Several studies have pointed out that MPs can adsorb and desorb contaminants present in the surrounding waters, acting as vectors of pollutants. This may affect organisms, which may ingest those MPs. In addition, MPs can be colonized by microorganisms, these may form biofilms that can modify the adsorption and desorption of pollutants from MPs. Wastewater treatment plants (WWTP) represent an important source of MPs, different pollutants, and microorganisms, implying that they might co-occur in the same site. The aim of this work is to evaluate the ability of polyethylene MPs to act as vectors of the triclosan (TCS) and how colonization of these MPs influences it. Colonization of MPs was carried out in waters from the influent and effluent from a WWTP, as well as using an Escherichia coli culture; furthermore, the biological impact of colonized and non-colonized MPs as vector of TCS on Daphnia magna was evaluated. For that, after 4 weeks of aging and subsequent 4 h of contact time of MPs with TCS, tests to evaluate the sorption and desorption of TCS were performed, as well as bioassays to evaluate D.magna survival in a chronic experiment to 0-400 mg MPs/L. The non-exposed MPs to TCS were toxic at the highest concentrations but aging in effluent waters further increased their toxicity. Although differences were observed depending on type of aging, both colonized and non-colonized MPs exposed to TCS were capable of adsorbing and releasing it, being in general more toxic to D.magna than those not exposed to TCS, except for those MPs colonized in influent. Likewise, MPs colonized in effluent were found to be the most toxic. These results indicate that the MPs can act as vectors of pollutants and that the colonization influences this toxicity by factors such as the load of organic matter or colonizing microorganisms.