Mobilisation kinetics of metals from microfibres in freshwater and under simulated digestive conditions

Anthropogenic microfibres are ubiquitous contaminants of the environment but little is known about their chemical makeup and the ecotoxicological risks of these chemicals. In this study, tumble dryer lint has been employed as a representative composite of heterogeneous environmental microfibres derived from the laundering of clothes and has been characterised by polymer composition of individual fibres and the overall content of metals (and metalloids). Under controlled and timed conditions (up to 72 h), the mobilisation of metals was studied in freshwater and two physiologically-based extraction tests (PBETs) that mimic the digestive tracts of birds and humans. Lint fibres were composed of rayon-cotton and polyester and the concentrations of metals, as additives and contaminants, ranged from <2 mg kg^-1 for Ag, As, Cd and Pb to about 6500 mg kg^-1 for Al. In most cases, mobilisation, where detected, was modelled with a parabolic diffusion equation. Rate constants were either greater in the PBETS than in freshwater (Al, Ba, Cr) or greater in freshwater than the PBETs (Mn, Sb). Availabilities, defined as concentrations mobilised after 72 h relative to total concentrations, ranged from <1.5 % for Cr and Ti in all media and Al, Ba, Fe in freshwater to >40 % for Mn and Zn in all media and Cu in one PBET solution. Mobilised concentrations were generally below corresponding metal standards for drinking water and fresh and marine waters, and under realistic conditions mobilisation is not predicted to present any significant risks to humans or wildlife.