Growth, photosynthesis and removal responses of the cyanobacteria Chroococcus sp. to malathion and malaoxon.

Malathion is an organophosphorus pesticide widely used in agricultural crops, despite its toxicity. In addition, malaoxon occurs by oxidation of malathion being more toxic. The toxic effects of malathion and malaoxon in humans include hepatoxicity, breast cancer, genetic damage and endocrine disruption. The aim of this study involved assessing the effect of malathion commercial grade on Chroococcus sp., and its potential as an alternative to the removal of this pesticide and its transformation product such as malaoxon. We evaluated the effect of malathion at different concentrations (1, 25, 50, 75 and 100 ppm) on the biomass of the cyanobacteria Chroococcus sp. grown in medium BG-11; also, we analyse its ability to degrade both malathion and malaoxon into a temperature of 28 ± 2 °C and at pH 6. The results showed that 50 ppm of malathion the cyanobacteria Chroococcus sp. reached the highest removal efficiency of malathion and malaoxon (69 and 65%, respectively); also, the growth rate of Chroococcus sp. increased without inhibiting the production of chlorophyll "a", this can be explained by the hormesis phenomenon. Therefore, we consider that the cyanobacteria Chroococcus sp. may be a good candidate for bioremediation of aquatic systems contaminated with organophosphorus pesticides such as malathion and its transformation product such as malaoxon.

Evaluation of colour temperatures in the cultivation of Dunaliella salina and Nannochloropsis oculata in the production of lipids and carbohydrates.

The production of biofuels from microalgae is a promising and sustainable alternative. Its production is determined by the content of lipids and carbohydrates, which is different for each microalgae species and is affected by environmental factors, being lighting one of the principal determining their biochemical composition. The colour temperature (electromagnetic radiation and light spectrum) is a determining factor for the production of lipids and carbohydrates in microalgae. The aim of this assay was to evaluate the effect of three colour temperatures (6500, 10,000 and 20,000 °K) on the biomass (cel mL-1), biomass production and productivity (g L-1 and g L-1 day-1), lipid and carbohydrate content (%), lipid and carbohydrate production and productivity (mg L-1 and mg L-1 day-1), composition and content of fatty acids (%) in two microalgae species: Dunaliella salina and Nannochloropsis oculata. The highest cell density was observed for N. oculata in stationary phase in the control (83.93 × 106 cel mL-1). However, higher lipid content was obtained in D. salina in stationary phase at 10,000 °K (80%), while N. oculata showed 67% at 6500 °K. The highest carbohydrate content was 25% in stationary phase for D. salina at 20,000 °K. Regarding the production of lipids, D. salina reached a maximum of 523 mg L-1 in exponential phase at 6500 and 10,000 °K. The highest carbohydrate production was 38 mg L-1 for D. salina in exponential phase at 20,000 °K. In both microalgae, 15 different fatty acids were identified; the most abundant was palmitic acid with 35.8% for N. oculata in stationary phase at 10,000 °K, while D. salina showed 67% of polyunsaturated fatty acids in exponential phase at 6500 °K. In conclusion, the ideal colour temperature for microalgae culture to obtain biofuels should be based on the biomolecule of interest, being necessary to individually evaluate for each species.

Effect of the pesticide lindane on the biomass of the microalgae Nannochloris oculata.

This study assesses the growth of the microalgae Nannochloris oculata in the presence of lindane and the ability of N. oculata to remove lindane from media. Algal biomass increased with 0.1 and 0.5 mg L-1 of lindane, and lindane concentrations in the media decreased. N. oculata removed 73% and 68.2% of lindane in the 0.1 and 0.5 mg L-1 media concentrations, respectively. Algal biomass decreased to the level of the control at lindane concentrations greater than 2.5 mg L-1, probably due to toxicity. N. oculata removed lindane from the media at concentrations lower than 1.0 mg L-1. Thus, N. oculata may be useful for lindane bioremediation in contaminated aquatic systems.

Comparing toxicity endpoints on Lecane quadridentata (Rotifera: Monogononta) exposed to two anticholinesterases pesticides.

Toxicity tests were performed on the freshwater rotifer Lecane quadridentata exposed to the pesticides carbaryl and methyl parathion (lethal, sublethal, and chronic) to compare the sensitivity between different endpoints: (a) 48-h mortality; (b) 30-min in vivo inhibition of esterase activity; (c) 5-day inhibition of the instantaneous growth rate. The emphasis of this work was to find the most appropriate endpoint to evaluate the toxicity of these pesticides in view of their sensitivity, duration, and ecological relevance. The comparison between the three toxicity tests show that the 5-day chronic tests have the lowest EC50 (2.22 and 6.6 mg/L), lowest-observed-effect concentration (2.5 and 2.5 mg/L), and no-observed-effect concentration (1.0 and 1.2 mg/L) values for carbaryl and methyl parathion, respectively. This indicates that the estimate of the instantaneous rate of natural increase r is the most sensitive endpoint regarding the toxicity of these pesticides. This sensitivity might be due to the effect on reducing the growth potential form the first generation on. Lethal and sublethal tests are closely related, suggesting that the immediate effect after inhibition of esterases is death. In general, the sensitivity of L. quadridentata is similar to other species of rotifers exposed to methyl parathion. Therefore, the 5-day chronic toxicity test with the freshwater rotifer L. quadridentata should be considered a good candidate to evaluate the effect of anticholinesterase pesticides, due to its high sensitivity and ecological relevance.

Phospholipase A2 activity in three species of littoral freshwater rotifers exposed to several toxicants.

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).

Toxicity testing using esterase inhibition as a biomarker in three species of the genus Lecane (Rotifera).

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.