Effects of [alpha]-Ag.sub.2WO.sub.4 crystals on photosynthetic efficiency and biomolecule composition of the algae Raphidocelis subcapitata

The [alpha]-Ag.sub.2WO.sub.4 (hexagonal rod-shaped) is a multifunctional material with interesting physical and chemical properties, such as good electronic, photocatalytic, anticancer and microbicidal performance. Considering this, its use can contribute to the presence and accumulation of this compound in freshwater ecosystems. Therefore, the present study investigated the effects of [alpha]-Ag.sub.2WO.sub.4 on the freshwater Chlorophyceae Raphidocelis subcapitata, at the level of cell density, chlorophyll a (Chl a), total carbohydrate contents, and photosynthetic activity (maximum quantum yield and oxygen-evolving complex-OEC). The [alpha]-Ag.sub.2WO.sub.4 reduced cell density by ~ 48% already in the first 24 h of exposure at 31.76 [mu]g L.sup.-1 (highest concentration). Moreover, at 31.76 [mu]g L.sup.-1, we observed a drastic reduction in the maximum quantum yield, and impact in the oxygen evolving complex at 24 h and 48 h. However, our results indicated a possible recovery of the photosynthetic activity in the surviving algal cells at 72 and 96 h. The contents of chlorophyll a (Chl a) and total carbohydrates decreased significantly (Dunnett's test, p < 0.05) at 4.11, 5.84, 10.55, and 10.67 [mu]g L.sup.-1 treatments and increased significantly (Dunnett's test, p < 0.05) at the highest concentration (31.76 [mu]g L.sup.-1), which is possibly a mechanism for the algal cells to optimize the amount of energy to be used in the photosynthetic process and maintaining the integrity of the cell wall. This study contributes to clarifying how [alpha]-Ag.sub.2WO.sub.4 interacts with R. subcapitata showing the toxicity mechanism of photosynthetic activity. This can help predict the fate and effect of these composites by providing a basis for their ecological risk assessment.