Comparative ecotoxicity of single and binary mixtures exposures of cadmium and nickel on growth and biomarkers of Lemna gibba.

The aim of the present study was to investigate the toxicity effects of cadmium-nickel (Cd-Ni) after single and mixtures exposures over the macrophyte Lemna gibba. Effects were assessed on growth, as frond number and fresh weight and biochemical parameters, such as total protein content and activity of antioxidant enzymes. Plants were exposed to single Cd and Ni in concentrations that ranged between 0.13-33 mg/L and 0.18 and 11.82 mg/L, respectively. For binary mixtures, individual metal IC50 values were used for selection of the evaluated concentrations. The experimental design consisted in three different ratios based on the concept of toxic units (TU), each ratio was evaluated by five different concentrations. Both single and mixture treatments were performed for 7 days following the conditions according to OECD (2006). Single and mixture exposures affected plant growth and the biomarkers of the antioxidant response. Growth parameters showed a differential sensitivity after individual metal exposures. Cd was more toxic for L. gibba plants when fresh weight was considered, but on the contrary, considering frond number, Ni was the most toxic metal. IC50-7d, based on growth rate calculated on frond number were 17.8 and 2.47 mg/L, and on fresh weight were 1.08 and 3.89 mg/L, for Cd and Ni respectively. LOEC values for Cd were obtained at 2.06 and 1.03 mg/L, for frond number and fresh weight, respectively; while for Ni, these values were 0.92 and 11.82 mg/L. The three evaluated ratios for binary mixtures resulted in a high toxicity considering the same response variables in single metal exposures. Ratio 1 (2/3 TU Cd-1/3 TU Ni) was the most toxic considering both frond number and fresh weight, showing percentage inhibition of growth rates of 96 and 90%, respectively for the highest concentration. A modification of the protein content was observed in single, but especially in the mixture treatments. The activity of catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APOX; EC 1.11.1.11) and guaiacol peroxidase (GPOX; EC 1.11.1.7) was also affected in single and mixtures assays. APOX and GPOX showed a higher increase of its activities respect the controls after mixture treatments than for single metal treatments. Such optimization of the antioxidant system could be one of the causes of the antagonistic toxicity observed in mixture exposures. Concentration addition (CA) reference model, based on frond number, in Cd-Ni mixtures was not a good predictor to evaluate toxicity from dissolved metal concentration since the results showed that toxicity was less than additive, with an average of ΣTU = 2.17. The observed antagonisms resulted to be stronger in mixtures with higher metal concentrations.

Comparative ecotoxicity of single and binary mixtures exposures of cadmium and zinc on growth and biomarkers of Lemna gibba.

In the present study, single and mixture effects of cadmium (Cd) and zinc (Zn) on Lemna gibba were analyzed and compared using growth parameters, based on frond number and fresh weight, and biochemical parameters, such as pigment, protein content and activity of antioxidant enzymes. Plants were exposed for 7 days to these metals in nutrient solution. Single and mixture exposures affected plant growth and the biomarkers of the antioxidant response. Considering the growth parameters, Cd was found to be much more toxic than Zn. IC50-7d, based on growth rate calculated on frond number, were 17.8 and 76.73 mg/L, and on fresh weight were 1.08 and 76.93 mg/L, for Cd and Zn respectively. For Cd, LOEC values were obtained at 2.06 and 1.03 mg/L, for frond number and fresh weight respectively; while for Zn, at 20.1 and 74.6 mg/L. A high toxicity effect, considering the same response variables, was observed in plants exposed to the mixtures. Three fixed ratios, based on toxic units (TU) were assayed, ratio 1: 2/3 Cd-1/3 Zn, ratio 2: 1/2 Cd-1/2 Zn and ratio 3: 1/3 Cd-2/3 Zn. Ratio 3 (where Zn was added in higher proportion) was the less toxic. All concentrations of Ratio 1 and 2 significantly inhibited plant growth, showing a 100% inhibition of growth rate at the highest concentrations when based on frond number. Catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APOX; EC 1.11.1.11) and guaiacol peroxidase (GPOX; EC 1.11.1.7) activities in single metals assays were higher than controls. In mixture tests, the activity of APOX and GPOX was significantly stimulated in plants exposed to all evaluated combinations, while CAT was mainly stimulated in Ratio 3. It was observed that the activity of the enzymes was increased in the mixtures compared with similar concentrations evaluated individually. APOX activity was observed to fit the CA model and following a concentration-response pattern. The response of this antioxidant enzyme could serve as a sensitive stressor biomarker for Cd-Zn interactions. Frond number in Cd-Zn mixtures was not well predicted from dissolved metal concentration in solution using concentration addition (CA) as reference model, as results showed that toxicity was more than additive, with an average of ΣTU = 0.75. This synergistic effect was observed up to 50 mg Zn/L in the mixture, but when it was present in higher concentrations a less than additive effect was observed, indicating a protective effect of Zn. A synergistic and dose-ratio deviations from CA model were also observed.

Comparative ecotoxicity of single and binary mixtures exposures of nickel and zinc on growth and biomarkers of Lemna gibba.

The aim of this study was to compare the ecotoxicity of nickel (Ni) and zinc (Zn) assayed as single and as binary mixture. In addition, how were affected the population growth rates and oxidative stress biomarkers, comparing single to binary exposures. The toxicity tests were performed on Lemna gibba using a 7-day test. All calculations were made using measured total dissolved metal concentrations. IC50-7d, based on growth rate calculated on frond number and fresh weight, were 2.47/3.89 mg/L, and 76.73/76.93 mg/L, for Ni and Zn, respectively. Single metals affected plant growth following a non-linear concentration-response relationship. LOEC values for each metal were obtained at 0.92 and 20.1 mg/L for Ni and Zn, respectively. Biomarkers of the antioxidant response like Catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APOX; EC 1.11.1.11) and guaiacol peroxidase (GPOX; EC 1.11.1.7) activities in single metals assays were higher than controls, but when similar concentrations were added as mixtures, that increase was reduced and inhibition with respect to the control was observed for GPOX. APOX showed the highest activity. The concentration addition (CA) approach was evaluated and resulted in a correct predictor of Ni-Zn mixture toxicity on Lemna gibba. This was made comparing the EC50 and LOEC, measured taking the growth rate as endpoint, with those expected values according to the CA model. However, the measured biomarkers indicating a positive response to free radicals did not fit to concentration addition model when assayed in the binary mixture. Also, the main activity response of these was observed within a range of concentrations below the LOEC values for the mixture.

Duckweed in Irrigation Water as a Replacement of Soybean Meal in the Laying Hens Diet

Water lentils (Duckweed [DW])(Lemna gibba), in irrigation ponds, was evaluated by replacing two levels of soybean meal (SBM) on performance and egg quality of laying hens of 54 weeks of age. A total of 72 white Lohmann laying hens were randomly allocated into 3 treatments with 6 replicates/treatment, 4 hens/replicate in a randomized complete block design. Treatments were: control group (DW0%) with (SBM) as the main source of protein, T1 (DW10%) and T2 (DW20%), where duckweed replaced 10% and 20% of SBM for 9 weeks. No significant differences were observed among the dietary treatments in body weight change, feed conversion ratio, egg weight and mortality rate. Replacement with (DW20%) decreased (p 0.05) feed intake, egg laying rate and egg mass. The dry albuminin (DW10%) decreased (p 0.05) from 7 to 9 weeks and in the total period. Yolk pigmentation was highly (p 0.001) improved by the replacement. Blood spots were increased (p 0.05) with (DW20%). Duckweed grown in good quality irrigation water can replace up to 10% of the SBM as a source of protein without adverse effects on hen performance and egg quality in addition to profitability.(AU)

Duckweed in Irrigation Water as a Replacement of Soybean Meal in the Laying Hens Diet

Water lentils (Duckweed [DW])(Lemna gibba), in irrigation ponds, was evaluated by replacing two levels of soybean meal (SBM) on performance and egg quality of laying hens of 54 weeks of age. A total of 72 white Lohmann laying hens were randomly allocated into 3 treatments with 6 replicates/treatment, 4 hens/replicate in a randomized complete block design. Treatments were: control group (DW0%) with (SBM) as the main source of protein, T1 (DW10%) and T2 (DW20%), where duckweed replaced 10% and 20% of SBM for 9 weeks. No significant differences were observed among the dietary treatments in body weight change, feed conversion ratio, egg weight and mortality rate. Replacement with (DW20%) decreased (p 0.05) feed intake, egg laying rate and egg mass. The dry albuminin (DW10%) decreased (p 0.05) from 7 to 9 weeks and in the total period. Yolk pigmentation was highly (p 0.001) improved by the replacement. Blood spots were increased (p 0.05) with (DW20%). Duckweed grown in good quality irrigation water can replace up to 10% of the SBM as a source of protein without adverse effects on hen performance and egg quality in addition to profitability.

Duckweed in Irrigation Water as a Replacement of Soybean Meal in the Laying Hens Diet

ABSTRACT Water lentils (Duckweed [DW])(Lemna gibba), in irrigation ponds, was evaluated by replacing two levels of soybean meal (SBM) on performance and egg quality of laying hens of 54 weeks of age. A total of 72 white Lohmann laying hens were randomly allocated into 3 treatments with 6 replicates/treatment, 4 hens/replicate in a randomized complete block design. Treatments were: control group (DW0%) with (SBM) as the main source of protein, T1 (DW10%) and T2 (DW20%), where duckweed replaced 10% and 20% of SBM for 9 weeks. No significant differences were observed among the dietary treatments in body weight change, feed conversion ratio, egg weight and mortality rate. Replacement with (DW20%) decreased (p 0.05) feed intake, egg laying rate and egg mass. The dry albuminin (DW10%) decreased (p 0.05) from 7 to 9 weeks and in the total period. Yolk pigmentation was highly (p 0.001) improved by the replacement. Blood spots were increased (p 0.05) with (DW20%). Duckweed grown in good quality irrigation water can replace up to 10% of the SBM as a source of protein without adverse effects on hen performance and egg quality in addition to profitability.

Sulfur metabolism: different tolerances of two aquatic macrophytes exposed to arsenic.

The toxicity of arsenic (As) and the mechanisms of response to this pollutant were analyzed in two aquatic plant species, one sensitive and one tolerant to the pollutant, Salvinia minima and Lemna gibba, respectively. The plants, grown in nutrient solution at pH 6.5, were exposed to As concentrations of 0.0 and 1.0mgL(-1) for 3 days. Both species accumulated As in their tissues, which resulted in increases in H2O2 production. L. gibba accumulated eleven times more As than S. minima. However, L. gibba was more tolerant, as shown by the absence of cell membrane damage and, despite greater accumulation, smaller growth reduction than S. minima. Indeed, the index of tolerance to As was twenty percent higher in L. gibba than in S. minima, which most likely results from the presence of a more efficient defense system. This defense system in L. gibba is most likely based on sulfate absorption, assimilation and metabolism. L. gibba showed an increase in sulfate absorption and adenosine-5'-triphosphate (ATP) sulfurylase activity (the first enzyme of the inorganic sulfate assimilation pathway) following exposure to As. Consequently, the plant produced greater concentrations of sulfur-containing compounds that are involved in cellular detoxification, such as glutathione and non-protein thiols, and demonstrated greater enzymatic activity of γ-glutamylcysteine synthetase, glutathione S-transferase and glutathione reductase. Therefore, the plant׳s ability to increase absorption, assimilation and metabolism of sulfur are key steps for tolerance to oxidative stress triggered by metals.

Efecto del nitrógeno, fósforo y potasio del medio de cultivo en el rendimiento y valor nutritivo de Lemna gibba L. (Lemnaceae)

Se cultivó Lemna gibba en exteriores para determinar el efecto de tres proporciones de N-NH4+:N-NO3- (1:3, 1:1 y 3:1) así como de las concentraciones de fósforo (1,5; 3,0 y 4,5 mg.L-1) y potasio (3,0; 6,0; y 9,0 mg.L-1) adicionadas en el medio de cultivo sobre el rendimiento y contenido de nitrógeno, fósforo y potasio. Los rendimientos de peso fresco y seco disminuyeron al incrementar la proporción del N-NH4+. El incremento de la concentración de potasio del medio de cultivo elevó el rendimiento del peso fresco. El contenido de materia seca disminuyó con proporciones de N-NH4+ superiores a las de N-NO3-, así como con el incremento de la concentración de potasio en el medio de cultivo. La absorción y contenido de nitrógeno aumentó al elevar la proporción de N-NH4+; e, incrementando las concentraciones de fósforo y potasio en el medio de cultivo. La absorción y contenido, tanto del fósforo como del potasio, se incrementan a medida que sus respectivas concentraciones en el medio de cultivo se elevan. Altas proporciones de N-NH4+ en el medio de cultivo disminuyen el contenido de fósforo y potasio en la materia seca. Los rendimientos y contenidos de proteína cruda de L. gibba se optimizan con proporciones N-NH4+:N-NO3- de 1:1 y 3:1 en el medio de cultivo respectivamente. Concentraciones superiores a 9 y 4,5 mg.L-1 de potasio y fósforo respectivamente son óptimas.

Lemna gibba was grown in outdoor to determine the effect of three N-NH4+:N-NO3- proportions (1:3, 1:1 and 3:1), as well as the phosphorus (1,5; 3,0 and 4,5 mg.L-1) and potassium (3,0; 6,0 and 9,0 mg.L-1) concentrations added to the culture medium, on the yield and nitrogen, phosphorus and potassium content. Both, fresh and dry weight yields decreased as N-NH4+ proportion increased. Increasing culture medium potassium concentration favored the fresh weight yield. Dry matter content decreased with both N-NH4+ proportions higher than N-NO3- and increasing the potassium concentration in the culture medium. Nitrogen uptake and content enhanced with high N-NH4+ proportions; and, by increasing phosphorus and potassium concentrations in the culture medium. Phosphorus and potassium uptake and content increased as their respective culture medium concentration increased. High proportions of N-NH4+ in the culture medium decreased phosphorus and potassium content in dry matter. L. gibba yields and crude protein content are optimize with culture medium N-NH4+:N-NO3- proportion of 1:1 and 3:1 respectively. Potassium and phosphorus concentrations over 9 and 4,5 mg.L-1 respectively are optimal.