Contaminant Sensitivity Research Articles

Driving selective upcycling of mixed polyethylene waste with table salt

Advanced recycling offers a unique opportunity for the circular economy, especially for mixed and contaminated plastics that are difficult to recycle mechanically. However, advanced recycling has barriers such as poor selectivity, contaminant sensitivity, and the need for expensive catalysts. Reported herein is a simple yet scalable methodology for converting mixed polyethylene (high-density and low-density polyethylene recycled polyethylene) into upcycled waxes with up to 94% yield. This high yield was possible by performing the reaction at a mild temperature and was enabled by using inexpensive and reusable table salt. Without table salt, in otherwise identical conditions, the plastic remained essentially undegraded. These upcycled waxes were used as prototypes for applications such as water- and oil-resistant paper, as well as rheology modifiers for plastics. Their performance is similar to that of commercial wax as well as rheology modifiers. A preliminary economic analysis shows that the upcycled waxes obtained by this table salt-catalyzed approach offer three times more revenue than those reported in the literature. This pioneering discovery opens the door for a circular economy of plastics in general and polyolefins in particular.

Assessment of Ecological Risk of Heavy Metals Using Probabilistic Risk Assessment Model (AQUARISK) in Surface Sediments from Wami Estuary, Tanzania.

Total concentrations of As, Cd, Cr, Cu, Pb, and Zn in sediment samples obtained from Wami Estuary in Tanzania were used to generate contaminant probability density distributions and species sensitivity distributions using the AQUARISK model. Results of tier 1 assessment showed that As, Cd, Cr, Pb, and Zn were not of concern as their measured values and the 99th percentile of the fitted distributions were lower than the SQG low-trigger values. However, Cu was identified as of concern in this estuary. According to the Bur III distributional analysis of the exotoxicological data, the estimated percentage of species likely to be affected is 3.4, 79.4, 79.8, 99.9, 98.4, and 98.0 for As, Cd, Cr, Cu, Pb, and Zn, respectively. Lowering of the current median concentrations of metals (Cd, Cr, Cu, Pb, and Zn) is recommended as they exceeded modeled median target sediment concentration to achieve 95% or higher for species protection. With the ongoing increase in anthropogenic activities in the Wami River catchment, the environmental regulatory bodies may use the findings of the present study and augmented with AQUARISK to set discharge standards for various contaminants in order to minimize impacts to the receiving ecosystems.

Probabilistic risk assessment and risk mapping of metals in tropical estuarine sediments using the Aquarisk model.

Total sediment concentrations of Cd, Cu, Pb, Zn, As, and Hg obtained from the Ankobra, Sakumo II, and Volta estuaries in Ghana were used to generate contaminant probability density distributions and species sensitivity distributions in AQUARISK. Results of the tier 1 assessment showed Cu, Cd, Zn, and Pb were not of concern in the Ankobra as their measured values and the 99th percentile of the fitted distributions were lower than the SQG low-trigger values. Mercury (Hg) and As were however, identified to be of concern in this estuary. In the Sakumo II estuary, Cu, Cd, Pb, and Hg have been identified to be of concern because their concentrations are higher than the SQG low-trigger values. Hg has been identified as the only metal of concern in the Volta estuary. The total proportion of species likely to be affected by the combined concentration of Cd, Cu, and Zn measured from Ankobra, Sakumo II, and Volta were 14%, 16%, and 12%, respectively, according to the Bur III distributional analysis of theecotoxicology data. The measured median sediment concentrations of As and Hg in the Ankobra estuary greatly exceeded the median sediment concentration targets to achieve a 5% or less exceedence of the SQG low value. Similarly, in the Sakumo II estuary, the measured median sediment concentrations of Cu, Pb, and Hg greatly exceeded the median sediment concentration targets to achieve a 5% or less exceedence of the SQG low. For the Volta estuary however, other metals except Hg fall below the target values.

Variation in malathion sensitivity among populations of Blanchard's cricket frogs (Acris blanchardi) and implications for risk assessment.

Intraspecific variability in contaminant sensitivity could undermine risk assessments for nontarget organisms such as amphibians. To test how amphibian populations vary in tolerance to anticipated lethal and sublethal exposures to a pesticide, we exposed Blanchard's cricket frogs (Acris blanchardi) from 3 populations across a broad portion of their range to the insecticide malathion. Exposure in mesocosms to a nominal concentration of 1 mg/L (measured concentrations at 1 h and 24 h postaddition of 0.160 mg/L and 0.062 mg/L, respectively), a realistic direct-overspray scenario, reduced survival to metamorphosis by 43% relative to controls and revealed variation in tolerance among populations. Survival ranged from 74% for the most tolerant population to 18% for the least tolerant population, a 4.1-fold difference. Mass at metamorphosis and time to metamorphosis were unaffected. Although malathion reduced zooplankton abundance, it did not alter food resources (periphyton or phytoplankton relative abundance), or a suite of water-quality variables (pH, temperature, and dissolved oxygen). A 96-h time-to-death assay designed to isolate direct, lethal effects also revealed variation in tolerance among populations. Time to death (mean ± standard error) ranged from 2.4 ± 0.18 h for the least tolerant population to 17.8 ± 4.72 h for the most tolerant population, a 7.4-fold difference. However, relative sensitivities of populations differed in the mesocosm and laboratory studies, which differed in exposure concentrations, suggesting that populations tolerant of high concentrations can be more sensitive to lower concentrations. We suggest that direct overspray could reduce larval survival in the field for this species. Studies assessing the role of contaminants in declines or extrapolating to untested populations, especially across large geographical regions, should quantify the range of intraspecific variation. Risk assessors could address intraspecific variability directly by using an intraspecific uncertainty factor. Environ Toxicol Chem 2017;36:1917-1923. © 2016 SETAC.

Acute Toxicity Prediction to Threatened and Endangered Species Using Interspecies Correlation Estimation (ICE) Models.

Evaluating contaminant sensitivity of threatened and endangered (listed) species and protectiveness of chemical regulations often depends on toxicity data for commonly tested surrogate species. The U.S. EPA's Internet application Web-ICE is a suite of Interspecies Correlation Estimation (ICE) models that can extrapolate species sensitivity to listed taxa using least-squares regressions of the sensitivity of a surrogate species and a predicted taxon (species, genus, or family). Web-ICE was expanded with new models that can predict toxicity to over 250 listed species. A case study was used to assess protectiveness of genus and family model estimates derived from either geometric mean or minimum taxa toxicity values for listed species. Models developed from the most sensitive value for each chemical were generally protective of the most sensitive species within predicted taxa, including listed species, and were more protective than geometric means models. ICE model estimates were compared to HC5 values derived from Species Sensitivity Distributions for the case study chemicals to assess protectiveness of the two approaches. ICE models provide robust toxicity predictions and can generate protective toxicity estimates for assessing contaminant risk to listed species.

Can Toxicity for Different Species be Correlated?

Experimental evaluation of the toxicity of a compound is an expensive practice, and it requires sacrifice of a large number of animals. As a consequence, in silico techniques for predictive toxicology are taking the central stage of attention of the scientific community. Interspecies quantitative structure-toxicity relationship (i-QSTR) modeling provides a tool for estimation of contaminant's sensitivity with known levels of uncertainty for a diverse pool of species. It is capable of extrapolating data for one toxicity endpoint to another toxicity endpoint when the data for the second species are unavailable. The emerging i-QSTR approach can overcome the cost of multiple toxicity tests, improve the understanding of the mechanism of toxic action (MOA) of chemicals for different organisms and endpoints and is very useful in order to fill the data gaps where toxicity value for a particular compound is absent for a specific endpoint.

Extrapolating between toxicity endpoints of metal oxide nanoparticles: Predicting toxicity to Escherichia coli and human keratinocyte cell line (HaCaT) with Nano-QTTR

Synthesis of novel nanoparticles should always be accompanied by a comprehensive assessment of risk to human health and to ecosystem. Application of in silico models is encouraged by regulatory authorities to fill the data gaps related to the properties of nanoparticles affecting the environment and human health. Interspecies toxicity correlations provide a tool for estimation of contaminant's sensitivity with known levels of uncertainty for a diverse pool of species. We propose here first interspecies cytotoxicity correlation models between Escherichia coli (prokaryotic system) and human keratinocyte cell line (HaCaT) (eukaryotic system) to assess the discriminatory features for cytotoxicity of metal oxide nanoparticles. The nano-QTTR models can be employed for extrapolating cytotoxicity to E. coli and human keratinocyte cell line (HaCaT) for metal nanoparticles when the data for the other species are available. Informative illustrations of the contributing mechanisms of toxic action of the metal oxide nanoparticles to the HaCaT cell line as well as to the E. coli are identified from the developed nano quantitative toxicity–toxicity relationship (nano-QTTR) models.

Contaminant Lock Life Prediction of Double Flapper-Nozzle Servo Valve

The thesis first analyzes the failure mechanism of contaminant lock, then the contaminant sensitivity theory or the Omega theory, which is first put forward by the Oklahoma state university hydrodynamic research center, is introduced and being applied to the servo valve contaminant lock life analysis and the contaminant sensitivity test method of servo valve is presented. After that, the value of servo valve contaminant lock sensitivity as well as the contaminant lock life can be calculated. It turned out that this method can accurately evaluate servo valves resistance on pollution lock and contaminant lock life, which can offer guidance on servo valve selecting and reliability analysis.

Effect of test duration and feeding on relative sensitivity of genetically distinct clades of Hyalella azteca

The amphipod Hyalella azteca is widely used in ecotoxicology laboratories for the assessment of chemical risks to aquatic environments, and it is a cryptic species complex with a number of genetically distinct strains found in wild populations. While it would be valuable to note differences in contaminant sensitivity among different strains collected from various field sites, those findings would be influenced by acclimation of the populations to local conditions. In addition, potential differences in metabolism or lipid storage among different strains may confound assessment of sensitivity in unfed acute toxicity tests. In the present study, our aim was to assess whether there are genetic differences in contaminant sensitivity among three cryptic provisional species of H. azteca. Therefore, we used organisms cultured under the same conditions, assessed their ability to survive for extended periods without food, and conducted fed and unfed acute toxicity tests with two anions (nitrate and chloride) whose toxicities are not expected to be altered by the addition of food. We found that the three genetically distinct clades of H. azteca had substantially different responses to starvation, and the presence/absence of food during acute toxicity tests had a strong role in determining the relative sensitivity of the three clades. In fed tests, where starvation was no longer a potential stressor, significant differences in sensitivity were still observed among the three clades. In light of these differences in sensitivity, we suggest that ecotoxicology laboratories consider using a provisional species in toxicity tests that is a regionally appropriate surrogate.

Species-dependent sensitivity to contaminants: An approach using primary hepatocyte cultures with three marine fish species

There is limited knowledge about the sensitivity of different fish species to environmental pollutants. Such information is pivotal in risk assessment and to understand why some species appear to be more tolerant to contaminants than others. The aim of the current study was to evaluate whether primary hepatocyte cultures of three marine fish species could be established in the field and whether their sensitivity to selected contaminants would differ. Primary hepatocyte cultures of three marine fish species (plaice, long rough dab, Atlantic cod) were established and exposed for 24 h to copper (20–2500 mg L −1) and statins (1–200 mg L −1). Endpoints were esterase activity, metabolic activity and reduced glutathione (GSH) content, all using fluorescent probes. Flatfish hepatocytes were more susceptible to copper and statin exposure than hepatocytes from cod. This study has shown that species-dependent differences in contaminant sensitivity can be investigated using primary hepatocyte cultures.

First report on interspecies quantitative correlation of ecotoxicity of pharmaceuticals

Pharmaceuticals being extensively and progressively used in human and veterinary medicine are emerging as significant environmental contaminants. Pharmaceuticals are designed to have a specific mode of action and many of them are persistent in the body. These features among others make pharmaceuticals to be evaluated for potential effects on aquatic flora and fauna. Low levels of pharmaceuticals have been detected in many countries in sewage treatment plant effluents, surface waters, groundwater and drinking waters. In contrast, there is a general scarcity of publicly available ecotoxicological data concerning pharmaceuticals. Interspecies toxicity correlations provide a tool for estimating contaminant sensitivity with known levels of uncertainty for a diversity of wildlife species. In this context, we have developed interspecies toxicity correlation between Daphnia magna (zooplankton) and fish (species according to OECD guidelines) assessing the ecotoxicological hazard potential of diverse 77 pharmaceuticals. The developed models are validated and consensus models are presented to predict toxicity of the individual compounds for any one species when the data for the other species are available. Informative illustrations of the contributing structural fragments which are responsible for the greater toxicity of the diverse pharmaceuticals are identified by the developed models. Developed models are also used to predict fish toxicities of 59 pharmaceuticals (for which Daphnia toxicities are present) and Daphnia toxicities of 30 pharmaceuticals (for which fish toxicities are present). This study will allow a better and comprehensive risk assessment of pharmaceuticals for which toxicity data is missing for a particular endpoint.

Improved interval-fuzzy quadratic programming for management of filters in a fluid power system under uncertainty

An improved mathematic model of management of filters in a fluid power system (FPS) under uncertainty was developed in this article based on the former hybrid optimization method. The model integrated the interval-fuzzy quadratic programming model into an improved model of contaminant control for the selection of filters finenesses, the estimation of service life of pumps, and replacement strategies of filters in an FPS under uncertainty. The fuzzy quadratic optimization approach was used in the model to handle the uncertainties existing not only in the contaminant holding capacity, but also in the contamination level and contaminant sensitivity. The integrated model has been applied in a case of selecting filter fineness and planning allocation and replacement strategies under uncertainty for an FPS with bypass filtration circuit. All of the scenarios with available filter fineness have been examined. The generated decision alternatives can help decision makers to identify desired policies for contamination control under various total costs, satisfaction degrees, and system-failure risks under different contaminant ingression/generation rates.

Toxicity of ivermectin on cladocerans: Comparison of toxic effects on Daphnia and Ceriodaphnia species

Interspecies differences in contaminant sensitivity are measured to assess environmental risk based on species sensitivity distribution. The present study was intended to demonstrate the importance of studying the effects of contaminants on the life-history traits of various species. To do this, we compared the effects of ivermectin on the survival, growth, and reproduction of two cladoceran species (Daphnia magna and Ceriodaphnia dubia) and two strains of D. magna (one Japanese and one European). Ivermectin is widely used against endo- and ectoparasites in livestock and pets and is known for its high toxicity. Local aquatic ecosystems can be contaminated due to direct excretion into surface waters, but few data are available about the chronic effects of ivermectin on aquatic organisms. Adult daphnids were exposed to concentrations from 0 to 1 ng/L. Our results show a significant effect on all the life-history traits measured and reveal inter- and intraspecies differences. The no-observed-effect concentration found for growth and reproduction is 0.0003 ng/L for D. magna versus 0.001 ng/L for C. dubia, and the lowest-observed-effect concentration is 0.001 ng/L for D. magna versus 0.01 ng/L for C. dubia. C. dubia is smaller than D. magna and appeared to be less sensitive to ivermectin. The European strain of D. magna exhibited less resistance than the Japanese strain. A bias in the sex ratio was observed for all strains tested.

Partitioning Species Variability from Soil Property Effects on Phytotoxicity: ECx Normalization Using a Plant Contaminant Sensitivity Index

Soil properties mitigate hazardous effects of contaminants through soil chemical sequestration and should be considered when evaluating ecological risk from terrestrial contamination. Empirical models that quantify relationships between soil properties and toxicity to ecological receptors are necessary for site-specific adjustments to ecological risk assessments. However, differential sensitivities of test organisms in dose-response studies may limit the utility of such models. We present a novel approach to toxicity estimation that partitions the effect of differential sensitivities of test organisms from that of soil chemical/physical properties. Five soils that ranged in selected properties were spiked with five concentrations of sodium arsenate. Bioassays were conducted where above ground dry matter growth and the corresponding tissue arsenic concentrations were evaluated for three terrestrial plants (Alfalfa, Medicago sativa L.; Perennial ryegrass, Lolium perrene L.; and Japanese millet, Echinochloa crusgalli L.). Estimates were combined into a plant contaminant sensitivity index (PCSI) and used to normalize phytotoxicity parameters to the most sensitive species (i.e., alfalfa) where necessary. Simple linear regression and ANCOVA indicated a 36.5% increase in the explanatory power of the modifying effects of soil properties on phytotoxicity when differential arsenate sensitivities were accounted for by PCSI (r(2) = 0.477-0.833). Normalization of ecotoxicity parameters by PCSI is a seemingly effective approach to quantify the modifying effects of soil properties on phytotoxicity endpoints when it is of interest to consider multiple plant species (or varieties within a species) with differential sensitivities to experimental contaminants.

Comparison of methods for evaluating acute and chronic toxicity in marine sediments

Sublethal test methods are being used with increasing frequency to measure sediment toxicity, but little is known about the relative sensitivity of these tests compared to the more commonly used acute tests. The present study was conducted to compare the sensitivity of several acute and sublethal methods and to investigate their correlations with sediment chemistry and benthic community condition. Six sublethal methods (amphipod: Leptocheirus plumulosus survival, growth, and reproduction; polychaete: Neanthes arenaceodentata survival and growth; benthic copepod: Amphiascus tenuiremis life cycle; seed clam: Mercenaria mercenaria growth; oyster: Crassostrea virginica lysosome destabilization; and sediment-water interface testing with mussel embryos, Mytilus galloprovincialis) and two acute methods (amphipod survival with Eohaustorius estuarius and L. plumulosus) were used to test split sediment samples from stations in California. The test with Amphiascus proved to be the most sensitive sublethal test and the most sensitive overall, identifying 90% of the stations as toxic. The Leptocheirus 10-d test was the most sensitive of the acute tests, identifying 60% of the stations as toxic. In general, the sublethal tests were not more sensitive to sediments than the acute tests, with the sublethal tests finding an average of 35% of the stations to be toxic while the acute found 44%. Of the sublethal tests, only the Amphiascus endpoints and Neanthes growth significantly (p <or= 0.05) correlated with sediment chemical concentrations. Poor correspondence occurred between the toxicity endpoints and the indicators of benthic community condition. Differences in test characteristics such as mode of exposure, species-specific contaminant sensitivity, changes in contaminant bioavailability, and influence of noncontaminant stressors on the benthos may have been responsible for variation in response among the tests and low correspondence with benthic community condition. The influence of these factors cannot be easily predicted, underscoring the need to use multiple toxicity methods, in combination with other lines of evidence, to provide an accurate and confident assessment of sediment toxicity.

Advances and opportunities in assessing contaminant sensitivity of freshwater mussel (unionidae) early life stages

Advances and opportunities in assessing contaminant sensitivity of freshwater mussel (unionidae) early life stages

Estimation of Chemical Toxicity to Wildlife Species Using Interspecies Correlation Models

Ecological risks to wildlife are typically assessed using toxicity data for relatively few species and with limited understanding of differences in species sensitivity to contaminants. Empirical interspecies correlation models were derived from LD50 values for 49 wildlife species and 951 chemicals. The standard wildlife test species Japanese quail (Coturnix japonica) and mallard (Anas platyrhynchos) were determined to be good surrogates for many species within the database. Cross-validation of all models predicted toxicity values within 5-fold and 10-fold of the actual values with 85 and 95% certainty, respectively. Model robustness was not consistently improved by developing correlation models within modes of action (MOA); however, improved models for neurotoxicants, carbamates, and direct acting organophosphorous acetylcholenesterase inhibiting compounds indicate that toxicity estimates may improve if MOA-specific models are built with robust datasets. There was a strong relationship between taxonomic distance and cross-validation prediction success (chi2 = 297, df = 12, p < 0.0001), with uncertainty increasing with larger taxonomic distance between the surrogate and predicted species. Interspecies toxicity correlations provide a tool for estimating contaminant sensitivity with known levels of uncertainty for a diversity of wildlife species.

Assessing Contaminant Sensitivity of Early Life Stages of Freshwater Mussels

Assessing Contaminant Sensitivity of Early Life Stages of Freshwater Mussels

Measuring the Two‐Phase Capillary Pressure‐Saturation Curves of Soil Samples Saturated with Nonpolar Liquids

The simulation of multiphase fluid flow in the subsurface of soil requires that the pressure‐saturation (P‐S) relations of the porous medium be known for all fluid pairs. The objective of this study was 1) to develop a technique for routinely measuring the pressure‐saturation (PS) curves of undisturbed soil samples saturated with NAPL 2) to build a database using the measured P‐S curves and the physical, chemical properties of the soils; and 3) to establish the dependence of nonaqueous phase liquids (NAPL) retention on the other soil properties. The soils in this investigation were taken from 35 horizons of 12 soil profiles in Hungary. Undisturbed soil samples were collected from each horizon with a core sampler. The P‐S curves with NAPL were determined by using a modified pressure cell apparatus, which was designed and constructed by our laboratory. Statistical analysis was performed involving selected soil parameters and the measured NAPL retention data. By the application of the linear regression equations, the NAPL retention curves can be calculated directly from the mechanical fractions, bulk density, and humus content values of the soil in question. The comparison of estimated and measured NAPL retention data demonstrates the improvement gained by using the regression approach instead of the Leverett type scaling method. The scaling method significantly underestimates the NAPL retention. The accuracy of this new estimation method (after extending the database) can be useful for modeling NAPL fate and migration or mapping the organic contaminant sensitivity of the soils.

Assessing Contaminant Sensitivity of Endangered and Threatened Aquatic Species: Part II. Chronic Toxicity of Copper and Pentachlorophenol to Two Endangered Species and Two Surrogate Species

Early life-stage toxicity tests with copper and pentachlorophenol (PCP) were conducted with two species listed under the United States Endangered Species Act (the endangered fountain darter, Etheostoma fonticola, and the threatened spotfin chub, Cyprinella monacha) and two commonly tested species (fathead minnow, Pimephales promelas, and rainbow trout, Oncorhynchus mykiss). Results were compared using lowest-observed effect concentrations (LOECs) based on statistical hypothesis tests and by point estimates derived by linear interpolation and logistic regression. Sublethal end points, growth (mean individual dry weight) and biomass (total dry weight per replicate) were usually more sensitive than survival. The biomass end point was equally sensitive as growth and had less among-test variation. Effect concentrations based on linear interpolation were less variable than LOECs, which corresponded to effects ranging from 9% to 76% relative to controls and were consistent with thresholds based on logistic regression. Fountain darter was the most sensitive species for both chemicals tested, with effect concentrations for biomass at < or = 11 microg/L (LOEC and 25% inhibition concentration [IC25]) for copper and at 21 microg/L (IC25) for PCP, but spotfin chub was no more sensitive than the commonly tested species. Effect concentrations for fountain darter were lower than current chronic water quality criteria for both copper and PCP. Protectiveness of chronic water-quality criteria for threatened and endangered species could be improved by the use of safety factors or by conducting additional chronic toxicity tests with species and chemicals of concern.