Release of Zinc and Polycyclic Aromatic Hydrocarbons From Tire Crumb Rubber and Toxicity of Leachate to Daphnia magna: Effects of Tire Source and Photoaging.

Tire crumb rubber (TCR) has been widely used in artificial turf fields, however, the potential environmental risk of TCR and the effect of sunlight exposure are scarcely studied. Here, we evaluated leachability of Zn and polycyclic aromatic hydrocarbons (PAHs) in four types of TCRs and acute toxicity of leachates to Daphnia magna. The results showed that all types of TCRs tested released Zn (0.20-1.3 µg/g) and PAHs (9.4-17 µg/g) but only two were lethal to D. magna (mortality 73%). Notably, ultraviolet (UV) irradiation induced TCR to generate acidic leachate (pH ~ 4.8), which contained 24- and 1.2-fold higher concentrations of Zn and PAHs and therefore was more toxic to D. magna than that in the absence of UV treatment. These findings demonstrate source-dependent toxicity of TCR and highlight the need to consider the effect of photoaging when evaluating the environmental risks of TCR.

Alginate affects agglomeration state and uptake of 14C-labeled few-layer graphene by freshwater snails: Implications for the environmental fate of graphene in aquatic systems.

Understanding of the interaction of graphene with natural polysaccharides (e.g., alginate) is crucial to elucidate its environmental fate. We investigated the impact of alginate on the agglomeration and stability of 14C-labeled few-layer graphene (FLG) in varying concentrations of monovalent (NaCl) and divalent (CaCl2) electrolytes. Enhanced agglomeration occurred at high CaCl2 concentrations (≥5 mM) due to the alginate gel networks formation in the presence of Ca2+. FLG enmeshed within extended alginate gel networks was observed under transmission electron microscope and atomic force microscope. However, background Na+ competition for binding sites with Ca2+ at the alginate surfaces shielded the gelation of alginate. FLG was readily dispersed by alginate under environmentally relevant ionic strength conditions (i.e., <200 mM Na+ and <5 mM Ca2+). In comparison with the bare FLG, the slow sedimentation of the alginate-stabilized FLG (158 µg/L) caused continuous exposure of this nanomaterial to freshwater snails, which ingested 1.9 times more FLG through filter-feeding within 72 h. Moreover, surface modification of FLG by alginate significantly increased the whole-body and intestinal levels of FLG, but reduced the internalization of FLG to the intestinal epithelial cells. These findings indicate that alginate will act as a stabilizing agent controlling the transport of FLG in aqueous systems. This study also provides the first evidence that interaction of graphene with natural polysaccharides affected the uptake of FLG in the snails, which may alter the fate of FLG in aquatic environments.