Radical change of Zn speciation in pig slurry amended soil: Key role of nano-sized sulfide particles

Abstract

Spreading livestock manure as fertilizer on farmlands is a widespread practice. It represents the major source of heavy metal(loid)s (HM) input in agricultural soils. Since zinc (Zn) is present at high concentrations in manure, it poses special environmental concerns related to phytotoxicity, groundwater contamination, and introduction in the food chain. Therefore, investigations on the fate and behavior of manure-borne Zn, when it enters the soil environment, are necessary to predict the environmental effects. Nevertheless, long-term field studies assessing Zn speciation in the organic waste matrix, as well as within the soil after manure application, are lacking. This study was designed to fill this gap. Using SEM-EDS and XAS analysis, we reported the following new results: (i) ZnS made up 100% of the Zn speciation in the pig slurry (the highest proportion of ZnS ever observed in organic waste); and (ii) ZnS aggregates were about 1-μm diameter (the smallest particle size ever reported in pig slurry). Moreover, the pig slurry containing ZnS was spread on the soil over an 11-year period, totaling 22 applications, and the resulting Zn speciation within the amended soil was analyzed. Surprisingly, ZnS, i.e. the only species responsible for a nearly 2-fold increase in the Zn concentration within the amended soil, was not detected in this soil. Based on SEM-EDS and XAS observations, we put forward the hypothesis that Zn in the pig slurry consisted of nano-sized ZnS crystallites that further aggregated. The low stability of ZnS nanoparticles within oxic and complex environments such as the studied soil was the key explanation for the radical change in pig slurry-borne Zn speciation after long-term amendments.

Anaerobic Digestion Alters Copper and Zinc Speciation

“…Zn sulfides have already been observed in OW 6,18 and were found to be nanostructured only in sewage sludge 29 and pig slurry. 9 Batch experiments in which the physicochemical conditions were similar to those of OW suggested the occurrence of a Zn sulfide nanoparticulate state. Indeed, Lau et al 30 suggested that the high OM content of OW hinders Zn sulfide crystal growth, which would lead to the formation of Zn sulfide nanoparticles.…”

Lead, zinc, and copper redistributions in soils along a deposition gradient from emissions of a Pb-Ag smelter decommissioned 100 years ago

“…Normalization and data reduction were performed according to standard methods (Doelsch et al, 2006) using Athena software (Ravel and Newville, 2005). A library of Zn reference compound spectra, described elsewhere (Formentini et al, 2017; was used to identify Zn species in the samples. Details on the fitting procedure and results are given in SI (Text S3, Figure S3 (a, b) and Table S2).…”

Drastic Change in Zinc Speciation during Anaerobic Digestion and Composting: Instability of Nanosized Zinc Sulfide

“…Very few studies have assessed the fate of this species in the soil after OW spreading. Formentini et al 21 showed that after spreading of pig slurry, in which nano-ZnS accounted for 100% of the Zn speciation, on a clay soil, all the Zn accumulated in the top 30 cm and was distributed between Zn-OM (41%), Zn-kaolinite (38%) and Zn-FeOx (23%). Zn applied to the soil via pig slurry spreading was no longer present in the form of nano-ZnS.…”

“…18 For instance, different toxicity mechanisms have been described when Escherichia coli were exposed to nanoparticulate ZnO or dissolved Zn. 19 Recent studies using X-ray absorption spectroscopy (XAS) have shown that part of Zn is present as zinc sulfide (ZnS) in raw OWs 20,21 and digestates. 20,[22][23][24][25][26] This technique is thus suitable to determine Zn speciation in a complex matrix such as OW.…”

“…20,[22][23][24][25][26] This technique is thus suitable to determine Zn speciation in a complex matrix such as OW. 27,28 Surprisingly, the proportion of ZnS present in OWs is wide, ranging from 0 to 100% in raw OWs 20,21 and 0 to 96% in digestates. 20,[22][23][24][25] These differences can be explained by several factors including (i) the type of reactor sampled (lab-scale vs. full-scale reactors), (ii) the origin and the nature of the OW (agricultural vs. urban, solid vs. liquid) and/or (iii) the processing steps that may differ from one laboratory/site to another (e.g.…”