Shyam K. Nair

: The US Environmental Protection Agency (USEPA) has historically used different methods to derive an aquatic level of concern (LoC) for atrazine, though all have generally relied on an expanding set of mesocosm and microcosm (“cosm”) studies for calibration. The database of results from ecological effects studies with atrazine in cosms now includes 108 data points from 39 studies and forms the basis for assessing atrazine's potential to impact aquatic plant communities. Inclusion of the appropriate cosm studies and accurate interpretation of each data point—delineated as binary scores of “effect” (effect score 1) or “no effect” (effect score 0) of a specific atrazine exposure profile on plant communities in a single study—is critical to USEPA's approach to determining the LoC. We reviewed the atrazine cosm studies in detail and carefully interpreted their results in terms of the binary effect scores. The cosm database includes a wide range of experimental systems and study designs, some of which are more relevant to natural plant communities than others. Moreover, the studies vary in the clarity and consistency of their results. We therefore evaluated each study against objective criteria for relevance and reliability to produce a weighting score that can be applied to the effect scores when calculating the LoC. This approach is useful because studies that are more relevant and reliable have greater influence on the LoC than studies with lower weighting scores. When the current iteration of USEPA's LoC approach, referred to as the plant assemblage toxicity index (PATI), was calibrated with the weighted cosm data set, the result was a 60-day LoC of 21.2 μg/L. Integr Environ Assess Manag 2018;14:489–497. © 2018 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of Society of Environmental Toxicology & Chemistry (SETAC) Key Points: The extensive body of microcosm and mesocosm (“cosm”) research with the herbicide atrazine has been a major source of data for establishing a regulatory level of concern (LoC)—the highest level of exposure considered by risk managers to be protective of aquatic plant communities. The approach described in this paper—evaluating cosm studies for relevance and reliability and weighting the LoC analysis with the information—is useful because studies that are more relevant and reliable have greater influence on the LoC than studies with lower weighting scores. The atrazine LoC derivation process used by the USEPA is highly influenced by interpretation of individual cosm studies, by the model used to predict cumulative atrazine effects, and by the results of the data evaluation. When the EPA's current LoC approach, referred to as the Plant Assemblage Toxicity Index, was calibrated with appropriate cosm data weighted according to the data evaluation scores, the result was a 60-day time-weighted average exposure of 21.2 µg/L.

Potential toxic effects of thiamethoxam on nontarget organisms and the community structure of a generic Midwestern farm pond and emergent wetland were assessed using 2 versions of the comprehensive aquatic system model: CASM_GFP, a generic farm pond model, and CASM_GWL, a generic wetland model. The CASM_GFP and CASM_GWL are integrated bioenergetics‐based and habitat quality models that describe the daily biomass values of selected producer and consumer populations representative of generalized Midwestern farm ponds and emergent wetlands. The CASM_GFP demonstrated the ability to reproduce values of population biomass reported for Midwestern (and other) pond ecosystems; the CASM_GWL provided a similar modeling capability for Midwestern emergent wetlands. Lethal and sublethal effects of thiamethoxam were modeled as extrapolations of laboratory toxicity assays using the CASM_GFP and the CASM_GWL. Time series of daily environmental concentrations of thiamethoxam constructed for 6 regional pesticide applications across the United States failed to produce any calculated impacts on modeled population biomass or changes in community structure of modeled trophic guilds in the CASM_GFP or the CASM_GWL. However, evaluation of systematically increased daily concentrations demonstrated the ability of both models to simulate direct and indirect toxic effects of this pesticide. The present model study suggests that process‐based food web/ecosystem models can be used to characterize the potential ecological effects of thiamethoxam on generalized farm pond and emergent wetland ecosystems. Environ Toxicol Chem 2018;37:738–754. © 2017 SETAC

Potential effects of atrazine on the nontarget aquatic plants characteristic of lower-order streams in the Midwestern United States were previously assessed using the Comprehensive Aquatic System Model (CASM_ATZ). Another similar bioenergetics-based, mechanistic model, AQUATOX, was examined in the present study, with 3 objectives: 1) to develop an AQUATOX model simulation similar to the CASM_ATZ model reference simulation in describing temporal patterns of biomass production by modeled plant populations, 2) to examine the implications of the different approaches used by the models in deriving plant community-based levels of concern (LOCs) for atrazine, and 3) to determine the feasibility of implementing alternative ecological models to assess ecological impacts of atrazine on lower-order Midwestern streams. The results of the present comparative modeling study demonstrated that a similar reference simulation to that from the CASM_ATZ model could be developed using the AQUATOX model. It was also determined that development of LOCs and identification of streams with exposures in excess of the LOCs were feasible with the AQUATOX model. Compared with the CASM_ATZ model results, however, the AQUATOX model consistently produced higher estimates of LOCs and generated non-monotonic variations of atrazine effects with increasing exposures. The results of the present study suggest an opportunity for harmonizing the treatments of toxicity and toxicity parameter estimation in the CASM_ATZ and the AQUATOX models. Both models appear useful in characterizing the potential impacts of atrazine on nontarget aquatic plant populations in lower-order Midwestern streams. The present model comparison also suggests that, with appropriate parameterization, these process-based models can be used to assess the potential effects of other xenobiotics on stream ecosystems. Environ Toxicol Chem 2015;34:2590–2602. © 2015 SETAC

The comprehensive aquatic systems model for atrazine (CASM_ATZ) estimates the potential toxic effects of atrazine on populations of aquatic plants and consumers in a generic lower-order midwestern stream. The CASM_ATZ simulates the daily production of 20 periphyton and 6 aquatic vascular plant species. The modeled consumer community consists of 17 functionally defined species of zooplankton, benthic invertebrates, bacteria, and fish. Daily values of population biomass (grams of carbon per square meter) are calculated as nonlinear functions of population bioenergetics, physical–chemical environmental parameters, grazing/predator–prey interactions, and population-specific direct and indirect responses to atrazine. The CASM_ATZ uses Monte Carlo methods to characterize the implications of phenotypic variability, environmental variability, and uncertainty associated with atrazine toxicity data in estimating the potential impacts of time-varying atrazine exposures on population biomass and community structure. Comparisons of modeled biomass values for plants and consumers with published data indicate that the generic reference simulation realistically describes ecological production in lower-order midwestern streams. Probabilistic assessments were conducted using the CASM_ATZ to evaluate potential modeled changes in plant community structure resulting from measured atrazine exposure profiles in 3 midwestern US streams representing watersheds highly vulnerable to runoff. Deviation in the median values of maximum 30-d average Steinhaus similarity index ranged from 0.09% to 2.52% from the reference simulation. The CASM_ATZ could therefore be used for the purposes of risk assessment by comparison of site monitoring–based model output to a biologically relevant Steinhaus similarity index level of concern. Used as a generic screening technology or in site-specific applications, the CASM_ATZ provides an effective, coherent, and transparent modeling framework for assessing ecological risks posed by pesticides in lower-order streams. Environ Toxicol Chem 2013;32:2402–2411. © 2013 SETAC

Summary: 1. Restoration of shallow turbid lakes to promote growth of submersed aquatic vegetation (SAV) requires knowledge of the environmental factors affecting SAV growth and persistence, and a means to predict the success of SAV reestablishment under different management scenarios to improve these environmental conditions. We used a dynamic ecological modelling approach relating SAV responses to changes in physical and chemical conditions, with information on water level, flow and transparency being provided by hydrodynamic and sediment transport models.2. The potential persistence of Vallisneria americana was similar under simulated environmental conditions in 1946 and in 1954, as was the potential persistence of Potamogeton pectinatus, indicating that the disappearance of V. americana from Peoria Lake (U.S.A.) previously attributed to an extended spring flood in 1954, may have been related to the combined effects of changes in water level, flow and water transparency as well as possibly other factors.3. Recent environmental conditions (for 2000) proved not to be conducive for the colonization and persistence potential of V. americana, but would allow colonization by P. pectinatus. The construction of a hypothetical levee along the eastern descending line of the navigation channel in Upper Peoria Lake, which was expected to reduce fetch‐ and navigation‐related turbidity, did not improve the situation for V. americana and overall deteriorated the situation for P. pectinatus. Thus, such a hydraulic alteration, generally considered as beneficial for SAV restoration, may not always be successful.4. The results of the simulations indicated that the environmental conditions for potential persistence in Peoria Lake were generally less favourable for V. americana than for P. pectinatus. Measures suggested to restore SAV communities in such a lake should aim at reducing concentrations of total suspended solids at the point of inflow by a factor of three to four and limiting fetch‐ and navigation‐related resuspension.

A series of locks and dams were constructed and put into operation on the Upper Mississippi River in the 1930s to facilitate commercial navigation. As a result, historical floodplain landscapes were altered. For example, islands characterized by floodplain forests experienced prolonged unfavourable hydrologic conditions and were eliminated from many areas of the river. The distribution and extent of other large river habitat types (e.g., wetlands, secondary channels) were also impacted. In addition, large areas of open water habitat were created through the impoundment of the river. Proposed management plans for the Upper Mississippi River include (1) modernization of the locks and dams to improve navigation efficiency, and (2) ecological restoration to conditions more characteristic of pre-impoundment. The purpose of the work reported here is to describe and apply a spatially explicit comprehensive aquatic systems model (SECASM). The SECASM is offered as one approach for evaluating the anticipated outcomes of alternative management and restoration actions (e.g., island creation, floodplain forest restoration, water level management). The model simulates spatial-temporal changes in the distribution and extent of five land-use types representative of the Upper Mississippi River floodplain: prairie, marsh, upland woody vegetation, surface water, and combined urban/agricultural areas. The SECASM has a spatial resolution defined by 100 x 100-meter grid elements (i.e., 1 ha) and operates using a daily time step for simulated durations up to 100 years. Transitions of habitat types within each grid element are determined by a combination of rule-based algorithms and ecological process equations. The model outputs are amenable to the production of landscape maps and the calculation of landscape metrics (e.g., lacunarity index) that usefully summarize landscape patterns. The ability of the SECASM to realistically describe alterations in Upper Mississippi River floodplain landscapes was evaluated by using Pool 5 land-use patterns reported for 1890 as an initial condition, simulating 100-y of landscape change (including impoundment), and comparing model results with reported conditions for 1989. The SECASM was subsequently used to examine several hypotheses concerning landscape impacts of impoundment, outcomes of alternative restoration actions, and the potential effects of nutrient enrichment.

This article presents a quantitative methodology for evaluating the probability of invasive pest species establishing persistent populations. The estimation of pest establishment relies on data and information describing the biology and ecology of the pest and its interactions with potential host species and the regional environment. This information is developed using a model construct borrowed from theoretical population ecology. The methodology for estimating the probability of pest establishment is part of an overall framework that explores the implications of reductions in pest invasions on subsequent establishment. The risk reduction framework integrates the engineering aspects of different technologies for reducing pest entry, the biology and ecology of pest species, the suitability of potentially susceptible hosts, and the quality of available habitats. The methodology for estimating the risk of establishment is presented using an example pest, the Asian longhorned beetle (Anoplophora glabripennis), which has been introduced into the United States via solid wood packing materials (SWPM) used in international commerce. Uncertainties inherent to the estimation of model parameters that determine the risk of establishment are defined, quantified, and propagated through the population model. Advantages and limitations of the proposed methodology are discussed along with recommendations to make the approach more useful in the management of risks posed by the establishment of pest populations.