Characterization of Environmental Nano- and Macrocolloid Particles Extracted from Selected Soils and Biosolids

Table 1

Physical and chemical characteristics of nano- and macrocolloids.

Properties	Colloids
	Smectitic		Mixed		Kaolinitic		Biosolid
Size class	Macro	Nano	Macro	Nano	Macro	Nano	Macro	Nano
DLS^† mean hydrodynamic diameter (𝑑ℎ) ± SD^‡ (nm)	487±10	181±3	596±21	205±4	545±25	187±4	4456±599	353±8
SEM/TEM^¶ mean smallest particle size ± SD^‡ (nm)	328±144	37±13	549±394	7±5	288±184	41±19	363±338	50±19
Surface area (m^2 g^−1) ± SD^‡	708±137	879±76	420±105	466±10	333±37	389±44	1674±70	1303±63
% water dispersible colloid recovered from bulk sample	33.41	0.67	37.17	0.33	11.00	0.07	4.95	0.03
Electrical conductivity (mmhos cm^−1)	3.93×10^−3	6.07×10^−3	2.91×10^−3	3.09×10^−2	2.87×10^−3	3.80×10^−3	1.56×10^−2	4.69×10^−2
Ionic strength^§ (mol L^−1)	4.99×10^−5	7.71×10^−5	3.70×10^−5	3.92×10^−4	3.64×10^−5	4.83×10^−5	1.97×10^−4	5.96×10^−4
Natural pH	4.92	5.12	5.07	4.92	4.91	5.38	5.39	5.25
CEC (cmolc kg^−1)^#	35.05±12.84	42.19±15.12	8.89±1.62	10.51±1.67	6.94±1.85	13.12±2.84	37.61±14.85	70.99±22.98
Ca^2+ (cmolc kg^−1)	27.60	32.64	3.80	4.00	4.40	7.12	31.60	51.68
Mg^2+ (cmolc kg^−1)	6.27	8.00	3.40	3.47	1.60	3.73	3.60	12.13
K^+ (cmolc kg^−1)	0.57	0.78	1.15	2.80	0.45	1.23	1.64	3.98
Na^+ (cmolc kg^−1)	0.61	0.77	0.54	0.24	0.49	1.04	0.77	3.20
SAR^††	0.15	0.17	0.28	0.12	0.28	0.45	0.18	0.57
OC (mg kg^−1)^‡‡	658	897	645	774	430	647	1.3K	16K
N (mg kg^−1)^§§	228	332	315	612	230	282	1.5K	62K

†DLS: dynamic light scattering was used to measure the mean intensity weighted hydrodynamic diameters (𝑧-average diameter, 𝑑_ℎ).
^‡SD: standard deviation was calculated based on the averages of duplicate or triplicate measurements (see Methods section).
§Ionic Strength (IS): estimated using Griffin and Jurinak’s equation where IS (mol L⁻¹) = 0.0127 × electrical conductivity (millimhos cm⁻¹) (1973).
¶SEM: scanning electron microscopy and TEM: transmission electron microscopy data represent the average smallest dimension of 300 representative particles from three to eight images of each size fraction as measured until the average and standard deviation values had less than 10% variation.
^#CEC: cation exchange capacity by sum of cations.
^††SAR: sodium adsorption ratio.
^‡‡OC: organic carbon was derived by subtracting dissolved organic carbon from total carbon measurements. Due to low pH conditions and the typical absence of carbonates in the region, inorganic carbon contributions were assumed to be minimal.
§§N: nitrogen.