Xiaoyu Hu

The role of earthworms (Eisenia fetida) in influencing bioavailability of heavy metals in soils

The effects of earthworm (Eisenia fetida) activity on soil pH, dissolved organic carbon (DOC), microbial populations, fraction distribution and bioavailability of heavy metals (Zn, Cu, Cr, Cd, Co, Ni, and Pb) in five Chinese soils were investigated using pot experiments. A three-step extraction procedure recommended by the European Community Bureau of Reference (BCR; now Standards, Measurements and Testing Programme of the European Community) was used to fractionate the metals in soils into water soluble, exchangeable and carbonate bound (B1), Fe-oxides and Mn-oxides bound (B2) and organic matter and sulfide bound (B3). After the soils were treated with earthworms, the soil pH, water-soluble metal fraction and DOC increased. A significant correlation was obtained between the increased DOC and the increased metals in the water-soluble fraction. The heavy metals in fraction B1 increased after earthworm treatments, while those in fraction B3 decreased. No significant differences were observed for heavy metals in fraction B2. The microbial populations in soil were enumerated with the dilution plate method using several media in the presence of earthworms. The microbial populations increased due to earthworm activity. The biomass of wheat shoots and roots, and the heavy metal concentrations in wheat roots and shoots, were also increased due to the earthworm activity. The present results demonstrated that earthworm activity increases the mobility and bioavailability of heavy metals in soils.

Survey of phthalate pollution in arable soils in China

The problem of pollution by phthalates is of global concern due to their widespread occurrence, toxicity and endocrine disruption properties. The contamination by phthalates such as dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP) in 23 arable soils throughout China was investigated to evaluate the present pollution situation. The survey results demonstrated that phthalates were ubiquitous pollutants in soils in China. The total concentrations of phthalates differed from one location to another, and ranged from 0.89 to 10.03 mg kg(-1) with a median concentration of 3.43 mg kg(-1). Among the phthalates, DEHP was dominant and detected in all 23 soils. DEP and DBP were also in abundance, and DMP was rarely detected. Similar contamination patterns were observed in all 23 soils. A distinct feature of phthalate pollution in China was that the average concentration in northern China was higher than that in southern China. In addition, a close relationship was observed between the concentration of phthalates in soils and the consumption of agricultural film. The correlation showed that the application of agriculture film might be a significant pollution source of phthalates in arable soils of China. The potential risk of phthalates in soils was assessed on the basis of current guide values and limits.

Bioavailability of pentachlorophenol to earthworms (Eisenia fetida) in artificially contaminated soils

Abstract The bioaccumulation of pentachlorophenol in earthworms (Eisenia fetida) was studied for two artificially contaminated soils (S1 and S2). The uptake kinetics of pentachlorophenol (PCP) in earthworms increased quickly within the initial 10 days. This was followed by a nearly steady state for the next 20 days that fit with the equilibrium partitioning model. The correlation coefficients were 0.812 and 0.715 for S1 and S2, respectively. The average biota-to-soil accumulation factor of PCP in S1 was 0.51 ± 0.09, whereas that of S2 was 0.79 ± 0.12. There was a significant correlation between log C soil and log C worm, demonstrating the validity of the equilibrium partitioning model. The bioavailability of PCP was assessed by chemical extraction methods. The results demonstrated a close correlation between extractable amounts of PCP freshly added in soils and those in earthworms. With increasing residence time of PCP in soil, there was a progressively smaller amount of PCP assimilated by the earthworms. In contrast, the amount extracted by Soxhlet extraction did not show a similar decline. However, the extractable amount of PCP by methanol and methanol–water (1:1) significantly decreased over 440 days. Compared with the methanol–water (1:1) extraction method, the methanol extraction method was preferred to the prediction of the bioavailability of PCP in aged soils.

Determination of fluorotelomer alcohols and their degradation products in biosolids-amended soils and plants using ultra-high performance liquid chromatography tandem mass spectrometry

Degradation of fluorotelomer alcohols (FTOHs) was recognized as an additional source of perfluorocarboxylic acids (PFCAs). Quantification of FTOHs and their degradation products can help shed light on the sources and fates of PFCAs in the environment. In this study, an analytical method was developed for the determination of 6:2 and 8:2 FTOHs, and their degradation products of poly- and perfluorinated acids, including fluorotelomer saturated and unsaturated carboxylic acids (FTCAs and FTUCAs), secondary polyfluorinated alcohols and PFCAs in biosolids-amended soils and plants using ultra-high performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). The extract efficiencies of different methods including ethyl acetate and methanol (MeOH) for FTOHs and acetonitrile, MeOH, methyl tert-butyl ether (MTBE), NaOH-MeOH and NaOH-MTBE for poly- and perfluorinated acids were tested. The results showed that 6:2 and 8:2 FTOHs and their degradation products could be simultaneously and satisfactorily extracted by MeOH, cleaned up by Envi-Carb graphitized carbon and solid phase extraction, respectively, and determined by UPLC-MS/MS separately. NaOH in the extractant caused the conversion of 6:2 FTCA and 8:2 FTCA into the corresponding FTUCAs. The selected methods have matrix recoveries ranged from 52% to 102%, and detection limits of 0.01-0.46ng/g dry weight for FTOHs and their degradation products in soil and plant. The optimized method was applied successfully to quantify FTOHs and their degradation products in two biosolids-amended soils and plants. The total concentrations of FTOHs in the soils were 44.1±5.8 and 82.6±7.1ng/g, and in plants tissues 3.58±0.25 and 8.33±0.66ng/g. The total concentrations of poly- and perfluorinated acids in the soils were 168.0±13.2 and 349.6±11.2ng/g, and in plants tissues 78.0±6.4 and 75.5±5.3ng/g.

Determination of perfluoroalkyl acid isomers in biosolids, biosolids-amended soils and plants using ultra-high performance liquid chromatography tandem mass spectrometry

Isomer-specific analysis of perfluoroalkyl acids (PFAAs) is important to accurately assess their environmental source, fate, and human risks. In this study, a method was developed for the determination of perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), and perfluorohexane sulfonate (PFHxS) isomers in biosolids, biosolids-amended soils and plants using ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The separation efficiencies of two chromatographic columns and extraction capacities of different methods were tested. Compared with the C18 column (ACQUITY UPLC BEH Shield RP18 column), the column with an alkyl perfluorinated C8 stationary phase (Epic FO LB column), in combination with the distinct MS/MS transitions of analytes, allowed better separation of most isomers. The ion-pair extraction method showed more effective matrix separation than that of the alkaline digestion method, with recoveries ranging from 79.6-105% for biosolids, 80.4-116% for soils, and 68.0-114% for plant tissues. The method detection limits ranged from 10 to 55, 3-13, and 8-58pg/g dry weight for biosolids, soil, and plants, respectively. This method was applied successfully to quantify individual isomers in biosolids, biosolids-amended soils and plants. Six PFOA, eight PFOS, and two PFHxS isomers were found in the samples, with linear isomers being the dominant species. Further analysis revealed that the translocation potentials of branched isomers within plants were higher than those of linear isomers.

Behavior of N-ethyl perfluorooctane sulfonamido acetic acid (N-EtFOSAA) in biosolids amended soil-plant microcosms of seven plant species: Accumulation and degradation

Perfluorooctane sulfonate (PFOS) precursors have been found extensively in sewage sludge and biosolids-amended soils. The degradation of these precursors are regarded as a significant source of PFOS in the environment. In this study, the accumulation of N-ethyl perfluorooctane sulfonamido acetic acid (N-EtFOSAA) in the plants of seven species, namely alfalfa, lettuce, maize, mung bean, radish, ryegrass, and soybean from biosolids-amended soil, and the degradation kinetics of N-EtFOSAA in soil-plant microcosms were evaluated over 60 days. N-EtFOSAA was found in the roots of all plant species, while was not in stems and leaves. The root concentration factors of N-EtFOSAA ranged 0.52-1.37 (pmol/groot)/(pmol/gsoil). Stepwise multiple regression analysis was used to elucidate the accumulation of N-EtFOSAA in the roots of plants. The results showed that the root protein and lipid contents explain 85.0% of the variation in root N-EtFOSAA levels (P < 0.05). Four degradation products, including N-ethyl perfluorooctane sulfonamide (N-EtFOSA), perfluorooctane sulfonamide acetate (FOSAA), perfluorooctane sulfonamide (FOSA) and PFOS were found in soils and plant roots, stems and leaves, indicating the degradation of N-EtFOSAA in soil-plant system. Degradation kinetics fitted a first-order kinetic model well. Degradation rate constants of N-EtFOSAA in the microcosms with plants ranged 0.063-0.165 d-1, which was 1.40-3.6 times higher than those without plants. Degradation rate constant of maize was relatively higher than those of other plant species. The results is the first to reveal N-EtFOSAA accumulation in plants and degradation in soil-plant microcosms.