<span style="font-size:15.0pt;mso-bidi-font-size: 14.0pt;font-family:"Times New Roman";mso-fareast-font-family:"Times New Roman"; mso-bidi-font-family:Arial;mso-ansi-language:EN-GB;mso-fareast-language:EN-US; mso-bidi-language:HI;mso-bidi-font-weight:bold" lang="EN-GB">Tide dependent seasonal changes in water quality and assimilative capacity of anthropogenically influenced Mormugao harbour water</span>

314-330Water quality data from Mormugao harbour area at the mouth of Zuari estuary in Goa have been obtained over two tidal cycles monthly for the year 2003 to 2004. R-mode factor analyses of the data indicated strong positive loadings of coliforms, nitrogenous substances, PHc and some heavy metals during post-monsoon, suggesting their dominance and significant increase relative to other seasons. Water quality index (WQI) studies showed overall index of pollution (OIP) values of 1.41 to 3.52, categorizing the harbour water as slightly polluted during pre-monsoon. During post-monsoon, the OIP values of 1.75 to 5.4 categorized the harbour water as polluted water, while it was acceptable quality water during the monsoon, with OIP values of 1.13 to 1.79. The higher chlorophyll a (1.4-19 mgm<span style="mso-bidi-font-family: " times="" new="" roman""="" lang="EN-GB">–3 g/l) and primary productivity (4.8-14.8 mg/l) of the monsoon was followed by that of the post-monsoon season, with the least during pre-monsoon. Modeling studies using Ecolab module of MIKE 21 suggested slightly higher assimilative capacity for harbour water during the pre-monsoon relative to post-monsoon, which showed a reduction in assimilative capacity. </span

Extraction, partial characterization and susceptibility to Hg2+ of acid phosphatase from the microalgae Pseudokirchneriella subcapitata Extração, caracterização parcial e susceptibilidade ao Hg2+ da fosfatase ácida da microalga Pseudokirchneriella subcapitata

Pseudokirchneriella subcapitata is a unicellular green algae widely distributed in freshwater and soils. Due to its cosmopolitan characteristic, its use is recommended by national and international protocols in ecotoxicity studies. The alteration of phosphatase activities by agriculture pollutants like heavy metals has been extensively used as a biomarker in risk assessment and biomonitoring. In this study, we compared the extraction of acid phosphatase from P. subcapitata by different procedures and we studied the stability, substrates specificity, kinetics and the effect of Hg2+ in the crude extract. The freezing and thawing technique associated with probe sonication was the most suitable method of extraction. The enzyme was stable when frozen at -20ºC for at least six months, showed an optimum pH of 5 and a Km value of 0.27 mM for p-nitrophenylphosphate (pNPP) as substrate. Some natural organic substrates were cleaved by a similar extent as the synthetic substrate pNPP. Short term exposure (24 hours) to Hg2+ had little effect but inhibition of the specific activity was observed after 7 days with EC50 (concentration of Hg2+ that promotes 50% decrease of specific activity) value of 12.63 &#956;M Hg2+.<br>Pseudokirchneriella subcapitata é uma alga verde unicelular amplamente distribuída em corpos d´agua e solos. Devido a sua natureza cosmopolita, seu uso é recomendado por protocolos nacionais e internacionais na realização de estudos de ecotoxicidade. A alteração da atividade de fosfatases por agentes poluentes de origem agrícola, como metais pesados, tem sido largamente usada como um biomarcador na avaliação de risco e biomonitoramento. No presente trabalho foi comparada a extração da fosfatase ácida de P. subcapitata por diferentes métodos e estudada a sua estabilidade, especificidade por substratos, cinética e efeito do Hg2+ no extrato bruto. O congelamento e descongelamento, associado com ultrassom, foi o método que proporcionou maior rendimento de extração. A enzima, praticamente estável por armazenamento a -20ºC, durante aproximadamente seis meses, demonstrou uma atividade ótima em pH 5 e um valor de Km para o p-nitrofenilfostato (pNPP) de 0,27 mM. Alguns substratos naturais foram hidrolisados com uma intensidade semelhante à do substrato sintético pNPP. Diferentemente dos estudos de exposição a curto prazo (24 horas), observou-se inibição da atividade específica nas culturas expostas durante 7 dias, com um valor de CE50 (concentração de Hg2+ que promove 50% de decréscimo da atividade específica) equivalente a 12,63 &#956;M Hg2+