The Role of Nanoengineered Biochar Activated with Fe for Sulfanilamide Removal from Soils and Water.

Biochar is a nanoengineered sorbent proposed to control the contamination derived from the presence of residual concentrations of sulfonamides in soil. In this work, we evaluated the sorption of sulfanilamide (SFA) in commercial biochar (BC) produced at 500 °C from oak hardwood (Quercus ilex) and its analog activated with 2% (w/w) Fe (BC-Fe). Subsequently, the effect on dissipation and transport of SFA in untreated soil and soil treated with BC and BC-Fe was also assessed. Laboratory batch studies revealed that BC-Fe increased the sorption of SFA as compared to the pristine BC with Kd of 278 and 98 L/kg, respectively. The dissipation of SFA in either untreated soil or soil treated with BC or BC-Fe was similar, displaying half-lives ranging between 4 and 6.4 days. Conversely, the concurrent determination of sorption during the incubation experiment showed that lower amounts of SFA in solution at the beginning of the experiments were bioavailable in BC-Fe-treated soil when compared to the rest of the treatments shortly after application. Leaching column studies confirmed the amendment's capability to bind the SFA compound. Therefore, the decrease in bioavailability and movement of SFA in treated soils suggest that biochar soil application can reduce SFA soil and water contamination. According to our results, BC surface modification after Fe activation may be more appropriate for water decontamination than for soil since there were no significant differences between the two types of biochar when added to the soil. Therefore, these outcomes should be considered to optimize the SFA mitigation potential of biochar.

Uptake, translocation, and metabolism of sulfamethazine by Arabidopsis thaliana: distinguishing between phytometabolites and abiotic transformation products in the media.

Plant accumulation of antibiotic residues presents potential risks to human and ecosystem health. However, the phytometabolic pathways of antibiotics following plant uptake are still largely uncharacterized. This study investigated the phytometabolism of sulfamethazine (SMT) by Arabidopsis thaliana, using 14C-labeled and unlabeled SMT. SMT was accumulated in both roots and shoots of axenic A. thaliana plants (123.7 ± 12.3 and 22.7 ± 1.0 µg/kg fw, respectively) after 21 days of exposure. However, the parent 14C-SMT accounted for only 1.7 ± 0.01% of the total 14C-radioactivity in plant tissues. The majority of 14C-radioactivity taken up by plants was present as bound residues (42.0-68.2% of initially applied 14C-SMT), while extractable 14C-residues accounted for only 7.7-12.6%. A. thaliana metabolized SMT primarily through glycosylation at the N4-nitrogen atom. Additionally, other products, including pterin-SMT, methylsalicylate-SMT, N4-formyl-SMT, desulfo-SMT, hydroxyl-SMT, N4-acetyl-SMT, desamino-SMT, and 2-amino-4,6-dimethylpyrimidine, were also identified. Notably, a portion of the extractable metabolites was excreted into the culture media, requiring characterization of these metabolites as either excreted phytometabolites or abiotic transformation products of SMT based on comparisons between experimental and control reactors.

Fate of 2,4,6-Tribromophenol in Soil Under Different Redox Conditions.

Fate of 2,4,6-tribromophenol (TBP) in environmental matrices is obscure. We used 14C-tracer to investigated mineralization, transformation, and non-extractable residue (NER)-formation of TBP in a soil under continuously oxic, continuously anoxic, and anoxic-oxic alteration conditions. In all cases, TBP rapidly dissipated, mineralized to CO2, and formed NERs in the soil. Considerable amounts of transformation products (2-12%) were detected during the incubation. Marked mineralization (13-26%) indicated that soil microorganisms used TBP as their energy source. About 62-70% of the initial radioactivity was transformed into NERs, being mainly attributed to binding to humic and fulvic acid fractions. TBP transformation was significantly faster under oxic conditions than under anoxic conditions, and was boosted when the soil redox changed from anoxic to oxic state. The results provide new insights into fate of TBP in soil and suggest the importance to evaluate the stability of NERs for risk assessment of TBP in soil.

Verification of Bound Aminoguanidine as the Marker Residue for the Banned Antibiotic, Nitrovin, in Pig Tissues.

Nitrovin (NTV) belongs to a class of antibiotics called nitrofurans, which are classified as nonallowed pharmacologically active substances that do not have a maximum residue limit listed in EU legislation. The objectives of this study were to confirm aminoguanidine (AGN) as a suitable marker residue to monitor NTV abuse and to investigate its persistence in porcine tissues. In this work, pigs were fed with NTV-medicated feed (50 mg/kg), and tissues (kidney, muscle, and liver) and plasma were collected on different withdrawal days. All samples were analyzed for bound AGN, total AGN, and the parent drug NTV itself. The highest concentrations of AGN residues were found in the liver, while the lowest were in muscle. Parent NTV was only detected in the kidney at low levels on day 0 of withdrawal. The findings are in support of using AGN as the marker residue for monitoring the illegal use of NTV in animal-derived products.

Fate of chlorpyrifos bound residues in paddy soils: Release, transformation, and phytoavailability.

Chlorpyrifos (CPF) is a widely used organophosphorus insecticide that tends to form bound residues (BRs) in soils. However, the stability and biological activity of CPF-BRs remain to be explored. Facilitated by carbon-14 tracing, this study obtained CPF-BRs initially formed in two typical paddy soils (14C-CPF-BRin), and further investigated their release, transformation and phytoavailability using duckweed (Lemna minor) as a model aquatic organism. Most 14C-CPF-BRin in soils were composed of the parent CPF and its metabolite 3,5,6-trichloro-2-pyridinol (2-OH-TCP), which was mainly formed through reversible entrapment by soil fulvic acids and humin (>80%). At 36 d, 66.67-80.90% of the 14C-CPF-BRin was released, of which only 2-OH-TCP could be released into the water and absorbed by the duckweed, with bioconcentration factors ranging from 247.99 to 324.68 L kg-1. The subsequent metabolism of released 14C-CPF-BRin in duckweed included phase I metabolism from 2-OH-TCP to 4-OH-TCP and phase II metabolism of conjugation of TCP with plant endogenous amino acids. The study suggested that CPF bound residues have high bioavailability in paddy field environments. Given that many pesticides and non-pesticide chemicals share structures analogous to CPF, the findings have important implications for better understanding the environmental and human health risks of man-made chemicals.

Reducing the Environmental Risk of Chlorpyrifos Application through Appropriate Agricultural Management: Evidence from Carbon-14 Tracking.

Chlorpyrifos (CPF) is one of the most critical insecticides in the world. However, many countries are gradually banning its use due to its reported hazardous impacts on humans. This study explored the possibility of reducing the environmental risk of CPF through appropriate agricultural management practices. Results showed that the environmental risk of CPF is lower under drainage conditions because there is more mineralization and less bound residues (BRs) than under submerged conditions. Bioaugmentation significantly enhanced the CPF mineralization and inhibited the formation of CPF-BRs. Biochar adsorbed CPF and thus reduced its bioavailability, but it could not completely eliminate the toxicity of CPF. In addition, bioaugmentation did not significantly affect the native microbial community of CPF-contaminated soil, suggesting its safety in reducing the environmental risk of CPF. The study indicated that the environmental risk of CPF could be reduced by appropriate agricultural management such as water management, bioaugmentation, soil biochar amendment, and selecting suitable soil types.

Enhanced mineralization of chlorpyrifos bound residues in soil through inoculation of two synergistic degrading strains.

Bioaugmentation methods are frequently employed for pesticide pollution remediation; however, it is not clear whether the introduced bacteria affect the pesticide bound residue (BRs) composition and whether the BRs can be catabolized by the introduced strains. This study aimed at answering these questions by using 14C-chlorpyrifos (14C-CPF) and two CPF-degrading strains (Pseudomonas sp. DSP-1 and Cupriavidus sp. P2). The results showed that the BRs can be up to 83.0%, and that the CPF-BRs formed can be further transformed into 14CO2 by the strains. Indeed, the microbial inoculation can increase the CPF mineralization by 1.0-22.1 times and can decrease the BRs by up to ~50% of the control (on day 20). Compared with the control without bioaugmentation, microbial inoculation enhanced the release of BRs by 2.2-18.0 times. Adding biochar to the soil can greatly inhibit CPF mineralization and maintain the BR content at a relatively stable level. The CPF residue can affect the composition of the indigenous soil microbial community, but the introduction of bacteria for remediation did not have a significant effect. The results indicate that Pseudomonas sp. DSP-1 and Cupriavidus sp. P2 are useful for remediating both CPF extractable and bound residues.

Biochar changes the bioavailability and bioefficacy of the allelochemical coumarin in agricultural soils.

BACKGROUND: Allelochemicals can act as biopesticides or enhance the action of synthetic pesticides. In this work, we assessed the bioavailability of the allelochemical coumarin in soils amended with fresh or field-aged biochars (BCs). The fresh BC from oak wood (Fresh BC) was prepared at 550 °C and was buried for aging in two different places: in a sandy loam soil in Spain for 15 months (Aged BC_1) and a sandy loam soil in USA for six months (Aged BC_2). RESULTS: Sorption experiments showed that all BCs were able to increase the affinity of soil towards coumarin, with the distribution coefficient following the order: unamended soil < Aged BC_2-amended soil < Aged BC_1-amended soil < Fresh BC-amended soil. All biochars ensure greater persistence of coumarin and the effect was more pronounced at high chemical dose (10 mg kg-1 ). Conversely, leaching studies in soil columns revealed that BCs were able to maintain coumarin within the first 5 cm of top-soil with total amount extracted ranging between 17% and 22% for BC-amended soil and <1% for unamended soil. Leaching was only observed when coumarin was added at the highest rate. Likewise, the bioefficacy of coumarin against lettuce was enhanced only at 10 kg ha-1 with BC-amended soil. CONCLUSIONS: Biochar application to agricultural soils is a promising tool for the management of natural compounds with potential use as biopesticides, such as coumarin, because it increases sorption, persistence and, in some cases, bioefficacy. The results reveal that this effect still persists with aging of BC in soils.

Fate characterization of bound residues of 14C-Pyraoxystrobin in soils.

Formation of bound residues (BR) has generally been considered as a detoxification process for organic contaminants. BR is an indispensable component for risk assessment of pesticides. In this study, BR of 14C-pyraoxystrobin in three soils cultivated for 100 days were characterized in light fraction (LF), loosely combined humus (LCH), stably combined humus (SCH), humic acid (HA), fulvic acid (FA), and humin. Isotope labeling technique was used to detect the distribution of BR of 14C-pyraoxystrobin in the six fractions of soil organic matter (SOM). The results showed that the amount of total BR was positively correlated with the SOM content (p < 0.05). The BR of 14C-pyraoxystrobin in cambisol soil was largest at 31.26 ± 0.04% of the induced radioactivity. During the whole incubation period, the BR of pyraoxystrobin in LCH of the three soils were consistently higher than that in SCH, and the amount of BR in FA was consistently greater than that in HA. The BR of 14C-pyraoxystrobin bound with humin increased over time. In addition, a degradation product 3-(4-chlorophenyl)-1-methyl-1H-pyrazol-5-ol (M1) from the hydrolysis of pyraoxystrobin was detected in cambisol soil, indicating the bonding of M1 with the HA separated from LCH (HALCH) via ester or ether linkages. The results provide new insights into the fate of BR of pyraoxystrobin in soils and may help to develop an understanding for the risk assessment of pyraoxystrobin and other strobilurin fungicides.

Fate of pendimethalin in soil and characterization of non-extractable residues (NER).

One important route of degradation of herbicide pendimethalin in soil leads to formation of non-extractable residues (NER). To investigate NER nature (irreversibly, chemically bound, including possible biogenic NER, or strongly sorbed and entrapped) residues of 14C-labelled pendimethalin in soil were investigated after conventional extraction with organic solvents by silylation. After 400 days of incubation, 32.0% of applied radioactivity (AR) was transformed into NER, 39.9% AR remained extractable. Mineralization reached 26.2% AR. Additionally, 14C-pendimethalin was incubated in soil amended with compost for 217 days to investigate the influence of organic amendments on NER formation. NER amounted to 37.8% AR, with 57.9% AR remaining extractable. Mineralization was negligible (1.4% AR). For all sampling times only low amounts of radioactivity were entrapped (<5% AR) in soil without compost amendment. Pendimethalin was present only in trace amounts (ca. 0.4% AR), other released residues consisted of undefined fractions (sum ≈2% AR). In soil amended with compost, silylation overall resulted in release of higher amounts of radioactivity (19% AR). Addition of compost led to an increase in potential entrapment and sorption sites for pendimethalin, forming higher amounts of strongly sorbed, entrapped residues. Furthermore, potential release of non-extractable pendimethalin residues was investigated by incubation of solvent-extracted soil (without compost amendment) mixed with fresh soil for additional 3 months. NER were partly mineralized (7% AR) and 20% became extractable with organic solvents. However, no pendimethalin or any known metabolites were found. It can be concluded that no parent pendimethalin was found and NER of pendimethalin in soil are mainly formed by covalent binding to organic matrix with only low potential of remobilization under natural conditions.

Plant litter enhances degradation of the herbicide MCPA and increases formation of biogenic non-extractable residues in soil.

Amendment of soils with plant residues is common practice for improving soil quality. In addition to stimulated microbial activity, the supply of fresh soluble organic (C) from litter may accelerate the microbial degradation of chemicals in soils. Therefore, the aim of this study was to test whether the maize litter enhances degradation of 4-chloro-2-methylphenoxyacetic acid (MCPA) and increases formation of non-toxic biogenic non-extractable residues (bioNERs). Soil was amended with 13C6-MCPA and incubated with or without litter addition on the top. Three soil layers were sampled with increasing distance from the top: 0-2 mm, 2-5 mm and 5-20 mm; and the mass balance of 13C6-MCPA transformation determined. Maize litter promoted microbial activity, mineralization of 13C6-MCPA and bioNER formation in the upper two layers (0-2 and 2-5 mm). The mineralization of 13C6-MCPA in soil with litter increased to 27% compared to only 6% in the control. Accordingly, maize addition reduced the amount of extractable residual MCPA in soil from 77% (control) to 35% of initially applied 13C6-MCPA. While non-extractable residues (NERs) were <6% in control soil, litter addition raised NERs to 21%. Thereby, bioNERs comprised 14% of 13C6-MCPA equivalents. We found characteristic differences of bioNER formation with distance to litter. While total NERs in soil at a distance of 2-5 mm were mostly identified as 13C-bioNERs (97%), only 45-46% of total NERs were assigned to bioNERs in the 0-2 and 5-20 mm layers. Phospholipid fatty acid analysis indicated that fungi and Gram-negative bacteria were mainly involved in MCPA degradation. Maize-C particularly stimulated fungal activity in the adjacent soil, which presumably facilitated non-biogenic NER formation. The plant litter accelerated formation of both non-toxic bioNERs and non-biogenic NERs. More studies on the structural composition of non-biogenic NERs with toxicity potential are needed for future recommendations on litter addition in agriculture.

Fate of 4-bromodiphenyl ether (BDE3) in soil and the effects of co-existed copper.

The quantitative fate of polybrominated diphenyl ethers (PBDEs) in soil is unknown. Furthermore, the effects of co-contamination by toxic copper on the behavior of PBDEs have not been investigated. Using a 14C-tracer, we studied mineralization, metabolism, and formation of non-extractable residues (NERs) of one PBDE congener, i.e., the 4-bromodiphenyl ether (BDE3) in oxic soil for 50 days, without and with amendment of Cu (400 mg kg-1 soil dw). BDE3 rapidly dissipated with a half-life of 5.5 days and large amounts of CO2 (38.8 ± 0.3% of initial applied amount at the end of incubation) and NERs (42.5 ± 0.4%) were rapidly produced. One hydroxylated metabolite (4'-HO-BDE3) was formed (8.1 ± 0.6%) at the beginning of the incubation, but then decreased to 2.2 ± 0.4%. Only BDE3 occurred in physico-chemically entrapped NERs, amounting to 9.2 ± 0.7%, while only 4'-HO-BDE3 in ester-linked NERs (10.9 ± 0.7%). The addition of Cu strongly reduced the kinetics constants of the transformations (including dissipation, mineralization, and NER-formation), the predicted maximal amounts of mineralization, as well as covalent binding of 4'-HO-BDE3 to soil. The results provide first quantitative insights into the fate of low-brominated congeners of PBDEs in soil and indicate that co-contamination by Cu may increase the environmental risks of biodegradable PBDEs in soil by increasing their persistence.

Dynamic Effect of Fresh and Aged Biochar on the Behavior of the Herbicide Mesotrione in Soils.

In this study, we assessed the sorption, dissipation, and leaching of the herbicide mesotrione in soil amended with fresh and field-aged biochars, when added to the soil. The aging process was performed by burying the fresh biochar at 10 cm depth in three soils located in different points across the USA [Wisconsin (ABC_WI), Idaho (ABC_ID), and South Carolina (ABC_SC)] for six months. ABC_ID and ABC_SC slightly increased the sorption of mesotrione in soils, whereas ABC_WI removed greater amounts of herbicide from the solution. This was attributed to differences in water-soluble components and metal content of this aged biochar. Consequently, the persistence of the herbicide in the amended soils with fresh biochar and ABC_ID and ABC_SC were similar to that in unamended soils, while ABC_WI slightly increased mesotrione half-life. Differences between treatments were detected in leaching studies although no direct relationship with the dissipation batch studies was observed. Mesotrione leaching could not be detected in soil columns amended with ABC_WI and was high for the rest of treatments. The outcomes from this work demonstrate that temporal variability of biochar sorption capacities due to soil exposure can occur altering mesotrione's behavior in biochar-amended soils.

Influence of the geophagous earthworm Aporrectodea sp. on fate of bisphenol A and a branched 4-nonylphenol isomer in soil.

Large amounts of endocrine disrupting chemicals (EDCs) including bisphenol A (BPA) and nonylphenol (NP) are released into the soil due to the application of biosolids. Earthworms are the predominant biomass in many terrestrial ecosystems and profoundly influence the physico-chemical and biological properties of soils. However, information about the effects of earthworm activities on the behaviors of EDCs in soil is still limited. Here, the effects of earthworms on mineralization, degradation, and bound residue formation of BPA and NP were investigated using the 14C tracer technique. The results showed that earthworms did not affect mineralization of BPA, but significantly inhibited bound residue formation of BPA and changed the size distribution of BPA residues within humic substances. Regarding NP, earthworms significantly inhibited mineralization and bound residue formation, and thus significantly promoted the degradation of NP and NP's metabolites in soil. After nine days of incubation, 75% and 46% of the initially applied 14C-BPA and 14C-NP were already present in bound residues, respectively, indicating that the major route of degradation of BPA and NP in soil was bound-residue formation. Among total 14C-BPA or 14C-NP residues accumulated in earthworms, bound residues were also predominant (>50%), implying that risk assessment of EDCs based on their concentrations of free form in earthworms might be significantly underestimated. Taken together, our results suggest that fate of EDCs in soil not only depended on their physico-chemical properties but also was intensively affected by earthworm activities, underlining that effects of earthworms should be considered when evaluating environmental behavior and potential risk of EDCs in soil.

Fate of 14C-bisphenol F isomers in an oxic soil and the effects of earthworm.

Bisphenol F (BPF) pollution in environment increased, but the studies on its fate and uptake in soil-earthworm systems were limited. Using 14C-tracers, environmental fate of BPF isomers in an oxic rice soil with/without earthworm Metaphire guillelmi was studied. After 59 days of incubation, mineralization increased in the order of 2,2'-BPF (18.7% ±â€¯0.3% of the initial amount) < 2,4'-BPF (21.7% ±â€¯0.2%) < 4,4'-BPF (26.9% ±â€¯0.1%). About 70% was converted to bound residues (BRs) and most of the BRs resided in the humin fraction by physical entrapment and ester-linkages. M. guillelmi decreased the mineralization and BRs of 4,4'-BPF in soil, indicating that earthworm increased the ecological risk of 4,4'-BPF. About 5.2% ±â€¯0.1% of the initial amount was accumulated in M. guillelmi and mostly in gut. Considerable amounts of the accumulated 4,4'-BPF were present as earthworm-bound residues (earthworm-BRs). The elimination of 4,4'-BPF from M. guillelmi was very slow, and there was still 96.2% of the initial accumulated radioactivity presented in earthworm after 5 days of depuration. The results of this study firstly provide the isomer - specific partitioning of three BPF isomers in an oxic soil and the uptake and depuration of 4,4'-BPF in earthworm during soil incubation.

Transformation, Conjugation, and Sequestration Following the Uptake of Triclocarban by Jalapeno Pepper Plants.

Plant uptake and metabolism of emerging organic contaminants, such as personal-care products, pose potential risks to human health. In this study, jalapeno pepper ( Capsicum annuum) plants cultured in hydroponic media were exposed to both 14C-labeled and unlabeled triclocarban (TCC) to investigate the accumulation, distribution, and metabolism of TCC following plant uptake. The results revealed that TCC was detected in all plant tissues; after 12 weeks, the TCC concentrations in root, stem, leaf, and fruit tissues were 19.74 ± 2.26, 0.26 ± 0.04, 0.11 ± 0.01, and 0.03 ± 0.01 mg/kg dry weight, respectively. More importantly, a substantial portion of the TCC taken up by plants was metabolized, especially in the stems, leaves, and fruits. Hydroxylated TCC (e.g., 2'-OH TCC and 6-OH TCC) and glycosylated OH-TCC were the main phase I and phase II metabolites in plant tissues, respectively. Bound (or nonextractable) residues of TCC accounted for approximately 44.6, 85.6, 69.0, and 47.5% of all TCC species that accumulated in roots, stems, leaves, and fruits, respectively. The concentrations of TCC metabolites were more than 20 times greater than the concentrations of TCC in the above-ground tissues of the jalapeno pepper plants after 12 weeks; crucially, approximately 95.6% of the TCC was present as metabolites in the fruits. Consequently, human exposure to TCC through the consumption of pepper fruits is expected to be substantially higher when phytometabolism is considered.

Unraveling microbial turnover and non-extractable residues of bromoxynil in soil microcosms with 13C-isotope probing.

Bromoxynil is a widely used nitrile herbicide applied to maize and other cereals in many countries. To date, still little is known about bromoxynil turnover and the structural identity of bromoxynil non-extractable residues (NER) which are reported to occur in high amounts. Therefore, we investigated the microbial turnover of 13C-labeled bromoxynil for 32 days. A focus was laid on the estimation of biogenic NER based on the turnover of 13C into amino acids (AA). At the end, 25% of 13C6-bromoxynil equivalents were mineralized, 2% assigned to extractable residues and 72.5% to NER. Based on 12% in the 13C-total AA and an assumed share of AA of 50% in microbial biomass we arrived at 24% of total 13C-biogenic NER. About 33% of the total 13C-NER could thus be explained by 13C-biogenic NER; 67% was unknown and by definition xenobiotic NER with potential for toxicity. The 13C label from 13C6-bromoxynil was mainly detected in the humic acids (28.5%), but significant amounts were also found in non-humics (17.6%), fulvic acids (13.2%) and humins (12.7%). The 13C-total amino acids hydrolyzed from humic acids, humins and fulvic acids amounted to 5.2%, 6.1% and 1.2% of 13C6-bromoxynil equivalents, respectively, corresponding to total 13C-biogenic NER amounts of 10.4%, 12.2% and 2.4%. The humins contained mostly 13C-biogenic NER, whereas the humic and fulvic acids may be dominated by the xenobiotic NER. Due to the high proportion of unknown 13C-NER and particularly in the humic and fulvic acids, future studies should focus on the detailed characterization of these fractions.

Bioaccumulation and elimination of bisphenol a (BPA) in the alga Chlorella pyrenoidosa and the potential for trophic transfer to the rotifer Brachionus calyciflorus.

In this study, we investigated the bioaccumulation and elimination of 14C-labeled BPA by the green alga Chlorella pyrenoidosa and the subsequent transfer of 14C-BPA residues from the contaminated alga to the rotifer Brachionus calyciflorus. After 10 days of BPA exposure, the algal cells accumulated 15% of the initial radioactivity from the medium, with 71% of the accumulated radioactivity occurring in the form of non-extractable bound residues. An approximate steady state of the accumulation of the 14C-BPA residues in the algae was reached after about 4 days of exposure. The bioconcentration factor of total radioactivity in the algae was 106 mL (g dry weight)-1 at steady state. During the elimination phase, only the extractable residues were released from the algae into the water whereas the bound residues, following their ingestion by the rotifers, were converted to extractable forms and then also released. Furthermore, our results demonstrated the biomagnification of BPA-related residues in the food chain between algae and rotifers. The trophic transfer of these BPA-derived residues from the algae to rotifers and thus the environmental hazard may posed by this pathway, because of subsequent effects on the food chain.

Formation of 2,4-D bound residues in soils: New insights into microbial metabolism.

The microbial contribution to the formation of bound residues in soils is studied by characterizing the metabolic activity of three microorganisms (Trametes versicolor, Fusarium solani and Ralstonia eutropha) on 14C-2,4-dichlorophenoxyacetic acid (2,4-D) during incubation in synthetic liquid media and soil. A fractionation protocol was applied to quantify the 14C-2,4-D that was incorporated into the biomass among biomolecular-like fractions. Successive fractionation of microbial biomass was implemented to break up and quantify the methanol/dichloromethane fraction (corresponding to the 14C-lipid-like fraction), the trichloroacetic acid fraction (or hydrolysed 14C-polysaccharide-like fraction) and the acid hydrolysable fraction (or the hydrolysed 14C-protein-like fraction). Relevant differences in the 2,4-D degradation and biomass radioactivity distribution among the three microorganisms were found. The 14C-protein-like fraction was the most consistent biomass fraction for reflecting the pesticide use capacity of the microorganisms under liquid and soil conditions. 2,4-D and its metabolite 4-chlorophenol were detected in methanol/dichloromethane and trichloroacetic acid fractions of the biomass of microorganisms exhibiting a low capacity to mineralize 2,4-D, thus proving that the microbial participation in the formation of bound residues while conserving the initial pesticide structure under natural soil conditions may be intimately associated with the lipid- and polysaccharide-like constituents. The fractionation protocol differentiates between 14C that is incorporated into biomass as a biomolecular constituent and the pesticide or its metabolites that accumulate in the biomass and thus correspond to the stricto sensu definition of bound residues.

Formation, characterization, and mineralization of bound residues of tetrabromobisphenol A (TBBPA) in silty clay soil under oxic conditions.

The nature and stability of bound residues (BRs) derived from the widely used brominated flame retardant tetrabromobisphenol A (TBBPA) in fine-textured soil is unknown. We incubated 14C-labeled TBBPA in silty clay rice paddy soil for 93days under oxic conditions. TBBPA dissipated with a first-order kinetic constant kd of 0.0474±0.0017day-1 (t1/2 14.6±0.3days) and mineralized with a km of 0.0011±0.00002day-1. At the end of the incubation, four metabolites, including two methylation products (TBBPA monomethyl and dimethyl ether), accounted for 7.9±0.1% of the initial TBBPA. The BRs continuously increased in amount to a maximum of 80.1±3.6%. About 86.3±0.9% of the BRs localized in the humin fraction and 55.9±1.5% was hydrolyzable with strong alkali (SAH-BRs), which represents reversible BRs. Together with results previously reported for coarse-textured soil, these results indicate that the absolute amounts of both BRs and SAH-BRs of TBBPA as well as the relative contribution of SAH-BRs to total BRs in fine-textured soil are markedly higher than in coarse-textured soil. When BRs-containing soil was incubated with fresh soil for 231days, 9.2±0.3% was mineralized (km 0.00047±0.00002day-1) and SAH-BRs decreased to 34.1±1.1%, accompanied by transformation into other BR forms. These indicate that BRs are bioavailable in the soil. Amendment with rice root exudates did not effectively affect the mineralization, release, and distribution of BRs, suggesting that bioavailability of BRs but not microbial activity limits the degradation of BRs in the silty clay soil. This study provides first insights into the nature and stability of TBBPA-derived BRs in fine-textured soil under oxic conditions and indicates the significant role of reversible BRs in the environmental risk of TBBPA.