Environmental hazards of nanobiomaterials - hydroxyapatite based NMs - a case study with Folsomia candida - effects from extended exposure

Hydroxyapatite (HA) is a calcium phosphate used in many fields, including biomedical
applications. In particular, ion-doped HA nanomaterials (nHA) are developed for their increased
bioactivity, particularly in the fields of regenerative medicine and nanomedicine. In this study, we
assessed the ecotoxicological impact of five nHA materials: a synthesized calcium hydroxyapatite
(CaP-HA), superparamagnetic iron-doped hydroxyapatite (Fe-HA), titanium-doped hydroxyapatite
(Ti-HA), alginate/titanium-doped hydroxyapatite hybrid composite (Ti-HA-Alg), and a commercial HA.
The soil ecotoxicology model species Folsomia candida (Collembola) was used, and besides the standard
reproduction test (28 days), an extension to the standard for one more generation was performed
(56 days). Assessed endpoints included the standard survival and reproduction, and additionally,
growth. Exposure via the standard (28 days) did not cause toxicity, but reproduction increased in
commercial HA (significantly at 320 mg HA/kg) whereas via the extension (56 days) it decreased in
all tested concentrations. Juveniles' size (56 days) was reduced in all tested nHA materials, except
commercial HA. nHA materials seem to trigger a compromise between reproduction and growth.
Long-term effects could not be predicted based on the standard shorter exposure; hence, the testing of
at least two generations (56 days) is recommended to assess the toxicity of nanomaterials, particularly
in F. candida. Further, we found that the inclusion of size as additional endpoint is highly relevant.