Experimental evidence of colloids and nanoparticles presence from 25 waste leachates

Abstract

The potential colloids release from a large panel of 25 solid industrial and municipal waste leachates, contaminated soil, contaminated sediments and landfill leachates was studied. Standardized leaching, cascade filtrations and measurement of element concentrations in the microfiltrate (MF) and ultrafiltrate (UF) fraction were used to easily detect colloids potentially released by waste. Precautions against CO(2) capture by alkaline leachates, or bacterial re-growth in leachates from wastes containing organic matter should be taken. Most of the colloidal particles were visible by transmission electron microscopy with energy dispersion spectrometry (TEM-EDS) if their elemental MF concentration is greater than 200 μgl(-1). If the samples are dried during the preparation for microscopy, neoformation of particles can occur from the soluble part of the element. Size distribution analysis measured by photon correlation spectroscopy (PCS) were frequently unvalid, particularly due to polydispersity and/or too low concentrations in the leachates. A low sensitivity device is required, and further improvement is desirable in that field. For some waste leachates, particles had a zeta potential strong enough to remain in suspension. Mn, As, Co, Pb, Sn, Zn had always a colloidal form (MF concentration/UF concentration>1.5) and total organic carbon (TOC), Fe, P, Ba, Cr, Cu, Ni are partly colloidal for more than half of the samples). Nearly all the micro-pollutants (As, Ba, Co, Cr, Cu, Mo, Ni, Pb, Sb, Sn, V and Zn) were found at least once in colloidal form greater than 100 μgl(-1). In particular, the colloidal forms of Zn were always by far more concentrated than its dissolved form. The TEM-EDS method showed various particles, including manufactured nanoparticles (organic polymer, TiO(2), particles with Sr, La, Ce, Nd). All the waste had at least one element detected as colloidal. The solid waste leachates contained significant amount of colloids different in elemental composition from natural ones. The majority of the elements were in colloidal form for wastes of packaging (3), a steel slag, a sludge from hydrometallurgy, composts (2), a dredged sediment (#18), an As contaminated soil and two active landfill leachates. These results showed that cascade filtration and ICP elemental analysis seems valid methods in this field, and that electronic microscopy with elemental detection allows to identify particles. Particles can be formed from dissolved elements during TEM sample preparation and cross-checking with MF and UF composition by ICP is useful. The colloidal fraction of leachate of waste seems to be a significant source term, and should be taken into account in studies of emission and transfer of contaminants in the environment. Standardized cross-filtration method could be amended for the presence of colloids in waste leachates.

Emerging patterns for engineered nanomaterials in the environment: a review of fate and toxicity studies

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Characteristics of municipal landfill leachate and its impact on surrounding agricultural land

“…In the waste transfer pollutants from the waste material to the percolating water is a combination of physical, chemical and biological processes (Christensen and Kjeldsen 1989). Mechanisms of contaminant removal include leaching of inherently soluble materials, leaching of soluble biodegradation products of complex organic molecules, leaching of soluble products of chemical reaction and washout of fines and colloids (Hennebert et al 2013). The characteristics of the leachate produced are highly variable, depending on the composition of the solid waste, precipitation rate, site hydrology, compaction, cover design, waste age and interaction of leachate with the environment and landfill design and operation (Nartey et al 2012).…”

Transport of graphene oxide in saturated porous media: Effect of cation composition in mixed Na–Ca electrolyte systems

“…But latest research explicitly indicates that exposure to GO might induce severe cyto-toxicity and lung disease in human (Wang et al, 2011), and significantly compromises bacterial metabolic activity (Akhavan and Ghaderi, 2010;Ahmed and Rodrigues, 2013). A key process of nanomaterial exposure is infiltration from the point of nanomaterial release to subsurface system (Hennebert and Avellan, 2013). Because of the large amounts of reactive surface Ofunctional groups with a range of acid dissociation coefficients and negative surface charges under relatively wide ranges of solution chemistry conditions (Konkena and Vasudevan, 2012), GO particles are regarded to be more resilient than many other nanoparticles to changes in solution chemistry that favor particle aggregation and deposition.…”