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Chemical activity quantifies the energetic level of an organic compound relative to its pure liquid [0–1], and several studies have reported that baseline toxicity generally requires chemical activities of 0.01–0.1. The first aim was to challenge this chemical activity range for baseline toxicity. Algal growth inhibition data (median effective concentrations, EC 50 ) were compiled from two recent studies and included 108 compounds categorised as non-polar (mode of toxic action, MOA1) and polar (MOA2) narcotics. These data were linked to chemical activity by (1) plotting them relative to a regression for (subcooled) liquid solubility (S L ), which served as visual reference for chemical activity of unity and (2) determining EC 50 /S L ratios that essentially equal median effective chemical activity (Ea 50 ). Growth inhibition required chemical activity >0.01 for MOA1 and >0.001 for MOA2 compounds. The second aim was to identify compounds exerting excess toxicity, i.e., when growth inhibition occurred at chemical activity <0.001. From a recent review with 2323 data entries, 315 EC 50 values passed our selection criteria. 280 of these EC 50 values were within or near the baseline toxicity range (Ea 50 >0.001), and 25 compounds were found to exert excess toxicity (Ea 50 <0.001). Of these compounds, 16 are pesticides or precursors. Methodologically, this study includes two methods for translating EC 50 values into the chemical activity framework, each having advantages and limitations. Scientifically, this study confirms that baseline toxicity generally requires chemical activities of 0.01–0.1 and extends the application of the chemical activity approach beyond baseline toxicity, by demonstrating its utility to identify compounds that exert excess toxicity. [ABSTRACT FROM AUTHOR]

Sediment cores and bottom water samples from across the Baltic Sea region were analyzed for freely dissolved concentrations (C free ), total sediment concentrations (C T ) and the dissolved aqueous fraction in water of seven indicator PCBs. Ex-situ equilibrium sampling of sediment samples was conducted with polydimethylsiloxane (PDMS) coated glass fibers that were analyzed by automated thermal desorption GC-MS, which yielded PCB concentrations in the fiber coating (C PDMS ). Measurements of C PDMS and C T were then applied to determine (i) spatially resolved freely dissolved PCB concentrations; (ii) baseline toxicity potential based on chemical activities (a); (iii) site specific mixture compositions; (iv) diffusion gradients at the sediment water interface and within the sediment cores; and (vi) site specific distribution ratios (K D ). The contamination levels were low in the Gulf of Finland and moderate to elevated in the Baltic Proper, with the highest levels observed in the western Baltic Sea. The SPME method has been demonstrated to be an appropriate and sensitive tool for area surveys presenting new opportunities to study the in-situ distribution and thermodynamics of hydrophobic organic chemicals at trace levels in marine environments. [ABSTRACT FROM AUTHOR]

Charged organic chemicals are a prevailing challenge for toxicity modelling. In this contribution we strive to recapitulate the lessons learned from the well-known modelling of narcosis (or baseline toxicity) of neutral chemicals and apply the concept to charged chemicals. First we reevaluate the organism- and chemical independent critical membrane concentration causing 50% mortality,. c mem t o x , based on a critical revision of a previously published toxicity dataset for neutral chemicals. In accordance to values reported in the literature we find a mean value for c mem t o x of roughly 100 mmol/kg (membrane lipid) for a broad variety of 42 aquatic organisms (333 different chemicals), albeit with a considerable scatter. Then we apply this concept to permanently charged ionic liquids (ILs). Using COSMO mic , a quantum mechanically based mechanistic model that makes use of the COSMO-RS theory, we predict membrane-water partition coefficients ( K mem/w ) of the anionic and cationic IL components. Doing so, c mem t o x ( t o t a l ) for permanently charged ILs can be estimated assuming independent, concentration additive contributions of the cationic and its respective anionic species. The resulting values for some of the toxicity data for ionic liquids are consistent with the expected range for baseline toxicity for neutral chemicals while other values are consistently greater or smaller. Based on the calculation of toxic ratios we identify ILs that exert a specific mode of toxic action. Limitations of the modelling approach especially but not exclusively due to the use of nominal concentrations instead of freely-dissolved concentrations in the published literature are critically discussed. [ABSTRACT FROM AUTHOR]

Three water contaminants were selected to be tested in the zebrafish embryo toxicity test (DarT) in order to investigate the sensitivity of the zebrafish embryo toxicity test with respect to mixture effect detection. The concentration-response curves for the observed effects lethality and hypo-pigmentation were calculated after an exposure of the embryos for 96 h with a fungicide (carbendazim), a plasticizer or propellent precursor (2,4-DNT: 2,4- dinitrotoluene) and an aromatic compound (AαC: 2-amino-9H-pyrido[2,3- b ]indol), respectively. Follow-up mixture tests were based on the calculated LC 50 or EC 50 of the single compounds and combined effects were predicted according to the mixture concepts of concentration addition (CA) and independent action (IA). The order of toxicity for the single substances was carbendazim (LC 50 = 1.25 μM) < AαC (LC 50 = 8.16 μM) < 2,4-DNT (LC 50 = 177.05 μM). For AαC and 2,4 DNT hypo-pigmentation was observed in addition (AαC EC 50 = 1.81 μM; 2,4-DNT EC 50 = 8.81 μM). Two binary and one ternary mixture were studied on lethality and one on hypo-pigmentation: 2,4-DNT/AαC (LC 50 = 119.21 μM, EC 50 = 5.37 μM), carbendazim/AαC (LC 50 = 4.49 μM) and AαC/Carbendazim/2,4 DNT (LC 50 = 108.62 μM). Results showed that the effects were in agreement with the CA model when substances were tested in mixtures. Therefore, in a reasonable worst case scenario substance combination effects in fish embryos were at maximum only prone to overestimation when using CA as the mixture concept. [ABSTRACT FROM AUTHOR]

Recently, high-quality data were published on the algal growth inhibition caused by 50 non-polar narcotic compounds, of which 39 were liquid compounds with defined water solubility. In the present study, the toxicity data for these liquids were applied to challenge the chemical activity range for baseline toxicity. First, the reported effective concentrations (EC 50 ) were divided by the respective water solubilities (S water ), since the obtained EC 50 /S water ratio essentially equals the effective chemical activity (Ea 50 ). The majority of EC 50 /S water ratios were within the expected chemical activity range of 0.01–0.1 for baseline toxicity, and none of the ratios were significantly below 0.01. On a practical level, these findings suggest EC 50 values for baseline toxicity to be at or above 1% of liquid solubility, which would have been accurate or conservative for all 39 liquids with defined water solubility in the applied dataset. On an environmental risk assessment level, predicted no-effect concentrations (PNECs) for baseline toxicity could even be set as a percentage of saturation, which can easily be extended to mixtures. However, EC 50 values well below 1% of liquid saturation can still occur and would be a direct indication of excess toxicity. [ABSTRACT FROM AUTHOR]

Polybrominated diphenylethers (PBDEs) and hexabromocyclododecane (HBCDD) are major brominated flame retardants (BFRs) that are now banned or under restrictions in many countries because of their persistence, bioaccumulation potential and toxicity (PBT properties). However, there is a wide range of alternative BFRs, such as decabromodiphenyl ethane and tribromophenol, that are increasingly used as replacements, but which may possess similar hazardous properties. This necessitates hazard and risk assessments of these compounds. For a set of 36 alternative BFRs, we searched 25 databases for chemical property data that are needed as input for a PBT assessment. These properties are degradation half-life, bioconcentration factor (BCF), octanol–water partition coefficient ( K ow ), and toxic effect concentrations in aquatic organisms. For 17 of the 36 substances, no data at all were found for these properties. Too few persistence data were available to even assess the quality of these data in a systematic way. The available data for K ow and toxicity show surprisingly high variability, which makes it difficult to identify the most reliable values. We propose methods for systematic evaluations of PBT-related chemical property data that should be performed before data are included in publicly available databases. Using these methods, we evaluated the data for K ow and toxicity in more detail and identified several inaccurate values. For most of the 36 alternative BFRs, the amount and the quality of the PBT-related property data need to be improved before reliable hazard and risk assessments of these substances can be performed. [ABSTRACT FROM AUTHOR]

Highlights: [•] REACH-relevant algal toxicity data were obtained for 50 nonpolar narcotic chemicals. [•] Most of the tested compounds so far lacked published algal growth inhibition values. [•] Toxicity of non-polar narcotic compounds correlated with hydrophobicity: R 2 =0.95. [•] MLR QSAR model was derived for non-polar and polar narcotic compounds: R 2 =0.92. [•] The Verhaar classification of non-polar narcotics appears to apply for algae. [Copyright &y& Elsevier]

Abstract: A computational model to predict acute aquatic toxicity to the ciliate Tetrahymena pyriformis has been developed. A general prediction of toxicity can be based on three consecutive steps: 1. Identification of a potential reactive mechanism via structural alerts; 2. Confirmation and quantification of (bio)chemical reactivity; 3. Establishing a relationship between calculated reactivity and toxicity. The method described herein uses a combination of a reactive toxicity (RT) model, including computed kinetic rate constants for adduct formation (log k) via a Michael acceptor mechanism of action, and baseline toxicity (BT), modelled by hydrophobicity (octanol–water partition coefficient). The maximum of the RT and BT values defines acute toxicity for a particular compound. The reactive toxicity model is based on site-specific steric and quantum chemical ground state electronic properties. The performance of the model was examined in terms of predicting the toxicity of 106 potential Michael acceptor compounds covering several classes of compounds (aldehydes, ketones, esters, heterocycles). The advantages of the computational method are described. The method allows for a closer and more transparent mechanistic insight into the molecular initiating events of toxicological endpoints. [Copyright &y& Elsevier]

In the current study, improved exposure control and measurements were applied for the aquatic toxicity testing of a highly hydrophobic organic compound. The aim was to reliably determine the ecotoxicity of the model compound dodecylbenzene (DDB, Log K OW = 8.65) by applying passive dosing for aquatic toxicity testing exactly at the solubility limit. Methodologically, silicone O-rings were saturated by immersion in pure liquid DDB (i.e., "loading by swelling") and then used as passive dosing donors. Daphnia immobilization and fish embryo toxicity tests were successfully conducted and provide, together with recently reported algal growth inhibition data, a full base-set of ecotoxicological data according to REACH. All tests were conducted in closed test systems to avoid evaporative losses, and exposure concentrations were measured throughout test durations. The Daphnia test was optimized by placing the O-rings in cages to prevent direct contact between daphnids and the passive dosing donor. Toxicologically, Daphnia magna immobilization was 19.3 ± 8% (mean ± 95% CI; 6 tests) within 72 h, whereas Danio rerio fish embryos did not show any significant lethal or sublethal toxic responses within 96 h. Growth rate inhibition for the algae Raphidocelis subcapitata was previously reported to be 13 ± 5% in a first and 8 ± 3% in a repeated test. These results for aquatic organisms, spanning three trophic levels, demonstrate toxicity of a highly hydrophobic compound and suggest that improvements of the current ecotoxicological standard tests are needed for these "difficult-to-test" chemicals. Furthermore, the obtained toxicity results significantly question the existence of a generic Log K OW cut-off in baseline toxicity. Image 1 • Aquatic toxicity testing of a highly hydrophobic liquid at its solubility limit. • Constant exposure by the application of passive dosing. • Suggested improvements of current standard test systems for hydrophobic chemicals. • Full base-set of ecotoxicological data according to REACH (three trophic levels). • Evidence against the existence of a generic Log K OW cut-off in baseline toxicity. [ABSTRACT FROM AUTHOR]