Graphene oxide (GO) is a very promising material because it is easy to process, water-soluble, and chemically versatile due to the presence of oxygenated groups on its surface. GO has been used in different areas such as electronics, biosensing, and environmental remediation. To design efficient materials, especially for biosensing and for remediating pollutants, the knowledge of surface noncovalent interaction and functionalization is crucial. Recently, it has been suggested revisions on the structural models of GO because the presence of highly oxidized polyaromatic carboxylated fragments (oxidative debris) on the GO surfaces. These debris are produced during acid treatments commonly employed in GO synthesis and purification. Here we applied chemical analysis, bioassays, and atomistic simulations to study the influence of oxidative debris on the noncovalent interaction of GO sheets with an important organic pollutant (e.g., 1nitropyrene). GO samples without oxidative debris were found to be 75% more effective to adsorb 1-nitropyrene than samples with debris. Our results suggest that small (∼1 nm) oxidative debris are responsible for preventing adsorption sites on GO surfaces from being reached by potentially adsorbate molecules.

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h i g h l i g h t s g r a p h i c a l a b s t r a c t Disperse Red 1 dye was found in river waters in concentrations above the PNEC.The PNEC was based on toxicity endpoints for a commercial dye and its purified form. The CRED method was used to evaluate the quality of endpoints used in PNEC derivation. a b s t r a c tWater quality criteria to protect aquatic life are not available for most disperse dyes which are often used as commercial mixtures in textile coloration. In this study, the acute and chronic toxicity of the commercial dye Disperse Red 1 (DR1) to eight aquatic organisms from four trophic levels was evaluated. A safety threshold, i.e. Predicted No-Effect Concentration (PNEC), was derived based on the toxicity information of the commercial product and the purified dye. This approach was possible because the toxicity of DR1 was accounting for most of the toxicity of the commercial mixture. A long-term PNEC of 60 ng L À1 was proposed, based on the most sensitive chronic endpoint for Daphnia similis. A short-term PNEC of 1800 ng L À1 was proposed based on the most sensitive acute endpoint also for Daphnia similis.Both key studies have been evaluated with the new "Criteria for Reporting and Evaluating ecotoxicity Data" (CRED) methodology, applying more objective criteria to assess the quality of toxicity tests, resulting in two reliable and relevant endpoints with only minor restrictions. HPLC-MS/MS was used to quantify the occurrence of DR1 in river waters of three sites, influenced by textile industry discharges, resulting in a concentration range of 50e500 ng L À1 . The risk quotients for DR1 obtained in this work Chemosphere 156 (2016) 95e100 Mixture PNEC suggest that this dye can pose a potential risk to freshwater biota. To reduce uncertainty of the derived PNEC, a fish partial or full lifecycle study should be performed.

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