Lowest Observed Effect Concentration Research Articles

Toxicity of sediment oiled with diluted bitumens to freshwater and estuarine amphipods

To address knowledge gaps and the lack of benchmarks on the toxicity of dilbit oiled sediments, weathered Cold Lake Blend (CLB) and Western Canadian Select (WCS) were assessed in 10-day sediment tests with the amphipods Hyalella azteca and Leptocheirus plumulosus. Lowest observed effect concentrations (LOECs) and 20% effect levels (EC20s) were determined for wet weight sediment concentrations of TPH and total PAHs normalized to 1% organic carbon. LOECs and EC20s for TPH ranged from 216 to 1165 mg/kg sediment in H. azteca, and from 64 to 75 mg/kg sediment in L. plumulosus. Dilbit LOECs and EC20s for total PAHs ranged from 2.9 to 11.8 mg/kg sediment in H. azteca, and from 0.75 to 0.87 mg/kg in L. plumulosus. Comparison of toxicity-based benchmarks derived from the current study to sediment concentrations from past spills indicate that dilbit spills in aquatic habitats may pose substantial risks to freshwater and estuarine benthic organisms.

Influence of triphenyltin on morphologic abnormalities and the thyroid hormone system in early-stage zebrafish (Danio rerio)

In the present study, we assessed the negative effects of triphenyltin (TPT) on zebrafish (Danio rerio) by exposing embryos and early-stage larvae to various concentrations of TPT from 2 h after fertilization (haf) until 30 days after hatching (dah). Whether test groups were fed or fasted during ecotoxicity studies using fish models has varied historically, and whether this experimental condition influences test results is unknown. Here, we confirmed that the lethal concentration of TPT to embryo and early-stage larvae (i.e., 3 dah or younger) showed in fed (lowest observed effect concentration (LOEC); 6.34 μg/L) and fasted (LOEC; 6.84 μg/L) groups. In addition, 84% and 100% of the larvae in the 2.95 and 6.64 μg/L exposure groups, respectively, had uninflated swim bladders; all affected larvae died within 9 dah. This finding suggests that morphologic abnormalities in early larval zebrafish are useful as endpoints for predicting the lethality of chemical substances after hatching. We then assessed the expression of several genes in the thyroid hormone pathway, which regulates swim bladder development in many fish species, including zebrafish. Larvae exposed to 6.64 μg/L TPT showed significant increases in the mRNA expression levels of thyroid hormone receptor α (trα) and trβ but not of thyroid stimulating hormone β subunit. These findings suggest that TPT disrupts the thyroid system in zebrafish.

Effects of Diclofenac on the embryonic development of freshwater crayfish

In recent years, there has been increasing concern about the ecotoxicological consequences of the drug Diclofenac on freshwater organisms. Influences on the largest freshwater invertebrates, the freshwater crayfish, are especially interesting in the context of cascading effects due to their important role as keystone species. In this study, lethality, influences on body weight, embryonic development and histological changes in embryos of marbled crayfish (Procambarus virginalis) as well as noble crayfish (Astacus astacus) were investigated in response to their exposure to different concentrations of Diclofenac. Additionally, the suitability of marbled crayfish as a model organism for endemic freshwater crayfish was established when studying the effects of Diclofenac. For both species, lethal effects started at concentrations of 10.24 mg/L Diclofenac, weight was not affected, embryonic development slowed down from concentrations of 0.16 mg/L and histological changes were visible from concentrations of 0.64 mg/L. The similarity of LOEC (Lowest Observed Effect Concentrations) between the two species showed that marbled crayfish can serve as a model for native crayfish when investigating the effects of exposure to Diclofenac.

Prescribing sea water quality criteria for arsenic, cadmium and lead through species sensitivity distribution

Water quality standards are essential for regulation of contaminants in marine environment. Seawater quality criteria (SWQC) for arsenic (As), cadmium (Cd) and lead (Pb) have not been developed for India. The aim of this study is to derive the SWQC for the metals based on Species Sensitivity Distribution (SSD). Eight species of sensitive marine organisms belonging to five phyla were assessed for their sensitivity to toxicity of As, Cd and Pb. Median effective concentrations (EC50) and Median Lethal Concentrations (LC50) were derived from the acute toxicity bio-assays. No Observed Effect Concentrations (NOEC), Lowest Observed Effect Concentrations (LOEC) and chronic values were derived from chronic toxicity bio-assays. Diatoms were more sensitive to As with 96 h EC50 of 0.1 mg/l and copepods were more sensitive to Cd and Pb with 96 h EC50 of 0.019 mg/l and 0.05 mg/l respectively. Estimated NOECs ranged from 4.87 to 21.55 µg/l of As, 1.0 to 120 µg/l of Cd and 5.67 to 91.67 µg/l of Pb. Similarly, chronic values (µg/l) were in the range of 6.71–26.1, 1.38–170, and 7.67–91.67 of As, Cd and Pb respectively. The Criterion Maximum Concentration (CMC), Criterion Continuous Concentration (CCC) and Predicted No Effect Concentration (PNEC) values were prescribed as SWQC. The CMC (µg/l) of 19, 1.7 and 17 for As, Cd, and Pb were derived respectively for acute exposure during accidental marine outfalls. The CCC (µg/l) for As was 4.6, 1.1 for Cd and 5.9 for Pb are recommended as SWQC for protection of 95% of marine organisms. PNEC (µg/l) of 3.8 for As, 0.92 for Cd and 4.3 for Pb are suggested for highly disturbed ecosystems, shell fishing and mariculture uses of water bodies. These values are recommended as a baseline for site specific water quality criteria for the coastal waters of the country.

Evaluation of Nile tilapia (Oreochromis niloticus) fingerlings exposed to the pesticide pyriproxyfen

Oreochromis niloticus (Nile tilapia) is one of the most produced fish for human consumption globally; however, these fish are susceptible to exposure to toxic chemicals in the water. Pyriproxyfen is a pesticide widely used to control mosquitoes in drinking water supplies and pests in crops. The present study aimed to examine pyriproxyfen's effects on fish O. niloticus fingerlings exposed using an acute 96 h and subchronic tests for 28 days. The lethal concentration LC50-96 h for O. niloticus was 2.77 mg L-1, no observed effect concentration (NOEC), and the lowest observed effect concentration (LOEC) was 1.0 and 2.5 mg L-1, respectively. The hepatic catalase activity was significantly changed after exposure to pyriproxyfen above 0.4 mg L-1. Pyriproxyfen also induced histopathological lesions in the hepatic tissue at 28 days in a dose-dependent pattern at concentrations above 0.4 mg L-1. Pyriproxyfen above 1.2 mg L-1 reduced the locomotor behavior, distance traveled inside the tank, mean speed, and angular variation. This pesticide also decreased weight gain, food conversion, and specific growth rate at concentrations above 1.2 mg L-1. In conclusion, exposure to pyriproxyfen in water from 0.4 mg L-1 may impair O. niloticus development; consequently, pyriproxyfen may affect this fish's production and quality at higher concentrations than commonly used in water (0.01 mg L-1).

Development and characterization of polyclonal antibodies against subtype specific vitellogenin of the dojo loach, Misgurnus anguillicaudatus

Fish vitellogenin (Vtg) has become an important biomarker for assessing the estrogenic potency of chemicals and the exposure of animals to estrogenic contaminants present in aquatic environments. In the current study, the polyclonal antibodies against subtype-specific Vtgs of the dojo loach (Misgurnus anguillicaudatus) were developed and identified by gene recombination and expression. Immuno-biochemical analyses revealed that VtgAo1 protein appeared to be the major Vtg type in this species. Enhanced chemiluminescent Western blotting was developed using the antiserum against VtgAo1. Exposure of male loach to 17α-ethinylestradiol (EE2) and 17β-estradiol (E2) via water induced the VtgAo1 protein induction with a lowest-observed-effect concentration (LOEC) by 100 ng L−1 and 1000 ng L−1group at 7 day post-initiation (dpi), respectively. The results indicated that this method provided a valuable tool for detecting estrogenic activities in aquatic environments and excluded any difficulties expected in purification procedures to separate a highly pure Vtg subtype from circulating proteins, and the other Vtg subtypes.

Fiproles as a proxy for ecological risk assessment of mixture of fipronil and its degradates in effluent-dominated surface waters

Environmental risk assessment of complex chemical mixtures has increasingly been prioritized as a management goal, especially in the regulatory sector. Although fipronil and its three degradates (-sulfone, -sulfide and -desulfinyl) have been frequently quantified in waterways, little information is available about the likelihood and magnitude of ecological risk posed by these chemical mixtures – collectively known as fiproles – in surface water. In the present study, a probabilistic risk assessment of mixtures of fipronil and its three degradates was conducted for three effluent-dominated southern California rivers: Los Angeles River (LAR), San Gabriel River (SGR) and Santa Clara River (SCR), California, USA. The assessments, which used fiproles as an integrated proxy, were based on three levels of toxicity endpoints: median lethal concentration (LC50), half-maximal effective concentration (EC50), and lowest observed effect concentration (LOEC), to gain comprehensive assessment information. Probabilistic approaches based on species sensitivity distribution (SSD) and exposure concentration distribution (ECD) were developed with the log-logistic model by pooling the toxicity and occurrence data, respectively. The 5th percentile hazardous concentrations (HC5s) were calculated to be at low parts per billion levels, enabling these values to be used to estimate the chemical-specific benchmarks for components that lack ecotoxicity data. The single substance potentially affected fraction (ssPAF) of fiproles revealed risk levels for the three rivers in descending order: LAR ≥ SGR > SCR. The overall risk probability estimated from the joint probability curve (JPC) by Monte Carlo simulation was 1.13 ± 0.20% (LC50), 9.31 ± 1.46% (EC50), and 6.58 ± 1.43% (LOEC) for the three rivers collectively. These results derived from the fiproles indicates that fipronil and its degradates pose risks to the aquatic organisms in the surface water of the three rivers. The present study provides a methodology for the use of a proxy in the risk assessment of chemical mixtures.

Chronic toxicity of waterborne thallium to Daphnia magna.

There is limited information regarding the toxicity of the trace element thallium (Tl) to aquatic biota, most of which assesses acute toxicity and bioaccumulation. The relative lack of chronic Tl toxicity data compromises the establishment of water quality criteria for this trace metal. In the presented work, chronic toxicity endpoints (final body weight (a proxy measure of growth), survival, and reproduction) and Tl body burden were measured in the freshwater crustacean Daphnia magna during a 21-day exposure to dissolved Tl. Thallium caused complete mortality in daphnids between exposure concentrations of 424 and 702μgL-1. In contrast with previously published work examining acute Tl toxicity, exposure to Tl for 21 days was not associated with changes in whole-body potassium concentration. This was despite a 710-fold increase in Tl body burden in animals exposed to 424μgL-1 relative to the control. Median effect concentrations (EC50's) for growth and reproduction (total neonates produced), were 1.6 (95% confidence interval: 1.0-3.1) and 11.1 (95% confidence interval: 5.5-21.8) μg Tl L-1, respectively. A no observable effect concentration (NOEC) of 0.9μgTl L-1 for growth, and a NOEC range of 0.9-83μgTl L-1 for a variety of reproductive metrics, was measured. A lowest observable effect concentration (LOEC) of 8.8μgTl L-1 was determined for the effects of Tl on growth and most of the reproductive endpoints examined. These data indicate that under controlled laboratory conditions D.magna is significantly less sensitive to Tl than the species on which the current Canadian Council of Ministers of the Environment regulatory guideline value of 0.8μgL-1 is based.

Lethal and Teratogenic Impacts of Imazapyr, Diquat Dibromide, and Glufosinate Ammonium Herbicide Formulations Using Frog Embryo Teratogenesis Assay-Xenopus (FETAX).

Globally, amphibians are experiencing widespread abnormalities and population declines. One potential contributor to these challenges is the use of pesticides, particularly aquatic herbicides applied to aquatic habitats inhabited by amphibians. Critical issues of concern are the potential toxicity and teratogenicity of these herbicides towards amphibians. Using the FETAX protocol, three globally used formulations, including diquat dibromide (Midstream), glufosinate ammonium (Basta), and imazapyr (Arsenal), were assessed for embryotoxicity, teratogenicity, and growth inhibition. Developing Xenopus laevis embryos were exposed for 96h atconcentrations of 0.5-3.0mg/L, 1.6-3.0mg/L, and 20-45mg/L for Midstream, Basta, and Arsenal respectively. The 96-h LC50 estimates were 0.83mg/L acid equivalent (a.e.), 36mg/L a.e., and 2.2mg/L a.e., whereas the EC50 estimates were 0.24mg/L a.e., 28.13mg/L a.e., and 2.01mg/L a.e. for the Midstream, Arsenal, and Basta formulations, respectively. These two estimates produced Teratogenic Index of 3.5, 1.3, and 1.1 for Midstream, Arsenal, and Basta, respectively, indicating a high risk of malformation induction by Midstream and moderate risk for Arsenal. Regarding growth inhibition, lowest observable effect concentrations of 0.5mg/L, 25mg/L, and 2.0mg/L were computed for Midstream, Arsenal, and Basta, respectively, producing the minimum concentration inhibiting growth (MCIG) ratios of 0.62, 0.69, and 0.89 for the three formulations. These MICG values are higher than the standard 0.30 growth inhibitors benchmark, suggesting that the formulations are not growth inhibitors at the evaluated concentrations. This study provides evidence of the embryotoxic and teratogenic status of Midstream and the embryotoxicity of Basta. There is a need to further characterise the physiological and ecological impacts of these formulations to ensure responsible use and the safety of amphibians and other wildlife.

Impact of the Application of Landfill Leachate on the Germination of Senna macranthera in Different Substrates

Landfill leachate is a potential environmental pollutant. Physicochemical analyses allow identifying its elements while the use of ecotoxicological tests aims to understand the relation with the environment. The germination assay of Senna macranthera in different substrates (filter paper, commercial-SCM, conventional-SCV and organic-SOR) was performed with different doses of leachate. The objective was to identify the potential impact of leachate by determining the concentration able to cause inhibition in 50% of the seeds (LC50) and the values of the no observable effect concentration (NOEC) and the lowest observed effect concentration (LOEC). The LC50
 and LOEC occurred in the treatments with 6.25 while NOEC was with 3.125%. The test in substrates, It was not possible to identify the LC50 in the SCM. For the SCV was with 66 and in SOR with 25%. The NOEC and LOEC for SCM and SCV were 25 and 50% and in SOR with 50 and 100%.

Applicability of hiPSC-Derived Neuronal Cocultures and Rodent Primary Cortical Cultures for In Vitro Seizure Liability Assessment.

Seizures are life-threatening adverse drug reactions which are investigated late in drug development using rodent models. Consequently, if seizures are detected, a lot of time, money and animals have been used. Thus, there is a need for in vitro screening models using human cells to circumvent interspecies translation. We assessed the suitability of cocultures of human-induced pluripotent stem cell (hiPSC)-derived neurons and astrocytes compared with rodent primary cortical cultures for in vitro seizure liability assessment using microelectrode arrays. hiPSC-derived and rodent primary cortical neuronal cocultures were exposed to 9 known (non)seizurogenic compounds (pentylenetetrazole, amoxapine, enoxacin, amoxicillin, linopirdine, pilocarpine, chlorpromazine, phenytoin, and acetaminophen) to assess effects on neuronal network activity using microelectrode array recordings. All compounds affect activity in hiPSC-derived cocultures. In rodent primary cultures all compounds, except amoxicillin changed activity. Changes in activity patterns for both cell models differ for different classes of compounds. Both models had a comparable sensitivity for exposure to amoxapine (lowest observed effect concentration [LOEC] 0.03 µM), linopirdine (LOEC 1 µM), and pilocarpine (LOEC 0.3 µM). However, hiPSC-derived cultures were about 3 times more sensitive for exposure to pentylenetetrazole (LOEC 30 µM) than rodent primary cortical cultures (LOEC 100 µM). Sensitivity of hiPSC-derived cultures for chlorpromazine, phenytoin, and enoxacin was 10-30 times higher (LOECs 0.1, 0.3, and 0.1 µM, respectively) than in rodent cultures (LOECs 10, 3, and 3 µM, respectively). Our data indicate that hiPSC-derived neuronal cocultures may outperform rodent primary cortical cultures with respect to detecting seizures, thereby paving the way towards animal-free seizure assessment.

A multibiomarker approach to assess lead toxicity on the black clam, Villorita cyprinoides (Gray, 1825), from Cochin estuarine system (CES), southwest coast, India.

The southwest coast of India along the Cochin region is seriously affected by metal contamination from increasing industrial activities. This contribution pertains to the chronic toxicity effects of lead and its biomarker responses on the black clam, Villorita cyprinoides, largely endemic to Southern India. The metal concentration (lead (Pb), copper (Cu), zinc (Zn), cadmium (Cd), nickel (Ni), and chromium (Cr)) and contamination indices such as geoaccumulation index and contamination factor suggests that the Cochin estuarine system (CES) is moderately to heavily polluted with metals. The 96h effective median lethal concentration (LC50) for Pb was 12.08mgL-1 at 95% confidence level, whereas the NOEC (no observed effect concentration) and LOEC (lowest observed effect concentration) were 0.46mgL-1 and 0.83mgL-1 respectively. The chronic toxicity value for Pb was 0.64mgL-1. Accumulation of Pb in V. cyprinoides after chronic toxicity test was several-fold higher than exposure concentration. On exposure to sublethal concentrations of lead, gills showed prominent pathological lesions such as damaged lateral cilia, congested hemolymph sinus, damaged abfrontal cilia, damaged ciliary filaments, fusion of gill lamellae, and reduced inter lamellar space. Filtration rate of clams exposed to Pb (86.69 ± 1.98ml clam-1h-1) was lower than that in control experiments (191.86 ± 6.48ml clam-1h-1). Antioxidant enzymes such as esterase (EST), superoxide dismutase (SOD), and malate dehydrogenase (MDH) exhibited different patterns in isoenzyme activity. Neutral red retention time (NRRT) showed a decrease from control to higher concentrations indicating membrane stability of hemocytic lysosomes decreased with the increasing metal exposure concentration. At LOEC and higher concentrations lysosomes showed enlargement and fragmentation. Lysosomal responses in V. cyprinoides can be used as a key cellular stress biomarker in assessing lead and other metal contamination.

Estrogenicity of agricultural runoff: A rainfall simulation study of worst-case scenarios using fresh layer and roaster litter, and farrowing swine manure

Scientists have correlated land application of animal wastes as fertilizer with the feminization of fish. Two questions were asked. 1) Under a worst case scenario when animal waste (layer and roaster litter, or farrowing swine slurry) is applied and tilled in 24 h prior to a surface-runoff producing rainfall, will estrogenic equivalents exceed the Lowest Observable Effect Concentration (LOEC) for fish (10 ng/L)? 2) Can calcium concentrations in runoff, measured using a rapid meter-based method, be used as a sentinel of elevated estrogenic activity? In a 3-yr study wastes were surface-applied and incorporated and 24 h later, 1.5 by 3 m plots were subjected to simulated rainfall and again 1 wk. and 3 wk. later. Nutrients in runoff were also measured, and in year 1 total coliforms and E. coli. were assessed. Except for an initial preliminary test run, runoff from all plots and years never exceeded 10 ng/L E2Eq equivalent. Calcium concentrations in runoff were not related to estrogenicity, negating its use as a sentinel marker. Specific estrogens in animal waste and runoff were identified by mass spectrometry with concentrations in runoff dependant on manure source and timing of rainfall. As expected, total coliform and E. coli concentrations in runoff were increased by the application of layer litter. Concentrations of nutrients in runoff would not be expected to result in surface water concentrations higher than guidelines for protection of aquatic species. Animal wastes applied in quantities appropriate for crop nutrient requirements, tilled into the soil surface, in observance of regulations avoiding application within 24 h of a predicted rain event, should not result in estrogen levels of environmental concern.

Ammonia toxicity to endemic fish (Rasbora maninjau) of Lake Maninjau as a reference for water quality guidelines

Unionized ammonia (NH3) is highly toxic to freshwater organisms. Yet, most of the available toxicity data on NH3 were predominantly generated from temperate regions, while toxicity data on NH3 derived from tropical species were limited. Bada (Rasbora maninjau) as an endemic fish in Lake Maninjau-West Sumatra, has an important economic value for local communities. They live in clearwater with sand to gravel lake/river beds. The catch of R. maninjau is decreasing along with the decline of the water quality. Nowadays, the water quality of Lake Maninjau is declining as the effect of organic wastes from domestic sources and floating cage aquaculture. Therefore, the information about toxicity of ammonia in fish is important as a management tool for fish conservation. This research was aimed to find the LC50 value of ammonia in R. maninjau. A static acute toxicity test was conducted for 96 hours. Mortality was recorded for calculating LC50-96h, No Observed Effect Concentration (NOEC) and Lowest Observed Effect Concentration (LOEC). Values of LC50-96h, NOEC and LOEC were 29.92 mg/L TAN or 0.7 mg/L NH3, 27 mg/L TAN or 0.63 mg/L NH3, and 38 mg/L TAN or 0.89 mg/L NH3, respectively. Maximum Acceptable Toxicant Concentration (MATC) of ammonia to Bada was 32 mg/l TAN or 0.59 mg/l NH3. The acute toxicity result showed that ammonia concentration affects the mortality of R manijau for 96 hours. The information about ammonia toxicity data will be used as a water quality guideline in Lake Maninjau.

Strategies of cellular energy allocation to cope with paraquat-induced oxidative stress: Chironomids vs Planarians and the importance of using different species

Paraquat (PQ) is still used in several countries worldwide as an herbicide for weed control in agricultural production, ponds, reservoirs and irrigation canals. Thus, PQ is frequently found in surface water systems and is potentially toxic to aquatic organisms, since it can cause mitochondrial dysfunction altering in the redox state of cells. This study aimed to investigate the chronic effects of PQ to Chironomus riparius and Girardia tigrina, and compare their physiological strategies to cope with environmental stress. The mean emergence time was the most sensitive endpoint for Chironomids, with the lowest observed effect concentrations (LOEC) being 0.02 for males and 0.1 mg PQ L−1 for females. Moreover, PQ reduced the body weight of male and female imagoes, with LOECs of 0.5 and 2.5 mg PQ L−1, respectively. Paraquat also decreased the respiration rate (LOEC = 2.5 mg PQ L−1) and total glutathione (tGSH) content (LOEC = 0.5 mg PQ L−1). Thus, the aerobic production of energy was not affected and allowed chironomids to cope with oxidative stress induced by PQ, but with consequent physiological costs in terms of development rates and weight of adults. In planarians, PQ decreased the locomotion and feeding activity, and delayed photoreceptor regeneration (LOECs = 2.5 mg PQ L−1 for all endpoints). Despite increased aerobic energy production (LOEC = 0.5 mg PQ L−1), planarians were not able to cope with oxidative stress induced by the highest PQ concentrations, since lipid peroxidation levels were significantly increased (LOEC = 2.5 mg PQ L−1) concomitantly with a significant decrease of tGSH (LOEC = 2.5 mg PQ L−1). These results showed that planarians were unable to cope with oxidative stress induced by PQ with consequent impairments of behavior and regeneration despite an increased aerobic energy production.

Lethal and sublethal effects of the saline stressor sodium chloride on Chironomus xanthus and Girardia tigrina.

Salinization in freshwaters is gradually increasing as a result of human activities and climatic changes. Higher salt content causes stress for freshwater organisms. Sodium chloride (NaCl) is among the most frequently occurring salts in freshwater ecosystems. The objective of the present study was to investigate the lethal and sublethal effects of NaCl on freshwater ecosystems, using as test organism the dipteran Chironomus xanthus and the planarian Girardia tigrina. Acute tests showed that C. xanthus was more sensitive (48-h LC50 (median lethal concentration) of 2.97gNaClL-1) than G. tigrina (48-h LC50 of 7.77gNaClL-1). C. xanthus larvae growth rate (larvae length and head capsule width) was significantly reduced under exposure to concentrations as low as 0.19gL-1 NaCl and higher. A delay in the emergence time (EmT50) was also demonstrated for the same concentration. Sublethal NaCl effects in G. tigrina included feeding inhibition (LOEC (lowest observed effect concentration) of 0.4gL-1), reduced locomotion (LOEC = 0.2gL-1), and 24-48-h blastema regeneration (LOEC = 0.2gL-1 and 0.1gL-1, respectively). The results demonstrated the toxicity of NaCl to C. xanthus and G. tigrina including sublethal effects that can result in negative consequences for populations in natural freshwaters under salinization.

Survival and Reproductive Effects in the Aquatic Invertebrate Ceriodaphnia dubia Exposed to Uranium Spiked Site Water Collected from Two Creeks in the Yukon, Canada.

This study evaluates aqueous uranium (U) toxicity in Ceriodaphnia dubia exposed to surface water collected from two creeks located in U-rich areas of Yukon, Canada. Water for toxicity testing was collected at two times of the year to represent water quality characteristics generally observed during open-water (high flows) and winter baseflow water (low flows) seasons. Collected water was transferred to the toxicological laboratory and spiked with U to achieve nominal concentrations of 50, 150, 350, 500, 650, 800, and 1000µgU/L. Toxicity endpoints included lethal concentrations (LC50) for survival, in addition to no observed effect concentration (NOEC) and lowest observed effect concentration (LOEC) for reproduction. All derived toxicity endpoints were significantly higher than applicable Canadian water-quality guidelines for U (15μg/L [Chronic] and 33μg/L [Acute]). No effects on C. dubia survival were observed at LC50 concentrations > 799μgU/L. Derived NOEC (381μgU/L) and LOEC (524μgU/L) values also were significantly above chronic water quality guidelines. The differences noted in the toxicity response between seasons were mainly due to the presence of toxicity ameliorating factors for U (i.e., dissolved organic carbon). These results highlight the high conservatism in applicable water-quality guidelines and the crucial need to consider site-specific water characteristics when deriving environmentally relevant, yet protective thresholds for uranium in aquatic environments.

Tolerance of Atlantic cod (Gadus morhua L.) larvae to acute ammonia exposure

Tolerance for acute ammonia exposure, defined to exist between NOEC (no observed effect concentration) and LOEC (lowest observed effect concentration), was validated in seven exposure experiments with Atlantic cod larvae from 15 to 63 days post-hatch, corresponding to larval sizes of 0.2 to 4.9 mg dry weight, respectively. LOEC was found in the range of 0.019–0.082 mg L−1 NH3-N, with corresponding NOECs of 0.013–0.045 mg L−1 NH3-N. Cod larvae of 1.0 and 1.7 mg dry weight (33 and 42 days after hatching) were found to be most sensitive and had the highest mortality to acute ammonia exposure, indicating ontogenetic changes in ammonia tolerance. The results suggest that specific care needs to be taken in designing and monitoring rearing systems, particularly recirculation systems, for toxic ammonia levels regarding larval rearing of Atlantic cod.

Balancing chemical function with reduced environmental health hazards: A joint probability approach to examine antimicrobial product efficacy and mammalian toxicity

The fourth principle of Green Chemistry, a critically important area of sustainability science, identifies that substances should maintain intended functions while possessing limited intrinsic hazards to public health and the environment. In the present study, we empirically determined efficacy of 20 cleaning products against E. coli attachment to surfaces. Subsequently, probabilistic assessments using novel chemical efficacy distributions (CEDs) were conducted. Results for most chemicals indicated bacterial detachment with increasing concentration. Using a threshold concentration of 5th centiles, these cleaning product ingredients were predicted to detach E. coli (Lowest Observable Effect Concentration) at or below 0.7 (0.2, 2.2) mg L−1 for 5% of ingredients. We then employed chemical toxicity distributions (CTDs) to examine acute toxicity, based on currently available information, for common mammalian models. Results demonstrate that probabilities of associated hazards for rat (oral exposure route), mouse (oral exposure route), rabbit (dermal exposure route), and rat (inhalation exposure route) were 43.2%, 36.7%, 38.6% and 75.5%, respectively. A novel joint probability distribution analysis approach was then developed and applied to identify substances with various efficacy (CED) and hazard (CTD) characteristics. Our observations indicate that combining efficacy and toxicity information using joint probability curves may be useful for identifying classes of antimicrobial products, and other chemical classes, to optimize efficacy while minimizing environment and health hazards.

Perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) acutely affect human \u03b11\u03b22\u03b32L GABAA receptor and spontaneous neuronal network function in vitro

Concerns about the neurotoxic potential of polyfluoroalkyl substances (PFAS) such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) increase, although their neurotoxic mechanisms of action remain debated. Considering the importance of the GABAA receptor in neuronal function, we investigated acute effects of PFAS on this receptor and on spontaneous neuronal network activity. PFOS (Lowest Observed Effect Concentration (LOEC) 0.1 µM) and PFOA (LOEC 1 µM) inhibited the GABA-evoked current and acted as non-competitive human GABAA receptor antagonists. Network activity of rat primary cortical cultures increased following exposure to PFOS (LOEC 100 µM). However, exposure of networks of human induced pluripotent stem cell (hiPSC)-derived neurons decreased neuronal activity. The higher sensitivity of the α1β2γ2L GABAA receptor for PFAS as compared to neuronal networks suggests that PFAS have additional mechanisms of action, or that compensatory mechanisms are at play. Differences between rodent and hiPSC-derived neuronal networks highlight the importance of proper model composition. LOECs for PFAS on GABAA receptor and neuronal activity reported here are within or below the range found in blood levels of occupationally exposed humans. For PFOS, LOECs are even within the range found in human serum and plasma of the general population, suggesting a clear neurotoxic risk.