pH dependence of the partitioning of triphenyltin and tributyltin between phosphatidylcholine liposomes and water

Bioconcentration of Organotin Cations during Molting Inhibits Heterocypris incongruens Growth

The densely populated North Sea region encompasses catchments of rivers such as Scheldt and Meuse. Herein, agricultural, industrial, and household chemicals are emitted, transported by water, and deposited in sediments, posing ecological risks. Though sediment monitoring is often costly and time-intensive, modeling its toxicity to biota has received little attention. Due to high complexity of interacting variables that induce overall toxicity, monitoring data only sporadically validates current models. Via a range of concepts, we related bio-physicochemical constituents of sediment in Flanders to results from toxicity bioassays performed on the ostracod Heterocypris incongruens. Depending on the water body, we explain up to 90% of the variance in H. incongruens growth. Though variable across Flanders' main water bodies, organotin cations and ammonia dominate the observed toxicity according to toxic unit (TU) assessments. Approximately 10% relates to testing conditions/setups, species variabilities, incoherently documented pollutant concentrations, and/or bio-physicochemical sediment properties. We elucidated the influence of organotin cations and ammonia relative to other metal(oxides) and biocides. Surprisingly, the tributylin cation appeared ∼1000 times more toxic to H. incongruens as compared to "single-substance" bioassays for similar species. We inferred indirect mixture effects between organotin, ammonia, and phosphate. Via chemical speciation calculations, we observed strong physicochemical and biological interactions between phosphate and organotin cations. These interactions enhance bioconcentration and explain the elevated toxicity of organotin cations. Our study aids water managers and policy makers to interpret monitoring data on a mechanistic basis. As sampled sediments differ, future modeling requires more emphasis on characterizing and parametrizing the interactions between bioassay constituents. We envision that this will aid in bridging the gap between testing in the laboratory and field observations.

Liposome-mediated delivery of challenging chemicals to aid environmental assessment of Bioaccumulative (B) and Toxic (T) properties

Standard aquatic toxicity tests of chemicals are often limited by the chemicals’ water solubility. Liposomes have been widely used in the pharmaceutical industry to overcome poor pharmacokinetics and biodistribution. In this work, liposomes were synthesized and used in an ecotoxicological context, as a tool to assure stable dosing of technically challenging chemicals to zooplankton. Three chemicals with distinctly different characteristics were successfully incorporated into the liposomes: Tetrabromobisphenol A (TBBPA, log K_ow 5.9, pK_a1 7.5, pK_a2 8.5), chlorinated paraffin CP-52 (log K_ow 8–12) and perfluorooctanoic acid (PFOA, pK_a 2.8). The size, production yield and stability over time was similar for all blank and chemical-loaded liposomes, except for when the liposomes were loaded with 10 or 100 mg g⁻¹ PFOA. PFOA increased the size and decreased the production yield and stability of the liposomes. Daphnia magna were exposed to blank and chemical-loaded liposomes in 48 hour incubation experiments. A dose-dependent increase in body burden in D. magna and increased immobilization (LD₅₀ = 7.6 ng CPs per individual) was observed. This confirms not only the ingestion of the liposomes but also the successful internalization of chemicals. This study shows that liposomes can be a reliable alternative to aid the study of aquatic toxicity of challenging chemicals.

Uptake and elimination of butyl- and phenyltins by Ceratophyllum demersum L

The widespread occurrence and distribution of organotin compounds (OTCs) in both marine and freshwater ecosystems has aroused considerable concerns in most countries worldwide. In this work, individual kinetics of the elimination of three butyltins and three phenyltins from C. demersum L. were systematically studied for over 240 h in clean water after a 48h period of accumulation. All OTCs were rapidly metabolized to nontoxic inorganic tin by C. demersum L. through stepwise debutylation or dephenylation. In addition to inorganic tin, monobutyltin (MBT) and monophenyltin (MPT) were the primary degradation products of tributyltin (TBT) and triphenyltin (TPT), with small amounts of dibutyltin (DBT) and diphenyltin (DPT), respectively, also being present. The estimated half-life of TPT (240 h) in C. demersum L. was longer than that of TBT (100 h), although the TPT was less hydrophobic. The corresponding degradation mechanisms may be attributed to a cascade of enzymatic reactions of CYP450 enzymes in C. demersum L. The pH played an important role in both plant growth and TBT degradation. Although pH 8.9 was more suitable for C. demersum L. growth, it uptook and metabolized more TBT at pH 5.0, which may be because the cationic species TBT⁺ (at pH 5.0) was metabolized more easily than the neutral hydroxide species TBTOH (at pH 8.9). C. demersum L. may thus be the plant with the most potential for the remediation of OTC-contaminated freshwater environments.

Relation of tributyltin and triphenyltin equilibrium sorption and kinetic accumulation in carp and Ceratophyllum demersum

Comparatively limited knowledge is known about the accumulation processes of tributyltin (TBT) and triphenyltin (TPT) in fish and aquatic plant in the freshwater environment, which has hindered a full understanding of their bioaccumulation potential and ecological risks. In the present study, sorption of TBT and TPT on dead biota of both carp and C. demersum from water via the batch equilibrium technique as well as uptake of them on live biota of both carp and C. demersum from water at a static and a dynamic kinetics tests were investigated, respectively. Both TBT and TPT exhibit a high affinity in carps and C. demersum. And C. demersum has a faster metabolism either for TBT or TPT than carp. The apparent uptake values (C_bio = 1904-8831 μg/kg) or bioconcentration factor (BCF = 3333-44000 L/kg) were one or two orders of magnitude higher than that of estimated by a simple sorption (405-472 μg/kg) or lipid model (74.5-149.6 μg/kg) for carp, indicating the uptake of TBT and TPT did not only depend on lipids but also oxygen ligands or macromolecules such as amino acids and proteins of the living organism. In contrast, the apparent C_bio values (149.1-926.4 μg/kg) of both TBT and TPT were lower than that of estimated by sorption model (1341-1902 μg/kg) for C. demersum, which were due to the rapid metabolic rate of them, especially for TBT. But no relation was observed between TBT and TPT concentrations and lipid contents in C. demersum.

The importance of environmental factors and matrices in the adsorption, desorption, and toxicity of butyltins: a review

Butyltins (BTs) are considered as a group of the most important organometallic compounds in industry and agriculture. Due to their widespread use, large amounts of BTs including tributyltin (TBT), dibutyltin (DBT), and monobutyltin (MBT) have entered into the environment, and subsequently causing detrimental effects on humans and aquatic organisms. This work provides a critical review of recent studies on the adsorption, desorption, bioaccumulation, and toxicity of BTs that can notably influence the distribution of BTs in the environment. Influence of environmental factors (e.g., pH and salinity) and adsorbents in the matrices (e.g., minerals, organic carbons, and quartz) on the adsorption, desorption, and toxicity of BTs is particularly addressed.

Including Bioconcentration Kinetics for the Prioritization and Interpretation of Regulatory Aquatic Toxicity Tests of Highly Hydrophobic Chemicals

Worldwide, regulations of chemicals require short-term toxicity data for evaluating hazards and risks of the chemicals. Current data requirements on the registration of chemicals are primarily based on tonnage and do not yet consider properties of chemicals. For example, short-term ecotoxicity data are required for chemicals with production volume greater than 1 or 10 ton/y according to REACH, without considering chemical properties. Highly hydrophobic chemicals are characterized by low water solubility and slow bioconcentration kinetics, which may hamper the interpretation of short-term toxicity experiments. In this work, internal concentrations of highly hydrophobic chemicals were predicted for standard acute ecotoxicity tests at three trophic levels, algae, invertebrate, and fish. As demonstrated by comparison with maximum aqueous concentrations at water solubility, chemicals with an octanol-water partition coefficient (K_ow) greater than 10⁶ are not expected to reach sufficiently high internal concentrations for exerting effects within the test duration of acute tests with fish and invertebrates, even though they might be intrinsically toxic. This toxicity cutoff was explained by the slow uptake, i.e., by kinetics, not by thermodynamic limitations. Predictions were confirmed by data entries of the OECD's screening information data set (SIDS) (n = 746), apart from a few exceptions concerning mainly organometallic substances and those with inconsistency between water solubility and K_ow. Taking error propagation and model assumptions into account, we thus propose a revision of data requirements for highly hydrophobic chemicals with log K_ow > 7.4: Short-term toxicity tests can be limited to algae that generally have the highest uptake rate constants, whereas the primary focus of the assessment should be on persistence, bioaccumulation, and long-term effects.

When will the TBT go away? Integrating monitoring and modelling to address TBT's delayed disappearance in the Drammensfjord, Norway

Despite a substantial decrease in the use and production of the marine antifouling agent tributyltin (TBT), its continuing presence in harbors remains a serious environmental concern. Herein a case study of TBT's persistence in the Drammensfjord, Norway, is presented. In 2005, severe TBT pollution was measured in the harbor of the Drammensfjord, with an average sediment concentration of 3387 μg kg(-1). To chart natural recovery in the Drammensfjord, an extensive sampling campaign was carried out over six years (2008-2013), quantifying TBT in water, settling particles and sediments. The monitoring campaign found a rapid decrease in sediment TBT concentration in the most contaminated areas, as well as a decrease in TBT entering the harbor via rivers and urban runoff. Changes observed in the more remote areas of the Drammensfjord, however, were less substantial. These data, along with measured and estimated geophysical properties, were used to parameterize and calibrate a coupled linear water-sediment model, referred to as the Drammensfjord model, to make prognosis on future TBT levels due to natural recovery. Unique to this type of model, the calibration was done using a Bayesian Monte Carlo (BMC) updating approach, which used monitoring data to calibrate predictions, as well as reduce the uncertainty of input parameters. To our knowledge, this is the first use of BMC updating to calibrate a model describing natural recovery in a lake/harbor type system. Prior to BMC updating, the non-calibrated model data agreed with monitoring data by a factor of 4.3. After BMC updating, the agreement was within a factor 3.2. The non-calibrated model predicted an average sediment concentration in the year 2025 of 2.5 μg kg(-1). The BMC calibrated model, however, predicted a higher concentration in the year 2025 of 16 μg kg(-1). This discrepancy was mainly due to the BMC calibration increasing the estimated riverine and runoff TBT emission levels relative to the initial input levels. Future monitoring campaigns can be used for further calibration of emission levels, and a clearer prognosis of when natural recovery will remove TBT pollution.

Kinetic characterization of Ca²⁺-ATPase (SERCA1) inhibition by tri-n-butyltin(IV) chloride. A docking conformation proposal

Organotin compounds, such as tri-n-butyltin(IV) chloride (TBT), are widespread toxicants which disrupt different functions in living organisms. TBT interacts with lipid membranes and membrane proteins. The inhibition of the calcium ATPase from sarcoplasmic reticulum membranes by TBT was studied. It was found that the ATPase inhibition could not be reverted in a large time scale; moreover, an excess of TBT over enzyme did not fully inhibit the ATPase activity; therefore, it was concluded that TBT irreversibly inhibits the enzyme, and this inhibition is accompanied by a decrease in the effective TBT concentration. The residual ATP hydrolysis activity was measured at different TBT concentrations with time, and the protective effect of different calcium concentrations on the TBT inhibition was also determined. The simplest kinetic mechanism to successfully explain all the observations and the kinetic behavior was found to be a single irreversible step of the inhibitor binding to the enzyme accompanied with a first-order inhibitor inactivation. A fluorescence study of fluorescein-5-isothiocyanate-labeled enzyme revealed that TBT binding to the enzyme entails a conformational change related to the high- to low-affinity calcium-binding state transition (E1 to E2 transition), resembling the conformational change induced by vanadate linked to the formation of E2 V complex from E1 state. A docking study allowed us to propose a binding pocket for TBT in the membrane region of E1 close to the high-affinity calcium-binding sites, as well as to define the interactions with amino acid residues interfering with calcium sites occupancy.

Fluorescence Sensing of the Interaction between Biomembranes with Different Lipid Composition and Endocrine Disrupting Chemicals

Fluorescence sensing of the interaction between biomembranes with different lipid composition and endocrine disrupting chemicals (EDCs) was carried out by using a liposome-encapsulating fluorescence dye (carboxyfluorescein (CF)-liposome). We detected a significant increase in fluorescence intensity in CF-liposome solutions due to the leakage of fluorescence caused by the interaction of EDCs with the biomembranes of liposomes. The temporal increases in fluorescent were significantly different among the lipid compositions of CF-liposome and the EDCs. Results were considered by summarizing the interactions in radar charts and by showing the pattern of interaction of each EDC. Each chart showed a dissimilar pattern reflecting the complexity of the biomembrane-EDC interaction. The results indicate that this fluorescence sensing could be useful to evaluate the interaction.

Biosorption and biodegradation of triphenyltin by Brevibacillus brevis

Triphenyltin (TPT) is an endocrine disruptor highly toxic to non-target organisms, and has contaminated the environment worldwide. To accelerate TPT elimination, the study on the behavior and mechanism of TPT biosorption and biodegradation by Brevibacillus brevis was conducted. The results revealed that TPT and coexisted Cu2+, Cd2+, Pb2+ and Zn2+ in solution could be adsorbed effectively by B. brevis, and TPT was further transformed to diphenyltin, monophenyltin and tin intracellularly. The removal efficiency of 0.5 mg L(-1) TPT after degradation by 0.3 g L(-1) biomass for 5d was about 60%. Suitable kinds and levels of oxygen, nutrient, surfactant and metals obviously improved TPT biodegradation. When concentrations of H2O2, glucose, rhamnolipid, Cu2+ and Zn2+ varied from 1.5 to 6 mmol L(-1), 0.5 to 5 mg L(-1), 5 to 25 mg L(-1), 0.5 to 6 mg L(-1) and 0.5 to 1 mg L(-1), separately, TPT biodegradation efficiencies increased 15-25%.

Crucial role of mechanisms and modes of toxic action for understanding tissue residue toxicity and internal effect concentrations of organic chemicals

This article reviews the mechanistic basis of the tissue residue approach for toxicity assessment (TRA). The tissue residue approach implies that whole-body or organ concentrations (residues) are a better dose metric for describing toxicity to aquatic organisms than is the aqueous concentration typically used in the external medium. Although the benefit of internal concentrations as dose metrics in ecotoxicology has long been recognized, the application of the tissue residue approach remains limited. The main factor responsible for this is the difficulty of measuring internal concentrations. We propose that environmental toxicology can advance if mechanistic considerations are implemented and toxicokinetics and toxicodynamics are explicitly addressed. The variability in ecotoxicological outcomes and species sensitivity is due in part to differences in toxicokinetics, which consist of several processes, including absorption, distribution, metabolism, and excretion (ADME), that influence internal concentrations. Using internal concentrations or tissue residues as the dose metric substantially reduces the variability in toxicity metrics among species and individuals exposed under varying conditions. Total internal concentrations are useful as dose metrics only if they represent a surrogate of the biologically effective dose, the concentration or dose at the target site. If there is no direct proportionality, we advise the implementation of comprehensive toxicokinetic models that include deriving the target dose. Depending on the mechanism of toxicity, the concentration at the target site may or may not be a sufficient descriptor of toxicity. The steady-state concentration of a baseline toxicant associated with the biological membrane is a good descriptor of the toxicodynamics of baseline toxicity. When assessing specific-acting and reactive mechanisms, additional parameters (e.g., reaction rate with the target site and regeneration of the target site) are needed for characterization. For specifically acting compounds, intrinsic potency depends on 1) affinity for, and 2) type of interaction with, a receptor or a target enzyme. These 2 parameters determine the selectivity for the toxic mechanism and the sensitivity, respectively. Implementation of mechanistic information in toxicokinetic-toxicodynamic (TK-TD) models may help explain time-delayed effects, toxicity after pulsed or fluctuating exposure, carryover toxicity after sequential pulses, and mixture toxicity. We believe that this mechanistic understanding of tissue residue toxicity will lead to improved environmental risk assessment.

A dynamic model for predicting chemical concentrations in water and biota during the planning phase of aquatic ecotoxicological tests

An unsteady-state fugacity model has been developed and validated as a predictive tool that will be useful in the planning phase of aquatic ecotoxicological tests. The model predicts the compound concentration trends in water and biota in experimental aquaria, with respect to the chemical and experimental conditions. The model has been validated with two echinoderm species, Paracentrotus lividus and Antedon mediterranea after a 28-days exposure to p,p'-DDE or triphenyltin chloride (TPT-Cl), respectively. Differences between the predicted vs. measured concentrations of these compounds in water and biota were generally below a factor of two for both compounds. The model here proposed considers three different compartments, water, animals, and glass, and five loss processes: volatilisation, glass adsorption, abiotic degradation, bioconcentration and biotransformation. In particular, adsorption onto glass materials was introduced into the model by means of two equations (R(2) values of 0.86 and 0.90) relating the adsorption rate constant and glass-water partition coefficient on the base of the physical-chemical properties of the compound (log K(ow)). The model can be applied during the planning phase of ecotoxicological tests and for understanding the behaviour of the compound at this micro-ecosystem scale after the tests have been performed.

QSAR analysis and specific endpoints for classifying the physiological modes of action of biocides in synchronous green algae

We propose the use of additional physiological endpoints in the 24h growth inhibition test with synchronous cultures of Scenedesmus vacuolatus for the classification of physiological modes of toxic action of chemicals in green algae. The classification scheme is illustrated on the example of one baseline toxicant (3-nitroaniline) and five biocides (irgarol, diuron, Sea-Nine, tributyltin (TBT) and norflurazon). The well-established endpoint of inhibition of reproduction is used for an analysis of the degree of specificity of toxicity by comparing the experimental data with predictions from a quantitative structure-activity relationship (QSAR) for baseline toxicity (narcosis). For those compounds with a toxic ratio greater than 10, i.e. a 10 times higher effect in reproduction than predicted by baseline toxicity, additionally the physiological endpoints inhibition of photosynthesis, cell division and cell volume growth were experimentally assessed. Depending on the relative sensitivity of the different endpoints the chemicals were classified into five different classes of modes of toxic action using a flow chart that was developed in the present study. The advantage of the novel classification scheme is the simplicity of the experimental approach. For the determination of the inhibition of reproduction, the cell size and numbers are quantified with a particle analyzer. This information can be used to derive also the physiological endpoints of cell volume growth and inhibition of cell division. The only additional measurement is the inhibition of the photosynthesis efficiency, which can be easily performed using the non-invasive saturation pulse method and pulse-modulated chlorophyll fluorometry with the Tox-Y-PAM instrument. This mechanistic approach offers a great future potential in ecotoxicology for the physiological mode of action classification of chemicals in algae, which should be a crucial step considered in the risk assessment of chemicals.

Degradation Kinetics of Water-Insoluble Lauroyl-lndapamide in Aqueous Solutions: Prediction of the Stabilities of the Drug in Liposomes

The aim of this study was to explore the degradation kinetics of water-insoluble lauroyl-indapamide in solutions and predict the stabilities of lauroyl-indapamide encapsulated in liposomes. Buffer-acetone (9:1) was used as the reaction solution and the reaction temperature was maintained at 60 degrees C. The correlation of the apparent degradation constants (k(obs)) of lauroyl-indapamide in liposomes and in buffer-acetone solutions at different pH has been explored. The degradation of lauroyl-indapamide in solutions was found to follow pseudo-first-order kinetics and was significantly dependent on the pH values. Lauroyl-indapamide was the most stable at pH 6.8, increasing or decreasing the pH of the solutions would decrease its stabilities. Buffer concentration had some effects on the stabilities of lauroyl-indapamide. The degradation active energies Ea were 68.19 kJ x mol(-1), 131.75 kJ x mol(-1) and 107.72 kJ x mol(-1) at pH3.6, 6.8 and 12 respectively in acetone-free buffer solutions (0.05M) calculated according to the Arrhenius equation with the extrapolation method. The apparent degradation constants (kobs) of lauroyl-indapamide in liposome and in buffer-acetone (9:1) solutions showed a good correlation at different pH levels, which indicates that the stabilities of the drug that dissolved in acetone-buffer mixture solutions can be used to predict the stabilities of the drug in liposomes as well.

Response to alkyltins of two Na+-dependent ATPase activities in Tapes philippinarum and Mytilus galloprovincialis

Organotin effects on the Na-dependent ATPases involved in ionic regulation of aquatic animals are poorly known, in spite of the largely documented contamination of seafood, especially bivalve molluscs. This study deals with the in vitro effect of TBT on the Na,K-ATPase and the ouabain-insensitive Na-ATPase in gill and mantle microsomes from the cultured bivalve molluscs Tapes philippinarum and Mytilus galloprovincialis. In the mussel also MBT, DBT and TeET were tested. While in both species the Na-ATPase showed an overall refractoriness to organotins, the Na,K-ATPase was progressively inhibited by increasing TBT concentrations (0-34 microM). In both species the Na,K-ATPase activity was more strongly inhibited in the gills than in the mantle. At the maximal TBT concentration tested (34.4 microM), while gill Na,K-ATPase activity was abolished, mantle enzyme activity was, respectively, reduced to 20% in T. philippinarum and to 50% in M. galloprovincialis. Mussel Na,K-ATPase was differently susceptive to the organotins tested and in both tissues showed an inhibition efficiency order TBT>DBT>>MBT=TeET (no effect), tentatively related to the different organotin polarity and to a possible interaction with membrane-bound enzyme complexes. The different response of the two ATPases to organotins is consistent with the known different susceptivity of the two enzyme activities to environmental contaminants, assay conditions and endogenous factors.

Organotin accumulation in an estuarine food chain: comparing field measurements with model estimations

The bioaccumulation model OMEGA (optimal modelling for ecotoxicological applications) is used to explore accumulation of organotins in the Western Scheldt food chain, consisting of herbi-detritivores, primary and secondary carnivorous fish and a piscivorous bird. Organotins studied are tributyltin (TBT) and triphenyltin (TPT) and the respective di- and mono-organotin metabolites. Empirical elimination rate constants are compared to model predictions for organic substances and metals. It is found that field bioaccumulation ratios are higher than predicted based on elimination kinetics relevant for organic compounds. The results indicate that uptake of organotins mainly occurs via hydrophobic mechanisms, whereas elimination may occur via metal-like kinetics. This results in very low elimination rates, which are comparable to model predictions for metals.

A predictive model for the selective accumulation of chemicals in tumor cells

Cationic lipophilic dyes can accumulate in mitochondria, and especially in mitochondria of tumor cells. We investigated the chemical properties and the processes allowing selective uptake into tumor cells using the Fick-Nernst-Planck equation. The model simulates uptake into cytoplasm and mitochondria and is valid for neutral molecules and ions, and thus also for weak electrolytes. The differential equation system was analytically solved for the steady-state and the dynamic case. The parameterization was for a generic human cell, with a 60 mV more negative potential at the inner mitochondrial membrane of generic tumor cells. The chemical input data were the lipophilicity (log K(OW)), the acid/base dissociation constant (pK(a)) and the electric charge (z). Accumulation in mitochondria occurred for polar acids with pK(a) between 5 and 9 owing to the ion trap, and for lipophilic bases with pK(a)>11 or permanent cations owing to electrical attraction. Selective accumulation in tumor cells was found for monovalent cations or strong bases with log K(OW) of the cation between -2 and 2, with the optimum near 0. The results are in agreement with experimental results for rhodamine 123, a series of cationic triarylmethane dyes, F16 and MKT-077, an anticancer drug targeting tumor mitochondria.

Elevated Ca2+i transients induced by trimethyltin chloride in HeLa cells: types and levels of response

Humans are exposed to organotins, like trimethyltin (TMT) chloride via air, water and food, and intoxication might result in severe health complications. Toxic effects of organotin compounds are well documented, but possible mechanisms remain unclear and only little information is available how organometallic species interact with calcium controlling mechanisms. Therefore, the aim of this work was to investigate the effects of TMT on calcium homeostasis in HeLa S3 cells. Dynamic changes of cytosolic calcium (Ca2+(i)) were monitored using laser-scanning microscopy and fluo-4 loaded cells. Application of TMT resulted in sustained as well as in transient elevations of Ca2+(i). The number of reacting cells was directly correlated to the concentration of TMT used: with 500 microM TMT all cells reacted, with 50 microM TMT 80% and with 5 microM 74%. The fast Ca2+(i)-transients (spikes), measured in single cells, occurred even with 0.25 microM TMT and varied in size and duration. The sustained increase of Ca2+(i), measured as the average over all cells, was dose dependent with an approximately 8% increase for 5 microM TMT, approximately 12.3% for 50 microM and approximately 145% for 500 microM TMT. Moreover, this effect was partly reversible. A second application resulted in a similar sustained rise of Ca2+(i) compared to the first application of TMT, there was also no difference when no calcium was added to the external solution (151+/-10% compared to 145+/-15%; 500 microM TMT). This rise of Ca2+(i) was highly reduced (<10% increase) when the internal calcium stores were depleted before TMT (500 microM) was applied. Our data suggest that TMT influences Ca2+(i)-homeostasis of HeLa S3 cells, which might be related to its toxicity in this cell line.

Role of speciation in organotin toxicity to the yeast Candida maltosa

Assessment of organometal pollution requires an understanding of the various processes that influence the bioavailability and toxicity of the contaminant. Organotins may exist as both cationic species and neutral hydroxides in aqueous solution, with the formation of chloride species in the presence of Cl-. Although these species have different chemical properties, there is very little information on the influence of speciation on organotin and microbial cell interactions. Tributyltin (TBT) and triphenyltin (TPT) interactions with the yeast Candida maltosa were investigated between pH 3.5 and 7.5 and in up to 0.5 M NaCl at pH 5.5. Toxicity increased with both pH and NaCl concentration and the mechanisms of interaction depended on the species present in solution. TBT and TPT interacted by different mechanisms, as evidenced by action on membrane fluidity. Furthermore, there was a strong correlation between toxicity and overall octanol-water distribution ratio (D(OW)) of organotin compounds. Triorganotin cations are less toxic than triorganotin hydroxides, which are in turn less toxic than triorganotin chlorides. These findings underline the importance of speciation effects on organotin interactions in the environment.

Uptake of tributyltin into willow trees

BACKGROUND

Organotins have been used world-wide as antifoulants in ship paints. Repeatedly, severe effects on aquatic species have resulted. The use of organotins for this purpose was ruled out, and dumping of contaminated harbor sludge into the sea was prohibited. Land-based dumping is seen as an alternative.

OBJECTIVE

This study investigates sorption, uptake and translocation of tributyltin (TBT) to willow trees in order to evaluate phytoremediation as treatment option. The study considers the influence of pH on the plant uptake of organotins. EXPERIMENTAL SET-UP: Chemicals investigated were the weak base tributyltin chloride (TBTCl) and the neutral tributyltin hydride (TBTH). Organotins were extracted from solution and plant material with toluene, and analyzed as tin by AAS with graphite oven. The pH in solution varied from pH 4 to pH 7. The sorption to living and dead roots, stems and leaves was measured in shaking experiments. The uptake into intact trees was measured at nominal levels of 1 and 10 mg TBT/l for TBTH and TBTCl at low and high pH.

RESULTS

The sorption to roots and leaves dropped for dead tissue, but did not vary much with pH. The sorption to stems increased for dead stems and with pH. The solubility of TBTCl in water was below 10 mg/l and lowest at pH 4. Concentrations of TBTCl and TBTH in solutions with trees dropped rapidly to low values. Highest TBT contents in trees were found in roots and lower stems. The concentrations followed the concentrations in solution. The pH had only a small effect on the plant uptake of TBTCl, and no effect on the uptake of TBTH. No effective translocation to higher stems or leaves was found.

DISCUSSION

An ion trap mechanism that accumulates the weak base TBTCl in the xylem sap of plants and leads to upward translocation could not be detected. Neither TBTCl at low or high pH, nor the neutral lipophilic chemical TBTH, were translocated effectively to leaves. The TBT+ cation sorbed strongly to plant tissue. The exact mechanism for the strong sorption of the cation is unknown, but similar effects have been observed for algae, liposomes and isolated biomembranes.

CONCLUSIONS

Both the uptake of the neutral TBTH and the uptake of the neutral molecule form of TBTCl into willows was as is to be expected from theory. The cation TBT+ showed an unexpected behavior which has been observed before. No ion trap occurs, and the phytoextraction of TBT is not feasible.

OUTLOOK

Planting trees, or other appropriate vegetation, could have a beneficial remediation effect by aeration of the TBT-contaminated soil or sludge. In a follow-up paper, the toxicity of TBT to willow trees will be described.

Plant uptake and transport models for neutral and ionic chemicals

BACKGROUND

Models for predicting uptake and transport of chemicals in plants are applied in pesticide design, risk assessment, and environmental biotechnology.

OBJECTIVE

This review considers the theoretical basics of the most popular models, and discusses what they have in common. The line is drawn between models for neutral compounds, and models for weak and strong electrolytes.

MAIN FEATURES

Neutral Compounds. Neutral compounds undergo only very few processes inside plants (lipophilic interactions, metabolism), in contrast to weak electrolytes. The models developed for neutral compounds are widely applied in the risk assessment of environmental contaminants, but are not of much use for weak electrolytes, such as pesticides. Weak electrolytes. A very important process for weak electrolytes is the 'ion trap', which traps chemicals that dissociate inside plant cells. This is considered in the popular models of Kleier, Satchivi and Briggs. Other relevant processes for electrolytes are electrophilic interactions, speciation and complex formation. None of the currently used models considers these processes.

CONCLUSIONS

The accuracy of models for neutral compounds is satisfactory, but the prediction of electrolyte behavior inside plants is still quite difficult due to gaps in knowledge.

Developing environmental quality standards for various pesticides and priority pollutants for French freshwaters

The French Ministry of the Environment and Water Agencies have derived environmental quality standards following the existing French framework called SEQ-Eau, for 28 pesticides and seven priority substances listed in the Water Framework Directive. Like other existing frameworks, SEQ-Eau relies upon the use of standard toxicity test results and assessment factors. This approach made it possible to derive the desired quality standards, but due to the lack of chronic toxicity data many of the standards are only provisional. In addition, emerging issues such as endocrine disruption should be taken into account in this framework. Depending on the available data, more flexible derivation approaches, such as the statistical distribution of NOECs, are recommended for future versions of SEQ-Eau. A comparison is made using SEQ-Eau and the methodology currently being discussed in Europe to develop environmental quality standards, showing that the European approach is more conservative. Conversely, the proposed approach under the Water Framework Directive does not cover the entire range of required quality classes.

Sorption of tributyltin onto a natural quartz sand

The aim of this study is to understand the sorption of tributyltin (TBT) onto natural quartz sand by classical batch experiments and spectroscopic surface analyses. At pH<6, the major species of TBT is the cation TBT(+). Due to the presence of both the cationic part and the butyl chains, TBT should present amphiphilic properties. For concentrations lower than 40 microM, TBT sorption occurs as a homovalent 1:1 cation exchange between either H(+) or Na(+) and TBT(+). The increasing affinity of TBT with respect to the different materials follows the series kaolinite<<natural sand<treated sand<pure quartz. From XPS analyses, where the chemical environment of Sn did not change, indicating possible complete reversibility of the TBT sorption, it seems that inner-sphere surface complexes could be formed due to the increase in the 3d-level binding energy. At TBT concentrations higher than 100 microM, we showed by flotation experiments and XPS analysis that the surface becomes hydrophobic. After one monolayer was formed, the TBT sorption could thus be due to hydrophobic interaction between the butyl chains of the sorbed TBT and those of the TBT still available from the bulk solution. This mechanism is consistent with surface condensation and the shape of the sorption isotherm.

Quantifying molecular partition into model systems of biomembranes: an emphasis on optical spectroscopic methods

Optical spectroscopies have been intensively used to determine partition coefficients by a plethora of methodologies. The present review is intended to give detailed and useful information for the determination of partition coefficients and addresses several relevant aspects, namely: (i) definition and calculation of the partition coefficient between aqueous and lipidic phases; (ii) partition coefficients vs. "binding" formalisms; (iii) advantages of spectroscopic methodologies over separation techniques; (iv) formalisms for various experimental approaches based on UV-Vis absorption or fluorescence parameters (fluorescence intensity, lifetime, anisotropy and quenching); (v) experimental hints, artifacts and model limitations; and (vi) a brief survey of nonoptical techniques.

Baseline toxicity (narcosis) of organic chemicals determined by in vitro membrane potential measurements in energy-transducing membranes

Baseline toxicity of a selection of industrial chemicals and pharmaceuticals is determined experimentally with a new in vitro test system (Kinspec) using membrane vesicles isolated from a photosynthetic bacterium, Rhodobacter sphaeroides. This test system is selective and more sensitive than other mechanistic test systems for baseline toxicity. The only concomitantly determined mechanism is uncoupling, which can be distinguished from baseline toxicity by pH-dependent measurements. Because the tests system contains only the target site for baseline toxicants, the biological membrane, effective target site concentrations can be directly related to observed effects by combining the in vitro test with membrane-water partition experiments. No differences were found between the effective membrane concentrations of nonpolar and polar compounds, confirming the earlier hypothesis that differences in lethal body burdens are primarily caused by unequal distribution of the compounds between target and nontarget lipids and not by different mechanisms. A selection of pharmaceuticals with various specific modes of toxic action exhibited the same constant effective membrane concentrations as found for pure baseline toxicants. In mixtures of four to six components, the pharmaceuticals were concentration-additive with each other and with the pure baseline toxicants. A potential application of the proposed test system lies, therefore, in assessing the cumulative baseline toxicity in complex environmental mixtures.