Chronic toxicity of core–shell SiC/TiO₂ (nano)-particles to Daphnia magna under environmentally relevant food rations in the presence of humic acid

Figures & data

Figure 1. Hydrodynamic sizes (mean ± standard error) of 60 and 500 nm SiC/TiO₂ between 0 and 48 hours of incubation in Elendt M7 medium with varying TOC concentrations (0, 0.5, 2, 5, and 10 mg L⁻¹).

Figure 2. Sedimentation rates (expressed as the percentage of the nominally applied particle mass remaining in suspension, A–F, mean ± standard error) and time-weighted average (TWA) water column concentrations (G–I, mean ± standard error) of 60 and 500 nm SiC/TiO₂ after 0, 24, and 48 hours measured in Elendt M7 medium in the presence of varying total organic carbon (TOC) concentrations (i.e. 0, 0.5, 2, 5, and 10 mg L⁻¹).

Figure 3. Correlation between time-weighted average hydrodynamic sizes and sedimentation rates (expressed as a percentage of the nominally applied particle mass remaining in suspension) of 60 and 500 nm SiC/TiO₂ in Elendt M7 medium (mean ± 95% confidence interval). Values of nominal SiC/TiO₂ concentrations (5, 25, and 50 mg L⁻¹) and total organic carbon (TOC) concentrations (i.e. 0, 0.5, 2, 5, and 10 mg L⁻¹) are aggregated.

Figure 4. Percentage of surviving D. magna (mean ± standard error) over 21 days of exposure to 60 and 500 nm SiC/TiO₂ (5, 25, and 50 mg L⁻¹) in the presence of varying total organic carbon (TOC) concentrations, i.e. 0.5 mg L⁻¹ (A and E), 2 mg L⁻¹ (B and F), 5 mg L⁻¹ (C and G), and 10 mg L⁻¹ (D and H).

Table 1. EC₅₀ values derived from dose–response models based on the percentage of surviving D. magna over 21 days of exposure to 60 and 500 nm SiC/TiO₂ (i.e. 5, 25, and 50 mg L⁻¹) in the presence of varying total organic carbon (TOC) concentrations (i.e. 0, 0.5, 2, 5, and 10 mg L⁻¹) calculated using different dose metrics.

Size	TOC (mg L^−1)	EC50 ± SE
		EC50 based on nominal SiC/TiO2 concentrations (mg L^−1)	EC50 based on TWA SiC/TiO2 concentrations (mg L^−1)
SiC/TiO2 60 nm	0.5	28.0 ± 11.5	19.8 ± 12.3
	2	21.1 ± 3.7	na ± na
	5	18.3 ± 5.4	14.6 ± 5.4
	10	17.8 ± 2.4	14.4 ± 2.2
SiC/TiO2 500 nm	0.5	34.9 ± 16.5	31.4 ± 45.1
	2	24.8 ± 5.6	13.8 ± 4.1
	5	28.0 ± 10.0	12.6 ± 4.2
	10	23.2 ± 4.1	13.8 ± 2.6

NA = not assessed due to poor model fit, TWA = Time-weighted average, SA = Surface area.

Figure 5. Dose–response curves (A and B) based on mortality rates and body sizes (C and D) of D. magna after 21 days of exposure to 60 and 500 nm SiC/TiO₂ (5, 25, and 50 mg L⁻¹) in the presence of varying total organic carbon (TOC) concentrations (i.e. 0.5, 2.0, 5, and 10 mg L⁻¹). Dose–response curves were calculated using nominal and time-weighted average (TWA) treatment concentrations. Error bars in dose-response curves represent standard errors.

Data availability statement

The data that support the findings of this study are available from the corresponding author, KS, upon reasonable request.