Contaminant characterization at pesticide production sites in the Yangtze River Delta: Residue, distribution, and environmental risk.

The Yangtze River Delta (YRD) is the largest pesticide-producing region in the world. Contamination of pesticide production sites has always been a focus of public attention. Twenty pesticide production sites in YRD were selected to analyze the residue, distribution, and environmental risk of organic contaminants in soil and groundwater. A total of 194 organic chemicals were detected in all soil and groundwater samples from the 20 sites. Eighty-eight constituents of concern (COCs) exceeded the comparison values of Regional Screening Levels (RSLs), and 80 % exceeded the RSLs by more than five times. The toxic effects of COCs in soil and groundwater were dominated by the carcinogenic risk, referred as "non-threshold". Benzene toluene ethylbenzene & xylene (BTEX) and chloroaliphatic hydrocarbons (CAHs) were the most prevalent at pesticide sites in YRD rather than pesticides, followed by chlorobenzene, chlorophenols, and polycyclic aromatic hydrocarbons (PAHs). CAHs and BTEX could penetrate up to 24 m, while the others were primarily limited to 12 m. Most pesticide production sites showed a great contamination depth of >8 m, some even deeper than 20 m, posing a great risk of contamination to the confined aquifer. Due to the close interconnection of soil with water bodies, the shallow groundwater and adjacent surface water resources are also susceptible to suffering from environmental risk. More than half of the pesticide production sites in the YRD consist primarily of low-permeable clay layers, making in-situ contamination remediation difficult. This study provides a basis for developing remediation technology for pesticide sites in YRD and an ecological reference for further cleaning production and green manufacturing in the pesticide industry.

[A Comparative Study of Soil Environmental Standards for Agricultural Land Among Different Countries and Its Implication for China].

Soil environmental quality of agricultural land plays a determinate role in the quality of agricultural products, human health, and the safety of the ecosystem. In 2018, China issued the "soil environment quality risk control standard for soil contamination of agriculture land" (GB 15618-2018), which has been essential to soil pollution prevention and the control of agricultural land. In this study, a systematic and comparative analysis of soil environmental standards for the agricultural land of 17 countries or regions was conducted, including the framework, protection objective, derivation method, contaminant elements, analyses methods, and standard values, as well as the impact factors. The results showed that the number of contaminants of GB 15618-2018 was insufficient with the simple consideration of total concentrations. Meanwhile, there was a lack of the standardized derivation method. On such a basis, we put forward some suggestions to improve GB 15618-2018 in light of the aforementioned problems, including strengthening the research of soil environmental benchmark and background values; establishing the scientific and standardized derivation method; and improving the number, form, and availability of indicators for risk control. In the meantime, the regional and local background environmental concentration of soil was highly proposed as a supplement and optimization to soil screening values.

Variations in Cadmium Concentrations in Rice and Oxidation-Reduction Potential at the Soil Surface with Supplementation of Fermented Botanical Waste-based Amendment in Large-scale Farmland.

We monitored the relationship between the cadmium (Cd) concentration uptake of rice and the oxidation-reduction potential (ORP) at the soil surface with the supplementation of fermented botanical waste-based amendment (FBWA), an organic fertilizer prepared from woody and food wastes. This study was carried out for 3 years in the western part of Jiangsu Province, China. It was found that the Cd concentration taken up by rice was correlated to a decreased the ORP of the cultivated soil. The yield of rice was ∼1.20 times higher than that of the control plot. The effects of reducing the Cd content in rice and increasing the rice yield remained for 2 years after FBWA application. Finally, Cd was immobilized in the soil with adsorption to FBWA or the decomposed products. The ORP measurement during rice cultivation might be a key index to predict the suppression effect of Cd uptake into the rice or limitation of the sustainable effect by the FBWA.

Insights into removal of tetracycline by persulfate activation with peanut shell biochar coupled with amorphous Cu-doped FeOOH composite in aqueous solution.

Peanut shell biochar (BC) supported on Cu-doped FeOOH composite (Cu-FeOOH/BC) was synthesized using a facile and scalable method. The Cu-FeOOH/BC samples were characterized by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), scanning electron microscopy equipped with an energy-dispersive spectrometer (SEM-EDS), x-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) techniques. Novel catalytic composites with different Cu/Fe molar ratios were compared systematically by activating persulfate (PS) for the tetracycline (TC) degradation. 0.5Cu-1FeOOH/BC (Cu/Fe molar ratio = 0.5:1) was confirmed as the optimum activation material and the removal of TC reached 98.0% after 120 min by combining with 20 mM PS at pH 7.0 and 25 °C. The influencing factors including catalyst loading, PS dosage, water matrix species, and pH on the performance system of 0.5Cu-1FeOOH/BC-PS were investigated, respectively. Reaction rate constants (Kobs) on catalyst dosages (0.05, 0.10, 0.20, and 0.30 g L-1) were 0.0072, 0.0101, 0.0244, and 0.0144 min-1, and 0.0090, 0.0146, 0.0244, and 0.0178 min-1 for the change of PS concentrations (5, 10, 20, and 30 mM), which indicated that increasing the concentrations of catalyst and PS appropriately improved TC degradation, but excessive dosages inhibited the reaction process of TC removal. The TC removal rate was inhibited by inorganic anions with the following order of HCO3- > Cl- > HPO42- > SO42- > NO3-. Free radical quenching and capture experiments under different pH values revealed that sulfate radicals existed predominantly in acidic conditions and hydroxyl radicals in alkaline conditions. The catalyst showed an excellent recyclability and stability and the removal efficiency of TC still remained over 90% after five consecutive uses. To conclude, coupling of 0.5Cu-1FeOOH/BC and PS can be successfully applied as an effective and stable technique for the treatment of refractory organic pollutants in wastewater.

Catalytic Degradation of Diatrizoate by Persulfate Activation with Peanut Shell Biochar-Supported Nano Zero-Valent Iron in Aqueous Solution.

An emerging pollutant, diatrizoate (DTZ) has been frequently detected in aqueous solution. Unique reticular peanut shell biochar (BC)-supported nano zero-valent iron (nZVI) composite (nZVI/BC) was successfully synthesized and used as a catalyst for activating persulfate (PS) to promote the removal of DTZ. The structure and morphology of the nanocomposite materials were characterized by scanning electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller measurements, and Fourier transform infrared spectroscopy. The degradation of DTZ (20 mg L-1) was achieved by activating PS with the nanocomposite material. The removal of DTZ reached nearly 100% using 25 mM PS and 0.45 g L-1 nZVI/2BC (mass ratio of nZVI and BC at 1:2) nanocomposite material at pH 3.0 and 25 °C. Influencing factors, such as dosages of nZVI/2BC and PS, temperature, and pH were also investigated. The mechanisms of PS activation with nZVI/2BC were discussed, including BC property, electron transfer, and the identification of free radicals in the reaction. The findings demonstrated that nZVI/BC-PS (peanut shell BC-supported nZVI activating PS) is a promising material for the treatment of refractory organic pollutants.

[Principal Component Analysis and Ecological Risk Assessment of Heavy Metals in Farmland Soils around a Pb-Zn Mine in Southwestern China].

The farmland soil around a Pb-Zn mine in southwestern China was studied. One hundred forty-nine surface soil samples were taken from 0-20 cm depth, and the contents of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn were tested. The correlations among these heavy metals were studied with multivariate analysis, and the potential sources of the metals were identified. The environmental risk of the metals was evaluated with the Potential Ecological Risk Index method. The results showed that the amounts of Cd, Pb, and Zn were at relatively high level, with average concentrations of 15.56, 419.4, and 933.4mg·kg-1 respectively, indicating the soil was heavily polluted. The average concentrations of Hg and As were 0.13 and 37.3mg·kg-1, suggesting moderate soil pollution. The average concentrations of Cu, Ni, and Cr were lower than Yunnan soil background values. The multivariate analysis suggested that the sources of Cd, Pb, Zn, Hg, and As were similar and came mainly from smelting activities in the mining area. The sources of Cu, Ni, and Cr were similar and can be attributed to natural sources. The comprehensive potential ecological risk index was 2294.8, which suggested a high potential ecological risk. In general, the farmland soils in the research area were polluted seriously by the mining and industrial activities.

Chemical oxidation of bis(2-chloroethyl) ether in the Fenton process: Kinetics, pathways and toxicity assessment.

Bis(2-chloroethyl) ether (BCEE) is a common chemical material and a frequently detected contaminant in groundwater. It has a strong toxicity and some other chemicals such as poly(vinyl chloride-co-isobutyl vinyl ether) contain similar chloroaliphatic ether structure. So the effective degradation method and transformation pathways for BCEE need to be learned. The present study compared the degradation rate of BCEE by Fenton's reagent and other common oxidation methods, and optimized the reaction conditions. Oxidation intermediates and pathways were also proposed and toxicities of the intermediates were investigated. Results showed that Fenton was highly effective to degrade BCEE. pH, Fe2+ and H2O2 concentration all affected the oxidation rate, among which Fe2+ was the most significant variable. A total of twelve chlorinated intermediates were detected. Three main reaction pathways involved cleavage of the ether bond, hydroxyl substitution for hydrogen, and radical coupling. The pathways could be well interpreted and supported by theoretical calculations. The reaction mixture showed a decreasing trend in TOC concentration and toxicity until totally harmless to Vibrio fischeri after 15 min, but it was noteworthy that toxicities of some dimeric intermediates were stronger than BCEE by calculation.

Thermoactivated persulfate oxidation of pesticide chlorpyrifos in aquatic system: kinetic and mechanistic investigations.

The widespread occurrence of organophosphorus pesticides (OPPs) in the environment poses risks to both ecologic system as well as human health. This study investigated the oxidation kinetics of chlorpyrifos (CP), one of the typical OPPs, by thermoactivated persulfate (PS) oxidation process, and evaluated the influence of key kinetic factors, such as PS concentrations, pH, temperature, bicarbonate, and chloride ions. The reaction pathways and mechanisms were also proposed based on products identification by LC-MS techniques. Our results revealed that increasing initial PS concentration and temperature favored the decomposition of CP, whereas the oxidation efficiency was not affected by pH change ranging from 3 to 11. Bicarbonate was found to play a detrimental role on CP removal rates, while chloride showed no effect. The oxidation pathways including initial oxidation of P=S bond to P=O, dechlorination, dealkylation, and the dechlorination-hydroxylation were proposed, and the detailed underlying mechanisms were also discussed. Molecular orbital (MO) calculations indicated that P=S bond was the most favored oxidation site of the molecule. The toxicity of reaction solution was believed to increase due to the formation of products with P=O structures. This work demonstrates that OPPs can readily react with SO4·- and provides important information for further research on the oxidation of these contaminants.

Ecotoxicological bioassays of sediment leachates in a river bed flanked by decommissioned pesticide plants in Nantong City, East China.

Traditionally, the toxicity of river contaminants is analyzed chemically or physically through river bed sediments. The biotoxicity of polluted sediment leachates has not caught our attention. This study aims to overcome this deficiency through a battery of biotests which were conducted to monitor comprehensive toxicity of sediment leachates for the Yaogang River in East Jiangsu Province of China, which is in close proximity to former pesticide plants. The general physical and chemical parameters of major pollutants were analyzed from river bed sediments collected at five strategic locations. The ecotoxicity analyses undertaken include overall fish (adult zebrafish) acute toxicity, luminescent bacteria (Vibrio fischeri) bioassay, and zebrafish embryo toxicity assay. Compared with the control group, sediment leachates increased the lethality, inhibited the embryos hatching and induced development abnormalities of zebrafish embryos, and inhibited the luminescence of V. fischeri. The results show that sediment leachates may assume various toxic effects, depending on the test organism. This diverse toxicity to aquatic organisms reflects their different sensitivity to sediment leachates. It is found clearly that V. fischeri was the organism which was characterized by the highest sensitivity to the sediment leachates. The complicated toxicity of leachates was not caused by one single factor but by multiple pollutants together. This indicates the need of estimations of sediment leachate not only taking into account chemical detection but also of applying the biotests to the problem. Thus, multigroup bioassays are necessary to realistically evaluate river ecological risks imposed by leachates.

Simultaneous Removal of Lindane, Lead and Cadmium from Soils by Rhamnolipids Combined with Citric Acid.

This study investigated the performance of rhamnolipids-citric acid mixed agents in simultaneous desorption of lindane and heavy metals from soils. The capacity of the mixed agents to solubilize lindane, lead and cadmium in aqueous solution was also explored. The results showed that the presence of citric acid greatly enhanced the solubilization of lindane and cadmium by rhamnolipids. A combined effect of the mixed agents on lindane and heavy metals removal from soils was observed. The maximum desorption ratios for lindane, cadmium and lead were 85.4%, 76.4% and 28.1%, respectively, for the mixed agents containing 1% rhamnolipidsand 0.1 mol/L citric acid. The results also suggest that the removal efficiencies of lead and cadmium were strongly related to their speciations in soils, and metals in the exchangeable and carbonate forms were easier to be removed. Our study suggests that the combining use of rhamnolipids and citric acid is a promising alternative to simultaneously remove organochlorine pesticides and heavy metals from soils.

Partitioning of hexachlorobenzene in a kaolin/humic acid/surfactant/water system: combined effect of surfactant and soil organic matter.

Understanding the combined effect of soil organic matter (SOM) and surfactants on the partitioning of hydrophobic organic compounds in soil/water systems is important to predict the effectiveness of surfactant-enhanced remediation (SER). In the present study we investigate the partitioning of hexachlorobenzene (HCB) within a humic acid (HA)-coated kaolin/Triton X-100 (TX100)/water system, with special emphasis on the interaction between TX100 and HA, and their combined effect on HCB sorption. HA firstly enhanced then suppressed TX100 sorption to kaolin as the amounts of HA increased, while the addition of TX100 led to a consistent reduction in HA sorption. In the HA-coated kaolin/TX100/water system, TX100 played a primary role in enhancing desorption of HCB, while the role could be suppressed and then enhanced as HA coating amounts increased. Only at HA coating above 2.4%, dissolved HA outcompeted clay-bound HA for HCB partitioning, resulting in dissolved HA enhanced desorption. The presence of dissolved HA at these conditions further promoted the effectiveness of TX100 enhanced desorption. Despite a reduced TX100 sorption to clay was achieved due to the presence of dissolved HA, the effect on HCB desorption was comparatively slight. A reliable cumulative influence of HA and TX100 on HCB desorption was observed, although HCB desorption by HA/TX100 mixed was less than the sum of HA and TX100 individually. Our study suggests that for soils of high organic contents, the combined effect of SOM and surfactants on HOCs desorption can be applied to improve the performance of SER.

[Removal of volatile organic compounds in soils by soil vapor extraction (SVE)].

An experiment study has been carried out to investigate effects of the diameter of soil columns, the size of soil particulate and different contaminants on efficiency of simulated soil vapor extraction (SVE). Experiments with benzene, toluene, ethylbenzene and n-propylbenzene contaminated soils showed that larger bottom area/soil height (S/H) of the columns led to higher efficiency on removal of contaminants. Experiments with contaminated soils of different particulate size showed that the efficiency of SVE decreased with increases in soil particulate size, from 10 mesh to between 20 mesh and 40 mesh and removal of contaminants in soils became more difficult. Experiments with contaminated soils under different ventilation rates suggested that soil vapor extraction at a ventilation rate of 0.10 L x min(-1) can roughly remove most contaminants from the soils. Decreasing of contaminants in soils entered tailing stages after 12 h, 18 h and 48 h for benzene, toluene and ethylbenzene, respectively. Removal rate of TVOCs (Total VOCs) reached a level as high as 99.52%. The results of the experiment have indicated that molecule structure and properties of the VOCs are also important factors which have effects on removal rates of the contaminants. Increases in carbon number on the benzene ring, decreases in vapor pressure and volatile capability resulted in higher difficulties in soil decontamination. n-propylbenzene has a lower vapor pressure than toluene and ethylbenzene which led to a significant retard effect on desorption and volatilization of benzene and ethylbenzene.

Remediation of hexachlorobenzene contaminated soils by rhamnolipid enhanced soil washing coupled with activated carbon selective adsorption.

The present study investigates the selective adsorption of hexachlorobenzene (HCB) from rhamnolipid solution by a powdered activated carbon (PAC). A combined soil washing-PAC adsorption technique is further evaluated on the removal of HCB from two soils, a spiked kaolin and a contaminated real soil. PAC at a dosage of 10 g L(-1) could achieve a HCB removal of 80-99% with initial HCB and rhamnolipid concentrations of 1 mg L(-1) and 3.3-25 g L(-1), respectively. The corresponding adsorptive loss of rhamnolipid was 8-19%. Successive soil washing-PAC adsorption tests (new soil sample was subjected to washing for each cycle) showed encouraging leaching and adsorption performances for HCB. When 25 g L(-1) rhamnolipid solution was applied, HCB leaching from soils was 55-71% for three cycles of washing, and HCB removal by PAC was nearly 90%. An overall 86% and 88% removal of HCB were obtained for kaolin and real soil, respectively, by using the combined process to wash one soil sample for twice. Our investigation suggests that coupling AC adsorption with biosurfactant-enhanced soil washing is a promising alternative to remove hydrophobic organic compounds from soils.

Biological indicators capable of assessing thermal treatment efficiency of hydrocarbon mixture-contaminated soil.

In China, there are many special sites for recycling and washing the used drums, which release a variety of C5-C40 hydrocarbon mixture into the soil around the site. The remediation of these contaminated sites by thermal treatment is adopted ubiquitously and needs to be assessed. Here we report the feasibility of biological indicators applied to assess thermal treatment efficiency in such contaminated soil. A series of biological indicators, including seed germination index (SGI), root elongation index (REI), plant growth height, biomass, carbon dioxide evolved (CDE), soil respiration inhibition (SRI) and soil enzymatic activities, were employed to monitor or assess hydrocarbon mixture removal in thermal treated soil. The results showed that residual hydrocarbon mixture content correlated strongly negatively with SGI for sesamum (Sesamum indicum L.), plant height, and biomass for ryegrass (Lolium perenne L.) in the concentration ranges of 0-3990, 0-3170 and 0-2910 mg kg(-1), respectively. In contrast, REI for sesamum was positively correlated with residual hydrocarbon mixture content from 0 to 1860 mg kg(-1). In addition, both CDE and SRI demonstrated that 600 mg kg(-1) of residual hydrocarbon mixture content caused the highest amount of soil carbon dioxide emission and inhabitation of soil respiration. The results of soil enzymes indicated that 1000 mg kg(-1) of residual hydrocarbon mixture content was the threshold value of stimulating or inhibiting the activities of phosphatase and catalase, or completely destroying the activities of dehydrogenase, invertase, and urease. In conclusion, these biological indicators can be used as a meaningful complementation for traditional chemical content measurement in evaluating the environmental risk of the contaminated sites before and after thermal treatment.