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

Abstract

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.

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“…The same amount of de-ionized water without TCS was pumped into the control microcosms. The nominal TCS concentrations were close to the analysed TCS concentrations (Eriksson et al 2015). Hence, nominal concentrations are presented in the following.…”

“…Johansson et al (2014) studied effects of TCS on bacterial carbon utilization in marine periphyton communities, in which TCS did not inhibit the carbon utilization and did also not cause changes in bacterial functional diversity at concentrations of up to 10 µM. Eriksson et al (2015) also studied effects of TCS on carbon utilization in marine periphyton using flow-through microcosms in which TCS did not cause effects at concentrations of up to 1 µM. These studies, however, focused mainly on gross parameters of bacterial function.…”

“…Taken together, these results demonstrate that 16S rRNA amplicon sequencing is an effective tool for detecting effects from toxicants in complex bacterial communities. Eriksson et al (2015). In short, seawater, with its indigenous microbiota, was continuously pumped into 20 L glass aquaria from 1.5 meters depth in the Gullmar fjord.…”

Chemical monitoring of Swedish coastal waters indicates common exceedances of environmental thresholds, both for individual substances as well as their mixtures

“…Assuming that NOEC data is also available for aquatic invertebrates and fish the REACH guidance suggest using an AF of 100 (ECHA, 2008), resulting in a PNEC of 0.15 ng/L. In contrast, two studies from the Swedish west coast, testing marine periphytic algal assemblages from a site close to Fiskebäckskil, have demonstrated a lower sensitivity towards triclosan, recording an EC10 of 4100 ng/l (Johansson et al, 2014) and a NOEC of 9100 ng/l (Eriksson et al, 2015). This lower sensitivity is likely a results of the tested marine algal assemblages being dominated by diatoms and cyanobacteria (Porsbring et al, 2007), while green algae have been shown to be most sensitive species group (Orvos, 2002).…”

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“…Assuming that NOEC data is also available for aquatic invertebrates and fish the REACH guidance suggest using an AF of 100 (ECHA, 2008), resulting in a PNEC of 0.15 ng/L. In contrast, two studies from the Swedish west coast, testing marine periphytic algal assemblages from a site close to Fiskebäckskil, have demonstrated a lower sensitivity towards triclosan, recording an EC10 of 4100 ng/l and a NOEC of 9100 ng/l (Eriksson et al, 2015). This lower sensitivity is likely a results of the tested marine algal assemblages being dominated by diatoms and cyanobacteria (Porsbring et al, 2007), while green algae have been shown to be most sensitive species group (Orvos, 2002).…”