The limits of bioaccumulation of organic pigments in fish: their relation to the partition coefficient and the solubility in water and octanol

Colorants in coatings

The aim of this chapter is to provide a compact overview of colorants and their use in coatings including a brief introduction to paint technology and its raw materials. In addition, it will focus on individual colorants by collecting information from the available literature mainly for their use in coatings. Publications on colorants in coatings applications are in many cases standard works that cover the wider aspects of color chemistry and paint technology and are explicitly recommended for a more detailed study of the subject [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]. Articles or information on paint formulation using coatings which contain colorants are rare [19]. This formulation expertise is often company property as it is the result of many years of effort built up over very long series of practical “trial-and-error” optimization tests and, more recently, supported by design of experiment and laboratory process automation [20, 21]. Therefore, it is protected by rigorous secrecy agreements. Formulations are in many ways part of a paint manufacturer’s capital, because of their use in automotive coatings, coil coatings, powder coatings, and specialist knowledge is indispensable to ensure their successful industrial use [22]. An important source to learn about the use of pigments in different coating formulations are guidance or starting formulations offered by pigment, additive, and resin manufacturers. These are available upon request from the technical service unit of these companies. Coating formulations can also be found scattered in books on coating and formulation technology [4, 5, 18, 23,24,25,26,27]. This overview can in no way claim to be complete, as the literature and relevant journals in this field are far too extensive. Nevertheless, it remains the author’s hope that the reader will gain a comprehensive insight into the fascinating field of colorants for coatings, including its literature and current research activities and last but not least its scientific attractiveness and industrial relevance.

Solubility of organic compounds in octanol: Improved predictions based on the geometrical fragment approach

Two new models are introduced to predict the solubility of chemicals in octanol (S_oct), taking advantage of the extensive character of log(S_oct) through a decomposition of molecules into so-called geometrical fragments (GF). They are extensively validated and their compliance with regulatory requirements is demonstrated. The first model requires just a molecular formula as input. Despite an extreme simplicity, it performs as well as an advanced random forest model involving 86 descriptors, with a root mean square error (RMSE) of 0.64 log units for an external test set of 100 molecules. For the second one, which requires the melting point T_m as input, introducing GF descriptors reduces the RMSE from about 0.7 to <0.5 log units, a performance that could previously be obtained only through the use of Abraham descriptors. A script is provided for easy application of the models, taking into account the limits of their applicability domains.

The solubility of liquid and solid compounds in dry octan-1-ol

Using literature data on solubilities, equations have been constructed for the correlation of solubilities of liquids and solids in dry octanol, as log Soct (M). The best equation statistically uses Abraham descriptors together with the compound melting point. For 282 compounds the equation standard deviation is no more than 0.47 log units. If the melting point term is omitted the standard deviation rises to 0.63 log units. It is suggested that if Abraham descriptors are available, these equations represent the most satisfactory equations for the correlation and estimation of solubilities in dry octanol. If these descriptors are not available, then the simple equation of Yalkowsky can be used, although for 223 compounds the equation standard deviation rises to 0.71 log units.

Physicochemical properties/descriptors governing the solubility and partitioning of chemicals in water-solvent-gas systems. Part 2. Solubility in 1-octanol

On the basis of octanol solubility data (log S(o)) for 218 structurally diverse solid chemicals it was shown that the exclusive consideration of melting points did not provide satisfactory results in the quantitative prediction of this parameter (s = 0.92). The application of HYBOT physicochemical descriptors separately (s = 0.94) and together with melting points (s = 0.70) in the framework of a common regression model also was not successful, although contributions of volume-related and H-bond terms to solubility in octanol were identified. It was proposed that the main reason for such behaviour was the different crystal lattice interaction of different classes of chemicals. Successful calculations of the solubility in octanol of chemicals of interest were performed on the basis of the experimental solubility of structurally/physicochemically/numerically similar nearest neighbours with consideration of their difference in physicochemical parameters (molecular polarisability, H-bond acceptor and donor factors (s = 0.66)) and of these descriptors together with melting point differences (s = 0.38). Good results were obtained for all compounds having nearest neighbours with sufficient similarity, expressed by Tanimoto indexes, and by distances in the scaled 3D descriptor space. Obviously the success of this approach depends on the size of the database.

Isolation and identification of xenobiotic aryl hydrocarbon receptor ligands in dyeing wastewater

Dyeing wastewater collected in Kyoto city, Japan, was investigated for the occurrence of aryl hydrocarbon receptor (AhR) ligands by using an AhR-responsive reporter gene assay. Concentrated extracts of wastewater samples elicited a dose-dependent increase in AhR ligand activity, and several hydrophobic HPLC fractions of the extracts were highly effective in inducing AhR ligand activity. Three potential AhR ligands were isolated from these fractions and identified to be Disperse Red 92, Disperse Yellow 64, and 3'-hydroxybenzo[b]quinophthalone by using HPLC and LC-MS/MS. Disperse Red 92, which has also been detected in the treated effluent from a sewage plant receiving the wastewater, is an anthraquinone disperse dye showing weak AhR binding affinity in the assay. Disperse Yellow 64 and 3'-hydroxybenzo[b]quinophthalone are quinoline disperse dyes capable of activating the AhR at nanomolar concentrations. In particular, Disperse Yellow 64 is a highly potent AhR ligand that was 3 times more effective in inducing AhR ligand activity than beta-naphthoflavone in the assay. Quinoline disperse dyes are suggested to be a new class of xenobiotic AhR ligands which pose a danger to aquatic biota and human health.

Animal use replacement, reduction, and refinement: development of an integrated testing strategy for bioconcentration of chemicals in fish

When addressing the use of fish for the environmental safety of chemicals and effluents, there are many opportunities for applying the principles of the 3Rs: Reduce, Refine, and Replace. The current environmental regulatory testing strategy for bioconcentration and secondary poisoning has been reviewed, and alternative approaches that provide useful information are described. Several approaches can be used to reduce the number of fish used in the Organization for Economic Cooperation and Development (OECD) Test Guideline 305, including alternative in vivo test methods such as the dietary accumulation test and the static exposure approach. The best replacement approach would seem to use read-across, chemical grouping, and quantitative structure-activity relationships with an assessment of the key processes in bioconcentration: Adsorption, distribution, metabolism, and excretion. Biomimetic extraction has particular usefulness in addressing bioavailable chemicals and is in some circumstances capable of predicting uptake. Use of alternative organisms such as invertebrates should also be considered. A single cut-off value for molecular weight and size beyond which no absorption will take place cannot be identified. Recommendations for their use in bioaccumulative (B) categorization schemes are provided. Assessment of biotransformation with in vitro assays and in silico approaches holds significant promise. Further research is needed to identify their variability and confidence limits and the ways to use this as a basis to estimate bioconcentration factors. A tiered bioconcentration testing strategy has been developed taking account of the alternatives discussed.

Bioconcentration of n-dodecane and its highly branched isomer 2,2,4,6,6-pentamethylheptane in fathead minnows

Petroleum products are complex mixtures of hydrocarbons. They are important as constituents of fuels and lubricants, and as key raw materials for the chemicals industry. Since there is a potential for accidental releases to the aquatic environment, bioaccumulation of higher hydrocarbons is of concern. Here, the bioconcentration behaviour of two representative hydrocarbons, the dodecane isomers n-dodecane and 2,2,4,6,6-pentamethylheptane (PMH), was investigated in fathead minnows at concentrations in water below their maximum aqueous solubility. The concentration of n-dodecane in fish did not exceed our method limit of detection of 60 microg/kg. In contrast, PMH could be quantified in fish. No significant increase in the ratio of PMH concentrations in fish to water could be detected indicating that an exposure time of 4-10 days is sufficient to approach steady-state. For n-dodecane the upper limit of the bioconcentration factor (BCF) is estimated by dividing the method limit of detection by the exposure concentration and a value of 240 l/kg is derived. For PMH the bioconcentration factor, estimated as the average fish/water concentration ratio during the steady-state part of the experiment, ranges between 880 and 3,500 l/kg. The BCFs of both compounds are small compared to their hydrophobicity. Given that both linear and branched hydrocarbons are known to be biotransformed by fish, it appears that efficient metabolism of the test compounds in fathead minnows prevents bioaccumulation.

Bioavailability of organochlorines in fish

1. An overview is presented of the process of chemical sorption and membrane permeation that control the bioavailability of organochlorines in natural waters. 2. The mechanisms of membrane permeation and chemical sorption to various types of dissolved and particulate matter is discussed and simple models are presented that can be used to estimate the bioavailability of organic chemicals in natural waters.

Use of polynomial expressions to describe the bioconcentration of hydrophobic chemicals by fish

For the bioconcentration of hydrophobic chemicals by fish, relationships have been previously established between uptake rate constants (k1) and the octanol/water partition coefficient (Kow), and also between the clearance rate constant (k2) and Kow. These have been refined and extended on the basis of data for chlorinated hydrocarbons, and closely related compounds including polychlorinated dibenzodioxins, that covered a wider range of hydrophobicity (2.5 less than log Kow less than 9.5). This has allowed the development of new relationships between log Kow and various factors, including the bioconcentration factor (as log KB), equilibrium time (as log teq), and maximum biotic concentration (as log CB), which include extremely hydrophobic compounds previously not taken into account. The shape of the curves generated by these equations are in qualitative agreement with theoretical prediction and are described by polynomial expressions which are generally approximately linear over the more limited range of log Kow values used to develop previous relationships. The influences of factors such as hydrophobicity, aqueous solubility, molecular weight, lipid solubility, and also exposure time were considered. Decreasing lipid solubilities of extremely hydrophobic chemicals were found to result in increasing clearance rate constants, as well decreasing equilibrium times and bioconcentration factors.

A novel method for measuring membrane-water partition coefficients of hydrophobic organic chemicals: comparison with 1-octanol-water partitioning

A novel method of measuring membrane-water partitioning characteristics of very hydrophobic organic chemicals is described. Partition coefficients are reported for a series of halogenated aromatic hydrocarbons of varying molar volume between water and L-a-phosphatidylcholine dimyristoyl (DMPC) membrane vesicles and two solvents, n-hexane and 1-octanol. The results indicate that n-hexane and 1-octanol are satisfactory surrogates for DMPC membranes for chemicals with 1-octanol-water partition coefficients (log KOW) less than 5.5 or molar volumes less than 230 cm3/mol. Chemicals with higher log KOW or molar volume values display marked differences in membrane-water, 1-octanol-water, and n-hexane-water partitioning. Implications for lipid- and organism-water partitioning of hydrophobic chemicals are discussed.