We evaluated the distributions of dental splatters and the corresponding control measure effects with high-speed videography and laser diffraction. Most of the dental splatters were small droplets (<50 μm). High-volume evacuation combined with a suction air purifier could clear away most of the droplets and aerosols.

Aggregation of colloidal clay particles (Na-montmorillonite) by CaCl2 and anionic polysaccharide (succinoglycan) in turbulent conditions was investigated using time-resolved size measurements by laser diffraction on diluted (50 mg l –1) and stirred suspensions. Excess of Ca2+ ions promotes coagulation of the clay, reducing interparticle repulsions, and allows adsorption of succinoglycan, inducing bridging flocculation. Growth/breakage cycles, characteristic of the turbulent conditions, cause the macromolecules to be incorporated in the innermost of the flocs, where the morphological units are shown by confocal microscopy to be the micrometric Ca-clay particles. Such incorporation results in an increased floc tensile strength, depending on the amount of macromolecules adsorbed, with a maximum at polysaccharide concentrations of 2 wt.% with respect to clay mass.

A new practical and precise method for determining soil aggregate stability is described. Four air-dry aggregate fractions (<0.25, 0.25–0.5, 0.5–1.0 and 1.0–2.0 mm) were added to thoroughly stirred water in a Mastersizer 2000 laser diffractometer. The suspension obtained was passed directly through the measuring system. The dynamics of median (equivalent diameter d50) particle-size distribution decrease (interpolated with a logarithmic function) was assumed to be the measure of soil aggregate stability. In order to show the applicability of the new method, the results obtained (for selected and diverse soils) were compared with those from the wet sieving standard method. The main conclusion is that the proposed method is convenient and can be successfully used for the estimation of soil aggregate stability. Moreover, it has wider application because standard sieving methods are restricted to aggregates >0.25 mm whereas, with the use of the laser diffraction method, smaller aggregates can be measured. The energy delivered to the aggregates in the process of aggregate disintegration is more reproducible in the method described here. The method also provides an opportunity to verify that the soil aggregates are completely destroyed (lack of the changes of the median value shows the end of soil aggregate disintegration).

To evaluate correlations between silt and clay fractions determined by pipette method and laser diffraction, samples from Dutch fine marine, fluvial, and loess deposits were analysed by both methods. For fluvial deposits, correlations for fractions <2 and >50 μm were excellent (R2 > 0.95), those for 2–4, 4–8, 16–32 and 32–50 μm were satisfactory (R2 = 0.80 – 0.95), while that for the fraction 8–16 μm had an R2 of only 0.68. For marine deposits, correlations for <2 and >50 μm were in the same range, but those of all other fractions except 8–16 μm were lower. In the loess samples, correlations for all but the 8–16 μm fraction were unsatisfactory. Laser diffraction gave 42% of pipette clay in marine samples, and 62% in fluvial and loess samples if regressions are forced through 0. Sand fractions detected by laser diffraction were 107% of the sieve fraction in marine samples, and 99% in the fluvial samples. Correlations for fractions smaller than reference size are generally better than those for individual size fractions. Both the 2 μm and the 50 μm boundary cause problems in the comparison. The first because of platy shape of clay minerals, and the second due to both a change in method in the pipette/sieving procedure, and to non-sphericity of particles. Apparently, correlations for clay- and silt-size fractions obtained by pipette method and laser diffraction will be different for each type of sediment.