Behavior
of TiO<sub>2</sub> Released from Nano-TiO<sub>2</sub>‑Containing
Paint and Comparison to Pristine Nano-TiO<sub>2</sub>
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Abstract
In the assessment of the fate and
effects of engineered nanomaterials
(ENM), the current focus is on studying the pristine, unaltered materials.
However, ENM are incorporated into products and are released over
the whole product life cycle, though mainly during the use and disposal
phases. So far, released ENMs have only been characterized to a limited
extent and almost nothing is known about the behavior of these materials
under natural conditions. In this work we obtained material that was
released from aged paint containing nano-TiO<sub>2</sub>, characterized
the particulate materials, and studied their colloidal stability in
media with different pH and ionic composition. A stable suspension
was obtained from aged paint powder by gentle shaking in water, producing
a dilute suspension of 580 μg/L TiO<sub>2</sub> with an average
particle size of 200–300 nm. Most particles in this suspension
were small pieces of paint matrix that also contained nano-TiO<sub>2</sub>. Some free nano-TiO<sub>2</sub> particles were observed by
electron microscopy, but the majority was enclosed by the organic
paint binder. The pristine nano-TiO<sub>2</sub> showed the expected
colloidal behavior with increasing stability with increasing pH and
strong agglomeration above the isoelectric point and settling in the
presence of Ca. The released TiO<sub>2</sub> showed very small variations
in particle size, ζ potential, and colloidal stability, even
in the presence of 3 mM Ca. The results show that the behavior of
released ENM may not necessarily be predicted by studying the pristine
materials. Additionally, effect studies need to focus more on the
particles that are actually released as we can expect that the toxic
effect will also be markedly different between pristine and product
released materials