Tenax Desorption Research Articles

The effect of black carbon on the chemical degradability of PCB1 via TENAX desorption technology from the perspective of adsorption states

Chemical degradation is one of the crucial methods for the remediation of hydrophobic organic compounds (HOCs) in soil/sediment. The sequestration effect of black carbon (BC) can affect the adsorption state of HOCs, thereby affecting their chemical degradability. Our study focused on the chemical degradability of 2-Chlorobiphenyl (PCB1) sequestrated on the typical BC (fly ash (FC), soot (SC), low-temperature biochar (BC400) and high-temperature biochar (BC900)) by iron-nickel bimetallic nanomaterials (nZVI/Ni) based on TENAX desorption technology. The results showed that PCB1 adsorbed in various states were simultaneously dechlorinated by nZVI/Ni. Specifically, rapid-desorption-state PCB1 tended to degrade more easily than resistant-desorption-state PCB1. Moreover, the degradation mechanism varied according to the type of BC. In the case of FC and SC, the degradation rate was lower than the desorption rate for the PCB1 in rapid and slow desorption states, and the degradation rate of PCB1 in the resistant desorption state was negligible. The PCB1 on FC and SC was first desorbed from BC and then degraded. However, in terms of BC400 and BC900, the degradation rate was higher than the desorption rate, and the degradation rate of the resistant-desorption-state PCB1 was 1.4 × 10−2 h−1 and 4.1 × 10−2 h−1, respectively. The graphitized structure of BC900 can directly transfer electrons, so more than 90% of the resistant-desorption-state PCB1 could be degraded. In addition, BC may affect the longevity of nZVI/Ni, thereby affecting its degradability. Therefore, the chemical degradability of BC-adsorbed HOCs should be comprehensively evaluated based on the adsorption state and the properties of BC.

Polydopamine-coated polyethylene sieve plate as an efficient and convenient adsorption sink for the bioaccessibility prediction of PAHs in soils

Bioaccessibility measurements of polycyclic aromatic hydrocarbons (PAHs) in soils are significant for exposure risk assessment. The current physicochemical methods require tedious operation processes, underestimate the actual risks, or are unsuitable for high organic content soils. In this work, an efficient and convenient method based on polydopamine-coated polyethylene sieve plate (PDA@PESP) and hydroxypropyl-β-cyclodextrin (HPCD) was developed to predict the bioaccessibility of PAHs in multi-type soils. The PDA@PESP can be prepared via in situ self-polymerization, allowing to extract PAHs from HPCD solution quantitatively and rapidly. When applied to evaluate the bioaccessibility with PDA@PESP as an adsorption sink and HPCD as a diffusive carrier, the proposed method can significantly improve the extractable fraction of PAHs compared to single HPCD extraction in particular for high organic carbon content soil and high-ring PAHs. The desorption kinetics data indicated that the method can predict the bioaccessible fraction of PAHs. In addition, the method predicted a satisfactory accumulation into earthworms (Eisenia fetida) with a slope statistically approximated to 1. A highly significant linear regression (R2 = 0.95) was also found between the proposed method and Tenax desorption in historically contaminated soils, demonstrating that the method is an efficient and convenient approach for the bioaccessibility prediction of PAHs in soils.

Effect of aging on bioaccessibility of DDTs and PCBs in marine sediment

Hydrophobic legacy contaminants like dichlorodiphenyltrichloroethane (DDT) and polychlorinated biphenyls (PCBs) were banned almost half a century ago. While their residues still remain in many environmental compartments, they have undergone extensive aging and likely have lower bioaccessibility (the available fraction) compared to fresh residues. However, risk assessment relies heavily on the use of total chemical concentration, rather than accounting for age-diminished bioaccessibility, likely leading to overestimated risks. In this study, we used 24 h Tenax desorption to measure the potential bioaccessibility of DDTs and PCBs in two sediment cores taken from the Palos Verdes Shelf Superfund site in the Pacific Ocean. The total concentrations of DDTs and PCBs from the core located at the sewage outfall (8C) were as high as 41,000–15,700 μg/kg (dry weight, dw) and 530-2600 μg/kg dw, respectively, while those from a location 7 km northeast of the outfall (3C) were 2–3 orders of magnitude lower. Bioaccessibility estimated by 24-h Tenax-aided desorption (F24h) decreased in the order of DDD > DDE > DDT for DDT derivatives, and PCB 52 > PCB 70 > PCB 153 for PCB congeners, showing a negative correlation with their log Kow. Due to the extensive aging, F24h values were <20% of the total chemical concentration for most contaminants and <5% for DDT, DDE and PCB 153, suggesting that aging greatly diminished their bioavailability. However, a quantitative relationship between F24h and sediment age along the vertical profile was not found, likely because the contaminant residues had undergone aging before their offsite transport and deposition onto the ocean floor. As the use of man-made chemicals such as DDT and PCBs was discontinued in the U.S. many decades ago, the reduction in their bioavailability due to aging may be universal and should be taken into consideration to avoid overly conservative risk predictions or unnecessary mitigation interventions.

Evaluation of different methods for assessing bioavailability of DDT residues during soil remediation

Compared to the total chemical concentration, bioavailability is a better measurement of risks of hydrophobic organic contaminants (HOCs) to biota in contaminated soil or sediment. Many different bioavailability estimation methods have been introduced to assess the effectiveness of remediation treatments. However, to date the different methods have rarely been evaluated against each other, leading to confusions in method selection. In this study, four different bioavailability estimation methods, including solid phase microextraction (SPME) and polyethylene passive sampling (PE) aiming to detect free chemical concentration (Cfree), and Tenax desorption and isotope dilution method (IDM) aiming to measure chemical accessibility, were used in parallel to estimate in bioavailability of DDT residues (DDXs) in a historically contaminated soil after addition of different black carbon sorbents. Bioaccumulation into earthworm (Eisenia fetida) was measured concurrently for verification. Activated carbon or biochar amendment at 0.2–2% decreased earthworm bioaccumulation of DDXs by 83.9–99.4%, while multi-walled carbon nanotubes had a limited effect (4.3–20.7%). While all methods correctly predicted changes in DDX bioavailability after black carbon amendment, passive samplers offered more accurate predictions. Predicted levels of DDXs in earthworm lipid using the estimated bioavailability and empirical BCFs matched closely with the experimentally derived tissue concentrations. However, Tenax and IDM overestimated bioavailability when the available DDX levels were low. Our findings suggested that both passive samplers and bioaccessibility methods can be used in assessing remediation efficiency, presenting flexibility in method selection. While accessibility-oriented methods offer better sensitivity and shorter sampling time, passive samplers may be more advantageous because of their better performance and computability for in situ deployment.

Application and validation of isotope dilution method (IDM) for predicting bioavailability of hydrophobic organic contaminants in soil.

Risk assessment of hydrophobic organic contaminants (HOCs) using the total chemical concentration following exhaustive extraction may overestimate the actual availability of HOCs to non-target organisms. Existing methods for estimating HOC bioavailability in soil have various operational limitations. In this study, we explored the application of isotope dilution method (IDM) to quantify the accessible fraction (E) of DDTs and PCBs in both historically-contaminated and freshly-spiked soils. After addition of 13C or deuterated analogues to a soil sample, the phase distribution of isotope-labeled and native chemicals reached an apparent equilibrium within 48 h of mixing. The derived E values in the three soils ranged from 0.19 to 0.82, depending on the soil properties and also the contact time of HOCs (i.e., aging). The isotope dilution method consistently predicted greater accumulation into earthworm (Eisenia fetida) than that by polyethylene (PE) or solid phase microextraction (SPME) sampler, likely because desorption in the gut enhanced bioavailability of soil-borne HOCs. A highly significant linear regression (R2 = 0.91) was found between IDM and 24-h Tenax desorption, with a slope statistically identical to 1. The IDM-derived accessible concentration (Ce) was further shown to accurately predict tissue residues in earthworm exposed in the same soils. Given the relatively short duration and simple steps, IDM has the potential to be readily adopted for measuring HOC bioaccessibility in soil and for improving risk assessment and evaluation of remediation efficiency.

Exploration of biodegradation mechanisms of black carbon-bound nonylphenol in black carbon-amended sediment

The present study aimed to investigate biodegradation mechanisms of black carbon (BC)-bound contaminants in BC-amended sediment when BC was applied to control organic pollution. The single-point Tenax desorption technique was applied to track the species changes of nonylphenol (NP) during biodegradation process in the rice straw carbon (RC)-amended sediment. And the correlation between the biodegradation and desorption of NP was analyzed. Results showed that microorganisms firstly degraded the rapid-desorbing NP (6 h Tenax desorption) in RC-amended sediment. The biodegradation facilitated the desorption of slow-desorbing NP, which was subsequently degraded as well (192 h Tenax desorption). Notably, the final amount of NP degradation was greater than that of NP desorption, indicating that absorbed NP by RC amendment can be degraded by microorganisms. Finally, the residual NP amount in RC-amended sediment was decided by RC content and its physicochemical property. Moreover, the presence of the biofilm was observed by the confocal laser scanning microscope (CLSM) and scanning electron microscope (SEM) so that microorganisms were able to overcome the mass transfer resistance and directly utilized the absorbed NP. Therefore, single-point Tenax desorption alone may not be an adequate basis for the prediction of the bioaccessibility of contaminants to microorganisms or bioremediation potential in BC-amended sediment.

Comparing different methods for assessing contaminant bioavailability during sediment remediation

Sediment contamination by persistent organic pollutants from historical episodes is widespread and remediation is often needed to clean up severely contaminated sites. Measuring contaminant bioavailability in a before-and-after manner lends to improved assessment of remediation effectiveness. However, a number of bioavailability measurement methods have been developed, posing a challenge in method selection for practitioners. In this study, three different bioavailability measurement methods, i.e., solid phase microextraction (SPME), Tenax desorption, and isotope dilution method (IDM), were compared in evaluating changes in bioavailability of DDT and its degradates in sediment following simulated remediation treatments. When compared to the unamended sediments, all three methods predicted essentially the same degrees of changes in bioavailability after amendment with activated carbon, charcoal or sand. After normalizing over the unamended control, measurements by different methods were linearly correlated with each other, with slopes close to 1. The same observation was further made with a Superfund site marine sediment. This finding suggests that different methods may be used in evaluating remediation efficiency. However, Tenax desorption or IDM consistently offered better sensitivity than SPME in detecting bioavailability changes. Results from this study highlight the value of considering bioavailability when evaluating remediation effectiveness and provide guidance on the selection of bioavailability measurement methods in such assessments.

Use of isotope dilution method to predict bioavailability of organic pollutants in historically contaminated sediments.

Many cases of severe environmental contamination arise from historical episodes, where recalcitrant contaminants have resided in the environment for a prolonged time, leading to potentially decreased bioavailability. Use of bioavailable concentrations over bulk chemical levels improves risk assessment and may play a critical role in determining the need for remediation or assessing the effectiveness of risk mitigation operations. In this study, we applied the principle of isotope dilution to quantify bioaccessibility of legacy contaminants DDT and PCBs in marine sediments from a Superfund site. After addition of 13C or deuterated analogues to a sediment sample, the isotope dilution reached a steady state within 24 h of mixing. At the steady state, the accessible fraction (E) derived by the isotope dilution method (IDM) ranged from 0.28 to 0.89 and was substantially smaller than 1 for most compounds, indicating reduced availability of the extensively aged residues. A strong linear relationship (R2 = 0.86) was found between E and the sum of rapid (Fr) and slow (Fs) desorption fractions determined by sequential Tenax desorption. The IDM-derived accessible concentration (Ce) was further shown to correlate closely with tissue residue in the marine benthic polychaete Neanthes arenaceodentata exposed in the same sediments. As shown in this study, the IDM approach involves only a few simple steps and may be readily adopted in laboratories equipped with mass spectrometers. This novel method is expected to be especially useful for historically contaminated sediments or soils, for which contaminant bioavailability may have changed significantly due to aging and other sequestration processes.

Desorption of pyrethroids from suspended solids

Pyrethroid insecticides have been widely detected in sediments at concentrations that can cause toxicity to aquatic organisms. Desorption rates play an important role in determining the bioavailability of hydrophobic organic compounds, such as pyrethroids, because these compounds are more likely to be sorbed to solids in the environment, and times to reach sorptive equilibrium can be long. In the present study, sequential Tenax desorption experiments were performed with three sorbents, three aging times, and four pyrethroids. A biphasic rate model was fit to the desorption data with r(2) > 0.99, and the rapid and slow compartment desorption rate constants and compartment fractions are reported. Suspended solids from irrigation runoff water collected from a field that had been sprayed with permethrin 1 d before were used in the experiments to compare desorption rates for field-applied pyrethroids with those for laboratory-spiked materials. Suspended solids were used in desorption experiments because suspended solids can be a key source of hydrophobic compounds in surface waters. The rapid desorption rate parameters of field-applied permethrin were not statistically different from those of laboratory spiked permethrin, indicating that desorption of the spiked pyrethroids is comparable to desorption of the pyrethroids added and aged in the field. Sorbent characteristics had the greatest effect on desorption rate parameters; as organic carbon content of the solids increased, the rapid desorption fractions and rapid desorption rate constants both decreased. The desorption rate constant of the slow compartment for sediment containing permethrin aged for 28 d was significantly different compared to aging for 1 d and 7 d, whereas desorption in the rapid and slow compartments did not differ between these treatments.

How quality and quantity of organic matter affect polycyclic aromatic hydrocarbon desorption from Norwegian harbor sediments

The desorption behavior of phenanthrene, pyrene, and benzo[a]pyrene was investigated for three Norwegian harbor sediments and their respective particle size fractions using the Tenax desorption method. Rate constants for rapidly, slowly, and very slowly desorbing fractions were on the order of 10(-1), 10(-2) to 10(-4), and 10(-4) to 10(-6)/h, respectively. Relatively small amounts were present in the rapidly desorbing fractions (F(rapid): < 6% for phenanthrene, 3-19% for pyrene, and 1-12% for benzo[a]pyrene). With the exception of benzo[a]pyrene, these F(rapid) values were generally lower than median F(rapid) values obtained from more than 100 literature values for native polycyclic aromatic hydrocarbons (PAHs) (22% for phenanthrene, 29% for pyrene, and 8% for benzo[a]pyrene). To understand which parameters influence PAH desorption, relations between desorption behavior and the sediment characteristics were investigated. A significant positive correlation was found between the extent of slow and very slow desorption and the ratios of black carbon to total organic carbon, as well as the temperature at which 50 and 90%, respectively, of the organic matter was oxidized, as obtained from oxidation-only Rock Eval analysis. Thus, black carbon-bound PAHs probably desorb slowly and very slowly. Furthermore, significant positive correlations between desorption behavior and the average particle size were observed, which could be explained by retarded intraparticle diffusion.

Desorption kinetics of neutral hydrophobic organic compounds from field-contaminated sediment

The chemical release rates from a field-contaminated sediment (Lake Charles, LA) using Tenax desorption were studied. Two dichlorobenzenes ( m-, p-), hexachlorobutadiene, and hexachlorobenzene were investigated. Contrary to reports that sorption rates are inversely related to K OW, the slow desorption rates were found to be similar for the four compounds. The data were modeled by a two-compartment irreversible adsorption and radial diffusion model. Desorption kinetics from the first irreversible compartment can be modeled by radial diffusion and assume an irreversible adsorption constant and soil tortuosity of 4.3. The desorption half-life is approximately 2–7 days. Desorption from the second irreversible compartment is very slow (half-life of approximately 0.32–8.62 years) presumably caused by entrapment in soil organic matter that increases the constrictivity of the solid phase to chemical diffusion. From the kinetic data, it is deduced that the diffusion pore diameter of the second irreversible compartment is approximately equal to the critical molecular diameter. The mass of chemicals in this highly constrictive irreversible compartment is approximately one-fourth of the maximum irreversible, or resistant, compartment. The slow kinetics observed in this study add additional support to the notion that the irreversibly sorbed chemicals are ‘benign’ to the environment.