Table 4.
Advantages and disadvantages of different methods for spiking soils with MNMs, identified at the NIN workshop
| Adding as powder | Adding in suspension without a dispersing agent | Add in suspension with a dispersing agent | |
|---|---|---|---|
| Yield | High concentrations possible (no limit) | Low concentrations (μg l−1 to mg l−1 range) | High concentrations possible (g l−1 range) |
| Ease of preparation | Potential occupational hazards from dusts. Short preparation (hours) | Easy to apply, but potentially long preparation time for the stock dispersion (for stirring methods, up to months) | Easy to apply, and short preparation time (hours) |
| Control of the dosing | If the soil is relatively dry and mixed with dry powder then a reasonable spread of the test material in the soil occurs | Poor reproducibility of the stock dispersion could produce variable dosing. Depending on the hydroscopic nature and viscosity of the solution, and properties of the MNM, the material may not evenly spread in the soil sample | Improved reproducibility of the stock dispersion, and more chance that the test material will spread evenly in the soil sample. However, dispersing agents controls are needed in the test design |
| Characterisation | Possible in the stock dispersion, but not in the soil matrix | Possible in the stock dispersion, but not in the soil matrix | Possible in the stock dispersion, but not in the soil matrix |
| Surface modification of the test material | Weathering effects less likely with dry mixing | Long preparation times of stock dispersions may lead to oxidation, hydroxylation or other chemical/physical modifications of the surface. Soil effect relative to the stock preparation effect on surface modifications are mostly unknown | Short preparation times imply less likely to produce spontaneous changes in the particle surface, but dispersing agents will coat/modify the surface. Interaction of dispersing agent with the soil and particle surface will depend on soil type and the stability of any surface coating in the soil matrix |
| Dosing for chronic tests | Suitable dosing method, but MNM may age, particle ageing control should be included in the experimental design | Suitable dosing method, but MNM may age, particle ageing control should be included in the experimental design | Suitable dosing method, particle ageing may be different with dispersing agent present. Degradation of the dispersing agent is likely |