Joop L. M. Hermens

Classifying environmental pollutants

Abstract In this paper a scheme is presented that makes it possible to classify a large number of organic pollutants into one of four classes, viz: [1] inert chemicals, [2] less inert chemicals, [3] reactive chemicals and [4] specifically acting chemicals. For chemicals that are thus classified as belonging to one of these four classes it is possible to calculate either an expected effect concentration (inert chemicals), such as the LC 50 , or an expected range of possible effect concentrations, from a compounds octanol/water partition coefficient (Log K ow ). For chemicals that cannot be classified as belonging to one of these four classes no prediction can be made. This approach can be implemented to estimate aquatic effect concentrations, which can be used to derive preliminary environmental quality objectives, or for the prioritisation of chemicals for subsequent testing. Moreover, these estimates could be of great value in risk and hazard assessment. To our opinion, this approach represents the current state-of-the-art in estimation methods for aquatic toxicology. This paper is especially focused on identifying the limits of applicability of Quantitative Structure-Activity Relationships for predicting aquatic toxicity, as, according to Hart (1991) it “…is important not to exaggerate the accuracy of prediction for models…” [and] “…to make clear to the user the limitations of the relationship.”

QSAR modelling of soil sorption. Improvements and systematics of log KOC vs. log KOW correlations

A systematic study was performed to evaluate the quality and reliability of the quantitative relationships between the soil sorption coefficients and the n-octanol/water partition coefficients (log KOC vs. log KOW). A system of QSAR models has been derived which is based on a reliable set of experimental log KOW data (LOGPSTAR data) or reliable estimates calculated with the latest version of the ClogP algorithm. Particular emphasis has been made to clearly define the boundaries for application of developed models as well as the quality of estimates. Thus, for each developed model the application domain is clearly defined through the chemical (structural) domain, substituents domain, and X-variable domain. Finally, the QSAR model with the first-order molecular connectivity indices has been incorporated in the derived system of QSAR models since the soil sorption estimates of the predominantly hydrophobic chemicals based on the log KOW data have large uncertainties, particularly in the log KOW data range from 4 to 7.5.

Quantitative structure-activity relationships and toxicity studies of mixtures of chemicals with anaesthetic potency: Acute lethal and sublethal toxicity to Daphnia magna

In this study quantitative structure-activity relationships (QSARs) were calculated between hydrophobicity of a group of organic chemicals with anaesthetic potency and toxicity (immobilization, mortality and inhibition of reproduction) to Daphnia magna. Differences in slopes of the high quality QSARs might be explained in terms of possible different sites of action for the three criteria of effect. The combined effects of mixtures of 5–50 chemicals on immobilization and mortality did not deviate from additivity, while the effect on reproduction deviated somewhat from it.

Comparison of the susceptibility of 22 freshwater species to 15 chemical compounds. I. (Sub)acute toxicity tests

Abstract The relative susceptibility of 22 taxonomically different species (bacteria, algae, protozoans, crustaceans, insects, coelenterates, molluscs, fishes and amphibians) to chemicals was determined by comparing the (sub)acute toxicity data of 15 test substances. Marked differences were observed in the susceptibility among the species with respect to the individual test compounds (up to a factor 9000). In contrast to this, differences were small (less than a factor 7) when the relative susceptibilities based on toxicity data on all compounds were taken into account. This tendency was also shown by comparing the susceptibilities based on quantitative structure-activity relationships. Thus, there is no such thing as the most susceptible species to chemicals. As the susceptibility of the species is highly pollutant-specific, at least a set of tests on different species will be required for toxicity screening. However, results indicated that a standard test combination with representative species of green algae, crustaceans and fishes failed to indicate the full toxic potential of chemicals. Since incorporation of a Microcystis aeruginosa test improved the combination in estimating acute toxic levels of chemicals, it is recommended to include this test in both national and international ecotoxicological testing programmes.

Measurement of free concentrations using negligible depletion-solid phase microextraction (nd-SPME)

Measurement of free concentration is necessary to determine the effective or bioavailable quantity of a chemical, and is also a way of determining the binding affinity or partition coefficient of a compound. This review gives a brief overview of the methods available to measure free concentrations and will focus on negligible depletion-solid phase microextraction (nd-SPME). Theoretical as well as experimental details of the method are discussed, including potential confounding factors, such as fouling, diffusion layer effects, and calibration.

Multivariate analysis of aquatic toxicity data with PLS

A common task in data analysis is to model the relationships between two sets of variables, the descriptor matrixX and the response matrixY. A typical example in aquatic science concerns the relationships between the chemical composition of a number of samples (X) and their toxicity to a number of different aquatic species (Y). This modelling is done in order to understand the variation ofY in terms of the variation ofX, but also to lay the ground for predictingY of unknown observations based on their knownX-data. Correlations of this type are usually expressed as regression models, and are rather common in aquatic science. Often, however, the multivariateX andY matrices invalidate the use of multiple linear regression (MLR) and call for methods which are better suited for collinear data. In this context, multivariate projection methods represent a highly useful alternative, in particular, partial least squares projections to latent structures (PLS). This paper introduces PLS, highlights its strengths and presents applications of PLS to modelling aquatic toxicity data. A general discussion of regression, comparing MLR and PLS, is provided.

A quantitative property-property relationship (QPPR) approach to estimate in vitro tissue-blood partition coefficients of organic chemicals in rats and humans.

Abstract The present study describes quantitative property-property relationships (QPPRs) for the partitioning of organic chemicals between blood and tissue homogenates from both rats and humans. The n-octanol/water partition coefficient (Kow) is used as a non-biological descriptor. QPPRs for human tissue-blood partition coefficients (PCs) were derived from a dataset of 24 volatile organic compounds in blood, liver, muscle, fat, kidney and brain tissue homogenates. QPPRs were also derived for the PCs of rat tissues, using a dataset of 42 volatile organic compounds in blood, liver, muscle and fat tissue homogenates. These QPPRs were evaluated using a test set of 10 compounds for human tissues and a test set of 14 compounds for rat tissues. For both human and rat test sets, it was generally observed that most estimated PCs were within a range of 50–200% of their experimental values. The present approach is concluded to offer a rapid means for the estimation of tissue-blood PCs of compounds on the basis of Kow values. In addition, indications for a possible role of tissue components other than lipid and water in the tissue-blood partitioning process of compounds were observed from the calibration results of the model.

Joint toxicity of mixtures of 8 and 24 chemicals to the guppy (Poecilia reticulata).

Abstract The acute median lethal concentrations of equitoxic mixtures of 8 and 24 toxicants with diverse modes of action to guppies were determined. To quantify the joint toxicity, the results are expressed by means of the Mixture Toxicity Index (MTI). The toxicity of the mixtures was near concentration addition. Concentrations of the chemicals of about 0.1 of their LC50s contributed to the toxicity of the mixtures.

Quantitative structure-activity relationships and mixture toxicity studies of chloro- and alkylanilines at an acute lethal toxicity level to the guppy (Poecilia reticulata)

Quantitative structure-activity relationships (QSARs) were calculated for the acute lethal toxicities (14-day LC50) to the guppy (Poecilia reticulata) of anilines, with several hydrophobicity characteristics and the Hammett sigma constant as parameters. Calculated and experimental Poct values and II constants were used as hydrophobicity characteristics. Introduction of Hammett constants improved the quality of the QSARs. Together with the QSAR studies the toxicities of mixtures of the anilines were determined. The toxicities of three mixtures did not deviate from concentration addition.

JOINT EFFECTS OF A MIXTURE OF 14 CHEMICALS ON MORTALITY AND INHIBITION OF REPRODUCTION OF DAPHNIA MAGNA

The toxicity to Daphnia magna of a mixture of 14 aquatic pollutants with several chemical structures and probable modes of action was determined. The joint effect of this mixture on acute mortality was compared with the effects on inhibition of reproduction. The joint toxicity in the reproduction test was lower in comparison with the mortality test. This study supports the idea that the potential for addition is reduced when more specific sublethal toxicity criteria are studied. Although the joint toxicity at sublethal level is lower than at lethal level, the toxicity of the mixtures remains much higher than that of the individual chemicals and is still near concentration addition.