Caddisfly emergence is substantially affected by the combined exposure of titanium dioxide nanoparticles, natural organic matter and UV irradiation

Nanoparticles serve various industrial and domestic purposes which is reflected in their steadily increasing production and ultimate release into the environment. Titanium dioxide nanoparticles pose due to their high production volume and their photoactive properties a potential environmental risk. Here we assessed their impact in combination with UV and natural organic matter (NOM) at field relevant intensities on the emergence dynamics and quality of the aquatic insect Chaetopteryx villosa (Insecta: Trichoptera) employing a factorial test design. While UV alone and the combination of TiO2 with UV or NOM reduced emergence by 50 %, the combination of all three factors (i.e., TiO2 x UV x NOM) caused an even stronger effect (i.e., reduction by 70 %). Following a similar pattern, the time until 50 % of the larvae emerged was, depending on the treatment, delayed by at least 5.9 and up to 16.4 days. In contrast, the nutritious quality of adult C. villosa, characterized in terms of energy reserves and fatty acid profiles, was hardly affected. Nonetheless, the substantial impact in emergence dynamics was at the same magnitude as reported for highly toxic chemicals, such as insecticides. Consequently, (photoactive) nanoparticles may be of similar environmental concern, particularly under joint exposure with further environmental factors (i.e., UV and NOM). Moreover, and in the light of the central ecological role of aquatic insects at the interface between aquatic and terrestrial ecosystems, the present study points towards farreaching consequences for the riparian food web and the productivity of this meta-ecosystem.