Risk assessment of amorphous silicon dioxide nanoparticles in a glass cleaner formulation

Figures & data

Table I. Characterisation and physico-chemical properties of the raw material: colloidal SAS.

Properties	Description	Reference
Molecular formula	SiO2
Molecular weight*	60.08 g/mol
Morphology	Amorphous	EKA Chemicals AB, 2010
Appearance	Transparent liquid	EKA Chemicals AB, 2003
Density	1.2 g/cm³ (20°C)	EKA Chemicals AB, 2003
pH	10	EKA Chemicals AB, 2003
Particle size	9 nm (monodiperse)	EKA Chemicals AB, 2003
Particle size distribution	10–20 nm (TEM) 4–40 nm (DLS)	See characterisation
Surface charge	Negative
Surface area	360 m²/g	EKA Chemicals AB, 2003
Coating	None
Log Pow*	0.53	US EPA, 2008
Vapour pressure	2300 Pa	EKA Chemicals AB, 2010
Water solubility	120 mg/l	Alexander et al. (1954)

*Values relate to the monomeric structure; DLS, dynamic light scattering; SAS, synthetic amorphous silicon dioxide; TEM, transmission electron microscopy.

Figure 1. Overview on the methodological approach and building blocks of the risk assessment. Methods mentioned in detail indicate experimental analyses performed in this case study.

Figure 2. Literature search for toxicological information: the search terms and links between search terms are given as well as the number of hits.

Table II. Aerosol droplet size distribution of the glass cleaner.

Test item no.	Dv^1 (10%) (µm)	Dv^1 (50%) (µm)	Dv^1 (90%) (µm)	Cv^2 (%) at 3.97 µm	Cv^2 (%) at 10.44 µm
Formulation 1: spray/open sieve
1	30.93^3	82.06	181.96	0.00	0.82
2	39.69	113.34	201.98	0.00	0.46
3	32.28	90.55	188.35	0.00	0.68
Mean	34	95	191	0.0	0.7
Formulation 1: foam/closed sieve
4	56.03	126.61	202.75	0.00	0.19
5	55.30	128.98	206.88	0.00	0.21
6	54.23	125.83	205.62	0.00	0.22
Mean	55	127	205	0.0	0.2
Formulation 2: spray/ open sieve
1	29.43^3	83.96	185.08	0.00	0.84
2	29.57	80.47	186.01	0.00	0.88
3	23.99	60.69	161.88	0.00	1.52
Mean	28	75	178	0.0	1.1
Formulation 2: foam/ closed sieve
4	52.87	126.11	205.25	0.00	0.22
5	57.33	128.91	207.12	0.00	0.19
6	51.67	127.93	205.03	0.00	0.25
Mean	54	128	206	0.0	0.2

¹Dv (xx %): average aerosol droplet diameter at a given percentage (xx) of the cumulative volume, for example a value of Dv (10%) = 30.93 µm for the test item no. 1 (open sieve) means that 10% of all droplets (volume share) had diameters <30.93 µm; ²Cv: average cumulative volume at a given droplet diameter, for example a value of Cv (at 10.44 µm) = 0.82% for the test item no. 1 (open sieve) means that 0.82% of all droplets (volume share) had diameters <10.44 µm; ³Numbers are an average of five measurements.

Figure 3. Analysis of size, shape and aggregation state of SAS particles in the raw material by transmission electron microscopy. A. Besides single particles, the state of aggregation and agglomerate on can be seen with lower resolution (1:250,000). The whole bar is 100 nm and one segment of it is 20 nm. B. With higher resolution, the size of the individual particles becomes more visible (1:560,000). The whole bar is 50 nm and one segment of it is 10 nm.

Figure 4. Particle size distribution of the raw material by dynamic light scattering.

Figure 5. Analysis of the colloidal SAS applied on a glass slide by atomic force microscopy.

Table III. Summary of literature data on the algal toxicity of SAS.

References	Particle size (nm)	EC20	NOEC	Remark
Wei et al. (2010)	10–20	48 h 144 mg/l 72 h 388 mg/l 96 h 216 mg/l		Concentration-dependent chlorophyll reduction
Van Hoecke et al. (2008)	12.5	72 h 20 mg/l		Plateau toxicity 50% growth reduction
	27	72 h 28.8 mg/l
Van Hoecke et al. (2011)	22	48 h 9.9 mg/l (pH 7.6)	4.6
		48 h 218.9 mg/l (pH 7.4)	100	4.7 mg C/l NOM
Fujiwara et al. (2008)	5, 26, 78	EC50 96 h 8000 mg/l 96 h 71,000 mg/l 96 h 91,000 mg/l		Faint of chlorophyll colour

NOEC, no observed effect concentration; NOM, natural organic matter; SAS, synthetic amorphous silicon dioxide.

Figure 6. Calculated air concentration of SAS during consumer exposure towards the glass cleaner spray.

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