Optimal choice of pH for toxicity and bioaccumulation studies of ionizing organic chemicals

Improving plant bioaccumulation science through consistent reporting of experimental data

Experimental data and models for plant bioaccumulation of organic contaminants play a crucial role for assessing the potential human and ecological risks associated with chemical use. Plants are receptor organisms and direct or indirect vectors for chemical exposures to all other organisms. As new experimental data are generated they are used to improve our understanding of plant-chemical interactions that in turn allows for the development of better scientific knowledge and conceptual and predictive models. The interrelationship between experimental data and model development is an ongoing, never-ending process needed to advance our ability to provide reliable quality information that can be used in various contexts including regulatory risk assessment. However, relatively few standard experimental protocols for generating plant bioaccumulation data are currently available and because of inconsistent data collection and reporting requirements, the information generated is often less useful than it could be for direct applications in chemical assessments and for model development and refinement. We review existing testing guidelines, common data reporting practices, and provide recommendations for revising testing guidelines and reporting requirements to improve bioaccumulation knowledge and models. This analysis provides a list of experimental parameters that will help to develop high quality datasets and support modeling tools for assessing bioaccumulation of organic chemicals in plants and ultimately addressing uncertainty in ecological and human health risk assessments.

Environmental and human health risks of antimicrobials used in Fenneropenaeus chinensis aquaculture production in China

This study aimed to quantify the environmental fate of antimicrobials applied in Fenneropenaeus chinensis aquaculture production in China and to assess their potential risks for surrounding aquatic ecosystems, for the promotion of antimicrobial resistance in target and non-target bacteria and for consumers eating shrimp products that contain antimicrobial residues. For this, we first used the results of an environmental monitoring study performed with the antimicrobial sulfamethazine to parameterize and calibrate the ERA-AQUA model, a mass balance model suited to perform risk assessments of veterinary medicines applied in aquaculture ponds. Next, a scenario representing F. chinensis production in China was built and used to perform risk assessments for 21 antimicrobials which are regulated for aquaculture in China. Results of the model calibration showed a good correspondence between the predicted and the measured sulfamethazine concentrations, with differences within an order of magnitude. Results of the ecological risk assessment showed that four antimicrobials (levofloxacin, sarafloxacin, ampicillin, sulfadiazine) are expected to have adverse effects on primary producers, while no short-term risks were predicted for invertebrates and fish exposed to farm wastewater effluents containing antimicrobial residues. Half of the evaluated antimicrobials showed potential to contribute to antimicrobial resistance in bacteria exposed to pond water and farm effluents. A withdrawal period of three weeks is recommended for antimicrobials applied via oral administration to F. chinensis in order to comply with the current national and international toxicological food safety standards. The results of this study indicate the need to improve the current regulatory framework for the registration of aquaculture antimicrobials in China and suggest compounds that should be targeted in future aquaculture risk assessments and environmental monitoring studies.

A Multimedia Fate Model to Support Chemical Management in China: A Case Study for Selected Trace Organics

SESAMe v3.3, a spatially explicit multimedia fate model for China, is a tool suggested to support quantitative risk assessment for national scale chemical management. The key advantage over the previous version SESAMe v3.0 is consideration of spatially varied environmental pH. We evaluate the model performance using estimates of emission from total industry usage of three UV filters (benzophenone-3, octocrylene, and octyl methoxycinnamate) and three antimicrobials (triclosan, triclocarban, and climbazole). The model generally performs well for the six case study chemicals as shown by the comparison between predictions and measurements. The importance of accounting for chemical ionization is demonstrated with the fate and partitioning of both triclosan and climbazole sensitivity to environmental pH. The model predicts ionizable chemicals (triclosan, climbazole, benzophenone-3) to primarily partition into soils at steady state, despite hypothetically only being released to freshwaters, as a result of agricultural irrigation by freshwater. However, further model calibration is needed when more field data becomes available for soils and sediments and for larger areas of water. As an example, accounting for the effect of pH in the environmental risk assessment of triclosan, limited freshwater areas (0.03% or ca. 55 km(2)) in mainland China are modeled to exceed its conservative environmental no-effect threshold. SESAMe v3.3 can be used to support the development of chemical risk assessment methodologies with the spatial aspects of the model providing a guide to the identification regions of interest in which to focus monitoring campaigns or develop a refined risk assessment.

Contaminants of emerging concern in a large temperate estuary

This study was designed to assess the occurrence and concentrations of a broad range of contaminants of emerging concern (CECs) from three local estuaries within a large estuarine ecosystem. In addition to effluent from two wastewater treatment plants (WWTP), we sampled water and whole-body juvenile Chinook salmon (Oncorhynchus tshawytscha) and Pacific staghorn sculpin (Leptocottus armatus) in estuaries receiving effluent. We analyzed these matrices for 150 compounds, which included pharmaceuticals, personal care products (PPCPs), and several industrial compounds. Collectively, we detected 81 analytes in effluent, 25 analytes in estuary water, and 42 analytes in fish tissue. A number of compounds, including sertraline, triclosan, estrone, fluoxetine, metformin, and nonylphenol were detected in water and tissue at concentrations that may cause adverse effects in fish. Interestingly, 29 CEC analytes were detected in effluent and fish tissue, but not in estuarine waters, indicating a high potential for bioaccumulation for these compounds. Although concentrations of most detected analytes were present at relatively low concentrations, our analysis revealed that overall CEC inputs to each estuary amount to several kilograms of these compounds per day. This study is unique because we report on CEC concentrations in estuarine waters and whole-body fish, which are both uncommon in the literature. A noteworthy finding was the preferential bioaccumulation of CECs in free-ranging juvenile Chinook salmon relative to staghorn sculpin, a benthic species with relatively high site fidelity.

Uptake, depuration, and bioconcentration of two pharmaceuticals, roxithromycin and propranolol, in Daphnia magna

The objective of the present study was to investigate the uptake, depuration, and bioconcentration of two pharmaceuticals, roxithromycin (ROX) and propranolol (PRP), in Daphnia magna via aqueous exposure. Additionally, dietary and pH effects on the bioconcentration of two pharmaceuticals in daphnia were studied. During the 24-h uptake phase followed by the 24-h depuration phase, the uptake rate constants (k(u)) of ROX for daphnia were 9.21 and 2.77 L kg(-1) h(-1), corresponding to the exposure concentrations of 5 and 100 μg L(-1), respectively; For PRP at the nominal concentrations of 5 and 100 μg L(-1), k(u) were 2.29 and 0.99 L kg(-1) h(-1), respectively. The depuration rate constants (k(d)) of ROX in daphnia, at the exposure concentrations of 5 and 100 μg L(-1), were 0.0985 and 0.207 h(-1), respectively; while those of PRP were 0.0276 and 0.0539 h(-1) for the nominal concentrations of 5 and 100 μg L(-1), respectively. With the decreasing exposure concentrations, the bioconcentration factors (BCFs) in daphnia ranged from 13.4 to 93.5 L kg(-1) for ROX, and 18.4 to 83.0 L kg(-1) for PRP, revealing the considerable accumulation potential of these two pharmaceuticals. Moreover, after 6h exposure, the body burdens of ROX and PRP in dead daphnia were 4.98-6.14 and 7.42-12.9 times higher than those in living daphnia, respectively, implying that body surface sorption dominates the bioconcentration of the two pharmaceuticals in daphnia. In addition, the presence of algal food in the media could significantly elevate the kd values for both ROX and PRP, thereby restraining their bioconcentration in daphnia. A pH-dependent bioconcentration study revealed that the bioconcentration of the two pharmaceuticals in daphnia increased with increasing pH levels, which ranged from 7 to 9. Finally, a model was developed to estimate the relationships between pH and the BCFs of the two pharmaceuticals in zooplankton. The predicted values based on this model were highly consistent with wildlife monitoring data, implying that this model will be useful in identifying the bioaccumulation risks that pharmaceuticals pose to zooplankton.

Narrow pH Range of Surface Water Bodies Receiving Pesticide Input in Europe

Fate and toxicity of the active ingredients (AI's) of plant protection products in surface waters is often influenced by pH. Although a general range of pH values is reported in literature, an evaluation targeting aquatic ecosystems with documented AI inputs is lacking at the larger scale. Results show 95% of European surface waters (n = 3075) with a documented history of AI exposure fall within a rather narrow pH range, between 7.0 and 8.5. Spatial and temporal variability in the data may at least be partly explained by the calcareous characteristics of parental rock material, the affiliation of the sampling site to a freshwater ecoregion, and the photosynthetic activity of macrophytes (i.e., higher pH values with photosynthesis). Nonetheless, the documented pH range fits well with the standard pH of most ecotoxicological test guidelines, confirming the fate and ecotoxicity of AIs are usually adequately addressed.

Biological fate and effects of propranolol in an experimental aquatic food chain

The aim of this study was to evaluate the trophic transfer of the β-blocker propranolol (PRP) in an experimental aquatic food chain involving the green algae Scenedesmus obliquus, the water flea Daphnia magna and the crucian carp Carassius auratus, as well as the metabolism and effects of PRP in the liver of crucian carp. After a 48 h PRP aqueous exposure for algae, with a subsequent 48 h dietary exposure for daphnia and an 8d dietary exposure for crucian carp, PRP was observed in each trophic level, despite significant bioaccumulation did not occur in daphnia and crucian carp. A portion of the absorbed PRP was metabolized by the crucian carp to N-desisopropylated propranolol, propranolol glucuronic acid, monohydroxylated propranolol, hydroxypropranolol glucuronide and dihydroxypropranolol glucuronide, which were similar to those in mammals. In addition, multiple biomarkers in the liver of crucian carp (7-ethoxyresorufin O-deethylase, EROD; 7-benzyloxyresorufin O-dealkylation, BROD; superoxide dismutase, SOD and malondialdehyde, MDA) were measured. BROD and MDA were not significantly affected by PRP, while EROD and SOD did change significantly during the 8d dietary exposure. This work indicated that the trophic transfer of PRP, resulting in biochemical perturbations of fish biological systems, should be a concern for the assessment of the environmental risks to aquatic food chains.

Uptake and Tissue Distribution of Pharmaceuticals and Personal Care Products in Wild Fish from Treated-Wastewater-Impacted Streams

A fish plasma model (FPM) has been proposed as a screening technique to prioritize potential hazardous pharmaceuticals to wild fish. However, this approach does not account for inter- or intraspecies variability of pharmacokinetic and pharmacodynamic parameters. The present study elucidated the uptake potency (from ambient water), tissue distribution, and biological risk of 20 pharmaceutical and personal care product (PPCP) residues in wild cyprinoid fish inhabiting treated-wastewater-impacted streams. In order to clarify the uncertainty of the FPM for PPCPs, we compared the plasma bioaccumulation factor in the field (BAFplasma = measured fish plasma/ambient water concentration ratio) with the predicted plasma bioconcentration factor (BCFplasma = fish plasma predicted by use of theoretical partition coefficients/ambient water concentration ratio) in the actual environment. As a result, the measured maximum BAFplasma of inflammatory agents was up to 17 times higher than theoretical BCFplasma values, leading to possible underestimation of toxicological risk on wild fish. When the tissue-blood partition coefficients (tissue/blood concentration ratios) of PPCPs were estimated, higher transportability into tissues, especially the brain, was found for psychotropic agents, but brain/plasma ratios widely varied among individual fish (up to 28-fold). In the present study, we provide a valuable data set on the intraspecies variability of PPCP pharmacokinetics, and our results emphasize the importance of determining PPCP concentrations in possible target organs as well as in the blood to assess the risk of PPCPs on wild fish.

Uptake, Translocation, and Metabolism of Phenols by Submerged Rooted Macrophyte, Water Milfoil (Myriophyllum elatinoides)

Shoot and root uptakes of (14)C-labeled phenol (1), 4-nitrophenol (2), 4-cyanophenol (3), 4-hydroxybenzamide (4), and 4-hydroxybenzoic acid (5) by Myriophyllum elatinoides were individually examined with water or sediment treatments using the sequestered chamber. Shoot uptake of each (14)C-phenol dissolved in water amounted to 21.0% (1), 14.3% (2), 12.8% (3), 4.2% (4) and 41.7% (5) of the applied radioactivity (AR) after 96 h without significant (14)C translocation from shoot to root (≤0.9% AR), and the major metabolite produced was the glucose conjugate. On the other hand, root uptake of (14)C-phenols from sediment was much slower/smaller (≤6.6% AR), and (14)C transportation from root to shoot was scarcely observed, except for compound 5 (≤1.5% AR). For the water treatment, a kinetic analysis on uptake/metabolism was conducted using the assumed compartment. Good correlation was observed between lipophilicity and shoot uptake rate constants, and the electronic state of the hydroxyl group (σ, σ(-), or EHOMO(OH)) and the transformation rate constant of glucosidation.

Development and application of the adverse outcome pathway framework for understanding and predicting chronic toxicity: I. Challenges and research needs in ecotoxicology

To elucidate the effects of chemicals on populations of different species in the environment, efficient testing and modeling approaches are needed that consider multiple stressors and allow reliable extrapolation of responses across species. An adverse outcome pathway (AOP) is a concept that provides a framework for organizing knowledge about the progression of toxicity events across scales of biological organization that lead to adverse outcomes relevant for risk assessment. In this paper, we focus on exploring how the AOP concept can be used to guide research aimed at improving both our understanding of chronic toxicity, including delayed toxicity as well as epigenetic and transgenerational effects of chemicals, and our ability to predict adverse outcomes. A better understanding of the influence of subtle toxicity on individual and population fitness would support a broader integration of sublethal endpoints into risk assessment frameworks. Detailed mechanistic knowledge would facilitate the development of alternative testing methods as well as help prioritize higher tier toxicity testing. We argue that targeted development of AOPs supports both of these aspects by promoting the elucidation of molecular mechanisms and their contribution to relevant toxicity outcomes across biological scales. We further discuss information requirements and challenges in application of AOPs for chemical- and site-specific risk assessment and for extrapolation across species. We provide recommendations for potential extension of the AOP framework to incorporate information on exposure, toxicokinetics and situation-specific ecological contexts, and discuss common interfaces that can be employed to couple AOPs with computational modeling approaches and with evolutionary life history theory. The extended AOP framework can serve as a venue for integration of knowledge derived from various sources, including empirical data as well as molecular, quantitative and evolutionary-based models describing species responses to toxicants. This will allow a more efficient application of AOP knowledge for quantitative chemical- and site-specific risk assessment as well as for extrapolation across species in the future.

Development and application of the adverse outcome pathway framework for understanding and predicting chronic toxicity: II. A focus on growth impairment in fish

Adverse outcome pathways (AOPs) organize knowledge on the progression of toxicity through levels of biological organization. By determining the linkages between toxicity events at different levels, AOPs lay the foundation for mechanism-based alternative testing approaches to hazard assessment. Here, we focus on growth impairment in fish to illustrate the initial stages in the process of AOP development for chronic toxicity outcomes. Growth is an apical endpoint commonly assessed in chronic toxicity tests for which a replacement is desirable. Based on several criteria, we identified reduction in food intake to be a suitable key event for initiation of middle-out AOP development. To start exploring the upstream and downstream links of this key event, we developed three AOP case studies, for pyrethroids, selective serotonin reuptake inhibitors (SSRIs) and cadmium. Our analysis showed that the effect of pyrethroids and SSRIs on food intake is strongly linked to growth impairment, while cadmium causes a reduction in growth due to increased metabolic demands rather than changes in food intake. Locomotion impairment by pyrethroids is strongly linked to their effects on food intake and growth, while for SSRIs their direct influence on appetite may play a more important role. We further discuss which alternative tests could be used to inform on the predictive key events identified in the case studies. In conclusion, our work demonstrates how the AOP concept can be used in practice to assess critically the knowledge available for specific chronic toxicity cases and to identify existing knowledge gaps and potential alternative tests.

Exposure and food web transfer of pharmaceuticals in ospreys (Pandion haliaetus): Predictive model and empirical data

The osprey (Pandion haliaetus) is a well-known sentinel of environmental contamination, yet no studies have traced pharmaceuticals through the water-fish-osprey food web. A screening-level exposure assessment was used to evaluate the bioaccumulation potential of 113 pharmaceuticals and metabolites, and an artificial sweetener in this food web. Hypothetical concentrations in water reflecting "wastewater effluent dominated" or "dilution dominated" scenarios were combined with pH-specific bioconcentration factors (BCFs) to predict uptake in fish. Residues in fish and osprey food intake rate were used to calculate the daily intake (DI) of compounds by an adult female osprey. Fourteen pharmaceuticals and a drug metabolite with a BCF greater than 100 and a DI greater than 20 µg/kg were identified as being most likely to exceed the adult human therapeutic dose (HTD). These 15 compounds were also evaluated in a 40 day cumulative dose exposure scenario using first-order kinetics to account for uptake and elimination. Assuming comparable absorption to humans, the half-lives (t1/2 ) for an adult osprey to reach the HTD within 40 days were calculated. For 3 of these pharmaceuticals, the estimated t1/2 in ospreys was less than that for humans, and thus an osprey might theoretically reach or exceed the HTD in 3 to 7 days. To complement the exposure model, 24 compounds were quantified in water, fish plasma, and osprey nestling plasma from 7 potentially impaired locations in Chesapeake Bay. Of the 18 analytes detected in water, 8 were found in fish plasma, but only 1 in osprey plasma (the antihypertensive diltiazem). Compared to diltiazem detection rate and concentrations in water (10/12 detects, <method detection limits [MDL]-173 ng/L), there was a lower detection frequency in fish (31/233 detects, <MDL-2400 ng/L); however when present in fish, all values exceeded the maximum diltiazem concentration found in water. Diltiazem was found in all 69 osprey plasma samples (540-8630 ng/L), with 41% of these samples exceeding maximum concentrations found in fish. Diltiazem levels in fish and osprey plasma were below the human therapeutic plasma concentration (30000 ng/L). Effect thresholds for diltiazem are unknown in ospreys at this time, and there is no evidence to suggest adverse effects. This screening-level exposure model can help identify those compounds that warrant further investigation in high-trophic level species.

Pharmaceutical bioaccumulation by periphyton and snails in an effluent-dependent stream during an extreme drought

Increasing evidence indicates that pharmaceutical bioaccumulate in fish collected downstream from municipal wastewater effluent discharges. However, studies of pharmaceutical bioaccumulation by other aquatic organisms, including primary producers (e.g., periphyton) and grazers (e.g., snails), are lacking in wadeable streams. Here, we examined environmental occurrence and bioaccumulation of a range of pharmaceuticals and other contaminants of emerging concern in surface water, a common snail (Planorbid sp.) and periphyton from an effluent-dependent stream in central Texas, USA, during a historic drought, because such limited dilution and instream flows may represent worst-case exposure scenarios for aquatic life to pharmaceuticals. Water and tissue samples were liquid-liquid extracted and analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) with electrospray ionization. Target analytes included 21 pharmaceuticals across multiple drug classes and 2 pharmacologically active metabolites. Several pharmaceuticals were detected at up to 4.7 μg kg(-1) in periphyton and up to 42 μg kg(-1) in Planorbid sp. We then identified limitations of several bioconcentration factor and bioaccumulation factor models, developed for other invertebrates, to assist interpretation of such field results. Observations from the present study suggest that waterborne exposure to pharmaceuticals may be more important than dietary exposure for snails.

pH-dependent biotransformation of ionizable organic micropollutants in activated sludge

Removal of micropollutants (MPs) during activated sludge treatment can mainly be attributed to biotransformation and sorption to sludge flocs, whereby the latter process is known to be of minor importance for polar organic micropollutants. In this work, we investigated the influence of pH on the biotransformation of MPs with cationic-neutral speciation in an activated sludge microbial community. We performed batch biotransformation, sorption control, and abiotic control experiments for 15 MPs with cationic-neutral speciation, one control MP with neutral-anionic speciation, and two neutral MPs at pHs 6, 7, and 8. Biotransformation rate constants corrected for sorption and abiotic processes were estimated from measured concentration time series with Bayesian inference. We found that biotransformation is pH-dependent and correlates qualitatively with the neutral fraction of the ionizable MPs. However, a simple speciation model based on the assumption that only the neutral species is efficiently taken up and biotransformed by the cells tends to overpredict the effect of speciation. Therefore, additional mechanisms such as uptake of the ionic species and other more complex attenutation mechanisms are discussed. Finally, we observed that the sorption coefficients derived from our control experiments were small and showed no notable pH-dependence. From this we conclude that pH-dependent removal of polar, ionizable organic MPs in activated sludge systems is less likely an effect of pH-dependent sorption but rather of pH-dependent biotransformation. The latter has the potential to cause marked differences in the removal of polar, ionizable MPs at different operational pHs during activated sludge treatment.

Accounting for dissociation and photolysis: a review of the algal toxicity of triclosan

Triclosan, an antimicrobial agent commonly used in down-the-drain consumer products, is toxic to freshwater microalgae. However, the rapid photolysis and pH-dependent dissociation of this compound may give rise to uncertainty in growth inhibition tests with freshwater microalgae, if these are not well characterized. Methods are presented to minimize these uncertainties by stabilizing pH with an organic buffering agent (Bis-Tris) and by the application of ultraviolet (UV) covers to remove UV wavelengths. Toxicity tests with these methods were in compliance with the validity criteria of the Organisation for Economic Co-operation and Development test 201, and no negative effects were seen in controls relative to the unmodified method. The methods were used for toxicity tests with triclosan at pH levels of 7.0, 8.0, and 8.5, yielding effective concentration, 10% values of 0.5 µg/L, 0.6 µg/L, and 12.1 µg/L, respectively. The observed change in toxicity with pH was proportional to the change in bioconcentration factor (BCF) as calculated using the cell model (a dynamic flux model based on the Fick-Nernst-Planck equations, in this case parameterized for an algal cell). Effect concentrations produced with the methods presented in the present study offer robust data on which to base risk assessment, and it is suggested that similar approaches be used to minimize uncertainty when other compounds that dissociate and photolyse are tested.

Reducing aquatic hazards of industrial chemicals: probabilistic assessment of sustainable molecular design guidelines

Basic toxicological information is lacking for the majority of industrial chemicals. In addition to increasing empirical toxicity data through additional testing, prospective computational approaches to drug development aim to serve as a rational basis for the design of chemicals with reduced toxicity. Recent work has resulted in the derivation of a "rule of 2," wherein chemicals with an octanol-water partition coefficient (log P) less than 2 and a difference between the lowest unoccupied molecular orbital and the highest occupied molecular orbital (ΔE) greater than 9 (log P<2 and ΔE >9 eV) are predicted to be 4 to 5 times less likely to elicit acute or chronic toxicity to model aquatic organisms. The present study examines potential reduction of aquatic toxicity hazards from industrial chemicals if these 2 molecular design guidelines were employed. Probabilistic hazard assessment approaches were used to model the likelihood of encountering industrial chemicals exceeding toxicological categories of concern both with and without the rule of 2. Modeling predicted that utilization of these molecular design guidelines for log P and ΔE would appreciably decrease the number of chemicals that would be designated to be of "high" and "very high" concern for acute and chronic toxicity to standard model aquatic organisms and end points as defined by the US Environmental Protection Agency. For example, 14.5% of chemicals were categorized as having high and very high acute toxicity to the fathead minnow model, whereas only 3.3% of chemicals conforming to the design guidelines were predicted to be in these categories. Considerations of specific chemical classes (e.g., aldehydes), chemical attributes (e.g., ionization), and adverse outcome pathways in representative species (e.g., receptor-mediated responses) could be used to derive future property guidelines for broader classes of contaminants.

Amelioration of acidic soil increases the toxicity of the weak base carbendazim to the earthworm Eisenia fetida

Ameliorating acidic soils is a common practice and may affect the bioavailability of an ionizable organic pollutant to organisms. The toxicity of the weak base carbendazim to the earthworm (Eisenia fetida) was studied in an acidic soil (pH-H₂O, 4.6) and in the ameliorated soil (pH-H₂O, 7.5). The results indicated that the median lethal concentration of carbendazim for E. fetida decreased from 21.8 mg/kg in acidic soil to 7.35 mg/kg in the ameliorated soil. To understand why the amelioration increased carbendazim toxicity to the earthworm, the authors measured the carbendazim concentrations in the soil porewater. The authors found increased carbendazim concentrations in porewater, resulting in increased toxicity of carbendazim to earthworms. The increased pore concentrations result from decreased adsorption because of the effects of pH and calcium ions.

Ecotoxicity of climbazole, a fungicide contained in antidandruff shampoo

Emerging pollutants such as personal care products can reach the environment via effluents from wastewater treatment plants (WWTPs) and digested sludge. Only recently, the antidandruff agent and antimycotic climbazole was detected for the first time in a WWTP effluent with concentrations up to 0.5 µg/L. Climbazole acts as a C14-demethylase inhibitor (DMI) fungicide and thus has a high efficacy against fungi, but knowledge of its potential environmental impact is lacking. Therefore, the aim of the present study was to characterize climbazole's ecotoxicity by conducting standard biotests with organisms representing different trophic levels from the aquatic as well as the terrestrial ecosystems. It was found that the toxicity of climbazole is mostly similar to that of other DMI fungicides, whereas it proved to be particularly toxic to primary producers. The lowest median effective concentrations (EC50s) were determined for Lemna minor, at 0.013 mg/L (biomass yield), and Avena sativa, at 18.5 mg/kg soil dry weight (shoot biomass). Reduction of frond size in water lentils and shoot length in higher plants suggested an additional plant growth-retarding mode of action of climbazole. In addition, it was demonstrated here that for an ionizable compound such as climbazole, the soil pH can have a considerable influence on phytotoxicity.

Distinct photolytic mechanisms and products for different dissociation species of ciprofloxacin

As many antibiotics are ionizable and may have different dissociation forms in the aquatic environment, we hypothesized that the different dissociation species have disparate photolytic pathways, products, and kinetics, and adopted ciprofloxacin (CIP) as a case to test this hypothesis. Simulated sunlight experiments and matrix calculations were performed to differentiate the photolytic reactivity for each dissociation species (H4CIP(3+), H3CIP(2+), H2CIP(+), HCIP(0), and CIP(-)). The results prove that the five dissociation species do have dissimilar photolytic kinetics and products. H4CIP(3+) mainly undergoes stepwise cleavage of the piperazine ring, while H2CIP(+) mainly undergoes defluorination. For H3CIP(2+), HCIP(0), and CIP(-), the major photolytic pathway is oxidation. By density functional theory calculation, we clarified the defluorination mechanisms for the five dissociation species at the excited triplet states: All the five species can defluorinate by reaction with hydroxide ions (OH(-)) to form hydroxylated products, and H2CIP(+) can also undergo C-F bond cleavage to produce F(-) and a carbon-centered radical. This study is a first attempt to differentiate the photolytic products and mechanisms for different dissociation species of ionizable compounds. The results imply that for accurate ecological risk assessment of ionizable emerging pollutants, it is necessary to investigate the environmental photochemical behavior of all dissociation species.

Toxicity of four sulfonamide antibiotics to the freshwater amphipod Hyalella azteca

Sulfonamides are a widely used class of antibiotics; however, there are few toxicological data available with which to conduct environmental risk assessments for these compounds. Therefore, the toxicity of four sulfonamides (sulfaguanidine, sulfathiazole, sulfamerazine, and sulfasalazine) to Hyalella azteca was assessed in chronic (four-week), water-only exposures. Survival was evaluated weekly, and growth was measured at the end of the test. Four-week lethal concentrations associated with 50% mortality (LC50s) for sulfaguanidine, sulfathiazole, and sulfamerazine were 0.90, 1.6, and 3.9 µM, respectively. Sulfaguanidine caused effects on survival more quickly and at lower concentrations than sulfathiazole or sulfamerazine. These differences were more pronounced at week 1 than week 4, when sulfaguanidine LC50s were 8 to 20 times lower and 2 to 4 times lower, respectively. Growth was affected by sulfathiazole but was a less sensitive end point than survival, with an effective concentration associated with 50% reduction in growth (EC50) of 13 µM, whereas sulfaguanidine and sulfamerazine caused negligible effects on growth. Sulfasalazine had no effect on survival or growth at any concentration tested, up to 13 µM. The effects observed in the present study occurred at concentrations exceeding those typically found in environmental waters. However, given that LC50s decreased with exposure duration (except for sulfasalazine), the present study demonstrates the importance of conducting longer-term tests to adequately assess the environmental toxicity of sulfonamides.

Making fate and exposure models for freshwater ecotoxicity in life cycle assessment suitable for organic acids and bases

Freshwater fate and exposure factors were determined for organic acids and bases, making use of the knowledge on electrical interaction of ionizing chemicals and their sorption to particles. The fate factor represents the residence time in the environment whereas exposure factors equal the dissolved fraction of a chemical. Multimedia fate, exposure, and effect model USES-LCA was updated to take into account the influence of ionization, based upon the acid dissociation constant (pK(a)) of a chemical, and the environmental pH. Freshwater fate (FF) and exposure (XF) factors were determined for 415 acids and 496 bases emitted to freshwater, air, and soil. The relevance of taking account of the degree of ionization of chemicals was tested by determining the ratio (R) of the new vs. fate and exposure factors determined with USES-LCA suitable for neutral chemicals only. Our results show that the majority of freshwater fate and exposure factors of chemicals that are largely ionized in the environment are larger with the ionics model compared to the factors determined with the neutrals model version. R(FF) ranged from 2.4×10(-1) to 1.6×10(1) for freshwater emissions, from 1.2×10(-2) to 2.0×10(4) for soil emissions and from 5.8×10(-2) to 6.0×10(3) for air emissions, and R(XF) from 5.3×10(-1) to 2.2×10(1). Prediction of changed solid-water partitioning, implying a change in runoff and in removal via sedimentation, and prediction of negligible air-water partition coefficient, leading to negligible volatilization were the main contributors to the changes in freshwater fate factors.

Influence of pH, light cycle, and temperature on ecotoxicity of four sulfonylurea herbicides towards Lemna gibba

In chemical regulation, e.g. the EU Water Framework Directive, REACH, or the Pesticide Directive, standardized ecotoxicological tests are applied to evaluate and rank the hazard of compounds and for deriving environmental quality standards (EQS). Standardized test methods prescribe fixed testing conditions e.g. specific temperature, pH, light intensity etc. However, environmental conditions under which the organisms live are rarely identical to the standard conditions. Thus, the ecotoxicity of compounds found in standard test is not only a function of the compounds inherent physico-chemical properties but is also affected by test conditions. It is therefore important to study the effect of changes in test conditions in order to get reliable input ecotoxicity data for assessing the potential risk posed by a compound. The objective of this study was to investigate the implications of changing test conditions on the toxicity of four sulfonylurea herbicides (SUs). The toxicity of the four SUs towards Lemna gibba was investigated at three pH levels (6, 7.5 and 9), at two temperatures (15 and 24 °C) and two light regimes (continuous and 12:12 h light:dark cycle) The EC50 increased twofold to tenfold for the four SUs when pH was increased from 6 to 9. Decreasing the temperature from 24 to 15 °C or introducing a dark:light cycle did not cause any trends in changes in toxicity. The results show that test conditions can have an effect on the toxicity and this should be considered when the standard test results are used for derivation of EQS.

Estimating the toxicity of the weak base carbendazim to the earthworm (Eisenia fetida) using in situ pore water concentrations in different soils

Both sorption by soil and uptake by organisms of ionizable organic pollutants depend on their speciation (i.e., neutral and ionized forms); thus, the bioavailability of ionizable organic pollutants is more complicated than that of neutral organic pollutants in soil. The toxicity of the weak base carbendazim to earthworms (Eisenia fetida) was estimated using Soxhlet extracted concentrations (C(SE)), an excess of water extracted concentrations (C(EEW)), ex situ pore water concentrations (C(EPW)) and in situ pore water concentrations (C(IPW)) in different soils. The results indicated that the median lethal concentrations (LC50) calculated from C(SE) ranged from 2.32 to 34.0 mg kg(-1) in the five tested soils and the coefficient of variation (CV) of LC50s was 69.8%. When the LC50 was calculated from the C(EEW), C(EPW) and C(IPW), the variability of the LC50 gradually became smaller in these soils, with the CVs of LC50s being 58.1%, 50.6% and 38.6% (for C(EEW), C(EPW) and C(IPW), respectively). However, the LC50 based on C(IPW) in strongly acidic soil (where carbendazim partially exists as ionized form) was significantly lower than in other soils, and the values of the LC50 calculated from the in situ pore water concentrations were approximately equal. The results indicated that the in situ pore water concentration could be used to estimate the toxicity of carbendazim in different soils especially in those soils where carbendazim exists in the neutral form.

Using in situ pore water concentrations to estimate the phytotoxicity of nicosulfuron in soils to corn (Zea mays L.)

The phytotoxicity of an herbicide in soil is typically dependent on the soil characteristics. To obtain a comparable value of the concentration that inhibits growth by 50% (IC50), 0.01 M CaCl(2) , excess pore water (EPW) and in situ pore water (IPW) were used to extract the bioavailable fraction of nicosulfuron from five different soils to estimate the nicosulfuron phytotoxicity to corn (Zea mays L.). The results indicated that the phytotoxicity of nicosulfuron in soils to corn depended on the soil type, and the IC50 values calculated based on the amended concentration of nicosulfuron ranged from 0.77 to 9.77 mg/kg among the five tested soils. The range of variation in IC50 values for nicosulfuron was smaller when the concentrations of nicosulfuron extracted with 0.01 M CaCl(2) and EPW were used instead of the amended concentration. No significant difference was observed among the IC50 values calculated from the IPW concentrations of nicosulfuron in the five tested soils, suggesting that the concentration of nicosulfuron in IPW could be used to estimate the phytotoxicity of residual nicosulfuron in soils.

Critical evaluation and further development of methods for testing ecotoxicity at multiple pH using Daphnia magna and Pseudokirchneriella subcapitata

To meet the requirements of risk assessment legislature regarding the ecotoxicity of ionizing compounds, the present study attempts to establish easy, robust methods for testing ecotoxicity at various pH levels. An overview is given of the buffering methods found in the literature. This is supplemented by a series of experiments where toxicity and ability to stabilize pH of seven common buffering compounds was tested on Daphnia magna and Pseudokirchneriella subcapitata. We consider a buffer applicable at a given concentration if the pH drift is below 0.2 pH units, and if there are no toxic effects. Twenty-four- and 48-h acute toxicity tests with D. magna were carried on a series of organic buffers with pH monitoring. Based on the experimental results it is possible to give recommendations for buffer concentrations for use in toxicity testing with D. magna at pH levels in the range of pH 6.0-7.8 for 48 h exposure, and pH 6.0-9.5 for 24 h exposure. Forty-eight- and 72-h growth inhibition tests with P. subcapitata were carried out, and recommendations for buffer concentrations at pH 7.5 and 8.0 are made for both 48 and 72 h of exposure.

Uptake and depuration of pharmaceuticals in aquatic invertebrates

The uptake and depuration of a range of pharmaceuticals in the freshwater shrimp (Gammarus pulex) and the water boatman (Notonecta glauca) was studied. For one compound, studies were also done using the freshwater snail Planobarius corneus. In G. pulex, bioconcentration factors (BCFs) ranged from 4.6 to 185,900 and increased in the order moclobemide < 5-fluoruracil < carbamazepine < diazepam < carvedilol < fluoxetine. In N. glauca BCFs ranged from 0.1 to 1.6 and increased in the order 5-fluorouracil < carbamazepine < moclobemide < diazepam < fluoxetine < carvedilol. For P. corneus, the BCF for carvedilol was 57.3. The differences in degree of uptake across the three organisms may be due to differences in mode of respiration, behaviour and the pH of the test system. BCFs of the pharmaceuticals for each organism were correlated to the pH-corrected liposome-water partition coefficient of the pharmaceuticals.

Predicting concentrations of organic chemicals in fish by using toxicokinetic models

Quantification of chemical toxicity continues to be generally based on measured external concentrations. Yet, internal chemical concentrations have been suggested to be a more suitable parameter. To better understand the relationship between the external and internal concentrations of chemicals in fish, and to quantify internal concentrations, we compared three toxicokinetic (TK) models with each other and with literature data of measured concentrations of 39 chemicals. Two one-compartment models, together with the physiologically based toxicokinetic (PBTK) model, in which we improved the treatment of lipids, were used to predict concentrations of organic chemicals in two fish species: rainbow trout (Oncorhynchus mykiss) and fathead minnow (Pimephales promelas). All models predicted the measured internal concentrations in fish within 1 order of magnitude for at least 68% of the chemicals. Furthermore, the PBTK model outperformed the one-compartment models with respect to simulating chemical concentrations in the whole body (at least 88% of internal concentrations were predicted within 1 order of magnitude using the PBTK model). All the models can be used to predict concentrations in different fish species without additional experiments. However, further development of TK models is required for polar, ionizable, and easily biotransformed compounds.

Human therapeutic plasma levels of the selective serotonin reuptake inhibitor (SSRI) sertraline decrease serotonin reuptake transporter binding and shelter-seeking behavior in adult male fathead minnows

Selective serotonin reuptake inhibitors (SSRIs) represent a class of pharmaceuticals previously reported in aquatic ecosystems. SSRIs are designed to treat depression and other disorders in humans, but are recognized to elicit a variety of effects on aquatic organisms, ranging from neuroendocrine disruption to behavioral perturbations. However, an understanding of the relationships among mechanistic responses associated with SSRI targets and ecologically important behavioral responses of fish remains elusive. Herein, linking Adverse Outcomes Pathways (AOP) models with internal dosimetry represent potential approaches for developing an understanding of pharmaceutical risks to aquatic life. We selected sertraline as a model SSRI for a 28-d study with adult male fathead minnows. Binding activity of the serotonin reuptake transporter (SERT), previously demonstrated in mammals and fish models to respond to sertraline exposure, was selected as an endpoint associated with therapeutic activity. Shelter-seeking behavior was monitored using digital tracking software to diagnose behavioral abnormalities. Fish plasma levels of sertraline exceeding human therapeutic doses were accurately modeled from external exposure concentrations when pH influences on ionization and log D were considered. We observed statistically significant decreases in binding at the therapeutic target (SERT) and shelter-seeking behavior when fish plasma levels exceeded human therapeutic thresholds. Such observations highlights the strengths of coupling physiologically based pharmacokinetic modeling and AOP approaches and suggest that internal dosimetry should be monitored to advance an understanding of the ecological consequences of SSRI exposure to aquatic vertebrates.