Haloacetic acids in the aquatic environment. Part II: ecological risk assessment

Haloacetic acids (HAAs) are environmental contaminants found in aquatic ecosystems throughout the world as a result of both anthropogenic and natural production. The ecological risk posed by these compounds to organisms in freshwater environments, with a specific focus on aquatic macrophytes, was characterized. The plants evaluated were Lemna gibba, Myriophyllum spicatum and M. sibiricum and the HAAs screened were monochloroacetic acid (MCA), dichloroacetic acid (DCA), trichloroacetic acid (TCA), trifluoroacetic acid (TFA) and chlorodifluoroacetic acid (CDFA). Laboratory toxicity data formed the basis of the risk assessment, but field studies were also utilized. The estimated risk was calculated using hazard quotients (HQ), as well as effect measure distributions (EMD) in a modified probabilistic ecological risk assessment. EMDs were used to estimate HAA thresholds of toxicity for use in HQ assessments. This threshold was found to be a more sensitive measure of low toxicity than the no observed effect concentrations (NOEC) or the effective concentration (EC10). Using both deterministic and probabilistic methods, it was found that HAAs do not pose a significant risk to freshwater macrophytes at current environmental concentrations in Canada, Europe or Africa for both single compound and mixture exposures. Still, HAAs are generally found as mixtures and their potential interactions are not fully understood, rendering this phase of the assessment uncertain and justifying further effects characterization. TCA in some environments poses a slight risk to phytoplankton and future concentrations of TFA and CDFA are likely to increase due to their recalcitrant nature, warranting continued environmental surveillance of HAAs.     

Comparing growth development of <Emphasis Type="Italic">Myriophyllum</Emphasis> spp. in laboratory and field experiments for ecotoxicological testing

BACKGROUND, GOALS AND SCOPE: Risk assessment of herbicides and the evaluation of contaminated sediments based on algae and the macrophyte Lemna sp. alone may underestimate the potential hazard of certain compounds. Therefore, various test systems with Myriophyllum spp. have been developed recently to assess the phytotoxicity in surface waters and natural sediments. In the present study, experiments investigating the growth development of Myriophyllum spp. were performed in the laboratory under defined conditions and in mesocosms under environmentally realistic exposure conditions to evaluate the suitability of these species as potential standard test organisms in ecotoxicological testing. This study provides data on the endpoints biomass, plant length and root development. MATERIALS AND METHODS: Six independent experiments were performed to investigate the plant development of Myriophyllum spp. under control conditions. The main difference in the experiments was the complexity of the test systems ranging from simple laboratory experiments to complex outdoor mesocosm studies. At the start of each experiment, uniform cuttings of Myriophyllum spp. were placed in vessels with or without sediments to reduce variability between replicates. The endpoints considered in this investigation were biomass (fresh weight of the whole plant), length of the main shoot, length of the side shoots, total length of the plant (calculated from the length of the main and side shoots) and root formation. Root to shoot ratios were calculated as a further measure for plant development. Relative growth rates (RGR) based on plant length (RG(L)R) and on biomass (RG(B)R) were calculated. RESULTS: Despite the various experimental conditions, comparable growth was obtained in all test systems and the variability of endpoints, such as total length and biomass of plants, was low. It was observed that the RGR of M. spicatum in the simple laboratory test system with sediment were comparable to growth data obtained for M. verticillatum and M. spicatum grown in indoor and outdoor mesocosms, thus indicating that Myriophyllum growth tends to increase by the addition of sediment. High variability was determined for the endpoints length of the side shoots, total root length and biomass of roots. DISCUSSION: One challenge for a test design to investigate phytotoxicity on aquatic plants is to obtain good growth of the plants. From the results, it can be concluded that the experimental conditions in the various test systems were suitable to study the plant development of Myriophyllum spp. because obtained growth rates were comparable between laboratory and field investigations. Another challenge for developing a plant biotest system is the definition of sensitive endpoints. Low variability is preferred to detect minor effects of chemicals or polluted sediments on plant development. In our studies, the variability of the endpoints biomass and total length of plant was low and, therefore, they have much potential as endpoints for assessing toxicity. CONCLUSIONS: The methodologies presented in this study have applications within the risk assessment for aquatic plants and have the advantage of assessing effects taking into account the relevant exposure pathways via water and/or sediment for compounds under investigation. RECOMMENDATIONS AND PERSPECTIVES: Setting safe quality criteria for surface water and sediments is one of the challenges authorities are facing today. Myriophyllum spp. is recommended as suitable test species to investigate phytotoxicity in surface water and sediments. These results, thus, might serve as a basis for the compilation of a new harmonised guideline for ecotoxicological testing with aquatic macrophytes.     

Toxicity of chlorophenols to Pseudokirchneriella subcapitata under air-tight test environment

A closed-system algal toxicity test with no headspace was applied to evaluate the toxicity of chlorophenols to Pseudokirchneriella subcapitata. The dissolved oxygen production and the growth rate based on cell density were the response endpoints. Phenol and seven chlorophenols were tested using the above test technique. Median effective concentrations (EC50) range from 0.004 to 25.93 mg/l (based on DO production) and 0.0134 to 20.90 mg/l (based on growth rate). No-observed-effect concentration (NOEC) is within the range of 0.001-8.19 mg/l. In general, growth rate is a more sensitive response endpoint than the oxygen production, except for the case of pentachlorophenol. However, the differences in sensitivity between the two parameters were marginal. Furthermore, quantitative structure-activity relationships (QSAR's) based on the n-octanol/water partition coefficient (log P) and the acid dissociation constant (pK(a)) values were established with R(2) ranged from 0.90 to 0.96. From literature data also based on P. subcapitata, the new test method is 1.65-108 times more sensitive than the conventional algal batch tests. A completely different relative-sensitivity relationship among various aquatic organisms was thus observed. The results of this study indicate that the toxicity data of volatile organic chemicals derived by conventional algal toxicity tests may severely underestimate the impact of these toxicants. Our results show that alga is very sensitive to chlorophenols compared to other aquatic organisms such as the luminescent bacteria (the Microtox test), Daphnia magna, and rainbow trout.     

Effects of a mixture of tetracyclines to Lemna gibba and Myriophyllum sibiricum evaluated in aquatic microcosms

The impact of a mixture of oxytetracycline, chlortetracycline, tetracycline and doxycycline on Myriophyllum sibiricum and Lemna gibba was investigated using fifteen 12,000-L microcosms (k=5, n=3). Significant concentration-response relationships were only found for M. sibiricum, where dry mass was 69, 47, 30, and 7% of controls at respective treatment concentrations of 0.080, 0.218, 0.668, and 2.289 micromol/L. Somatic endpoints were strongly and negatively correlated with percent light transmission, except plant length, which was positively correlated. Treated microcosms experienced a reduction in the percent of surface irradiance penetrating the water column as high as 99.8% at a depth of 70 cm, relative to controls. Position relative to the water column was likely responsible for the differential effects observed between floating (L. gibba) and submerged (M. sibiricum) species of macrophytes. A hazard quotient assessment of the lowest EC10 value indicated significant risk, exceeding the critical HQ value, but not the lowest EC25 value.     

Comparative acute freshwater hazard assessment and preliminary PNEC development for eight fluorinated acids

Short-term 48, 72 and 96-h aquatic toxicity tests were conducted to evaluate the acute toxicity of eight fluorinated acids to the cladoceran, Daphnia magna, the green alga, Pseudokirchneriella subcapitata, and the rainbow trout, Oncorhynchus mykiss or the fathead minnow, Pimephales promelas. The eight fluorinated acids studied were tridecafluorohexyl ethanoic acid (6:2 FTCA), heptadecafluorooctyl ethanoic acid (8:2 FTCA), 2H-dodecafluoro-2-octenoic acid (6:2 FTUCA), 2H-hexadecafluoro-2-decenoic acid (8:2 FTUCA), 2H,2H,3H,3H-undecafluoro octanoic acid (5:3 acid), 2H,2H,3H,3H-pentadecafluoro decanoic acid (7:3 acid), n-perfluoropentanoic acid (PFPeA) and n-perfluorodecanoic acid (PFDA). The results of the acute toxicity tests conducted during this study suggest that the polyfluorinated acids, 8:2 FTCA, 8:2 FTUCA, 6:2 FTCA, 6:2 FTUCA, 7:3 acid and 5:3 acid, and the perfluorinated acids PFPeA and PFDA, are generally of low to medium concern based on evaluation of their acute freshwater toxicity (EC/LC50s typically between 1 and >100 mg L⁻¹) using the USEPA TSCA aquatic toxicity evaluation paradigm. For the polyfluorinated acids, aquatic toxicity generally decreased as the number of fluorinated carbons decreased and as the overall carbon chain length decreased from 12 to 8. Acute aquatic toxicity of the 5 and 10 carbon perfluorocarboxylic acids (EC/LC50s between 10.6 and >100 mg L⁻¹) was greater or similar to that of the 6-9 carbon perfluorocarboxylic acids (EC/LC50s > 96.5 mg L⁻¹). This study also provides the first report of the acute aquatic toxicity of the 5:3 acid (EC/LC50s of 22.5 to >103 mg L⁻¹) which demonstrated less aquatic toxicity than the 7:3 acid (EC/LC50s of 0.4-32 mg L⁻¹). The cladoceran, D. magna and the green alga, P. subcapitata had generally similar EC50 values for a given substance while fish were typically equally or less sensitive with the exception that PFPeA was most toxic to fish. Predicted no-effect concentrations (PNECs) were estimated using approaches consistent with REACH guidance and when compared with available environmental concentrations, these PNECs suggest that the fluorinated acids tested pose little risk for aquatic organisms.     

A microcosm system to evaluate the toxicity of the triazine herbicide simazine on aquatic macrophytes

This study evaluates the effects of the triazine herbicide simazine in an outdoor pond microcosm test system that contained two submerged rooted species (Myriophyllum spicatum and Elodea canadensis) and two emergent rooted species (Persicaria amphibia and Glyceria maxima) over a period of 84 days. Simazine was applied to the microcosms at nominal concentrations of 0.05, 0.5 and 5 mg/L. General biological endpoints and physiological endpoints were used to evaluate herbicide toxicity on macrophytes and the algae developing naturally in the system.Concentration-related responses of macrophytes and algae were obtained for the endpoints selected, resulting in a no observed ecologically adverse effect concentration (NOEAEC) at simazine concentrations of 0.05 mg active ingredient/L after 84 days. E. canadensis was the most negatively affected species based on length increase, which was consistently a very sensitive parameter for all macrophytes. The experimental design presented might constitute a suitable alternative to conventional laboratory single-species testing.     

Toxic effects of Hydrilla verticillata exposed to toluene, ethylbenzene and xylene and safety assessment for protecting aquatic macrophytes

Little information is available about the toxicity of toluene, ethylbenzene and xylene acting on macrophytes, and their toxicity data are rarely used in regulation and criteria decisions. The results extended the knowledge on toxic effects of toluene, ethylbenzene and xylene on aquatic plants. The responses of Hydrilla verticillata to these pollutants were investigated. Chlorophyll levels, lipid peroxidation, and antioxidant enzymes (superoxide dismutase and guaiacol peroxidase) showed diverse responses at different concentrations of toluene, ethylbenzene and xylene. The linear regression analyses were performed respectively, suggesting the concentrations of toluene, ethylbenzene and xylene expected to protect aquatic macrophytes were 7.30 mg L⁻¹, 1.15 mg L⁻¹ and 2.36 mg L⁻¹, respectively. This study emphasized that aquatic plants are also sensitive to organic pollutants as fishes and zooplanktons, indicating that macrophytes could be helpful in predicting the toxicity of these pollutants and should be considered in regulation and criteria decisions for aquatic environment protection.     

Determination of selected fate and aquatic toxicity characteristics of acrylic acid and a series of acrylic esters

Acrylic acid, methyl acrylate, ethyl acrylate, and butyl acrylate are commercially important and widely used materials. This paper reports the results of a series of fate and aquatic toxicity studies. The mobility in soil of acrylic acid and its esters ranged from 'medium' to 'very high'. Calculated bioconcentration factors ranged from 1 to 37, suggesting a low bioconcentration potential. Acrylic acid and methyl acrylate showed limited biodegradability in the five day biochemical oxygen demand (BOD5) test, while ethyl acrylate and butyl acrylate were degraded easily (77% and 56%, respectively). Using the OECD method 301D 28-d closed bottle test, degradability for acrylic acid was 81% at 28 days, while the acrylic esters ranged from 57% to 60%. Acrylic acid degraded rapidly to carbon dioxide in soil (t1/2 < 1 day). Toxicity tests were conducted using freshwater and marine fish, invertebrates, and algae. Acrylic acid effect concentrations for fish and invertebrates ranged from 27 to 236 mg/l. Effect concentrations (LC50 or EC50) for fish and invertebrates using methyl acrylate, ethyl acrylate, and butyl acrylate ranged from 1.1 to 8.2 mg/l. The chronic MATC for acrylic acid with Daphnia magna was 27 mg/l based on length and young produced per adult reproduction day and for ethyl acrylate was 0.29 mg/l based on both the reproductive and growth endpoints. Overall these studies show that acrylic acid and the acrylic esters studied can rapidly biodegrade, have a low potential for persistence or bioaccumulation in the environment, and have low to moderate toxicity.     

Spore release by the green alga Ulva: a quantitative assay to evaluate aquatic toxicants

A toxicity test using spore release of the aquatic green alga, Ulva, was developed and evaluated by assessing the toxicity of different organic and inorganic chemicals and elutriates of sewage or waste sludge. The toxic ranking of four metals was: Cu (EC50 of 0.040mgL(-1))>Cd (0.095mgL(-1))>Pb (0.489mgL(-1))>Zn (0.572mgL(-1)). The EC50 for TBTO ranged from 24 to 63microgL(-1). The most toxic VOC was formalin (EC50 of 0.788microlL(-1)) and the least toxic was acetone. Spore release was significantly inhibited in all elutriates; the greatest and least toxic effects were for industrial sewage (3.29%) and filtration bed (10.08%), respectively. The bioassay is simple, inexpensive and sensitive. The cosmopolitan distribution of Ulva means that the test would have a potential application worldwide.     

Biodegradability and ecotoxicity of amine oxide based surfactants

The aerobic and anaerobic biodegradability as well as the aquatic toxicity of two fatty amine oxides and one fatty amido amine oxide were investigated. Aerobic biodegradation was evaluated using the CO(2) headspace test (ISO 14593) and biodegradation under anaerobic conditions was assessed employing a standardised batch test. The three amine oxide based surfactants tested were readily biodegradable under aerobic conditions but only the alkyl amido amine oxide was found to be easily biodegradable under anaerobic conditions. Toxicity to Photobacterium phosphoreum and Daphnia magna was evaluated. Bacteria (EC(50) from 0.11 to 11 mg l(-1)) proved to be more sensitive to the toxic effects of the amine oxide based surfactants than crustacea (IC(50) from 6.8 to 45 mg l(-1)). The fatty amido amine oxide showed the lowest aquatic toxicity.     

Sensitivity of submersed freshwater macrophytes and endpoints in laboratory toxicity tests

The toxicological sensitivity and variability of a range of macrophyte endpoints were statistically tested with data from chronic, non-axenic, macrophyte toxicity tests. Five submersed freshwater macrophytes, four pesticides/biocides and 13 endpoints were included in the statistical analyses. Root endpoints, reflecting root growth, were most sensitive in the toxicity tests, while endpoints relating to biomass, growth and shoot length were less sensitive. The endpoints with the lowest coefficients of variation were not necessarily the endpoints, which were toxicologically most sensitive. Differences in sensitivity were in the range of 10-1000 for different macrophyte-specific endpoints. No macrophyte species was consistently the most sensitive. Criteria to select endpoints in macrophyte toxicity tests should include toxicological sensitivity, variance and ecological relevance. Hence, macrophyte toxicity tests should comprise an array of endpoints, including very sensitive endpoints like those relating to root growth.     

Acute and chronic effects of nano- and non-nano-scale TiO2 and ZnO particles on mobility and reproduction of the freshwater invertebrate Daphnia magna

Among the emerging literature addressing the biological effects of nanoparticles, very little information exists, particularly on aquatic organisms, that evaluates nanoparticles in comparison to non-nanocounterparts. Therefore, the potential effects of nano-scale and non-nano-scale TiO₂ and ZnO on the water flea, Daphnia magna, were examined in 48-h acute toxicity tests using three different test media, several pigment formulations – including coated nanoparticles – and a variety of preparation steps. In addition, a 21-d chronic Daphnia reproduction study was performed using coated TiO₂ nanoparticles. Analytical ultracentrifugation analyses provided evidence that the nanoparticles were present in a wide range of differently sized aggregates in the tested dispersions. While no pronounced effects on D. magna were observed for nano-scale and non-nano-scale TiO₂ pigments in 19 of 25 acute (48-h) toxicity tests (EC50 > 100 mg L⁻¹), six acute tests with both nano- and non-nano-scale TiO₂ pigments showed slight effects (EC10, 0.5–91.2 mg L⁻¹). For the nano-scale and non-nano-scale ZnO pigments, the acute 48-h EC50 values were close to the 1 mg L⁻¹ level, which is within the reported range of zinc toxicity to Daphnia. In general, the toxicity in the acute tests was independent of particle size (non-nano-scale or nano-scale), coating of particles, aggregation of particles, the type of medium or the applied pre-treatment of the test dispersions. The chronic Daphnia test with coated TiO₂ nanoparticles demonstrated that reproduction was a more sensitive endpoint than adult mortality. After 21 d, the NOEC for adult mortality was 30 mg L⁻¹ and the NOEC for offspring production was 3 mg L⁻¹. The 21-d EC10 and EC50 values for reproductive effects were 5 and 26.6 mg L⁻¹, respectively. This study demonstrates the utility of evaluating nanoparticle effects relative to non-nano-scale counterparts and presents the first report of chronic exposure to TiO₂ nanoparticles in D. magna.     

Duckweed (Lemna gibba) growth inhibition bioassay for evaluating the toxicity of olive mill wastes before and during composting

Two-phase olive mill waste (TPOMW) is considered the main problem confronting the modern oil extraction and processing industry. Composting has been recently proposed as a suitable method to treat TPOMW so that it is suitable for use in agriculture. In the work reported here, the Lemna gibba bioassay was tested to assess the toxicity of TPOMW before and during the composting process. The method was compared with the Lepidium sativum bioassay and with other chemical maturity indices traditionally reported in the literature. The L. gibba test proved to be a simple, sensitive, and accurate method to evaluate toxicity before and during the composting of TPOMW. Plant growth response was measured by two methods: counting the number of fronds (leaves) and measuring total frond area (TFA) with image analysis software. Compared to the counting of fronds (L. gibba) or seeds (L. sativum), the use of area-measuring software permitted a very rapid, unbiased and easy way of analysing the toxicity of TPOMW before and during composting. Although the accuracy of the frond count method was similar to the traditional cress seed test, data analysis showed that the TFA measurement method was statistically more accurate (significantly lower variance) than the frond count approach. Highly significant correlations were found between TFA and some important maturation indices commonly reported in literature indicating that the L. gibba bioassay can be a useful tool to determine the degree of maturity of TPOMW composts.     

Ecotoxicity and biodegradation of phthalate monoesters

Little is known about the fate and the effects of phthalic acid monoesters. Various of these monoesters ranging from n-butyl to isononyl monoester have been evaluated in respect to their biodegradation behaviour and their acute aquatic toxicity. All esters are readily biodegradable, achieving degradation rates of 90% and more. The acute toxicity values strongly depend on the carbon chain length of the alcohol moiety. The short chain specimen have LC/EC50 around and above 100 mg/l, with values levelling off to around 30 mg/l for the isononyl monoester.     

Isonychia spp. and macroinvertebrate community responses to stressors in streams utilizing the benthic in situ toxicity identification evaluation (BiTIE) method

Exposures of caged organisms in situ have proven to be a useful way to improve exposure realism and link to stressor effects in aquatic assessments of hazard or risk. A novel cage system, the benthic in situ toxicity identification evaluation (BiTIE), was developed for benthic macroinvertebrates (surrogate species, resident populations and communities) to separate low and high flow effects, and major chemical classes of stressors in streams. Three resin types were used to separate the chemical stressors in the streams Honey Creek and Little Beavercreek, Ohio, USA: Dowex Optipore (non-polar organics), zeolite (ammonia), and polywool (control). Isonychia spp. sensitivity was compared to Chironomus tentans, and no significant differences were found (p>0.05). Isonychia spp. growth (length) showed a stressor response in the zeolite treatments, and community testing revealed improved metric responses in the Dowex treatments. The BiTIE chamber system demonstrated stressor-response relationships using sublethal and multimetric endpoints.     

A fluorescence-based bioassay for aquatic macrophytes and its suitability for effect analysis of non-photosystem II inhibitors

Background, Goals and Scope During the last years the miniaturization of toxicity test systems for rapid and parallel measurements of large quantities of samples has often been discussed. For unicellular algae as well as for aquatic macrophytes, fluorescence-based miniaturized test systems have been introduced to analyze photosystem II (PSII) inhibitors. Nevertheless, high-throughput screening should also guarantee the effect detection of a broad range of toxicants in order to ensure routinely applicable, high-throughput measuring device experiments which can cover a broad range of toxicants and modes of action others than PSII inhibition. Thus, the aim of this study was to establish a fast and reproducible measuring system for non-PSII inhibitors for aquatic macrophyte species to overcome major limitations for use. Methods A newly developed imaging pulse-amplitude-modulated chlorophyll fluorometer (I-PAM) was applied as an effect detector in short-term bioassays with the aquatic macrophyte species Lemna minor. This multiwell-plate based measuring device enabled the incubation and measurement of up to 24 samples in parallel. The chemicals paraquat-dichloride, alizarine and triclosan were chosen as representatives for the toxicant groups of non-PSII herbicides, polycyclic aromatic hydrocarbons (PAHs) and pharmaceuticals and personal care products (PPCPs), which are often detected in the aquatic environment. The I-PAM was used (i) to establish and validate the sensitivity of the test system to the three non-PSII inhibitors, (ii) to compare the test systems with standardized and established biotests for aquatic macrophytes, and (iii) to define necessary time scales in aquatic macrophyte testing. For validation of the fluorescence-based assay, the standard growth test with L. minor (ISO/DIS 20079) was performed in parallel for each chemical. Results The results revealed that fluorescence-based measurements with the I-PAM allow rapid and parallel analysis of large amounts of aquatic macrophyte samples. The I-PAM enabled the recording of concentration-effect-curves with L. minor samples on a 24-well plate with single measurements. Fluorescence-based concentration-effect-curves could be detected for all three chemicals after only 1 h of incubation. After 4–5 h incubation time, the maximum inhibition of fluorescence showed an 80–100% effect for the chemicals tested. The EC50 after 24 h incubation were estimated to be 0.06 mg/L, 0.84 mg/L and 1.69 mg/L for paraquatdichloride, alizarine and triclosan, respectively. Discussion The results obtained with the I-PAM after 24 h for the herbicide paraquat-dichloride and the polycyclic aromatic hydrocarbon alizarine were in good accordance with median effective concentrations (EC50s) obtained by the standardized growth test for L. minor after 7 d incubation (0.09 mg/L and 0.79 mg/L for paraquat-dichloride and alizarine, respectively). Those results were in accordance with literature findings for the two chemicals. In contrast, fluorescence-based EC50 of the antimicrobial agent triclosan proved to be two orders of magnitude greater when compared to the standard growth test with 7 d incubation time (0.026 mg/L) as well as with literature findings. Conclusion Typically, aquatic macrophyte testing is very time consuming and relies on laborious experimental set-ups. The I-PAM measuring device enabled fast effect screening for the three chemicals tested. While established test systems for aquatic macrophytes need incubation times of ≥ 7 d, the I-PAM can detect inhibitory effects much earlier (24 h), even if inhibition of chemicals is not specifically associated with PSII. Thus, the fluorescence-based bioassay with the I-PAM offers a promising approach for the miniaturization and high-throughput testing of chemicals with aquatic macrophytes. For the chemical triclosan, however, the short-term effect prediction with the I-PAM has been shown to be less sensitive than with long-term bioassays, which might be due to physicochemical substance properties such as lipophilicity. Recommendations and Perspectives The results of this study show that the I-PAM represents a promising tool for decreasing the incubation times of aquatic macrophyte toxicity testing to about 24 h as a supplement to existing test batteries. The applicability of this I-PAM bioassay on emergent and submerged aquatic macrophyte species should be investigated in further studies. Regarding considerations that physicochemical properties of the tested substances might play an important role in microplate bioassays, the I-PAM bioassay should either be accompanied by evaluating physicochemical properties modeled from structural information prior to an experimental investigation, or by intensified chemical analyses to identify and determine nominal concentrations of the toxicants tested. The chemicals paraquat-dichloride, alizarine and triclosan were chosen as representatives for the toxicant groups of non-PSII herbicides, PAHs and PPCPs which are often detected in the aquatic environment. Nevertheless, in order to ensure a routinely applicable measuring device, experiments with a broader range of toxicants and samples of surface and/or waste waters are necessary. ESS-Submission Editor: Dr. Markus Hecker (MHecker@Entrix.com)     

Acute toxicity of 353-nonylphenol and its metabolites for zebrafish embryos

Background, aim and scope  Nonylphenol (NP) can be detected in the aquatic environment all over the world. It is applied as a technical mixture of isomers of which 353-NP is the most relevant both in terms of abundance (about 20% of total mass) and endocrine potential. 353-NP is metabolised in sewage sludge. The aims of the present study were to determine and to compare the acute toxicity of t-NP, 353-NP and its metabolites as well as to discuss if the toxicity of 353-NP changes during degradation. Materials and methods  353-NP and two of its metabolites were synthesised. The zebrafish embryo test was performed according to standard protocols. Several lethal and non-lethal endpoints during embryonal development were reported. NOEL, LOEL and EC₅₀ were calculated. Results  All tested compounds caused lethal as well as non-lethal malformations during embryo development. 353-NP showed a higher toxicity (EC₅₀ for lethal endpoints 6.7 mg/L) compared to its metabolites 4-(3.5-dimethyl-3-heptyl)-2-nitrophenol (EC₅₀ 13.3 mg/L) and 4-(3,5-dimethyl-3-heptyl)-2-bromophenol (EC₅₀ 27.1 mg/L). Discussion  In surface water, concentrations of NP are far below the NOEC identified by the zebrafish embryo test. However, in soils and sewage sludge, concentrations may reach or even exceed these concentrations. Therefore, sludge-treated sites close to surface waters should be analysed for NP and its metabolites in order to detect an unduly high contamination due to runoff events. Conclusions  The results of the present study point out that the toxicity of 353-NP probably declines during metabolisation in water, sediment and soil, but does not vanish since the major metabolites exhibit a clear toxic potential for zebrafish embryos. Recommendations and perspectives  Metabolites of environmental pollutants should be included in the ecotoxicological test strategy for a proper risk assessment. An erratum to this article can be found at     

Biodegradation of haloacetic acids by bacterial enrichment cultures

Haloacetic acids (HAAs) are toxic organic chemicals that are frequently detected in surface waters and in drinking water distribution systems. The aerobic biodegradation of HAAs was investigated in serum bottles containing a single HAA and inoculated with washed microorganisms obtained from enrichment cultures maintained on either monochloroacetic acid (MCAA) or trichloroacetic acid (TCAA) as the sole carbon and energy source. Biodegradation was observed for each of the HAAs tested at concentrations similar to those found in surface waters and in drinking water distribution systems. The MCAA culture was able to degrade both MCAA and monobromoacetic acid (MBAA) with pseudo-first order rate constants of 1.06 x 10(-2) and 1.13 x 10(-2) l(mg protein)(-1) d(-1), respectively, for concentrations ranging from 10(-5) to 2 mM. The pseudo-first order rate constant for TCAA degradation by the TCAA culture was 6.52 x 10(-3) l(mg protein)(-1) d(-1) for concentrations ranging from 5.33 x 10(-5) to 0.72 mM. The TCAA culture was also able to degrade MCAA with the rate accelerating as incubation time increased. Experiments with radiolabeled HAAs indicated that the 14C was primarily converted to 14CO2 with minor incorporation into cell biomass. The community structure of the enrichment cultures was analyzed by both cultivation-dependent and cultivation-independent approaches. Denaturing gradient gel electrophoresis (DGGE) of the PCR-amplified 16S rRNA gene fragments showed that each of the two enrichment cultures had multiple bacterial populations, none of which corresponded to HAA-degrading bacteria cultivated on HAA-supplemented agar plates. This research indicates that biodegradation is a potential loss mechanism for HAAs in surface waters and in drinking water distribution systems.     

Multi-generation cadmium acclimation and tolerance in Daphnia magna Straus

The cladoceran Daphnia magna was acclimated for seven generations to cadmium concentrations ranging from 0 (control) to 250 microg/l Cd (corresponding to a free ion activity of 4.60 nM Cd2+). Acute and chronic cadmium tolerance as well as cadmium accumulation were monitored as a function of acclimation time. After two to three generations of acclimation to concentrations ranging from 0.23 to 1.11 nM Cd2+ increases in acute tolerance were maximal (factor 7.2) and significant. Acclimation for seven generations to the same acclimation concentrations did result in an increased chronic cadmium tolerance (21 days EC50 values increased). Organisms acclimated to 1.93 nM Cd2+ were equally or more sensitive than non-acclimated daphnids in acute and chronic toxicity tests. Cadmium contents in D. magna increased significantly as a function of the acclimation concentration. Maximum body burdens of 236+/-30 microg Cd/g dry weight were measured in organisms exposed to 4.60 nM Cd2+, but detoxification mechanisms were only successful up to 82+/-20 microg Cd/g dry weight as this concentration did not cause major decreases in survival and reproduction in chronic toxicity tests. As the potential positive effect of acclimation on cadmium tolerance disappeared with successive acclimation generations and increasing acclimation concentrations, it is concluded that multi-generation acclimation studies are important for the evaluation of the long-term effects of environmental toxicants.     

Acute and chronic toxicity of veterinary antibiotics to Daphnia magna

The acute and chronic toxicity of nine antibiotics used both therapeutically and as growth promoters in intensive farming was investigated on the freshwater crustacean Daphnia magna. The effect of the antibiotics metronidazole (M), olaquindox (OL), oxolinic acid (OA), oxytetracycline (OTC), streptomycin (ST), sulfadiazine (SU), tetracycline (TC), tiamulin (TI) and tylosin (TY) was tested in accordance to the ISO (1989) and OECD (1996) standard procedures. The acute toxicities (48-h EC50 value, mg/l) in decreasing order were OA (4.6), TI (40), SU (221), ST (487), TY (680) and OTC (approximately 1000). NOECs were 340 mg/l for TC and 1000 mg/l for M and OL. Toxic effect on reproduction occurred generally at concentrations, which were one order of magnitude below the acute toxic levels. The chronic toxicity (EC50 values, mg/l) in the D. magna reproduction test in decreasing order were TI (5.4), SU (13.7), TC (44.8) and OTC (46.2). The NOECs (mg/l) obtained in the reproduction test with OA, ST, TY and M were 0.38 for OA, 32 for ST, 45 for TY and 250 for M. The observed toxicity of OA to D. magna indicates that this substance, which is a commonly used feed additive in fish farms, has a potential to cause adverse effects on the aquatic environment.