Acute toxicity evaluation of olive oil mill wastewaters: A comparative study of three aquatic organisms

Acute toxicity of olive mill wastewaters (traditional and continuous processes) collected from different regions of Portugal was evaluated using three test species (Vibrio fischeri formerly Photobacterium phosphoreum, Thamnocephalus platyurus, and Daphnia magna) and correlated with several physical and chemical parameters. Acute toxicity of these effluents, expressed in LC₅₀ or EC₅₀, ranged from: 0.16 to 1.24% in Microtox test, 0.73 to 12.54% in Thamnotoxkit F test, and 1.08 to 6.83% in Daphnia test. These values reflect the high toxicity of the olive mill wastewaters to all test species. Statistical analysis of the results shows a high correlation between the two microcrustacean bioassays. Microtox test did not correlate significantly with the other bioassays used. A significative correlation (p≤0.05) could also be established between L(E)C₅₀ obtained in the microcrustacean tests and some physicochemical parameters of the effluent. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 263–269, 1999     

A comparison of techniques used to extract solid samples prior to acute toxicity analysis using the microtox test

To date, there has been no widely accepted or standardized procedure for preparing leachates of solid samples for acute toxicity bioassays such as Microtox. Leaching procedures reported in the literature were evaluated for use with nonspecific environmental sample submissions. Using toxic environmental samples, two experiments were conducted to compare the effect that varying selected parameters would have on the effectiveness of the leaching procedure in removing toxicants from a solid sample matrix. Parameters that were varied included the type of toxicant, aqueous solvent system used to leach the sample, ratio of solid:liquid, type of mixing action, length of extraction time, and method of removing suspended solids from the leachate. Results from these experiments demonstrated that unacceptable variations of measured toxicity of a solid sample occurs with simple modifications of the method. The most dramatic shifts in 15 min EC₅₀ values were observed between vacuum filtering (EC₅₀ mean = 55.8%) and centrifuging (EC₅₀ mean = 22.3%) samples to clarify leachates. This and other significant interactions, between sample contaminant and aqueous system, suggest that no standard procedure will give readily interpretable results for different types of contamination. Investigators should carefully consider the application of the assay (e.g., the detection of toxicants using a sensitive method, or modeling the leaching of toxicants under specific environmental conditions) before selecting a leaching procedure. © 1996 by John Wiley & Sons, Inc.     

Acute aquatic toxicity of tire and road wear particles to alga,daphnid, and fish

Previous studies have indicated that tire tread particles are toxic to aquatic species, but few studies have evaluated the toxicity of such particles using sediment, the likely reservoir of tire wear particles in the environment. In this study, the acute toxicity of tire and road wear particles (TRWP) was assessed in Pseudokirchneriella subcapita, Daphnia magna, and Pimephales promelas using a sediment elutriate (100, 500, 1000 or 10000 mg/l TRWP). Under standard test temperature conditions, no concentration response was observed and EC/LC₅₀ values were greater than 10,000 mg/l. Additional tests using D. magna were performed both with and without sediment in elutriates collected under heated conditions designed to promote the release of chemicals from the rubber matrix to understand what environmental factors may influence the toxicity of TRWP. Toxicity was only observed for elutriates generated from TRWP leached under high-temperature conditions and the lowest EC/LC₅₀ value was 5,000 mg/l. In an effort to identify potential toxic chemical constituent(s) in the heated leachates, toxicity identification evaluation (TIE) studies and chemical analysis of the leachate were conducted. The TIE coupled with chemical analysis (liquid chromatography/mass spectrometry/mass spectrometry [LC/MS/MS] and inductively coupled plasma/mass spectrometry [ICP/MS]) of the leachate identified zinc and aniline as candidate toxicants. However, based on the high EC/LC₅₀ values and the limited conditions under which toxicity was observed, TRWP should be considered a low risk to aquatic ecosystems under acute exposure scenarios.     

Acute toxicity of parabens and their chlorinated by‐products with Daphnia magna and Vibrio fischeri bioassays

The acute toxicity of 21 parabens and their chlorinated derivatives was investigated by means of two toxicity bioassays: Daphnia magna immobilization test and the inhibition of bioluminescence of Vibrio fischeri. The median effective concentration (EC₅₀) values of the tested parabens ranged from 2.2 to 62 mg l^?1 in the D. magna test and from 0.0038 to 5.9 mg l^?1 in the V. fischeri test at 15 min after exposure. The toxicity of dichlorinated methyl‐ and n‐propylparaben, the most commonly used preservatives in cosmetics, toward D. magna was 3.9‐ and 2.8‐fold that of their corresponding parent compounds. Toxicity toward D. magna showed a linear relationship with log P, indicating that toxicity increases with increasing hydrophobicity. On the other hand, the correlations of toxicity toward V. fischeri with hydrophobicity and with the degree of chlorination were poor. In addition, the results of the present study indicated that the V. fischeri test was more sensitive than the D. magna test for the determination of the acute toxicity of parabens. A complete assessment of the ecological and toxicological risks of parabens may require the examination of chlorinated parabens as well as the parent pollutants, as described in the present study. Copyright © 2008 John Wiley & Sons, Ltd.     

Ecotoxicological effects of larvicide used in the control of Aedes aegypti on nontarget organisms: Redefining the use of pyriproxyfen

The continued widespread use of larvicides in Aedes aegypti control programs is still a necessary strategy, since there are no apparent efficient vaccines against arboviruses. However, chemical approaches may affect nontarget organisms and produce detrimental effects to environmental health. Therefore, the aim of this study was to conduct toxicity testing for pyriproxyfen at different concentrations using Daphnia magna and Artemia salina as model organisms to evaluate the ecotoxicological parameters. This study describes the toxicological effects of pyriproxyfen on both microcrustaceans, which are widely used in bioassays because of their sensitivity to changes in hydrosphere. Data demonstrated that the calculated EC_50-48h value of pyriproxyfen was 2.5 μg/for D. magna and A. salina; the no-observed-effect concentration (NOEC) and the lowest-observed-effect concentration (LOEC) of pyriproxyfen were found to be 0.63 and 1.25 μg/L for Artemia salina and Daphnia magna, respectively. In chronic toxicity and reproduction tests on D. magna, a calculated CL_50-7day (lethality on 50% of daphnids after 7 days of chronic test) and an EC_50-21day (50% reduction in the reproductive output of parental daphnids after 21 days of exposure) higher than 1.25 μg/L pyriproxyfen were observed. The time of first reproduction was significantly increased in D. magna after exposure to environmentally relevant concentrations of pyriproxyfen, but other reproduction parameters were not markedly altered. Environmental risk assessment revealed that pyriproxyfen is highly toxic for both branchiopods. Data demonstrated that pyriproxyfen may produce adverse effects on the aquatic ecosystem at concentrations required to control Ae. aegypti.     

An assessment of the potential of the microbial assay for risk assessment (MARA) for ecotoxicological testing

Rapid microscale toxicity tests make it possible to screen large numbers of compounds and greatly simplify toxicity identification evaluation and other effect directed chemical analyses of effluents or environmental samples. Tests using Vibrio fischeri (such as Microtox?) detect toxicants that cause non-specific narcosis, but are insensitive to other important classes of contaminants. The microbial assay for risk assessment (MARA) is a 24 h multi-species test that seeks to address this problem by using a battery of ten bacteria and a fungus. But there has been little independent evaluation of this test, and there is no published information on its sensitivity to pesticides. Here, we assess the performance of MARA using a range of toxicants including reference chemicals, fungicides and environmental samples. Mean MARA microbial toxic concentrations and IC₂₀s (20% Inhibitory concentrations) indicate the toxicant concentrations affecting the more sensitive micro-organisms, while the mean IC₅₀ (50% Inhibitory concentration) was found to be the concentration that was toxic to most MARA species. For the two fungicides tested, the yeast (Pichia anomalia) was the most sensitive of the ten MARA species, and was more sensitive than the nine other yeasts tested. The test may be particularly valuable for work with fungicides. Mean MARA IC₅₀s were comparable to values for nine other yeast species and the lowest individual IC₅₀s for each toxicant were comparable to reported IC₅₀s for Daphnia magna, Selenastrum capricornutum and Microtox? bioassays. MARA organisms exhibited more variable sensitivities, with the most sensitive organism being different for different samples, enhancing the likelihood of toxicity detection and giving a toxicity “fingerprint” that may help identify toxicants. The test, therefore, has great potential and would be valuable for ecotoxicological testing of pollutants.     

Evaluation of the toxic and genotoxic potential of landfill leachates using bioassays

Landfill leachates are liquid effluents with elevated concentrations of chemical compounds that can cause serious environmental pollution. In the south of the state of Santa Catarina, Brazil, a sanitary landfill was installed that employs a system of anaerobic/facultative lagoons for the treatment of its leachate. The present work examined the toxic and genotoxic potential of untreated and treated landfill leachates using bioassays. The chemical, toxic, genotoxic and mutagenic properties of the untreated leachate and the treated leachate were determined. Examination of the chemical properties showed a marked decrease in parameters after treatment, as well as in toxicity towards all the organisms tested. The results of the comet assay demonstrated that both leachates showed genotoxicity in all of the organisms tested, indicating the persistence of genotoxic substances even after treatment. A significant decrease in micronucleated cells was detected in Geophagus brasiliensis exposed to the treated leachate compared to untreated.     

Water and sediment ecotoxicity studies in Temuco and Rapel River Basin,Chile

Five samples were collected from the Rapel River Basin near the city of Rancagua and three from the city of Temuco. Three of the samples were collected from raw drinking water supplies. The following bioassays were performed on some or all of the samples: Microtox; Microtox solid phase test; SOS-Chromotest with and without S9; Toxi-Chromotest; Sediment-Chromotest; Panagrellus redivivus percent survival and percent maturation; submitochondrial reverse electron transfer and forward electron transfer tests; Daphnia magna 24 h acute toxicity; ECHA biocide monitor, and the competitive immunoassay tests for benomyl, metolachlor, atrazine, and triazines. All the sampling sites were positive for the presence of genotoxicants requiring S9 activation while three sites also indicated the presence of direct-acting genotoxicants/mutagens (−S9). Also, all the sites were positive for the presence of pesticides. In some samples there was 100% inhibition of P. redivivus maturation. Details and discussion on the implication of the results are presented. © 1996 by John Wiley & Sons, Inc.     

The relative sensitivity of microtox®, daphnid,rainbow trout,and fathead minnow acute lethality tests

Relative sensitivity and correlations between the Microtox® test and three commonly used acute lethality bioassays (i.e., rainbow trout, fathead minnow, Daphnia) are reviewed and discussed. All relevant data available for comparison were separated and evaluated based on chemical groupings. Generally, Microtox was more sensitive than or as sensitive as the acute lethality tests for pure individual organics, but was less sensitive to most inorganics. Microtox was not as sensitive as acute lethality tests to effluents or leachates with a high component of insecticides, herbicides, inorganics, pharmaceuticals or textiles, or highly lipophilic contaminants. As the complexity and toxicity of industrial effluents increased, the correlations and sensitivity of Microtox increased, with a corresponding decrease in data variability. Additionally, limitations of the available data are that (1) comparisons of relative sensitivity varied with the compounds and organisms tested; (2) there was a lack of standardization in approach and a failure to provide adequate details on the origin of the cited toxicity data, which confused and obscured comparisons; and (3) published reviews commonly failed to identify fish species and test details for cited data.     

Effect-directed investigation and interactive effect of organic toxicants in landfill leachates combining Microtox test with RP-HPLC fractionation and GC/MS analysis

Landfill leachates contain a large amount of unknown harmful compounds derived from domestic and industrial sources. A toxicity effect-directed approach was used to identify biologically active compounds in three landfill leachate samples (S1–S3) by combining the Microtox test with reverse-phase high performance liquid chromatography (RP-HPLC) fractionation and gas chromatography/mass spectrometry (GC/MS) analysis. Organic toxicants were recovered from coarse fractions only in S1 and in S2. Fine fractionation exhibited a somewhat different toxicity pattern in S1 and S2. GC/MS analysis positively identified Bisphenol A (BPA) and 4-t-butylphenol (4-t-BP) in both samples, N-ethyltoluenesulfoneamide (NETSA) was detected only in S1. However, their concentrations were not high enough to be responsible for the observed toxicity in original samples. A synergistic effect among detected organic compounds (BPA, NETSA, and 4-t-BP) was demonstrated. Each compound present at 1/7 of its individual EC₅₀, might lead to undesirable mixture toxicity, which indicated that interactive effects may, to a certain extent, play a role in landfill leachates with complex matrices. The results from further hydrophobicity analysis and estrogen receptor (ER) competitive binding assays of fraction 13 of both samples gave evidence that some possible toxicants that failed to be identified by GC/MS might be endocrine disrupting chemical(s) (EDC) with a log K _ow range of 3.5–3.7 in both samples.     

Bioassays for the Evaluation of Landfill Leachate Toxicity

This article reviews the application of bioassays for assessing the toxicity hazard posed by landfill leachate discharged to an aquatic environment. Landfill leachate is a complex mixture of chemicals; thus it is difficult to assess the risk posed to aquatic wildlife using standard chemical identification techniques, such as gas chromatography–mass spectroscopy (GC-MS). From this review it is clear that toxicity testing, using species that represent the different trophic levels, is a superior way to predict the risk posed by discharge than chemical analysis. Previous studies assessed leachate toxicity using bacteria, algae, plants, invertebrates, fish, and genotoxicity. Studies showed that leachate exhibits a wide range of toxicities to the species tested. Ammonia, alkalinity, heavy metals, and recalcitrant organics were identified to be the cause of adverse responses from the test organisms. Concentrations of these chemicals were found to depend upon the types of waste landfilled. As part of this review, Slooff analysis was applied to published results to calculate the sensitivity of test species. It was concluded that Lemna minor and Thamnocephalus platyurus were the most sensitive tests and, Vibrio fischeri (Microtox) was the least sensitive test available. Little is known about the sensitivity of each species to the different types of waste that might have been landfilled. A battery of tests needed for a more accurate assessment of landfill leachate is proposed. Some of the more common tests have been replaced by more sensitive tests that produce more relevant results for the industry and regulators.     

A multispecies toxicity assessment procedure using flow microcalorimetry: Comparison with other toxicity evaluation methods

The acute toxicity of various contaminants and effluents towards a heterogenous aerobic culture has been determined using flow microcalorimetry. The toxicity of these contaminants and effluents was also evaluated towards a marine bacteria (type Photobacterium phosphoreum, Microtox test), a green algae (Selenastrum capricornutum, inhibition of growth) and a small crustacean (Daphnia magna, inhibition of mobility). The 50% (IC₅₀) or 20% (IC₂₀) inhibitory concentrations were obtained for each toxicity test, and compared to each other. The results of the present study suggest that, under proper conditions, a mixed aerobic culture could yield toxicity estimates comparable to those obtained from a combination of single species tests.     

Toxicity assessment of Tehran water treatment sludges using bioassay tests

The 48-, 72- and 96-h acute toxicity and 14-d chronic toxicity of the sludge of treatment plant No. 1, 3 and 5 were examined based on the survival percentage and fertility changes of Daphnia magna and Eisenia fetida. The highest percentage of D. magna death in the acute toxicity test appeared in treatment plant No. 1 sludge sample. The 48-h and 72-h LC₅₀ of treatment plant No. 1 sludge on D. magna were calculated to be 86.81 and 44.307% volume of the sludge, respectively. The release of untreated sludge into the environment could adversely affect the life of organisms.     

Toxicity evaluation of trap and skeet shooting targets to aquatic test species

Large quantities of trap and skeet clay targets are used in shooting activities around the United States. For example, the number of targets used since 1970 has averaged approximately 560 million a year. A number of acute and chronic tests were performed to determine the toxicity of Remington Arms Company Blue Rock^® trap and skeet target fragments upon selected freshwater and marine organisms. These studies were undertaken in support of an environmental impact study of trap and skeet shooting activities at a major gun club in the northeast United States. Targets were composed of approximately 67% dolomitic limestone, 32% petroleum pitch and 1% fluorescent aqueous paint (painted targets only). The majority of samples were painted, new targets obtained from the manufacturer and painted and aged targets collected around a shooting range. Additional tests were conducted using non-painted, new targets and leachates prepared from both painted, new and aged targets. Targets were crushed to small fragments and were either directly added to the test vessels at extremely high concentrations ranging from 670 to 600 000 mgl^-1 or used in leachate tests. In direct tests all target materials were essentially non-toxic to marine and freshwater organisms, except for the non-painted new targets which exhibited minimal acute toxicity to Daphnia magna (48 h ec ₅₀=2200 mgl^-1). In leachate tests, the leachate was not-toxic to mysid shrimp, the only organism tested. Additional samples of crushed targets were analysed for the presence of selected priority pollutants (EP toxicity test) and polycyclic aromatic hydrocarbons (PAHs). The targets did not exhibit the characteristics of toxicity as determined by the EP toxicity test but did contain substantial amounts of PAHs. However, results from new and aged targets suggest that PAH are tightly bound in the petroleum pitch and limestone matrix and are unlikely to be readily available in the environment. The potential impact of targets on the environment is further discussed.     

Multilaboratory evaluation of 15 bioassays for (eco)toxicity screening and hazard ranking of engineered nanomaterials: FP7 project NANOVALID

Within EU FP7 project NANOVALID, the (eco)toxicity of 7 well-characterized engineered nanomaterials (NMs) was evaluated by 15 bioassays in 4 laboratories. The highest tested nominal concentration of NMs was 100?mg/l. The panel of the bioassays yielded the following toxicity order: Ag?>?ZnO?>?CuO?>?TiO_2?>_?MWCNTs?>?SiO_2?>_?Au. Ag, ZnO and CuO proved very toxic in the majority of assays, assumingly due to dissolution. The latter was supported by the parallel analysis of the toxicity of respective soluble metal salts. The most sensitive tests/species were Daphnia magna (towards Ag NMs, 24-h EC_50?=_?0.003?mg Ag/l), algae Raphidocelis subcapitata (ZnO and CuO, 72-h EC_50?=_?0.14?mg Zn/l and 0.7?mg Cu/l, respectively) and murine fibroblasts BALB/3T3 (CuO, 48-h EC_50?=_?0.7?mg Cu/l). MWCNTs showed toxicity only towards rat alveolar macrophages (EC_50?=_?15.3?mg/l) assumingly due to high aspect ratio and TiO₂ towards R. subcapitata (EC_50?=_?6.8?mg Ti/l) due to agglomeration of TiO₂ and entrapment of algal cells. Finally, we constructed a decision tree to select the bioassays for hazard ranking of NMs. For NM testing, we recommend a multitrophic suite of 4 in vitro (eco)toxicity assays: 48-h D. magna immobilization (OECD202), 72-h R. subcapitata growth inhibition (OECD201), 30-min Vibrio fischeri bioluminescence inhibition (ISO2010) and 48-h murine fibroblast BALB/3T3 neutral red uptake in vitro (OECD129) representing crustaceans, algae, bacteria and mammalian cells, respectively. Notably, our results showed that these assays, standardized for toxicity evaluation of “regular” chemicals, proved efficient also for shortlisting of hazardous NMs. Additional assays are recommended for immunotoxicity evaluation of high aspect ratio NMs (such as MWCNTs).     

Chemical composition and toxicity of waste dump leachates using Selenastrum capricornutum Printz (Chlorococcales,Chlorophyta)

Chemical composition and toxicity of leachates from a municipal waste dump in Buenos Aires Province were analyzed. Three sets of samples, obtained in 1996 and 1997, were compared. Levels of nitrogen, phosphorus, and organics (expressed as COD) were distinctly lower in 1997. Such differences were mainly attributed to higher rainfall in that year. The Selenastrum capricornutum assay showed a high sensitivity to heavy metals (Cd=0.049 mg L⁻¹; Cr hexavalent=0.247 mg L⁻¹ and Zn=0.037 mg L⁻¹). Cu, Zn, and Pb concentrations were toxic to algae in leachate samples of the first year, while the EC₅₀ leachates were slightly toxic (86.6 and 99.31%). Most likely, high levels of organics (COD=4640 and 3470 mg L⁻¹) form complex mixtures with metals reducing their toxicity. The EC₅₀ leachate=48.5% in the last year may be explained by high concentrations of Pb and Cu. © 2000 John Wiley & Sons, Inc. Environ Toxicol 15: 76–80, 2000     

Toxicity evaluation of metal plating wastewater employing the Microtox assay: a comparison with cladocerans and fish

The relative sensitivity of the Microtox assay is closely related to the type of toxicant, and hence its utility in biomonitoring effluents is better evaluated on a case-by-case basis. The Microtox assay, employing the marine bacterium Vibrio fischeri, was evaluated for its applicability in monitoring metal plating wastewater for toxicity. The results of the Microtox assay after 5, 15, and 30 min of exposure, were compared with data obtained from conventional whole effluent toxicity testing (WET) methods that employed Daphnia magna, Ceriodaphnia dubia, and the fathead minnow (Pimephales promelas). The Microtox assay produced notably comparable EC50 values to the LC50 values of the acute fathead minnow toxicity test (< 0.5 order of difference). The Spearman's rank correlation analyses showed that the bacterial assay, regardless of exposure duration, correlated better with the acute fish than the daphnid results (p < 0.05). These observations were consistent to other studies conducted with inorganic contaminants. The relative sensitivity of the 30-min Microtox assay was within the range of the two frequently used acute daphnid/fish toxicity tests. In conclusion, the Microtox assay correlated well with the acute fathead minnow data and is well suited for toxicity monitoring for these types of industrial wastes.     

A practical and user-friendly toxicity classification system with microbiotests for natural waters and wastewaters

Various types of toxicity classification systems have been elaborated by scientists in different countries, with the aim of attributing a hazard score to polluted environments or toxic wastewaters or of ranking them in accordance with increasing levels of toxicity. All these systems are based on batteries of standard acute toxicity tests (several of them including chronic assays as well) and are therefore dependent on the culturing and maintenance of live stocks of test organisms. Most systems require performance of the bioassays on dilution series of the original samples, for subsequent calculation of L(E)C50 or threshold toxicity values. Given the complexity and costs of these toxicity measurements, they can only be applied in well-equipped and highly specialized laboratories, and none of the classification methods so far has found general acceptance at the international level. The development of microbiotests that are independent of continuous culturing of live organisms has stimulated international collaboration. Coordinated at Ghent University, Belgium, collaboration by research groups from 10 countries in central and eastern Europe resulted in an alternative toxicity classification system that was easier to apply and substantially more cost effective than any of the earlier methods. This new system was developed and applied in the framework of a cooperation agreement between the Flemish community in Belgium and central and eastern Europe. The toxicity classification system is based on a battery of (culture-independent) microbiotests and is particularly suited for routine monitoring. It indeed only requires testing on undiluted samples of natural waters or wastewaters discharged into the aquatic environment, except for wastewaters that demonstrate more than 50% effect. The scoring system ranks the waters or wastewaters in 5 classes of increasing hazard/toxicity, with calculation of a weight factor for the concerned hazard/toxicity class. The new classification system was applied during 2000 by the participating laboratories on samples of river water, groundwaters, drinking waters, mine waters, sediment pore waters, industrial effluents, soil leachates, and waste dump leachates and was found to be easy to apply and reliable.     

Single and Combined Effects of Sediment-Associated PAHs on Three Species of Freshwater Macroinvertebrates

Polycyclic Aromatic Hydrocarbons (PAHs) are ubiquitous pollutants of sediments. Sediment quality criteria often use toxicity data for individual PAHs. However, PAHs always occur in field sediments as a complex mixture of compounds. In this study, the toxicity of phenanthrene (P), fluoranthene (FLA) and benzo(k)fluoranthene (B), alone or in combination, was assessed using monospecific sediment tests of acute toxicity (between 24h and 14 days). The test sediments were spiked formulated sediments. Toxicity of PAHs was determined on a freshwater pelagic organism, Daphnia magna, on an epibenthic organism, Hyalella azteca, and on a benthic organism, Chironomus riparius. The phototoxicity of fluoranthene and phenanthrene was verified. Benzo(k)fluoranthene was not phototoxic and presented no toxicity for the three organisms tested up to 300mg/kg, concentration rarely found in the environment. For all PAHs, the toxicity towards Daphnia magna was two-fold higher in the sediment toxicity tests than in the water-only standard tests, probably due to suspended contaminated particles and contact of daphnids with sediment. For phenanthrene, the LC50s found were 50, 15 and 20mg/kg dry weight sediment, respectively for Daphnia magna, Hyalella azteca and Chironomus riparius. The bioassays on fluoranthene yielded LC50s of 10, 5 and 15mg/kg dw respectively for Daphnia magna, Hyalella azteca and Chironomus riparius. LC50s of the PAHs mixture (1/3 of each compound by weight) were around 10mg/kg dry weight sediment for Hyalella azteca and 20mg/kg for Chironomus riparius. The effects of PAHs in the mixture seemed to be synergistic. This study gives new data about PAH toxicity and showed that the additivity of PAH effects could be inadequate to assess the environmental risk.     

Ecotoxicity of pesticide formulations and their mixtures: the case of potato crops in Costa Rica

Despite their environmental implications, ecotoxicological information regarding pesticide mixtures is relatively scarce. This study aimed to determine the ecotoxicity of individual pesticide formulations and their mixtures (insecticides and fungicides), which are applied during the production cycle of potato, according to agricultural practices from a Latin American region in Costa Rica. Two benchmark organisms were employed: Daphnia magna and Lactuca sativa. First, the evaluation of individual formulations (chlorothalonil, propineb, deltamethrin+imidacloprid, ziram, thiocyclam and chlorpyrifos) revealed differences between available EC₅₀ for active ingredients (a.i.) and their respective formulations toward D. magna; on the contrary, no information could be retrieved from scientific literature for comparison in the case of L. sativa. In general, acute toxicity was higher toward D. magna than L. sativa. Moreover, interactions could not be determined on L. sativa, as the chlorothalonil formulation was not toxic at high levels and the concentration-response to propineb could not be fitted to obtain an IC₅₀ value. The commercial formulation composed of deltamethrin+imidacloprid followed the concentration addition model (when compared with parameters retrieved from individual a.i.) and the other three mixtures evaluated (I: chlorothalonil-propineb-deltamethrin+imidacloprid; II: chlorothalonil-propineb-ziram-thiocyclam; III: chlorothalonil-propineb-chlorpyrifos) produced an antagonistic effect on D. magna, thus suggesting less acute toxicity than their individual components. Subsequent chronic studies showed that one of the most toxic mixtures (II) negatively affected D. magna reproduction at sublethal concentrations indicating that this mixture poses a risk to this species if these pesticides co-exist in freshwater systems. These findings provide useful data to better estimate the impact of real agricultural practices related to the use of agrochemicals.