Investigating potential toxic effects of pollutants on population growth rates and probability of extinction for a representative squamate.

Chemical contamination has been suggested as an important contributing factor to reptile population declines, but direct links are rarely reported. Population modeling provides a quantitative method to understand the long-term effects of contaminants on population persistence. We created a matrix model for Sceloporus lizards and investigated hypothetical toxic effects by reducing survival and reproductive parameters by 0 to 100% in 10% increments. We report effects on population growth rate (λ) and elasticity values for each stage due to these reductions. We then incorporated stochasticity to the model to simulate the variation seen in demographic data and quantified extinction risk. The deterministic model yielded a λ of 1.07 suggesting stability in some wild Sceloporus populations. A yearly reduction of 20 to 30% in demographic parameters was needed to push λ to decline in both our deterministic and stochastic simulations. Surprisingly, our baseline stochastic simulations had a 30% extinction probability despite a stable deterministic model. We tested three adjustments to the stochastic model, (1) increased survival/fecundity parameters, (2) higher starting densities, and (3) a density-dependent juvenile survival function. The model with density-dependent juvenile growth had the lowest extinction risk. Ultimately, 20 or 30% mortality every year is likely unrealistic, but our results provide insight in linking toxicity to population effects. Ultimately, very little reduction in demographics is needed to cause declines in these populations. Our generalized models provide important tools for screening-level risk assessment of chemical contamination, especially for taxonomic groups that tend to receive less research interest.

Steady-State Land Cover but Non-Steady-State Major Ion Chemistry in Urban Streams.

Sources of many major ions in urban streams remain ambiguous, particularly for ions unrelated to deicing salt use, and temporal patterns in concentrations are unstudied. We used 16 years of water chemistry data based on weekly samples from the Baltimore, MD, USA, metropolitan area and the Weighted Regressions on Time, Discharge, and Season approach to investigate connections between major ions, land cover, and time. All watersheds were underlain by silicate bedrock, contained no regulated point sources, and had stable land cover. Major ion concentrations were higher with greater urban land cover. Notably, concentrations of most ions increased with time in (sub)urban streams and had higher annual variability than in watersheds without impervious surface cover. Nonpoint source contributions from deicing salt and concrete were the predominant influences on major ion concentrations and produced stream chemistry that was distinctly different from forested streams. The novel finding that concentrations of most major ions were not only elevated but increasing in urban streams even with no substantial changes in land cover during the study period has important implications for ecosystem health and water quality, particularly given recent work demonstrating the high correlation between elevated ion concentrations and changes in freshwater biotic communities.

Cadmium Compartmentalization in the Pulmonate Snail Lymnaea stagnalis: Improving Our Understanding of Exposure.

In ecotoxicology, analytical compartmentalization analysis can be used to better understand metal sequestration and detoxification. Metals are typically found in two main compartments, biologically detoxified metal (BDM) and metal sensitive fractions (MSF). The purpose of this study was to analyze the subcellular distribution of cadmium (Cd) in Lymnaea stagnalis. Adult snails were exposed to three concentrations of Cd for 56 days as part of a global ring test for L. stagnalis. At the end of the 56-day exposure, organisms were separated in two sections (viscera and foot). Each section was subsequently divided by differential centrifugation into five total fractions including (metal rich granules, debris, Organelles, heat denatured proteins, and heat stable proteins) followed by Cd analysis. The concentration in each compartment, BDM, MSF, and bioconcentration factors were estimated as well. There was significantly higher bioconcentration of Cd in the viscera section compared with the foot. Cadmium accumulation in all five fractions also increased with increasing exposure concentrations. Cadmium accumulated the most in the heat denatured protein fraction (enzymes) and accumulated the least in the heat stable protein fraction (metallothionein-like proteins). The MSF compartment (~65%) was in higher proportion than the BDM (~30%), but only in the lowest Cd exposure concentration was there a significant difference between these compartments. The results indicated that, in general, there was more Cd accumulated in the metal sensitive fractions, and that the detoxification mechanisms were not efficient enough to avoid toxicity at the two highest concentrations. This study provides evidence that improves our understanding of Cd tissue distribution in freshwater gastropods.

The pros and cons of ecological risk assessment based on data from different levels of biological organization.

Ecological risk assessment (ERA) is the process used to evaluate the safety of manufactured chemicals to the environment. Here we review the pros and cons of ERA across levels of biological organization, including suborganismal (e.g., biomarkers), individual, population, community, ecosystem and landscapes levels. Our review revealed that level of biological organization is often related negatively with ease at assessing cause-effect relationships, ease of high-throughput screening of large numbers of chemicals (it is especially easier for suborganismal endpoints), and uncertainty of the ERA because low levels of biological organization tend to have a large distance between their measurement (what is quantified) and assessment endpoints (what is to be protected). In contrast, level of biological organization is often related positively with sensitivity to important negative and positive feedbacks and context dependencies within biological systems, and ease at capturing recovery from adverse contaminant effects. Some endpoints did not show obvious trends across levels of biological organization, such as the use of vertebrate animals in chemical testing and ease at screening large numbers of species, and other factors lacked sufficient data across levels of biological organization, such as repeatability, variability, cost per study and cost per species of effects assessment, the latter of which might be a more defensible way to compare costs of ERAs than cost per study. To compensate for weaknesses of ERA at any particular level of biological organization, we also review mathematical modeling approaches commonly used to extrapolate effects across levels of organization. Finally, we provide recommendations for next generation ERA, submitting that if there is an ideal level of biological organization to conduct ERA, it will only emerge if ERA is approached simultaneously from the bottom of biological organization up as well as from the top down, all while employing mathematical modeling approaches where possible to enhance ERA. Because top-down ERA is unconventional, we also offer some suggestions for how it might be implemented efficaciously. We hope this review helps researchers in the field of ERA fill key information gaps and helps risk assessors identify the best levels of biological organization to conduct ERAs with differing goals.

Integrating copper toxicity and climate change to understand extinction risk to two species of pond-breeding anurans.

Chemical contamination is often suggested as an important contributing factor to amphibian population declines, but direct links are rarely reported. Population modeling provides a quantitative method to integrate toxicity data with demographic data to understand the long-term effects of contaminants on population persistence. In this study we use laboratory-derived embryo and larval toxicity data for two anuran species to investigate the potential for toxicity to contribute to population declines. We use the southern toad (Anaxyrus terrestris) and the southern leopard frog (Lithobates sphenocephalus) as model species to investigate copper (Cu) toxicity. We use matrix models to project populations through time and quantify extinction risk (the probability of quasi-extinction in 35 yr). Life-history parameters for toads and frogs were obtained from previously published literature or unpublished data from a long-term (>35 yr) data set. In addition to Cu toxicity, we investigate the role of climate change on amphibian populations by including the probability of early pond drying that results in catastrophic reproductive failure (CRF, i.e., complete mortality of all larval individuals). Our models indicate that CRF is an important parameter for both species as both were unable to persist when CRF probability was >50% for toads or 40% for frogs. Copper toxicity alone did not result in significant effects on extinction risk unless toxicity was very high (>50% reduction in survival parameters). For toads, Cu toxicity and high probability of CRF both resulted in high extinction risk but no synergistic (or greater than additive) effects between the two stressors occurred. For leopard frogs, in the absence of CRF survival was high even under Cu toxicity, but with CRF Cu toxicity increased extinction risk. Our analyses highlight the importance of considering multiple stressors as well as species differences in response to those stressors. Our models were consistently most sensitive to juvenile and adult survival, further suggesting the importance of terrestrial stages to population persistence. Future models will incorporate multiple wetlands with different combinations of stressors to understand if our results for a single wetland result in a population sink within the landscape.

A cost or a benefit? Counterintuitive effects of diet quality and cadmium in Lymnaea stagnalis.

Diet quality can have a strong impact on organismal fitness although diet quality is infrequently considered as a factor in toxicity tests. The purpose of this study was to assess how diets differing in nutritional content affect sensitivity to Cd as measured by several sublethal responses related directly to bioenergetics. We evaluated feeding rate, growth rate, behavior and macronutrient content in the pond snail Lymnaea stagnalis exposed to Cd and fed two different diets. Hatchlings were fed either lettuce or high-caloric pellets, and exposed to 5, 10, and 20 µg/L Cd for 12 days. Length and weight were measured at the beginning and end of the test. The amount of food eaten and behavior were determined every two days. Total lipids, proteins and carbohydrates were biochemically measured at test end. For the second part of the study, snails were fed either lettuce or pellets for 2 weeks and then exposed to high challenge concentrations of Cd. Growth coefficients based on length and weight were significantly higher for snails fed pellets. In addition, snails exposed to Cd had significantly smaller growth coefficients than those in the control for both diets. Total carbohydrates and lipids were higher for snails fed pellets while the protein content was not significantly affected by Cd or diets. Even though snails fed pellets grew significantly faster, contrary to expectations they were significantly more sensitive to Cd compared to those fed lettuce. This study provides evidence that a bioenergetics-based approach can been used to better understand how diet can affect the ecotoxicity of chemical stressors to freshwater gastropods.

Chronic effects of 17α-ethinylestradiol, fluoxetine, and the mixture on individual and population-level end points in Daphnia magna.

Many pharmaceuticals and personal care products (PPCPs) enter the environment continuously. Because these chemicals are not intended for environmental applications, testing for environmental effects is not mandatory, and thus relatively little is known about their ecological effects, particularly on invertebrate species. To better understand the effects of PPCPs on freshwater invertebrates, we exposed the water flea Daphnia magna to environmentally relevant concentrations of the pharmaceuticals 17α-ethinylestradiol (EE2) and fluoxetine both individually and as a mixture for 40 days. Exposure to EE2 decreased the number of neonates produced per female at 0.1 and 1.0 µg/L EE2, whereas fluoxetine increased mortality and neonate production at 100 µg/L. Exposure to the mixture of EE2 + fluoxetine increased time to first reproduction in medium and high mixture treatments and decreased time to death and neonate production in the high mixture treatment. When these individual parameters were integrated into a demographic model, population growth rate decreased when D. magna were exposed to 0.1 and 1.0 µg/L EE2, 100 µg/L fluoxetine, and low and high mixture treatments. When we compared the results of our extended 40 day exposures with data from only the first 21 days, the standard duration of chronic toxicity tests with D. magna, the effects of pharmaceutical exposure were generally significant at lower chemical concentrations during the 21-day period compared with the 40-day exposures, which points to the importance of exposure duration in drawing inferences from toxicity studies.

Complex interactions between climate change and toxicants: evidence that temperature variability increases sensitivity to cadmium.

The Intergovernmental Panel on Climate Change projects that global climate change will have significant impacts on environmental conditions including potential effects on sensitivity of organisms to environmental contaminants. The objective of this study was to test the climate-induced toxicant sensitivity (CITS) hypothesis in which acclimation to altered climate parameters increases toxicant sensitivity. Adult Physa pomilia snails were acclimated to a near optimal 22 °C or a high-normal 28 °C for 28 days. After 28 days, snails from each temperature group were challenged with either low (150 µg/L) or high (300 µg/L) cadmium at each temperature (28 or 22 °C). In contrast to the CITS hypothesis, we found that acclimation temperature did not have a strong influence on cadmium sensitivity except at the high cadmium test concentration where snails acclimated to 28 °C were more cadmium tolerant. However, snails that experienced a switch in temperature for the cadmium challenge, regardless of the switch direction, were the most sensitive to cadmium. Within the snails that were switched between temperatures, snails acclimated at 28 °C and then exposed to high cadmium at 22 °C exhibited significantly greater mortality than those snails acclimated to 22 °C and then exposed to cadmium at 28 °C. Our results point to the importance of temperature variability in increasing toxicant sensitivity but also suggest a potentially complex cost of temperature acclimation. Broadly, the type of temporal stressor exposures we simulated may reduce overall plasticity in responses to stress ultimately rendering populations more vulnerable to adverse effects.

Evaluation of the Chronic Reproductive Toxicity of a Fluorine-Free Firefighting Foam and a Short-Chain Fluorinated Foam to Northern Bobwhite Quail (Colinus virginianus).

The development of fluorine-free firefighting foams has been proposed as a way to reduce the adverse environmental consequences of foams containing per- and poly-fluoroalkyl substances. While there are likely fewer environmental and ecological concerns with these new fluorine-free foams in terms of persistence and bioaccumulation, it is prudent to evaluate the ecotoxicity of these fluorine-free foam products given the absence of data. Oral chronic drinking water exposure studies on adult pairs of northern bobwhite quail (Colinus virginianus) were conducted with a short-chain fluorinated and a fluorine-free foam: Buckeye Platinum Plus C6 and National Foam Avio Green KHC, respectively, at three exposure concentrations (0.01%, 0.1%, and 0.25%). Adults were monitored for survival, growth, and reproductive output; and chicks were monitored for survival and growth. Growth parameters in adult quail were not affected by exposure to the Buckeye or Avio foam. However, liver lipid content was higher in adult males exposed to the Buckeye foam or the Avio foam at the highest exposure concentrations. Chicks were heavier and had higher growth rates after adult exposure to Avio at the highest exposure level (0.25%) and to Buckeye at the two lowest exposure levels but not at the highest exposure level. The two adverse reproductive effects observed from avian exposure to Buckeye were an increased percentage of cracked eggs and earlier arrested embryonic development. Similarly, chronic exposure to Avio also induced earlier arrested embryonic development. These results show that the fluorine-free foams tested did cause toxicity to bobwhite quail, but whether they pose a risk at contaminated sites requires further laboratory and field study and additional exposure data. Environ Toxicol Chem 2024;43:211-221. © 2023 SETAC.

Wildlife ecological risk assessment in the 21st century: Promising technologies to assess toxicological effects.

Despite advances in toxicity testing and the development of new approach methodologies (NAMs) for hazard assessment, the ecological risk assessment (ERA) framework for terrestrial wildlife (i.e., air-breathing amphibians, reptiles, birds, and mammals) has remained unchanged for decades. While survival, growth, and reproductive endpoints derived from whole-animal toxicity tests are central to hazard assessment, nonstandard measures of biological effects at multiple levels of biological organization (e.g., molecular, cellular, tissue, organ, organism, population, community, ecosystem) have the potential to enhance the relevance of prospective and retrospective wildlife ERAs. Other factors (e.g., indirect effects of contaminants on food supplies and infectious disease processes) are influenced by toxicants at individual, population, and community levels, and need to be factored into chemically based risk assessments to enhance the "eco" component of ERAs. Regulatory and logistical challenges often relegate such nonstandard endpoints and indirect effects to postregistration evaluations of pesticides and industrial chemicals and contaminated site evaluations. While NAMs are being developed, to date, their applications in ERAs focused on wildlife have been limited. No single magic tool or model will address all uncertainties in hazard assessment. Modernizing wildlife ERAs will likely entail combinations of laboratory- and field-derived data at multiple levels of biological organization, knowledge collection solutions (e.g., systematic review, adverse outcome pathway frameworks), and inferential methods that facilitate integrations and risk estimations focused on species, populations, interspecific extrapolations, and ecosystem services modeling, with less dependence on whole-animal data and simple hazard ratios. Integr Environ Assess Manag 2024;20:725-748. © 2023 His Majesty the King in Right of Canada and The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC). Reproduced with the permission of the Minister of Environment and Climate Change Canada. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Toxicological effects assessment for wildlife in the 21st century: Review of current methods and recommendations for a path forward.

Model species (e.g., granivorous gamebirds, waterfowl, passerines, domesticated rodents) have been used for decades in guideline laboratory tests to generate survival, growth, and reproductive data for prospective ecological risk assessments (ERAs) for birds and mammals, while officially adopted risk assessment schemes for amphibians and reptiles do not exist. There are recognized shortcomings of current in vivo methods as well as uncertainty around the extent to which species with different life histories (e.g., terrestrial amphibians, reptiles, bats) than these commonly used models are protected by existing ERA frameworks. Approaches other than validating additional animal models for testing are being developed, but the incorporation of such new approach methodologies (NAMs) into risk assessment frameworks will require robust validations against in vivo responses. This takes time, and the ability to extrapolate findings from nonanimal studies to organism- and population-level effects in terrestrial wildlife remains weak. Failure to adequately anticipate and predict hazards could have economic and potentially even legal consequences for regulators and product registrants. In order to be able to use fewer animals or replace them altogether in the long term, vertebrate use and whole organism data will be needed to provide data for NAM validation in the short term. Therefore, it is worth investing resources for potential updates to existing standard test guidelines used in the laboratory as well as addressing the need for clear guidance on the conduct of field studies. Herein, we review the potential for improving standard in vivo test methods and for advancing the use of field studies in wildlife risk assessment, as these tools will be needed in the foreseeable future. Integr Environ Assess Manag 2024;20:699-724. © 2023 His Majesty the King in Right of Canada and The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC). Reproduced with the permission of the Minister of Environment and Climate Change Canada. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Size matters: insights from an allometric approach to evaluate control methods for invasive Australian Rhinella marina.

Invasive species are costly and difficult to control. In order to gain a mechanistic understanding of potential control measures, individual-based models uniquely parameterized to reflect the salient life-history characteristics of invasive species are useful. Using invasive Australian Rhinella marina as a case study, we constructed a cohort- and individual-based population simulation that incorporates growth and body size of terrestrial stages. We used this allometric approach to examine the efficacy of nontraditional control methods (i.e., tadpole alarm chemicals and native meat ants) that may have indirect effects on population dynamics mediated by effects on body size. We compared population estimates resulting from these control methods with traditional hand removal. We also conducted a sensitivity analysis to investigate the effect that model parameters, specifically those associated with growth and body size, had on adult population estimates. Incremental increases in hand removal of adults and juveniles caused nonlinear decreases in adult population estimates, suggesting less return with increased investment in hand-removal efforts. Applying tadpole alarm chemicals or meat ants decreased adult population estimates on the same level as removing 15-25% of adults and juveniles by hand. The combined application of tadpole alarm chemicals and meat ants resulted in approximately 80% decrease in adult abundance, the largest of any applied control method. In further support of the nontraditional control methods, which greatly affected the metamorph stage, our model was most sensitive to changes in metamorph survival, juvenile survival, metamorph growth rate, and adult survival. Our results highlight the use and insights that can be gained from individual-based models that incorporate growth and body size and the potential success that nontraditional control methods could have in controlling established, invasive Rhinella marina populations.

Plasticity in offspring contaminant tolerance traits: developmental cadmium exposure trumps parental effects.

Parental effects are non-genotypic influences on offspring phenotype that occur via parental phenotypes or environments, while developmental plasticity is phenotypic variation that arises during development in response to environmental cues. We evaluated the relative contribution of these two sources of phenotypic variation on offspring toxicant tolerance in Physa pomilia snails exposed to cadmium. We exposed adult snails to 0, 2, or 20 µg/L cadmium for 7 days, then exposed egg masses collected from these adults to 0 or 2 µg/L cadmium in a factorial design (adult cadmium exposure × egg mass cadmium exposure). Starting at 2 days old, we recorded time to death for hatchlings exposed to 150 µg/L cadmium for 72 h at 8 h intervals. Juveniles hatched from cadmium-exposed egg masses displayed higher cadmium tolerance than juveniles from unexposed egg masses. Among juveniles from egg masses not exposed to cadmium, offspring of parents exposed to 20 µg/L cadmium had higher cadmium tolerance than offspring of parents exposed to 0 or 2 µg/L cadmium. Our results show that both parental effects and developmental plasticity can impact offspring toxicant tolerance and point to the potential importance of both processes in understanding how offspring respond to chemical contaminants. When both parents and offspring are exposed to a toxicant, our results showed that the effects of parental exposure on offspring toxicant tolerance may be eclipsed by the effects of offspring exposure during development.

Environmentally relevant concentrations of a common insecticide increase predation risk in a freshwater gastropod.

Ecological receptors are faced with a multitude of stressors that include abiotic and biotic factors creating a challenge for assessing risk of chemical exposure. Of particular interest and importance are the effects of contaminants on inter-species interactions such as competition and predator-prey relationships. The objective of this study was to determine whether environmentally relevant concentrations of the commonly used insecticide, malathion, would alter predator avoidance behavior in a freshwater gastropod that could translate to increased predation risk. We exposed adult Physa pomilia snails to 0, 0.25, or 1.0 mg/L malathion for 2, 24, or 48 h and evaluated predator avoidance using a behavioral assay in which snails were exposed to cues from predatory crayfish. We found a significant reduction in predator avoidance in snails exposed to both concentrations of malathion after 48 h of exposure. To evaluate whether observed effects of malathion on predator avoidance actually increased susceptibility of snails to predators, we conducted a predator challenge experiment. Snails exposed to 0.25 mg/L malathion for 48 h were significantly more susceptible to predation. That increased predation risk was evident 48 h after initial malathion exposures is a unique result because most studies have evaluated behavioral responses soon after (<12 h) initiation of pesticide exposure. The extent to which the observed interactions affect natural populations, and the mechanisms through which they are mediated are largely unexplored. However, our study is the first to show that a commonly used insecticide decreases predator avoidance and may actually increase predation susceptibility in gastropods at concentrations several orders of magnitude below acute toxicity levels.

Transgenerational cross-tolerance to stress: parental exposure to predators increases offspring contaminant tolerance.

Transgenerational effects of stressors can have important implications for offspring fitness and the responses of offspring to future stressful conditions. Parental effects, a common type of transgenerational effect, are non-genetic influences on offspring phenotype that result from parental phenotypes or environments. Little is known, however, about how parental exposure to a stressor effects offspring responses to other stressors despite this type of multi-stressor scenario being common. To better understand the role that parental effects have on offspring contaminant tolerance, we raised freshwater snails, Biomphalaria glabrata, in the presence or absence of predator threat (crayfish + crushed snail) for 12 weeks. Predators are common stressors in aquatic systems and can co-occur with chemical contaminants. We then collected egg masses from parental snails and exposed their offspring to cadmium and malathion survival challenges. Snails raised in the presence of predator threat displayed indicators of stress, including increased time to first reproduction, lower production of egg masses per snail per day and fewer eggs per egg mass, and had smaller shell lengths at 6.5 weeks old compared to snails not exposed to predator threat. Parental exposure to predator threat increased the cadmium tolerance of offspring but did not affect malathion tolerance. These results may have important implications for understanding effects of multiple stressors and indicate that the parental environment can influence responses to contaminants in offspring. To our knowledge, this is the first study to demonstrate that a biotic stressor in the parental environment can significantly affect the contaminant tolerance of their offspring.

Organochlorine pesticides in squamate reptiles from southern Arizona, USA.

Despite recognition of the lack of reptile ecotoxicology data, the taxon remains poorly studied. Contaminant body burdens are useful in demonstrating exposures to contaminants do occur and may provide insight regarding risks. The purpose of this study was to determine organochlorine pesticide burdens in various tissues of terrestrial reptiles opportunistically collected in Arizona. Heptachlor, DDE, and endrin were the most common analytes detected in fat samples. Liver samples contained methoxychlor and heptachlor at greater frequency than other organochlorines. Investigations into chronic low-level exposures are rare for reptiles and research is needed to determine critical body residues associated with adverse impacts.

Ecotoxicity and Accumulation of Perfluorononanoic Acid in the Fathead Minnow (Pimephales promelas) and an Approach to Developing Protective Thresholds in the Aquatic Environment Through Species Sensitivity Distribution.

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous in the environment. Locations where PFAS-containing aqueous film-forming foam (AFFF) has been used or accidentally released have resulted in persistently high concentrations of PFAS, including in surface water that may be adjacent to release sites. Perfluorooctane sulfonic acid (PFOS) is most frequently measured near AFFF release sites; however, other PFAS are being quantified more frequently and, of those, perfluorononanoic acid (PFNA) is common. The goal of our study was to fill data gaps on PFNA toxicity to freshwater fish using the fathead minnow (Pimephales promelas). We aimed to understand how PFNA may impact apical endpoints following a 42-day exposure to mature fish and a 21-day exposure to second-generation larval fish. Exposure concentrations were 0, 124, 250, 500, and 1000 µg/L for both adult (F0) and larval (F1) generations. The most sensitive endpoint measured was development in the F1 generation at concentrations of ≥250 µg/L. The 10% and 20% effective concentration of the tested population for the F1 biomass endpoint was 100.3 and 129.5 µg/L, respectively. These data were collated with toxicity values from the primary literature on aquatic organisms exposed to PFNA for subchronic or chronic durations. A species sensitivity distribution was developed to estimate a screening-level threshold for PFNA. The resulting hazard concentration protective of 95% of the freshwater aquatic species was 55 µg PFNA/L. Although this value is likely protective of aquatic organisms exposed to PFNA, it is prudent to consider that organisms experience multiple stressors (including many PFAS) simultaneously; an approach to understand screening-level thresholds for PFAS mixtures remains an uncertainty within the field of ecological risk assessment. Environ Toxicol Chem 2023;42:2229-2236. © 2023 SETAC.

Spatial and temporal variability of per- and polyfluoroalkyl substances (PFAS) in environmental media of a small pond: Toward an improved understanding of PFAS bioaccumulation in fish.

Per- and polyfluoroalkyl substances (PFAS) are highly fluorinated compounds with many industrial applications, for instance as ingredients in fire-suppressing aqueous film-forming foams (AFFF). Several PFAS have been demonstrated to be persistent, bioaccumulative and toxic. This study better characterizes the bioaccumulation of PFAS in freshwater fish through a spatial and temporal analysis of surface water and sediment from a stormwater pond in a former Naval air station (NAS) with historic AFFF use. We sampled environmental media from four locations twice per week for five weeks and sampled fish at the end of the sampling effort. The primary PFAS identified in surface water, sediment, and biota were perfluorooctane sulfonate (PFOS) and perfluorohexane sulfonate (PFHxS) followed by perfluorooctanoic acid (PFOA) in environmental media and perfluoroheptane sulfonate (PFHpS) in biota. We observed significant temporal variability in surface water concentrations at the pond headwaters following stochastic events such as heavy rainfall for many compounds, particularly PFHxS. Sediment concentrations varied most across sampling locations. In fish, liver tissue presented the highest concentrations for all compounds except PFHxS, which was highest in muscle tissue, suggesting the influence of fine-scale aqueous PFAS fluctuations on tissue distribution. Calculated log bioaccumulation factors (BAFs) ranged from 0.13 to 2.30 for perfluoroalkyl carboxylates (PFCA) and 0.29-4.05 for perfluoroalkane sulfonates (PFSA) and fluctuated greatly with aqueous concentrations. The variability of PFAS concentrations in environmental media necessitates more frequent sampling efforts in field-based studies to better characterize PFAS contamination in aquatic ecosystems as well as exercising caution when considering single time-point BAFs due to uncertainty of system dynamics.

Comparative Toxicity of Herbicide Active Ingredients, Safener Additives, and Commercial Formulations to the Nontarget Alga Raphidocelis Subcapitata.

Chloroacetanilide herbicides are used worldwide to control weeds that affect crops such as corn, soybeans, and cotton. These herbicides are frequently paired with a "safener," which prevents herbicidal damage to the crop without diminishing weed control. Formulated herbicide products that include safeners and other ingredients are infrequently assessed for toxicity. Our goal was to understand the potential toxicity of safeners and herbicide + safener formulations relative to the toxicity of associated active ingredients. We quantified the concentration of safeners in commercially available formulations and tested effects on nontarget algae, Raphidocelis subcapitata, when exposed to individual herbicide active ingredients, safeners, and commercial formulations. The median effective concentrations (EC50s) causing 50% reduction in population growth for the herbicide active ingredients S-metolachlor and acetochlor were 0.046 and 0.003 ppm, respectively. The safeners benoxacor, AD-67, furilazole, and dichlormid were all substantially less toxic than the herbicides and were not toxic at environmentally relevant concentrations. The commercial formulations Dual II Magnum®, Me-Too-Lachlor II®, Harness®, and Surpass EC® all resulted in EC50 values that fell within the 95% confidence interval of the associated active ingredient herbicide. Interestingly, a significant increase in cell size was observed when algae were exposed to all the formulations, herbicides (acetochlor and S-metolachlor), and safener (dichlormid). The safener furilazole caused a significant decrease in cell size, whereas benoxacor and AD-67 had no observed effect on algae cell size. Significant algae cell size effects all occurred at or above the EC50 concentrations for each chemical, suggesting that other morphological effects may be occurring. Importantly, safeners in commercial formulations appeared not to impact toxicity to R. subcapitata compared with the active ingredient alone. Environ Toxicol Chem 2022;41:1466-1476. © 2022 SETAC.

Perfluoroalkyl acids in sediment and water surrounding historical fire training areas at Barksdale Air Force Base.

Perfluoroalkyl acids (PFAAs) are environmentally persistent components of surfactants that consist of fully fluorinated carbon chains and a terminal sulfonate or carboxylate polar head moiety. Due to their unique amphiphilic properties, PFAAs are used in the manufacturing of products such as aqueous film forming foams (AFFF). There is cause for concern for PFAA contamination resulting from runoff and groundwater infiltration of AFFF that were used during fire training. This study analyzed water and sediment samples that were collected over a 13-month sampling period from bayous upstream and downstream of two former fire training areas located near Barksdale Air Force Base (BAFB); the occurrence and magnitude of PFAAs supported an aquatic ecological risk assessment of potential impacts of PFAAs at the site. Liquid chromatography coupled with mass spectrometry was used for determination of 6 PFAAs listed under the third Unregulated Contaminant Monitoring Rule (UCMR 3). Total PFAA concentrations in surface water and sediment samples ranged from 0 (ND) -7.1 ng/mL and 0 (ND) -31.4 ng/g, respectively. Perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) were the predominant PFAAs detected. In general, perfluorosulfonates were quantified more frequently and at higher concentrations than perfluorocarboxylates. The perfluoroalkyl chain length of PFAAs also showed significant influence on PFAA concentrations when analyzed by Spearman's rank correlation analysis. Some contamination we observed in surface water and sediment samples from reference locations could be a result of local runoff from the use of commercial products containing per- and poly-fluoroalkyl substances (PFAS), but AFFF appears to be the primary source given the close proximity of the historical fire training areas.