The aim of this study was to evaluate the effects of chromium exposure on the growth of P. subcapitata using the Central Composite Design (CCD) and Response Surface Methodology (RSM). The highest values for algal density and biomass were obtained in the longest exposure times and for the lowest chromium concentrations. The CCD used for the analysis of treatment combinations showed that a second order polynomial regression model was in good agreement with experimental results, with R (2) = 81.50 and 89.90; for algal density and biomass (p < 0.05), respectively. Only the exposure time was significant for algal density. For chlorophyll, in contrast, the exposure time, chromium concentration and their interaction significantly affected the growth of P. subcapitata. The findings confirmed the sensitivity of P. subcapitata to chromium (VI), which makes it a suitable bioindicator of environmental contamination for this metal.

The effects of chromium bioaccumulation in Pseudokirchneriella subcapitata were evaluated by Central Composite Design (CCD), factorial 22 and Response Surface Methodology (RSM). All the models of regression generated by CCD were highly significant, with R2 between 77 and 88%, which is the percentual variability in the response that the model can account for. This is indicative of a satisfactory representation of the process models whose data can be used for simulations of response. The maximum shrinkage biovolume presented 28–69% reduction compared to controls. Results from this study suggest that the smaller algal cells amplify metal binding sites, leading to an increased bioaccumulation and a consequential increased capacity to accumulate chromium. Nevertheless, the absorption capacity decreases for more elevated chromium concentrations and for longer exposure.