Acute and reproductive toxicity of nano-sized metal oxides (ZnO and TiO2) to earthworms (Eisenia fetida)

Abstract

An increase in nanomaterial applications will likely lead to an increased probability of environmental exposures, raising concerns regarding the safety of these materials. Recent studies have indicated that manufactured nanomaterials, such as metal oxides, have the potential to be harmful to aquatic and terrestrial organisms. The majority of nano-metal oxide research addressing potential toxicological issues has been focused in aquatic environments with very little terrestrial data. This study characterized the acute and reproductive toxicity of zinc oxide (ZnO) and titanium dioxide (TiO(2)) to earthworms (Eisenia fetida) in a terrestrial system. Following a 14 d exposure, nano-sized ZnO on filter paper was acutely toxic to E. fetida, while nano-sized TiO(2) did not exhibit acute toxicity. In contrast, neither nano-sized ZnO nor TiO(2) exhibited acute toxicity to earthworms in sand. Both nano-sized ZnO and TiO(2), following a 4 week exposure, caused reproductive effects in earthworms in artificial soil. Overall, nano-sized ZnO exhibited greater toxicity than nano-sized TiO(2) in Eisenia fetida.

Metal‐based nanoparticles in soil: Fate, behavior, and effects on soil invertebrates

“…The same authors also determined the effects of ZnO NPs on earthworm reproduction in sand and artificial soil. Reproduction showed a decrease with increasing NPs concentration in both tested media; however, the values were not significantly different from the control [93].…”

“…No effects were observed in either soil on survival, growth, and reproduction, up to 10,000 mg TiO 2 /kg soil. Reproduction (cocoon production) of earthworms decreased in artificial soil and sand with increasing TiO 2 concentration, but it was only significantly different from the control in the artificial soil test at 1,000 mg/kg [93].…”

“…First, the presence of NPs in the organisms' tissue indicates the assimilation of nanosized particles is possible [54,68]. Second, NP core elements clearly influence toxicity; for example, TiO 2 was found to be less toxic than Ag [92] and ZnO NPs [93]. Third, tests should be conducted in media that are as close to realistic conditions as possible to have relevance and enable a better understanding of NPs' toxicity in the environment (e.g., K-media leads to greater aggregation and is more similar to the pore water conditions than agar [82]).…”

“…Effects of ZnO NPs on the survival of E. fetida were evaluated in sand and on filter paper [93]. Although high toxicity occurred in the filter paper test, it is a less realistic medium and causes greater stress to the organisms [93].…”

“…Although high toxicity occurred in the filter paper test, it is a less realistic medium and causes greater stress to the organisms [93]. In addition, for ZnO, which is photo reactive, the filter paper test would also have added a potentially new mechanism of toxicity through effects of ROS generation from noninternalized ZnO, something that would not occur in the more realistic soil tests.…”