Reproductive and behavioral responses of earthworms exposed to nano-sized titanium dioxide in soil

Nanometer-sized titanium dioxide (nano-TiO2) is found in a number of commercial products; however, its effects on soil biota are largely unknown. In the present study, earthworms (Eisenia andrei and Eisenia fetida) were exposed to three types of commercially available, uncoated TiO2 nanomaterials with nominal diameters of 5, 10, and 21nm. Nanomaterials were characterized for particle size, agglomeration, surface charge, chemical composition, and purity. Standard lethality, reproduction, and avoidance tests, as well as a juvenile growth test, were conducted in artificial soil or field soil amended with nano-TiO2 by two methods, liquid dispersion and dry powder mixing. All studies included a micrometer-sized TiO2 control. Exposure to field and artificial soil containing between 200 and 10,000mg nano-TiO2 per kilogram of dry soil (mg/kg) had no significant effect (p>0.05) on juvenile survival and growth, adult earthworm survival, cocoon production, cocoon viability, or total number of juveniles hatched from these cocoons. However, earthworms avoided artificial soils amended with nano-TiO2. The lowest concentration at which avoidance was observed was between 1,000 and 5,000mg nano-TiO2 per kilogram of soil, depending on the TiO2 nanomaterial applied. Furthermore, earthworms differentiated between soils amended with 10,000mg/kg nano-TiO2 and micrometer-sized TiO2. A positive relationship between earthworm avoidance and TiO2 specific surface area was observed, but the relationship between avoidance and primary particle size was not determined because of the agglomeration and aggregation of nano-TiO2 materials. Biological mechanisms that may explain earthworm avoidance of nano-TiO2 are discussed. Results of the present study indicate that earthworms can detect nano-TiO2 in soil, although exposure has no apparent effect on survival or standard reproductive parameters. Environ. Toxicol. Chem. 2012;31:184193. (C) 2011 SETAC