Effects of a chronic lower range of triclosan exposure on a stream mesocosm community

Abstract

Triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol) is an antimicrobial found in consumer soaps and toothpaste. It is in treated wastewater effluents at low parts-per-billion concentrations, representing a potentially chronic exposure condition for biota inhabiting receiving streams. For the present study, a naturally colonized benthos was created using flow-through indoor mesocosms; then, the benthic communities were dosed to achieve different in-stream triclosan concentrations (control, 0.1 μg/L, 0.5 μg/L, 1.0 μg/L, 5.0 μg/L, and 10 μg/L) for 56 d. Water quality parameters and endpoints from bacteria to macroinvertebrates, as well as interacting abiotic components, were measured. Effects of triclosan on specific microbial endpoints were observed at all doses, including an effect on litter decomposition dynamics at doses of 1.0 μg/L and higher. Resistance of periphytic bacteria to triclosan significantly increased at doses of 0.5 μg/L and above. By the end of dosing, the antimicrobial appeared to stimulate the stream periphyton at the 3 lowest doses, while the 2 highest doses exhibited decreased stocks of periphyton, including significantly lower bacteria cell densities and cyanobacteria abundance compared with the control. Other than an effect on benthic ostracods, the changes that occurred in the periphyton did not translate to significant change in the colonizing nematodes, the macroinvertebrate community as a whole, or other measurements of stream function. The results shed light on the role a low, chronic exposure to triclosan may play in effluent-dominated streams.

Resilience and recovery: The effect of triclosan exposure timing during development, on the structure and function of river biofilm communities

“…TCS effects on a microbial community may occur both directly (toxicity) and indirectly (ecological interactions), as indicated previously (Nietch et al, 2013;Lawrence et al, 2009). Hypothetically, longer exposures may cause greater indirect effects on the microbial community through effects on bacterial-phototroph interactions and grazing, as seen in this study (see below).…”

“…Cyanobacteria, such as Anabaena flos-aquae, are also sensitive with a NOEC of 0.67 g l −1 . In contrast, Nietch et al (2013) reported that based on enumeration of identified taxa and Chl-a determinations, stimulation occurred at low doses (0.1 g l −1 TCS) relative to the control but suppression at 5 and 10 g l −1 doses over an extended exposure. For example, cyanobacteria were stimulated at <1 g l −1 , although there were mostly undetectable effects at 5 and 10 g l −1 .…”

“…Triplicate reactors that received river water alone (R8) acted as the reference condition or control for all other treatments. TCS concentration used was several orders of magnitude below medical-industrial application levels (0.2-1.0%) and within the range reported for aquatic environments (i.e., Ricart et al, 2010;Nietch et al, 2013). After 8 weeks of biofilm development, the twelve, 1 × 10 cm polycarbonate coupons were removed from replicate reactors for immediate analysis (confocal laser scanning microscopy (CLSM) microscopic analyses of bacterial, algal, cyanobacterial and exopolymer composition and biomass, carbon utilization, thymidine incorporation, TCS degradation, pigments, and dry weight) and also frozen at −80 • C and stored for subsequent DNA extraction and molecular analyses.…”

“…Community-level testing in ecotoxicology can be a useful tool due to its relatively high ecological realism and reliability (Porsbring et al, 2007;Sabater et al, 2007). Several studies have addressed triclosan's impacts on complex aquatic communities (Drury et al, 2013;Franz et al, 2008;Lawrence et al, 2009;Ricart et al, 2010;Proia et al, 2011;Nietch et al, 2013). Lawrence et al (2009) reported that TCS exposure at 10 g l −1 resulted in significant reductions in algal biomass, carbon utilization, changes in bacterial community composition and alteration of the community structure.…”

Chronic arsenic exposure and microbial drug resistance

“…Similarly, triclosan, another antimicrobial with broad activity against bacteria and many parasitic protists, is a common component of toothpaste, hand-washes, and other manmade products. The ubiquitous presence of triclosan in the environment, as well as long-term human exposure, could contribute to the development of triclosan-resistant pathogens (18) or microbial resistance to other drugs that share similar modes of action, such as the antituberculosis drug, isoniazid (19). Although a link between environmental triclosan levels and antibiotic resistance has yet to be established (20), the study by Perry et al (2) provides a cautionary lesson.…”