Long-term effects of the antibacterial agent triclosan on marine periphyton communities.

Triclosan is a widely used antibacterial agent that has become a ubiquitous contaminant in freshwater, estuary, and marine environments. Concerns about potential adverse effects of triclosan have been described in several recent risk assessments. Its effects on freshwater microbial communities have been well studied, but studies addressing effects on marine microbial communities are scarce. In the present study, the authors describe short- and long-term effects of triclosan on marine periphyton (microbial biofilm) communities. Short-term effects on photosynthesis were estimated after 60 min to 210 min of exposure. Long-term effects on photosynthesis, chlorophyll a fluorescence, pigment content, community tolerance, and bacterial carbon utilization were studied after exposing periphyton for 17 d in flow-through microcosms to 0.316 nM to 10,000 nM triclosan. Results from the short-term studies show that triclosan is toxic to periphyton photosynthesis. Half maximal effective concentration (EC50) values of 1080 nM and 3000 nM were estimated using (14)CO2-incorporation and pulse amplitude modulation (PAM) fluorescence measurements, respectively. After long-term triclosan exposure in flow-through microcosms, photosynthesis estimated using PAM fluorometry was not inhibited by triclosan concentrations up to 1000 nM but instead increased with increasing triclosan concentration. Similarly, at exposure concentrations of 31.6 nM and higher, triclosan caused an increase in photosynthetic pigments. At 316 nM triclosan, the pigment amounts were increased by a factor of 1.4 to 1.9 compared with the control level. Pollution-induced community tolerance was observed for algae and cyanobacteria at 100 nM triclosan and higher. Despite the widespread use of triclosan as an antibacterial agent, the compound did not have any effects on bacterial carbon utilization after long-term exposure.

Toxicity of ciprofloxacin and sulfamethoxazole to marine periphytic algae and bacteria.

Ciprofloxacin and sulfamethoxazole are two antibiotics commonly detected in the aquatic environment, but information on their toxicity towards natural microbial communities is largely absent. In particular no data are available for marine microorganisms. The aim of the current study was therefore to evaluate the chronic toxicity of ciprofloxacin and sulfamethoxazole to natural marine biofilms (periphyton), a complex ecological community comprising a variety of bacterial and algal species. The biofilms were sampled along the Swedish west coast and subsequently exposed over 4 days in a semi-static system to a concentration series of each antibiotic. Effects on the bacterial part of the periphyton community were assessed using Biolog Ecoplates, reflecting total respiration and functional diversity of the bacterial community. Exposure to either antibiotic resulted in a clear concentration-response relationship with EC10 and EC50 values for the inhibition of total carbon source utilization of 46.1nmol/L and 490.7nmol/L for ciprofloxacin, and 56nmol/L and 1073nmol/L for sulfamethoxazole. The NOEC for ciprofloxacin was 26nmol/L, with a minimum significant difference of 19.24%, for sulfamethoxazole it was 140nmol/L with a minimum significant difference of 14%. Multivariate data exploration of the whole carbon source utilization pattern confirmed these results. The data indicate that sulfamethoxazole leads to a general decrease in carbon source utilization, while ciprofloxacin exposure leads to a re-arrangement of the carbon-utilization pattern in the region of 20- 50% effect. This corresponds with the higher specificity of ciprofloxacin for certain bacterial species. Effects on the algal part of the communities were evaluated by analyzing the amount and composition of photosynthetic pigments, and neither ciprofloxacin nor sulfamethoxazole caused any inhibitory effects up to the maximum tested concentration of 9000nmol/L. However, sulfamethoxazole exposure did lead to a significant stimulation (75% above control level) of the total pigment content of the biofilm already at the lowest tested concentration of 5nmol/L. The stimulation then decreased with increasing concentrations to finally return to control level at 3000nmol/L. No shifts in the relative pigment composition were observed, indicating a generally increased algal biomass without major shifts in community composition.

Triclosan causes toxic effects to algae in marine biofilms, but does not inhibit the metabolic activity of marine biofilm bacteria.

Effects of the antimicrobial agent triclosan to natural periphyton communities (biofilms, comprising primarily microalgae and bacteria) were assessed in two independent experiments during spring and summer. For that purpose a semi-static test system was used in which periphyton was exposed to a concentration range of 5-9054 nmol/L triclosan. Effects on algae were analyzed as content and composition of photosynthetic pigments. The corresponding EC50 values were 39.25 and 302.45 nmol/L for the spring and summer experiment, respectively. Effects on periphytic bacteria were assessed as effects on carbon utilization patterns, using Biolog Ecoplates. No inhibition of either total carbon utilization or functional diversity was observed, indicating a pronounced triclosan tolerance of the marine bacteria. In contrast, a small stimulation of the total carbon utilization was observed at triclosan concentrations exceeding 100 nmol/L.