Filter feeders increase sedimentation of titanium dioxide: the case of zebra mussels.
Titanium dioxide particles (TiO2) are widely used to produce whitens (titanium white) and different class of nanomaterials (semiconductors, photo catalysts and nanotubes). Nanomaterials are excellent adsorbents and catalysts with a wide range of applications. However, these are reported to induce biological and genetic alterations among several invertebrate groups. Invasive species such as zebra mussels can be used as model organisms to study the behavior of particles and nanoparticles (NPs) due to their wide distribution; mussels have been extensively used for monitoring water pollution. In the present study, TiO2 particles were dispersed and added to a Chlorella culture to emulate a natural scenario. To study the reaction of zebra mussels to different TiO2 concentrations, they were fed with 0.35, 0.7 and 3.5 mgTiO2/L of the suspension for 3 days and the titanium was measured in the water column, mussels and sediments with ICP-AES. Zebra mussels obtained from the Port of Quebec had up 61.62 mg Ti/kg wet tissue at the time of capture. After 10 days of depuration, they had from 0.23 to 16.28 mgTi/kg wet tissue. Mussels accumulated TiO2 after 36 h of exposition as a function of TiO2 concentration, but mussels did not present significant mortality due to TiO2 toxicity until concentrations higher than 0.7 ppm. A second set of experiments was run to understand the TiO2 pathway attached to microalgae vs free TiO2. Results indicated that mussels accumulated slightly more Ti when it was mixed with microalgae. However, the statistical difference was non-significant. A 100 times higher accumulation of Ti in sediments was identified when mussels are present. Thus, it was concluded that the sedimentation of TiO2 is enhanced by the zebra mussels' filtration activity.