Uptake Of Organic Contaminants Research Articles

Mutual Effects and Uptake of Organic Contaminants and Nanoplastics by Lettuce in Co-Exposure.

Organic contaminants, such as pesticides and pharmaceuticals, are commonly found in agricultural systems. With the growing use of plastic products, micro- and nanoplastics (MNPs) are increasingly detected in these agricultural systems, necessitating research into their interactions and joint effects to truly understand their impact. Unfortunately, while there has been a long history of research into the uptake of organic pollutants by plants, similar research with MNPs is only beginning, and studies on their mutual effects and plant uptake are extremely rare. In this study, we examined the effects of three agriculturally relevant organic pollutants with distinctive hydrophobicity as measured by log KOW (trimethoprim: 0.91, atrazine: 2.61, and ibuprofen: 3.97) and 500 nm polystyrene nanoplastics on their uptake and accumulation by lettuce at two different salinity levels. Our results showed that nanoplastics increased the shoot concentration of ibuprofen by 77.4 and 309% in nonsaline and saline conditions, respectively. Alternatively, organic co-contaminants slightly lowered the PS NPs uptake in lettuce with a more pronounced decrease in saline water. These results underscore the impactful interactions of hydrophobic organic pollutants and increasing MNPs on a dynamic global environment.

Assessing plant uptake of organic contaminants by food crops tomato, wheat, and corn through sap concentration factor

This study investigated uptake of two organic compounds including hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and exogenous caffeine by tomato (Solanum lycopersicum L.), corn (Zea mays L.), and wheat (Triticum aestivum L.). The plants were grown in a growth chamber under recommended conditions and then were exposed to these compounds for 19 days. The uptake of the compounds was measured by sap concentration factor. The plant samples (stem transpiration stream) and solution in the exposure media were taken and analyzed by high performance liquid chromatography-tandem mass spectrometry. The plant stem samples were analyzed after a freeze-thaw centrifugation process. The average sap concentration factor for the RDX by tomato, wheat, and corn was 0.71, 0.67, and 0.65. The average sap concentration factor for the exogenous caffeine by tomato, wheat, and corn was 0.72, 0.50, and 0.34. These relatively high sap concentration factor values were expected as available predictive models offer high sap concentration factor values for moderately hydrophobic and hydrophilic compounds. The generated sap concentration factor values for the RDX and exogenous caffeine are important for improving the accuracy of previously developed machine learning models predicting the uptake and translocation of emerging contaminants.

Modeling plant uptake of organic contaminants by root vegetables: The role of diffusion, xylem, and phloem uptake routes

The uptake of organic contaminants by root vegetables involves diffusion, transport by xylem and phloem saps, degradation, and volatilization. To understand the role of uptake and elimination routes in the bioconcentration modeling of organic contaminants, a two-compartment uptake model (root and leaf compartments) was proposed. The results showed that for the root compartment, logarithm values of bioconcentration factors (log BCF, the concentration ratio between plant tissues and soil) of chemicals fell within a narrow range when the logarithm of octanol-water partition coefficient (log KOW) was less than 3.0, whereas log BCF values decreased rapidly with increasing log KOW values when log KOW was greater than 3.0. This is because the diffusion route had a significant impact on the root uptake of chemicals, wherein the first-order rate constant dropped rapidly for high-lipophilicity chemicals, resulting in very low log BCF values. For the leaf compartment, chemicals with moderate lipophilicity (log KOW of 3.0–4.0) had the highest simulated log BCF values. This is because moderate log KOW values generated the highest transpiration stream concentration factors (TSCFs, the concentration ratio between xylem or phloem saps and water), resulting in high uptake efficiency of chemicals by leaves. Furthermore, we improved the uptake model by considering the surface-deposition route for pesticides (foliar spray), and the simulation results indicated that this uptake route cannot be neglected for lipophilic compounds. Although the simulations agreed with an experimental study and some reported data, future studies should focus on factors, such as plant physiology (plant varieties, periderm effects and compositions of xylem and phloem saps) and environmental conditions (soil properties and weather conditions), to improve the plant uptake model.

In-situ quantitative monitoring the organic contaminants uptake onto suspended microplastics in aquatic environments

Microplastics act as a source of organic contaminants in aquatic environments and thus affect their environmental fate and toxicity. Because of the weak and reversible interactions between microplastics and organic species, the organic coronas vary with their surrounding environments. Thus, in order to evaluate the possible environmental risks of microplastics, methods for evaluating the dynamic uptake of organic contaminants onto suspended microplastics in aquatic environments are greatly desired. In this work, a UV–vis spectroscopy-based approach was developed for in-situ monitoring organic contaminants uptake onto suspended microplastics after correcting the light scattering interference from microplastics suspensions and establishing the nonlinear relationship between concentration and light absorbance of organic species. The inverse adding-doubling method based on radiative transfer theory was adopted to correct the light scattering effect of suspensions. Then, the resulting mixed absorption spectra were decomposed to calculate the concentrations of the aqueous and adsorbed organic species simultaneously with a nonlinear calibration method. The uptake processes of bisphenol A and p-nitrophenol onto nylon 66 microparticles were monitored with this approach and confirmed by high-performance liquid chromatography analysis. The approach was validated by applying it to natural water samples, and the equilibrium adsorption capacity was found to be interfered mainly by the protein-like substances. This approach has high accuracy, good reproducibility, remarkable universality, and ease of handling, and also provides a potential tool for characterizing the corona formation process on suspended particles both in natural and artificial environments, such as eco-corona formation and engineering surface modification on nano/micro-particles.

Risk Assessment of Contaminants in Sewage Sludge Applied on Norwegian Soils

The Norwegian Scientific Committee for Food Safety (VKM) was asked by the Norwegian Food Safety Authority to assess the risk of using sewage sludge as fertilizer and soil conditioner in agricultural lands and park areas as well as sludge mixed with soil sold to private households. VKM was specifically asked to evaluate the potential risk of dispersal of sewage sludge for soil living organisms, the aquatic environment, grazing animals, animals eating feed based on plants from sludge-treated soil, children eating soil, and humans consuming drinking water, crop plants and/or meat affected by the use of sludge as soil conditioner, in total a list of 12 defined exposure routes.
 VKM was asked to perform a risk assessment of all these exposure routes for the following contaminants:
 
 Cadmium (Cd)
 Phthalates (DEHP, DBP)
 Lead (Pb)
 Octylphenols and octylphenol ethoxylates
 Mercury (Hg)
 Nonylphenols and nonylphenol ethoxylates
 Nickel (Ni)
 Alkylbenzenesulfonate, linear (LAS)
 Zink (Zn)
 Polychlorinated biphenyls (PCBs)
 Cobber (Cu)
 Polycyclic aromatic hydrocarbons (PAHs)
 Chromium (Cr)
 
 VKM was also asked to evaluate the risk associated with pharmaceuticals belonging to the groups; hormones, fluoroquinolone and tetracyclines and other relevant pharmaceuticals depending on the findings from a screening study of pharmaceuticals in sewage sludge from the Norwegian Pollution Control Authority (SFT, 2007). Included in the request to VKM was as far as possible to assess a list of other substances for which insufficient data was available to complete the risk assessment. The VKM Scientific Panel on Contaminants has been responsible for this risk assessment.
 The application of sewage sludge as fertilizer implies a potential dispersal of a wide range of contaminants to agricultural soils. These contaminants may be further transported to different environmental compartments such as air, surface water, ground water and nearby streams. Furthermore the contaminants in soil may be absorbed by crop plants or plants used for feed production or grazing purposes and result in animal and human exposure to the contaminants through feed or food. Concentration data for all these compounds in sludge-treated soil or other environmental compartments following the application of sludge are not available. The predicted environmental concentrations (PECs) in soil, as well as human and animal exposure to the contaminants following the use of sewage sludge as soil conditioner have therefore been estimated by use of mathematical modelling based on the guidelines given in the European Union‘s (EU) Technical Guidance Document on Risk Assessment (TGD). The guidelines were adapted to Norwegian conditions whenever relevant. The exposure of the aquatic environment has been estimated by use of models developed, validated and used for pesticides. The risk assessment should cover both an evaluation after one application and the potential accumulation of contaminants following repeated use of sewage sludge. The risks associated with estimated exposure levels were assessed.
 There is very limited information on the occurrence of medicines in Norwegian sewage sludge. The selection of medicines included in the few studies available appears not to be based on risk of effect or probability of occurrence. The Panel on Contaminants therefore decided to develop a tiered approach to estimate the concentrations of pharmaceuticals in sludge. A cut-off concentration of 100 g/kg soil was used in the tiered approach. The environmental risk associated with concentrations of drug substances below this level are regarded as negligible by The European Medicines Agency (EMEA). For drug substances like hormones and anticancer drugs that usually exert an effect at very low concentrations, The Panel on Contaminants has applied an additional safety factor of 10, and the cut-off concentration for these substances was set to 10 μg/kg soil.The potential concentrations in sewage sludge were estimated based on statistical information on sold amounts of medicines and sewage sludge production volumes. The estimations were gradually refined by taking factors such as water solubility, biotransformation, and environmental degradation into account. The output of the tiered approach was a list of 14 drug substances with potential occurrence on soil after sewage sludge application exceeding the cut off values of 100 or 10 g/kg soil. A more detailed risk assessment of these 14 drug substances was performed by using the same methods as used for other contaminants.
 The potential risk of eutrophication of the aquatic environment following sewage sludge application and the effects of application of sewage sludge on areas with grazing animals without ploughing within 18 hours have not been assessed.
 Hazard Characterisations:
 The hazard characterisation has been based on available hazard assessments made by international organizations like The Joint FAO/WHO Expert Committee on Food Additives (JECFA), EU Chemical Bureau, European Food Safety Authority (EFSA), etc. For substances where no hazard characterisation has been made by any of these organisations, relevant national hazard characterisations have been used. For certain compounds in certain environmental compartments, no toxicological safe exposure limits have been found. The lack of available toxicological hazard characterisations has therefore been pointed out as knowledge gaps in this assessment. Establishment of new tolerable daily intake (TDI) or predicted no-effect concentration (PNEC) values has not been the scope of this assessment.
 Exposure Assessments:
 All levels of exposure have been estimated by use of mathematical models. The models are based on the guidelines in TGDs. Some modifications in the models have been made to adapt the exposure assessments to Norwegian conditions. To a large extent, this applies to soil parameters, weather parameters and agricultural practice. Soil concentrations have been calculated based on the levels of contaminants in sludge and the present use of sludge (class 1: 40 tons/hectare/10 year) and a possible 50% increase in the maximum permitted use of sludge (60 tons/hectare/10 year). To allow for the potential accumulation in soil with repeated use of sludge, the soil concentrations have been calculated in a 100 year perspective, background concentrations, evaporation, biodegradation, removal through plants and leaching to aquatic environments into account. The maximum concentration for each contaminant, either immediately after application of sewage sludge or after 100 years with repeated use (application every 10th year), has been used as the exposure estimate in the risk assessment. Leaching to the aquatic environment has been estimated by the models developed and used for pesticides applied on soil. The model is validated for both organic and inorganic pesticides and is therefore considered suitable for the prediction of leaching to surface water as well as ground water.
 Uptake of contaminants by plants was calculated, both to be able to estimate the potential accumulation of contaminants in soil and to provide concentrations for the calculations of animal and human exposure through ingestion of crop plants. The uptake of contaminants in plants was calculated according to the guidelines in TGD when possible. The guidelines in TGDs do, however, only allow for estimations of concentrations in root parts and was therefore used in estimations of concentrations in root plants such as potatoes and carrots. Other models from the scientific literature had to be used to estimate the concentrations in edible plant parts above the ground, such as lettuce and cereals. A comparison between several models was made and the most conservative model considered to be realistic was chosen. The resulting plant concentrations were then used in calculations of animal and human intakes of contaminants.
 The models used for estimating plant uptake of organic contaminants from soil have not been validated for polar and ionisable compounds. Most drug substances have such chemical properties, and the concentrations of drug substances in plants could therefore not be estimated. Consequently, animal and human exposure to drug substances through plant derived feed or food could not be estimated.
 There is no model available from the TGD to assess the transfer of metals from feed to animalderived food products. A transfer of Cd, Pb and Hg in food producing animals has been estimated based on available values in the literature on intake and tissue concentrations. The concentrations of organic contaminants in animal-derived food items were estimated using a model from the TGD.
 Human intakes of contaminants from food producing animals were calculated using the estimated plant concentrations combined with typical feeding rations to the different animals (species and age/type of production).
 The human intakes were estimated based on the individual food consumption data from Norkost 1997 (Norwegian food consumption survey), estimated crop plant concentrations, estimated levels in animal-derived food items and estimated water concentrations. A consumption of drinking water of 2 L/day has been used, which is the water consumption used by WHO when the drinking water guidelines are prepared.
 Risk Characterizations:
 Soil environment:
 The estimated predicted environmental concentration (PEC) for each contaminant was compared with the available predicted no-effect concentration (PNEC) for soil.
 The estimations showed that no metals would reach the PNEC values within the timeframe of 100 years. Consequently the Panel on Contaminants considers metals in sludge to constitute a low risk to soil living organisms. However, the model estimations indicate that the soil concentrations of Cd, Hg, Cu and Zn, and partly also Pb will increase following repeated use of sewage sludge. Cadmium and Hg, as well as Pb are of particular concern due to their inherent toxic properties and the increase is undesirable even if the soil concentrations are not estimated to exceed the PNEC values. Cadmium is also taken up in plants to a significant degree. Increased Cd concentrations in soil will therefore increase the human exposure to this metal. After 100 years with repeated use of sewage sludge on an average soil, the estimated soil concentration of Cd is still below the present maximum permitted soil concentration for further application of sewage sludge.
 Octylphenols, nonylphenols and LAS were the only contaminants where the PEC exceeded the PNEC. However, these are rapidly degradable substances (t1/2 in soil = 8-10 days) where the highest concentrations were found immediately after application of sewage sludge followed by a rapid decrease. Taking into account the uncertainties related to the occurrence levels, and the rapid degradation in soil, VKM considers octylphenols, nonylphenols and LAS to be of low concern. Only a few PAHs and PCBs are expected to accumulate with repeated use (every 10th year) of sewage sludge in a 100 years period and the model indicates that the concentrations of these substances will be well below the PNEC value even at the end of the 100 year period. VKM considers all the assessed organic contaminants to constitute a low risk to the soil environment.
 Of the more than 1400 drug substances sold in Norway, only 14 have been estimated to exceed the cut-off values of 100 or 10 g/kg soil after sludge application. For the 14 identified drug substances no PNEC values in soil have been available to VKM. Soil PNEC values for pharmaceuticals have therefore been estimated from the aquatic PNEC values when available. The estimated soil concentrations of drug substances were low (concentration range 0.01 – 2 mg/kg dry weight (DW)) and well below the estimated PNEC values. The Panel on Contaminants considers drug substances in sewage sludge to constitute a low risk for soil-living organisms.
 Aquatic environment:
 Neither metals, organic contaminants nor the drug substances assessed are expected to reach the environmental PNEC values on short or long-term. Most of the assessed contaminants reach maximum concentrations well below the PNEC values. Two PAHs (pyrene and indeno (1, 2, 3-cd)pyrene) are estimated to reach a water concentration approaching the PNEC value (Risk quotient of 0.99 and 0.88 respectively). The Panel on Contaminants considers the use of sewage sludge as soil conditioner therefore to be of low concern for the aquatic environment.
 Food producing animals:
 From this risk assessment based on a contaminant based approach, the risk of adverse effects in farm animals grazing on or receiving feed from sewage sludge treated areas seem to be neglicible for a range of contaminants. Meat-producing animals have in general a short life span and are consequently not expected to be subject to effects following long-term exposure to substances with a potential accumulation. Milk-producing and breeder animals have longer life span, but the exposure of food producing animals to contaminants through application of sewage sludge may anyway be regarded as low. However, lead seems to be an exception and may constitute a risk in young animals as the estimated extra contribution from sewage sludge to a high background level may imply an intake level close to that shown to reduce learning capability in lambs. In addition, there are limited data in the literature on the effects of several contaminants in food producing animals and the assessments of these contaminants are hampered with uncertainty. Furthermore, the knowledge of effects of combined exposure to the coctail of various known and unknown chemicals in sewage sludge is lacking. Even not directly comparable to the Norwegian use of sewage sludge, perturbated development of young ruminants pre- and postnatally exposed to sewage sludge treated areas has been revealed. However, such use of sewage sludge directly on grazing areas without ploughing has not been an issue in Norway and has therefore not been adressed in this report.
 Human exposure:
 Human intake from food and drinking water
 Presently about 60% of the sewage sludge produced is dispersed on agricultural soil. This would cover <5% of the cereal-producing areas at the maximum allowed amounts (40 tons/10 years). Due to this limited availability of sewage sludge, the fraction of agricultural soil receiving the maximum doses of sewage sludge will be so small that the added contribution from sewage sludge to the dietary intake for the general population will be low. For specific individuals, for example farmers, consuming only vegetables grown on such fields, the dietary intake may potentially exceed the tolerable daily intake (TDI) for Cd and the tolerable upper intake level (UL) for Cu in the long term. The Panel on Contaminants has not assessed the probability of this scenario to occur.
 The human dietary intakes via the different exposure routes assessed are combined – i.e. drinking water and plants and animal derived food products. The estimated concentrations of contaminants in soil indicate that repeated application (every 10th year) of sewage sludge on a field during a 100 year time period will lead to an increase in soil concentrations of certain heavy metals such as Cd and Hg. A consequence of this accumulation in soil may result in an undesirable increase in human dietary intake of particularly Cd, but also Hg.
 The additional intake of metals from animal-derived food products or drinking water as a consequence of use of sewage sludge as fertilizer is estimated to be very low (<5% of estimated total intake) and of low concern.
 The organic contaminants addressed in the present risk assessment are either degraded in the soil
 or poorly absorbed into crop plants. The estimates therefore indicate a low increase in human dietary exposure to organic contaminants from sewage treated soil and the Panel considers this additional exposure to constitute a low risk to the consumers.
 Children eating soil
 The highest concentrations of contaminants are found in soil mixtures sold for use in private homes. These mixtures may contain 30% sewage sludge. There is no requirement for further mixing of this product. The estimated intake of metals when children ingest 0.2 g of this soil products are low in comparison with the toxicological safety parameters (TDIs or ULs), with Pb being the highest, reaching approximately 13% of the TDI. Taking into consideration that this route of exposure only is likely to occur in a limited time period, and the relatively low intake in comparison with the TDI, the Panel on Contaminants considers this exposure route to be of low risk.
 Development of antibacterial resistance:
 It is unlikely that antibacterial resistance may be promoted in the STP water, in the sludge or in the soil following application of sewage sludge as fertilizer. An exception may be a potential development of resistance to the fluoroquinolone ciprofloxacin in soil due to persistence and limited mobility of these substances into the subsoil.
 Conclusions:
 Octylphenols, nonylphenols and LAS are the only contaminants in this assessment that is estimated to reach soil concentrations exceeding the PNEC in agricultural soils. These compounds are rapidly degradable in soil and the highest soil concentrations are reached immediately after each sewage sludge application. However, concentrations are uncertain and available occurrence data for octylphenols, nonylphenols and LAS in Norwegian sludge are limited. There is also limited information available on the effects of these compounds in soil, and the PNEC values for octylphenols and nonylphenols were derived from available aquatic PNEC and large safety factors were used in the assessment. Based on these findings, the Panel of Contaminants of VKM considers the use of sewage sludge to constitute a low risk to the soil ecosystem. The model does, however, indicate a potential increase in the soil concentration of the inherent toxic metals Cd and Hg as well as Cu and Zn. It is therefore recommended that the concentrations of these metals in sewage sludge used for agricultural purposes should be monitored. Furthermore, continued efforts to reduce the content of these metals in sludge are encouraged.
 The use of sewage sludge is not expected to constitute a significant risk to the aquatic environment nor to food producing animals.
 The Panel does not consider the risk associated with the use of sewage sludge as soil conditioner for the dietary intake (including drinking water) of the assessed contaminants to be of significance for the general population. The estimations do, however, indicate that a scenario of exclusive consumption of vegetables grown on sludge-treated soil could result in a dietary intake of Cd and Cu close to or above toxicological safe exposure limits (TDI or UL). The probability for such a scenario, for example a farmer only consuming vegetables grown on his own sludgetreated soil, to occur has not been assessed.
 The risks have been assessed chemical by chemical, since no methodology for the risk assessment of the mixture occurring in sewage sludge is available. Most of the estimated exposures are well below any predicted effect concentration, making any interaction less likely, unless the contaminants have the same mode of action.

Investigating plant uptake of organic contaminants through transpiration stream concentration factor and neural network models

Uptake of seven organic contaminants including bisphenol A, estriol, 2,4-dinitrotoluene, N,N-diethyl-meta-toluamide (DEET), carbamazepine, acetaminophen, and lincomycin by tomato (Solanum lycopersicum L.), corn (Zea mays L.), and wheat (Triticum aestivum L.) was measured. The plants were grown in a growth chamber under recommended conditions and dosed by these chemicals for 19 days. The plant samples (stem transpiration stream) and solution in the exposure media were taken to measure transpiration stream concentration factor (TSCF). The plant samples were analyzed by a freeze-thaw centrifugation technique followed by high performance liquid chromatography-tandem mass spectrometry detection. Measured average TSCF values were used to test a neural network (NN) model previously developed for predicting plant uptake based on physicochemical properties. The results indicated that moderately hydrophobic compounds including carbamazepine and lincomycin have average TSCF values of 0.43 and 0.79, respectively. The average uptake of DEET, estriol, acetaminophen, and bisphenol A was also measured as 0.34, 0.29, 0.22, and 0.1, respectively. The 2,4-dinitrotoluene was not detected in the stem transpiration stream and it was shown to degrade in the root zone. Based on these results together with plant physiology measurements, we concluded that physicochemical properties of the chemicals did predict uptake, however, the role of other factors should be considered in the prediction of TSCF. While NN model could predict TSCF based on physicochemical properties with acceptable accuracies (mean squared error less than 0.25), the results for 2,4-dinitrotoluene and other compounds confirm the needs for considering other parameters related to both chemicals (stability) and plant species (role of lipids, lignin, and cellulose).

Role of photo- and biodegradation of two PAHs on leaves: Modelling the impact on air quality ecosystem services provided by urban trees

Urban trees provide important ecosystem services, including air quality improvement. Polycyclic aromatic hydrocarbons (PAHs) are among the most important pollutants in air, due to their elevated concentrations and toxicity. Plants can act as filters of PAHs and as “chemical reactors” for pollutant removal, therefore reducing air concentrations. Here, the first assessment of photo- vs. biodegradation of PAHs on leaves of urban trees is presented. A dynamic air-vegetation-soil model (SoilPlusVeg) was improved to simulate the fate of two representative PAHs with contrasting physico-chemical properties (phenanthrene and benzo[a]pyrene). Simulations were performed for two different environmental scenarios from Italy (Como and Naples), selected for their dissimilar meteorological parameters, plant species and emission levels. The effect of photo- and biodegradation on leaf concentrations and fluxes towards air and soil was investigated comparing deciduous (maple, cornel and hazelnut) and evergreen (holm oak) broadleaf woods. The results showed that biodegradation in the phyllosphere could not be neglected when evaluating the ecosystem services provided by urban trees, as this process contributed significantly to the reductions (up to 25% on average) in PAH leaf concentrations and fluxes to air and soil; however, the reductions revealed ample variations with time (up to more than two orders of magnitude) showing the dependence on meteorological parameters, air compartment structure, as well as type of woods. These findings permitted to improve the ecological realism of the simulations and obtain more accurate results when predicting organic contaminant uptake and release by plant leaves, including potential for food chain transfer and long-range transport.

A surface functionalized with per-(6-amino-6-deoxy)-β-cyclodextrin for potential organic pollutant removal from water

In this work, we present a solid silicon substrate functionalized with modified β-cyclodextrin monolayers as an optimal surface for organic contaminant uptake. The inclusion and capture of three potential pollutants, 4-chlorophenoxyacetic acid, 4-aminobenzoic acid and phenylethylamine, were studied. 1H-NMR and ROESY studies revealed the complete inclusion and details of the conformational orientation of the three guests in the per-(6-amino-6-deoxy)-β-cyclodextrin matrix, forming three new inclusion complexes that have not yet been reported. Capture assays for the guests were carried out by immersing the substrates in an aqueous pollutant solution and by measuring the UV–vis spectra. This substrate showed a high sorption capacity at equilibrium, between 2.5 × 10−5 and 6.0 × 10−5 mmol/substrate, for the studied pollutants. In addition, this surface can be reused four times with an efficiency equal to the initial use. Therefore, it could be a versatile platform that could be applied for the capture of other organic pollutants from water.

Characterization of Biofilm Formed by Phenanthrene-Degrading Bacteria on Rice Root Surfaces for Reduction of PAH Contamination in Rice.

One effective method in to reduce the uptake of organic contaminants by plants is the development of a root barrier. In this study, the characterization of biofilm structure and function by phenanthrene-degrading Pseudomonas sp. JM2-gfp on rice root surfaces were carried out. Our results showed that root surfaces from three rice species, namely Liaojing401, Koshihikari, and Zhenzhuhong all present hydrophobicity and a high initial adhesion of strain JM2-gfp. Matured robust biofilm formation occurred at 48 h on the root surfaces. The biofilm exhibited cell dense aggregates and biomass embedded in the extracellular polymeric substance (EPS) matrix. EPS composition results showed that the proteins, carbohydrates, lipids and nucleic acids are produced in the biofilm, while the content varied with rice species. Under the initial concentration of phenanthrene 50 mg·L−1, the residual phenanthrene in plant roots from ‘Zhengzhuhong’, ‘Koshihikari’ and ‘Liaojing401’ with biofilm mediated were significantly decreased by 71.9%, 69.3% and 58.7%, respectively, compared to those without biofilm groups after 10 days of exposure. Thus, the biofilm colonized on roots plays an important role of degradation in order to reduce the level of phenanthrene uptake of plants. Thereby, the present work provides significant new insights into lowering the environmental risks of polycyclic aromatic hydrocarbons (PAHs) in crop products from contaminated agriculture soils.

Prediction of organic contaminant uptake by plants: Modified partition-limited model based on a sequential ultrasonic extraction procedure

Predicting the translocation of organic contaminants to plants is crucial to ensure the quality of agricultural goods and assess the risk of human exposure through the food web. In this study, the performance of a modified plant uptake model was evaluated considering a number of chemicals, such as polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs) and polybrominated diphenyl ethers (PBDEs), with a range of physicochemical properties; different plant species (Ipomoea aquatica Forsk (swamp morning glory), Chrysanthemum coronarium L. (crown daisy), Zea mays L. (corn), Brassica rapa pekinensis (Chinese cabbage), Cucurbita moschata (pumpkin), Raphanus sativus L. (radish), Spinacia oleracea L. (spinach) and Capsicum annuum L. (pepper)); and different types of soil (paddy soil, laterite soil and black soil). The biases of predictions from a previously used partition-limited model were −76.4% to −99.9% relative to the measured concentrations. An overall transmission factor (αtf=0.39), calculated from a linear regression of the measured bioavailable fraction (Cbio) and the total concentration in plants, was considered a crucial modification and was included in the modified model. Cbio was found to better represent the chemical content available in soil for root uptake. The results from this study improve the accuracy of predictions for vegetation-uptake assessments by modifying the partition-limited model and then validating the modified model using comparisons between predicted data and measured values. The accuracy of the concentrations of organic contaminants in plants improved: when using the modified model, 89.5% of the predictions were within 40% of the actual value. The average bias was limited to 1.5%–30.5%. The model showed great potential to predict plant uptake using the bioavailable fraction concentration in soil.

Adsorption of phenanthrene by earthworms - A pathway for understanding the fate of hydrophobic organic contaminants in soil-earthworm systems

The fate of hydrophobic organic contaminants (HOCs) in soil-earthworm systems is an important foundation for soil pollution risk assessment and pollution control. Equilibrium partitioning is considered to be the main mechanism by which HOCs enter earthworms and, as such, a mechanistic model has been developed to estimate the earthworm-water partition coefficients (Kw-w). In the present study, the adsorption of phenanthrene (PHE) by earthworm tissue was investigated to evaluate the validity of the mechanistic models. Results revealed that Kw-w derived from the mechanistic model (346.90) was lower than that derived from the sorption experiments (410.76), indicating that apart from lipid fractions, other components in earthworms, such as protein fractions, might also play an important role in the adsorption of HOCs by earthworm. Besides, the difference between the mechanistic model for earthworm and partition-limited model used for plants are few, indicating that uptake and accumulation mechanisms of HOCs by earthworms and plants are highly consistent internally and are, essentially actually identical. It is also suggested that environmental fate of HOCs in soil-soil biota systems is dominated by their high hydrophobicity. Based on these conclusions, an improved mechanistic model for predicting the uptake of organic contaminants by earthworms has been proposed, which needs to be further evaluated. Furthermore, the feasibility of using vermiaccumulation in vermiremediation of soil contaminated by HOCs was discussed.The adsorption of PHE by earthworm sub-organism fractions (pre-clitellum, clitellum and post-clitellum) and tissue fractions (body wall and gut) were also investigated to interpret the distribution pattern of HOCs in earthworms. At the sub-organism level, the adsorption capacity of PHE by different regions of the earthworm followed the order: post-clitellum > clitellum > pre-clitellum, meaning the distribution of PHE along the earthworm contributes not only to their chemical composition but also to the life activity of earthworms such as circular system. At the tissue level, the gut showed greater affinity with PHE than that of the body wall indicating that the distribution of PHE is mainly due to chemical components at the tissue levels. These results might provide additional understanding of the fate of HOCs in soil-earthworm systems.

Effect of soil biochar concentration on the mitigation of emerging organic contaminant uptake in lettuce

Although crop uptake of emerging organic contaminants (EOC) from irrigation water and soils has been previously reported, successful mitigation strategies have not yet been established. In this study, soil was amended with a wood-based biochar (BC) at two rates (0, 2.5 and 5% w/w) to evaluate the effect on mitigation of EOC uptake (i.e. bisphenol A, caffeine, carbamazepine, clofibric acid, furosemide, ibuprofen, methyl dihydrojasmonate, tris(2-chloroethyl)phosphate, triclosan, and tonalide) in lettuce (Lactuca sativa L.). After 28 days of irrigation with water containing EOCs at 15μgL−1, the average EOC concentration in roots and leaves decreased by 20–76% in biochar amended soil relative to non BC-amended soil. In addition, the enantiomeric fractions (EF) of ibuprofen (IBU) in biochar amended soils (EF=0.58) and unamended soils (EF=0.76) suggest that the IBU sorbed fraction in BC is more recalcitrant to its biodegradation.

Evaluation of Exposure Metrics for Effect Assessment of Soil Invertebrates

Risk and hazard assessments for the soil environment are performed on the basis of the total content of a contaminant in the dry bulk soil. Presently, scientific evidence is emerging and indicating that pore water may be a more relevant exposure medium for uptake of chemicals by biota and plants in soil. To deduce the degree to which pore water concentrations are indeed a better metrics for quantifying uptake of organic chemicals by terrestrial biota (mostly invertebrates), a literature search was performed and the available evidence in favor of any metrics was gathered in the context of a mandate of the European Food Safety Authority. It is concluded that knowledge on uptake routes of contaminants by soil invertebrates is far from complete. Overall it is clear that uptake of organic contaminants depends on species, soil type, and the chemical properties. The mode of exposure of soil invertebrates is determined by the way animals are in contact with their local environment. Morphology, physiology, and behavior are important factors in this respect, as is the mode of uptake of food, water, and oxygen. The contribution of oral uptake may vary within a specific taxon but for soil organisms in close contact with the soil solution, pore water–mediated uptake is in general the dominant pathway and it is commonly modified by soil specific ageing and speciation, and by specific factors of the organisms, such as nutrition status. Residual uptake appears to be the most important uptake route following pore water–mediated uptake. It is likely that in this case, too, pore water is involved as carrier in or at the surface of the soil in which the chemicals are dissolved. Intraspecies (especially between different life stages) and interspecies variances (e.g., size and ecological preferences) will most likely modify the actual contribution of potential exposure pathways, and a distinction must be made between hard-bodied and soft-bodied organisms. Hard-bodied organisms rely for uptake of oxygen and water on specialized organs, whereas water (pore water) and oxygen are mainly taken up via the skin in soft-bodied organisms. Hard-bodied animals are nevertheless in contact with pore water, as shown for spiders, woodlice, and collembolans. Uptake of nutrients and chemicals is possible for all invertebrates via their food, and this may be an important route in case of food sources in which high concentrations of chemicals are present. The assimilation efficiency will however depend on species-specific properties of the digestive tract and no general conclusions are to be generated in this respect.

Partitioning of Phenanthrene by Root Cell Walls and Cell Wall Fractions of Wheat (Triticum aestivum L.)

Plant cells have been reported to play an important role in the uptake of organic contaminants. This study was undertaken to provide an insight into the role of the root cell walls and their subfractions on sorption of phenanthrene to roots of wheat (Triticum aestivum L.). Root cell walls were isolated and further sequentially fractioned by removing pectin, hemicellulose one, and hemicellulose two. They were characterized by elemental analysis, Fourier transform infrared spectroscopy, and solid-state (13)C NMR. Root cell walls had a greater proportion of aromatic carbon and exhibited a lower polarity than the bulk roots. There was a stepwise increase in aromatic carbon content and a decrease in polarity following the sequential fractionation. The sorption affinity of phenanthrene increased gradually following the sequential extraction of root cells. A significant positive correlation between the sorption affinity K(OC) values and the aromatic carbon contents (r(2) = 0.896, p < 0.01) and a negative correlation between the sorption affinity K(OC) values and polarity ((O + N)/C) of root cell fractions (r(2) = 0.920, p < 0.01) were obtained. Improved modeling was achieved for phenanthrene sorption by involving the contribution of root cell walls as a source of root carbohydrates instead of using root lipids alone, which further confirms the significant contribution of root cell walls to phenanthrene sorption on wheat roots. The results provide evidence for the importance of the root cell walls in the partitioning of phenanthrene by plant roots.

PHYLOGENETIC VARIATION IN THE TOLERANCE AND UPTAKE OF ORGANIC CONTAMINANTS

An investigation into the phylogenetic variation of plant tolerance and the root and shoot uptake of organic contaminants was undertaken. The aim was to determine if particular families or genera were tolerant of, or accumulated organic pollutants. Data were collected from sixty-nine studies. The variation between experiments was accounted for using a residual maximum likelihood analysis to approximate means for individual taxa. A nested ANOVA was subsequently used to determine differences at a number of differing phylogenetic levels. Significant differences were observed at a number of phylogenetic levels for the tolerance to TPH, the root concentration factor and the shoot concentration factor. There was no correlation between the uptake of organic pollutants and that of heavy metals. The data indicate that plant phylogeny is an important influence on both the plant tolerance and uptake of organic pollutants. If this study can be expanded, such information can be used when designing plantings for phytoremediation or risk reduction during the restoration of contaminated sites.

Concentration Effects on Competitive Sorption of Trichloroethylene and Tetrachloroethylene to the Roots of Typha latifolia: Implications for Phytomonitoring

Uptake of organic contaminants by plant roots consists of two consecutive steps: sorption to plant roots and entrance into root xylem tissues through epidermal and endodermic membranes. Most research pertaining to phytoremediation assumed that sorption to plant roots is linear and non-competitive. A growing body of evidence, however, is suggesting that sorption to plant roots is nonlinear and competitive. The objective of this study was to examine the concentration effects of chemical constituents on the competitive sorption of trichloroethylene (TCE) and tetrachloroethylene (PCE) to the roots of Typha latifolia. Competitive sorption was clearly demonstrated by the reduced sorption of TCE and PCE in bi-solute systems than in single-solute systems. Concentration is an important factor affecting the extent of competition. In bi-solute systems, the PCE/TCE ratio on root surface approximately reflected the contaminant footprints in solution. The result was attributed to limited high energetically favorable sorption sites on the root surface and similar sorption mechanisms of TCE and PCE. The results hold significant importance for the application of phytomonitoring of organic contaminant mixtures.

Phenanthrene uptake by Medicago sativa L. under the influence of an arbuscular mycorrhizal fungus

Phenanthrene uptake by Medicago sativa L. was investigated under the influence of an arbuscular mycorrhizal fungus. Inoculation of lucerne with the arbuscular mycorrhizal fungus Glomus etunicatum L. resulted in higher phenanthrene accumulation in the roots and lower accumulation in the shoots compared to non-mycorrhizal controls. Studies on sorption and desorption of phenanthrene by roots and characterization of heterogeneity of mycorrhizal and non-mycorrhizal roots using solid-state 13C nuclear magnetic resonance spectroscopy ( 13C NMR) demonstrated that increased aromatic components due to mycorrhizal inoculation resulted in enhanced phenanthrene uptake by the roots but lower translocation to the shoots. Direct visualization using two-photon excitation microscopy (TPEM) revealed higher phenanthrene accumulation in epidermal cells of roots and lower transport into the root interior and stem in mycorrhizal plants than in non-mycorrhizal controls. These results provide some insight into the mechanisms by which arbuscular mycorrhizal inoculation may influence the uptake of organic contaminants by plants.

Role of the Extractable Lipids and Polymeric Lipids in Sorption of Organic Contaminants onto Plant Cuticles

The distinct role of extractable and polymeric lipids in plant cuticle, precursors of SOM, has received scarce attention to elucidate plant uptake and soil affinity with organic contaminants. Sorption of naphthalene and 1-naphthol to fruit cuticular fractions isolated from two species were investigated. The polarity index, physical conformation, and glass transition temperature (Tg) of these cuticular fractions were characterized by elemental analysis, Fourier transform infrared spectroscopy, and differential scanning calorimetry, respectively. Cutin, a polymeric lipid, is the major sorption medium of the cuticle due to its large mass fraction and liquid-like nature (Tg approximately -30 degrees C). Sorption of cutin is suppressed by the extractable lipids (wax, Tg approximately 44 degrees C) acting as an antiplasticizer (enhance cutin's Tg) over nonpolar contributor. Whereas polysaccharide, as a plasticizer (lower Tg value) and polar contributor, regulates affinity of polymeric lipids (cutin and cutan). The contribution of cutin to sorption by bulk cuticle overshadows the role of waxes, and the sorption capability (K(oc)) of cutin overwhelms the octanol-water partition coefficient (K(ow)). Therefore, uptake of organic contaminants by these plants would be seriously under-predicted by their extractable lipid content and compound's K(ow) values. Along with the observed linear relationships of K(oc) with cutin content in these cuticular fractions, we suggest for the first time that the depolymerizable lipid fraction (cutin) is required to accurately predict plant accumulation of organic contaminants.

Using Semi-Permeable Membrane Devices and Stable Nitrogen Isotopes to Detect Anthropogenic Influences on the Truckee River, USA

Stable nitrogen isotopes (δ15N) and semipermeable membrane devices (SPMDs) were used together to provide evidence of potential anthropogenic connections to aquatic organisms in the Truckee River, which flows through the Reno/Sparks metropolitan area in Nevada. Crayfish, snail, and periphyton δ15N values, and SPMD toxicity data collected during high and low flow periods at seven primary sites on the river were used with water quality and flow data for the assessment. All biota showed an increase of δ15N on both dates at sites downstream of inflows of a water-quality impaired tributary and urban drain relative to upstream. In addition, most of the lowest δ15N values on each date occurred at the most downstream site on the river. SPMDs sample lipophilic organic contaminants and can be used to assess organic contaminant toxicity to aquatic organisms because they use a membrane that mimics organic contaminant uptake by fish. In this study, results from a fluoroscan test [pyrene index (PI)] of SPMD extracts that responds to higher molecular weight polycyclic aromatic hydrocarbons (PAHs) showed patterns similar to stable isotope data, although observed peaks in PI values occurred in the urban area upstream of where peak δ15N values occurred. The CYP1A biomarker test, which responds to PAHs, certain polychlorinated biphenyls (PCBs), and organochlorines, showed peak toxic equivalents (TEQ) values farther downstream of the urban area. Thus, it is likely that PAHs were contributing to toxicity in the urban area, whereas other nonurban sources of organic carbon may have been present farther downstream. The combined use of stable isotope measurements and SPMDs provided a means of simultaneously examining whether aquatic biota are incorporating constituents from potential food sources (via stable isotopes) or exposure through water (via SPMDs).

Improved Approaches for Modeling the Sorption of Phenanthrene by a Range of Plant Species

Equilibrium sorption of phenanthrene and its relationship with plant lipid contents were investigated using roots and shoots of alfalfa, ryegrass, tomato, potato, carrot, cucumber, zucchini, and pumpkin. Lipid extractions using chloroform and hexane were compared, and the influence of dechlorophyllization on lipid determinations was evaluated. The sorption isotherms were close to linear (R2 > 0.923, P < 0.05) and the plant-water partition coefficients (K(pl)) of phenanthrene obtained from the isotherms exhibited significant and positive correlations with plantlipid contents (R2 > 0.664, P < 0.05). The correlations were more significant (R2 > 0.906, P < 0.001) when dechlorophyllization was included in the lipid extraction. The measured sorption was higher than that estimated using the octanol-water partition coefficient (K(ow)) but was very close to the estimate using the triolein-water partition coefficient (K(tw)). This study leads us to conclude that dechlorophyllization is necessary for plant lipid determination and that K(tw) is more accurate as a substitute for the lipid-water partition coefficient (K(lip)) than K(ow). These novel approaches may provide substantial improvements in the application of partition-limited models for the estimation of plant uptake of organic contaminants.