Implications of dissolved organic carbon, turbidity and salinity on detection and monitoring of cyanobacteria using UV–VIS derivative spectrophotometry

Cyanobacterial blooms are now a long-standing and recurring environmental issue around the globe due to their potential toxicity and accompanying negative impacts, such as the formation of taste and odor compounds, water discoloration, scum formation, to name a few. Early detection and routine monitoring of source water is, therefore, an increasing need, and methods to promptly identify cyanobacterial presence are critical. In this study, M. aeruginosa was used to test the impact of three water quality parameters (WQP), including salinity, DOC (dissolved organic carbon), and turbidity, on the detection and monitoring of cyanobacteria using UV-Vis derivative spectrophotometry. The study established the method detection limits under a wide range of WQP. Further, the effect of two cuvette pathlengths (50-, and 100-mm) and two exposure times (90 and 180 mins) at two peaks, corresponding to photopigments chlorophyll-a (Chl-a) and phycocyanin (PC), were investigated while applying and Savitzky-Golay (S-G) first derivative of absorbance technique to improve sensitivity. Results indicate that the relationship between the two photopigments and absorbance was generally strong (R² > 0.9), except for higher turbidity tests (R² > 0.8), and 100 mm pathlength was found to be the most sensitive in terms of detection. Additionally, there was no significant change in absorbance, detection limit, or slope observed between the two exposure times. The lowest detection limits using the established method were found to be 11,083 cells/mL and 12,632 cells/mL for 1 mg/L DOC for Chl-a and PC, respectively. Sensitivity analyses revealed slight variations in slopes of regression with increasing WQP concentration, which was expected with increasing interfering contaminants. Overall, the results demonstrate that despite varying WQPs, with the aid of derivate spectrophotometry and longer cuvette pathlength (100 mm), the method can be successfully used for potential detection and monitoring of cyanobacteria in different source waters.