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Phytoplankton deal with metal toxicity using a variety of biochemical strategies. One of the strategies involves glutathione (GSH) and phytochelatins (PCs), which are metal-binding thiol peptides produced by eukaryotes and these compounds have been related to several intracellular functions, including metal detoxification, homeostasis, metal resistance and protection against oxidative stress. This paper assesses our state of knowledge on the production of PCs and GSH by marine phytoplankton in laboratory and field conditions and the possible applications of PCs for environmental purposes. Good relationships have been observed between metal exposure and PC production in phytoplankton in the laboratory with Cd, Pb, and Zn showing the greatest efficacy, thereby indicating that PCs have a potential for application as a biomarker. Fewer studies on PC distributions in particulate material have been undertaken in the field. These studies show that free Cu has a strong relationship with the levels of PC in the particulate material. The reason for this could be because Cu is a common contaminant in coastal waters. However it could also be due to the lack of measurements of other metals and their speciation. GSH shows a more complex relationship to metal levels both in the laboratory and in the field. This is most likely due to its multifunctionality. However, there is evidence that phytoplankton act as an important source of dissolved GSH in marine waters, which may form part of the strong organic ligands that control metal speciation, and hence metal toxicity.

A maioria dos métodos para análise de esteróides em sedimentos marinhos é laboriosa, consome grandes volumes de solventes orgânicos (muitas vezes clorados) e produz grandes quantidades de material de descarte. Neste trabalho desenvolveu-se um método de extração com etanol e um "clean up" rápido, que oferece uma alternativa de menor custo e minimiza o uso de solventes clorados. As porcentagens de recuperação de esteróides (coprostanol, epicoprostanol, cholesterol, cholestanol, 5a-coprostanona and 5b-coprostanona) ficaram na faixa de 70 a 93%, comparáveis às análises mais tradicionais. A eficiência do método foi avaliada através de material de referência e os resultados obtidos para coprostanol, colesterol e colestanol encontram-se próximos aos valores médios certificados e perfeitamente dentro dos valores aceitáveis. Os desvios-padrão relativos para triplicatas foram baixos (6-12%). Os testes indicaram que o "clean-up" simplificado (sem fracionamento) não produz interferência na quantificação dos esteróides fecais.The majority of the analytical methods for steroids in marine sediments are laborious and time consuming and involve the use of large volumes of organic (frequently chlorinated) solvents. A method has been developed utilising ethanol extraction with a rapid alumina-ethanol elution clean up, providing an environmentally friendly and inexpensive alternative. Recoveries of steroids (coprostanol, epicoprostanol, cholesterol, cholestanol, 5a-coprostanone and 5b-coprostanone) ranged from 70 to 93% and compared favourably with more traditional analyses. Analytical performance was tested through analysis of reference material and concentrations recorded for coprostanol, cholesterol and cholestanol were close to the mean certified values and were within acceptable values. Relative standard deviations from triplicate analyses were small (6-12%). These initial tests also indicate that the simplified clean up (without fractionation) is not subject to interference in the quantification of the selected faecal steroids.

Copper, Cd and Zn can be found at elevated concentrations in contaminated estuarine and coastal waters and have potential toxic effects on phytoplankton species. In this study, the effects of these metals on the intracellular production of the polypeptides phytochelatin and glutathione by the marine diatom Phaeodactylum tricornutum were examined in laboratory cultures. Single additions of Cu and Cd (0.4 microM Cu2 and 0.45 microM Cd2+) to the culture medium induced the production of short-chained phytochelatins ((gamma-Glu-Cys)n-Gly where n = 2-5), whereas a single addition of Zn (2.2 microM Zn2+) did not stimulate phytochelatin production. Combination of Zn with Cu resulted in a similar phytochelatin production compared with a single Cu addition. The simultaneous exposure to Zn and Cd led to an antagonistic effect on phytochelatin production, which was probably caused by metal competition for cellular binding sites. Glutathione concentrations were affected only upon exposure to Cd (85% increase) or the combination of Cd with Zn (65% decrease), relative to the control experiment. Ratios of phytochelatins to glutathione indicated a pronounced metal stress in response to exposures to Cu or Cd combined with Zn. This study indicates that variabilities in phytochelatin and glutathione production in the field can be explained in part by metal competition for cellular binding sites.

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