Using life-history trait variation to inform ecological risk assessments for threatened and endangered plant species

Developing population models for assessing risks to terrestrial plant species listed as threatened or endangered under the Endangered Species Act (ESA) is challenging given a paucity of data on their life histories. The purpose of this study was to develop a novel approach for identifying relatively data-rich nonlisted species that could serve as representatives for species listed under the ESA in the development of population models to inform risk assessments. We used the USDA PLANTS Database, which provides data on plants present in the US territories, to create a list of herbaceous plants. A total of 8742 species was obtained, of which 344 were listed under the ESA. Using the most up-to-date phylogeny for vascular plants in combination with a database of matrix population models for plants (COMPADRE) and cluster analyses, we investigated how listed species were distributed across the plant phylogeny, grouped listed and nonlisted species according to their life history, and identified the traits distinguishing the clusters. We performed elasticity analyses to determine the relative sensitivity of population growth rate to perturbations of species' survival, growth, and reproduction and compared these across clusters and between listed and nonlisted species. We found that listed species were distributed widely across the plant phylogeny as well as clusters, suggesting that listed species do not share a common evolution or life-history characteristics that would make them uniquely vulnerable. Lifespan and age at maturity were more important for distinguishing clusters than were reproductive traits. For clusters that were intermediate in their lifespan, listed and nonlisted species responded similarly to perturbations of their life histories. However, for clusters at either extreme of lifespan, the response to survival perturbations varied depending on conservation status. These results can be used to guide the choice of representative species for population model development in the context of ecological risk assessment. Integr Environ Assess Manag 2023;19:213-223. © 2022 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Pop-guide: Population modeling guidance, use, interpretation, and development for ecological risk assessment

The assimilation of population models into ecological risk assessment (ERA) has been hindered by their range of complexity, uncertainty, resource investment, and data availability. Likewise, ensuring that the models address risk assessment objectives has been challenging. Recent research efforts have begun to tackle these challenges by creating an integrated modeling framework and decision guide to aid the development of population models with respect to ERA objectives and data availability. In the framework, the trade-offs associated with the generality, realism, and precision of an assessment are used to guide the development of a population model commensurate with the protection goal. The decision guide provides risk assessors with a stepwise process to assist them in developing a conceptual model that is appropriate for the assessment objective and available data. We have merged the decision guide and modeling framework into a comprehensive approach, Population modeling Guidance, Use, Interpretation, and Development for Ecological risk assessment (Pop-GUIDE), for the development of population models for ERA that is applicable across regulatory statutes and assessment objectives. In Phase 1 of Pop-GUIDE, assessors are guided through the trade-offs of ERA generality, realism, and precision, which are translated into model objectives. In Phase 2, available data are assimilated and characterized as general, realistic, and/or precise. Phase 3 provides a series of dichotomous questions to guide development of a conceptual model that matches the complexity and uncertainty appropriate for the assessment that is in concordance with the available data. This phase guides model developers and users to ensure consistency and transparency of the modeling process. We introduce Pop-GUIDE as the most comprehensive guidance for population model development provided to date and demonstrate its use through case studies using fish as an example taxon and the US Federal Insecticide Fungicide and Rodenticide Act and Endangered Species Act as example regulatory statutes. Integr Environ Assess Manag 2021;17:767-784. © 2020 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Guidance for Developing Amphibian Population Models for Ecological Risk Assessment

Despite widespread acceptance of the utility of population modeling and advocacy of this approach for a more ecologically relevant perspective, it is not routinely incorporated in ecological risk assessments (ERA). A systematic framework for situation-specific model development is one of the major challenges to broadly adopting population models in ERA. As risk assessors confront the multitude of species and chemicals requiring evaluation, an adaptable stepwise guide for model parameterization would facilitate this process. Additional guidance on interpretation of model output and evaluating uncertainty would further contribute to establishing consensus on good modeling practices. We build on previous work that created a framework and decision guide for developing population models for ERA by focusing on data types, model structure, and extrinsic stressors relevant to anuran amphibians. Anurans have a unique life cycle with varying habitat requirements and high phenotypic plasticity. These species belong to the amphibian class, which is facing global population decline in large part due to anthropogenic stressors, including chemicals. We synthesize information from databases and literature relevant to amphibian risks to identify traits that influence exposure likelihood, inherent sensitivity, population vulnerability, and environmental constraints. We link these concerns with relevant population modeling methods and structure in order to evaluate pesticide effects with appropriate scale and parameterization. A standardized population modeling approach, with additional guidance for anuran ERA, offers an example method for quantifying population risks and evaluating long-term impacts of chemical stressors to populations. Integr Environ Assess Manag 2020;16:223-233. © 2019 SETAC.

Comparative Analysis of Plant Demographic Traits Across Species of Different Conservation Concern: Implications for Pesticide Risk Assessment

Pesticide risk assessment for "listed" (threatened and endangered) plant species is hampered by a lack of quantitative demographic information. Demographic information for nonlisted plant species could provide risk-assessment data and inform recovery plans for listed species; however, it is unclear how representative demography of the former would be for the latter. We performed a comparison of plant demographic traits and elasticity metrics to explore how similar these are between listed and nonlisted species. We used transition matrices from the COMPADRE Plant Matrix Database to calculate population growth rate (λ), net reproductive rate (R_o ), generation time (T_g ), damping ratio (ρ), and summed elasticities for survival (stasis), growth, fertility (reproduction), and evenness of elasticity (EE). We compared these across species varying in conservation status and population trend. Phylogenetic generalized least squares (PGLS) models were used to evaluate differences between listed and nonlisted plants. Overall, demographic traits were largely overlapping for listed and nonlisted species. Population trends had a significant impact on most demographic traits and elasticity patterns. The influence of T_g on elasticity metrics was consistent across all data groupings. In contrast, the influence of λ on elasticity metrics was highly variable, and correlated in opposite directions in growing and declining populations. Our results suggested that population models developed for nonlisted plant species may be useful for assessing the risks of pesticides to listed species. Environ Toxicol Chem 2019;38:2043-2052. © 2019 SETAC.

Adapting population models for application in pesticide risk assessment: A case study with Mead's milkweed

Population models can facilitate assessment of potential impacts of pesticides on populations or species rather than individuals and have been identified as important tools for pesticide risk assessment of nontarget species including those listed under the Endangered Species Act. Few examples of population models developed for this specific purpose are available; however, population models are commonly used in conservation science as a tool to project the viability of populations and the long-term outcomes of management actions. We present a population model for Mead's milkweed (Asclepias meadii), a species listed as threatened under the Endangered Species Act throughout its range across the Midwestern United States. We adapted a published population model based on demographic field data for application in pesticide risk assessment. Exposure and effects were modeled as reductions of sets of vital rates in the transition matrices, simulating both lethal and sublethal effects of herbicides. Two herbicides, atrazine and mesotrione, were used as case study examples to evaluate a range of assumptions about potential exposure-effects relationships. In addition, we assessed buffers (i.e., setback distances of herbicide spray applications from the simulated habitat) as hypothetical mitigation scenarios and evaluated their influence on population-level effects in the model. The model results suggest that buffers can be effective at reducing risk from herbicide drift to plant populations. These case studies demonstrate that existing population models can be adopted and integrated with exposure and effects information for use in pesticide risk assessment. Environ Toxicol Chem 2018;37:2235-2245. © 2018 SETAC.

Assessing and mitigating simulated population-level effects of 3 herbicides to a threatened plant: Application of a species-specific population model of Boltonia decurrens

Extrapolating from organism-level endpoints, as generated from standard pesticide toxicity tests, to populations is an important step in threatened and endangered species risk assessments. We apply a population model for a threatened herbaceous plant species, Boltonia decurrens, to estimate the potential population-level impacts of 3 herbicides. We combine conservative exposure scenarios with dose-response relationships for growth and survival of standard test species and apply those in the species-specific model. Exposure profiles applied in the B. decurrens model were estimated using exposure modeling approaches. Spray buffer zones were simulated by using corresponding exposure profiles, and their effectiveness at mitigating simulated effects on the plant populations was assessed with the model. From simulated exposure effects scenarios that affect plant populations, the present results suggest that B. decurrens populations may be more sensitive to exposures from herbicide spray drift affecting vegetative stages than from runoff affecting early seedling survival and growth. Spray application buffer zones were shown to be effective at reducing effects on simulated populations. Our case study demonstrates how species-specific population models can be applied in pesticide risk assessment to bring organism-level endpoints, exposure assumptions, and species characteristics together in an ecologically relevant context. Environ Toxicol Chem 2018;37:1545-1555. © 2018 SETAC.

Developing population models: A systematic approach for pesticide risk assessment using herbaceous plants as an example

Population models are used as tools in species management and conservation and are increasingly recognized as important tools in pesticide risk assessments. A wide variety of population model applications and resources on modeling techniques, evaluation and documentation can be found in the literature. In this paper, we add to these resources by introducing a systematic, transparent approach to developing population models. The decision guide that we propose is intended to help model developers systematically address data availability for their purpose and the steps that need to be taken in any model development. The resulting conceptual model includes the necessary complexity to address the model purpose on the basis of current understanding and available data. We provide specific guidance for the development of population models for herbaceous plant species in pesticide risk assessment and demonstrate the approach with an example of a conceptual model developed following the decision guide for herbicide risk assessment of Mead's milkweed (Asclepias meadii), a species listed as threatened under the US Endangered Species Act. The decision guide specific to herbaceous plants demonstrates the details, but the general approach can be adapted for other species groups and management objectives. Population models provide a tool to link population-level dynamics, species and habitat characteristics as well as information about stressors in a single approach. Developing such models in a systematic, transparent way will increase their applicability and credibility, reduce development efforts, and result in models that are readily available for use in species management and risk assessments.

Population modeling for pesticide risk assessment of threatened species-A case study of a terrestrial plant, Boltonia decurrens

Although population models are recognized as necessary tools in the ecological risk assessment of pesticides, particularly for species listed under the Endangered Species Act, their application in this context is currently limited to very few cases. The authors developed a detailed, individual-based population model for a threatened plant species, the decurrent false aster (Boltonia decurrens), for application in pesticide risk assessment. Floods and competition with other plant species are known factors that drive the species' population dynamics and were included in the model approach. The authors use the model to compare the population-level effects of 5 toxicity surrogates applied to B. decurrens under varying environmental conditions. The model results suggest that the environmental conditions under which herbicide applications occur may have a higher impact on populations than organism-level sensitivities to an herbicide within a realistic range. Indirect effects may be as important as the direct effects of herbicide applications by shifting competition strength if competing species have different sensitivities to the herbicide. The model approach provides a case study for population-level risk assessments of listed species. Population-level effects of herbicides can be assessed in a realistic and species-specific context, and uncertainties can be addressed explicitly. The authors discuss how their approach can inform the future development and application of modeling for population-level risk assessments of listed species, and ecological risk assessment in general. Environ Toxicol Chem 2017;36:480-491. © 2016 SETAC.

How to use mechanistic effect models in environmental risk assessment of pesticides: Case studies and recommendations from the SETAC workshop MODELINK

Mechanistic effect models (MEMs) are useful tools for ecological risk assessment of chemicals to complement experimentation. However, currently no recommendations exist for how to use them in risk assessments. Therefore, the Society of Environmental Toxicology and Chemistry (SETAC) MODELINK workshop aimed at providing guidance for when and how to apply MEMs in regulatory risk assessments. The workshop focused on risk assessment of plant protection products under Regulation (EC) No 1107/2009 using MEMs at the organism and population levels. Realistic applications of MEMs were demonstrated in 6 case studies covering assessments for plants, invertebrates, and vertebrates in aquatic and terrestrial habitats. From the case studies and their evaluation, 12 recommendations on the future use of MEMs were formulated, addressing the issues of how to translate specific protection goals into workable questions, how to select species and scenarios to be modeled, and where and how to fit MEMs into current and future risk assessment schemes. The most important recommendations are that protection goals should be made more quantitative; the species to be modeled must be vulnerable not only regarding toxic effects but also regarding their life history and dispersal traits; the models should be as realistic as possible for a specific risk assessment question, and the level of conservatism required for a specific risk assessment should be reached by designing appropriately conservative environmental and exposure scenarios; scenarios should include different regions of the European Union (EU) and different crops; in the long run, generic MEMs covering relevant species based on representative scenarios should be developed, which will require EU-level joint initiatives of all stakeholders involved. The main conclusion from the MODELINK workshop is that the considerable effort required for making MEMs an integral part of environmental risk assessment of pesticides is worthwhile, because it will make risk assessments not only more ecologically relevant and less uncertain but also more comprehensive, coherent, and cost effective.

A risk assessment example for soil invertebrates using spatially explicit agent-based models

Current risk assessment methods for measuring the toxicity of plant protection products (PPPs) on soil invertebrates use standardized laboratory conditions to determine acute effects on mortality and sublethal effects on reproduction. If an unacceptable risk is identified at the lower tier, population-level effects are assessed using semifield and field trials at a higher tier because modeling methods for extrapolating available lower-tier information to population effects have not yet been implemented. Field trials are expensive, time consuming, and cannot be applied to variable landscape scenarios. Mechanistic modeling of the toxicological effects of PPPs on individuals and their responses combined with simulation of population-level response shows great potential in fulfilling such a need, aiding ecologically informed extrapolation. Here, we introduce and demonstrate the potential of 2 population models for ubiquitous soil invertebrates (collembolans and earthworms) as refinement options in current risk assessment. Both are spatially explicit agent-based models (ABMs), incorporating individual and landscape variability. The models were used to provide refined risk assessments for different application scenarios of a hypothetical pesticide applied to potato crops (full-field spray onto the soil surface [termed "overall"], in-furrow, and soil-incorporated pesticide applications). In the refined risk assessment, the population models suggest that soil invertebrate populations would likely recover within 1 year after pesticide application, regardless of application method. The population modeling for both soil organisms also illustrated that a lower predicted average environmental concentration in soil (PECsoil) could potentially lead to greater effects at the population level, depending on the spatial heterogeneity of the pesticide and the behavior of the soil organisms. Population-level effects of spatial-temporal variations in exposure were elucidated in the refined risk assessment, using ABMs and population-level endpoints while yielding outputs that directly address the protection goals. We recommend choosing model outputs that are closely related to specific protection goals, using available toxicity data and accepted fate models to the extent possible in parameterizing models to minimize additional data needs and testing, evaluating, and documenting models following recent guidance.

Interactions between suspension characteristics and physicochemical properties of silver and copper oxide nanoparticles: a case study for optimizing nanoparticle stock suspensions using a central composite design

The preparation of a stable nanoparticle stock suspension is the first step in nanotoxicological studies, but how different preparation methods influence the physicochemical properties of nanoparticles in a solution, even in Milli-Q water, is often under-appreciated. In this study, a systematic approach using a central composite design (CCD) was employed to investigate the effects of sonication time and suspension concentration on the physicochemical properties (i.e. hydrodynamic diameter, zeta potential and ion dissolution) of silver (Ag) and copper oxide (CuO) nanoparticles (NPs) and to identify optimal conditions for suspension preparation in Milli-Q water; defined as giving the smallest particle sizes, highest suspension stability and lowest ion dissolution. Indeed, all the physicochemical properties of AgNPs and CuONPs varied dramatically depending on how the stock suspensions were prepared and differed profoundly between nanoparticle types, indicating the importance of suspension preparation. Moreover, the physicochemical properties of AgNPs and CuONPs, at least in simple media (Milli-Q water), behaved in predictable ways as a function of sonication time and suspension concentration, confirming the validity of our models. Overall, the approach allows systematic assessment of the influence of various factors on key properties of nanoparticle suspensions, which will facilitate optimization of the preparation of nanoparticle stock suspensions and improve the reproducibility of nanotoxicological results. We recommend that further attention be given to details of stock suspension preparation before conducting nanotoxicological studies as these can have an important influence on the behavior and subsequent toxicity of nanoparticles.

Using an Ecosystem Approach to complement protection schemes based on organism-level endpoints

Radiation protection goals for ecological resources are focussed on ecological structures and functions at population-, community-, and ecosystem-levels. The current approach to radiation safety for non-human biota relies on organism-level endpoints, and as such is not aligned with the stated overarching protection goals of international agencies. Exposure to stressors can trigger non-linear changes in ecosystem structure and function that cannot be predicted from effects on individual organisms. From the ecological sciences, we know that important interactive dynamics related to such emergent properties determine the flows of goods and services in ecological systems that human societies rely upon. A previous Task Group of the IUR (International Union of Radioecology) has presented the rationale for adding an Ecosystem Approach to the suite of tools available to manage radiation safety. In this paper, we summarize the arguments for an Ecosystem Approach and identify next steps and challenges ahead pertaining to developing and implementing a practical Ecosystem Approach to complement organism-level endpoints currently used in radiation safety.

Pairing behavior and reproduction in Hyalella azteca as sensitive endpoints for detecting long-term consequences of pesticide pulses

The aim of the present study was to examine acute and delayed effects of pulse exposure of the pyrethroid pesticide, permethrin, on precopulatory pairs of Hyalella azteca. Pairs of H. azteca were exposed to a single 1h pulse of different nominal concentrations of permethrin: 0, 0.3, 0.9 or 2.7 μg/L. During exposure, pairing behavior was observed, and during a 56 day post-exposure period the treatments were monitored for pairing behavior, survival and reproductive output. All permethrin-exposed pairs separated within minutes during exposure and shortly thereafter became immobile; however they regained mobility after transfer to clean water. The time to re-form pairs was significantly longer in all tested concentrations compared to the control, although all surviving pairs re-formed within the 56 day test period. Nevertheless not all pairs exposed to 0.9 and 2.7 μg/L reproduced. Furthermore the numbers of juveniles produced by pairs exposed to 0.9 and 2.7 μg/L, but not 0.3 μg/L, were lower throughout the entire post-exposure period compared to the control groups, and the total numbers of juveniles produced during 56 days were significantly lower in organisms exposed to 0.9 and 2.7 μg/L, but not 0.3 μg/L, compared to the control groups. The long-term effects of short-term exposure on reproductive behavior of pairs could potentially have consequences for the population dynamics of H. azteca. However, since individual-level responses can both overestimate and underestimate effects at the population level, appropriate population models are needed to reduce the uncertainty in extrapolating between these levels of biological organization.

Cellular differentiation and proliferation in the ovine lung during gestation and early postnatal development

This study investigates epithelial cell differentiation and proliferation in specific anatomical regions of the ovine lung during prenatal and postnatal development. Immunohistochemistry was used to identify ciliated epithelial cells, Clara cells, neuroepithelial bodies and type II pneumocytes in the lungs of preterm (67, 127 and 140 days of gestation), full-term (147 days) and postnatal (9, 16 and 91 days old) lambs. Differentiation of ciliated epithelial cells was seen at 67 days of gestation and at term for Clara cells. Neuroepithelial bodies were first detected at 127 days of gestation. From 16 to 91 days of age there was a significant (P <0.05) increase in beta-tubulin (present in ciliated epithelial cells) and Clara cell protein (present in Clara cells) in multiple regions of the lung. Detection of Ki67, a marker of proliferation, in preterm lambs showed a reduction in proliferation index in multiple anatomical regions of the lung between 70 days of gestation and term. Cell proliferation increased following parturition, and then decreased between 16 and 91 days of age, with the largest reduction occurring in the alveolar compartment. Knowledge of which cells are present at specific times of lung development provides valuable information on the anatomy of the ovine lung, improving its use as a model for ovine and human neonatal disease. In addition, the antibodies used here will be valuable for future studies requiring the identification and quantification of respiratory epithelial cell phenotypes in the sheep lung.

Development of a framework based on an ecosystem services approach for deriving specific protection goals for environmental risk assessment of pesticides

General protection goals for the environmental risk assessment (ERA) of plant protection products are stated in European legislation but specific protection goals (SPGs) are often not precisely defined. These are however crucial for designing appropriate risk assessment schemes. The process followed by the Panel on Plant Protection Products and their Residues (PPR) of the European Food Safety Authority (EFSA) as well as examples of resulting SPGs obtained so far for environmental risk assessment (ERA) of pesticides is presented. The ecosystem services approach was used as an overarching concept for the development of SPGs, which will likely facilitate communication with stakeholders in general and risk managers in particular. It is proposed to develop SPG options for 7 key drivers for ecosystem services (microbes, algae, non target plants (aquatic and terrestrial), aquatic invertebrates, terrestrial non target arthropods including honeybees, terrestrial non-arthropod invertebrates, and vertebrates), covering the ecosystem services that could potentially be affected by the use of pesticides. These SPGs need to be defined in 6 dimensions: biological entity, attribute, magnitude, temporal and geographical scale of the effect, and the degree of certainty that the specified level of effect will not be exceeded. In general, to ensure ecosystem services, taxa representative for the key drivers identified need to be protected at the population level. However, for some vertebrates and species that have a protection status in legislation, protection may be at the individual level. To protect the provisioning and supporting services provided by microbes it may be sufficient to protect them at the functional group level. To protect biodiversity impacts need to be assessed at least at the scale of the watershed/landscape.

The role of ecological models in linking ecological risk assessment to ecosystem services in agroecosystems

Agricultural practices are essential for sustaining the human population, but at the same time they can directly disrupt ecosystem functioning. Ecological risk assessment (ERA) aims to estimate possible adverse effects of human activities on ecosystems and their parts. Current ERA practices, however, incorporate very little ecology and base the risk estimates on the results of standard tests with several standard species. The main obstacles for a more ecologically relevant ERA are the lack of clear protection goals and the inherent complexity of ecosystems that is hard to approach empirically. In this paper, we argue that the ecosystem services framework offers an opportunity to define clear and ecologically relevant protection goals. At the same time, ecological models provide the tools to address ecological complexity to the degree needed to link measurement endpoints and ecosystem services, and to quantify service provision and possible adverse effects from human activities. We focus on the ecosystem services relevant for agroecosystem functioning, including pollination, biocontrol and eutrophication effects and present modeling studies relevant for quantification of each of the services. The challenges of the ecosystem services approach are discussed as well as the limitations of ecological models in the context of ERA. A broad, multi-stakeholder dialog is necessary to aid the definition of protection goals in terms of services delivered by ecosystems and their parts. The need to capture spatio-temporal dynamics and possible interactions among service providers pose challenges for ecological models as a basis for decision making. However, we argue that both fields are advancing quickly and can prove very valuable in achieving more ecologically relevant ERA.

Investigation of the fate and effects of acetyl cedrene on Capitella teleta and sediment bacterial community

The fate of the fragrance material, acetyl cedrene (AC), in sediment was examined in a 16 day laboratory experiment using the sediment microbial community subjected to the following treatments: AC (nominal concentration; 0 and 50 microg g(-1) dw sediment) and macrofaunal worms (with/without Capitella teleta (formerly Capitella sp. I)). Furthermore effects of AC on microbial respiration in the system were determined by examining CO(2) flux. T-RFLP (terminal restriction fragment length polymorphism) was used to analyze PCR (polymerase chain reaction) amplified 16S DNA gene fragments from the sediments to detect changes in the structure and diversity of the bacterial community. In addition, survival of C. teleta in sediment was determined. Lastly, we examined how the interactions between microbes and C. teleta in the sediment affected the above-mentioned parameters. The results showed that there was an interaction between worm treatment and time of sampling on the loss of AC from the sediment. This was caused by AC loss initially being fastest in the sediment with C. teleta present, but at experimental termination there was no significant difference between the two treatments (i.e., with/without worms) in the amount of AC remaining in the sediment. Survival of C. teleta was significantly reduced by AC at experimental termination, but neither microbial respiration nor structure and diversity of the bacterial community were significantly affected.

Effects of the polycyclic musk HHCB on individual- and population-level endpoints in Potamopyrgus antipodarum

Although the polycyclic musk 1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethylcyclopenta[gamma]-2-benzopyran (HHCB) is frequently detected in aquatic sediments, very little is known about its effects on sediment-feeding organisms. Effects of sediment-associated HHCB on growth, feeding rate, survival and reproduction in the gastropod Potamopyrgus antipodarum were measured in the laboratory. Snails were exposed to six nominal HHCB concentrations: 0, 0.1, 1, 10, 30 and 100microg g(-1) dry weight (dw) sediment. Adult survival and growth were not affected by HHCB. However, juvenile growth and survival, reproduction, time to first reproduction and adult feeding rate were more sensitive endpoints and declined with increasing HHCB concentration. Individual-level endpoints for P. antipodarum were integrated into a population model to investigate the effects of HHCB on population growth rate. Under otherwise favorable laboratory conditions, population growth rate was slightly (by ca. 2%), but not significantly, reduced with increasing HHCB exposure concentration. Model simulations were performed to explore the consequences of HHCB exposure under more ecologically realistic conditions (i.e., survival and reproduction of unexposed snails were markedly reduced relative to the laboratory). The results suggest that despite detectable effects of HHCB on individual-level endpoints measured in the laboratory, impacts on population dynamics of this deposit feeder are not likely to occur at environmentally relevant exposure concentrations.

Characterizing sediment acid volatile sulfide concentrations in European streams

Sediment acid volatile sulfide (AVS) concentrations were measured in wadeable streams of a wide variety of ecoregions of western Europe (84 sites in 10 countries and nine ecoregions) to better understand spatial distribution and ecoregion relationships. Acid volatile sulfide has been shown to be a major factor controlling the bioavailability and toxicity of many common trace metals, such as Cd, Cu, Ni, Pb, and Zn. Sediment characteristics varied widely. The ratio of the sum of the simultaneously extracted metals (SEM) to AVS ranged from 0.03 to 486.59. The sigmaSEM-AVS ranged from -40.02 to 17.71 micromol/g. On a regional scale, sediment characteristics such as dominant parent soil material showed significant trends in AVS distribution and variation by ecoregion. Total Fe and Mn were correlated weakly with SEM concentrations. Three AVS model approaches (i.e., the SEM:AVS ratio, SEM-AVS difference, and carbon normalization) were compared at threshold exceedance levels of SEM/AVS > 9, SEM-AVS > 2, and SEM-AVS/foc > 150 micromol/g organic carbon (OC). Only 4.76% of the sediments exceeded all three AVS thresholds; 22.6% of the sediments exceeded two models; and 13% of the sediments exceeded one model only. Using the SEM:AVS, SEM-AVS, and fraction of organic carbon models, and including site-specific data and regional soil characteristics, ecoregions 1 (Portugal), 3 (Italy), 4 (Switzerland), and 9 (Belgium/Germany) had the highest potential metals toxicity; ecoregions 13 and 8 (Belgium/France) showed the lowest potential toxicity. However, because AVS can vary widely spatially and temporally, these data should not be considered as representative of the sampled ecoregions. The general relationship between AVS levels and sediment characteristics provides some predictive capability for wadeable streams in the European ecoregions.

Effects of food type, feeding frequency, and temperature on juvenile survival and growth of Marisa cornuarietis (Mollusca: Gastropoda)

The present experiments are part of a larger study designed to investigate the influence of husbandry parameters on the life history of the ramshorn snail, Marisa cornuarietis, in order to identify suitable husbandry conditions for maintaining multi-generation populations in the laboratory for use in ecotoxicological testing. In this paper we focus on the effects of a combination of food types and feeding frequencies (i.e., the frequency with which the snails were offered food) on juvenile growth and survival at different temperatures. Offspring produced in the laboratory by wild specimens of M. cornuarietis, from Puerto Rico, were used to test the effects of three types of food (lettuce, alginate with fish food, alginate with snail mix) fed at three frequencies (given ad libitum on 4/4, 2/4, or 1/4 d) on juvenile survival and growth. The 4-d feeding regimens were repeated four times, giving a total of 16 d for the experiments. The experiments were conducted at two temperatures (22 degrees and 25 degrees C) under a 12 h light:12 h dark photoperiod. Juvenile growth rates increased with increasing feeding frequency for all food types. The most rapid growth rates occurred in the high-frequency lettuce treatments and the slowest growth rates in the low-frequency lettuce and alginate with snail mix treatments. Juvenile snails grew faster at 25 degrees than at 22 degrees C, and mortality was about twice as high at the lower temperature. Growth rates were used to provide a rough estimate of time to maturity, which was determined to take about twice as long at 22 degrees than at 25 degrees C. The results showed that lettuce is the best food if supplied in abundance, but effects on growth are very dependent on feeding frequency and temperature. We conclude that 25 degrees C is a more appropriate temperature for maintaining populations than 22 degrees C, that lettuce provides a suitable food source, and that food should be supplied continuously for husbandry and toxicity testing of populations of M. cornuarietis.

Effects of husbandry parameters on the life-history traits of the apple snail, Marisa cornuarietis: effects of temperature, photoperiod, and population density

These experiments are part of a larger study designed to investigate the influence of husbandry parameters on the life history of the apple snail, Marisa cornuarietis. The overall objective of the program is to identify suitable husbandry conditions for maintaining multi-generation populations of this species in the laboratory for use in ecotoxicological testing. In this article, we focus on the effects of photoperiod, temperature, and population density on adult fecundity and juvenile growth. Increasing photoperiod from 12 to 16 h of light per day had no effect on adult fecundity or egg hatching and relatively minor effects on juvenile growth and development. Rearing snails at temperatures between 22 degrees C and 28 degrees C did not influence the rates of egg production or egg clutch size. However, the rates of growth and development (of eggs and juveniles) increased with increasing temperature in this range, and when temperatures were reduced to 22 degrees C egg-hatching success was impaired. Juvenile growth and development were more sensitive to rearing density than adult fecundity traits. On the basis of the present results, we conclude that rearing individuals of M. cornuarietis at a temperature of 25 degrees C, a photoperiod of 12L:12D, and a density of <0.8 snails L(-1) (with lower densities for juvenile snails) should provide favorable husbandry conditions for maintaining multi-generation populations of this species.