Abstract
Due to their enhanced stability and contaminant transport potential, environmental nanoparticles derived from soil and biosolid materials may pose a considerable risk to groundwater quality. Very little information exists on the stability and transportability of environmental or natural nanocolloids in the presence of As, Se, Pb and Cu contaminants, all of which are considered to represent substantial threats to human and animal populations through groundwater contamination. This study involved stability settling experiments of nanocolloids (NCs) (-1 of As, Se, Pb and Cu. The results indicated greater stability in the mineral than the biosolid colloid fractions, and enhanced stability of NCs over corresponding MCs in the presence or absence of contaminants at low contaminant loads. At high contaminant loads nearly all colloids were unstable except for the bio-nanocolloids which still sustained considerable stability. At low contaminant loads, the MC fraction stability sequence was smectitic > mixed > kaolinitic > biosolid. Among the nano-fractions, the smectitic and kaolinitic colloids demonstrated lower stability than the MCs, but higher than those of the mixed and biosolid fractions. Physicochemical characterizations indicated that extensive organic carbon surface coatings and higher Al/Fe:Si ratios may have induced higher stability in the NC fractions, but their overall stability may also have been hindered in some cases by nano-aggregation phenomena.
Highlights
Water dispersed colloids (WDC) are known to disperse from soil aggregates and remain mobile in subsurface environments [1] [2]
This study filled a previous void on the stability behavior of natural soil and biosolid water dispersible NCs and their differences from their corresponding larger MC fractions
The findings demonstrated that soil and biosolid NCs are more stable in the absence and presence of up to 2 mg·L−1 As, Se, Cu and Pb contaminants than corresponding MCs
Summary
Water dispersed colloids (WDC) are known to disperse from soil aggregates and remain mobile in subsurface environments [1] [2] They have average diameters between 1 and 1000 nm, which includes nanoparticles, with one dimension equal to or less than 100 nm [3]-[5]. The tendency for particles to aggregate or remain stable in solution may be affected by the complex mineralogical and physico-chemical attributes of the particle, including particle size, surface chemistry, and the aqueous environment surrounding transport [5] [6]. An important consideration in natural systems includes their complex composition, which consists of mixed colloidal phases This encompasses the interactions with other NCs and solutes in the system, since nanoparticle mobility is controlled mainly by Brownian motion and not by gravitational settling like their larger counterparts [10]
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