The feasibility of a sequentially enhanced process for the remediation of soils contaminated by mixed contaminants, specifically multiple polycyclic aromatic hydrocarbons (PAHs) and heavy metals, was investigated. This process consists of sequential flushing using two chemical agents: a surfactant and a chelate. A series of laboratory column experiments was conducted with three different sequential schemes, designated as SEQ1, SEQ2, and SEQ3, in two distinct flushing stages, to remove PAHs and heavy metals from a field-contaminated soil. The SEQ1 scheme involved flushing 0.2 M ethylenediaminetetraacetic acid (EDTA) followed by flushing 5 % Igepal. The SEQ2 scheme involved flushing 5 % Igepal followed by flushing 0.2 M EDTA. SEQ1 was investigated under a constant hydraulic gradient of 1.2, while the SEQ2 scheme was investigated under hydraulic gradients that increased from 1.2 to 4.0. The SEQ3 scheme consisted of sequential flushing of 5 % Igepal (first stage) and 0.2 M EDTA (second stage) under a constant low hydraulic gradient of 0.2. The selected sequential schemes allowed an assessment of the efficacy of sequencing the surfactant and chelating flushing for the removal of multiple heavy metals and PAHs under various hydraulic gradients. The hydraulic conductivity (or flow) was found to vary depending on the flushing agent and the sequence scheme. Under the high hydraulic gradient, the hydraulic conductivity was lower during chelant flushing stage as compared with surfactant flushing stage in both SEQ1 and SEQ2. However, under a low gradient condition (SEQ3), the hydraulic conductivity was approximately the same during both chelant and surfactant flushing stages. The contaminant removal was also significantly affected by the flushing agent and sequence and the applied hydraulic gradient. Heavy metals were removed during chelant flushing, while PAHs were removed during surfactant flushing. The total removal efficiencies of Pb, Zn, and Cu were 76 %, 63 %, and 11 % in SEQ1 and 42 %, 40 %, and 7 % in SEQ2, respectively, while the total removal efficiencies of phenanthrene, anthracene, benz(a)anthracene, and pyrene were 51 %, 35 %, 58 %, and 39 % in SEQ1 and 69 %, 50 %, 65 %, and 69 % in SEQ2, respectively. Overall, the total mass removal of heavy metals and PAHs was higher in SEQ1 as compared with SEQ2, demonstrating that SEQ1 is the effective sequence scheme. Comparison of the results of high and low gradient conditions (SEQ2 and SEQ3) reveals that the removal of contaminants, especially heavy metals, is rate-limited. Overall, this study showed that the removal of co-existing heavy metals and PAHs from soils is possible through the careful selection of the sequence under which the flushing of chelant and surfactant occurs and depends on the site-specific soil and contaminant conditions. Additional research is needed to establish the most optimal flushing scheme (sequence duration and flow velocity) to remove the mixed contaminants effectively and efficiently. © 2013 Springer Science+Business Media Dordrecht.

Being predominant inorganic arsenicals, methylarsenicals also occur in anaerobic paddy soils. Therefore, this study investigated the influence of Fe concentrations and arsenic speciation [arsenate (As(V)) and dimethylarsinate (DMA)] in paddy soils on arsenic uptake in rice plant. Rice seedlings were grown in soil irrigated with a Murashige and Skoog (MS) growth solution containing As(V) or DMA with or without 1.8 mM Fe in excess to the background concentration of total iron (0.03 mM) in the soil. Arsenic concentration in rice roots increased initially and then decreased gradually when the seedlings were grown with excess Fe and As(V). In contrast, arsenic concentration in the roots increased steadily ( P < 0.01) when the seedlings were grown without excess Fe and As(V). When the form of the arsenic was DMA, total arsenic (tAs) concentration in rice roots increased gradually ( P < 0.01) and was not affected by the addition of excess Fe in the soil. When rice seedlings were grown with As(V), tAs concentration in rice roots and shoots increased steadily ( P < 0.01) for gradual increase of Fe concentrations in soil. However, tAs concentration in roots and shoots was independent of Fe concentrations in soil when the form of arsenic was DMA. The tAs concentrations in rice shoots also increased significantly ( P < 0.01) with increasing exposure time for both As(V) and DMA. Thus, Fe concentrations in soil affect arsenic uptake in rice plant depending on the speciation of arsenic.

The aim of this study was to statistically compare sampling sites identified along the Berg River system to identify the major point sources of metal pollution from June 2004 to May 2005. Three sites were selected [site A—agricultural farming area, site B—Plot 8000 (close to the informal settlement), and site C—the Newton pumping station] representing different sectors which the river services. Aluminium (Al), iron (Fe), manganese (Mn), and lead (Pb) concentrations were determined using Inductively Coupled Plasma Atomic Emission Spectrometry and were statistically compared and analysed with one-way ANOVAs. For all the metals analysed, site C (industrial area) proved to be the site where the highest average metal concentrations were recorded. Generally, the concentrations recorded at site A (site furthest from the industrial area) were significantly (p < 0.05) lower than the concentrations recorded at both sites B and C. While the Al and Fe concentrations were consistently higher than any of the other metals analysed for, site C was identified as the primary source of metal contamination in the Berg River, resulting from the runoff from industrial activities at this particular site.

Three pot experiments were carried out to evaluate the phytoextraction efficiency of cadmium (Cd) by an amaranth (Amaranthus hypochondriacus L.). To enhance phytoremediation potential, this study examined the effect of fertilization, repeated harvests, and growth time on the efficiency of Cd removal from soil. The result showed that fertilizing with NPK increased dry biomass by a factor of 4.2, resulting in a large increment of Cd accumulation. Repeated harvests had a significant effect on the plant biomass and thus on overall Cd removal and an optimal cutting position influenced the amount of Cd extracted from soils. Plant growth time was found to significantly affect the amount of Cd extracted by A. hypochondriacus. This study indicates that A. hypochondriacus has great phytoremediation potential in Cd-contaminated soil. For best practice, the recommendation is to maximize the phytoextraction efficiency of A. hypochondriacus by repeated harvests, harvesting at the squaring stage (soon after the flower begins to appear), and apply NPK compound fertilizer as base application.

Remediation of anthracene from soil was faster in the topsoil than in the lower layers. It was not clear whether this was due to a higher anthracene bioavailability or an increased microbial degradation in the topsoil layer. Therefore, an arable soil was contaminated with 500 mg anthracene kg⁻¹ dry soil, and its removal was monitored with an exhaustive technique and with n-butanol to determine its bioavailability in three layers. Additionally, part of the contaminated soil was stored aerobically for 112 days (considered the aged soil), and the anthracene was monitored thereafter. After 112 days, 360 mg anthracene kg⁻¹ was removed from the soil, but its dissipation was not affected by the layer, depth, and fluctuations in water content or the interaction between. In the aged soil stored for 112 days, only 170 mg anthracene kg⁻¹ was removed. In the subsequent incubation of the aged soil, 273 mg anthracene kg⁻¹ was removed within 28 days, and after 112 days, no contaminant was detectable in the soil. An additional experiment confirmed the hypothesis that simply mixing the soil accelerated the removal of anthracene. Mixing the soil every 7 days removed all anthracene from the soil within 28 days, while in the undisturbed soil, 301 mg anthracene kg⁻¹ was still extractable. It can be concluded that mixing the soil accelerated the removal of anthracene, but fluctuations in water content did not. The anthracene extracted with n-butanol was not related to the amount removed and is thus not a good indicator of bioavailability of anthracene in soil.

Field experiments were conducted in the 2008–2009 soybean and winter wheat-growing seasons to assess soil respiration (SR) and nitrous oxide (N₂O) emission as affected by enhanced UV-B radiation and straw incorporation. The SR rate was measured using a soil CO₂ flux system; the N₂O flux was measured using a static chamber–gas chromatograph technique. The results showed that in the soybean and winter wheat-growing seasons, enhanced UV-B radiation significantly decreased the SR rates and that straw incorporation increased the SR rates compared to the control treatment. The combined treatment of UV-B and straw incorporation had no obvious influence on the SR rates. Enhanced UV-B radiation, straw incorporation, and the combination treatment increased the temperature sensitivity of SR in the soybean-growing season. The study also showed that N₂O emissions were reduced by enhanced UV-B radiation and that straw incorporation had no significant effects on the mean N₂O emission fluxes in the soybean and winter wheat-growing seasons. Our findings suggest that enhanced UV-B radiation may lead to a decrease in SR and in N₂O emissions, straw incorporation may increase SR, and the combined treatment may have no significant influence on SR and N₂O emissions from soybean–winter wheat rotation systems.

Biodegradation of chlorpyrifos was studied in mineral medium and soil with a novel fungal strain JAS1 isolated from a paddy field soil. The molecular characterization based on 18S rRNA sequence homology confirmed its identity as Aspergillus terreus. The 300-mg L⁻¹ chlorpyrifos and its major metabolite 3,5,6-trichloro-2-pyridinol (TCP) were completely degraded within 24 h of incubation in the mineral medium. In soil enriched with chlorpyrifos and nutrients (carbon, nitrogen, and phosphorous), A. terreus JAS1 was able to degrade chlorpyrifos and its metabolite TCP (300 mg kg⁻¹ soil) in 24 and 48 h, respectively. The soil was spiked with chlorpyrifos (300 mg kg⁻¹ soil) devoid of nutrients and the fungal strain was capable of degrading both chlorpyrifos and TCP in 24 and 48 h, respectively. The course of the degradation process was studied using high-performance liquid chromatography and Fourier transform infrared analyses. These results showed that the chlorpyrifos-degrading fungal strain had the potential to degrade the pesticide-contaminated agricultural soils even without addition of nutrients.

The use of peracetic acid (PAA) in the disinfection of sanitary effluents has been proposed by various authors. However, there are still doubts about its influence on the physical-chemical characteristics of the effluent after application. In the present study, it was observed that the composition of PAA leads to an increase in organic material, resulting in an increase of approximately 20 mg/L in the chemical oxygen demand of the effluent for every 10 mg/L of PAA applied. According to the kinetic tests, the degradation of PAA in the effluent was represented by a first-order reaction and its half-life in the effluent was estimated at 79 min. The formation of by-products resulting from degradation of PAA in the effluent was evaluated by considering by-products already detected by other authors in disinfection trials, these being nonanal, decanal, chlorophenols, and 1-methoxy-4-methylbenzene, which were not observed in the effluent being studied after application of PAA at a dosage of 10 mg/L. © 2013 Springer Science+Business Media Dordrecht.

Understanding denitrification rates in groundwater ecosystems can help predict where agricultural reactive nitrogen (N) contributes to environmental degradation. In situ groundwater denitrification rates were determined in subsoil, at the bedrock interface and in bedrock at two sites, grassland and arable, using an in situ 'push-pull' method with 15N-labelled nitrate (NO3 --N). Measured groundwater denitrification rates ranged from 1.3 to 469.5 μg N kg-1 day-1. Exceptionally high denitrification rates observed at the bedrock interface at grassland site (470 ± 152 μg N kg-1 day-1; SE, standard error) suggest that deep groundwater can serve as substantial hotspots for NO 3 --N removal. However, denitrification rates at the other locations were low and may not substantially reduce NO3 --N delivery to surface waters. Denitrification rates were negatively correlated with ambient dissolved oxygen, redox potential, k s and NO3 - (all p values, p < 0.01) and positively correlated with SO4 2- (p < 0.05). Higher mean N 2O/(N2O + N2) ratios at an arable (0.28) site than the grassland (0.10) revealed that the arable site has higher potential to indirect N2O emissions. Identification of areas with high and low denitrification and related site parameters can be a tool to manage agricultural N to safeguard the environment. © 2013 Springer Science+Business Media Dordrecht.

Perfluorooctane sulfonate (PFOS), which has numerous uses besides being an ingredient in the formulation of aqueous film-forming foams, is considered as an emerging pollutant of increasing public health and environmental concern due to recent reports of its worldwide distribution, environmental persistence and bioaccumulation potential. In an attempt to recommend a 'risk-based' remediation strategy, this study investigates the removal of PFOS from impacted waters and fixation of PFOS in impacted soils using a novel modified clay adsorbent (MatCARE™, patent number 2009905953). Batch adsorption tests demonstrated a much faster adsorption kinetics (only 60 min to reach equilibrium) and remarkably higher PFOS adsorption capacity (0.09 mmol g-1) of the MatCARE™ compared to a commercial activated carbon (0.07 mmol g -1). Treatability studies, performed by treating the PFOS-contaminated soils with the MatCARE™ (10 % w/w) and then incubating at 25 and 37 C temperatures maintaining 60 % of the maximum water holding capacity of the soils for a period of a year, demonstrated a negligible release (water extractable) of the contaminant (only 0.5 to 0.6 %). The fixation of PFOS in soils by the new adsorbent was exothermic in nature. Soils with higher clay and organic matter content, but lower pH values, retained PFOS to a much greater extent. A cost analyses confirmed that the MatCARETM could be an economically viable option for the 'risk-based' remediation of PFOS in contaminated waters and soils. © 2013 Springer Science+Business Media Dordrecht.