Determination of dissolved organic nitrogen in seawater using Kjeldahl digestion after inorganic nitrogen removal

8 páginas, 6 tablas, 1 figura[EN] An update of the Kjeldahl method is presented for the direct determination of dissolved organic nitrogen (DON) in seawater. Dissolved inorganic nitrogen is previously removed: ammonium as NH3 with NaOH at pH 9.4; and, subsequently, nitrate and nitrite as nitric oxide with FeSO4 in acid medium. The sample is then mineralized to ammonium, which is measured with a Technicon autoanalyzer by the indophenol blue method. The range of recovery for tested standard compounds is similar to those obtained by high temperature oxidation (HTO) techniques. Direct determination of DON by the method described in this work marks an improvement in precision, in comparison with other methods; the standard deviation obtained for samples of seawater is +/-0.2 mu mol.l(-1). The precision of DON measurements is not dependent on dissolved inorganic nitrogen analysis. For several stations in the Northeast Atlantic Ocean, DON values ranged between 3 and 10 mu mol.l(-1).[FR] La méthode de Kjeldahl a été modifiée pour réaliser la mesure directe de l'azote organique dissous (NOD) dans l'eau de mer. Les composés inorganiques dissous dans l'échantillon sont préalablement éliminés comme suit: l'ammonium, en rendant le milieu basique avec de la soude; le nitrate et le nitrite, en les transformant en oxyde nitrique par le FeS04 en milieu acide. L'échantillon est ensuite minéralisé pour transformer le NOD en ammonium dont la concentration est déterminée sur un AutoAnalyseur Technicon. La récupération des produits standard est identique à celle obtenue par des techniques d'oxydation à haute température. La détermination du NOD par cette méthode est améliorée car elle ne dépend plus de la mesure des concentrations en azote minéral comme dans les autres méthodes. L'écart-type est d'environ ±0,2 J.Lmol.l-1 pour des échantillons d'eau de mer. Les concentrations, mesurées par cette technique à plusieurs stations de l'océan Atlantique NE, varient de 3 à 10 J.Lmol.l- 1•Support for this work came from the EEC project MAST2- CT93-0065.Peer reviewe

Implications of water hardness in ecotoxicological assessments for water quality regulatory purposes: a case study with the aquatic snail Biomphalaria glabrata (Say, 1818)

Water hardness is a property depending on the presence of alkaline earth metals, mainly calcium and magnesium. Among the strategies for water quality monitoring, ecotoxicological assays are performed to minimize impacts and classify water bodies. For these laboratory evaluations parameters are previously defined in the guidelines, including water hardness for both cultivation and testing medium. The present work was performed to evaluate the effects of different levels of water hardness on the survival and reproduction of the freshwater snail Biomphalaria glabrata and discuss the influence of natural water hardness on the results of ecotoxicological tests with these environmental samples. Comparing the groups it was possible to observe that those maintained in waters with least hardness had lower reproductive success, while the groups maintained in highest hardness showed better reproduction. These data show that waters with low hardness make the reproduction of the snail B. glabrata unfeasible, and this reveal a problem for ecotoxicity assays using natural water samples

Stress response and changes in amino acid requirements in Senegalese sole (Solea senegalensis Kaup 1858)

Fish in aquaculture are often exposed to various stressors that may change their ability to survive or limit growth. Amino acids are used for processes other than growth, including stress response. This study intended to analyse how repeated acute handling stress can affect growth and amino acid requirements in fish. Senegalese sole juveniles were weekly held in the air during 3min (Handling) for 9 weeks; Control groups were left undisturbed. Growth and plasma levels of stress indicators and of free amino acids were assessed at the end of the experiment. Plasma cortisol and osmolality levels showed that fish in the Handling treatment were stressed, but growth was unaffected. Plasma amino acid concentrations indicate that their requirements in stressed fish were altered, which probably reflects the synthesis of proteins or other specific compounds related to stress response

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Interactive effects of a high-quality protein diet and high stocking density on the stress response and some innate immune parameters of Senegalese sole Solea senegalensis

Amino acids (AA) regulate key metabolic pathways, including some immune responses. Therefore, this study aimed to assess whether an increased availability of dietary AA can mitigate the expected increase in plasma cortisol and metabolites levels due to high stocking density and its subsequent immunosuppression. Senegalese sole (Solea senegalensis) were maintained at low stocking density (LSD; 3.5 kg m−2) or high stocking density (HSD; 12 kg m−2) for 18 days. Additionally, both treatments were fed a control or a high protein (HP) diet (LSD, LSD HP, HSD and HSD HP). The HP diet slightly increased the levels of digestible indispensable AA, together with tyrosine and cysteine. HSD was effective in inducing a chronic stress response after 18 days of treatment since fish held at HSD presented higher plasma cortisol, glucose and lactate levels. Moreover, this increase in stress indicators translated in a decrease in plasma lysozyme, alternative complement pathway (ACP) and peroxidase activities, suggesting some degree of immunosuppression. Interestingly, while plasma glucose and lactate levels in HSD HP specimens decreased to similar values than LSD fish, plasma lysozyme, ACP and peroxidase activities increased, with even higher values than LSD groups for ACP activity. It is suggested that the HP diet may be used as functional feed since it may represent a metabolic advantage during stressful events and may counteract immunosuppression in sole

Avaliação da qualidade de vida geral de agentes comunitários de saúde: a contribuição relativa das variáveis sociodemográficas e dos domínios da qualidade de vida Evaluation of overall quality of life of community health agents: the relative contribution of sociodemographic variables and domains of quality of life

OBJETIVO: Avaliar a contribuição relativa de cada domínio da qualidade de vida (físico, psicológico, relações sociais e meio ambiente) e das variáveis sociodemográficas para a qualidade de vida geral de agentes comunitários de saúde de um município do interior do Paraná, Brasil. MÉTODO: Estudo descritivo, de corte transversal e com abordagem quantitativa. O grupo de estudo foi composto por 169 agentes (86,2% do total), que responderam o World Health Organization Quality of Life Instrument Bref, instrumento genérico para avaliar qualidade de vida, proposto pela Organização Mundial da Saúde. Foram utilizados testes de correlação e regressão linear multivariada. O nível de significância adotado para as análises foi de 5%. RESULTADOS: Das variáveis sociodemográficas analisadas, nenhuma contribuiu de modo significativo para o domínio geral da qualidade de vida. Para os quatro domínios, o que mais contribuiu para a qualidade de vida geral foi o físico, seguido do psicológico e do meio ambiente, os três explicando 47,9% da variância. O domínio das relações sociais não contribuiu significativamente para a qualidade de vida geral. CONCLUSÃO: Observou-se que a variância da qualidade de vida geral não foi completamente explicada pelas variáveis sociodemográficas e pelos domínios da qualidade de vida. Assim, maior atenção deve ser dada pelos pesquisadores aos diferentes modos de entender qualidade de vida, em especial valorizando métodos de pesquisa e avaliação interdisciplinar.<br>OBJECTIVE: This study aimed at evaluating the relative contribution of each life quality domain (physical, psychological, social relationships and environment) and of sociodemographic variables to overall quality of life of community health agents from a municipality located in the State of Paraná, Brazil. METHODS: A descriptive and cross-sectional study was carried out using a quantitative approach. The sample was composed of 169 agents (86.2% of the total). The World Health Organization Quality of Life Instrument Bref was used as a generic instrument to evaluate quality of life. Correlation tests and multivariate linear regression were used, considering a significance level of 5%. RESULTS: None of the sociodemographic variables significantly interfered with overall quality of life. Among the four domains, the physical domain contributed the most to overall quality of life, followed by the psychological and environment domains, all of them accounting for 47.9% of variance. The domain of social relationships did not show significant contribution to overall quality of life. CONCLUSION: It was observed that variance of overall quality of life was not completely explained by sociodemographic variables neither by quality of life domains. Thus, more attention should be given by researchers to different forms of understanding quality of life, especially research methods and interdisciplinary evaluation