Effects of aqueous suspensions of titanium dioxide nanoparticles on Artemia salina: assessment of nanoparticle aggregation, accumulation, and toxicity

Abstract

Aquatic stability and impact of titanium dioxide nanoparticles (TiO2 NPs, 10-30 nm) were investigated using Artemia salina. Acute exposure was conducted on nauplii (larvae) and adults in seawater in a concentration range from 10 to 100 mg/L TiO2 NPs for 24 and 96 h. Rapid aggregation occurred in all suspensions of TiO2 NPs to form micrometer size particles. Yet, both nauplii and adults accumulated the aggregates significantly. Average TiO2 content in nauplii ranged from 0.47 to 3.19 and from 1.29 to 4.43 mg/g in 24 and 96 h, respectively. Accumulation in adults was higher ranging from 2.30 to 4.19 and from 4.38 to 6.20 mg/g in 24 and 96 h, respectively. Phase contrast microscopy images revealed that Artemia were unable to excrete the particles. Thus, the TiO2 aggregates filled inside the guts. No significant mortality or toxicity occurred within 24 h at any dose. Lipid peroxidation levels characterized with malondialdehyde concentrations were not statistically different from those of the controls (p > 0.05). These results suggested that suspensions of the TiO2 NPs were nontoxic to Artemia, most likely due to the formation of benign TiO2 aggregates in water. In contrast, both mortality and lipid peroxidation increased in extended exposure to 96 h. Highest mortality occurred in 100 mg/L TiO2 NP suspensions; 18 % for nauplii and 14 % for adults (LC50 > 100 mg/L). These effects were attributed to the particle loading inside the guts leading to oxidative stress as a result of impaired food uptake for a long period of time.

Fig. 1

Size distribution of TiO₂ NPs in exposure medium (pH 8.3). TEM Images are gathered from dried aliquots of 10 mg/L TiO₂ NPs by multiple scans from different coordinates of the TEM sample plate. (A) Immediately after preparation of NP suspension, (B) 12 h after the start of exposure. Note that TiO₂ NPs aggregated to micrometer size particles in 12 h.

Fig. 2

Phase contrast microscopy images of the TiO₂ NPs inside Artemia nauplii and adults. The images were taken 24 h after the start of exposure. The guts are completely empty in controls. Aggregates of TiO₂ are visible as a dark line inside the guts of the treatments.

Fig. 3

Accumulation and elimination profiles of TiO₂ NP suspensions by Artemia nauplii and adults. Values are given as average ± standard deviation of triplicate exposures. Bars with the same letter are not significantly different (p>0.05). The bars for elimination indicate the average loss in ingested TiO₂ content within 24 h in clean seawater at the conclusion of exposure for 24 h and 96 h.