Zinc oxide

Sediment toxicity

Link to relevant study record(s)

Reference

Endpoint:

sediment toxicity: short-term

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

equivalent or similar to guideline

Guideline:

other: EPA 600/R-99/064

GLP compliance:

not specified

Remarks:

GLP compliance not specified in publication

Specific details on test material used for the study:

Zinc sulphate heptahydrate (101% purity Sigma-Aldrich, St Louis, MO)
Zinc oxide nanopowder 20 nm - NanoAmor Inc. Houston TX

Vehicle:

no

Details on sediment and application:

Test suspensions for the exposures were prepared just prior to the initiation of the exposures by pipetting the appropriate volume of the stock suspension during constant stirring and adding it to 2 L of R-MHRW. Test suspensions were stirred for a minimum of 5 min and dispensed into exposure vessels with a 50-mL syringe

Test organisms (species):

Hyalella sp.

Details on test organisms:

maintained at US EPA aquatic culturing facility in Cincinatti OH according to standard methods

Study type:

laboratory study

Test type:

static

Water media type:

freshwater

Limit test:

no

Duration:

96 h

Exposure phase:

total exposure duration

Test temperature:

23 +/-1°C

pH:

7.7-7.8

Dissolved oxygen:

8.2-8.8 mg/l

Conductivity:

370-400 µs/cm

Reference substance (positive control):

yes

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

154 µg/L

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

ZnSO4

Basis for effect:

mortality

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

77.3 µg/L

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

nano ZnO

Basis for effect:

mortality

Validity criteria fulfilled:

yes

Conclusions:

The present study places H. azteca as one of the most sensitive animals to ZnO NP toxicity.
In comparative toxicology studies of ZnO NPs and Zn2+, generally the ZnO NPs have been found to be less toxic.4 In fact, there is only one other study known to the authors which found the opposite to be true

Description of key information

Two studies were done to assess the toxicity of zinc oxide nanoforms on microorganisms. A study by Fabrega et al (2012) on the Sequestration of Zinc from Zinc Oxide Nanoparticles and Life Cycle effects in the sediment dweller Amphipod Corophium volutator and a study by Poynton et al (2013) on the Toxicity and Transcriptomic Analysis in Hyalella azteca Suggests Increased Exposure and Susceptibility of Epibenthic Organisms to Zinc Oxide Nanoparticles.

The study by Fabrega et al (2012) found that Exposure via water to all forms of zinc in the range of 0.2− 1.0 mg L−1 delayed growth and affected the reproductive outcome of the exposed populations.

The study by Poynton et al (2013) places H. azteca is one of the most sensitive animals to ZnO NP toxicity. In comparative toxicology studies of ZnO NPs and Zn2+, generally the ZnO NPs have been found to be less toxic. There is only one other study known to the authors which found the opposite to be true.

The details of LOEC’s and LC50’s are in the table attached as additional background information.

Additional information

The study by Fabrega et al (2012) was done according to the 600/R-01/020 USEPA 2001 method for assessing the chronic toxicity of marine and estuarin sediment associated contaminants with amphipod Leptocherius plumulosus. Zinc oxide nanopowder (ZnO NP, Nanosun, Microniser) and a bulk counterpart (micrometer-sized ZnO powder) were used. C. volutator neonates were collected from the acclimated laboratory stock cultures. Dosing of ZnO NP, bulk ZnO, and the same mass of Zn ions (from ZnCl2) was conducted via the water. A total of nine vessels were set up for each treatment regime (including for controls), and three replicate vessels were sampled from each treatment at 23, 63, and 100 days. Survival, growth, and reproduction were measured at day 28, day 63, and day 100 after the onset of exposure.
Specific growth rate (SGR) was significantly reduced 23 days after the onset of exposure, with the highest concentrations of ZnO NPs, bulk ZnO, and Zn+ causing about 11, 12, and 21% reduction of growth, respectively, from unexposed populations. After 63 days from the onset of exposure, only the populations exposed to bulk ZnO and Zn+ showed a slower growth rate. After 100 days, in most populations individuals had reached adult size (5.11 ± 0.84 mm). The one exception to this was the population exposed to 1 mg L−1 bulk ZnO, where the organisms were still significantly smaller (ANOVA, p < 0.05).

The study by Poynton et al (2013) was done equivalent to EPA guideline 600/R-99/064, with test materials Zinc sulphate heptahydrate (101% purity) Zinc oxide nanopowder (20 nm). The study was conducted at 23 +/- 1°C, pH 7.7-7.8 and dissolved oxygen of 8.2 – 8.8 mg/L. The authors place H. azteca is one of the most sensitive animals to ZnO NP toxicity. In comparative toxicology studies of ZnO NPs and Zn2+, the found that the ZnO NPs have generally been found to be less toxic. They only found one other study which found the opposite to be true.

The details of LOEC’s and LC50’s are in the table attached as additional background information.