Laboratory Waters Research Articles

Common laboratory reagents: Are they a double-edged sword in microplastics research?

Understanding and communicating instances of microplastic contamination is critical for enabling plastic-free transitions. While microplastics research uses a variety of commercial chemicals and laboratory liquids, the impact of microplastics on these materials remains unknown. To fill this knowledge gap, the current study investigated microplastics abundance and their characteristics in laboratory waters (distilled, deionized, and Milli-Q), salts (NaCl and CaCl2), chemical solutions (H2O2, KOH and NaOH), and ethanol from various research laboratories and commercial brands. The mean abundance of microplastics in water, salt, chemical solutions, and ethanol samples was 30.21 ± 30.40 (L−1), 24.00 ± 19.00 (10 g−1), 187.00 ± 45.00 (L−1), and 27.63 ± 9.53 (L−1), respectively. Data comparisons revealed significant discrepancies between the samples in terms of microplastic abundance. Fibers (81 %) were the most common microplastics, followed by fragments (16 %) and films (3 %); 95 % of them were <500 μm, with the smallest and largest particle sizes recorded being 26 μm and 2.30 mm, respectively. Microplastic polymers discovered included polyethylene, polypropylene, polyester, nylon, acrylic, paint chips, cellophane, and viscose. These findings lay the groundwork for identifying common laboratory reagents as a potential contributor to microplastic contamination in samples, and we offer solutions that should be integrated into data processing to produce accurate results. Taken together, this study shows that commonly used reagents not only play a key role in the microplastic separation process but also contain microplastic contamination themselves, requiring the attention of researchers to promote quality control during microplastic analysis and commercial suppliers in formulating novel prevention strategies.

Using the Daphnia magna Transcriptome to Distinguish Water Source: Wetland and Stormwater Case Studies.

A major challenge in ecotoxicology is accurately and sufficiently measuring chemical exposures and biological effects given the presence of complex and dynamic contaminant mixtures in surface waters. It is impractical to quantify all chemicals in such matrices over space and time, and even if it were practical, concomitant biological effects would not be elucidated. Our study examined the performance of the Daphnia magna transcriptome to detect distinct responses across three water sources in Minnesota: laboratory (well) waters, wetland waters, and storm waters. Pyriproxyfen was included as a gene expression and male neonate production positive control to examine whether gene expression resulting from exposure to this well‐studied juvenoid hormone analog can be detected in complex matrices. Laboratory‐reared (<24 h) D. magna were exposed to a water source and/or pyriproxyfen for 16 days to monitor phenotypic changes or 96 h to examine gene expression responses using Illumina HiSeq 2500 (10 million reads per library, 50‐bp paired end [2 × 50]). The results indicated that a unique gene expression profile was produced for each water source. At 119 ng/L pyriproxyfen (~25% effect concentration) for male neonate production, as expected, the Doublesex1 gene was up‐regulated. In descending order, gene expression patterns were most discernable with respect to pyriproxyfen exposure status, season of stormwater sample collection, and wetland quality, as indicated by the index of biological integrity. However, the biological implications of the affected genes were not broadly clear given limited genome resources for invertebrates. Our study provides support for the utility of short‐term whole‐organism transcriptomic testing in D. magna to discern sample type, but highlights the need for further work on invertebrate genomics. Environ Toxicol Chem 2022;41:2107–2123. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Uranium removal from laboratory and environmental waters by oxidised biochar prepared from palm tree fibres

Uranium removal from laboratory and environmental waters by oxidised biochar prepared from palm tree fibres

Single-use surgical face masks as radionuclide (U-232 and Ra-226) carriers

The adsorption of U-232 and Ra-226 at ultra-trace levels by single-use surgical face masks has been investigated in different aqueous media (e.g. de-ionized water, seawater, ground water and treated waste water). The measurements show that under the given concentration levels (picomole range) there is significant adsorption of the radionuclides by the face masks in laboratory and environmental waters. Evaluation of the adsorption data reveals that the partition coefficient values (Kd) differ significantly between the two radionuclides and that particularly in the case of uranium, pH and solution composition govern the adsorption efficiency because of hydrolysis and complex formation reactions. Based on the experimental results and having in mind the enormous amounts of uncontrolled face mask disposal, these are expected to play a significant role as radionuclide carries in the environment.

Inorganic nanoparticle embedded Polydimethyl siloxane nanocomposites for biofouling mitigation

Polydimethyl siloxane (PDMS) CuO nanocomposites (NCs) were prepared using plain CuO and cetyltrimethyl ammonium bromide (CTAB) capped (0.05 & 1.0M) CuO nanoparticles as nanofillers. Incorporation of plain CuO and CuO-1M capped NP as nanofillers into PDMS altered their surface roughness and imparted biocidal activity by release of metal ions. CTAB capping increased the zeta potential of synthesized nanoparticles with 0.05M CTAB yielding monodispersed CuO-NP with enhanced broad spectrum antifouling activity in PDMS matrix. Nanocomposites were tested for their efficacy against inhibition of bacterial (in vitro) and diatom adhesion (in situ) in laboratory and coastal waters respectively. PDMS-CuO-CTAB (0.05M) capped nanoparticles showed significant (p<0.05) antibiofilm property against Staphylococcus lentus and Vibrio natriegens. Diatoms extensively colonized plain PDMS surfaces (1.2 × 103 cm−2), whereas PDMS-CuO, PDMS-CuO-0.05M CTAB, PDMS-CuO-1M CTAB NCs showed 1.20 × 103, 4.86 × 102 and 5.82 × 102 cells cm−2 respectively. Field exposure trials showed reduction in fouling biomass from 9 Kg m−2 (on plain PDMS) to 0.6 Kg m-2 on PDMS-CuO (0.05M CTAB) NC after 90 days of exposure in coastal waters. Percentage surface area coverage of fouling organisms also reduced significantly (p<0.05) from 98.3 ± 0.6% on plain PDMS to 36.8 ± 2.34% on PDMS-CuO-(0.05M CTAB) nanocomposite. Overall, PDMS-CuO-(0.05M CTAB) nanocomposite exhibited broad spectrum antifouling activity against different levels of fouling organisms and offers a potential antifouling surface.

Geochemical factors affecting the solubility of copper in seawater

Environmental contextMany trace metals, including copper, are only sparingly soluble in seawater and may exist in both dissolved and particulate forms (e.g. as precipitates). Aquatic organisms may experience different toxic effects from exposure to dissolved and particulate trace metals. This study investigates how concentration, reaction time and changes to precipitate composition/mineral formation affect copper solubility in seawater, thus influencing metal bioavailability and toxicity in the field and laboratory. AbstractA lack of knowledge on the solubility of metals such as copper affects the ability to predict the forms (dissolved and particulate) that organisms are exposed to in field and laboratory waters. Laboratory tests were conducted where copper (total concentrations of 0.5 to 20mg L−1) was added to natural and artificial seawater (pH 8.15, 22°C), equilibrated for 28 days and dissolved copper monitored at periodic intervals. At 0.5mg L−1, dissolved copper concentrations remained stable over 28 days and no precipitates were detected. However, at higher total copper concentrations, an initial rapid precipitation phase was followed by the establishment of a metastable equilibrium that persisted for periods of days to weeks, and whose solubility concentrations and duration were influenced by the total copper concentration and typically in the range 0.6 to 0.9mg L−1. After 5 to 15 days, a step change decrease in dissolved copper concentration followed by a slow decline was observed in the &amp;gt;2mg L−1 total copper treatments. The minimum solubility measured after 28 days was 0.053mg L−1. Elemental and X-ray diffraction analyses indicated that the copper precipitates comprised similar proportions of amorphous copper hydroxycarbonate and amorphous dicopper trihydroxide chloride after 1 day and transformed to predominantly mineralised dicopper trihydroxide chloride in the clinoatacamite polymorph form after 28 days. These observations have particular relevance for toxicity tests of less sensitive organisms and highlight the need to consider metal solubility, exposure to precipitates and changes in precipitate mineral phases.

Residual Maintenance Using Sodium Hypochlorite, Sodium Dichloroisocyanurate, and Chlorine Dioxide in Laboratory Waters of Varying Turbidity

Sodium hypochlorite (NaOCl) and sodium dichloroisocyanurate (NaDCC) are commonly used for household water treatment (HWT); chlorine dioxide (ClO2) is a potential new HWT option. We compared the residual maintenance of NaOCl, NaDCC, and ClO2 over 24 hours using recommended dosages (2 and 4 mg/L) in waters of varying turbidity (0–300 NTU, from kaolin clay or creek-bottom sediments) and total organic carbon (TOC) concentrations (0–100 mg/L), for a total of 324 reactors. NaOCl and NaDCC had similar free chlorine decay rates, and ClO2 decayed more rapidly across all of the tested conditions. Little variability was observed across clay-based turbidity levels and TOC concentrations. With a dosage of 2 mg/L, a residual ≥0.2 mg/L was maintained at 30 NTU for NaOCl and 100 NTU for NaDCC; for ClO2, 4 mg/L were required to maintain ≥0.2 mg/L under all conditions except at zero turbidity. Comparisons with data from the literature suggest that the three compounds would inactivate E. coli, rotavirus, and Giardia cysts within 1 hour under all conditions, except 300 NTU for NaOCl and NaDCC. All three disinfectants are similarly efficacious for this usage; however, differences are seen in decay rates that may influence disinfectant selection depending on water storage time.

Water-effect ratio of copper and its application on setting site-specific water quality criteria for protecting marine ecosystems of Hong Kong.

Generic water quality criteria (WQC) of a chemical are usually set based on results generated from toxicity tests which were conducted using standard laboratory water with well-controlled physiochemical properties. However, in natural aquatic environments, physiochemical characteristics, such as salinity, total suspended solid, total organic carbon and the co-existence of chemical contaminants, often vary spatially and temporally. These parameters can, in turn, alter the bioavailability of target chemicals and, thus, influence their toxicity to marine organisms. To account for site specificity, the US Environmental Protection Agency's water-effect ratio (WER=site water-LC50/laboratory water-LC50) procedure can be applied to derive site-specific WQC. Most past studies, however, were conducted for freshwater systems. Here, for the first time, the WER of copper (Cu) was determined for three marine water control zones (WCZs) in Hong Kong: Victoria Harbour, Deep Bay and Southern WCZs. Samples of water were collected from three locations within each WCZ, while acute toxicities to the marine diatom Skeletonema costatum, intertidal copepod Tigriopus japonicus and larvae of marine medaka Oryzias melastigma were determined in site or laboratory (artificial seawater) waters. Results of this study showed that conservative final WER relative coefficients for Cu ranged from 0.57 to 0.73 for the three WCZs, and water from some locations caused >30% mortality in the fish larvae in the controls (without Cu addition). These results suggested that current generic WQC for Cu are likely under-protective for marine organisms in the three areas, and it should be tightened by multiplying it with site-specific WER to offer better protection to marine biodiversity and integrity of the ecosystem.

Effect of Fe (III) on Pseudokirchneriella subcapitata at circumneutral pH in standard laboratory tests is explained by nutrient sequestration.

The complex chemistry of iron (Fe) at circumneutral pH in oxygenated waters and the poor correlation between ecotoxicity results in laboratory and natural waters have led to regulatory approaches for iron based on field studies (US Environmental Protection Agency Water Quality Criteria and European Union Water Framework Directive proposal for Fe). The results of the present study account for the observed differences between laboratory and field observations for Fe toxicity to algae (Pseudokirchneriella subcapitata). Results from standard 72-h assays with Fe at pH 6.3 and pH 8 resulted in similar toxicity values measured as algal biomass, with 50% effect concentrations (EC50) of 3.28 mg/L and 4.95 mg/L total Fe(III), respectively. At the end of the 72-h exposure, however, dissolved Fe concentrations were lower than 30 μg/L for all test concentrations, making a direct toxic effect of dissolved iron on algae unlikely. Analysis of nutrient concentrations in the artificial test media detected phosphorus depletion in a dose-dependent manner that correlated well with algal toxicity. Subsequent experiments adding excess phosphorus after Fe precipitation eliminated the toxicity. These results strongly suggest that observed Fe(III) toxicity on algae in laboratory conditions is a secondary effect of phosphorous depletion. Environ Toxicol Chem 2017;36:952-958. © 2016 SETAC.

Silver Biotic Ligand Model (BLM): Refinement of an Acute BLM for Silver

The biotic ligand model (BLM) is a computational tool that may be used to predict toxic effect levels of metals, including Ag. The BLM considers the effect of site-specific water quality characteristics on Ag speciation and bioavailability. This provides a basis for extrapolating from laboratory waters, used for most Ag toxicity tests, to natural waters, where the bioavailability and toxicity of Ag may differ. The original version of the BLM for the acute toxicity of Ag was reviewed by the USEPA Science Advisory Board (SAB) in 1999 and they recommended the completion of additional Ag chemistry and toxicity studies to provide data to test and refine the model. This project was completed to satisfy these recommendations. A chemistry component was completed to improve the representation of Ag speciation in natural waters and to characterize the important effect of sulfide on Ag bioavailability. These investigations added to the information that was available to characterize Ag chemistry and provided a basis for updating the earlier version of the Ag BLM. The BLM was also calibrated to laboratory toxicity data that were generated for a Ag-sensitive invertebrate, Ceriodaphnia dubia, a cladoceran that had previously been tested to only a limited degree. The studies were carried out in laboratory waters in which the chemistry was systematically varied to provide a basis for calibration of the BLM to the toxicity data for C. dubia. Toxicity tests were also performed with both Pimephales promelas and C. dubia in natural water samples that were well characterized chemically, with the data then used to test the model. While the C. dubia BLM results were relatively successful at simulating the observed effect levels the P. promelas results highlighted the need for further testing and refinement of the Ag BLM as it was applied to this fish species. Physiological tests were performed to explore the apparent increase in sensitivity of P. promelas in some of the test waters that were relatively low in ionic strength. It was determined that acclimation to such low ionic strength waters, in the absence of Ag, did not significantly reduce their sensitivity to Ag. Rather, it appeared that any benefit that may have been realized by acclimation, such as an enhanced ability to upregulate ion uptake rates in low ionic strength waters, was apparently offset by a concomitant increase in the rate at which Ag was accumulated. The Ag BLM was modified to account for the effect of low ionic strength water on the sensitivity to Ag of > 4-day old P. promelas. This led to an improved ability of the BLM to predict P. promelas effect levels in the natural waters. Physiological tests were also performed to investigate the apparent species-specific protection against Ag toxicity that is provided by chloride. Investigations with P. promelas suggested that the differences in degree of protection may be related to differences in how Ag affects the ionoregulation of Na+ and Cl− by different fish species. Although questions remain with regard to chloride, it appears that the BLM is able to predict this response reasonably well, particularly for the relatively sensitive <4 day old P. promelas. In summary, the WERF program yielded an improved chemistry and toxicity database, including data over an extended range of water quality characteristics and for an additional Ag-sensitive invertebrate, thereby providing a basis for refining the acute Ag BLM and improving its overall predictive ability.This title belongs to WERF Research Report SeriesISBN: 9781780403656 (eBook)ISBN: 9781843397960 (Print)

Learning from the Eco-Toxicology of Fire-Fighting Foams in Aquatic Organisms: Altered Eco-Toxicity of Sodium Alkyl Sulfonates on Green Paramecia and Medaka Fish Maintained in Different Waters

A variety of ciliated and flagellated protozoan species have been used as bio-indicators of the eco-toxic impacts of polluting chemicals, especially in aquatic environments such as rivers, ponds, lakes, and wetlands. To date, both the short-term and long-term impacts of fire-fighting foams (FFFs) in aquatic (freshwater environment) and semi-aquatic (wetland) ecosystems have been assessed in laboratory-scale model assays and in biotope-based assays. Little attention has been given to the fact that water qualities, such as hardness, drastically alter the toxic actions of various chemicals against living aquatic organisms including fishes, algae, and other microbes, suggesting that the laboratory water often employed in toxicity assays for fishes and microorganisms might not reflect the actual impact of chemicals in the ecosystem. Therefore, for examining the toxicity of certain chemicals (chiefly detergent-based and soap-based FFFs) in aquatic organisms, we have previously proposed that a series of simple eco-toxicity tests using natural waters sampled from the natural organism’s habitats or blends of mineralcontaining water preparations mimicking the natural habitat waters be used in addition to tests in standard laboratory waters. Based on the knowledge of the eco-toxicity of FFFs obtained through past studies using model aquatic organisms such as green paramecia (Paramecium bursaria), we conducted a study aiming to uncover the toxic mechanism of sodium alkyl sulfonates, a series of synthetic detergents known as SAS, using a strain ofP. bursariaoriginally sampled from a river, both in laboratory water and habitat river water (river water from whereP. bursariawas collected; HRW). Here, we employedP. bursariamaintained in both a natural HRW-based assay medium and an ultrapure water-based low-mineral standard culturing medium for comparing the apparent toxicity of SAS. Data strongly suggested that the toxicities of most SAS detergents (alkyl chains shorter than 9 carbons or longer than 14 carbons) are minimized in the mineral-rich HRW compared to the commonly used UPW-based low-mineral ciliateculturing conditions. The toxicity of SAS members with moderate chain lengths, such as sodium dodecan sulfonate, tended to be minimized with elevated mineral content. A similar tendency was also observed in medaka fish, a tiny model fish.

A semi-automated image analysis procedure for in situ plankton imaging systems.

Plankton imaging systems are capable of providing fine-scale observations that enhance our understanding of key physical and biological processes. However, processing the large volumes of data collected by imaging systems remains a major obstacle for their employment, and existing approaches are designed either for images acquired under laboratory controlled conditions or within clear waters. In the present study, we developed a semi-automated approach to analyze plankton taxa from images acquired by the ZOOplankton VISualization (ZOOVIS) system within turbid estuarine waters, in Chesapeake Bay. When compared to images under laboratory controlled conditions or clear waters, images from highly turbid waters are often of relatively low quality and more variable, due to the large amount of objects and nonlinear illumination within each image. We first customized a segmentation procedure to locate objects within each image and extracted them for classification. A maximally stable extremal regions algorithm was applied to segment large gelatinous zooplankton and an adaptive threshold approach was developed to segment small organisms, such as copepods. Unlike the existing approaches for images acquired from laboratory, controlled conditions or clear waters, the target objects are often the majority class, and the classification can be treated as a multi-class classification problem. We customized a two-level hierarchical classification procedure using support vector machines to classify the target objects (< 5%), and remove the non-target objects (> 95%). First, histograms of oriented gradients feature descriptors were constructed for the segmented objects. In the first step all non-target and target objects were classified into different groups: arrow-like, copepod-like, and gelatinous zooplankton. Each object was passed to a group-specific classifier to remove most non-target objects. After the object was classified, an expert or non-expert then manually removed the non-target objects that could not be removed by the procedure. The procedure was tested on 89,419 images collected in Chesapeake Bay, and results were consistent with visual counts with >80% accuracy for all three groups.

Analysis of Algaecide Exposures: an Evaluation of the I3 − Method to Measure Sodium Carbonate Peroxyhydrate Algaecides

Algaecides are commonly used to control noxious algal growths in water resources. In order to make accurate predictions about responses of target and non-target species to algaecide exposures, reliable methods are needed to confirm exposures in the laboratory and the field. The focus of this research was to evaluate the I3− method for measuring hydrogen peroxide (H2O2) exposures associated with applications of a sodium carbonate peroxyhydrate (SCP)-based algaecide. To meet this overall objective, method detection limits, interferences from field waters (turbidity, color, and algal cell density), and storage stability of samples were measured. The method detection limits were 0.2 (p < 0.0001) and 0.25 mg H2O2/L (p = 0.0002) for laboratory and field waters, respectively. The upper method detection limit was 7.5 mg H2O2/L for both waters. Turbidity (25.3 NTU) and color of field-collected water did not interfere with measurements. Algal cell densities of 104, 105, and 106 cells/mL of two planktonic algal species in laboratory water did not interfere with measurements. Measurements of samples stored in dark refrigeration and on ice remained stable over 4 days, while measurements of samples stored in direct sunlight in ambient temperatures were altered after 1 day. The I3− method accurately measured H2O2 exposures in the laboratory water, field water, and laboratory water containing planktonic algae used in this experiment within the range of concentrations that would be applied in a field setting. These data demonstrated that this method has utility for confirming exposures after laboratory and field treatments of SCP-based algaecides.

Development of a regression model to predict copper toxicity to Daphnia magna and site-specific copper criteria across multiple surface-water drainages in an arid landscape.

The water effect ratio (WER) procedure developed by the US Environmental Protection Agency is commonly used to derive site-specific criteria for point-source metal discharges into perennial waters. However, experience is limited with this method in the ephemeral and intermittent systems typical of arid climates. The present study presents a regression model to develop WER-based site-specific criteria for a network of ephemeral and intermittent streams influenced by nonpoint sources of Cu in the southwestern United States. Acute (48-h) Cu toxicity tests were performed concurrently with Daphnia magna in site water samples and hardness-matched laboratory waters. Median effect concentrations (EC50s) for Cu in site water samples (n=17) varied by more than 12-fold, and the range of calculated WER values was similar. Statistically significant (α=0.05) univariate predictors of site-specific Cu toxicity included (in sequence of decreasing significance) dissolved organic carbon (DOC), hardness/alkalinity ratio, alkalinity, K, and total dissolved solids. A multiple-regression model developed from a combination of DOC and alkalinity explained 85% of the toxicity variability in site water samples, providing a strong predictive tool that can be used in the WER framework when site-specific criteria values are derived. The biotic ligand model (BLM) underpredicted toxicity in site waters by more than 2-fold. Adjustments to the default BLM parameters improved the model's performance but did not provide a better predictive tool compared with the regression model developed from DOC and alkalinity.

Development of a model to predict the effect of water chemistry on the acute toxicity of cadmium to Photobacterium phosphoreum

Cadmium (Cd) compounds are widely distributed toxic environmental and industrial pollutants, and they may bring danger to growth and development of aquatic organisms. The effects of Ca2+ (as CaCl2), Mg2+ (as MgSO4), K+ (as KCl), pH and complexants (EDTA, the commercial DOM, and three homemade DOMs) on Cd toxicity to Photobacterium phosphoreum were evaluated in standardized 15min acute toxicity tests. Increases in Ca2+ concentration resulted in higher EC50 values, indicating the competition between the two ions for uptake sites at the biotic ligand. Increased waterborne Mg2+ also reduced Cd toxicity, but to a slightly lesser degree compared with Ca2+. The overall decline in EC50 data with increasing K+ in test solutions suggested that Cd toxicity was enhanced at larger K+ concentration. The toxicity alleviation by H+ was observed over the tested pH range of 5.0–9.0. Additions of complexing agents into the exposure water reduced Cd bioavailability via complexation of Cd2+, and complexants from different sources displayed different protective effect. The influence of these toxicity modifying factors was finally incorporated into a model that can predict acute cadmidum toxicity for Photobacterium phosphoreum. After validation with laboratory and natural waters, the developed model could support efforts to improve the ecological relevance of presently applied risk assessment procedures.

Phototransformations of selected pharmaceuticals under low-energy UVA–vis and powerful UVB–UVA irradiations in aqueous solutions—the role of natural dissolved organic chromophoric material

The kinetics of simulated low-energy daylight (UVA-vis) and powerful combined ultraviolet B and A (UVB-UVA) induced direct and indirect phototransformations of four pharmaceuticals, i.e., ibuprofen, metoprolol, carbamazepine, and warfarin, which were investigated in dilute solutions of pure laboratory and natural humic waters. The results strengthen the essential function of natural chromophores in dissolved organic material (CDOM) as principal photosensitizer toward indirect phototransformations of pharmaceuticals in natural conditions under available low-energy UVA-vis and slight UVB radiations. The results confirmed that organic micropollutants are able to undergo a direct photolysis if their absorbance spectra overlap the spectral range of the available radiation but only if the radiation is strong enough, e.g., ibuprofen is able to undergo only indirect photolysis via different pathways in all realistic conditions. The action of nitrate anions as photosensitizers in the applied conditions proved to be of little importance. High-performance size-exclusion chromatographic experiments verified that the rate constants obtained under the low-energy UVA-vis and powerful UVB-UVA irradiations for the decreased amounts of the two largest molecular size fractions of CDOM were quite close to the rate constants detected for the increased amounts of the next five molecular size fractions with smaller molecular sizes. The decreased contents of the two largest molecular size fractions correlated quite well with the decreased contents of the studied pharmaceuticals under the low-energy UVA-vis irradiation process but somewhat less under the powerful UVB-UVA irradiation. The photochemically induced decomposition of the CDOM aggregates appears to increase the amounts of smaller molecular size fractions and simultaneously produce via CDOM-stimulated radical reactions indirect structural transformations of pharmaceuticals. Apparent quantum yields were estimated for the transformation-degradation of the two largest molecular-size CDOM aggregates under low-energy UVA-vis and powerful UVB-UVA irradiations.

Effects of Water Quality Parameters on Boron Toxicity to Ceriodaphnia dubia

The potential modifying effects of certain water quality parameters (e.g., hardness, alkalinity, pH) on the acute toxicity of boron were tested using a freshwater cladoceran, Ceriodaphnia dubia. By comparison, boron acute toxicity was less affected by water quality characteristics than some metals (e.g., copper and silver). Increases in alkalinity over the range tested did not alter toxicity. Increases in water hardness appeared to have an effect with very hard waters (>500 mg/L as CaCO(3)). Decreased pH had a limited influence on boron acute toxicity in laboratory waters. Increasing chloride concentration did not provide a protective effect. Boron acute toxicity was unaffected by sodium concentrations. Median acute lethal concentrations (LC(50)) in natural water samples collected from three field sites were all greater than in reconstituted laboratory waters that matched natural waters in all respects except for dissolved organic carbon. Water effect ratios in these waters ranged from 1.4 to 1.8. In subsequent studies using a commercially available source of natural organic matter, acute toxicity decreased with increased dissolved organic carbon, suggesting, along with the natural water studies, that dissolved organic carbon should be considered further as a modifier of boron toxicity in natural waters where it exceeds 2 mg/L.

Oestrogenic activity using a recombinant yeast screen assay (RCBA) in South African laboratory water sources

Many chemicals released into the environment are believed to disrupt normal endocrine functions in humans and animals. These endocrine disrupting chemicals (EDCs) affect reproductive health and development. A major group of EDCs that could be responsible for reproductive effects are those that mimic natural oestrogens, known as xeno-oestrogens. A number of in vivo and in vitro screening strategies are being developed to identify and classify xeno-oestrogens, in order to determine whether they pose a health risk to humans and animals. It is also important to be able to apply the assays to environmental samples for monitoring purposes. In South Africa information on the levels of EDCs in water is limited. While establishing the recombinant yeast screen bioassay (RCBA) using the yeast strain Sacchyromyces cerivisiae for oestrogenic activity, problems were experienced with contamination. Four South African laboratory water sources were assessed. From the results it was clear that the water used in the preparation of the medium for the assay was the source of oestrogenic contamination. Care should be taken to eliminate all possible sources of contamination in the test procedures to eliminate the reporting of false positive results. The fact that South African laboratory and surface waters tested positive for estrogenic activity has far reaching implications regarding reproductive and general health. Water SA Vol. 31 (2) 2005: pp.253-256

Evaluation of the Biotic Ligand Model relative to other site-specific criteria derivation methods for copper in surface waters with elevated hardness

The goal of this study was to evaluate the reliability of the Biotic Ligand Model to predict Cu toxicity in very hard surface water (>200 mg/L as CaCO 3), relative to current copper criteria methodologies (hardness-based equation and the water-effect ratio; WER). To test these methods, we conducted acute Cu toxicity tests with three aquatic test species ( Ceriodaphnia dubia, Daphnia pulex and Pimephales promelas) in seven surface waters. The sites were representative of effluent-dependent or effluent-dominated streams common to the arid western United States of America (arid West) and a wide range of water quality variables were tested. In addition, concurrent Cu toxicity tests were conducted in laboratory waters that were matched to hardness and alkalinity of the sites to facilitate calculation of WER values. Results were used to characterize empirical relationships between water quality characteristics and Cu toxicity, and to compare measured Cu toxicity with Biotic Ligand Model (BLM) predictions. Acute toxicity tests were also conducted with C. dubia and P. promelas in a range of Ca or Mg-dominated hardness concentrations to determine the independent effects of Ca or Mg on Cu toxicity at high hardness levels. Conclusions from this study suggest that the BLM generates appropriate criteria for the waters tested in this study when compared to the hardness-based equation or WER approach. Although the historical site-specific methods are useful for surface waters with hardness ≤250 mg/L as CaCO 3, the unique conditions of arid West streams require site-specific methods that account for the influences of critical water quality variables (i.e., pH, dissolved organic carbon, alkalinity, Ca, Mg and Na). Therefore, the BLM offers an improved alternative to the hardness-based and WER approaches, particularly for situations where the current methods would be under-protective of sensitive aquatic life.

Photodegradation of Metolachlor Applying UV and UV/H2O2

Metolachlor is one of the most widely used herbicides in the world for controlling weeds. It has been detected in both ground and surface waters in the United States, and there are rising concerns in regard to its health risks and in developing effective treatment processes for its removal from water. Degradation of metolachlor via ultraviolet (UV) photolysis and an UV/hydrogen peroxide advanced oxidation process (AOP) was studied. The quantum yield of metolachlor at 254 nm was found to be 0.302 +/- 0.001 mol E-1 through direct UV photolysis in the range of pH 6-8. The second-order rate constant of the reaction between metolachlor and hydroxyl radical was determined to be 9.07 (+/-0.21) x 10(9) M-1 s-1 by using a competition kinetics model that utilized nitrobenzene as a reference compound. In addition, these parameters were successfully applied in modeling the kinetics of elimination of metolachlor using an UV/H2O2 process in both laboratory and natural waters. The formation of several photolysis byproducts was identified using gas chromatography/mass spectrometry, and a scheme for the metolachlor photodegradation pathway is proposed.