Classifying environmental pollutants: Part 3. External validation of the classification system

In order to validate a classification system for the prediction of the toxic effect concentrations of organic environmental pollutants to fish, all available fish acute toxicity data were retrieved from the ECETOC database, a database of quality-evaluated aquatic toxicity measurements created and maintained by the European Centre for the Ecotoxicology and Toxicology of Chemicals. The individual chemicals for which these data were available were classified according to the rulebase under consideration and predictions of effect concentrations or ranges of possible effect concentrations were generated. These predictions were compared to the actual toxicity data retrieved from the database. The results of this comparison show that generally, the classification system provides adequate predictions of either the aquatic toxicity (class 1) or the possible range of toxicity (other classes) of organic compounds. A slight underestimation of effect concentrations occurs for some highly water soluble, reactive chemicals with low log K(ow) values. On the other end of the scale, some compounds that are classified as belonging to a relatively toxic class appear to belong to the so-called baseline toxicity compounds. For some of these, additional classification rules are proposed. Furthermore, some groups of compounds cannot be classified, although they should be amenable to predictions. For these compounds additional research as to class membership and associated prediction rules is proposed.     

Application of a computational model for Michael addition reactivity in the prediction of toxicity to Tetrahymena pyriformis

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.     

Effects assessment: boron compounds in the aquatic environment

In previous studies, boron compounds were considered to be of comparatively low toxicity in the aquatic environment, with predicted no effect concentration (PNEC) values ranging around 1 mg B/L (expressed as boron equivalent). In the present study, we describe an evaluation of toxicity data for boron available for the aquatic environment by different methods.For substances with rich datasets, it is often possible to perform a species sensitivity distribution (SSD). The typical outcome of an SSD is the Hazardous Concentration 5% (HC₅), the concentration at which 95% of all species are protected with a probability of 95%. The data set currently available on the toxic effects of boron compounds to aquatic organisms is comprehensive, but a careful evaluation of these data revealed that chronic data for aquatic insects and plants are missing. In the present study both the standard assessment factor approach as well as the SSD approach were applied. The standard approach led to a PNEC of 0.18 mg B/L (equivalent to 1.03 mg boric acid/L), while the SSD approach resulted in a PNEC of 0.34 mg B/L (equivalent to 1.94 mg boric acid/L). These evaluations indicate that boron compounds could be hazardous to aquatic organisms at concentrations close to the natural environmental background in some European regions. This suggests a possible high sensitivity of some ecosystems for anthropogenic input of boron compounds. Another concern is that the anthropogenic input of boron could lead to toxic effects in organisms adapted to low boron concentration.     

The evaluation of the equilibrium partitioning method using sensitivity distributions of species in water and soil

The equilibrium partitioning method (EqP-method) can be used to calculate soil quality standards (expressed in mg/kg) from aquatic quality standards (expressed in microg/l) using a partitioning coefficient. The validity of this application of the EqP-method was studied comparing aquatic with terrestrial toxicity data. The data set collected for deriving environmental quality standards in the Netherlands, was used for this study. For 10 organic substances (chlorpyrifos, atrazine, carbofuran, pentachlorophenol, chlordane, aldrin, trichlorobenzene, heptachlor, trichlorophenol and trichloroethene) and for 8 metals, sufficient data were available. The aquatic toxicity data were multiplied by the partitioning coefficient in order to obtain aquatic data expressed in mg/kg. For some compounds the terrestrial toxicity data were significantly higher than the aquatic data but for other compounds it was the other way around. These differences indicate that the EqP-method can give significant over-or underestimations, due to inaccurate partitioning coefficients or differences in species sensitivities. These over- or underestimations can have an impact on the setting of environmental quality standards which are based on the hazardous concentration 5% (HC5) values. The uncertainty in the calculation of HC5 values attributed to the use of the EqP-method, was quantified. The HC5 values derived using the EqP-method were in 5% of the cases more than 20 times higher than the corresponding HC5 values that were derived directly from soil toxicity tests. Despite of this uncertainty the use of the EqP-method can still be advocated for setting soil quality guidelines when only a very limited number of terrestrial toxicity data are available.     

The effect of acidification on the accumulation and toxicity of metals to freshwater invertebrates

This paper reviews the literature to determine if lowered water pH (a) affects metal bioaccumulation in freshwater invertebrates, (b) enhances the toxicity of a given metal, and (c) increases waterborne metal concentrations to levels toxic to invertebrates. The elements considered are mercury, lead, cadmium and aluminum. The available evidence suggests that of these elements only mercury is biomagnified in aquatic foodchains. The bioaccumulation of all these elements is influenced by water pH, but data concerning invertebrates is meagre for mercury and lead. The effect of pH on mercury and lead toxicity to invertebrates is unclear and may be largely species specific. Cadmium toxicity is reduced by lower pH, while aluminum toxicity to invertebrates is markedly higher due to changes in aluminum speciation at low pH.     

A multispecies study to assess the toxic and genotoxic effect of pharmaceuticals: furosemide and its photoproduct

Pharmaceutical products for humans and animals, as well as their related metabolites end up in the aquatic environment after use. Recent investigations show that concentrations of pharmaceuticals are detectable in the order of ng/l-mug/l in municipal wastewater, groundwater and also drinking water. Little is known about the effects, and the hazard of long-term exposure to low concentrations of pharmaceuticals for non-target aquatic organisms. This study was designed to assess the ecotoxicity of furosemide, a potent diuretic agent, and its photoproduct in the aquatic environment. Bioassays were performed on bacteria, algae, rotifers and microcrustaceans to assess acute and chronic toxicity, while the SOS Chromotest and the Ames test were utilized to detect the genotoxic potential of the investigated compounds. A first approach to risk characterization was to calculate the environmental impact of furosemide by measured environmental concentration and predicted no effect concentration ratio (MEC/PNEC). To do so we used occurrence data reported in the literature and our toxicity results. The results showed that acute toxicity was in the order of mg/l for the crustaceans and absent for bacteria and rotifers. Chronic exposure to these compounds caused inhibition of growth population on the consumers, while the algae did not seem to be affected. A mutagenic potential was found for the photoproduct compared to the parental compound suggesting that byproducts ought to be considered in the environmental assessment of drugs. The risk calculated for furosemide suggested its harmlessness on the aquatic compartment.     

An evaluation of global QSAR models for the prediction of the toxicity of phenols to Tetrahymena pyriformis

This study presents an analysis of the ability of a two-parameter response surface, a multiple linear regression and a neural network model to produce global quantitative structure-activity relationships (QSARs) to predict the toxic potency of phenols to Tetrahymena pyriformis. The phenolic toxicity data set analysed is characterised by multiple mechanisms of toxic action. The study aimed to evaluate the confidence that can be applied to the modelling of the differing mechanisms of action. Assessment of confidence was decided in terms of whether the statistics for the global models reflect the ability of the QSARs to model the individual mechanisms of toxic action present in the data set. The results showed that the global statistics only reflected the ability of models to predict the two non-covalent mechanisms (polar narcosis and respiratory uncoupling), with the metabolically transformed and electrophilic mechanism (pre-electrophiles and soft electrophiles) being modelled poorly by all three model building methods. The results confirm the difficulty in modelling electrophilic mechanisms of toxic action. The results also highlight the fact that this poor predictivity is often 'hidden' in good statistical fit of some global models. In particular these results emphasise that for practical predictive purposes the mechanistic applicability domain is required to give confidence to estimated toxicity values.     

The identification of readily bioavailable pollutants in lake shkodra/skadar using semipermeable membrane devices (SPMDs), bioassays and chemical analysis

GOAL, SCOPE AND BACKGROUND: Lake Shkodra/Skadar is the largest lake in the Balkans region and located on the border between Albania to the south and Montenegro to the north. Because of the wide range of endemic, rare or endangered plant and animal species it supports, Lake Shkodra/Skadar and its extensive associated wetlands are internationally recognised as a site of significance and importance (Ramsar site). In recent years, social and economic changes in both Albania and Montenegro have lead to unprecedented levels of urban and industrial effluent entering the lake. Of particular concern is the increasing input of toxic hydrophobic organic pollutants (HOPs) into the lake and the degree to which these compounds are available for uptake by aquatic biota. Semipermeable membrane devices (SPMDs) have been shown to sample the readily bioavailable fraction (dissolved phase) of waterborne HOPs and in doing so provide relevant data for exposure assessment. The aim of the current study was to use SPMD-based sampling in conjunction with appropriate bioassays and chemical analysis to identify readily bioavailable HOPs in the lake. METHODS: SPMDs were constructed and deployed at three sites in the Albanian sector and three sites in the Montenegrin sector of Lake Skadar/Shkodra for 21 days. Following the dialytic recovery of target analytes and size exclusion chromatographic clean-up, aliquots of SPMD samples were subjected to GC-MS scan analysis for major components, GC-MS SIM analysis for 16 priority pollutant polycyclic aromatic hydrocarbons (PP-PAHs) and assayed for EROD-inducing, estrogenic and mutagenic potential using rainbow trout liver cells (RTL-W1), the yeast estrogen screen (YES) and the Ames Test, respectively. RESULTS AND DISCUSSION: A total of 39 compounds were tentatively identified in SPMD samples from the six sampling sites. Alkylated PAHs were the most abundant and ubiquitous compounds present along with various sterols and sterol derivatives. Numerous other compounds remain unidentified. 15 of the 16 targeted PP-PAHs were present in samples from one or more of the sampling sites indicating these compounds are both readily bioavailable and widely distributed in Lake Shkodra/Skadar. Total PP-PAH concentrations ranged between 3991 ng/SPMD and 10695 ng/SPMD. Bioassays carried out on SPMD samples revealed significant EROD-inducing and estrogenic potential at five of the six sampling sites indicating toxicologically relevant compounds are readily available for uptake by resident aquatic biota. EROD-inducing potential was positively correlated with targeted PP-PAH concentration (r2 = 0.74). However, comparison of bioassay- and analytically-derived toxicity equivalents revealed targeted PP-PAHs were responsible for less than 0.06% of the total EROD-inducing potential. CONCLUSIONS AND OUTLOOK: The combination of SPMD-based sampling with appropriate bioassays and chemical analysis provided an effective tool for the identification of environmentally relevant waterborne pollutants in Lake Shkodra/Skadar. Our results show that toxicologically relevant HOPs including EROD-inducing and potentially estrogenic compounds are widely distributed in the lake and readily available for uptake by aquatic biota. Our results also suggest that alkylated PAHs rather than parent compounds may be of greater toxicological relevance in the lake. As anthropogenic influences continue to increase, SPMD-based sampling is expected to play a central role in future research concerned with the identification, monitoring and assessment of the risk posed by HOPs to Lake Shkodra/Skadar's aquatic biota.     

Application of the criteria for classification of existing chemicals as dangerous for the environment

The criteria for classification and labelling of substances as “dangerous for the environment” agreed upon within the European Union (EU) were applied to two sets of existing chemicals. One set (sample A) consisted of 41 randomly selected compounds listed in the European Inventory of Existing Chemical Substances (EINECS). The other set (sample B) comprised 115 substances listed in Annex I of Directive 67/548/EEC which were classified by the EU Working Group on Classification and Labelling of Existing Chemicals. The aquatic toxicity (fish mortality,Daphnia immobilisation, algal growth inhibition), ready biodegradability and n-octanol/water partition coefficient were measured for sample A by one and the same laboratory. For sample B, the available ecotoxicological data originated from many different sources and therefore was rather heterogeneous. In both samples, algal toxicity was the most sensitive effect parameter for most substances. Furthermore, it was found that, classification based on a single aquatic test result differs in many cases from classification based on a complete data set, although a correlation exists between the biological end-points of the aquatic toxicity test systems.     

The impact of pesticides toward parrotfeather when applied at the predicted environmental concentration

Pesticides pose a serious risk for aquatic macrophytes in the environment. They are also detrimental to the rooted macrophytes used in bioassays for assessment. Currently, no data is available for impact of pesticides toward parrotfeather when present at the predicted environmental concentration. The calculated expected environmental concentration was applied to the plants and the effect was compared. Eight of the 18 pesticides showed significantly different impact. All of the other tested pesticides induced a significant change in pigment content of parrotfeather. The RQ values for risk quotient had a value higher than 0.5, so need regulatory action for environment. This study may be the first to evaluate the predicted environmental concentrations reported by pesticide registration in Europe. Additional studies are required to test all pesticides within one group since the compounds tested may depict a wide toxicity level. Furthermore, the tests should include more than one macrophyte, e.g. one rooted and one non-rooted species, in order to provide a better understanding on pesticide toxicity.     

The health effects and ecological significance of chlorine residuals in water

During the past several years, chlorine residuals and chlorinated organic compounds in drinking waters and aquatic environments have become a significant topic of study for scientists concerned about the quality of life in aquatic ecosystems as well as general public health. The effects of direct toxicity and/or carcinogenicity to human and aquatic life are the focal points for this concern.The effects of chloramines and chlorinated organic compounds present in the water distribution system after chlorination treatments are reviewed. Also discussed are the effects of chlorinated discharges from municipal secondary treatment plants and power plants on human health and aquatic life. The toxic significance of environmental chemicals are described.     

Photo-induced toxicity of PAHs to Hyalella azteca and Chironomus tentans: effects of mixtures and behavior

In the aquatic environment, polycyclic aromatic hydrocarbon (PAH) contamination can result from several anthropogenic sources such as petroleum runoff, industrial processes, and petroleum spills. When ultraviolet light (UV) is present at sufficient intensity, the acute toxicity of some PAHs to aquatic biota is greatly enhanced. This photo-induced toxicity of PAHs is directly influenced by the amount of PAH and by the level of UV intensity present in the aquatic environment. Thus, behavioral responses and habits that affect an aquatic organism's exposure to UV as well as exposure to PAHs can influence the extent to which damage due to photo-induced toxicity occurs. Experiments demonstrated the effects of photo-induced toxicity of anthracene and fluoranthene on the survival of two benthic macroinvertebrates, the midge Chironomus tentans and the freshwater amphipod Hyalella azteca. This study further investigated the survival and behavior of the test organisms in different substrates (no substrate, a sand monolayer, leaf discs, and sediment) with and without UV. The free-swimming, epibenthic H. azteca avoided the effects of photo-induced toxicity of PAHs to some extent by hiding in leaves when this substrate was available. Results emphasize the importance of organisms' behavior in affecting the photo-induced toxicity of PAHs in the aquatic environment.     

Toxicity of the mixture of selected antineoplastic drugs against aquatic primary producers

The residues of antineoplastic drugs are considered as new and emerging pollutants in aquatic environments. Recent experiments showed relatively high toxicity of 5-fluorouracil (5-FU), imatinib mesylate (IM), etoposide (ET) and cisplatin (CP) that are currently among most widely used antineoplastic drugs, against phytoplankton species. In this study, we investigated the toxic potential of the mixture of 5-FU?+?IM?+?ET against green alga Pseudokirchneriella subcapitata and cyanobacterium Synechococcus leopoliensis, and the stability and sorption of these drugs to algal cells. Toxic potential of the mixture was predicted by the concepts of ‘concentration addition’ and ‘independent action’ and compared to the experimentally determined toxicity. In both test species, the measured toxicity of the mixture was at effects concentrations EC₁₀–EC₅₀ higher than the predicted, whereas at higher effect concentration (EC₉₀), it was lower. In general, P. subcapitata was more sensitive than S. leopoliensis. The stability studies of the tested drugs during the experiment showed that 5-FU, IM and CP are relatively stable, whereas in the cultures exposed to ET, two transformation products with the same mass as ET but different retention time were detected. The measurements of the cell-linked concentrations of the tested compounds after 72 h exposure indicated that except for CP (1.9 % of the initial concentration), these drugs are not adsorbed or absorbed by algal cells. The results of this study showed that in alga and cyanobacteria exposure to the mixture of 5-FU?+?ET?+?IM, in particular at low effect concentration range, caused additive or synergistic effect on growth inhibition, and they suggest that single compound toxicity data are not sufficient for the proper toxicity prediction for aquatic primary producers.     

Bioassays with Vibrio fischeri for the assessment of delayed toxicity

The standardized bioluminescence assay with Vibrio fischeri underestimates the aquatic toxicity of chemicals which interfere with metabolic pathways supporting long term processes like growth and reproduction due to its short incubation time (30 min). Therefore this short term assay was compared with two alternative bioassays with prolonged incubation times using the same test organism: the growth inhibition assay (7 h) and the long term bioluminescence assay (24 h). Two sets of compounds were selected to reflect acute and delayed toxicity. The first group comprised pentachlorophenol, dodecylpyridiniumbromide and 3,4-dichloroaniline and the second nalidixic acid, chloramphenicol and streptomycinsulfate. The effects of compounds with acute toxicity are determined with similar sensitivity in all bioassays. Substances with delayed toxicity show only minor or no toxicities in the standardized short term bioassay but severe effects in both long term bioassays independent of the parameter used. It is concluded that the standardized short term bioluminescence assay exhibits serious limitations for the assessment of aquatic toxicity. The long term bioassays, however, may help to overcome these limitations.     

Acute toxicity of leachates of tire wear material to Daphnia magna--variability and toxic components

Large amounts of tire rubber are deposited along the roads due to tread wear. Several compounds may leach from the rubber and cause toxicity to aquatic organisms. To investigate the toxic effects of tire wear material from different tires, rubber was abraded from the treads of twenty-five tires. Leachates were prepared by allowing the rubber to equilibrate with dilution water at 44 degrees C for 72 h. Then the rubber was filtered from the leachates, and test organisms (Daphnia magna) were added. Forty-eight hour EC50s ranged from 0.5 to >10.0 g l(-1). The toxicity identification evaluation (TIE) indicated that non-polar organic compounds caused most of the toxicity. UV exposure of the filtered tire leachates caused no significant increase in toxicity. However, when tested as unfiltered leachates (the rubber was not filtered from the leachates before addition of D. magna) photo-enhanced toxicity was considerable for some tires, which means that test procedures are important when testing tire leachates for aquatic (photo) toxicity. The acute toxicity of tire wear for Daphnia magna was found to be <40 times a predicted environmental concentration based on reports on the concentration of a tire component found in environmental samples, which emphasizes the need for a more extensive risk assessment of tire wear for the environment.     

Toxic effects of endocrine disrupters on freshwater sponges: common developmental abnormalities

Endocrine disrupters are of substantial concern, in large part because effects of these compounds on the growth and development of many aquatic organisms are unknown. We examined toxic effects of three substances (ethylbenzene, nonylphenol, and bisphenol A), that are known to be hormonally active in many animals, on growth and development of two species of freshwater sponge. A common developmental abnormality was observed when sponges were treated with each of these compounds. The three compounds also caused significant reductions in growth rates. Lower concentrations resulted in malformed water vascular systems in several replicates. The utility of freshwater sponge bioassays is discussed as it relates to understanding possible mechanisms of action of endocrine disrupters on aquatic invertebrates.     

Humic substances as catalysts in condensation reactions

Humic substances (HS) demonstrate appreciable impact on the rate of the condensation reactions as shown in the example of the reaction between hydrazine and 4-(dimethylamino)-benzaldhyde in an aquatic environment. The catalytic activity of HS has also been demonstrated in Knoevenagel and Claisen-Schmidt reactions for condensation of carbonyl compounds with CH acids. The aquatic fulvic acids are the most active in these reactions. The velocity of the studied reactions also depends on pH, temperature, the concentration and origin of HS used. A possible micellar and acid-base catalysis mechanism in aquatic media has been suggested.