Partition coefficients of organic contaminants with carbohydrates

Uptake, translocation, and degradation of spirotetramat in tomato (Lycopersicon esculentum Miller): Impact of the mixed-application with pymetrozine

In this study, we investigated the impact of the mixed-application with pymetrozine on the behavior (i.e., uptake, translocation, and degradation) of spirotetramat in tomatoes under laboratory conditions. Results showed that pymetrozine promoted the uptake of spirotetramat from the nutrition solution after root application. The root concentration factor was 0.290 and 1.566 after spirotetramat single application and mixed-application with pymetrozine, respectively. It had little effect on the degradation of spirotetramat, with the metabolites of M-keto, M-enol, and M-glu in tomato issue (root, stems, and leaves). After foliar treatments, pymetrozine accelerated the translocation of spirotetramat from leaves to stems, with the translocation factor of 0.145 and 0.402 after spirotetramat single application and mixtures with pymetrozine, respectively. Pymetrozine also promoted the degradation of spirotetramat to M-kto and M-enol in leaves. Besides, a partition-limited model was used to describe the distribution processes of spirotetramat in the tomato-water system after root application. It showed that pymetrozine accelerated the distribution balance of spirotetramat in the whole system. Our result indicates that the interaction among pesticides should be considered when studied for the uptake, translocation, and degradation of pesticides in crops.

Organophosphate pesticides sequestered in tissues of a seagrass species - Zostera capensis from a polluted watershed

Organophosphate pesticides (OPPs) are persistent in the environment, but little information is available on their bioaccumulation in seagrass. In this study, the seagrass - Zostera capensis was collected from Swartkops Estuary in South Africa to investigate the bioaccumulation of OPPs from contaminated sediments and the water column. This plant was chosen because it grows abundantly in the estuary's intertidal zone, making it a viable phytoremediator in the urban environment. Extraction was performed by the QuEChERS method followed by GC-MS analysis. The mean concentration of ∑OPPs ranged from 0.01 to 0.03 μg/L for surface water; 6.20-13.35 μg/kg dw for deep-rooted sediments; 18.79-37.75 μg/kg dw for leaf tissues and 12.14-39.80 μg/kg dw for root tissues of Z. capensis. The biota-sediment accumulation factors (BSAFs) were greater than one, indicating the potential for Z. capensis to bioaccumulate and intercept the targeted pesticides. A weak insignificant correlation observed between log BSAFs and log Kow indicates that the bioaccumulation of OPPs in tissues of Z. capensis were not dependent on the Kow. Eight of the selected pesticides had root-leaf translocation factors (TFr-l) greater than 1, indicating that Z. capensis can transport these chemicals from roots to leaves. The results from this study implies that this plant species can clean up OPP contamination in the environment.

Nonlinear sorption of phenols and anilines by organobentonites: Nonlinear partition and space limitation for partitioning

Organobentonites, i.e., bentonites coated with surfactants such as cetyltrimethylammonium (CTAB), are superior and low-cost sorbents for removal of organic contaminants from wastewater. Nonlinear sorption of polar organic compounds such as phenols and anilines by organobentonites were widely observed and interpreted by adsorption mechanism. However, in this study, it was observed that the nonlinear sorption of phenols and anilines by CTAB coated bentonites (CTAB-bentonites) should be attributed to nonlinear partition mechanism with the additional space limitation in CTAB-bentonites for nonlinear partitioning, rather than adsorption mechanism. This nonlinear partition mechanism is supported by that (i) organobentonites is a partition medium, identified by the linear isotherms of polycyclic aromatic hydrocarbons (PAHs) and nitrobenzenes; (ii) sorption coefficients (logK_d), the ratio of adsorbed amount (q_e) to equilibrium concentration (C_e), and Dubinin-Ashtakhov (DA) model fitted sorption capacity (logQ⁰) of organic compounds, by a given CTAB-bentonite, are positively correlated with their octanol-water distribution coefficients (logK_OW) and solubility in octanol (logS_o) respectively; (iii) logK_d and logQ⁰ of a given organic compound by CTAB-bentonites are positively correlated with organic carbon contents (f_oc) of CTAB-bentonites, but not specific surface area. Specific interaction (i.e., hydrogen-bonding interaction), in addition to van der Waals force, is responsible for the nonlinear partitioning of phenols and anilines into CTAB-bentonites, because of the positively linear relationship between DA model fitted sorption affinity (E) and hydrogen-bonding donor parameter (α_m) of organic compounds. These results could help the recognizing of the nonlinear sorption behaviors of organic compounds by organobentonites and promote their environmental applications in wastewater treatment.

Microplastics in aquatic environments: Toxicity to trigger ecological consequences

The prevalence of microplastic debris in aquatic ecosystems as a result of anthropogenic activity has received worldwide attention. Although extensive research has reported ubiquitous and directly adverse effects on organisms, only a few published studies have proposed the long-term ecological consequences. The research in this field still lacks a systematic overview of the toxic effects of microplastics and a coherent understanding of the potential ecological consequences. Here, we draw upon cross-disciplinary scientific research from recent decades to 1) seek to understand the correlation between the responses of organisms to microplastics and the potential ecological disturbances, 2) summarize the potential ecological consequences triggered by microplastics in aquatic environments, and 3) discuss the barriers to the understanding of microplastic toxicology. In this paper, the physiochemical characteristics and dynamic distribution of microplastics were related to the toxicological concerns about microplastic bioavailability and environmental perturbation. The extent of the ecological disturbances depends on how the ecotoxicity of microplastics is transferred and proliferated throughout an aquatic environment. Microplastics are prevalent; they interfere with nutrient productivity and cycling, cause physiological stress in organisms (e.g., behavioral alterations, immune responses, abnormal metabolism, and changes to energy budgets), and threaten the ecosystem composition and stability. By integrating the linkages among the toxicities that range from the erosion of individual species to the defective development of biological communities to the collapse of the ecosystem functioning, this review provides a bottom-up framework for future research to address the mechanisms underlying the toxicity of microplastics in aquatic environments and the substantial ecological consequences.

Iron Plaque Prevents Partitioning of Polycyclic Aromatic Hydrocarbons on Rice (Oryza sativa) Root Surface

Adsorption of polycyclic aromatic hydrocarbons (PAHs) on root surfaces has essential impacts on PAH phytoremediation. An Fe plaque is commonly formed on the root surface of aquatic plants. Therefore, it is worth investigating the impact of the Fe plaque on PAH adsorption on rice root surfaces. Using Bayesian linear water-methanol cosolvent models, we estimated accurate water-biosorbent partition coefficient values for phenanthrene, pyrene, and benzo[a]pyrene between water and rice root biosorbent fractions, including rice root materials with Fe plaque, removed Fe plaque, and removed Fe plaque and lipids. Our results showed that Fe plaque inhibited the adsorption of PAHs on rice root surface; the inhibition impacts increased with hydrophobicity of PAHs. This result highlights the need for considering the impact of Fe plaque on PAH adsorption during phytoremediation. Integr Environ Assess Manag 2020;16:392-399. © 2020 SETAC.

Clothing-Mediated Exposures to Chemicals and Particles

A growing body of evidence identifies clothing as an important mediator of human exposure to chemicals and particles, which may have public health significance. This paper reviews and critically assesses the state of knowledge regarding how clothing, during wear, influences exposure to molecular chemicals, abiotic particles, and biotic particles, including microbes and allergens. The underlying processes that govern the acquisition, retention, and transmission of clothing-associated contaminants and the consequences of these for subsequent exposures are explored. Chemicals of concern have been identified in clothing, including byproducts of their manufacture and chemicals that adhere to clothing during use and care. Analogously, clothing acts as a reservoir for biotic and abiotic particles acquired from occupational and environmental sources. Evidence suggests that while clothing can be protective by acting as a physical or chemical barrier, clothing-mediated exposures can be substantial in certain circumstances and may have adverse health consequences. This complex process is influenced by the type and history of the clothing; the nature of the contaminant; and by wear, care, and storage practices. Future research efforts are warranted to better quantify, predict, and control clothing-related exposures.

Improved prediction of the bioconcentration factors of organic contaminants from soils into plant/crop roots by related physicochemical parameters

There has been an on-going pursuit for relations between the levels of chemicals in plants/crops and the source levels in soil or water in order to address impacts of toxic substances on human health and ecological quality. In this research, we applied the quasi-equilibrium partition model to analyze the relations for nonionic organic contaminants between plant/crop roots and external soil/water media. The model relates the in-situ root concentration factors of chemicals from external water into plant/crop roots (RCF(water)) with the system physicochemical parameters and the chemical quasi-equilibrium states with plant/crop roots (αpt, ≤1). With known RCF(water) values, root lipid contents (flip), and octanol-water Kow's, the chemical-plant αpt values and their ranges of variation at given flipKow could be calculated. Because of the inherent relation between αpt and flipKow, a highly distinct correlation emerges between log RCF(water) and log flipKow (R2 = 0.825; n = 368), with the supporting data drawn from 19 disparate soil-plant studies covering some 6 orders of magnitude in flipKow and 4 orders of magnitude in RCF(water). This correlation performs far better than any relationship previously developed for predicting the contamination levels of pesticides and toxic organic chemicals in plant/crop roots for assessing risks on food safety.

A combined quantitative property-property relationship (QPPR) for estimating packaging-food and solid material-water partition coefficients of organic compounds

The packaging-food partition coefficient (K_pf) is a key parameter to estimate the chemical migration from packaging to food and resulting ingestion exposures. As a particular case of K_pf, the solid material-water partition coefficient (K_mw) is also important in relating the material to the water phase-based skin permeation coefficient to further assess dermal contact exposure to chemicals in solid consumer products. Existing correlations to estimate K_pf or K_mw are applicable for a limited number of chemical-food-packaging or chemical-material combinations without considering the temperature effect. The present study develops a combined quantitative property-property relationship (QPPR) to predict K_pf and K_mw with a wide applicability. We compiled a dataset of 1846 measured K_pf or K_mw for 232 chemicals in 19 consolidated material types. A regression model predicts K_pf or K_mw as a function of chemical's K_ow, food or water's ethanol equivalency, temperature and material type, which shows good fitting performance with R²_adj of 0.93, and has been verified by internal and external validations to be robust, stable and has good predicting ability (R²_ext > 0.80). A generic QPPR is also developed to predict K_pf or K_mw from chemical's K_ow, food or water's ethanol equivalency, and temperature only (R²_adj = 0.90), without the need to assign a specific material type. These QPPRs provide a comprehensive correlation method to estimate K_pf for diverse chemical-food-packaging combinations or to estimate K_mw for materials other than food packaging, which will facilitate high-throughput assessments of consumer exposures to chemicals in food packaging and in other solid materials such as building materials, furniture and toys.

Translocation of polybrominated diphenyl ethers from field-contaminated soils to an edible plant

Polybrominated diphenyl ethers (PBDEs), recognised emerging contaminants, widely exist and persist in the environment. Samples were taken from a heavily contaminated farm in Taiwan located near a factory known to regularly use PBDEs. Sweet potato vines (Ipomoea batatas L., a commonly consumed vegetable in Asia) growing in the surrounding farmlands were found to contain a high concentration of PBDEs of 19.36 ng/g. The possibility of PBDEs translocation into sweet potato vines from soil samples was evaluated. To prevent the PBDEs from air through that factory, the pot experiments were performed in a greenhouse, which showed that the PBDEs concentration of 24 congeners (tri- through deca-BDE) in the sweet potato vine after 14-days cultivation was 29.90 ng/g, 40-times higher than that in the contaminated soil. After another 14-days, the PBDE concentration decreased to 12.30 ng/g as high-brominated PBDEs were transformed to medium- and/or low-brominated PBDEs in the sweet potato vine. The bioconcentration factor (BCF) values exceeded 20.0 for most of the deca-, nona-, and octa-BDEs but BCFs were below 18.9 for the rest of the medium- and low-brominated PBDEs. Our results demonstrate that high-brominated PBDEs can translocate into leafy vegetables from soils, and sweet potato vines tend to accumulate high-brominated PBDEs into their edible parts.

Bioconcentration model for non-ionic, polar, and ionizable organic compounds in amphipod

The present study presents a bioconcentration model for non-ionic, polar, and ionizable organic compounds in amphipod based on first-order kinetics. Uptake rate constant k₁ is modeled as logk1=10.81logKOW + 0.15 (root mean square error [RMSE] = 0.52). Biotransformation rate constant k_M is estimated using an existing polyparameter linear free energy relationship model. Respiratory elimination k₂ is calculated as modeled k₁ over theoretical biota-water partition coefficient K_biow considering the contributions of lipid, protein, carbohydrate, and water. With negligible contributions of growth and egestion over a typical amphipod bioconcentration experiment, the bioconcentration factor (BCF) is modeled as k₁ /(k_M + k₂ ) (RMSE = 0.68). The proposed model performs well for non-ionic organic compounds (log K_OW range = 3.3-7.62) within 1 log-unit error margin. Approximately 12% of the BCFs are underpredicted for polar and ionizable compounds. However, >50% of the estimated k₂ values are found to exceed the total depuration rate constants. Analyses suggest that these excessive k₂ values and underpredicted BCFs reflect underestimation in K_biow , which may be improved by incorporating exoskeleton as a relevant partitioning component and refining the membrane-water partitioning model. The immediate needs to build up high-quality experimental k_M values, explore the sorptive role of exoskeleton, and investigate the prevalence of k₂ overestimation in other bioconcentration models are also identified. The resulting BCF model can support, within its limitations, the ecotoxicological and risk assessment of emerging polar and ionizable organic contaminants in aquatic environments and advance the science of invertebrate bioaccumulation. Environ Toxicol Chem 2018;37:1378-1386. © 2018 SETAC.

Quantitative risk assessment of antimicrobials in biosolids applied on agricultural land and potential translocation into food

The use of biosolids as a fertiliser may be an indirect route for contaminants into the food chain. One of the main concerns regarding the spreading of biosolids on agricultural land is the potential uptake of contaminants into plants which may bio-transfer into grazing animals that supply the food chain directly (e.g. meat and milk) and hence are subsequently consumed. The aim of this project was to create a quantitative risk assessment model to estimate the fate and translocation of triclosan (TCS) and triclocarban (TCC) into the feed (grass) and food chain with subsequent human exposure. The model's results indicate that TCS and TCC have low potential to transfer into milk and beef following the ingestion of contaminated grass by dairy cows. Mean estimated TCS and TCC residues in milk and beef show that TCC had the greatest concentration (mean values of 7.77×10^-6mgkg^-1 in milk and 1.36×10^-4mgkg^-1 in beef). Human exposure results show that TCC was greater for milk consumption in infants (1-4years) (mean value 1.14×10^-7mgkg^-1bwd^-1) and for beef consumption by teens (12-17years) (mean value 6.87×10^-8mgkg^-1bwd^-1). Concentrations of TCS and TCC were well below the estimated acceptable daily intake (ADI). Human health risk was estimated by evaluation of the hazard quotient (HQ), which used the NOAEL as a toxicity endpoint, combined with milk and beef human exposure estimates. HQ results show that all values were <0.01 (no existing risk). A sensitivity analysis revealed that the K_ow and initial concentration in biosolids as the parameters of greatest importance (correlation coefficients 0.91 and 0.19, respectively). This highlights the importance of physio-chemical properties of the compounds and their detection in biosolids post wastewater treatment along with their persistence in soil following application. This model is a valuable tool in which to ascertain the potential transfer of contaminants in the environment into animal forage with knock on consequences for exposure through the human food chain.

Leaching of propellant compounds from munition residues may be controlled by sorption to nitrocellulose

Sustainable management of military ranges requires effective assessment of surface mobility and leaching potential of propellant compounds (PCs). Previous studies have focused mostly on PCs' dissolution from fired residues and their sorption to soil components. This work investigated the potential role of nitrocellulose, a major component in propellants, in the binding of PCs to propellant residues. Sorption isotherms of military grade nitrocellulose for dissolved nitroglycerine (NG) or 2,4-dinitrotoluene (2,4-DNT) was measured in batch experiments and were determined to be S_NG=10^2.39(±0.05)C_NG^{0.916(±0.032)} and S_2,4-DNT=10^3.08(±0.01)C_2,4-DNT^{0.668(±0.010)} (S and C in mg/kg_{nitrocellulose} and mg/L_wat, respectively). Solid-to-water partitioning for NG and 2,4-DNT was 100 times greater in propellant residues than in typical military ranges soils. Since nitrocellulose can sorb NG and 2,4-DNT up to 23 and 5% of its mass, respectively, it can slow down, through retarded diffusion, the leaching of PCs from fired residues over the typical composition ranges of common propellants. The slow leaching of PCs from propellant grains in column studies can be better interpreted by considering their sorptive interaction with nitrocellulose in addition to dissolution kinetics. With nitrocellulose as the carrying matrix, residue-bound PCs may migrate farther and persist longer in subsurface environment.

Estimating Grass-Soil Bioconcentration of Munitions Compounds from Molecular Structure

A partitioning-based model is presented to estimate the bioconcentration of five munitions compounds and two munition-like compounds in grasses. The model uses polyparameter linear free energy relationships (pp-LFERs) to estimate the partition coefficients between soil organic carbon and interstitial water and between interstitial water and the plant cuticle, a lipid-like plant component. Inputs for the pp-LFERs are a set of numerical descriptors computed from molecular structure only that characterize the molecular properties that determine the interaction with soil organic carbon, interstitial water, and plant cuticle. The model is validated by predicting concentrations measured in the whole plant during independent uptake experiments with a root-mean-square error (log predicted plant concentration-log observed plant concentration) of 0.429. This highlights the dominant role of partitioning between the exposure medium and the plant cuticle in the bioconcentration of these compounds. The pp-LFERs can be used to assess the environmental risk of munitions compounds and munition-like compounds using only their molecular structure as input.

Converting Carbohydrates to Carbon-Based Photocatalysts for Environmental Treatment

Carbohydrates in biomass can be converted to semiconductive hydrothermal carbonation carbon (HTCC), a material that contains plenty of sp²-hybridization structures. Under solar light illumination, HTCC generates photoexcited electrons, holes, and hydroxyl radicals. These species can be used for photocatalytic treatment such as water disinfection and degradation of organic pollutants. The photocatalytic activity of HTCC can be significantly enhanced by iodine doping. The enhancement mechanism is investigated by density functional theoretical calculations and electrochemical measurements. The iodine dopants twist and optimize the structures of the sp²-hybridization in HTCC, thereby favoring photon-induced excitation. Moreover, the iodine dopants facilitate the charge transfer between different sp²-hybridization structures, thus increasing the conductivity and activity of the HTCC. An added benefit is that the I-doped HTCC exhibits lower cytotoxic effect than the pure HTCC. In addition to monosaccharides (glucose), disaccharides (sucrose), and polysaccharides (starch), we have also transformed crops (e.g., rice), plants (e.g., grass), and even agricultural waste (e.g., straw) and animal waste (e.g., cow dung). The conversion of carbohydrates to HTCC may be considered as a "Trash to Treasure" approach. We believe this discovery will attract a lot of attention from researchers involved in environmental catalysis, waste recycling, and pollution treatment.

Dermal uptake of phthalates from clothing: Comparison of model to human participant results

In this research, we extend a model of transdermal uptake of phthalates to include a layer of clothing. When compared with experimental results, this model better estimates dermal uptake of diethylphthalate and di-n-butylphthalate (DnBP) than a previous model. The model predictions are consistent with the observation that previously exposed clothing can increase dermal uptake over that observed in bare-skin participants for the same exposure air concentrations. The model predicts that dermal uptake from clothing of DnBP is a substantial fraction of total uptake from all sources of exposure. For compounds that have high dermal permeability coefficients, dermal uptake is increased for (i) thinner clothing, (ii) a narrower gap between clothing and skin, and (iii) longer time intervals between laundering and wearing. Enhanced dermal uptake is most pronounced for compounds with clothing-air partition coefficients between 10⁴ and 10⁷ . In the absence of direct measurements of cotton cloth-air partition coefficients, dermal exposure may be predicted using equilibrium data for compounds in equilibrium with cellulose and water, in combination with computational methods of predicting partition coefficients.

Partition uptake of a brominated diphenyl ether by the edible plant root of white radish (Raphanus sativus L.)

Polybrominated diphenyl ethers (PBDEs) are of a class of emerging contaminants. In this study, the accumulation of 4-bromodiphenyl ether (BDE-3) by different parts of a live white radish was investigated. Different cultural media (hydroponics, silica sand, and soil) were used to sustain the radish plant during its uptake and in-plant translocation of BDE-3. The results showed that BDE-3 can be translocated from the roots to the aboveground organs and the accumulated levels of BDE-3 in different parts of the white radish followed the order for the three types of cultivation: fibrous roots > peels > main roots > leaves. The results were analyzed by the aid of the partition-limited model for the plant uptake. The relevant partition coefficients (K_OC and K_d) and uptake parameters of BDE-3 with plant components (K_pt and K_lip) were obtained for analyzing the BDE-3 distribution. The partition-limited model offers a significant insight into the uptakes of BDE-3 by the various components of live white radishes. The types of cultivation affected the total sorption level, translocation factors (TFs), extent to equilibrium (α_pt), and root concentration factors (RCFs).

Predicting Partitioning and Diffusion Properties of Nonpolar Chemicals in Biotic Media and Passive Sampler Phases by GC × GC

The chemical parameters needed to explain and predict bioavailability, biodynamics, and baseline toxicity are not readily available for most nonpolar chemicals detected in the environment. Here, we demonstrate that comprehensive two-dimensional gas chromatography (GC × GC) retention times can be used to predict 26 relevant properties for nonpolar chemicals, specifically: partition coefficients for diverse biotic media and passive sampler phases; aquatic baseline toxicity; and relevant diffusion coefficients. The considered biotic and passive sampler phases include membrane and storage lipids, serum and muscle proteins, carbohydrates, algae, mussels, polydimethylsiloxane, polyethylene, polyoxymethylene, polyacrylate, polyurethane, and semipermeable membrane devices. GC × GC-based chemical property predictions are validated with a compilation of 1038 experimental property data collected from the literature. As an example application, we overlay a map of baseline toxicity to fathead minnows onto the separated analyte signal of a polychlorinated alkanes (chlorinated paraffins) technical mixture that contains 7820 congeners. In a second application, GC × GC-estimated properties are used to parametrize multiphase partitioning models for mammalian tissues and organs. In a third example, we estimate chemical depuration kinetics for mussels. Finally, we illustrate an approach to screen the GC × GC chromatogram for nonpolar chemicals of potentially high concern, defined based on their GC × GC-estimated biopartitioning properties, diffusion properties, and baseline toxicity.

Differential bioavailability of polychlorinated biphenyls associated with environmental particles: Microplastic in comparison to wood, coal and biochar

Microplastic particles are increasingly being discovered in diverse habitats and a host of species are found to ingest them. Since plastics are known to sorb hydrophobic organic contaminants (HOCs) there is a question of what risk of chemical exposure is posed to aquatic biota from microplastic-associated contaminants. We investigate bioavailability of polychlorinated biphenyls (PCBs) from polypropylene microplastic by measuring solid-water distribution coefficients, gut fluid solubilization, and bioaccumulation using sediment invertebrate worms as a test system. Microplastic-associated PCBs are placed in a differential bioavailability framework by comparing the results to several other natural and anthrogenic particles, including wood, coal, and biochar. PCB distribution coefficients for polypropylene were higher than natural organic materials like wood, but in the range of lipids and sediment organic carbon, and smaller than black carbons like coal and biochars. Gut fluid solubilization potential increased in the order: coal < polypropylene < biochar < wood. Interestingly, lower gut fluid solubilization for polypropylene than biochar infers that gut fluid micelles may have solubilized part of the biochar matrix while bioaccessibility from plastic can be limited by the solubilizing potential of gut fluids dependent on the solid to liquid ratio or renewal of fluids in the gut. Biouptake in worms was lower by 76% when PCBs were associated with polypropylene compared to sediment. The presence of microplastics in sediments had an overall impact of reducing bioavailability and transfer of HOCs to sediment-ingesting organisms. Since the vast majority of sediment and suspended particles in the environment are natural organic and inorganic materials, pollutant transfer through particle ingestion will be dominated by these particles and not microplastics. Therefore, these results support the conclusion that in most cases the transfer of organic pollutants to aquatic organisms from microplastic in the diet is likely a small contribution compared to other natural pathways of exposure.

Re-analysis of narcotic critical body residue data using the equilibrium distribution concept and refined partition coefficients

Narcosis occurs as a result of the accumulation of chemicals in the phospholipid membrane. The toxic threshold concentration in the membrane is thought to be relatively constant across different chemicals and species. Hence, estimating chemical concentrations in the membrane is expected to reduce the variability of narcotic critical body residue (CBR) data. In this study, a high quality CBR dataset for three aquatic species reported recently in the literature was evaluated with the internal equilibrium distribution concept. The raw wet-weight-based CBR values were converted to membrane-weight-based CBR values by assuming that the chemical is distributed in storage lipids, membranes, proteins, and water according to the respective equilibrium partition coefficients. Several sets of partition coefficients were compared for this analysis. The results were consistent with the notion that the use of a structural protein instead of serum albumin as a surrogate for the body protein fraction could reduce the variability of CBRs. Partition coefficients predicted by polyparameter linear free energy relationships (PP-LFERs) reduced the variability of CBRs as much as or even more than experimental partition coefficients did. It is suggested that CBR data for chemicals with larger structural diversity and biological species with more distinct compositions are needed to evaluate further the equilibrium distribution concept and the constant membrane threshold hypothesis.

Sorption equilibrium of emerging and traditional organic contaminants in leafy rape, Chinese mustard, lettuce and Chinese cabbage

Emerging and petroleum contaminants could transfer into food chains by plant uptake, potentially causing food security problems. To build a prediction model, the sorption equilibrium and uptake kinetics of toluene, p-xylene, naphthalene, bisphenol A, and 4-bromo-diphenyl ether in some common leafy vegetables including leafy rape, Chinese mustard, lettuce and Chinese cabbage were examined. The kinetic experiments revealed that high sorption rates were observed for these plants that had high lipid contents. For two emerging contaminants with polar functional groups, their resulting isotherms were strongly linear (R(2) = 0.92 to 1.00), indicating that the sorption was dominated by partitioning. Moreover, regression correlation showed that log Klip, the lipid-water partition coefficient, and log Kow, the octanol-water coefficient, for these organic chemicals were strongly linear-related, following the equation: log Klip = 0.894 × log Kow+0.219 (R(2) = 0.953). The correlation equation allows the prediction of the sorption capacity of plant species for an organic compound when the plant composition and the log Kow of the chemical are determined. This improved model containing different organic chemicals with a wide range of log Kow (2.73-4.80) and including emerging contaminants was established, which shows further utilization for predicting the sorption of organic contaminants by plants.

Screening-level models to estimate partition ratios of organic chemicals between polymeric materials, air and water

Polymeric materials flowing through the technosphere are repositories of organic chemicals throughout their life cycle. Equilibrium partition ratios of organic chemicals between these materials and air (KMA) or water (KMW) are required for models of fate and transport, high-throughput exposure assessment and passive sampling. KMA and KMW have been measured for a growing number of chemical/material combinations, but significant data gaps still exist. We assembled a database of 363 KMA and 910 KMW measurements for 446 individual compounds and nearly 40 individual polymers and biopolymers, collected from 29 studies. We used the EPI Suite and ABSOLV software packages to estimate physicochemical properties of the compounds and we employed an empirical correlation based on Trouton's rule to adjust the measured KMA and KMW values to a standard reference temperature of 298 K. Then, we used a thermodynamic triangle with Henry's law constant to calculate a complete set of 1273 KMA and KMW values. Using simple linear regression, we developed a suite of single parameter linear free energy relationship (spLFER) models to estimate KMA from the EPI Suite-estimated octanol-air partition ratio (KOA) and KMW from the EPI Suite-estimated octanol-water (KOW) partition ratio. Similarly, using multiple linear regression, we developed a set of polyparameter linear free energy relationship (ppLFER) models to estimate KMA and KMW from ABSOLV-estimated Abraham solvation parameters. We explored the two LFER approaches to investigate (1) their performance in estimating partition ratios, and (2) uncertainties associated with treating all different polymers as a single "bulk" polymeric material compartment. The models we have developed are suitable for screening assessments of the tendency for organic chemicals to be emitted from materials, and for use in multimedia models of the fate of organic chemicals in the indoor environment. In screening applications we recommend that KMA and KMW be modeled as 0.06 ×KOA and 0.06 ×KOW respectively, with an uncertainty range of a factor of 15.

Mechanistic modelling of toxicokinetic processes within Myriophyllum spicatum

Effects of chemicals are, in most cases, caused by internal concentrations within organisms which rely on uptake and elimination kinetics. These processes might be key components for assessing the effects of time-variable exposure of chemicals which regularly occur in aquatic systems. However, the knowledge of toxicokinetic patterns caused by time-variable exposure is limited, and gaining such information is complex. In this work, a previously developed mechanistic growth model of Myriophyllum spicatum is coupled with a newly developed toxicokinetic part, providing a model that is able to predict uptake and elimination of chemicals, as well as distribution processes between plant compartments (leaves, stems, roots) of M. spicatum. It is shown, that toxicokinetic patterns, at least for most of the investigated chemicals, can be calculated in agreement with experimental observations, by only calibrating two chemical- specific parameters, the cuticular permeability and a plant/water partition coefficient. Through the model-based determination of the cuticular permeabilities of Isoproturon, Iofensulfuron, Fluridone, Imazamox and Penoxsulam, their toxicokinetic pattern can be described with the model approach. For the use of the model for predicting toxicokinetics of other chemicals, where experimental data is not available, equations are presented that are based on the log (P oct/wat) of a chemical and estimate parameters that are necessary to run the model. In general, a method is presented to analyze time-variable exposure of chemicals more in detail without conducting time and labour intensive experiments.

Lipid-water partition coefficients and correlations with uptakes by algae of organic compounds

In view of the scarcity of the lipid-water partition coefficients (Ktw) for organic compounds, the logKtw values for many environmental contaminants were measured using ultra-pure triolein as the model lipid. Classes of compounds studied include alkyl benzenes, halogenated benzenes, short-chain chlorinated hydrocarbons, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and organochlorine pesticides. In addition to logKtw determination, the uptakes of these compounds from water by a dry algal species were measured to evaluate the lipid effect on the algal uptake. The measured logKtw are closely related to their respective logKow (octanol-water), with logKow=1.9 to 6.5. A significant difference is observed between the present and early measured logKtw for compounds with logKow>∼5, which is attributed to the presence and absence of a triolein microemulsion in water affecting the solute partitioning. The observed lipid-normalized algae-water distribution coefficients (logKaw/lipid) are virtually identical to the respective logKtw values, which manifests the dominant lipid-partition effect of the compounds with algae.

Quantitative modelling to estimate the transfer of pharmaceuticals through the food production system

Use of pharmaceuticals in animal production may cause an indirect route of contamination of food products of animal origin. This study aimed to assess, through mathematical modelling, the transfer of pharmaceuticals from contaminated soil, through plant uptake, into the dairy food production chain. The scenarios, model parameters, and values refer to contaminants in emission slurry production, storage time, immission into soil, plant uptake, bioaccumulation in the animal's body, and transfer to meat and milk. Modelling results confirm the possibility of contamination of dairy cow's meat and milk due the ingestion of contaminated feed by the cattle. The estimated concentration of pharmaceutical residues obtained for meat ranged from 0 to 6 ng kg(-1) for oxytetracycline, from 0.011 to 0.181 μg kg(-1) for sulfamethoxazole, and from 4.70 to 11.86 μg kg(-1) for ketoconazole. The estimated concentrations for milk were: zero for oxytetracycline, lower than 40 ng L(-1) for sulfamethoxazole, and from 0.98 to 2.48 μg L(-1) for ketoconazole. Results obtained for the three selected pharmaceuticals indicate a minor risk for human health. This study showed that supply chain modelling could be an effective tool in assessing the indirect contamination of feedstuff and animal products by residues of pharmaceuticals. The model can easily be adjusted to other contaminants and supply chain and, in this way, present a valuable tool to underpin decision making.

A generic emission model to predict release of organic substances from materials in consumer goods

Organic chemicals may be released when consumer goods are used, contributing to environmental and human levels of potentially hazardous chemicals. A generic model was developed to predict emissions of organic chemicals from various materials in consumer products. The model involved three modules, which each predict a key parameter needed to calculate the mass of individual chemicals emitted. Partition coefficients between a material and the surrounding air were predicted using Abraham solvation parameters, diffusion coefficients in materials were calculated using the Piringer equation, and convective mass transfer coefficients were evaluated by applying the Chilton-Colburn analogy. The calculated emission rates from predicted parameters were evaluated and agreed well with literature data. The release of plasticizers from vinyl flooring used in Sweden was calculated to demonstrate the utility of the generic model. The estimated emitted masses of di(2-ethylhexyl)phthalate (DEHP), di-iso-nonylphthalate (DINP), and 1,2-cyclohexanedicarboxylic acid di-iso-nonyl ester (DINCH) in 2012 were 210 kg, 40 kg, and 3.6 kg respectively. Emissions from vinyl flooring were estimated for the period 1990 to 2035 and it was shown that the recent substitution of DEHP with DINP will help to reduce plasticizer emissions. Model calculations for alternative plasticizers revealed that DINCH would yield similar emissions to DINP, whereas use of diethyl hexyl-iso-sorbide or diethyl hexyl adipate would result in higher emissions.

Uptake of oxytetracycline, sulfamethoxazole and ketoconazole from fertilised soils by plants

This study was performed to investigate the potential for a set of two antibiotics and one antifungal compound to be taken up from the soil by plants. Plants are used for animal or human consumption, and so the measured concentrations in the plant material will be used to model potential human exposure to these compounds. The uptake by two types of plants (grass and watercress) from two types of soil was studied. The compounds used for these experiments were sulfamethoxazole, oxytetracycline and ketoconazole at concentrations of 5 and 10 mg kg(-1) in the soil. The compounds of interest were extracted out of the plant matrix by applying accelerated solvent extraction. Analyses were carried out by a LC-MS/MS. From the results, it was concluded that the plant materials used for this study were able to take up sulfamethoxazole and ketoconazole when the soil was contaminated with these compounds at a concentration ranging from 5 to 10 mg kg(-1). Sulfamethoxazole was detected in all samples, at levels ranging from 7 to 21 µ kg(-1) for grass and 4 to 7.5 µ kg(-1) for watercress. For ketoconazole, the results showed low absorption. Oxytetracycline was not detected in any sample. A partition-limited model approach was applied for the comparison of experimental and estimated data, and the relationship between physicochemical properties of the compounds and plant uptake was highlighted.

Uptake of natural and synthetic estrogens by maize seedlings

Runoff from manure-fertilized crop fields constitutes a significant source of natural estrogens (e.g., estradiol [17β-E2] and estrone [E1]) and synthetic estrogen mimics (e.g., zeranol [α-ZAL] and zearalanone [ZAN]) in the environment. However, processes such as sorption to and uptake by plants may inhibit the environmental mobility of hormonally active compounds. Sorption to dried root tissue was assessed in batch sorption tests, and resulting sorption isotherms were nonlinear at aqueous concentrations below 0.1 μM and linear above that limit. To evaluate the role of crop plants in the environmental fate of such compounds, we exposed hydroponic solutions containing 2 μM 17β-E2, E1, α-ZAL, or ZAN to maize seedlings. After 22 days of exposure, α-ZAL and ZAN concentrations decreased by more than 96%, and 17β-E2 and E1 were undetectable. The decrease in α-ZAL and ZAN concentrations in maize-exposed solutions was initially slow, but the observed uptake exceeded that predicted by sorption alone within 3 d. All four estrogens were detected in root tissues at concentrations up to 0.19 μmol g(-1), with concentrations peaking after 1-3 days of exposure. Only 17β-E2 and α-ZAL were detected in shoots, and maximum concentrations were measured after 2 days for 17β-E2 (0.02 μmol g(-1)) and 16 days for α-ZAL (0.8 nmol g(-1)). Concentrations measured in root and shoot tissues were 82% or less than those predicted by a partition-limited uptake model, which is attributed to transformation and possibly irreversible binding processes.