Study on the possibility of hydrogen peroxide pretreatment and plant system to remediate soil pollution

Hydrogen peroxide was widely selected as the chemical oxidant in chemical remediation or as the donor of oxygen in in situ aerobic bioremediation of organic pollutants. In this paper, hydrogen peroxide pretreatment and plant system was done to examine its possibility to remediate the heavy metal contaminated soil or heavy metal-organic combined contaminated soil. Heavy metal contaminated soil was collected from the heavily industrialized area, in Fuyang county, Zhejiang province, China. And heavy metal-organic combined contaminated soil was prepared from the same contaminated soil by spiking 100 microg g(-1) 2,4-dichlorophenol (2,4-DCP). Results showed that H2O2 could improve the dissipation of 2,4-DCP and enhance the availability of Cu and Zn in soil. The greatly increased DOC (dissolved organic carbon) in the oxidation process was probably the main reason for the greatly increased water soluble Cu in higher pH condition. Water soluble Zn, however, easily rebound to soil components with the time being and had no positive relation with dissolved organic carbon. Planting with ryegrass influenced the behavior of pollutants in soil. It was observed that the dissipation of 2,4-DCP could be enhanced by the presence of plant roots and the availability of Cu and Zn in the planted soil was changed due to the mobilization and rebound mechanisms in the rhizosphere. Co-contamination of 2,4-DCP caused the greater availability of Cu and Zn in H2O2 pretreatment. But with the ryegrass planting, it was easier to rebound to the less available phase in the rhizosphere. Both Cu and Zn concentration in shoots increased with the H2O2 treatment. Therefore our results suggested that H2O2 pretreatment was probably a promising way for promoting the dissipation of persistent organic pollutants and enhancing the solubility of Cu and Zn in soil. A combination of H2O2 pretreatment and suitable plant might be an efficient alternative for remedying heavy metal or heavy metal-organic contaminated soil.     

Mobilization of phenol and dichlorophenol in unsaturated soils by non-uniform electrokinetics

The poor mobility of organic pollutants in contaminated sites frequently results in slow remediation processes. Organics, especially hydrophobic compounds, are generally retained strongly in soil matrix as a result of sorption, sequestration, or even formation into non-aqueous-phase liquids and their mobility is thus greatly reduced. The objective of this study was to evaluate the feasibility of using non-uniform electrokinetic transport processes to enhance the mobility of organic pollutants in unsaturated soils with no injection reagents. Phenol and 2,4-dichlorophenol (2,4-DCP), and kaolin and a natural sandy loam soil were selected as model organics and soils, respectively. The results showed that non-uniform electrokinetics can accelerate the desorption and movement of phenol and 2,4-DCP in unsaturated soils. Electromigration and electroosmotic flow were the main driving forces, and their role in the mobilization of phenol and 2,4-DCP varied with soil pH. The movement of 2,4-DCP in the sandy loam towards the anode (about 1.0 cmd(-1)V(-1)) was 1.0-1.5 cmd(-1)V(-1) slower than that in the kaolin soil, but about 0.5 cmd(-1)V(-1) greater than that of phenol in the sandy loam. When the sandy loam was adjusted to pH 9.3, the movement of phenol and 2,4-DCP towards the anode was about twice and five times faster than that at pH 7.7, respectively. The results also demonstrated that the movement of phenol and 2,4-DCP in soils can be easily controlled by regulating the operational mode of electric field. It is believed that non-uniform electrokinetics has the potential for practical application to in situ remediation of organics-contaminated sites.     

Effects of 2,4-dichlorophenol,pentachlorophenol and vegetation on microbial characteristics in a heavy metal polluted soil

The aim of this study was to evaluate the soil microbial characteristics in historically heavy-metal polluted soil, which was also affected by organic co-contaminants, 2,4-dichlorophenol or pentachlorophenol, which often occur due to the conventional use of pesticides. It was observed that the normalized microbial biomass (microbial biomass per unit soil organic C) of the contaminated soil was very low, less than 1% in both non-planted and ryegrass planted soil, and showed a decreasing trend with the treatment of organic co-contaminants. The microbial biomass and substrate-induced respiration (SIR) in the ryegrass planted soil were much larger, as compared with the non-planted soil with or without organic pollutants. The different resistant bacterial community and its physiological diversity in the rhizosphere further suggested that the effect of vegetation on microbial activity was not just a general increase in the mass or activity of pre-existing microorganisms, but rather acted selectively on microbial growth so that the relative abundance of different microbial groups in soil was changed. In sum, high concentrations of organic co-contaminants, especially pentachlorophenol (PCP), could strengthen the deterioration of microbial ecology. The adverse effect of heavy metal-organic pollutants on the soil microbial biomass and activity might be the reason for the slow degradation of PCP that has high chlorinated and high toxicity. Vegetation might be the efficient way to assist in improving and restoring the utilization of agricultural ecosystems. The beneficial microbial effect of vegetation could cause the rapid dissipation of 2,4-dichlorophenol (2,4-DCP) that has less chlorinated and less toxicity in the planted soils.     

Effects of 2,4-dichlorophenol, pentachlorophenol and vegetation on microbial characteristics in a heavy metal polluted soil

The aim of this study was to evaluate the soil microbial characteristics in historically heavy-metal polluted soil, which was also affected by organic co-contaminants, 2,4-dichlorophenol or pentachlorophenol, which often occur due to the conventional use of pesticides. It was observed that the normalized microbial biomass (microbial biomass per unit soil organic C) of the contaminated soil was very low, less than 1% in both non-planted and ryegrass planted soil, and showed a decreasing trend with the treatment of organic co-contaminants. The microbial biomass and substrate-induced respiration (SIR) in the ryegrass planted soil were much larger, as compared with the non-planted soil with or without organic pollutants. The different resistant bacterial community and its physiological diversity in the rhizosphere further suggested that the effect of vegetation on microbial activity was not just a general increase in the mass or activity of pre-existing microorganisms, but rather acted selectively on microbial growth so that the relative abundance of different microbial groups in soil was changed. In sum, high concentrations of organic co-contaminants, especially pentachlorophenol (PCP), could strengthen the deterioration of microbial ecology. The adverse effect of heavy metal-organic pollutants on the soil microbial biomass and activity might be the reason for the slow degradation of PCP that has high chlorinated and high toxicity. Vegetation might be the efficient way to assist in improving and restoring the utilization of agricultural ecosystems. The beneficial microbial effect of vegetation could cause the rapid dissipation of 2,4-dichlorophenol (2,4-DCP) that has less chlorinated and less toxicity in the planted soils.     

Sorption of polar and nonpolar aromatic compounds to four surface soils of eastern China

Improved predictions on the fate of organic pollutants in surface environments require a better understanding of the underlying sorption mechanisms that control their uptake by soils. In this study, we monitored sorption of nine aromatic compounds with varying physicochemical properties (hydrophobicity, electron-donor/acceptor ability and polarity), including two polycyclic aromatic hydrocarbons, two chlorobenzenes, two nitroaromatic compounds, dichlobenil, carbaryl and 2,4-dichlorophenol in aqueous suspension of four surface soils of eastern China. The tested soils were characterized with respect to organic carbon (OC) content, black carbon content, mineralogy, morphology and size fraction to assess the role of the diverse soil characteristics in sorption. The results of this study show that not only the solute hydrophobicity and the OC content of soil are important to the retention of organic pollutants, but also the solute molecular structure and the soil nature.     

Toxicological responses of red-backed salamanders (Plethodon cinereus) to subchronic soil exposures of 2,4-dinitrotoluene

Dinitrotoluenes are used as propellants and in explosives by the military and as such have been found at relatively high concentrations in the soil. To determine whether concentrations of 2,4-dinitrotoluene (2,4-DNT) in soil are toxic to amphibians, 100 red-backed salamanders (Plethodon cinereus) were exposed to either 1500, 800, 200, 75 or 0mg 2,4-DNT/kg soil for 28 days and evaluated for indicators of toxicity. Concentrations of 2,4-DNT were less than targets and varied with time. Most salamanders exposed to concentrations exceeding 1050 mg/kg died or were moribund within the first week. Salamanders exposed to soil concentrations exceeding 345 mg/kg lost >6% of their body mass though no mortality occurred. Overt effects included a reduction in feed consumption and an increase in bucco-pharyngeal oscillations in salamanders. These results suggest that only high soil concentrations of 2,4-DNT have the potential to cause overtly toxic effects in terrestrial salamanders.     

Treatment and reuse of wastewater in pesticide 2,4-D production

Waste-water from the production of pesticide 2,4-D often contains high concentrations of 2,4-DCP and 2,6-D as the primary pollutants. Treatment of waste-water collected from a 2,4-D manufacturer was carried out using a technology combining acidification with hyper-crosslinked resin NDA-150 adsorption process. The overall process recovered 5.4 kg of 2,4-DCP and 0.6 kg of 2,6-D per cubic metre of the wastewater. The treatment reduced the concentration of 2,4-DCP in the wastewater from >6000 mg/L to <0.5 mg/L. The optimal operation parameters of adsorption and desorption were determined. The hyper-crosslinked resin adsorbent can be re-used after regeneration by NaOH aqueous solution. The recovered 2,4-DCP with a sufficiently high purity may be re-used in the production of 2,4-D. The technology may thus be applied to the treatment of waste-water for reclamation of chemicals for 2,4-D production while minimising the environmental nuisances and hazards that may be caused by these chemicals.     

Sorption and desorption behavior of chloroanilines and chlorophenols on montmorillonite and kaolinite

The bioavailability of pollutants, pesticides and/or their degradation products in soil depends on the strength of their sorption by the different soil components, particularly by the clay minerals. This study reports the sorption-desorption behavior of the environmentally hazardous industrial pollutants and certain pesticides degradation products, 3-chloroaniline, 3,4-dichloroaniline, 2,4,6-trichloroaniline, 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol on the reference clays kaolinite KGa-1 and Na-montmorillonite SWy-l. In batch studies, 2.0 g of clay were equilibrated with 100.0 mL solutions of each chemical at concentrations ranging from 10.0 to 200.0 mg/L. The uptake of the compounds was deduced from the results of HPLC-UV-Vis analysis. The lipophilic species were best retained by both clay materials. The most lipophilic chemical used in the study, 2,4,6-trichloroaniline, was also the most strongly retained, with sorption of up to 8 mg/g. In desorption experiments, which also relied on HPLC-UV-Vis technique, 2,4,6-trichloroaniline was the least desorbed from montmorillonite. However, on kaolinite all of the compounds under study were irreversibly retained. The experimental data have been modelled according to the Langmuir and Freundlich isotherms. A hypothesis is proposed concerning the sorption mechanism and potential applications of the findings in remediation strategies have been suggested.     

Sorption and Desorption Behavior of Chloroanilines and Chlorophenols on Montmorillonite and Kaolinite

The bioavailability of pollutants, pesticides and/or their degradation products in soil depends on the strength of their sorption by the different soil components, particularly by the clay minerals. This study reports the sorption-desorption behavior of the environmentally hazardous industrial pollutants and certain pesticides degradation products, 3-chloroaniline, 3,4-dichloroaniline, 2,4,6-trichloroaniline, 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol on the reference clays kaolinite KGa-1 and Na-montmorillonite SWy-l. In batch studies, 2.0 g of clay were equilibrated with 100.0 mL solutions of each chemical at concentrations ranging from 10.0 to 200.0 mg/L. The uptake of the compounds was deduced from the results of HPLC-UV-Vis analysis. The lipophilic species were best retained by both clay materials. The most lipophilic chemical used in the study, 2,4,6-trichloroaniline, was also the most strongly retained, with sorption of up to 8 mg/g. In desorption experiments, which also relied on HPLC-UV-Vis technique, 2,4,6-trichloroaniline was the least desorbed from montmorillonite. However, on kaolinite all of the compounds under study were irreversibly retained. The experimental data have been modelled according to the Langmuir and Freundlich isotherms. A hypothesis is proposed concerning the sorption mechanism and potential applications of the findings in remediation strategies have been suggested.     

Effects of sorption on biodegradation rates of 2,4-D: Improvement of Rao''s model

In the presence of sorbents, the biodegradation rates of organic compounds can be decreased or increased. Four kinds of interactions have to be considered as follows: (1) chemicals in solution reacted with bacteria in solution; (2) sorbed chemicals reacted with bacteria in solution; (3) chemicals in solution reacted with sorbed bacteria and (4) sorbed chemicals reacted with sorbed bacteria. The corresponding rate constants K can be solved in our improved model. Some special situations are discussed.

The biodegradation of 2,4-D, as an example, reacted with a pure strain (Pseudomanos sp.) which was isolated from soil polluted by 2,4-D then labeled by radioactive ³²P were performed in the presence of sediment (or soil). The results showed that 2,4-D sorbed on sediment (or soil) were available to neither bacteria in solution nor bacteria on sediment (or soil), but 2,4-D in solution can be degraded by both bacteria in solution and bacteria on sediment (or soil). Biodegradation of 2,4-D in the presence of sediment (or soil) agreed with results of Rao's model.     

Spiking solvent, humidity and their impact on 2,4-D and 2,4-DCP extractability from high humic matter content soils

The 2,4-dichlorophenoxyacetic acid (2,4-D) is a hormone-like herbicide widely used in agriculture. Although its half life in soil is approximately two weeks, the thousands of tons introduced in the environment every year represent a risk for human health and the environment. Considering the toxic properties of this compound and its degradation products, it is important to assess and monitor the 2,4-D residues in agricultural soils. Furthermore, experiments of phyto/bioremediation are carried out to find economic and environmental friendly tools to restore the polluted soils. Accordingly, it is essential to accurately measure the amount of 2,4-D and its metabolites in soils. There is evidence that 2,4-D extraction from soil samples seriously depends on the physical and chemical properties of the soil, especially in those soils with high content of humic acids. The aim of this work was to assess the variables that influence the recovery and subsequent analysis of 2,4-D and its main metabolite (2,4-dichlorophenol) from those soils samples. The results showed that the recovery efficiency depends on the solvent and method used for the extraction, the amount and kind of solvent used for dissolving the herbicide and the soil water content at the moment of spiking. An optimized protocol for the extraction and quantification of 2,4-D and its main metabolite from soil samples is presented.     

2,4-Dichlorophenoxy acetic acid mineralization in amended soil

The application of municipal biosolid or liquid hog manure to agricultural soils under laboratory conditions at 20 degrees C influenced the fate of the herbicide 2,4-D [2,4-(dichlorophenoxy)acetic acid] in soil. When 2,4-D was added to soil at agronomic rates immediately after the addition of manure or biosolids to a coarse-textured soil, the percentage of 2,4-D mineralized at 100 days was about 47% for both treatments, compared to only 31% for control soils without amendments. The enhanced 2,4-D mineralization as a result of amendment addition was due to an increased heterotrophic microbial activity, with the greatest increases in soil respiration occurring for soils amended with biosolids. When additions of 2,4-D were delayed for one, two, or four weeks after the amendments were applied, the additions of amendments generally reduced 2,4-D mineralization in soil, particularly for manure, indicating that the effect of amendments on enhancing soil microbial activities diminished over time. In contrast, the mineralization of 2,4-D in control soils was less dependent on when 2,4-D was applied in relation to pre-incubations of soil for zero, one, two, or four weeks. The effect of manure on decreasing 2,4-D mineralization in specific soils was as large as the effect of soil texture on differences in 2,4-D mineralization across soils. Because manure was not found to impact 2,4-D sorption by soil, it is possible that 2,4-D mineralization decreased because 2,4-D transformation products were strongly sorbed onto organic carbon constituents in manure-amended soils and were therefore less accessible to microorganisms. Alternatively, microorganisms were less likely to metabolize the herbicide because they preferentially consumed the type of organic carbon in manure that is a weak sorbent for 2,4-D.     

2,4-Dichlorophenoxy Acetic Acid Mineralization in Amended Soil

The application of municipal biosolid or liquid hog manure to agricultural soils under laboratory conditions at 20°C influenced the fate of the herbicide 2,4-D [2,4-(dichlorophenoxy)acetic acid] in soil. When 2,4-D was added to soil at agronomic rates immediately after the addition of manure or biosolids to a coarse-textured soil, the percentage of 2,4-D mineralized at 100 days was about 47% for both treatments, compared to only 31% for control soils without amendments. The enhanced 2,4-D mineralization as a result of amendment addition was due to an increased heterotrophic microbial activity, with the greatest increases in soil respiration occurring for soils amended with biosolids. When additions of 2,4-D were delayed for one, two, or four weeks after the amendments were applied, the additions of amendments generally reduced 2,4-D mineralization in soil, particularly for manure, indicating that the effect of amendments on enhancing soil microbial activities diminished over time. In contrast, the mineralization of 2,4-D in control soils was less dependent on when 2,4-D was applied in relation to pre-incubations of soil for zero, one, two, or four weeks. The effect of manure on decreasing 2,4-D mineralization in specific soils was as large as the effect of soil texture on differences in 2,4-D mineralization across soils. Because manure was not found to impact 2,4-D sorption by soil, it is possible that 2,4-D mineralization decreased because 2,4-D transformation products were strongly sorbed onto organic carbon constituents in manure-amended soils and were therefore less accessible to microorganisms. Alternatively, microorganisms were less likely to metabolize the herbicide because they preferentially consumed the type of organic carbon in manure that is a weak sorbent for 2,4-D.     

Factors influencing 2,4-D sorption and mineralization in soil

This study quantified 2,4-D [(2,4-dichlorophenoxy)acetic acid] sorption and mineralization rates in five soils as influenced by soil characteristics and nutrient contents. Results indicated that 2.4-D was weakly sorbed by soil, with Freundlich distribution coefficients ranging from 0.81 to 2.89 microg(1 - 1/n) g(-1) mL(1/n). First-order mineralization rate constants varied from 0.03 to 0.26, corresponding to calculated mineralization half-lives of 3 and 22 days, respectively. Herbicide sorption generally increased with increasing soil organic carbon content, but the extent of 2,4-D sorption per unit organic carbon varied among the soils due to differences in soil pH, clay content and/or organic matter quality. Herbicide mineralization rates were greater in soils that sorbed more 2,4-D per unit organic carbon, and that had greater soil nitrogen contents. We conclude that the effect of sorption on herbicide degradation cannot be generalized without a better understanding of the effects of soil characteristics and nutrient content on herbicide behavior in soil.     

Monitoring transport of selected pesticides and phenols in soil columns by high performance liquid chromatography

Abstract

Soil columns were used to study pesticides and phenols transport under rapid infiltration land treatment conditions. An analytical procedure is described for the quantitative determination of atrazine, diuron, carbofuran, phenol, 2,4‐dinitrophenol, 2,4‐dimethylphenol, and 2,4‐dichlorophenol in soil and wastewater. Recoveries of all analytes were greater than 90%. The method detection limits for all analytes were ≤0.03 μg/ml (s/n=4) in wastewater and ≤ 0.1 μg/ml (s/n=5) in soil.     

2,4-Dichlorophenoxyacetic acid (2,4-D) sorption and degradation dynamics in three agricultural soils

The fate and transport of 2,4-dichlorophenoxyacetic acid (2,4-D) in the subsurface is affected by a complex, time-dependent interplay between sorption and mineralization processes. 2,4-D is biodegradable in soils, while adsorption/desorption is influenced by both soil organic matter content and soil pH. In order to assess the dynamic interactions between sorption and mineralization, 2,4-D mineralization experiments were carried using three different soils (clay, loam and sand) assuming different contact times. Mineralization appeared to be the main process limiting 2,4-D availability, with each soil containing its own 2,4-D decomposers. For the clay and the loamy soils, 45 and 48% of the applied dose were mineralized after 10 days. By comparison, mineralization in the sandy soil proceeded initially much slower because of longer lag times. While 2,4-D residues immediately after application were readily available (>93% was extractable), the herbicide was present in a mostly unavailable state (<2% extractable) in all three soils after incubation for 60 days. We found that the total amount of bound residue decreased between 30 and 60 incubation days. Bioaccumulation may have led to reversible immobilization, with some residues later becoming more readily available again to extraction and/or mineralization.     

The effect of propanil co-application on 2,4-D sorption by soil

The herbicide 2,4-D is often applied as a tank mixture in combination with other herbicide products. However, current information on 2,4-D sorption by soil is largely based on batch-equilibrium experiments without considering the competition of other herbicides for sorption sites by soil. This study quantified the effect of the herbicide propanil on the sorption of 2,4-D in soil. Results indicated that propanil competed with 2,4-D for sorption sites, particularly in soils with an organic carbon content greater than 3.6%. The decrease in 2,4-D sorption by soil, as a result of propanil competition, was most notably for herbicide concentrations that are typical of recommended field rates. We conclude that herbicide co-applications on agricultural fields have the potential to increase the mobility of herbicides in soil.     

Dissipation of 2,4-D in soils of the Humid Pampa region, Argentina: a microcosm study

Phenoxy herbicides like 2,4-dichlorophenoxyacetic acid (2,4-D) are widely used in agricultural practices. Although its half life in soil is 7-14d, the herbicide itself and its first metabolite 2,4-dichlorophenol (2,4-DCP) could remain in the soil for longer periods, as a consequence of its intensive use. Microcosms assays were conducted to study the influence of indigenous microflora and plants (alfalfa) on the dissipation of 2,4-D from soils of the Humid Pampa region, Argentina, with previous history of phenoxy herbicides application. Results showed that 2,4-D was rapidly degraded, and the permanence of 2,4-DCP in soil depended on the presence of plants and soil microorganisms. Regarding soil microbial community, the presence of 2,4-D degrading bacteria was detected even in basal conditions in this soil, possibly due to the adaptation of the microflora to the herbicide. There was an increment of two orders of magnitude in herbicide degraders after 15d from 2,4-D addition, both in planted and unplanted microcosms. Total heterotrophic bacteria numbers were about 1x10(8) CFUg(-1) dry soil and no significant differences were found between different treatments. Overall, the information provided by this work indicates that the soil under study has an important intrinsic degradation capacity, given by a microbial community adapted to the presence of phenoxy herbicides.     

Enhancement of chlorophenol sorption on soil by geophagous earthworms (Metaphire guillelmi)

Earthworms are the dominant soil biomass of many terrestrial ecosystems and markedly influence the physico-chemical and biological properties of soil; however, little is known about the effects of earthworm activities on the environmental behavior of micropollutants in soil. We studied the sorption and desorption of 2,4-dichlorophenol, 2,4,6-trichlorophenol, and pentachlorophenol on geophagous earthworm (anecic Metaphire guillelmi) casts of various aging times and on the parent soil. The casts were characteristic of lower pH and higher content of fine particles (silt and clay) than the parent soil. The sorption of the chlorophenols on the soil and casts were well fitted to linear isotherms, with sorption capacity in the order of pentachlorophenol > 2,4-dichlorophenol > 2,4,6-trichlorophenol. The sorption on the cast with different aging time was quite similar and was higher than on the parent soil. The sorption on the soil did not change between pH 7.07 of the soil and pH 6.76 of the casts. The desorption hysteresis of the chlorophenols on the soil and casts was compound specific and 2,4,6-trichlorophenol showed the highest hysteresis. The higher sorption capacity of the casts was not owing to the lowered pH of the casts, but mainly to the higher fine particles in the casts and the possible changes of nature of the soil organic matter through the earthworm gut passage. Our results indicate that geophagous earthworms may change sorption behavior and thus the bioavailability and transport of chlorophenols in soil. Earthworm effects should be considered when evaluating the environmental behavior and risk of organic pollutants in the ecosystems where earthworms are abundant.     

Leaching of 2,4-D from a soil in the presence of beta-cyclodextrin: laboratory columns experiments

This study reports on the effect of the presence of beta-cyclodextrin (beta-CD) on the adsorption and mobility of the pesticide 2,4-dichlorophenoxyacetic acid (2,4-D) through soil columns. The previous application of beta-CD to the soil produced a retarded leaching of 2,4-D through the soil column, due probably to herbicide adsorption on the soil through beta-CD adsorbed. However, the application of beta-CD solution to the soil column where 2,4-D had been previously adsorbed, led to the complete desorption of the herbicide, due to the formation of water-soluble 1:1 inclusion complexes between 2,4-D and beta-CD. Beta-CD can be viewed as a microscopic organic-phase extractant. It can be an advantage to remove from soil pesticides which are able to form inclusion complexes with cyclodextrins, making them possible candidates for use in in situ remediation efforts.