Impairment of the Bacterial Biofi lm Stability by Triclosan
Triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol) ,also known as irgasan, is a broad-spectrum antibacterial and antifungal compound that has been widely used since the 1970s in pharmaceutical personal care products (PPCPs), textiles, cleaning supplies, toys and computer equipment . About 96% of triclosan (TCS) originating from consumer products is discarded in residential drains , leading to considerable loads of the chemical in waters entering wastewater treatment plants (WWTP). While biological sewage treatment had been regarded as an effective barrier for TCS due to removal efficiencies of 98% in the aqueous phase, Heidler & Halden  showed that the particle-associated TCS was sequestered into
waste-water residuals and accumulated in the sludge with less than half of the total mass being bio-transformed or lost. Consequently, substantial quantities of the chemical can be transferred into soils and groundwater by sludge recycling  or directly enters rivers with estimated concentrations usually between 11 – 98 ng/L  but with up to 2.7 μg/L  recorded. In the aqueous phase, the transformation of TCS into a variety of polychlorinated dibenzo-p-dioxins under the exposure of sunlight and especially at high pH values becomes problematic; the levels of the four main dioxins derived from triclosan have risen by 200 to 300% in the last 30 years . Although there is evidence that TCS is readily biodegradable under aerobic conditions in the water column , TCS is still regarded as one of the top 10 of persistent contaminants in U.S. rivers, streams, lakes, and underground aquifers due to its continuous replenishment and its accumulation within the sediments , . Increasing TCS concentrations have been reported world-wide from many countries for rivers, lakes and streams, being currently in the range of 18 ng/L – 2.7 μg/L in the water column , , ,  while 0.27 to 130.7 μg/kg TCS have been determined in sediments , .