Seasonal dynamics of the macrophyte test species Myriophyllum spicatum over two years in experimental ditches for population modeling application in risk assessment

Myriophyllum spicatum is a sediment-rooted, aquatic macrophyte growing submerged, with a wide geographical distribution and high ecological relevance in freshwater ecosystems. It is used in testing and risk assessment for pesticides in water and sediment. Population models enable effects measured under laboratory conditions to be extrapolated to effects expected in the field with time-variable environmental factors including exposure. These models are a promising tool in higher-tier risk assessments. However, there is a lack of data on the seasonal dynamics of M. spicatum, which is needed to test model predictions of typical population dynamics in the field. To generate such data, a two-year study was set up in outdoor experimental systems from May 2017 to May 2019. The growth of M. spicatum was monitored in 0.2025 m² plant baskets installed in an experimental ditch. Parameters monitored included biomass (fresh weight [FW] and dry weight [DW]), shoot length, seasonal short-term growth rates of shoots, relevant environmental parameters, and weather data. The results showed a clear seasonal pattern of biomass and shoot length and their variability. M. spicatum reached a maximum total shoot length (TSL) of 279 m m^-2 and a maximum standing crop above-ground DW of 262 g m^-2 . Periodical growth rates reached up to 0.072, 0.095, and 0.085 day^-1 for total length, FW, and DW, respectively. Multivariate regression revealed that pH (as a surrogate for the availability of carbon species) and water temperature could explain a significant proportion of the variability in M. spicatum growth rates (p < 0.05). This study has provided an ecologically relevant data set on seasonal population dynamics representative of shallow freshwater ecosystems, which can be used to test and refine population models for use in chemical risk assessment and ecosystem management. Integr Environ Assess Manag 2022;18:1375-1386. © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

A freshwater mesocosm study into the effects of the neonicotinoid insecticide thiamethoxam at multiple trophic levels

Thiamethoxam is a neonicotinoid insecticide used widely in agriculture to control a broad spectrum of insect pests. To assess potential risks from this compound to non-target aquatic organisms, an outdoor mesocosm study was performed. Mesocosms (1300 L) were treated once with a formulated product with the active substance (a.s.) thiamethoxam at nominal concentrations of 1 (n = 3), 3 (n = 3), 10 (n = 4), 30 (n = 4), and 100 (n = 2) μg a.s./L, plus untreated controls (n = 4). Primary producers (phytoplankton), zooplankton, and macroinvertebrates were monitored for up to 93 days following treatment. Thiamethoxam was observed to have a water column dissipation half-life (DT50) of ≤1.6-5.2 days in the mesocosms. Community-based principal response curve analysis detected no treatment effects for phytoplankton, zooplankton, emergent insects, and macroinvertebrates, indicating a lack of direct and indirect effects. A number of statistically significant differences from controls were detected for individual phytoplankton and zooplankton species abundances, but these were not considered to be treatment-related due to their transient nature and lack of concentration-response. After application of 30 μg a.s./L, slight temporary effects on Asellus aquaticus could not be excluded. At 100 μg a.s./L, there was an effect with no clear recovery of Asellus observed, likely due to their inability to recolonize these isolated test systems. A statistically significant but transient reduction in the emergence of chironomids by day 23 at the 100 μg a.s./L treatment was observed and possibly related to direct toxicity from thiamethoxam on larval stages. Therefore, a conservative study specific No Observed Ecological Adverse Effect Concentration (NOEAEC) is proposed to be 30 μg a.s./L. Overall, based on current concentrations of thiamethoxam detected in North American surface waters (typically <0.4 μg/L), there is low likelihood of direct or indirect effects from a pulsed exposure on primary producers, zooplankton, and macroinvertebrates, including insects, as monitored in this study.

Response of the mayfly (Cloeon dipterum) to chronic exposure to thiamethoxam in outdoor mesocosms

Thiamethoxam is a widely used neonicotinoid insecticide that has been detected in surface water monitoring programs in North America and Europe. This has led to questions about its toxicity to nontarget insects, specifically those with an aquatic life stage. To address the uncertainty associated with possible impacts from environmental exposures, a chronic (35-d) outdoor mesocosm study with a formulated product containing thiamethoxam was conducted. The specific focus of the study was the response of mayflies (Ephemeroptera), which have been reported to be particularly sensitive in laboratory studies. A range of concentrations (nominally 0.1, 0.3, 1.0, 3.0, and 10.0 µg/L thiamethoxam), plus untreated controls were tested, and the abundance and emergence of mayflies (Cloeon dipterum) were assessed weekly for 35 d. Mean measured time-weighted average exposures were within 6% of nominal over the duration of the study, with the mean half-life of thiamethoxam in each treatment ranging from 7 to 13 d. Statistically significant reductions in both larval abundance and adult emergence were observed at 10.0, 3.0, and 1.0 μg/L following 1, 2, and 3 wk of exposure, respectively. Exposure to 0.1 and 0.3 µg/L thiamethoxam had no statistically significant effect on larval mayfly abundance or adult emergence at any point in the study. These findings support a 35-d no-observed-effect concentration (NOEC) of 0.3 µg thiamethoxam/L for mayflies (C. dipterum) under chronic conditions. Furthermore, because the 95th percentile of environmental concentrations has been reported to be 0.054 µg/L, these results indicate that populations of C. dipterum and similarly sensitive aquatic insects are unlikely to be significantly impacted by thiamethoxam exposure in natural systems represented by the conditions in our study. Environ Toxicol Chem 2018;37:1040-1050. © 2017 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Pesticide exposure assessment for surface waters in the EU. Part 2: Determination of statistically based run-off and drainage scenarios for Germany

BACKGROUND

In order to assess surface water exposure to active substances of plant protection products (PPPs) in the European Union (EU), the FOCUS (FOrum for the Co-ordination of pesticide fate models and their USe) surface water workgroup introduced four run-off and six drainage scenarios for Step 3 of the tiered FOCUSsw approach. These scenarios may not necessarily represent realistic worst-case situations for the different Member States of the EU. Hence, the suitability of the scenarios for risk assessment in the national authorisation procedures is not known.

RESULTS

Using Germany as an example, the paper illustrates how national soil-climate scenarios can be developed to model entries of active substances into surface waters from run-off and erosion (using the model PRZM) and from drainage (using the model MACRO). In the authorisation procedure for PPPs on Member State level, such soil-climate scenarios can be used to determine exposure endpoints with a defined overall percentile.

CONCLUSION

The approach allows the development of national specific soil-climate scenarios and to calculate percentile-based exposure endpoints. The scenarios have been integrated into a software tool analogous to FOCUS-SWASH which can be used in the future to assess surface water exposure in authorisation procedures of PPPs in Germany. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Reintroducing Environmental Change Drivers in Biodiversity-Ecosystem Functioning Research

For the past 20 years, research on biodiversity and ecosystem functioning (B-EF) has only implicitly considered the underlying role of environmental change. We illustrate that explicitly reintroducing environmental change drivers in B-EF research is needed to predict the functioning of ecosystems facing changes in biodiversity. Next we show how this reintroduction improves experimental control over community composition and structure, which helps to provide mechanistic insight on how multiple aspects of biodiversity relate to function and how biodiversity and function relate in food webs. We also highlight challenges for the proposed reintroduction and suggest analyses and experiments to better understand how random biodiversity changes, as studied by classic approaches in B-EF research, contribute to the shifts in function that follow environmental change.

Pesticide exposure assessment for surface waters in the EU. Part 1: Some comments on the current procedure

In 2001, the European Commission introduced a risk assessment project known as FOCUS (FOrum for the Coordination of pesticide fate models and their USe) for the surface water risk assessment of active substances in the European Union. Even for the national authorisation of plant protection products (PPPs), the vast majority of EU member states still refer to the four runoff and six drainage scenarios selected by the FOCUS Surface Water Workgroup. However, our study, as well as the European Food Safety Authority (EFSA), has stated the need for various improvements. Current developments in pesticide exposure assessment mainly relate to two processes. Firstly, predicted environmental concentrations (PECs) of pesticides are calculated by introducing model input variables such as weather conditions, soil properties and substance fate parameters that have a probabilistic nature. Secondly, spatially distributed PECs for soil-climate scenarios are derived on the basis of an analysis of geodata. Such approaches facilitate the calculation of a spatiotemporal cumulative distribution function (CDF) of PECs for a given area of interest and are subsequently used to determine an exposure concentration endpoint as a given percentile of the CDF. For national PPP authorisation, we propose that, in the future, exposure endpoints should be determined from the overall known statistical PEC population for an area of interest, and derived for soil and climate conditions specific to the particular member state. © 2016 Society of Chemical Industry.

A microcosm study to support aquatic risk assessment of nickel: Community-level effects and comparison with bioavailability-normalized species sensitivity distributions

The aquatic risk assessment for nickel (Ni) in the European Union is based on chronic species sensitivity distributions and the use of bioavailability models. To test whether a bioavailability-based safe threshold of Ni (the hazardous concentration for 5% of species [HC5]) is protective for aquatic communities, microcosms were exposed to 5 stable Ni treatments (6-96 μg/L) and a control for 4 mo to assess bioaccumulation and effects on phytoplankton, periphyton, zooplankton, and snails. Concentrations of Ni in the periphyton, macrophytes, and snails measured at the end of the exposure period increased in a dose-dependent manner but did not indicate biomagnification. Abundance of phytoplankton and snails decreased in 48 μg Ni/L and 96 μg Ni/L treatments, which may have indirectly affected the abundance of zooplankton and periphyton. Exposure up to 24 μg Ni/L had no adverse effects on algae and zooplankton, whereas the rate of population decline of the snails at 24 μg Ni/L was significantly higher than in the controls. Therefore, the study-specific overall no-observed-adverse-effect concentration (NOAEC) is 12 μg Ni/L. This NOAEC is approximately twice the HC5 derived from a chronic species sensitivity distribution considering the specific water chemistry of the microcosm by means of bioavailability models. Thus, the present study provides support to the protectiveness of the bioavailability-normalized HC5 for freshwater communities.

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.

Ecological Recovery Potential of Freshwater Organisms: Consequences for Environmental Risk Assessment of Chemicals

Chemical contaminants released into the in the environment may have adverse effects on (non-target) species, populations and communities. The return of a stressed system to its pre-disturbance or other reference state, i.e. the ecological recovery, may depend on various factors related to the affected taxon, the ecosystem of concern and the type of stressor with consequences for the assessment and management of risks associated with chemical contaminants. Whereas the effects caused by short-term exposure might be acceptable to some extent, the conditions under which ecological recovery can serve as a decision criterion in the environmental risk assessment of chemical stressors remains to be evaluated. For a generic consideration of recovery in the risk assessment of chemicals, we reviewed case studies of natural and artificial aquatic systems and evaluate five aspects that might cause variability in population recovery time: (1) taxonomic differences and life-history variability, (2) factors related to ecosystem type and community processes, (3) type of disturbance, (4) comparison of field and semi-field studies, and (5) effect magnitude, i.e., the decline in population size following disturbance. We discuss our findings with regard to both retrospective assessments and prospective risk assessment.

How TK-TD and population models for aquatic macrophytes could support the risk assessment for plant protection products

This case study of the Society of Environmental Toxicology and Chemistry (SETAC) workshop MODELINK demonstrates the potential use of mechanistic effects models for macrophytes to extrapolate from effects of a plant protection product observed in laboratory tests to effects resulting from dynamic exposure on macrophyte populations in edge-of-field water bodies. A standard European Union (EU) risk assessment for an example herbicide based on macrophyte laboratory tests indicated risks for several exposure scenarios. Three of these scenarios are further analyzed using effect models for 2 aquatic macrophytes, the free-floating standard test species Lemna sp., and the sediment-rooted submerged additional standard test species Myriophyllum spicatum. Both models include a toxicokinetic (TK) part, describing uptake and elimination of the toxicant, a toxicodynamic (TD) part, describing the internal concentration-response function for growth inhibition, and a description of biomass growth as a function of environmental factors to allow simulating seasonal dynamics. The TK-TD models are calibrated and tested using laboratory tests, whereas the growth models were assumed to be fit for purpose based on comparisons of predictions with typical growth patterns observed in the field. For the risk assessment, biomass dynamics are predicted for the control situation and for several exposure levels. Based on specific protection goals for macrophytes, preliminary example decision criteria are suggested for evaluating the model outputs. The models refined the risk indicated by lower tier testing for 2 exposure scenarios, while confirming the risk associated for the third. Uncertainties related to the experimental and the modeling approaches and their application in the risk assessment are discussed. Based on this case study and the assumption that the models prove suitable for risk assessment once fully evaluated, we recommend that 1) ecological scenarios be developed that are also linked to the exposure scenarios, and 2) quantitative protection goals be set to facilitate the interpretation of model results for risk assessment.

The minimum detectable difference (MDD) and the interpretation of treatment-related effects of pesticides in experimental ecosystems

In the European registration procedure for pesticides, microcosm and mesocosm studies are the highest aquatic experimental tier to assess their environmental effects. Evaluations of microcosm/mesocosm studies rely heavily on no observed effect concentrations (NOECs) calculated for different population-level endpoints. Ideally, a power analysis should be reported for the concentration-response relationships underlying these NOECs, as well as for measurement endpoints for which significant effects cannot be demonstrated. An indication of this statistical power can be provided a posteriori by calculated minimum detectable differences (MDDs). The MDD defines the difference between the means of a treatment and the control that must exist to detect a statistically significant effect. The aim of this paper is to expand on the Aquatic Guidance Document recently published by the European Food Safety Authority (EFSA) and to propose a procedure to report and evaluate NOECs and related MDDs in a harmonised way. In addition, decision schemes are provided on how MDDs can be used to assess the reliability of microcosm/mesocosm studies and for the derivation of effect classes used to derive regulatory acceptable concentrations. Furthermore, examples are presented to show how MDDs can be reduced by optimising experimental design and sampling techniques.

Ecological interactions affecting population-level responses to chemical stress in Mesocyclops leuckarti

Higher tiers of ecological risk assessment (ERA) consider population and community-level endpoints. At the population level, the phenomenon of density dependence is one of the most important ecological processes that influence population dynamics. In this study, we investigated how different mechanisms of density dependence would influence population-level ERA of the cyclopoid copepod Mesocyclops leuckarti under toxicant exposure. We used a combined approach of laboratory experiments and individual-based modelling. An individual-based model was developed for M. leuckarti to simulate population dynamics under triphenyltin exposure based on individual-level ecological and toxicological data from laboratory experiments. The study primarily aimed to-(1) determine which life-cycle processes, based on feeding strategies, are most significant in determining density dependence (2) explore how these mechanisms of density dependence affect extrapolation from individual-level effects to the population level under toxicant exposure. Model simulations showed that cannibalism of nauplii that were already stressed by TPT exposure contributed to synergistic effects of biotic and abiotic factors and led to a twofold stress being exerted on the nauplii, thereby resulting in a higher population vulnerability compared to the scenario without cannibalism. Our results suggest that in population-level risk assessment, it is easy to underestimate toxicity unless underlying ecological interactions including mechanisms of population-level density regulation are considered. This study is an example of how a combined approach of experiments and mechanistic modelling can lead to a thorough understanding of ecological processes in ecotoxicology and enable a more realistic ERA.

Recovery based on plot experiments is a poor predictor of landscape-level population impacts of agricultural pesticides

Current European Union regulatory risk assessment allows application of pesticides provided that recovery of nontarget arthropods in-crop occurs within a year. Despite the long-established theory of source-sink dynamics, risk assessment ignores depletion of surrounding populations and typical field trials are restricted to plot-scale experiments. In the present study, the authors used agent-based modeling of 2 contrasting invertebrates, a spider and a beetle, to assess how the area of pesticide application and environmental half-life affect the assessment of recovery at the plot scale and impact the population at the landscape scale. Small-scale plot experiments were simulated for pesticides with different application rates and environmental half-lives. The same pesticides were then evaluated at the landscape scale (10 km × 10 km) assuming continuous year-on-year usage. The authors' results show that recovery time estimated from plot experiments is a poor indicator of long-term population impact at the landscape level and that the spatial scale of pesticide application strongly determines population-level impact. This raises serious doubts as to the utility of plot-recovery experiments in pesticide regulatory risk assessment for population-level protection. Predictions from the model are supported by empirical evidence from a series of studies carried out in the decade starting in 1988. The issues raised then can now be addressed using simulation. Prediction of impacts at landscape scales should be more widely used in assessing the risks posed by environmental stressors.

A list of fish species that are potentially exposed to pesticides in edge-of-field water bodies in the European Union--a first step towards identifying vulnerable representatives for risk assessment

Surrogate species are used in standard toxicity tests for the environmental risk assessment of chemicals. Test results are then extrapolated to the situation in the field, which is often associated with a large degree of uncertainty. Since a vulnerable species in the field is not only characterised by its intrinsic sensitivity to a stressor but also by its potential for exposure and its population resilience, the identification of focal species based on these three components of vulnerability is needed for a more ecologically relevant risk assessment. This study listed European fish species that are susceptible to pesticide exposure in the field and thus achieved the first step towards identifying focal species for the risk assessment of pesticides for fish in Europe. A step-wise filtering approach was applied to list freshwater fish species that are native to Europe and widespread in the European Union, which inhabit streams, ditches or ponds in agricultural landscapes and therefore, are at an elevated risk of being exposed to pesticides. Out of the 579 fish species occurring in European freshwater, 27 species met the filtering criteria. The resulting list was verified based on monitoring studies that were conducted in agricultural landscapes over the past 20 years. Focal fish species that can be used for a more ecologically relevant environmental risk assessment of pesticides in Europe can be identified from the produced list of species by further assessing their ecological (life history and dispersal characteristics) and intrinsic sensitivities.

The relative sensitivity of macrophyte and algal species to herbicides and fungicides: an analysis using species sensitivity distributions

Lemna spp. are the standard test species representing aquatic macrophytes in the current risk assessment schemes for herbicides and plant growth regulators in the European Union and North America. At a Society of Environmental Toxicology and Chemistry (SETAC) 2008 workshop on Aquatic Macrophyte Risk Assessment for Pesticides (AMRAP), a Species Sensitivity Distribution (SSD) working group was formed to address uncertainties about the sensitivity of Lemna spp. relative to other aquatic macrophyte species. For 11 herbicides and 3 fungicides for which relevant and reliable data were found for at least 6 macrophyte species, SSDs were fitted using lognormal regression. The positions of L. gibba (the most commonly tested Lemna species) and Myriophyllum spicatum (for which standardized test methods are under development) in each SSD were determined where data were available. The sensitivity of standard algal test species required for pesticide registration in the United States under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) relative to the macrophytes in each SSD was also examined (algae were not included in the SSD). L. gibba was among the most sensitive macrophyte species for approximately 50% of the chemicals examined. M. spicatum was among the most sensitive macrophytes for approximately 25% of the chemicals. In most cases, the lowest FIFRA algal species endpoint was lower than the most sensitive macrophyte endpoint. Although no single species consistently represented the most sensitive aquatic plant species, for 12 of 14 chemicals L. gibba and the FIFRA algae included an endpoint near or below the 5th percentile of the macrophyte SSD. For the other compounds, M. spicatum was the most sensitive species of all aquatic plants considered.

Environmental quality standards for mixtures: a case study with a herbicide mixture tested in outdoor mesocosms

Traces of pesticides are frequently detected in surface waters. As a consequence, specific environmental quality criteria (EQS) for a set of single pesticides in surface waters were defined by the environmental authorities in several countries. In this context, the aim of this study was to investigate if the sum of the five percentile hazard concentration (ΣHC(5-95 percent), meaning that 5 percent of the aquatic assemblage remains affected considering a 95 percent confidence interval) of three herbicides with the same mode of action derived from a species sensitivity distribution based on acute toxicity data (EC(50) values) of the most sensitive taxonomic group is a suitable EQS for surface water addressing the occurrence of herbicide mixtures as common exposure scenario. Therefore, an outdoor mesocosm study was performed with three replicates per treatment for a period of 173 days. Results demonstrated that a constant long-term exposure over 35 days to the HC(5-95 percent) of a mixture of three PSII inhibitors did not lead to adverse effects on the aquatic community in this field mesocosm study. Neither adverse effects on very sensitive functional endpoints such as photosynthesis measurements of algae and macrophytes nor adverse effects on structural endpoints such as abundance data and species composition were determined. In contrast and as a positive control, the HC(30) treatment affected statistically significant all investigated endpoints and it was demonstrated that the PSII inhibitors acted additive on various level of organization (Knauert et al., 2008). This study is filling the gap that no empirical evidence is published indicating that the chronic exposure at the HC(5-95 percent) estimate is leading to no adverse effects for the aquatic community and is therefore a suitable EQS for surface waters in the agriculture landscape.

A plea for the use of copepods in freshwater ecotoxicology

Standard species used in ecological risk assessment are chosen based on their sensitivity to various toxicants and the ease of rearing them for laboratory experiments. However, this mostly overlooks the fact that species in the field that may employ variable life-history strategies, which may have consequences concerning the vulnerability of such species to exposure with contaminants. We aimed to highlight the importance of copepods in ecology and to underline the need to include freshwater copepods in ecotoxicology. We carried out a literature search on copepods and Daphnia in ecology and ecotoxicology to compare the recognition given to these two taxa in these respective fields. We also conducted a detailed analysis of the literature on copepods and their current role in ecotoxicology to characterize the scale and depth of the studies and the ecotoxicological information therein. The literature on the ecology of copepods outweighed that in ecotoxicology when compared with daphnids. Copepods, like other zooplankton, were found to be sensitive to toxicants and important organisms in aquatic ecosystems. The few studies that were conducted on the ecotoxicology of copepods mainly focused on marine copepods. However, very little is known about the ecotoxicology of freshwater copepods. To enable a more realistic risk higher tier environmental risk assessment, we recommend considering freshwater copepods as part of the hazard assessment process. This could include the establishment of laboratory experiments to analyse the effects of toxicants on copepods and the development of individual-based models to extrapolate effects across species and scenarios.

Sensitivity, variability, and recovery of functional and structural endpoints of an aquatic community exposed to herbicides

A mesocosm study with three photosystem-II inhibitors and an equipotent mixture was performed to address the value of functional and structural endpoints in evaluating the impact of herbicides on aquatic systems. The herbicides atrazine, diuron, and isoproturon were dosed in the ratio of their relative potencies as HC30 for the single substance treatments and as 1/3 HC30 for the mixture treatment to obtain comparable effect concentrations. To investigate the effects of the three herbicides and their mixture on photosynthesis of the whole system, the physical-chemical parameters pH, dissolved oxygen, and conductivity were monitored. To address effects on photosynthesis more specifically, the photosynthetic efficiency of phytoplankton and three submersed macrophytes (Elodea canadensis, Myriophyllum spicatum, and Potamogeton lucens) were investigated applying in vivo chlorophyll fluorescence as an indicator for their activity. As a structural endpoint, the species abundance and community structure of the phytoplankton community was determined. Effects were continuously monitored over a five week period of constant exposure, and during a 3 month post-exposure period. The sensitivity, expressed as maximum effect during constant exposure, was higher for the structural parameters (total and single species abundances and PRC) than for the functional parameters. The mean coefficient of variation (CV) for the physical-chemical parameters was below 10%, for the photosynthesis measurement of the phytoplankton and macrophytes below 10 and 30%, respectively. Structural parameters, however, yielded higher variability with mean CVs for phytoplankton abundance data and single sensitive species reaching up to 96%. Effects on the phytoplankton photosynthesis measured via in vivo chlorophyll fluorescence were constant during the exposure period; whereas macrophytes recovered quickly from photosynthesis inhibition despite constant exposure. Effects on total system photosynthesis, determined via physical-chemical parameters, lasted for a shorter period than for the phytoplankton photosynthesis demonstrating the importance of the macrophytes for total primary production. Thus, the evaluation of effects on communities in model ecosystems such as micro- and mesocosms should not be based on structural endpoints only due to their comparably high inherent variability. Instead, we recommend complementing the risk assessment with data obtained from sensitive functional endpoints addressing the specific mode of action of the respective compound for the most sensitive group of organisms to avoid over-estimation of the recovery potential of the aquatic system.

Identification of realistic worst case aquatic macroinvertebrate species for prospective risk assessment using the trait concept

PURPOSE

Approaches in environmental risk assessment for pesticides are becoming more and more realistic. Thereby, risk assessment has to be protective in a way that no long-lasting (adverse) effects on populations will occur in the environment. Since this imperative includes species generally showing high population vulnerability due to their life history traits, prospective risk assessment should be based on realistic worst cases. Based on life history traits, the purpose of the current study was to verify whether a worst case combination of low potential for intrinsic recovery and low ability for recolonisation can be found in the field.

METHODS

Combinations of traits related to dispersal ability and reproduction of macroinvertebrates were investigated using monitoring data from edge of field water bodies in Germany. The relative distribution of traits was analyzed across different agricultural regions and across sites of different potential for exposure to pesticides. Species were sorted in a tiered approach in order to gain a list of realistic worst case species.

RESULTS

Life history traits were found equally distributed across different regions. Thereby, dispersal ability and voltinism were not randomly combined. Within the data analysed, low dispersal ability was found to be exclusive to semivoltine taxa. Owing to their appearance in reference sites, poor dispersal ability and a long time reproduction, three species were considered potentially worst case.

CONCLUSIONS

The trait approach was found to be suitable in comparing trait distributions within different regions and in compiling a list of critical taxa for consideration in environmental risk assessment.

Potential application of population models in the European ecological risk assessment of chemicals. II. Review of models and their potential to address environmental protection aims

Whereas current chemical risk assessment (RA) schemes within the European Union (EU) focus mainly on toxicity and bioaccumulation of chemicals in individual organisms, most protection goals aim at preserving populations of nontarget organisms rather than individuals. Ecological models are tools rarely recommended in official technical documents on RA of chemicals, but are widely used by researchers to assess risks to populations, communities and ecosystems. Their great advantage is the relatively straightforward integration of the sensitivity of species to chemicals, the mode of action and fate in the environment of toxicants, life-history traits of the species of concern, and landscape features. To promote the usage of ecological models in regulatory risk assessment, this study tries to establish whether existing, published ecological modeling studies have addressed or have the potential to address the protection aims and requirements of the chemical directives of the EU. We reviewed 148 publications, and evaluated and analyzed them in a database according to defined criteria. Published models were also classified in terms of 5 areas where their application would be most useful for chemical RA. All potential application areas are well represented in the published literature. Most models were developed to estimate population-level responses on the basis of individual effects, followed by recovery process assessment, both in individuals and at the level of metapopulations. We provide case studies for each of the proposed areas of ecological model application. The lack of clarity about protection goals in legislative documents made it impossible to establish a direct link between modeling studies and protection goals. Because most of the models reviewed here were not developed for regulatory risk assessment, there is great potential and a variety of ecological models in the published literature.

Potential application of ecological models in the European environmental risk assessment of chemicals. I. Review of protection goals in EU directives and regulations

Several European directives and regulations address the environmental risk assessment of chemicals. We used the protection of freshwater ecosystems against plant protection products, biocidal products, human and veterinary pharmaceuticals, and other chemicals and priority substances under the Water Framework Directive as examples to explore the potential of ecological effect models for a refined risk assessment. Our analysis of the directives, regulations, and related guidance documents lead us to distinguish the following 5 areas for the application of ecological models in chemical risk assessment: 1) Extrapolation of organism-level effects to the population level: The protection goals are formulated in general terms, e.g., avoiding "unacceptable effects" or "adverse impact" on the environment or the "viability of exposed species." In contrast, most of the standard ecotoxicological tests provide data only on organism-level endpoints and are thus not directly linked to the protection goals which focus on populations and communities. 2) Extrapolation of effects between different exposure profiles: Especially for plant protection products, exposure profiles can be very variable and impossible to cover in toxicological tests. 3) Extrapolation of recovery processes: As a consequence of the often short-term exposures to plant protection products, the risk assessment is based on the community recovery principle. On the other hand, assessments under the other directives assume a more or less constant exposure and are based on the ecosystem threshold principle. 4) Analysis and prediction of indirect effects: Because effects on 1 or a few taxa might have consequences on other taxa that are not directly affected by the chemical, such indirect effects on communities have to be considered. 5) Prediction of bioaccumulation within food chains: All directives take the possibility of bioaccumulation, and thus secondary poisoning within the food chain, into account.

AMEG: the new SETAC advisory group on aquatic macrophyte ecotoxicology

INTRODUCTION AND BACKGROUND

Primary producers play critical structural and functional roles in aquatic ecosystems; therefore, it is imperative that the potential risks of toxicants to aquatic plants are adequately assessed in the risk assessment of chemicals. The standard required macrophyte test species is the floating (non-sediment-rooted) duckweed Lemna spp. This macrophyte species might not be representative of all floating, rooted, emergent, and submerged macrophyte species because of differences in the duration and mode of exposure; sensitivity to the specific toxic mode of action of the chemical; and species-specific traits (e.g., duckweed's very short generation time).

DISCUSSION AND PERSPECTIVES

These topics were addressed during the workshop entitled "Aquatic Macrophyte Risk Assessment for Pesticides" (AMRAP) where a risk assessment scheme for aquatic macrophytes was proposed. Four working groups evolved from this workshop and were charged with the task of developing Tier 1 and higher-tier aquatic macrophyte risk assessment procedures. Subsequently, a SETAC Advisory Group, the Macrophyte Ecotoxicology Group (AMEG) was formed as an umbrella organization for various macrophyte working groups. The purpose of AMEG is to provide scientifically based guidance in all aspects of aquatic macrophyte testing in the laboratory and field, including prospective as well as retrospective risk assessments for chemicals. As AMEG expands, it will begin to address new topics including bioremediation and sustainable management of aquatic macrophytes in the context of ecosystem services.

Co-tolerance of phytoplankton communities to photosynthesis II inhibitors

Natural variability in sensitivity and pollution induced community tolerance (PICT) to atrazine, isoproturon and diuron and a mixture of these three herbicides to natural algal assemblages in mesocosms was determined. The specificity of PICT was examined by evaluating co-tolerance pattern for these photosystem-II (PSII) inhibitors. Phytoplankton communities were constantly exposed to equipotent concentrations of atrazine, isoproturon, diuron namely the 30% hazard concentration (HC(30)) obtained from species sensitivity distributions and an equitoxic mixture (Sigma3 x 1/3 x HC(30) of each herbicide) for five weeks in outdoor mesocosms. Induction of tolerance to the various herbicides was investigated by photosynthetic efficiency measurements of the algal assemblages in short-term laboratory tests. The composition of the algal communities in the various treatments was determined and ordination techniques such as the principal component analysis (PCA) were applied to log-transformed data to compare the seasonal community structure development. Temporal variation in sensitivity of the control algal assemblage to atrazine and isoproturon, but less to diuron was observed. The results further demonstrated that the control communities were in general more sensitive than the treated ones over the whole period tested indicating an enhanced tolerance of pre-exposed phytoplankton in the mesocosms. Co-tolerance was also observed for atrazine pre-exposed algal community to isoproturon, however, not vise versa. A pre-exposure to diuron induced similar tolerance to all three herbicides. A pre-exposure to the mixture treatment also lead to tolerance to isoproturon and diuron, less to atrazine. Overall, the observed co-tolerance pattern indicates that co-tolerance was not comparable between the herbicides with strong similarity in their biochemical mode of action.

Effects of photosystem II inhibitors and their mixture on freshwater phytoplankton succession in outdoor mesocosms

Effects of three photosystem II inhibitors and of their mixture on a freshwater phytoplankton community were studied in outdoor mesocosms. Atrazine, isoproturon, and diuron were applied as 30% hazardous concentrations (HC30s) obtained from species-sensitivity distributions. Taking concentration addition into account, the mixture comprised one-third of the HC30 of each substance. Effects were investigated during a five-week period of constant concentrations and a five-month posttreatment period when the herbicides dissipated. Total abundance, species composition, and diversity and recovery of the community were evaluated. Ordination techniques, such as principal component analysis and principal response curve, were applied to compare the various treatments on the community level. The three herbicides stimulated comparable effects on total abundance and diversity of phytoplankton during the period of constant exposure because of the susceptibility of the dominant cryptophytes Chroomonas acuta and Cryptomonas erosa et ovata and the prasinophyte Nephroselmis cf. olivacea. Moreover, concentration addition described combined effects of atrazine, isoproturon, and diuron on total abundance and diversity in the constant-exposure period, because their mixture induced effects on abundance and diversity similar to those of the single substances. Principal component and principal response curve analyses revealed that the community structure of diuron- and isoproturon-treated phytoplankton recovered two weeks after constant exposure, which might be related to the fast dissipation of the phenylureas. Species compositions of mixture- and atrazine-treated communities were not comparable to that of the control community five months after the end of constant exposure. This might be explained by the slower dissipation of atrazine relative to the phenylureas and by differences in the species sensitivities, resulting in a different succession of phytoplankton.

Ecological models in support of regulatory risk assessments of pesticides: developing a strategy for the future

This brief communication reports on the main findings of the LEMTOX workshop, held from 9 to 12 September 2007, at the Helmholtz Centre for Environmental Research (UFZ) in Leipzig, Germany. The workshop brought together a diverse group of stakeholders from academia, regulatory authorities, contract research organizations, and industry, representing Europe, the United States, and Asia, to discuss the role of ecological modeling in risk assessments of pesticides, particularly under the European regulatory framework. The following questions were addressed: What are the potential benefits of using ecological models in pesticide registration and risk assessment? What obstacles prevent ecological modeling from being used routinely in regulatory submissions? What actions are needed to overcome the identified obstacles? What recommendations should be made to ensure good modeling practice in this context? The workshop focused exclusively on population models, and discussion was focused on those categories of population models that link effects on individuals (e.g., survival, growth, reproduction, behavior) to effects on population dynamics. The workshop participants concluded that the overall benefits of ecological modeling are that it could bring more ecology into ecological risk assessment, and it could provide an excellent tool for exploring the importance of, and interactions among, ecological complexities. However, there are a number of challenges that need to be overcome before such models will receive wide acceptance for pesticide risk assessment, despite having been used extensively in other contexts (e.g., conservation biology). The need for guidance on Good Modeling Practice (on model development, analysis, interpretation, evaluation, documentation, and communication), as well as the need for case studies that can be used to explore the added value of ecological models for risk assessment, were identified as top priorities. Assessing recovery potential of exposed nontarget species and clarifying the ecological relevance of standard laboratory test results are two areas for which ecological modeling may be able to provide considerable benefits.

Aquatic macroinvertebrates in the altes land, an intensely used orchard region in Germany: Correlation between community structure and potential for pesticide exposure

To assess the impact of pesticides on aquatic organisms under realistic worst-case conditions, a macroinvertebrate community of small ditches was sampled at 40 sites of the orchard region Altes Land near Hamburg, Germany. To differentiate between pesticide impact and other variables, the ditches selected for sampling were located at different distances along grassland, unused apple orchards, and orchards managed with integrated and/or organic crop protection methods. Samples of macroinvertebrates were taken on five dates over two years. In addition to biological data, water chemistry and structural parameters were measured. For each sampling site, a potential for exposure was calculated on the basis of the distance of the ditch to the nearest row of trees and the depth and width of the ditch. The neighborhood to either grassland or orchards turned out to have a larger impact on the macroinvertebrate community than the potential for exposure. Therefore, grassland sites were omitted from further evaluation. Remaining sites were grouped into low exposure (sites at unused orchards), medium exposure (distance of 3-5 m [track] between trees and ditch), and high exposure (trees close to the ditch, mean distance < or = 1.5 m). Principal response curves showed differences in community structure between the three exposure groups over time. Whereas for sites from the high exposure group significant differences from low exposure was observed in all seasons, significant differences between low and medium were observed only occasionally. Effects were less pronounced in samples taken at springtime before the starting pesticide applications, suggesting some community recovery. Species richness was negatively correlated to exposure potential. Isopoda, Eulamellibranchiata, and insects, especially Ephemeroptera, showed a high negative correlation with the potential for pesticide exposure, suggesting that these taxa are sensitive to the pesticide use in the orchards.

Long-term variability of zooplankton populations in aquatic mesocosms

The natural variability on a spatial and temporal scale was examined in the zooplankton community of mesocosms from Syngenta Crop Protection AG (Stein, Switzerland), with the focus on improving the experimental design and evaluation of mesocosm studies. Analysis was performed using zooplankton data collected during a three-year period in 3 (1996 and 1998) to 12 (1997) ponds. Interreplicate variability was measured as the variance among the 3 to 12 replicates at each sampling date. Temporal variation was examined as seasonal variability by comparing different sampling dates within a year and as year-to-year variation by comparing pooled data year by year. Univariate and multivariate methods were used for the evaluation of population and community data, respectively. Results from the present study indicate that because of the low interreplicate variability, only data from high-abundance species could be evaluated with a precision able to detect effects less than 20%. For the majority of the zooplankton populations, abundances were lower than 10 organisms/L, with frequent zero counts resulting in a weak evaluation of the data with a precision able to detect effects of greater than 20 and 110%. Ordination analysis of the community data from the three years revealed that approximately 29% of the total variance could be explained by year-to-year differences, whereas 11% could be attributed to seasonal variability within a year. The residual variance can be attributed to interreplicate variability and sampling error. These results were in line with findings for individual populations. The present analysis demonstrated that the inherent variability of a system should be investigated for a proper design and evaluation of mesocosm studies and promotes the use of multivariate tools for a more comprehensive interpretation of mesocosm data.