments with electrochemical advanced oxidation processes resulted with the highest toxicity and COD removals (96 % for both parameters) in comparison to biological and physicochemical treatments. Adsorption with activated carbon, zeolite and chelex ion-exchange resins removed 60 - 90 % of COD and 60 - 99 % toxicity. These results could be used to improve operation of the Industrial Park WTP and to plan future modifications to the plant.
    Journal of Environmental Science and Health Part A Toxic/Hazardous Substances & Environmental Engineering 03/2012; 47(4):589-97.
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    ABSTRACT: We studied how lead is bioconcentrated and distributed in the rotifer Brachionus calyciflorus using metal histochemistry to locate lead granules, Leadmium Green® analysis to establish the route of uptake, atomic absorption to determined the bioconcentration factor (BCF), and detected the presence of microelements in the cuticle by X-ray microanalysis with scanning electron microscopy. Our results indicate: (a) the digestive system is the main route of lead uptake in the rotifer B. calyciflorus, (b) after 24-h lead is deposited in granules in the mastax and vitellarium, (c) our energy-dispersive X-ray microanalysis indicates decalcification taking place in the cuticle of the rotifer after a 24-h lead exposure, and (d) we determined a BCF = 115 for lead after a 24 h exposure. However, the route of mobilization and storage of intracellular lead are still not fully understood in B. calyciflorus.
    Aquatic toxicology (Amsterdam, Netherlands) 12/2011; 109:127-32.
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    ABSTRACT: This report includes atomic absorption data from water column, elutriates and zooplankton that demonstrate that lead biomagnifies at El Niágara reservoir, Mexico. Results include field data (bioaccumulation factors) (BAFs) and laboratory data (bioconcentration factors) (BCFs). Two findings: high BAFs for invertebrate predator like Acanthocyclops robustus, Asplanchna brightwellii, Culex sp. larvae, and Hyalella azteca, compared to grazer species Moina micrura and Simocephalus vetulus; low BCF's found for some predators, suggested that lead biomagnifications were taking place. The presence of Moina micrura in the gut of Asplanchna allowed us to design experiments where A. brightwellii was fed lead-exposed M. micrura neonates. The BAF of Asplanchna was 123,684, BCF was 490. Asplanchna individuals fed exposed Moina had 13.31 times more lead than Asplanchna individuals just exposed 48-h to lead, confirming that lead biomagnification occurs. Results of two fish species showed no lead biomagnification, suggesting that lead biomagnification might be restricted to invertebrate predators.
    Environmental Pollution 07/2011; 159(7):1831-5.
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    ABSTRACT: The title compound, [Zn(3)(C(9)H(21)SiS)(6)] or [((i)Pr(3)SiS)Zn(mu-SSi(i)Pr(3))(2)Zn(mu-SSi(i)Pr(3))(2)Zn(SSi(i)Pr(3))], is the first structurally characterized homoleptic silanethiolate complex of zinc. A near-linear arrangement of three Zn(II) ions is observed, the metals at the ends being three-coordinate with one terminally bound silanethiolate ligand. The central Zn(II) ion is four-coordinate and tetrahedral, with two bridging silanethiolate ligands joining it to each of the two peripheral Zn(II) ions. The nonbonding intermetallic distances are 3.1344 (11) and 3.2288 (12) A, while the Zn...Zn...Zn angle is 172.34 (2) degrees. A trimetallic silanethiolate species of this type has not been previously identified by X-ray crystallography for any element.
    Acta Crystallographica Section C Crystal Structure Communications 12/2009; 65(Pt 12):m475-7.
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    ABSTRACT: We have determined lead concentration of water, sediment, and zooplankton samples of El Niágara, a reservoir in Aguascalientes, Mexico. Our results include the first report of bioconcentration factor (BCF) obtained in an actual ecosystem (as opposed to the experimental setups in the laboratory) for a rotifer species; Asplanchna brigthwellii (BCF ca. 49 300). The BCF of this predatory zooplanktonic species (A. brigthwellii) are up to four times greater than those of two grazing zooplanktonic species (Daphnia similis and Moina micrura). In this contaminated reservoir that lacks fishes, Asplanchna, and Culex sp. together with ducks and other bigger invertebrates might represent the top predators. Our data suggest that biomagnification of lead through at least one trophic level can occur in freshwater systems. Biomagnification in A. brigthwellii might be explained in part by predation of this voracious predator on young of the herbivorous cladoceran, M. micrura. Our findings stand opposite to the current theoretical framework where lead biomagnification occurs only in lower trophic levels.
    Environmental Toxicology 09/2008; 23(4):459-65.
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    ABSTRACT: 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 CL(50) 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 LC(50) 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.
    Journal of Environmental Science and Health Part A 09/2007; 42(10):1403-10.
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    ABSTRACT: We have developed chronic toxicity reproductive 5-day tests to study the effects of Pb, as Pb(NO(3))(2), and Hg, as HgCl(2), exposure in the freshwater rotifer Lecane quadridentata. We used "r" (the instantaneous growth rate) as the endpoint. The test was performed using EPA medium at two food levels (10(5) and 10(6) cells/mL of Nannochloris oculata) at a controlled temperature of 25 degrees C and an L/D cycle of 16:8 h. We monitored the levels of both metals, using atomic absorption, at days 0, 2, and 5 of each experiment. Our results showed that rotifers fed at higher food concentrations were capable of withstanding higher levels of metal toxicity than those fed at lower food concentrations (EC50 = 0.704 versus 0.664 mg/L(-1) for lead, P < 0.05; EC50 = 0.057 versus 0.054 for mercury, P < 0.05). Our atomic absorption analysis showed that although 66% of lead nitrate can be taken up by algal cells efficiently and removed from the medium, rotifers also play an important role removing additional lead from the medium (up to 44% in some treatments). In the case of mercuric chloride, most of the mercury is bound by the salts contained in EPA medium or discarded by the organisms, and the remainder is removed by N. oculata in <48 h.
    Environmental Toxicology 10/2006; 21(5):533-40.
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    ABSTRACT: We analyzed three species of Lecane, a littoral rotifer, for susceptibility to six metals and four organic toxicants using a fluorometric assay based on inhibition of activity of the enzyme phospholipase A2. The metallic toxicants that we tested included Cd, Cr, Cu, Pb, Hg (as HgCl2), and Ti; the organic toxicants included benzene, ethyl acetate, toluene, and vinyl acetate. The three species differed greatly with respect to their susceptibility to the various toxicants. Lecane quadridentata, for example, was particularly sensitive to the four organic compounds (median effective concentration values [EC50] ranged from 6.6 x 10(-4)-0.987 mg/L). Lecane luna, in contrast, seemed particularly sensitive to metals (EC50 values ranged from 2 x 10(-6)-1.92 mg/L). Lecane hamata was relatively insensitive to organic solvents (EC50 values ranged from 4.25-126.5 mg/L).
    Environmental Toxicology and Chemistry 11/2003; 22(10):2349-53.
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    ABSTRACT: We have developed an esterase inhibition test to investigate the effects of 10 toxicants, including six metals (cadmium, chromium, copper, lead, mercuric chloride, and titanium) and four organics (benzene, ethyl acetate, toluene, and vinyl acetate) in three species of the benthic rotifer genus Lecane (L. hamata, L. luna, and L. quadridentata). Metals affect esterase inhibition by an average value of 4,957-fold greater than the four organics tested for the three rotifer species. Most of the EC50 (effect concentration where a 50% reduction in esterase activity is observed) values correspond to environmentally realistic concentrations. Comparisons of acute-to-chronic ratios among these three species showed that in two species, L. luna and L. quadridentata, esterase inhibition is an outstanding biomarker for most of the toxicants tested.
    Environmental Toxicology and Chemistry 05/2002; 21(4):776-82.
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