Toxicological effects of ciprofloxacin and chlorhexidine on growth and chlorophyll a synthesis of freshwater cyanobacteria

Abstract

Cyanobacteria are phytoplanktonic microorganisms that are susceptible to the deleterious effects of pharmaceutical residues in the aquatic environment, which poses a challenge to the environment exposed to diverse pharmaceutical products and their potential effects. The objective of this study was to evaluate the effects of the antibiotic substances ciprofloxacin and chlorhexidine in pharmaceutical preparations on the growth and production of chlorophyll of two cyanobacterial strains, Microcystis aeruginosa and Microcystis panniformis, isolated from a lake in a Brazilian environmental protection area. The EC 50 and EC 10 of chlorhexidine for M. aeruginosa were 206.4 μg/L and 108.5 μg/L, respectively, and for M. panniformis were 171.4 μg/L and 116.6 μg/L, respectively. The EC 50 and EC 10 of ciprofloxacin for M. aeruginosa were 17.24 μg/L and 3.21 μg/L, respectively, and for M. panniformis were 13.56 μg/L and 1.50 μg/L, respectively. The toxicity of the antibiotic ciprofloxacin (drug) and chlorhexidine (standard solution) to the Microcystis species was demonstrated, and these species were both very sensitive to ciprofloxacin. Our results suggest that the strains of M. aeruginosa and M. panniformis may be affected by exposure to residues of ciprofloxacin (>1.5 μg/L), which may represent a risk to the survival of aquatic species.

A Bioavailability Model to Predict the Impact of pH and Dissolved Organic Carbon on Ciprofloxacin Ecotoxicity to the Cyanobacterium Microcystis aeruginosa

“…The value reported by Liu et al (2017) is between 3.40 and 3.83 μg L −1 (15 days, 25 ± 1.0 °C). Azevedo et al (2019) found a CIP EC50 up to 206 µg L −1 (4 days, 25 ± 2.0 °C) in their toxicity test conducted at neutral pH and using an initial cell density (4 × 10 6 cells ml −1 ) which was 100-fold higher than in our study (4 × 10 4 cells ml −1 ). Despite these differences, in our experiments, medium O with neutral pH also showed an average cell growth rate (0.58 day −1 ) that was significantly lower (Tukey's honestly significant difference) than the other media.…”

“…This medium showed the highest 96‐h EC50, 7.0 µg L −1 , which is also 30% higher than the EC50 total predicted by our bioavailability model (4.9 µg L −1 ). This observation together with that of Azevedo et al (2019) hint at a possible linkage between pH, cell growth rate, and CIP toxicity, which is discussed later in this section.…”

Removal of Pharmaceutical Micropollutants with Integrated Biochar and Marine Microalgae

“…In this study minimum cell viability (22%), chlorophyll (1.5 µg L −1 ) and protein content (1.3 mg L −1 ) of Chaetoceros muelleri were recorded at the contact time (96 h) and micropollutant concentration (100 mg L −1 ). Azevedo et al [ 50 ] expressed that the inhibitory impact of ciprofloxacin on the growth of cyanobacteria was accentuated after 48 h. The drug should penetrate the cell for its act, it means taking time to get maximum effects of PPCPs on the cell. Changes in protein, chlorophyll contents and cell viability are shown in Figure 6 .…”

Emerging contaminants in the aquatic environment: phytoplankton structure in the presence of sulfamethoxazole and diclofenac

“…For cyanobacteria, the highest abundances were at higher and intermediate concentrations of diclofenac, showing differences over the days of exposure as well as between the concentrations of the drug. This group has presented negative effects of some drugs such as antibiotics (Gomaa et al 2021), and it has also reported inhibition of growth in the first 48h at low concentrations of disinfectant chlorhexidine (197.0 μg L −1 and 236.0 μg L −1 ), developing only after 3 days (Azevedo et al 2019). In contrast, desmids had their highest abundances mainly associated with lower and intermediate (Garraza et al 2019).…”