Acute and chronic effects of carrier solvents in aquatic organisms: a critical review

Fathead minnow response to broad-range exposure of β-sitosterol concentrations during life-cycle testing

The β-sitosterol concentration in pulp and paper mill effluents is typically greater than that of other phytosterols and has been shown to cause a variety of effects in fish. The authors exposed fathead minnow (Pimephales promelas) to low (22 ± 0.93 µg/L), medium-low (70 ± 2.1 µg/L), medium-high (237 ± 5.5 µg/L), and high (745 ± 16.2 µg/L) concentrations of β-sitosterol as well as negative (water), positive (ethynyl estradiol, 16 ± 0.58 ng/L), and carrier (0.6 mL/L acetone) controls. Fish were monitored over a full life cycle for population-level endpoints including growth and survival, reproductive endpoints (e.g. fecundity, sex steroids and vitellogenin, gonado-/hepatosomatic indices, and gonad histology). No significant differences were seen in fish growth, mortality, or reproduction with β-sitosterol exposure, although a trend for lower egg production in β-sitosterol exposures relative to the water control may be related to the acetone carrier. All ethynyl estradiol-exposed fish were smaller, showed female characteristics, and did not spawn. Sex steroid and vitellogenin were highly variable with no detectable treatment-related differences. Gonadal tissue showed no β-sitosterol-related differences in reproductive development and spawning capability, although most ethynyl estradiol-exposed males had ovarian tissue and were not spawning-capable. The results indicate that β-sitosterol exposure had little apparent impact on fathead minnow survival, growth, and reproduction even at concentrations >10 times that of typical effluents, although small sample size and variability precluded fully evaluating treatment responses on sex steroids and vitellogenin.

Effects of low concentrations of the antiprogestin mifepristone (RU486) in adults and embryos of zebrafish (Danio rerio): 1. Reproductive and early developmental effects

Effects of synthetic progestins have recently been reported in fish, but potential effects of the synthetic antiprogestin mifepristone (MIF), also called RU486, have not been studied. The present study provides first insights into reproductive effects of MIF in zebrafish in comparison to the progesterone receptor agonist, progesterone (P4). We carried out a reproductive study using breeding groups of adult zebrafish. After a 14 day pre-exposure, zebrafish were exposed for 21 days to 5, 39, 77 ng/L MIF, 25 ng/L P4 and water and solvent controls. In addition, embryos originating from exposed adult fish were continuously exposed to 3, 15, 26 ng/L MIF, and 254 ng/L P4, respectively, for 96 h post fertilization. We found a significant U-shaped increase in egg production after exposure to 5 and 77 ng/L MIF, but no effects at 25 ng/L P4. Levels of sex steroid hormones in blood plasma of adult males (11-ketotestosterone) and females (17 β-estradiol) were not altered. In addition to an increase of mature vitellogenic oocytes in ovaries of females exposed to MIF and P4, we observed several histopathological changes in ovaries, including post-ovulatory follicles, atretic follicles and proteinaceous fluid. Male gonads showed no or less alterations and no histopathological effects. Fertility of eggs and hatching success of embryos (F1 generation) was not affected at 3-26 ng/L MIF and 254 ng/L P4, respectively. The data lead to the conclusion that trace quantities of MIF affect reproduction of zebrafish and ovaries of female zebrafish. Effects on transcriptional changes in adult and embryonic zebrafish of this study in comparison to in vitro effects are reported in the associated report (Blüthgen et al., 2013a).

The use of carrier solvents in regulatory aquatic toxicology testing: practical, statistical and regulatory considerations

Solvents are often used to aid test item preparation in aquatic ecotoxicity experiments. This paper discusses the practical, statistical and regulatory considerations. The selection of the appropriate control (if a solvent is used) for statistical analysis is investigated using a database of 141 responses (endpoints) from 71 experiments. The advantages and disadvantages of basing the statistical analysis of treatment effects to the water control alone, solvent control alone, combined controls, or a conditional strategy of combining controls, when not statistically significantly different, are tested. The latter two approaches are shown to have distinct advantages. It is recommended that this approach continue to be the standard used for regulatory and research aquatic ecotoxicology studies. However, wherever technically feasible a solvent should not be employed or at least the concentration minimized.

A microplate assay to assess chemical effects on RBL-2H3 mast cell degranulation: effects of triclosan without use of an organic solvent

Mast cells play important roles in allergic disease and immune defense against parasites. Once activated (e.g. by an allergen), they degranulate, a process that results in the exocytosis of allergic mediators. Modulation of mast cell degranulation by drugs and toxicants may have positive or adverse effects on human health. Mast cell function has been dissected in detail with the use of rat basophilic leukemia mast cells (RBL-2H3), a widely accepted model of human mucosal mast cells(3-5). Mast cell granule component and the allergic mediator β-hexosaminidase, which is released linearly in tandem with histamine from mast cells(6), can easily and reliably be measured through reaction with a fluorogenic substrate, yielding measurable fluorescence intensity in a microplate assay that is amenable to high-throughput studies(1). Originally published by Naal et al.(1), we have adapted this degranulation assay for the screening of drugs and toxicants and demonstrate its use here. Triclosan is a broad-spectrum antibacterial agent that is present in many consumer products and has been found to be a therapeutic aid in human allergic skin disease(7-11), although the mechanism for this effect is unknown. Here we demonstrate an assay for the effect of triclosan on mast cell degranulation. We recently showed that triclosan strongly affects mast cell function(2). In an effort to avoid use of an organic solvent, triclosan is dissolved directly into aqueous buffer with heat and stirring, and resultant concentration is confirmed using UV-Vis spectrophotometry (using ε280 = 4,200 L/M/cm)(12). This protocol has the potential to be used with a variety of chemicals to determine their effects on mast cell degranulation, and more broadly, their allergic potential.

Organic solvents impair life-traits and biomarkers in the New Zealand mudsnail Potamopyrgus antipodarum (Gray) at concentrations below OECD recommendations

Potamopyrgus antipodarum is a gastropod mollusk proposed for use in the development of reproduction tests within the Organization for Economic Cooperation and Development (OECD). Numerous chemicals, including endocrine disrupters, are relatively water-insoluble, and water-miscible solvents are currently used for testing them. OECD recommends a maximum concentration of 100 μll(-1). As several studies highlighted effects of lower concentrations of solvents, this study assessed the effects of 20 μll(-1) acetone, ethanol, methanol and dimethylsulfoxide (DMSO) on juvenile and adult snails during 42 days. Ethanol decreased juvenile growth, while acetone increased the rate of embryonic development. All solvents increased estradiol-like levels in adult snails. DMSO only increased mRNA expression of vitellogenin-like gene, while acetone, ethanol and methanol decreased mRNA expression of three nuclear receptor (estrogen receptor-like, ecdysone-induced protein and chicken ovalbumin upstream promoter transcription factor) genes as well as of genes encoding proteins involved in genomic (prohibitin-2) and non-genomic (striatin) pathways of estrogens activity in vertebrates. This study highlights the confounding effects of low concentrations of solvents and recommends avoiding their use. Where solvent use is inevitable, their concentrations and type should be investigated for suitability for the measured endpoints prior to use in chemical testing strategies.

DMSO modifies the permeability of the zebrafish (Danio rerio) chorion-implications for the fish embryo test (FET)

Since 2007, when REACH came into force, the fish embryo test has received increasing attention as a potential alternative for the acute fish test. Due to its low toxicity and the ability to permeate biological membranes without significant damage to their structural integrity, dimethyl sulfoxide (DMSO) is a commonly used solvent in the fish embryo test. Little is known, however, about the membrane penetration properties of DMSO, the impact of different concentrations of DMSO on the potential barrier function of the zebrafish chorion and on changes in the uptake of chemicals into the embryo. Therefore, in the present study, the fluorescent dyes fluorescein (mol wt 332; Pow 3.4) and 2,7-dichlorofluorescein (mol wt 401; Pow 4.7), both substances with limited water solubility, were used to visualize the uptake into the egg as well as the accumulation in the embryo of the zebrafish depending on different concentrations of DMSO. The distribution of fluorescein within the egg compartments varied with DMSO concentration: When dissolved in 0.01% DMSO, fluorescein did not pass the chorion. In contrast, concentrations ≥ 0.1% DMSO increasingly facilitated the uptake into the perivitelline space. In contrast, the uptake of 2,7-dichlorofluorescein was not substantially increased with rising DMSO concentrations, indicating the importance of factors other than the solvent (e.g. mol wt). With respect to the fish embryo test, results indicate that DMSO may be used without complications as a solvent, however, only at a maximum concentration of 0.01% (0.1 mL/L) as already indicated in the OECD difficult substances paper (OECD, 2000).

Biochemical and genotoxic response of naphthalene to fingerlings of milkfish Chanos chanos

The present study investigated the acute toxicity, sub-lethal toxicity and biochemical response of naphthalene in fingerlings of milkfish Chanos chanos. The 96 h acute toxicity LC50 values for C. chanos exposed to naphthalene was 5.18 μg l(-1). The estimated no observed effect concentration and lowest observed effect concentration values for naphthalene in C. chanos were 0.42 and 0.69 μg l(-1) respectively for 30 days. The estimated maximum allowable toxicant concentration for naphthalene was 0.53 μg l(-1). Biochemical enzyme markers such as lipid peroxidation, catalase, glutathione S transferase and reduced glutathione were measured in gills and liver tissues of C. chanos exposed to sub-lethal concentrations of naphthalene. Fluctuation in lipid peroxidation and catalase level suggests that naphthalene concentrations play a vital role in induction of oxidative stress in fish. Induction of reduced glutathione level and inhibition of glutathione S-transferase level was observed in naphthalene exposed C. chanos suggesting that there may be enhanced oxidative damage due to free radicals. Increasing concentration increases in number of nuclear abnormalities. The formation of micronuclei and binucleated micronuclei induction by naphthalene confirm its genotoxic potential. The highest levels of DNA damage (% tail length) were observed at 1.24 μg l(-1) of naphthalene. The study suggests that biochemical enzymes, nuclear abnormalities and DNA damage index can serve as a biological marker for naphthalene contamination.

Different effects of subchronic exposure to low concentrations of the organophosphate insecticide chlorpyrifos in a freshwater gastropod

Chlorpyrifos is an organophosphate insecticide used for pest control on a number of food crops in many parts of the world. In recent years, there has been an important decrease in the number of organisms of Planorbarius corneus. Since the presence of pesticides in the water can be one of the reasons for this decrease, it is very important to study the effect of subchronic exposure to environmental concentrations of pesticides on these organisms. The aim of the present work was to investigate different effects of the subchronic exposure to low concentrations of the organophosphate chlorpyrifos in P. corneus and the possibility to use these as biomarkers. To this end, we have exposed the organisms to 0.4 and 5 μg L(-1) of chlorpyrifos for 14 days and recorded the number of egg masses, the number of eggs per mass, the number of eggs without embryo, the time for hatching, and the % of hatching and survival. We have also determined the activities of cholinesterases, carboxylesterases and glutathione S-transferase in whole organism soft tissue and in the gonads. A 14 days exposure to 0.4 μg L(-1) caused an increase in the number of egg masses without eggs and a decrease in carboxylesterases measured with p-nitrophenyl butyrate. However the exposure to 5 μg L(-1) also caused an increase in the time for hatching, a decrease in the % of hatching and survival and also inhibition of cholinesterases and carboxylesterases with p-nitrophenyl acetate and butyrate. In contrast, the glutathione S-transferase has not been modified with the tested concentrations. We concluded that when P. corneus exposed to chlorpyrifos for 14 days, the CES determined with p-nitrophenyl butyrate proved to be the most sensitive biomarker. However, exposure to environmental concentrations showed a decrease in the reproduction ability which could cause a decrease in the number of organisms of this species.

The synthetic progestin levonorgestrel is a potent androgen in the three-spined stickleback (Gasterosteus aculeatus)

The use of progestins has resulted in contamination of aquatic environments and some progestins have in experimental studies been shown to impair reproduction in fish and amphibians at low ng L(-1) concentrations. The mechanisms underlying their reproductive toxicity are largely unknown. Some progestins, such as levonorgestrel (LNG), exert androgenic effects in mammals by activating the androgen receptor (AR). Male three-spined stickleback (Gasterosteus aculeatus) kidneys produce spiggin, a gluelike glycoprotein used in nest building, and its production is directly governed by androgens. Spiggin is normally absent in females but its production in female kidneys can be induced by AR agonists. Spiggin serves as the best known biomarker for androgens in fish. We exposed adult female sticklebacks to LNG at 5.5, 40, and 358 ng L(-1) for 21 days. Androgenic effects were found at LNG concentrations ≥40 ng L(-1) including induction of spiggin transcription, kidney hypertrophy, and suppressed liver vitellogenin transcription. These are the first in vivo quantitative data showing that LNG is a potent androgen in fish supporting the contention that androgenic effects of certain progestins contribute to their reproductive toxicity.

Measuring aqueous solubility in the presence of small cosolvent volume fractions by passive dosing

A new passive dosing method was developed to determine aqueous solubility of hydrophobic chemicals. In the passive dosing method, chemical crystals were loaded to a polydimethylsiloxane (PDMS) phase to maintain the maximum chemical activity and to prevent direct contact of chemical crystals with the aqueous solution. Eight polycyclic aromatic hydrocarbons (PAHs) were chosen covering their literature aqueous solubility from 0.001 to 30 mg L(-1). Values of the aqueous solubility for less hydrophobic PAHs (naphthalene, 2-methylnaphthalene, and fluorene) were measured by an Organization for Economic Co-ordination and Development (OECD)-recommended generator column method and those for more hydrophobic PAHs (anthracene, chrysene, and benzo(a)pyrene) were measured by the passive dosing method. For phenanthrene and pyrene, both methods were used for comparison. The results obtained by the passive dosing method were very close to those obtained by the generator column method. Aqueous solubilities in deionized water for more hydrophobic PAHs obtained using the passive dosing method agreed very well with values reported in the literature, suggesting the utility of the passive dosing method for the determination of aqueous solubility for highly hydrophobic chemicals. Because hydrophobic chemicals are often introduced in aqueous solutions by using a cosolvent, the solubility enhancement for PAHs at low cosolvent volume fractions was also evaluated. Three cosolvents (dimethyl sulfoxide, ethanol, and acetone) were chosen and their volume fractions in water were between 0.2% and 2%. The enhancement of the aqueous solubility could be well explained quantitatively by using a log-linear cosolvency model. The measured values of cosolvency power at the range of volume fraction investigated (σ(0.02)) correlated very well with log K(ow) of the PAHs. The combination of the log-linear model and semiempirical relationships between σ(0.02) and log K(ow) would be useful for the prediction of the solubility enhancement of hydrophobic chemicals.

Testing the effects of ethinylestradiol and of an environmentally relevant mixture of xenoestrogens as found in the Douro River (Portugal) on the maturation of fish gonads--a stereological study using the zebrafish (Danio rerio) as model

In natural environments fish populations are exposed to many potential xenoestrogens, whereby understanding the impacts of mixtures continue to be of great interest. The main objective of this study was, therefore, to understand whether and how an environmentally relevant mixture of xenoestrogens found in the Douro River estuary can disrupt the normal gametogenesis in fish. For this purpose, adult zebrafish of both sexes were exposed for 21 days to an environmental mixture (MIX) of 11 xenoestrogens from diverse sources. A 100 ng/L ethinylestradiol (EE2) positive control was added. A quantitative (stereological) analysis with systematic sampling was made in the gonads, and using light microscopy both the relative and the absolute volumes of the gametogenic stages were estimated. Data point that the EE2 stimulus induced changes in structural compartments; with decreasing trends for the advanced maturation stages both in males and females. There was also a trend for a greater amount of interstitial tissue in males. Along with an interstitial fibrosis increase detected, the presence of a proteinaceous fluid was observed in both sexes and experimental groups (EE2 and MIX). Other histopathologic alterations were observed in the EE2 female group, such as the presence of foci of granulomatous inflammation and follicular mineralization in the germinal parenchyma and luminal areas. The most interesting finding of this study was that the exposure to the MIX caused a decrease of the relative volume of spermatozoa in zebrafish. This kind of estrogenic effect has not earlier been structurally quantified in such a fine detail with unbiased stereology in fish gonads. Despite the ultimate consequences of such disruptions being unknown, it could be logically argued that reduction or slowing-down of the appearance of the most mature cohorts and/or eventual interstitial fibrosis and other pathologic changes can adversely affect breeding. The findings add further explanatory bases for understanding the negative impacts of xenoestrogens.

Responses of laboratory exposed catfish (Clarias gariepinus) to environmentally relevant concentrations of p,p'-DDT

Technical grade DDT is annually sprayed for malaria control in many under developed countries world wide. Despite the controversy surrounding the use of DDT, minimal research concerning the effects on indigenous fish species in these areas has been conducted. In this study, the objectives were to identify some of the effects of sprayed p,p'-DDT on the common African sharptooth catfish species (Clarias gariepinus) under laboratory conditions. The effects were assessed by exposing specimens to three environmentally relevant concentrations of p,p'-DDT (0.66, 1.36 and 2.72 μg/l) for 21 days and analysing a suite of biomarkers in the plasma, gonads and body morphometrics. The biomarkers were specifically selected based on their practicality in developing countries, which could potentially be utilised for continued monitoring, and included alkali-labile phosphate (ALP), calcium, magnesium and zinc as the indirect measures of vitellogenin, gonadosomatic index, gonad mass manipulated using analysis of covariance, and condition factor. The results showed no significant (p<0.05) dose-dependent changes in the plasma, gonads and body condition of C. gariepinus, indicating that these species were not responsive to the p,p'-DDT concentrations when exposed sub-chronically. This lack of a response suggested that mature C. gariepinus are tolerant to 21 days exposure of low levels of p,p'-DDT.

Toxic effects of two brominated flame retardants BDE-47 and BDE-183 on the survival and protein expression of the tubificid Monopylephorus limosus

The toxic effects of two brominated diphenyl ethers (BDE), BDE-47, and BDE-183, on a benthic oligochaete tubificid, Monopylephorus limosus were studied under laboratory conditions. Investigated responses included survival, growth, and protein expression profiles, at BDE concentrations of 1, 10, 100, and 700 ng/g on a dry soil weight basis, with isooctane as the carrier solvent. Body weight losses among treatments were insignificant after 8 weeks of exposure. The 8-wk LC(50) of BDE-47 and -183 were 2311 and 169 ng/g, respectively. By applying multivariate analysis techniques, protein expression patterns were compared and correlated with stressful sources of long-term culture, carrier solvent, BDE-47 and -183. The treatment of 8-wk 100 ng/g BDE-47 was most closely clustered to the 10 ng/g BDE-183 treatment, based on the 40 examined protein spots. This indicated that BDE-183 was more potent to M. limosus, than was BDE-47. The 2-wk and 8-wk controls clustered into different groups indicating the occurrence of physiological changes due to long-term laboratory culture. Additionally, solvent effect was shown by grouping the isooctane carrier to different clusters. With further characterization by principle component analysis, it was found that the separation was mainly contributed by the 2nd principal-component. And, the primarily inhibitory variation was at spots 2 (UMP-CMP kinase) and 40 (plasma retinol-binding protein precursor) in the 8-wk groups. On the contrary, protein spots 16 (cell division control protein 2 homolog) and 24 (mitochondrial DNA mismatch repair protein) showed stimulatory variation. In all, the observed proteomic responses suggest that BDEs disrupted metabolic function in M. limosus and multivariate analysis tool offers significant potential for the assessment of various stress sources at biochemical level.

Development of an embryo toxicity test with the pond snail Lymnaea stagnalis using the model substance tributyltin and common solvents

The development of a chronic mollusc toxicity test is a current work item on the agenda of the OECD. The freshwater pond snail Lymnaea stagnalis is one of the candidate snail species for such a test. This paper presents a 21-day chronic toxicity test with L. stagnalis, focussing on embryonic development. Eggs were collected from freshly laid egg masses and exposed individually until hatching. The endpoints were hatching success and mean hatching time. Tributyltin (TBT), added as TBT-chloride, was chosen as model substance. The selected exposure concentrations ranged from 0.03 to 10 μg TBT/L (all as nominal values) and induced the full range of responses. The embryos were sensitive to TBT (the NOEC for mean hatching time was 0.03 μg TBT/L and the NOEC for hatching success was 0.1 μg TBT/L). In addition, data on maximum limit concentrations of seven common solvents, recommended in OECD aquatic toxicity testing guidelines, are presented. Among the results, further findings as average embryonic growth and mean hatching time of control groups are provided. In conclusion, the test presented here could easily be standardised and is considered useful as a potential trigger to judge if further studies, e.g. a (partial) life-cycle study with molluscs, should be conducted.

An amphibian model for studies of developmental reproductive toxicity

The developmental programming of the reproductive system is vulnerable to chemical exposure. It is therefore important to evaluate long-term consequences of early life-stage exposure to endocrine disrupting chemicals. The African clawed frog Xenopus tropicalis has several characteristics which facilitates studies of developmental reproductive toxicity. Here, I present a X. tropicalis test protocol, including study design, exposure regime, and endpoints for chemical disruption of sex differentiation, reproductive organ development, the thyroxin-regulated metamorphosis, oestrogen synthesis (activity of the CYP19 aromatase enzyme), and fertility.

Recreating the seawater mixture composition of HOCs in toxicity tests with Artemia franciscana by passive dosing

The toxicity testing of hydrophobic organic compounds (HOCs) in aquatic media is generally challenging, and this is even more problematic for mixtures. The hydrophobic properties of these compounds make them difficult to dissolve, and subsequently to maintain constant exposure concentrations. Evaporative and sorptive losses are highly compound-specific, which can alter not only total concentrations, but also the proportions between the compounds in the mixture. Therefore, the general aim of this study was to explore the potential of passive dosing for testing the toxicity of a PAH mixture that recreates the mixture composition found in seawater from a coastal area of Spain, the Bay of Algeciras. First, solvent spiking and passive dosing were compared for their suitability to determine the acute toxicity to Artemia franciscana nauplii of several PAHs at their respective solubility limits. Second, passive dosing was applied to recreate the seawater mixture composition of PAHs measured in a Spanish monitoring program, to test the toxicity of this mixture at different levels. HPLC analysis was used to confirm the reproducibility of the dissolved exposure concentrations for the individual PAHs and mixtures. This study shows that passive dosing has some important benefits in comparison with solvent spiking for testing HOCs in aquatic media. These include maintaining constant exposure concentrations, leading to higher reproducibility and a relative increase in toxicity. Passive dosing is also able to faithfully reproduce real mixtures of HOCs such as PAHs, in toxicity tests, reproducing both the levels and proportions of the different compounds. This provides a useful approach for studying the toxicity of environmental mixtures of HOCs, both with a view to investigating their toxicity but also for determining safety factors before such mixtures result in detrimental effects.

Brain circuit imprints of developmental 17α-Ethinylestradiol exposure in guppies (Poecilia reticulata): persistent effects on anxiety but not on reproductive behaviour

The effects of endocrine disruptors may vary with the timing of exposure. The physiological implications of adult exposure are present during and shortly after exposure while embryonic exposure can imprint changes manifested in adulthood. In this study, guppy (Poecilia reticulata) embryos were exposed to 2 and 20 ng/L of 17α-ethinylestradiol during development via the mother and reared in clean water from gestation until 6 months of age. As adults, fish exposed to 20 ng/L during development showed significantly altered behaviour in the Novel Tank test, where anxiety is determined as the tendency to remain at the bottom upon introduction into an unfamiliar tank. 17α-ethinylestradiol treatment increased the latency time before swimming to the upper half of the tank and decreased the number of transitions to the upper half. In control females the basal stress behaviour responses were significantly higher than in males, as indicated by longer latency period and fewer and shorter visits to the upper half, supporting the importance of gonadal hormones for the behaviour. The anxiety increased, however, with treatment in both sexes, suggesting that the observed response is not entirely due to feminisation of the males. Shoaling behaviour, analysed as tendency to leave a shoal of littermates, was neither sex-differentiated nor changed by treatment. Also male reproductive behaviour, brain aromatase activity and testes histology, previously shown to respond to oestrogen exposure in adult guppy, were unaffected by the developmental treatment. This suggests that the stress system in the guppy is very sensitive to 17α-ethinylestradiol, which possibly causes an early organisational imprint on the brain circuit that regulates stress reactions.

Interference with xenobiotic metabolic activity by the commonly used vehicle solvents dimethylsulfoxide and methanol in zebrafish (Danio rerio) larvae but not Daphnia magna

Organic solvents, such as dimethylsulfoxide (DMSO) and methanol are widely used as vehicles to solubilise lipophilic test compounds in toxicity testing. However, the effects of such solvents upon innate detoxification processes in aquatic organisms are poorly understood. This study assessed the effect of solvent exposure upon cytochrome P450 (CYP)-mediated xenobiotic metabolism in Daphnia magna and zebrafish larvae (4d post fertilisation). Adult D. magna were demonstrated to have a low, but detectable, metabolism of ethoxyresorufin in vivo and this activity was not modulated by pre-exposure to DMSO or methanol (24 h, up to 0.1% and 0.05% v/v, respectively). In contrast, the metabolism of ethoxyresorufin in zebrafish larvae was significantly reduced by both solvents (0.1% and 0.05% v/v, respectively) after 24 h of exposure. In zebrafish, these observed decreases in activity towards ethoxyresorufin were accompanied by decreased expression of a variety of genes coding for drug metabolising enzymes (corresponding to CYP1, CYP2, CYP3 and UDP-glucuronyl transferase [UGT] family enzymes), measured by quantitative PCR. Reduction of gene expression and CYP1 enzyme activities by methanol (0.05% v/v) in zebrafish larvae was partially reversed by co-exposure with Aroclor 1254 (100 μg L(-1)). Overall this study suggests that relatively low concentrations of organic solvents can impact upon the biotransformation of certain xenobiotics in zebrafish larvae, and that this warrants consideration when assessing compounds for metabolism and toxicity in this species.

Aquatic toxicity tests with substances that are poorly soluble in water and consequences for environmental risk assessment

Aquatic toxicity tests with substances that are poorly soluble in water have been conducted using different methods, and estimates of toxicity have varied accordingly. The present study illustrates differences in toxicity values resulting from variation in test designs and solution preparation methods, and offers guidance on the best way to conduct these tests. Consequences for environmental risk assessment and classification are also discussed. The present study mainly considers active ingredients of plant protection products, but is also considered relevant to other chemicals. It is recommended that toxicity tests be conducted only up to the saturation limit, dispersants avoided, and solvents used only if necessary to support handling and speed of dissolution. Analytical measurements of exposure concentrations should reflect what organisms are exposed to. If acute toxicity testing at the saturation limit yields no adverse effects, further testing should not normally be required; the toxicity value of the endpoints should be considered as the saturation limit and adverse classification should not be required. Chronic testing, if required, should then be conducted at the practical saturation limit as this is the most realistic worst-case exposure scenario. If no adverse effects occur, the risk should be acceptable because higher aqueous exposure cannot occur. This could be substantiated by testing additional species. Assessment factors on no observed effect concentration (NOEC) values at the saturation limit require careful consideration in the risk assessment to avoid unnecessarily low regulatory acceptable concentrations.

Effects of the anti-androgen, bicalutamide, in a reduced life-cycle study with the fathead minnow (Pimephales promelas)

In support of the environmental risk assessment (ERA) of the non-steroidal anti-androgen bicalutamide, a reduced fish full life-cycle (FFLC) was conducted. The traditional FFLC is deemed to be the "gold standard" for evaluating the potential environmental impact of human pharmaceuticals, covering all life-stages and measuring long term effects. However, such studies require large numbers of animals and take considerable effort and time. The reduced FFLC, employed here, used fewer animals and was shorter in duration, yet still included sensitive life-stages and measured long term effects to provide robust information in support of the ERA for an endocrine disrupting chemical. Fathead minnows (Pimephales promelas) were held in breeding pairs and their reproductive performance assessed over 28 days. Embryos from at least two pairs per treatment were subsequently grown up until 85 days post hatch and a subset allowed to spawn to assess the developmental and reproductive effects of the parental exposure on this F1 generation. Fish were exposed in a flow-through system, at 25±1°C. Nominal (mean measured) test concentrations of bicalutamide were 0.01 (0.055), 0.10 (0.10), 1.0 (0.9), 10 (9.2) and 100 (92.1) μg L⁻¹. There were no significant effects on F0 fecundity or growth (wet weight and standard length), but a significant decrease in nuptial tubercle prominence (a secondary sexual characteristic, SSC) was observed in male fish exposed to 100 μg L⁻¹. In the F1 generation, there were no treatment-related effects on hatching success or SSC, but survival was significantly decreased in fish exposed to the top concentration (100 μg L⁻¹. In female fish, wet weight and standard length were also significantly increased at this concentration. Gonadal histopathology revealed no treatment related effects on sex ratio, sexual differentiation or sexual development. However, there was a concentration related effect on gonad lesion severity in female fish exposed to 100 μg L⁻¹ and reproduction (number of eggs spawned) was also significantly reduced in breeding groups exposed to this concentration. Taking into account these data, the overall no observed effect concentration and lowest observed effect concentration values for bicalutamide were 10 and 100 μg L⁻¹, respectively.

Discrepancies in the acute versus chronic toxicity of compounds with a designated narcotic mechanism

In this study, it was illustrated that even for certain simple organic compounds with a designated mode of action (MOA) (i.e. narcotic toxicity) unexpected differences in acute and chronic toxicity can be observed. In a first part of the study, species sensitivity distributions (SSDs) based on either acute or chronic toxicity data of three narcotic test compounds (methanol, ethanol and 2-propanol) were constructed. The results of the acute SSDs were as expected for narcotic compounds: rather similar sensitivity and small differences in toxicity were observed among different species. On the contrary, the chronic SSDs of methanol and ethanol indicated larger interspecies variation in sensitivity. Furthermore, the chronic toxicity trend (ethanol>methanol>2-propanol) was unexpectedly different from the acute toxicity trend (2-propanol>ethanol>methanol) and acute versus chronic extrapolation could not be successfully described for methanol and ethanol using an ACR of 10 (as suggested for narcotic compounds). In contrast to the interspecies approach in the first part of this study, the second part of the study was focused on the assessment of acute and chronic toxicity of the three test compounds in Daphnia magna, which was identified as one of the most sensitive organisms to methanol and ethanol. Here, the differences in acute and chronic toxicity trend were in accordance to the results of the SSDs. The enhancement of membrane penetration due to the small molecular size of methanol and ethanol, in combination with the higher toxicity of their respective biotransformation products were suggested as potential causes of the increased chronic toxicity. Furthermore, it was stressed that larger awareness of these irregularities in acute to chronic extrapolations of narcotic compounds is required and should receive additional attention in further environmental risk assessment procedure.

Effect of chronic exposure to pendimethalin on the susceptibility of rainbow trout, Oncorhynchus mykiss L., to viral hemorrhagic septicemia virus (VHSV)

In this study, the in vivo effects of chronic pollution by the active substance (AS) pendimethalin, a dinitroaniline herbicide, on the susceptibility of rainbow trout, Oncorhynchus mykiss L., to an experimental challenge with viral hemorrhagic septicemia virus (VHSV) were assessed. After four weeks of exposure to fresh water (C group) or 500 ng L(-1) of AS (P500 group), the fish were challenged by immersion in water containing 10(4) TCID(50) mL(-1) of VHSV. While exposure to pendimethalin was maintained throughout the experiment, mortalities were recorded during the 40 days post-infection (dpi) and organs were collected from dead fish for virological examination. At the end of the experiment, anti-VHSV antibodies and the classical pathway of complement activity were assessed in trout plasma. Exposure to pendimethalin significantly affected the distribution of cumulative mortality accelerating death in fish infected by VHSV. Pendimethalin appeared to decrease the Mean Time to Death (MTD) after virus treatment from 14.9 days (C-VHSV) to 10.2 days (P500-VHSV). Nevertheless, by the end of the experiment, differences in cumulative mortality were no longer observed between the two groups, which had reached the same stage (50 percent). Furthermore, a higher concentration of the virus was recovered from the pools of organs from the P500-VHSV group than the C-VHSV group. Moreover, at 40 dpi, although no significant difference was observed in the immune response between the two groups, more fish in the P500-VHSV group had set up an immune response by secreting antibodies than in the control viral group (C-VSHV).

Effects of 17α-ethinylestradiol on individual life-history parameters and estimated population growth rates of the freshwater gastropods Radix balthica and Bithynia tentaculata

Studies of aquatic environments exposed to 17α-ethinylestradiol (EE2) have demonstrated detrimental effects on fish communities. However, much less is known about effects on macro-invertebrates and especially how long-term exposure may affect critical life stages and ultimately population dynamics. We studied the effects of EE2 on relevant endpoints for population growth in two common freshwater gastropods, Radix balthica and Bithynia tentaculata, that differ in reproductive, foraging and anti-predator strategies and endocrine systems. We quantified critical life-history parameters (mortality, somatic growth rate, days to and size at first reproduction, egg production and hatching success) in a concentration-response, life cycle experiment. The two species responded to EE2 exposure in different ways, B. tentaculata showing a significantly lower somatic growth rate and R. balthica a higher somatic growth rate. However, the magnitudes of the effects were small and EE2 exposure did not have any significant effect on estimated population growth rates for the two snail species. The significant effects of EE2 on individual endpoints, but not on population growth rate for both species, emphasise the importance of evaluating higher level effects from long-term exposure studies.

Comparative study on the toxicity of pyrethroids, α-cypermethrin and deltamethrin to Ceriodaphnia dubia

Two synthetic pyrethroid pesticides, α-cypermethrin and deltamethrin were investigated as potential toxic contaminants. The acute and chronic bioassays were conducted using Ceriodaphnia dubia. The toxicity of α-cypermethrin and deltamethrin to C. dubia increased with increasing concentrations and exposure time. C. dubia was three times more sensitive to deltamethrin than to α-cypermethrin with 48-h EC(50) of 0.06 μg/L and 0.23 μg/L, respectively. The chronic EC(50) values for α-cypermethrin and deltamethrin were 97.8 and 34.7 ng/L, respectively. Eight-day growth of Ceriodaphnia neonates during chronic exposures was the most sensitive endpoint measured in comparison to the endpoints of survival and number of neonates produced. To gain a better understanding of the link between acute and chronic toxicity, the acute-to chronic ratios (ACRs) were also calculated for survival, growth and reproduction endpoints. ACRs varied between 11 and 224 for the two pyrethroids. These results suggest that at environmentally relevant low concentrations, α-cypermethrin and deltamethrin could have significant adverse effects on the survival, reproduction and growth of C. dubia.

Implications of the solvent vehicles dimethylformamide and dimethylsulfoxide for establishing transcriptomic endpoints in the zebrafish embryo toxicity test

Current aquatic chemical testing guidelines recognize that solvents can potentially interfere with the organism or environmental conditions of aquatic ecotoxicity tests and therefore recommend concentration limits for their use. These recommendations are based on evidence of adverse solvent effects in apical level tests. The growing importance of subapical and chronic endpoints in future test strategies, however, suggests that the limits may need reassessment. To address this concern, microarrays were used to determine the effects of organic solvents, dimethylformamide (DMF) and dimethylsulfoxide (DMSO), on the transcriptome of zebrafish (Danio rerio) embryos. Embryos were exposed for 48 h to a range of concentrations between 0.025 and 32.0 ml/L. Effects on survival and development after 24 and 48 h were assessed microscopically, with no effects on mortality or morphology up to 2.0 and 16.0 ml/L for DMF and DMSO. However, analysis of 48-h embryonic RNA revealed large numbers of differentially expressed genes at concentrations well below the 0.1 ml/L solvent limit level. The enrichment of differentially expressed genes was found for metabolic, developmental, and other key biological processes, some of which could be linked to observed morphological effects at higher solvent concentrations. These findings emphasize the need to remove or lower as far as possible the concentrations of solvent carriers in ecotoxicology tests.

Acute and chronic toxicity of polychlorinated biphenyl 126 to Tigriopus japonicus: effects on survival, growth, reproduction, and intrinsic rate of population growth

The harpacticoid copepod Tigriopus japonicus has a wide geographical distribution and is considered as a suitable model species for the assessment of toxicity of marine pollutants. The aim of the present study was to test the impacts of polychlorinated biphenyl (PCB) 126 (3,3',4,4',5-pentachlorobiphenyl) on the growth, development, and reproduction of T. japonicus in two successive generations. We first quantified the 96-h 50% lethal concentration (2.83 mg/L; all reported concentrations are nominal values), the no-observed-effect concentration (0.6 mg/L), and the lowest-observed-effect concentration (LOEC; 1.2 mg/L) of PCB126 in the nauplii. Nauplii were more sensitive than the adults, which still survived at the highest tested PCB126 concentration (8 mg/L). In the chronic toxicity testing, 10 life history traits were quantified for T. japonicus. No obvious effect on any of these traits was observed in the first generation (F0) at tested concentrations (<100 µg/L) lower than the LOEC. During the second generational life-cycle exposure (F1), however, PCB126 had an obvious toxic effect on the reproduction (>1 µg/L) and growth (>0.1 µg/L). Thus, copepods became more sensitive to PCB126 exposure as generations developed. Among the different traits tested, body size was the most sensitive parameter. Reproduction (fecundity, number of clutches, nauplii/clutch) and intrinsic population growth were also significantly impacted by PCB exposure. The survivorship, sex ratio, hatching time, and development were not affected. Environmental risk assessment of contaminants must therefore be based on a long-term multigenerational exposure to provide a realistic measurement of the influences of pollutants on aquatic life.

Freshwater mudsnail (Potamopyrgus antipodarum) estrogen receptor: identification and expression analysis under exposure to (xeno-)hormones

Molluscs are raising attention as ecotoxicological test organisms due to their high diversity and ecological importance. The ovoviviparous prosobranch gastropod Potamopyrgus antipodarum (freshwater mudsnail) responds very sensitively to xenobiotics and has therefore been proposed as OECD standard test organism. Endocrine disrupting chemicals influence the reproduction of P. antipodarum, which can be assessed by embryo numbers in the brood pouch. However, the knowledge about the endocrine system of P. antipodarum is rather limited. The aim of this study was to identify an estrogen receptor in the endocrine system of P. antipodarum and to investigate if this receptor is differentially expressed under exposure to (xeno-)hormones (17α-ethinylestradiol, bisphenol A and 17α-methyltestosterone). The DNA-binding domain of the identified ER-like transcript has an amino acid identity of 92 percent compared to the ER of the gastropod Nucella lapillus (84 percent to human ERα) and 83 percent in the ligand binding domain (38 percent to human ERα). Furthermore, the P. antipodarum ER is transcriptionally regulated as shown by quantitative real-time PCRs of (xeno-)hormone exposed snails. 17α-ethinylestradiol and bisphenol A exposure resulted in a transitory ER-mRNA increase while17α-methyltestosterone caused a transitory reduction of ER-mRNA. In addition the solvent dimethyl sulfoxide had also a modulating effect on the receptor.

Biochemical response of anthracene and benzo [a] pyrene in milkfish Chanos chanos

Polycyclic aromatic hydrocarbons (PAHs) are common toxic pollutants found in the aquatic environment, and the assessment of their impact on biota is of considerable concern. The aim of the present research was to study the acute toxicity, bioaccumulation and biochemical response of milkfish Chanos chanos (Forsskal) to two selected PAHs: anthracene and benzo [a] pyrene. Acute toxicity test results were evaluated by the Probit analysis method and 96h LC(50) values for C. chanos exposed to anthracene was 0.030mgl(-1) and 0.014mgl(-1) for benzo [a] pyrene. Bioaccumulation concentration of anthracene was high when compared to benzo [a] pyrene. Biomarkers indicative of neurotoxicity (acetylcholinesterase, AchE), oxidative stress (lipid peroxidation, LPO and catalase, CAT) and phase II biotransformation of xenobiotics (glutathione S transferase, GST and reduced glutathione, GSH) were measured to assess effects of selected PAHs. Anthracene and benzo [a] pyrene increase LPO and CAT level of C. chanos suggesting that these PAHs may induce oxidative stress. Both the PAHs inhibited AchE indicating that they have at least one mechanism of neurotoxicity in common: the disruption of cholinergic transmission by inhibition of AChE. An induction of C. chanos glutathione S-transferase (GST) activity was found in fish exposed to benzo [a] pyrene, while an inhibition was observed after exposure to anthracene. These results suggest that GST is involved in the detoxification of benzo [a] pyrene, but not of anthracene.

Zebrafish developmental screening of the ToxCast™ Phase I chemical library

Zebrafish (Danio rerio) is an emerging toxicity screening model for both human health and ecology. As part of the Computational Toxicology Research Program of the U.S. EPA, the toxicity of the 309 ToxCast™ Phase I chemicals was assessed using a zebrafish screen for developmental toxicity. All exposures were by immersion from 6-8 h post fertilization (hpf) to 5 days post fertilization (dpf); nominal concentration range of 1 nM-80 μM. On 6 dpf larvae were assessed for death and overt structural defects. Results revealed that the majority (62%) of chemicals were toxic to the developing zebrafish; both toxicity incidence and potency was correlated with chemical class and hydrophobicity (logP); and inter-and intra-plate replicates showed good agreement. The zebrafish embryo screen, by providing an integrated model of the developing vertebrate, compliments the ToxCast assay portfolio and has the potential to provide information relative to overt and organismal toxicity.

Anxiogenic behaviour induced by 17α-ethynylestradiol in male guppies (Poecilia reticulata)

Behaviour studies are used in toxicology research as they are excellent tools to measure physiological end-points caused by exogenous chemicals. In mammals both reproductive and non-reproductive behaviours have been used for a long period of time, whereas in teleost fishes non-reproductive behaviours have received little attention compared to reproductive behaviours. Recent advances in measuring stress related behaviours in zebrafish have provided additional tools to understand behaviour toxicology in fish. One species with well documented reproductive behaviour disturbed by different toxicants is the guppy, which is better suited than zebrafish for reproductive behaviour studies and therefore might be a better model organism for comparative behaviour studies in fish toxicology. Here we report new applications for non-reproductive behaviours in guppy and test these behaviours on males treated with the endocrine disruptor 17α-ethynylestradiol at environmentally relevant concentrations. 17α-ethynylestradiol increased freezing and bottom-dwelling when fish were placed in a non-familiar aquarium, but did not significantly affect shoaling behaviour. These results are similar to the anxiogenic behaviours seen in rats treated perinatally with 17α-ethynylestradiol and add more concern to the impacts of endocrine disruptors on aquatic wildlife.

Effect of the organochlorine pesticide endosulfan on GnRH and gonadotrope cell populations in fish larvae

Endocrine-disrupting chemicals can influence the hypothalamus-pituitary-gonad axis and possibly affect reproduction in vertebrates. We analyzed the effect of 30-day endosulfan (ES) exposure in sexually undifferentiated larvae of the cichlid fish Cichlasoma dimerus. The number, area, mean cytoplasmic and nuclear diameter, and mean cytoplasmic optical density of gonadotropin-releasing hormone (GnRH) I, II, and III immunoreactive (ir-) neurons and β follicle-stimulating hormone (βFSH) ir-cells were measured. Animals exposed to the highest ES concentration (0.1 μg/l) showed a decrease in GnRH I nucleus/cytoplasm area ratio upon exposure. Nuclear area and mean nuclear diameter of βFSH ir-cells was higher in ES treated fish. βFSH nucleus/cytoplasm area ratio was high in exposed animals, and animals exposed to 0.1 μg/l ES showed smaller mean cytoplasmic optical density. These findings suggest that ES affects GnRH I and βFSH protein synthesis/release. However, these responses seem to be insufficient to affect gonadal differentiation at this stage of development.

Development of an ex vivo brown trout (Salmo trutta fario) gonad culture for assessing chemical effects on steroidogenesis

A variety of natural and synthetic environmental substances have been shown to disrupt vertebrate reproduction through mimicking or modifying the regulation of the endocrine system. Tests to screen for any such chemicals that directly interact with the steroid hormone receptors are widely available; however, few tests have been developed to identify chemicals that affect endocrine function through non-receptor mediated mechanisms. The aim of this study was, therefore, to develop an assay for the identification of substances that disrupt the activity of enzymes involved in the sex steroid biosynthesis cascade, in particular the aromatase enzyme, CYP19, that catalyses the final conversion of androgens to estrogens. A gonad ex vivo assay was developed using gonad explants harvested from juvenile brown trout and cultured in a modified Leibovitz medium. Effects on sex steroid biosynthesis were quantified through measurement of 17β-estradiol (E2) and testosterone (T) concentrations in the medium after 2 days incubation. Exposure of ovary explants to 100 ng/mL 1,4,6-androstatriene-3,17-dione (ATD), a potent pharmaceutical aromatase inhibitor, reduced E2 concentrations and elevated T concentrations confirming that CYP19 activity could be inhibited in the assay. Exposure of ovary explants to 250 ng/mL prochloraz, an imidazole fungicide, also reduced E2 concentrations but did not affect T levels, consistent with reports that in addition to inhibiting CYP19 activity, prochloraz also inhibits enzymes in the steroidogenic pathway upstream of the CYP19 enzyme. Exposure to a third chemical, tributyltin (TBT), did not affect T or E2 concentrations, further supporting previous evidence that the CYP19 modulating effects of this chemical are not mediated through direct inhibition of CYP19 activity. These results demonstrate that the gonad ex vivo assay developed here can be successfully used to identify substances that disrupt sex steroid biosynthesis and further that it has the potential to inform on their specific mode of action.

Dose-response modelling with two agents: application to the bioassay of oil and shoreline cleaning agents

Single and joint effects of hydrocarbons and a shoreline cleaning agent (SCA) were studied by measuring the inhibition of the larval growth of sea urchin. Different dosage methods of hydrophobic compounds were compared. The results obtained in the evaluation of CytoSol toxicity revealed that the method of variable dilution of water accommodated fraction (WAF) led to the more conservative toxicological approach. Regarding to Libyan oil, the use of DMSO as carrier allowed us the evaluation of its potential toxicity in comparison with the limitations imposed to the use of WAF method. A reparametrised form of the Weibull equation was slightly modified to be useful for dose-response analysis. This was the basis for modelling single sigmoid responses, which were used to simulate biphasic profiles with addition of effects and to describe both the concentration addition (CA) and independent action (IA) hypotheses. In all cases, its descriptive ability was graphically and statistically satisfactory. The IA model was the best option to explain the combined experimental responses obtained.

Effect of triazophos, fipronil and their mixture on miRNA expression in adult zebrafish

MicroRNA (miRNA) plays a crucial role in gene expression regulation. However, no data are available on change of miRNA expression of zebrafish (Danio rerio) after treatment with pesticides. We evaluated the effect of fipronil (5-amino-1-[2, 6-dichloro-4-(trifluoromethyl) phenyl]-4-[(trifluoromethyl) sulfinyl]-1H-pyrazole-3-carbonitrile) and triazophos (3-(O, O-diethyl)-1-phenyl thiophosphoryl-1, 2, 4-triazol) and their mixture on miRNA expression in zebrafish.MiRNA expression profiles in zebrafish were altered after treatment with these chemicals. An association between these chemicals and the expression of 21 miRNAs was found 96 h after treatment. Among them, 14 miRNAs were differentially expressed due to the treatments with fipronil, triazophos and their mixture; 5 miRNAs showed altered expression level after treatment with formulations of these chemicals; miR-29b and miR-738 were differentially expressed after treatment with adjuvants. MiRNAs might present a novel toxicological response that could be used as a toxicological biomarker and have a different direction for future investigations of their association with miRNAs involved in chemical related diseases.

Mammalian glucocorticoid metabolites act as androgenic endocrine disruptors in the medaka (Oryzias latipes)

Glucocorticoid metabolites enter the aquatic environment via mammalian excrements. Molecular structures of their C19O3 metabolites strongly resemble the major fish androgen 11-ketotestosterone. Therefore, we tested the hypothesis that the cortisol metabolite 5alpha-androstan-3,11,17-trione acts similarly to 11-ketotestosterone by employing a fish screening assay for endocrine-active substances. After 21 d, both 11-oxygenated compounds had masculinized sex characteristics of the anal fin in female medaka in a dose-dependent manner.

Controlling and maintaining exposure of hydrophobic organic compounds in aquatic toxicity tests by passive dosing

The risk assessment of hydrophobic organic compounds (HOCs) in aquatic toxicity or bioconcentration tests is a challenge due to their low aqueous solubilities, sorption and losses leading to poorly defined exposure and reduced test sensitivity. Passive dosing overcomes these problems via the continual partitioning of HOCs from a dominating reservoir loaded in a biocompatible polymer such as silicone, providing defined and constant freely dissolved concentrations and eliminating spiking with co-solvents. This study characterised the performance of a passive dosing format for aquatic tests with small organism such as invertebrates and algae, consisting of PDMS silicone cast into the base of the glass test vessel. The PDMS silicone was loaded by partitioning from a methanol solution containing PAHs (logK(OW) 3.56-6.63) as model compounds, followed by removal of the methanol with water. This resulted in highly reproducible PDMS silicone HOC concentrations. When shaking, release of PAHs into aqueous solution was rapid and reproducible, and equilibrium partitioning was reached within 5h for all compounds. The buffering capacity was sufficient to maintain stable concentrations over more than 10 weeks. This format was applied in a 48h Daphnia magna immobilisation assay to test the toxicity of a range of PAHs at their aqueous solubility. D. magna immobilisation did not show a trend with aqueous solubility or hydophobicity (K(OW)) of the PAHs. However, the immobilisation data for all compounds could be fitted with one maximum chemical activity response curve. Those PAHs with the lowest maximum chemical activities resulted in no immobilisation. Naphthalene and phenanthrene showed full toxicity at aqueous solubility, and passive dosing was also used for the concentration-response testing of these compounds. The freely dissolved aqueous concentrations causing 50% immobilisation (EC-50) were 1.96 mg L(-1) for naphthalene and 0.48 mg L(-1) for phenanthrene. Therefore, passive dosing is a practical and economical means of improving the exposure of HOCs in aquatic toxicity or bioconcentration tests.

Effects on guppy brain aromatase activity following short-term steroid and 4-nonylphenol exposures

Brain estrogen production, performed by the enzyme aromatase, can be disrupted/affected in teleost fish exposed to endocrine disruptors found in polluted aquatic environments. The guppy (Poecilia reticulata) was previously studied and confirmed to suffer negative effects on reproductive behaviors following inhibition of the brain aromatase reaction. Here adult guppies (Poecilia reticulata) of both genders were subjected to known endocrine disruptors: the androgen androstenedione (A), the synthetic estrogen 17alpha-ethinylestradiol (EE(2)), and the estrogenic surfactant 4-nonylphenol (NP), at high (50 microg/L) and at environmentally relevant concentrations (10 ng/L EE(2), 5 microg/L NP, and 0.7 microg/L A) for 2 weeks followed by measurements of brain aromatase activity (bAA). In the adult males, bAA was stimulated by A and EE(2) at 50 microg/L. Female activity was also stimulated by the higher estrogenic treatment. At environmentally relevant concentrations only the EE(2) treatment affected bAA, and only in males. The alkylphenolic substance NP produced no effect in either of the experiments, not on males nor females. The results indicate that short-term steroid treatments have stimulatory effects on guppy brain aromatase even at concentrations that can be found in the environment. We thus suggest bAA of adult guppies to be a suitable bioindicator of endocrine disruptors.

Effects of a weak oestrogenic active chemical (4-tert-pentylphenol) on pair-breeding and F1 development in the fathead minnow (Pimephales promelas)

A fish full life-cycle (FFLC) is the most comprehensive test to determine reproductive toxicity of chemicals to fish and this is likely to apply equally to endocrine active chemicals (EACs). However, FFLC tests use large numbers of animals, are expensive and time consuming. Alternative chronic tests, to the FFLC, potentially include sensitive life-stage windows of effect, such as sexual differentiation, early gonadal development and reproduction. In this paper, a fish pair-breeding study was applied to assess the biological effects of a weak environmental oestrogen, 4-tert-pentylphenol (4TPP), on reproduction and subsequent development of the F1 generation. The results of this study were then compared with the results for a published FFLC study, with this chemical. Fathead minnows (Pimephales promelas) were held in pairs and their reproductive performance assessed over two concurrent 21-day periods, the first without exposure to the test chemical, followed by the second with exposure to the test chemical, in a flow-through system at 25+/-1 degrees C. Embryos from two pairs, per treatment, were subsequently grown up in clean water until 90 days post-hatch to assess developmental effects of the parental exposure on the F1 generation. Nominal (measured geometric mean, time weighted) test concentrations of 4TPP were 56 (48), 180 (173) and 560 (570) microg l(-1). A significant decrease in fecundity was observed in all 4TPP exposed fish (mean number of eggs spawned per pair and number of spawns per pair) when compared to the solvent control. Vitellogenin (VTG) was significantly elevated in F0 males exposed to 560 microg 4TPPl(-1). Somatic endpoints, secondary sexual characteristics (SSC) and gonadosomatic index (GSI) were not affected by the 4TPP exposure. In the F1 generation, there were no treatment-related effects on hatching success, survival, growth, SSC or GSI. Histological examination of the gonads of the F1 fish revealed no treatment-related effects on sex ratio, sexual differentiation or sexual development. However, plasma VTG concentrations were significantly elevated in F1 male fish, derived from parents that had previously been exposed to 4TPP at concentrations of > or = 180 microg l(-1). These data show that the reproductive performance test is suitable for detecting weak environmental oestrogenic chemicals and that exposure of adult fish to oestrogens can result in altered biomarker expression (VTG) of the F1 generation. Our findings indicate that the reproductive performance test was as sensitive for detecting effects on reproduction when compared with a published FFLC test for 4TPP.

Uptake and biological effects of environmentally relevant concentrations of the nonsteroidal anti-inflammatory pharmaceutical diclofenac in rainbow trout (Oncorhynchus mykiss)

Diclofenac, a nonsteroidal anti-inflammatory drug, is widely detected in surface waters and can potentially cause deleterious effects in fish. Here, we investigated the biological effects of 21-day exposure to waterborne diclofenac at environmentally relevant concentrations (0, 0.5, 1, 5, and 25 μg/L) in rainbow trout Accumulation of diclofenac in the bile was measured and responses in selected tissues were assessed via changes in the expression of selected genes (cytochrome P450 (cyp) 1a1, cyclooxygenase (cox) 1 and 2, and p53) involved in metabolism of xenobiotics, prostaglandin synthesis, and cell cycle control, respectively, together with histopathological alterations in these tissues. Diclofenac accumulated in the bile by a factor of between 509 ± 27 and 657 ± 25 and various metabolites were putatively identified as hydroxydiclofenac, diclofenac methyl ester, and the potentially reactive metabolite hydroxydiclofenac glucuronide. Expression levels of both cox1 and cox2 in liver, gills, and kidney were significantly reduced by diclofenac exposure from only 1 μg/L. Expression of cyp1a1 was induced in the liver and the gills but inhibited in the kidney of exposed fish. Diclofenac exposure induced tubular necrosis in the kidney and hyperplasia and fusion of the villi in the intestine from 1 μg/L. This study demonstrates that subchronic exposure to environmental concentrations of diclofenac can interfere with the biochemical functions of fish and lead to tissue damage, highlighting further the concern about this pharmaceutical in the aquatic environment.

Effects of chronic exposure to nonylphenol on locomotor activity and social behavior in zebrafish (Danio rerio)

Nonylphenol (NP), a xenoestrogen ubiquitously found in aquatic ecosystems, is of high environmental concern. The present work assessed the effects of exposure to NP on locomotor activity and social behavior in male and female zebrafish (Danio rerio), to evaluate the possible hazard of NP to fish behavior and to pursue a potential biomarker of NP contamination. Fish were randomly divided into six groups. Five groups were receiving 0.1, 1, 10, 50 and 100 microg/L nominal concentrations of NP for 60 days, respectively. A sixth control group was given the same treatment as the other five groups, but no NP. Locomotor activity, aggressive behavior, group preference and leaving shoal were examined. NP exposure showed marked influence on locomotor activity of the male zebrafish, whereas that of the female was not significantly affected by NP. Aggressive behavior and group preference were significantly affected by NP exposure in both male and female groups. Locomotor activity and aggressive behavior of the male and group preference of both male and female zebrafish were clearly inhibited at 100 microg/L NP. No significant alteration in leaving shoal was observed under NP exposure. The results suggested that changes in locomotor activity and aggressive behavior of the male and group preference of both male and female may be used as an ecologically relevant integrative biomarker of NP contamination.

Amphibians and agricultural chemicals: review of the risks in a complex environment

Agricultural landscapes, although often highly altered in nature, provide habitat for many species of amphibian. However, the persistence and health of amphibian populations are likely to be compromised by the escalating use of pesticides and other agricultural chemicals. This review examines some of the issues relating to exposure of amphibian populations to these chemicals and places emphasis on mechanisms of toxicity. Several mechanisms are highlighted, including those that may disrupt thyroid activity, retinoid pathways, and sexual differentiation. Special emphasis is also placed on the various interactions that may occur between different agro-chemicals and between chemicals and other environmental factors. We also examine the indirect effects on amphibian populations that occur when their surrounding pond communities are altered by chemicals.

Toxic masking and synergistic modulation of the estrogenic activity of chemical mixtures in a yeast estrogen screen (YES)

BACKGROUND, AIM AND SCOPE

Estrogenic and non-estrogenic chemicals typically co-occur in the environment. Interference by non-estrogenic chemicals may confound the assessment of the actual estrogenic activity of complex environmental samples. The aim of the present study was to investigate whether, in which way and how seriously the estrogenic activity of single estrogens and the observed and predicted joint action of estrogenic mixtures is influenced by toxic masking and synergistic modulation caused by non-estrogenic chemical confounders.

MATERIALS AND METHODS

The yeast estrogen screen (YES) was adapted so that toxicity and estrogenicity could be quantified simultaneously in one experimental run. Mercury, two organic solvents (dimethyl sulfoxide (DMSO) and 2,4-dinitroaniline), a surfactant (LAS-12) and the antibiotic cycloheximide were selected as toxic but non-estrogenic test chemicals. The confounding impact of selected concentrations of these toxicants on the estrogenic activity of the hormone 17ss-estradiol was determined by co-incubation experiments. In a second step, the impact of toxic masking and synergistic modulation on the predictability of the joint action of 17ss-estradiol, estrone and estriol mixtures by concentration addition was analysed.

RESULTS

Each of the non-estrogenic chemicals reduced the apparent estrogenicity of both single estrogens and their mixtures if applied at high, toxic concentrations. Besides this common pattern, a highly substance- and concentration-dependent impact of the non-estrogenic toxicants was observable. The activity of 17ss-estradiol was still reduced in the presence of only low or non-toxic concentrations of 2,4-dinitroaniline and cycloheximide, which was not the case for mercury and DMSO. A clear synergistic modulation, i.e. an enhanced estrogenic activity, was induced by the presence of slightly toxic concentrations of LAS-12. The joint estrogenic activity of the mixture of estrogens was affected by toxic masking and synergistic modulation in direct proportion to the single estrogens, which allowed for an adequate adaptation of concentration addition and thus unaffected predictability of the joint estrogenicity in the presence of non-estrogenic confounders.

DISCUSSION

The modified YES proved to be a reliable system for the simultaneous quantification of yeast toxicity and estrogen receptor activation. Experimental results substantiate the available evidence for toxic masking as a relevant phenomenon in estrogenicity assessment of complex environmental samples. Synergistic modulation of estrogenic activity by non-estrogenic confounders might be of lower importance. The concept of concentration addition is discussed as a valuable tool for estrogenicity assessment of complex mixtures, with deviations of the measured joint estrogenicity from predictions indicating the need for refined analyses.

CONCLUSIONS

Two major challenges are to be considered simultaneously for a reliable analysis of the estrogenic activity of complex mixtures: the identification of known and suspected estrogenic compounds in the sample as well as the substance- and effect-level-dependent confounding impact of non-estrogenic toxicants.

RECOMMENDATIONS AND PERSPECTIVES

The application of screening assays such as the YES to complex mixtures should be accompanied by measures that safeguard against false negative results which may be caused by non-estrogenic but toxic confounders. Simultaneous assessments of estrogenicity and toxicity are generally advisable.

Effects of endosulfan and ethanol on the reproduction of the snail Biomphalaria tenagophila: a multigeneration study

Endosulfan (END) is an insecticide used in agriculture and as a wood preservative. Since END is practically insoluble in water, ethanol (ETOH) is often employed as a carrier solvent to spike it in the test medium in aquatic toxicity assays. In this study were investigated the effects of END and ETOH on the reproduction of the freshwater snail Biomphalaria tenagophila exposed over three successive generations. END (0, 0.001, 0.01, 0.1 mg L(-1)) was dissolved in the medium water using ETOH (up to 19.8 mg L(-1)) as carrier solvent. ETOH (19.8, 198, 1980 mg L(-1)) alone was tested as well. Adult snails (F(0)-generation) were exposed to END and ETOH for 8 weeks. The F(1)-generation continued to be exposed from embryo to reproductive maturity, while their descendants (F(2)) were exposed until day 10 after spawning. Effects on the fecundity (8-week production of eggs and egg-masses) of mature F(0) and F(1) snails were evaluated. Developmental toxicity was investigated in F(1) and F(2) embryos. END at the highest level tested (0.1 mg L(-1)) inhibited egg production by F(0) and F(1) snails. ETOH at levels 198 mg L(-1) also reduced fecundity of F(0) and F(1) an effect that was apparently aggravated by exposure over successive generations. END 0.1 mg L(-1) increased mortality and malformations and decreased hatching among F(1) embryos. ETOH drastically reduced the proportion of hatchings among F(2) embryos. The study-derived NOECs (no-observed-effect-concentrations) for END was 0.01 mg L(-1) (reduction in fecundity), and for ETOH were 19.8 mg L(-1) for reduction in fecundity and <19.8 mg L(-1) for developmental toxicity (hatching retardation).

Toxicity of the pharmaceutical clotrimazole to marine microalgal communities

Clotrimazole belongs to the group of 14alpha-demethylase inhibiting fungicides. It is widely used in human and veterinary medicine and has been identified as a priority pollutant for the marine environment. However, the toxicity of clotrimazole to marine primary producers is largely unknown. We therefore sampled natural microalgal communities (periphyton) and exposed them to concentration series of clotrimazole over 4 days. 50 pmol/L clotrimazole caused a concentration-dependent accumulation of C14alpha-methylated sterol precursors, which coincided with a decrease in algal-specific C14-desmethyl sterols. This indicates an inhibition of algal 14 alpha-demethylases already at environmental concentrations. A clotrimazole concentration of 500 pmol/L reduced total sterol content to 64% of control level. Community chlorophyll a content was affected by clotrimazole in a bi-phasic manner with first reductions becoming visible at 500 pmol/L, along with indications of an altered cycling of photoprotective xanthophyll pigments. Concentrations of 10-100 nmol/L and higher caused large reductions in community growth, and changed community pigment profiles in a concentration-dependent monotonous manner. The study further indicated that diatoms use obtusifoliol as a natural substrate for 14alpha-demethylase, just as higher plants do but also utilize norlanosterol.

The organophosphorous pesticide, fenitrothion, acts as an anti-androgen and alters reproductive behavior of the male three-spined stickleback, Gasterosteus aculeatus

Fenitrothion (FN) is a widely used organophosphorous pesticide that has structural similarities with the clinical anti-androgen flutamide. The potential for FN to act as an anti-androgen (at exposures of 1, 50, and 200 microg FN/l over a 26-day period) was assessed in male three-spined sticklebacks, Gasterosteus aculeatus, by measuring kidney spiggin concentration, nest-building, and courtship behavior. Spiggin is the glue protein that male sticklebacks use to build their nests and is directly controlled by androgens. FN exposure significantly reduced spiggin production as well as nest-building activity. It also adversely affected courtship--especially the 'zigzag dance' and biting behavior of the males. FN thus appears to have anti-androgenic effects on both the physiology and behavior of the male stickleback.