Evaluation of extraction procedures for removing lead from contaminated soil

Super adsorption performance of carboxymethyl cellulose/copper oxide-nickel oxide nanocomposite toward the removal of organic and inorganic pollutants

A novel nanocomposite bead based on polymeric matrix of carboxymethyl cellulose and copper oxide-nickel oxide nanoparticles was synthesized, characterized, and applied for adsorptive removal of inorganic and organic contaminants at trace level of part per million (mgL^-1) from aqueous sample. Carboxymethyl cellulose/copper oxide-nickel oxide (CMC/CuO-NiO) adsorbent beads were selective toward the removal of Pb(II) among other metal ions. The removal percentage of Pb(II) was more than 99% with 3 mgL^-1. The waste beads after Pb (II) adsorption (Pb@CMC/CuO-NiO) and CMC/CuO-NiO nanocomposite beads were employed as adsorbents for removing of various dyes. It was found that Pb@CMC/CuO-NiO can be reused as adsorbent for the removal of Congo Red (CR), while CMC/CuO-NiO nanocomposite beads were more selective for removal of Eosin Yellow (EY) from aqueous media. The adsorption of CR and EY was optimized, and the removal percentages were 93% and 96.4%, respectively. The influence of different parameters was studied on the uptake capacity of Pb(II), CR, and EY, and lastly, the CMC/CuO-NiO beads exhibited responsive performance in relation to pH and other parameters. Thus, the prepared CMC/CuO-NiO beads were found to be a smart material which is effective and played super adsorption performance in the removal of Pb(II), CR, and EY from aqueous solution. These features make CMC/CuO-NiO beads suitable for numerous scientific and industrial applications and may be used as an alternative to high-cost commercial adsorbents.

Characterization and within-site variation of environmental metal concentrations around a contaminated site using a community-engaged approach

Historic industrial activity led to extensive lead and arsenic contamination within residential areas of East Chicago, Indiana, United States. Although remediation is underway, community concerns about this contamination remain. Therefore, the goal for this analysis was to characterize environmental contamination in soil within and around these areas. A total of 228 samples from 32 different sites (addresses) were collected by community members or study staff. These were analyzed for metals using portable x-ray fluorescence or inductively coupled plasma ̶ optical emission spectroscopy. Concentrations exceeding EPA screening levels were found for 42% of the soil arsenic samples, 35% of the soil lead samples, and 79% of the soil manganese samples; a few samples also contained elevated copper or zinc. Concentrations above EPA screening levels were identified both within and outside of the formally designated contaminated area. Roughly 30% of all sites had at least one sample above and one sample below the screening level for arsenic, lead, and manganese. For sites within the contaminated area, more than 90% (arsenic), 60% (lead) and 60% (manganese) of the samples exceeded EPA screening levels. There was a significant association of proximity to the historic industrial site with elevated soil concentrations of arsenic and lead; a similar association was present for manganese. These results are consistent with existing data for lead and arsenic and we additionally report elevated concentrations of manganese and a high within-site variability of all metal concentrations. These findings should be considered in future remediation efforts.

Soil particle size fraction and potentially toxic elements bioaccessibility: A review

In the last decade, extensive studies have been conducted to quantify the influence of different factors on potentially toxic elements (PTE) bioaccessibility in soil; one of the most important is soil size fraction. However, there is no agreement about the size fraction and the methods to investigate bioaccessibility, as very few review articles are available on soil PTE bioaccessibility and none addressed the influence of particle size on PTE bioaccessibility. This study provides a review of the relations between PTE bioaccessibility and soil particle size fractions. The available research indicates that PTE bioaccessibility distribution across different size fractions varies widely in soil, but a general trend of higher bioaccessibility in finer size fraction was found. The different elements may exhibit different relationships between bioaccessibility and soil size fraction and, in some cases, their bioaccessibility seems to be more related to the source and to the chemico-physical form of PTE in soil. Often, soil pollution and related health risk are assessed based on PTE total concentration rather than their bioaccessible fraction, but from the available studies it appears that consensus must be pursued on the methods to determine PTE bioaccessibility in the fine soil size fractions to achieve a more accurate human health risk assessment.

Genotoxic endpoints in a Pb-accumulating pea cultivar: insights into Pb2+ contamination limits

Lead (Pb) persists among the most hazardous contaminant metals. Pb-induced genotoxic effects remain a matter of debate as they are a major cause of plant growth impairment, but assessing Pb genotoxicity requires the selection of Pb-sensitive genotoxic biomarkers. Seedlings of the ecotoxicological model species Pisum sativum L. were exposed to Pb2+ (≤ 2000 mg L-1). Flow cytometry (FCM) revealed that 28 days after, Pb2+ arrested root cell cycle at G2 but no eu/aneuploidies were found. Comet assay and FCM-clastogenicity assays showed that Pb2+ increased DNA breaks in roots at concentrations as low as 20 mg L-1. Leaves showed no variation in DNA-ploidy or cell cycle progression but had increased DNA breaks at the highest Pb2+ dose. We conclude that both Comet assay and the full-peak coefficient of variation (FPCV) were the most relevant endpoints of Pb-phytogenotoxicity. Also, the Pb-induced DNA breaks may be related with the arrest at the G2-checkpoint. Data will be relevant to better define Pb2+ ecogenotoxicological effects and their measuring tools and may contribute to a regulatory debate of this pollutant limits.

Efficient removal of Pb(II) from aqueous solution by a novel ion imprinted magnetic biosorbent: Adsorption kinetics and mechanisms

It is vital to understand the adsorption mechanisms and identify the adsorption kinetics when applying an adsorbent to remove heavy metals from aqueous solution. A Pb(II) imprinted magnetic biosorbent (Pb(II)-IMB) was developed for the removal of Pb²⁺ via lead ion imprinting technology and crosslinking reactions among chitosan (CTS), Serratia marcescens and Fe₃O₄. The effect of different parameters such as solution pH, adsorbent dosage, selectivity sorption and desorption were investigated on the absorption of lead ion by Pb(II)-IMB. The adsorbent was characterized by a Brunauer-Emmett Teller (BET) analysis, X-ray diffraction (XRD), vibrating sample magnetometry (VSM), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The adsorption kinetics, equilibrium and thermodynamics of Pb(II)-IMB for Pb(II) were studied. The results of the abovementioned analyses showed that the adsorption kinetic process fit well with the second-order equation. The adsorption isotherm process of Pb(II) on the Pb(II)-IMB was closely related to the Langmuir model. Thermodynamic studies suggested the spontaneous and endothermic nature of adsorption of Pb(II) by Pb(II)-IMB. The adsorption mechanism of Pb(II)-IMB was studied by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results indicated that the nitrogen in the amino group and the oxygen in the hydroxyl group of Pb(II)-IMB were coordination atoms.

Photosynthesis light-independent reactions are sensitive biomarkers to monitor lead phytotoxicity in a Pb-tolerant Pisum sativum cultivar

Lead (Pb) environmental contamination remains prevalent. Pisum sativum L. plants have been used in ecotoxicological studies, but some cultivars showed to tolerate and accumulate some levels of Pb, opening new perspectives to their use in phytoremediation approaches. However, the putative use of pea plants in phytoremediation requires reliable toxicity endpoints. Here, we evaluated the sensitivity of a large number of photosynthesis-related biomarkers in Pb-exposed pea plants. Plants (cv. "Corne de Bélier") were exposed to Pb concentrations up to 1,000 mg kg(-1) soil during 28 days. The photosynthetic potential biomarkers that were analyzed included pigments, chlorophyll (Chl) a fluorescence, gas exchange, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) activity, and carbohydrates. Flow cytometry (FCM) was also used to assess the morpho-functional status of chloroplasts. Finally, Pb-induced nutrient disorders were also evaluated. Net CO2 assimilation rate (A) and RuBisCO activity decreased strongly in Pb-exposed plants. Plant dry mass (DM) accumulation, however, was only reduced in the higher Pb concentrations tested (500 and 1,000 mg kg(-1) soil). Pigment contents increased solely in plants exposed to the largest Pb concentration, and in addition, the parameters related to the light-dependent reactions of photosynthesis, Fv/Fm and ΦPSII, were not affected by Pb exposure. In contrast to this, carbohydrates showed an overall tendency to increase in Pb-exposed plants. The morphological status of chloroplasts was affected by Pb exposure, with a general trend of volume decrease and granularity increase. These results point the endpoints related to the light-independent reactions of photosynthesis as more sensitive predictors of Pb-toxicity than the light-dependent reactions ones. Among the endpoints related to the light-independent photosynthesis reactions, RuBisCO activity and A were found to be the most sensitive. We discuss here the advantages of using these parameters as biomarkers for Pb toxicity in plants. Finally, we report that, despite showing physiological disorders, these cultivar plants survived and accumulated high doses of Pb, and their use in environmental/decontamination studies is open to debate.

Long-term performance of subsurface-flow constructed wetlands treating Cd wastewater

This study was conducted to investigate the long-term performance of subsurface-flow constructed wetland (SFCW) units treating a wastewater containing cadmium (Cd). The hydraulic retention time (HRT) was found to have significant effects on the SFCW performance, especially on Cd removal. During the 320 days of Cd feeding, the HRTs of 1, 3, 5 and 8 days resulted in the Cd removal efficiencies of 50, 90, 99 and 99%, respectively. The actual Cd breakthrough times in the SFCW effluent were found to be longer than the theoretical values calculated from the maximum adsorption capacities only, especially at the HRTs longer than 1 day, and were dependent on the operating HRT and Cd loading. Other mechanisms such as filtration, sedimentation and plant uptake were also responsible for Cd removal in the SFCW beds. The extents of Cd plant uptake were 21 and 6% of the Cd inputs for the SFCW units operating at the HRTs of 3 and 1 days, respectively. Based on Cd mass balance and fractionation analysis, the SFCW media were found to be most effective in Cd removal through adsorption of the residual and Fe/Mn oxide bound fractions. The results of this long-term study re-affirmed the necessity to determine actual breakthrough times of Cd or other heavy metals in the SFCW effluent which are dependent on HRT and Cd loading and are usually longer than the theoretical values calculated from the maximum adsorption capacity only.