CULTURE STUDIES ON ARSENIC (AS III, AS V, MMAA) INTERACTION WITH THREE FRESHWATER ALGAE (MICROCYSTIS AERUGINOSA, ACTINASTRUM HANTZSCHII AND ASTERIONELLA FORMOSA) (MONOMETHYLARSONIC ACID).

摘要

Algal As metabolism was studied by laboratory incubation experiments for elucidating environmental character of various As forms {lcub}arsenate (Na(,2)HAsO(,4)), arsenite (NaAsO(,2)), and monomethylarsonic acid (CH(,3)AsO(,3)H(,2) = MMAA){rcub}. Unialgal batch cultures of Microcystis aeruginosa (Cyanophyta), Actinastrum hantzschii (Chlorophyta), and Asterionella formosa (Bacillariophyta) were employed for the work. This work provides insight into algal role in mediating the geochemical behavior of this widespread element and into mechanisms and factors controlling As partitioning with phytoplankton.; The bioavailability and differential uptake patterns of chemical As forms were established. As uptake varied with its form and concentration as well as algal species.; External nutrient (P) concentration was found to control the extent of As accumulation. Phosphorus enrichment inhibited As uptake in a concentration dependent fashion. Moreover, As appeared to alter algal P utilization. Although the antagonism was most conspicuous in the case of arsenate, was not restricted to this species, relation was observed also between arsenite, monomethylarsonic acid and phosphorus. These findings lead to some implications about the ecological role of the antagonism with regard to nutrient dynamics. Inorganic and organic As exhibited different uptake modes, suggesting several binding mechanisms. Inorganic arsenical uptake appeared to be a multistep process. Time course studies of As excretion from algal cells revealed that biphasic retention and removal processes would be at least partly governing uptake. Organic As uptake followed a less complex mode.; Differential sensitivity of As species uptake to light-dark conditions and metabolic inhibitors indicated different transport mechanisms for the three arsenicals.; The impact of sublethal As levels on algal biochemical and physiological functions: growth, photosynthesis, ATP and pigment contents, were monitored.; Biological effects of arsenicals seemed to depend on As level, chemical form and P concentration. A great deal of variability was observed among different algae in their sensitivity and responses to As exposure. The diatom, A. formosa displayed the most sensitive and the blue-green and green algae, M. aeruginosa and, A. hantzschii the most tolerant responses. High P levels mitigated algal reactions. As induced changes in algal metabolism ranged from inhibition of growth, photosynthesis and ATP formation to their enhancement. Arsenicals stimulated algal chlorophyll accumulation.