Uptake Rate Constants Research Articles

Passive sampling hydrophilic and hydrophobic bisphenol analogues using hydrophilic-lipophilic balance sorbent-embedded cellulose acetate membrane in surface waters

Bisphenol analogues (BPs) are ubiquitous emerging contaminants in water environments and have wide polarity ranges (1.65 < log Kow < 7.2). Integrated passive sampling strategy rarely contains hydrophilic and hydrophobic organics simultaneously, while the method has good application perspective in monitoring organic contaminants. This work evaluated passive sampling performance for fifteen BPs in a newly developed passive sampler, i.e., hydrophilic-lipophilic balance sorbent-embedded cellulose acetate membrane (HECAM). In the dynamic accumulation experiments, both hydrophilic and hydrophobic BPs (including moderately hydrophilic BPs) well followed first-order kinetic uptake in the HECAMs. The estimated uptake rate constants, elimination rate constants, and equilibrium partition coefficients for BPs ranged from 4.4 L g−1 d−1 to 14.7 L g−1 d−1, 0.22 d−1 to 0.72 d−1, and 3.99 to 4.64, respectively. The kinetic parameters for BPs in HECAM show limited correlations to log Kow values, which the rule differs from traditional passive sampler. In the study of elimination kinetics, three deuterium labeled compounds showed incomplete elimination in HECAM and did not follow first-order isotropic exchange kinetics. Dual sorption mechanisms including both adsorption and partition were found for chemicals in HECAM, which the partitioned part could release to water and the adsorbed part could not easily release to water from HECAM. As a result, performance reference compounds (PRCs) calibration may be inapplicable to HLB sorbent-based passive sampler. The field deployment of HECAM in coastal waters of Guangdong, China resulted in the detection of eleven BPs, which indicated that the waters have been polluted by various BPs. Finally, monitoring strategy of simultaneous passive sampling hydrophobic and hydrophilic organic contaminants in surface waters was recommended.

Decreasing arsenic accumulation but promoting arsenate biotransformation in Microcystis aeruginosa regulated by nano-Fe2O3.

Iron oxide nanoparticles (nano-Fe2O3) widely distribute in waters with low toxicity to aquatic organisms. But it is unclear for nano-Fe2O3 to affect the fate of coexisting arsenic (As) with its bioaccumulation and biotransformation. In this study, we thus mainly investigated arsenate (As(V)) toxicity, uptake kinetics, biotransformation and subcellular distribution in Microcystis aeruginosa influenced by nano-Fe2O3. The results showed that M. aeruginosa was more sensitive to As(V) associated with nano-Fe2O3. Due to the exaggerated increase of efflux rate constants of As compared with the uptake rate constants in algal cells affected by different levels of nano-Fe2O3, the As(V) bioconcentration factor decreased with nano-Fe2O3 increasing correspondingly, indicating that As bioaccumulation was diminished by nano-Fe2O3. The decreased As accumulation in M. aeruginosa could be supported by the evidential As(V) sequestration through high adsorption of nano-Fe2O3, which resulted in decreasing free As level for algae uptake in media. Meanwhile, As subcellular distribution was adjusted by nano-Fe2O3 with decreasing in cell walls and rising in cytoplasmic organelles compared with nano-Fe2O3 free. As(V) reduction and methylation were enhanced with increasing nano-Fe2O3, stimulating by its sensitivity to the interaction of nano-Fe2O3 and As(V) as well as the rising level of As in cytoplasmic organelles of this algae. It is confirmed by the higher relative gene expression levels of arsC and arsM in elevated nano-Fe2O3. Accordingly, it is highlighted to be deserved more attention that the changing behavior of As(V) by nano-Fe2O3 that reduce As bioaccumulation and accelerate its biotransformation in algae in As contaminated water.

The uptake and excretion rate of 137Cs from the silver Prussian carp (Carassius gibelio) at different feeding routine

Throughout 2016 - 2021, a series of experimental studies on 137Cs uptake and excretion rate constants for the silver Prussian carp (Carassius gibelio) were conducted in the Chornobyl exclusion zone (ChEZ) under natural conditions. To confirm the metabolic parameters of 137Cs in the silver Prussian carp under strictly controlled conditions at different feed amounts real supporting laboratory experiments have been conducted. The excretion rate of the 137Cs from the silver Prussian carp increased with increasing feed amount from 0.0068 ± 0.0003 day-1 to 0.0085 ± 0.0005 day-1 at water temperatures of 26 °C. The biological half-life of 137Cs activity concentration in fish can be reduced by 2 times by increasing fish growth using clean feeding. The excretion rate of the 137Cs from the silver Prussian carp agreed with data collected in natural conditions in the ChEZ during 2016 - 2020 at different water temperatures.

Tissue-specific accumulation, transformation, and depuration of fipronil in adult crucian carp (Carassius auratus)

Accumulation and biotransformation of pesticides in fish tissues are essential to assess their toxicity and associated human exposure risk. The mechanisms on time-dependent and tissue-specific accumulation and transformation of fipronil in adult fish are limited. An experiment consisting of 25-d uptake of fipronil at two levels (10 and 50 μg/L) and 25-d depuration in adult crucian carp (Carassius auratus) was conducted. Fipronil concentration at 25-d exposure was tissue-specific with the order of liver > kidney > blood > muscle. The uptake rate constant of fipronil in the liver (low exposure group: 2.38 ± 0.27 L/kg/d; high exposure group: 1.10 ± 0.11 L/kg/d) was significantly higher than that in other tissues (p < 0.05), and the lowest in muscle (low exposure group: 0.10 ± 0.01 L/kg/d; high exposure group: 0.16 ± 0.11 L/kg/d). The bioconcentration factors of fipronil in different tissues were 1.04–12.7 L/kg wet weight and 177–4268 L/kg lipid. The tissue–blood distribution coefficients of the liver and kidney were lower than 1 based on lipid normalized concentration but higher than 1 based on wet weight concentration, suggesting fipronil was dispersed into other tissues mainly via blood in the lipid-combination pattern. Fipronil sulfone had 1.2–32 times higher concentration and longer depuration time than fipronil, implying fipronil sulfone was more retender in fish bodies. The estimated daily intake of fipronil via fish muscle consumption at 25-d exposure was 8.5–101 and 27–320 ng/kg bw/d for adults and children, respectively. Overall, the human health risk of fipronil and its metabolites with consumption of the polluted fish cannot be negligible.

Screening of pesticide distributions in foods of animal origin: a matrix-based approach for biotransfer factor modeling of grazing mammals.

Pesticides are detected in a wide array of foods of animal origin, posing a threat to food safety and human health. Here, to facilitate the management of pesticide residues in livestock products, we proposed a screening model for simulating pesticide biotransfer factors (BTFs, ratio of steady-state pesticide concentration between animal tissues and feed) in mammalian bodies. The proposed model was developed based on simple matrix algebra using first-order kinetics. Simulation of over 700 pesticides in common food products derived from cattle and sheep indicated that pesticide biotransfer is a balancing process between uptake efficiency from the gut lumen and the uptake-elimination ratio (ratio of the overall uptake and elimination rate constants) in individual tissues. Furthermore, we parameterized the developed BTF model using the octanol-water partition coefficient. The simulated pesticide BTFs could be categorized into three lipophilicity phases, namely, the lipophilicity-boosting (log KOW < 4), lipophilicity-balancing (4 ≤ log KOW ≤ 8), and lipophilicity-limiting (log KOW > 8) phases, and the simulated general trends of BTFs were consistent with the experimental data. Although the metabolic rate constants of pesticides in mammalian bodies warrant further evaluation, the model proposed here can assist in the risk assessment and regulatory management of pesticide residues in foods of animal origin.

Systematic Underestimation of Pesticide Burden for Invertebrates under Field Conditions: Comparing the Influence of Dietary Uptake and Aquatic Exposure Dynamics.

Pesticides used in agriculture can end up in nearby streams and can have a negative impact on nontarget organisms such as aquatic invertebrates. During registration, bioaccumulation potential is often investigated using laboratory tests only. Recent studies showed that the magnitude of bioaccumulation in the field substantially differs from laboratory conditions. To investigate this discrepancy, we conducted a field bioaccumulation study in a stream known to receive pollutant loadings from agriculture. Our work incorporates measurements of stream pesticide concentrations at high temporal resolution (every 20 min), as well as sediment, leaves, and caged gammarid analyses (every 2-24 h) over several weeks. Of 49 investigated pesticides, 14 were detected in gammarids with highly variable concentrations of up to 140 ± 28 ng/gww. Toxicokinetic modeling using laboratory-derived uptake and depuration rate constants for azoxystrobin, cyprodinil, and fluopyram showed that despite the highly resolved water concentrations measured, the pesticide burden on gammarids remains underestimated by a factor of 1.9 ± 0.1 to 31 ± 3.0, with the highest underestimations occurring after rain events. Including dietary uptake from polluted detritus leaves and sediment in the model explained this underestimation only to a minor proportion. However, suspended solids analyzed during rain events had high pesticide concentrations, and uptake from them could partially explain the underestimation after rain events. Additional comparison between the measured and modeled data showed that the pesticide depuration in gammarids is slower in the field. This observation suggests that several unknown mechanisms may play a role, including lowered enzyme expression and mixture effects. Thus, it is important to conduct such retrospective risk assessments based on field investigations and adapt the registration accordingly.

The Impact of &lt;sup&gt;242&lt;/sup&gt;Pu Speciation on the Bioaccumulation of Plutonium by &lt;i&gt;Babylonia spirata&lt;/i&gt; from Jakarta Bay

The research of bioaccumulation Plutonium of Babylonia spirata from Jakarta Bay using 242Pu radiotracer has been conducted. The aquaria experiments were applied by two oxidation states of Pu speciation with three replications. The experiment was carried out by 2 steps, such as uptake and depuration. The bioavailability of 242Pu in the (III) and (IV) oxidation states from sea has been studied for Babylonia spirata. Biokinetics parameters, such as concentration factors (CFss), uptake rate constants (ku), elimination rate constants (ke), bioconcentration factors (BCF), and biological half-life (tb1/2), were investigated. The dissection is carried out to separate the parts of the gastropod's body so that the target organs for Plutonium contamination can be identified. Each part of the gastropod's body was prepared radiochemically and analyzed using an alpha spectrometer. The research shows that Pu4+ is potentially accumulated in greater value than Pu3+ by B. spirata, in which Pu is more rapidly distributed and retained longer in proboscis and gastrointestinal tract.

Probing the Bioavailability of Dissolved Iron to Marine Eukaryotic Phytoplankton Using In Situ Single Cell Iron Quotas.

We present a new approach for quantifying the bioavailability of dissolved iron (dFe) to oceanic phytoplankton. Bioavailability is defined using an uptake rate constant (kin‐app) computed by combining data on: (a) Fe content of individual in situ phytoplankton cells; (b) concurrently determined seawater dFe concentrations; and (c) growth rates estimated from the PISCES model. We examined 930 phytoplankton cells, collected between 2002 and 2016 from 45 surface stations during 11 research cruises. This approach is only valid for cells that have upregulated their high‐affinity Fe uptake system, so data were screened, yielding 560 single cell k in‐app values from 31 low‐Fe stations. We normalized k in‐app to cell surface area (S.A.) to account for cell‐size differences.The resulting bioavailability proxy (k in‐app/S.A.) varies among cells, but all values are within bioavailability limits predicted from defined Fe complexes. In situ dFe bioavailability is higher than model Fe‐siderophore complexes and often approaches that of highly available inorganic Fe′. Station averaged k in‐app/S.A. are also variable but show no systematic changes across location, temperature, dFe, and phytoplankton taxa. Given the relative consistency of k in‐app/S.A. among stations (ca. five‐fold variation), we computed a grand‐averaged dFe availability, which upon normalization to cell carbon (C) yields k in‐app/C of 42,200 ± 11,000 L mol C−1 d−1. We utilize k in‐app/C to calculate dFe uptake rates and residence times in low Fe oceanic regions. Finally, we demonstrate the applicability of k in‐app/C for constraining Fe uptake rates in earth system models, such as those predicting climate mediated changes in net primary production in the Fe‐limited Equatorial Pacific.

Measuring SPECT myocardial blood flow at the University of Ottawa Heart Institute

The introduction of new cardiac SPECT cameras has made it practical to do dynamic SPECT imaging and opened the door to performing myocardial blood flow (MBF) imaging with SPECT. In this paper, we describe in detail our approach to dynamic SPECT MBF imaging using a multi-pinhole cardiac SPECT camera and commercially available kinetic analysis software. We use a 1-day rest/stress protocol with 370 MBq injected at rest and 1,000 MBq at stress with a 1- to 2-hour interval between rest and stress imaging. The tracer is injected mechanically over 30 seconds using a syringe pump. Projection data are acquired in listmode for a duration of 11 minutes and then reframed into a dynamic series. Each image is reconstructed independently using vendor-supplied software. The dynamic images are corrected for residual activity and manually corrected for motion using rigid-body translation. The uptake rate constant, K1, is calculated using a 1-tissue-compartment kinetic model and converted to MBF using a previously determined extraction fraction correction.

Measuring Metal Uptake and Loss in Individual Organisms: A Novel Double Stable Isotope Method and its Application in Explaining Body Size Effects on Cadmium Concentration in Mussels.

Interindividual variabilities in metal bioaccumulation confound our interpretation of the biomonitoring data. Measuring metal toxicokinetics in organism "individuals" may provide insights into the processes underlying the variabilities. Therefore, we developed a double stable isotope method that can simultaneously measure uptake and elimination of metals in individual organisms and thus the distribution of the toxicokinetic parameters. Specifically, we exposed organisms to both isotopes (113Cd and 114Cd; Cd = cadmium) during the first stage and to only one isotope (114Cd) during the second stage. Metal uptake and elimination rate constants (i.e., ku and ke) were simultaneously estimated from the content of the two isotopes measured in each organism at the end of the second stage. We applied the method to investigate the interindividual variability in Cd concentrations caused by body size in two marine mussel species. Cd concentrations are higher in larger Xenostrobus atratus but lower in smaller Perna viridis. Size-dependent Cd uptake is found to be responsible for size effects on Cd concentrations in the mussels and the interspecies differences in the relationship between Cd concentration and body size. Specifically, Cd ku increases with size in X. atratus (0.057-0.297 L g-1 d-1) but decreases with size in P. viridis (0.155-0.351 L g-1 d-1). In contrast, Cd ke is not influenced by body size (X. atratus: 0.002-0.060 d-1; P. viridis: 0.008-0.060 d-1). Overall, we extended the applicability of the stable isotope methods to measure metal toxicokinetics in "individual" organisms, providing a readily available tool for investigating problems related to metal bioaccumulation.

Dynamic interaction processes of rare earth metal mixtures in terrestrial organisms interpreted by toxicokinetic and toxicodynamic model

Despite the progress in explanation of mixture toxicity of rare earth elements (REEs), a large knowledge gap still exists in interpreting their mixed effects from a dynamic perspective. Here, we investigated the effects of La-Ce mixtures in Enchytraeus crypticus at different exposure times. The single and mixture toxicity of La and Ce increased with time, as reflected by the reduced LC50/MT50 values. With concentration addition as the reference model, the interactions between La and Ce were quantified by MIXTOX modelling tool, showing a time-dependent pattern with antagonistic effect after 1 and 2 d but additive effects afterwards. The dynamic accumulation and toxicity of La/Ce in organisms exposed to REE mixtures was fitted using a process-based toxicokinetic and toxicodynamic (TK-TD) model to unravel how the elements interacted. Generally, the estimated uptake, elimination, and damage rate constants of La/Ce declined with increasing level of each other, suggesting inhibited uptake and subsequently reduced toxicity of La/Ce due to competition effect. The interplay of La and Ce in TK and TD processes seemed responsible for the observed antagonism. Our study showed that mixture toxicity and interaction of REEs are time-dependent processes and application of TK-TD model may provide more insight into this dynamic effect.

Tissue-specific accumulation, elimination, and toxicokinetics of illicit drugs in adult zebrafish (Danio rerio)

The abuse of illicit drugs has led to their extensive detection worldwide and subsequently exerted adverse effects upon aquatic organisms and ecosystem. However, less attention has been paid to the uptake, biotransformation, internal distribution, and toxicokinetic processes in the exposed organisms. In this study, zebrafish (Danio rerio) was exposed to methamphetamine (METH) and ketamine (KET) at three different concentrations in a semi-static exposure system. METH and KET, together with their metabolites, amphetamine (AMP) and norketamine (NK), were consistently detected in zebrafish. Over 14-day exposure, the relative magnitude of mean concentrations of illicit drugs in zebrafish generally followed the order of brain > liver > intestine > ovary > muscle. The uptake rate constants (Ku) of METH and KET were in the range of 0.590–1.38 × 103 L/(kg·d), the elimination rate constants (Ke) were in the range of 0.18–6.98 1/d, and the half-lives were in the range of 0.18–6.98 d, respectively. METH and KET demonstrated relatively rapid uptake and elimination kinetics and short half-lives, and concentrations in organs were driven by external concentrations. Illicit drugs were not persistent within zebrafish organs when there were no substantial external contaminant sources. The observed values of bioconcentration factor (BCFo, L/kg) and kinetically-derived bioconcentration factor (BCFk, L/kg) were at the similar level. The ability of different zebrafish organs accumulating target chemicals from the aquatic environment was different, and brain was the target organ of the test illicit drugs.

Biodynamics and adverse effects of CuO nanoparticles and CuCl2 in the oligochaete T. tubifex: Cu form influence biodynamics in water, but not sediment

The use of copper oxide (CuO) NPs results in the release of these particles into the aquatic environment. Here, the particles settle out and accumulate in the sediment. However, little is known about the biodynamics of sediment-associated NPs in benthic organisms. We compared the toxicity and biodynamics of CuO NPs (7 nm) and dissolved Cu (CuCl2) in the sediment-dwelling oligochaete, Tubifex tubifex, to gain insights into the relative importance of metal form (CuCl2 vs CuO NPs) and exposure route (water vs sediment). Isotopically enriched 65Cu was used as a tracer to distinguish background from newly accumulated 65Cu in worms. For each exposure route, we conducted three experiments: one uptake, one elimination, and one longer-term net accumulation experiment to parameterize uptake and elimination of 65CuCl2 and 65CuO NPs in T. tubifex. 65Cu accumulation was detected for both 65CuCl2 and 65CuO NPs regardless of whether T. tubifex were exposed in sediment- or water-only setups. Water exposures to 65CuCl2 resulted in tail trauma whereas limited effects were seen for sediment exposures or exposures to 65CuO NPs via either exposure route. Uptake rate constants and accumulation of 65Cu in T. tubifex were higher following 65CuCl2 exposure than 65CuO NPs, in water, but not in sediment. Thus, the relative importance of exposure route and Cu form for uptake dynamics is not straightforward suggesting that findings on bioaccumulation and toxicity in water exposures cannot be directly extrapolated to sediment.

Calibration of silicone for passive sampling of semivolatile organic contaminants in indoor air

Semivolatile organic compounds (SVOCs) are mostly man-made chemicals that distribute between the gas and solid phase in the environment. Many of them could pose harm to people and therefore it is important to know their concentrations in the indoor environment to evaluate the related risks. Inhalation exposure can be assessed using passive sampling. In this study, we employed silicone elastomer as a passive sampler for monitoring gaseous polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and polybrominated diphenyl ethers (PBDEs) in indoor air. We performed a sampler calibration study in which samplers consisting of 0.5 mm thick silicone sheets with a total surface area of 300 cm2 were exposed to indoor air in a university lecture theatre for up to 56 days. Uptake kinetics of SVOCs was studied by collecting 2 samplers every week. The results were used to develop a model based on mass transfer theory that can be used to estimate the air sampling rate RS as a function of compound’s molecular volume. We examined release kinetics of performance reference compounds that covered a broad range of silicone-air partition coefficient (log KSA 5.95–9.49) and investigated a hypothesis of isotropic exchange kinetics, i.e. equality of rate constants for uptake and release, of SVOCs. PCBs and OCPs concentration in air calculated from contaminant amounts accumulated in passive samplers were in good agreement with those determined by active sampling running simultaneously during the entire study. The use of performance reference compounds is suitable for in situ passive sampler calibration.

Organ-Specific Accumulation and Toxicokinetics of Ephedrine in Adult Zebrafish (Danio rerio)

Ephedrine (EPH) is an alkaloid commonly used to relieve nasal congestion caused by colds, allergic rhinitis, rhinitis, and sinusitis, and to control bronchial asthma. It is also be used as a raw material in the manufacture of methamphetamine. Although the distribution of EPH in surface waters has been widely studied, its uptake, internal distribution, and toxicokinetic processing in exposed organisms have not been well investigated. In this study, we investigated the uptake, disposition, and toxicokinetics of EPH in zebrafish (Danio rerio) in a semi-static exposure system. EPH was consistently detected in zebrafish biological samples, with the highest concentrations of 84.97 ng·g-1 detected in the brain tissue of fish in the high treatment group. Over the 14-d exposure period, the relative abundance of mean concentrations of EPH in biological samples generally followed the order of brain > ovary > liver > intestine > muscle. The uptake rate constants (Ku), elimination rate constants (Ke), and half-lives of EPH in the biological tissues were in the ranges 0.23-570.31 L·(kg·d)-1, 1.22-6.11 d-1, and 0.12-0.57 d, respectively. The observed bioconcentration factor (BCFo) and kinetically-derived bioconcentration factor (BCFk) were similar, ranging 0.24-337.33 L·kg-1 and 0.13-316.43 L·kg-1, respectively. These results are helpful for understanding the behavior of psychoactive substances in aquatic organisms and have directive significance for studying their toxicity and ecological risks to aquatic organisms.

Toxicokinetics of silver nanoparticles in the mealworm Tenebrio molitor exposed via soil or food.

Silver nanoparticles (AgNPs) may reach the soil compartment via sewage sludge or nanoagrochemical applications. Understanding how NPs interact with biological systems is crucial for an accurate hazard assessment. Therefore, this study aimed at determining the Ag toxicokinetics in the mealworm Tenebrio molitor, exposed via Lufa 2.2 soil or via food to different Ag forms (uncoated 50nm AgNPs, paraffin coated 3-8nm and PVP-stabilised 60nm, Ag2S NPs 20nm, and ionic Ag). Mealworms were exposed for 21days followed by a 21-day elimination phase (clean soil/food). A one-compartment kinetics model with inert fraction (simulating a storage compartment, where detoxified forms are located) was used to describe Ag accumulation. Fully understanding the uptake route in mealworms is difficult. For that reason several approaches were used, showing that food, soil and pore water all are valid uptake routes, but with different importance. Silver taken up from soil pore water or from soil showed to be related to Ag dissolution in soil pore water. In general, the uptake and elimination rate constants were similar for 3-8nm and 60nm AgNPs and for AgNO3, but significantly different for the uncoated 50nm AgNPs. Upon food exposure, uptake rate constants were similar for 50nm AgNPs and AgNO3, while those for 60nm and 3-8nm AgNPs and for Ag2S NPs also grouped together. NP exposure in soil appeared more difficult to characterize, with different patterns obtained for the different NPs. But it was evident that upon soil or food exposure, particle characteristics highly affected Ag bioavailability and bioaccumulation. Although Ag2S NPs were taken up, their elimination was faster than for other Ag forms, showing the lowest inert fraction. The significantly different elimination rate constants suggest that the mechanism of elimination may not be the same for different AgNPs either.

Biokinetics of 110mAg in Baltic shrimp Palaemon adspersus under elevated pCO2

Ocean acidification impacts the physiology of crustaceans as well as marine calcifiers although most of the hitherto studies has focused on calcifiers. Bioconcentration of elements in a marine animal depends on seawater chemistry and the animal's physiology. Here we studied biokinetics and body distribution of Ag in Baltic shrimp Palaemon adspersus for 47 days by using radiotracer method (110mAg). The bioconcentration of 110mAg was assessed under three pCO2 levels: 370, 795 and 1634 μatm. Uptake rate constants of 110mAg were inversely related to pH (3.1 at pH: 8.1, 4.2 at pH: 7.8 and 4.9 at pH: 7.5). A higher percentage of Ag accumulated in edible parts in the shrimps reared in acidified seawater compared to control. The moulting frequency was significantly higher in acidified seawater conditions compared to the control condition. The results of this study suggest that seawater acidification may partly modify Ag bioconcentration in Baltic shrimp Palaemon adspersus as well as energy-demanding physiological processes like moulting.

Uptake kinetics and accumulation of pesticides in wheat (Triticum aestivum L.): Impact of chemical and plant properties.

Plant uptake is an important process in determining the transfer of pesticides through a food chain. Understanding how crops take up and translocate pesticides is critical in developing powerful models to predict pesticide accumulation in agricultural produce and potential human exposure. Herein, wheat was selected as a model plant species to investigate the uptake and distribution of eleven widely used pesticides in a hydroponic system as a function of time for 144h. The time-dependent uptake kinetics of these pesticides were fitted with a first-order 1-compartment kinetic model. During 144h, flusilazole and difenoconazole, with relative high log Kow (3.87 and 4.36, respectively), displayed higher root uptake rate constants (k). To clarify the role of root lipid content (flip) in plant accumulation of pesticides, we conducted a lipid normalization meta-analysis using data from this and previous studies, and found that the flip value was an important factor in predicting the root concentration factor (RCF) of pesticides. An improved correlation was observed between log RCF and log flipKow (R2=0.748, N=26, P<0.001), compared with the correlation between log RCF and log Kow (R2=0.686, N=26, P<0.001). Furthermore, the hydrophilic pesticides (e.g. log Kow < 2) were found to reach partition equilibrium faster than lipophilic pesticides (e.g. log Kow > 3) during the uptake process. The quasi-equilibrium factor (αpt) was inversely related to log Kow (R2=0.773, N=11, P<0.001) suggesting a hydrophobicity-regulated uptake equilibrium. Findings from this study could facilitate crop-uptake model optimization.

Effect of Nanoparticle Size and Natural Organic Matter Composition on the Bioavailability of Polyvinylpyrrolidone-Coated Platinum Nanoparticles to a Model Freshwater Invertebrate.

The bioavailability of dissolved Pt(IV) and polyvinylpyrrolidone-coated platinum nanoparticles (PtNPs) of five different nominal hydrodynamic diameters (20, 30, 50, 75, and 95 nm) was characterized in laboratory experiments using the model freshwater snail Lymnaea stagnalis. Dissolved Pt(IV) and all nanoparticle sizes were bioavailable to L. stagnalis. Platinum bioavailability, inferred from conditional uptake rate constants, was greater for nanoparticulate than dissolved forms and increased with increasing nanoparticle hydrodynamic diameter. The effect of natural organic matter (NOM) composition on PtNP bioavailability was evaluated using six NOM samples at two nanoparticle sizes (20 and 95 nm). NOM suppressed the bioavailability of 95 nm PtNPs in all cases, and DOM reduced sulfur content exhibited a positive correlation with 95 nm PtNP bioavailability. The bioavailability of 20 nm PtNPs was only suppressed by NOM with a low reduced sulfur content. The physiological elimination of Pt accumulated after dissolved Pt(IV) exposure was slow and constant. In contrast, the elimination of Pt accumulated after PtNP exposures exhibited a triphasic pattern likely involving in vivo PtNP dissolution. This work highlights the importance of PtNP size and interfacial interactions with NOM on Pt bioavailability and suggests that in vivo PtNP transformations could yield unexpectedly higher adverse effects to organisms than dissolved exposure alone.

Temperature-Dependent Toxicokinetics of Phenanthrene in Enchytraeus albidus (Oligochaeta).

Although the toxicokinetics of organic pollutants in soil invertebrates under optimal and constant temperature has been widely reported, their uptake, elimination, and bioaccumulation under suboptimal temperatures, and especially daily fluctuating temperature (FT) regimes have received only little research attention. In this study, the uptake, elimination, and bioaccumulation of phenanthrene (PHE) in Enchytraeus albidus (Oligochaeta) under different constant temperatures, and an FT regime were investigated in a natural soil. In general, the PHE concentrations in worm tissues reached steady state within 14 days at different temperatures. The uptake (ku) and elimination (ke) rate constants and the bioaccumulation increased with increasing temperature likely because of an increased diffusivity of PHE into the worms and an increased metabolic rate. Interestingly, the bioaccumulation factor of PHE in E. albidus showed a positive relationship with temperature because the slope of the ku-temperature relationship was larger than that of the ke-temperature relationship. Further, the uptake and elimination rate constants were larger under the FT regime than at the constant average of the fluctuating temperature. These findings suggest that, climatic conditions, especially daily fluctuating temperatures, should be considered for the assessment of the toxicokinetics of organic pollutants in terrestrial organisms.