Browsing by Author "Silva, Nelson A. F."
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- Determination of antioxidants and total polyphenols in cabbages (Brassica Oleracea) irrigated wiht wastewater contaminated with toxic metalsPublication . Silva, Hugo F.A.; Barreiros, Ana Maria; Silva, Nelson A. F.; Oliveira, Cristina; Coelho, Jose; Matos, ManuelWater is a natural resource essential to all kinds of life. The reuse of treated wastewater (TWW) for irrigation is a possibility with challenges to be clarified at scientific level, in particular, its use in irrigation activities due to the eventual contamination of vegetables, like cabbages (Brassica oleracea), by toxic metals and other compounds harmful to humans present in these waters. On the other hand, the use of TWW for vegetable irrigation may allow significant water saving and also providing the cultivated species with nutrients, which may dispense the use of fertilizers. In this work, vegetables such as Brassica oleracea (cabbage), were planted in a greenhouse with a controlled environment (temperature and humidity) located at ISEL campus. Part of the vegetables was irrigated with tap water, and another part with TWW from two wastewater treatment plants (WWTP) located in Lisbon´s District. One of the WWTP receives only domestic wastewater (A), whilst the other one receives industrial and domesti
- Development of a flow injection analytical system for short chain amide determination based on a tubular bioreactor and an ammonium sensorPublication . Veríssimo, M.I.S.; Oliveira, Sara B.; Silva, Nelson A. F.; Matos, Manuel; Karmali, Amin; Gomes, Maria Teresa SRPseudomonas aeruginosa (P. aeruginosa) possesses intracellular amidase activity, which catalyses the hydrolysis of short aliphatic amides producing NH4 +, and has already been used along with an ammonium ion selective electrode for amide quantification. However, the incorporation of a biological membrane turned to be a challenging process and either the final arrangement was prone to amidase losses or the recovery of the sensor coating after the interaction took too long. In this article a flow injection system with an ammonium acoustic wave sensor is proposed, and after testing several different arrangements for the biological element, the ultimate choice consisted of the immobilization of a P. aeruginosa cell-free extract in the inner wall of a tubular glass reactor, which resulted in a reliable analytical system. Response times less than one minute and complete recovery in less than two minutes assured conveniently fast analysis. The analytical system, as long as the column was properly stored in HEPES buffer containing 2 mM β-mercaptoethanol and 1 mM benzamidine and refrigerated when not in use, could be used at least for 20 working days, along a period of one month, maintaining the initial sensitivity.
- A Flow Injection Methodology for Acetamide Determination Using a Tubular Bioreactor and na Ammonium Sensor †Publication . Veríssimo, Marta I. S.; Silva, Nelson A. F.; Karmali, Amin; Gomes, Maria Teresa S. R.Pseudomonas aeruginosa (P. aeruginosa) is a Gram-negative bacterium quite versatile that grows in the soil, in coastal marine habitats, as well as in the tissues of plants and animals. P. aeruginosa is the source of amidase (acylamide amidohydrolase E.C. 3.5.1.4) which catalyzes the hydrolysis of a small range of short aliphatic amides into the corresponding carboxylic acids and ammonia. A low cost piezoelectric quartz crystal coated with a selective membrane for ammonium was used to detect the reaction product. Conversion of amide into the correspondent amine was achieved both with cell-free extract of P. Aeruginosa or the whole cells. This conversion was first performed in batch and later on injected into the sensor system where a buffer carrier was flowing over the coated crystal. Another approach consisted in incorporating a conversion reactor with the immobilized cell-free extract of P. Aeruginosa in the FIA system. Amide solutions were injected and carried by the buffer stream through the reactor and then directed to the sensor. Different supports were used for immobilization, such as calcium alginate beads, glass beads and the inside walls of a hollow glass column. The best arrangement allowed acetamide determination without sensitivity lost for 1-month period.
- Heavy metals contamination of urban soils—a decade study in the city of Lisbon, PortugalPublication . Silva, Hugo; Silva, Nelson A. F.; Oliveira, Cristina; Matos, ManuelThere is an intense and continuous growth of the world population living in cities. This increase in population means an increase in car traffic, an increase in new constructions and an increase in the production of waste that translates into an intensive use of land, particularly in terms of soil contaminants. Among other environmental contaminants, toxic metals, such as lead (Pb), cadmium (Cd), nickel (Ni) and chromium (Cr) represent a public health problem. In this study the content of toxic metals in Lisbon’s (Portugal) soils was determined. The study was conducted over approximately a decade in six city locations, with a total of about 700 samples. Each site has different urban characteristics: traffic zone, residential area, urban park and mixed areas. The study allowed to verify the heterogeneity of metal content values in the city soils and their dependence on local traffic. Metal contents were determined by graphite furnace atomic absorption spectroscopy (GFAAS). For each site the geo-accumulation index, pollution factor, degree of contamination, pollution load índex and ecological risk factor were calculated. The mean concentrations of Cd, Cr, Ni and Pb in soils were 0.463, 44.0, 46.6 and 5.73 mg/kg of dry soil, respectively. In the last year of the study the values were 0.417, 51.5, 62.4 and 8.49 mg/kg of dry soil, respectively. Cd and Ni exceeded the typical content values of these metals in the earth’s crust, indicating their anthropogenic origin. The correlation analysis revealed a significant correlation between Cr and Ni, Cd and Ni and Cd and Pb contents in the city soils. Regarding the results obtained in this long monitoring campaign, Lisbon’s soils can be considered as having low levels of pollution by these metals.
- A systematic procedure to enhance reproducibility of SWASV cycles in the determination of toxic metals in real samplesPublication . Silva, Nelson A. F.; Leitão, Ruben A. E.; Matos, Manuel J.This work presents for the first time a systematic study on the optimization of the electrochemical cleaning time of a mercury film when it is used as a working electrode material in the analysis of toxic metals, such as Pb2+, used as model metal, in real samples by SWASV. The optimization study for the film’s cleaning time aimed at attaining a Pb2+ minimum value in the film after the re-oxidation step of the pre-concentrated metal, given the impossibility of complete removal of traces of the electroactive species from the film. This value was kept constant in each concentration range studied ensuring thus that all assays were performed in initial identical conditions. An assay performed on a synthetic sample was taken as reference. In it, given the absence of matrix effects, and after the electrochemical cleaning step, a direct proportionality was observed between the residual amounts of Pb2+ in the film (which for the cleaning time used was never completely removed) and Pb2+ concentration in the solution. This fact determined a high correlation between Pb2+ peak current and Pb2+ concentration which was not observed when real samples (tree leaves) were analyzed. This behavior may result from the presence of the interfering surfactants always present in real samples of complex matrix. Cleaning time optimization was performed for the following Pb2+ concentration ranges in the real samples of complex matrix: 0.006-0.020, 0.020-0.080, 0.060-0.200 and 0.100-0.600 ppb. As expected, in order to obtain identical levels of film’s cleaning efficiency, the need for longer cleaning times has been observed for higher concentrations. The optimized cleaning times for the concentration ranges under study were 120, 150, 180 e 300 s, respectively.