A new interpretation of avian and Mammalian reproduction toxicity test data in ecological risk assessment

Using Pop-GUIDE to Assess the Applicability of MCnest for Relative Risk of Pesticides to Hummingbirds

Hummingbirds are charismatic fauna that provide important pollination services, including in the continental US, where 15 species regularly breed. Compared to other birds in North America, hummingbirds (family Trochilidae) have a unique exposure route to pesticides because they forage on nectar. Therefore, hummingbirds may be exposed to systemic pesticides borne in nectar. They also may be particularly vulnerable to pesticide exposure due to their small size and extreme metabolic demands. We review relevant factors including hummingbird life history, nectar residue uptake, and avian bioenergetic considerations with the goal of clearly identifying and articulating the specific modeling challenges that must be overcome to develop and/or adapt existing modeling approaches. To help evaluate these factors, we developed a dataset for ruby-throated hummingbirds (Archilochus colubris) and other avian species potentially exposed to pesticides. We used the systemic neonicotinoid pesticide imidacloprid as an illustration and compared results to five other common current use pesticides. We use the structure of Pop-GUIDE to provide a conceptual modeling framework for implementation of MCnest and to compile parameter values and relevant algorithms to predict the effects of pesticide exposure on avian pollinators. Conservative screening assessments suggest the potential for adverse effects from imidacloprid, as do more refined assessments, though many important limitations and uncertainties remain. Our review found many areas in which current USEPA avian models must be improved in order to conduct a full higher-tier risk assessment for avian pollinators exposed to neonicotinoid insecticides, including addition of models suitable for soil and seed treatments within the MCnest environment, ability to include empirical residue data in both nectar and invertebrates rather than relying on existing nomograms, expansion of MCnest to a full annual cycle, and increased representation of spatial heterogeneity. Although this work focuses on hummingbirds, the methods and recommendations may apply more widely to other vertebrate pollinators.

Pesticide impacts on avian species with special reference to farmland birds: a review

For decades, we have observed a major biodiversity crisis impacting all taxa. Avian species have been particularly well monitored over the long term, documenting their declines. In particular, farmland birds are decreasing worldwide, but the contribution of pesticides to their decline remains controversial. Most studies addressing the effects of agrochemicals are limited to their assessment under controlled laboratory conditions, the determination of lethal dose 50 (LD₅₀) values and testing in a few species, most belonging to Galliformes. They often ignore the high interspecies variability in sensitivity, delayed sublethal effects on the physiology, behaviour and life-history traits of individuals and their consequences at the population and community levels. Most importantly, they have entirely neglected to test for the multiple exposure pathways to which individuals are subjected in the field (cocktail effects). The present review aims to provide a comprehensive overview for ecologists, evolutionary ecologists and conservationists. We aimed to compile the literature on the effects of pesticides on bird physiology, behaviour and life-history traits, collecting evidence from model and wild species and from field and lab experiments to highlight the gaps that remain to be filled. We show how subtle nonlethal exposure might be pernicious, with major consequences for bird populations and communities. We finally propose several prospective guidelines for future studies that may be considered to meet urgent needs.

Realism, Conservatism, and Tiered Ecological Risk Assessment

Recent research has provided valuable momentum for the development and use of population models for ecological risk assessment (ERA). In general, ERA proceeds along a tiered strategy, with conservative assumptions deployed at lower tiers that are relaxed at higher tiers with ever more realistic models. As the tier increases, so do the levels of time and effort required by the assessor. When faced with many stressors, species, and habitats, risk assessors need to find efficiencies. Conservative lower-tier approaches are well established, but higher-tier models often prioritize accuracy, and conservative approaches are relatively unexplored at higher tiers. A principle of efficiency for ecological modeling for population-level ecological risk assessment is articulated and evaluated against a conceptual model and an existing set of avian models for chemical risk assessment. Here, four published avian models are reviewed in increasing order of realism (risk quotient → Markov chain nest productivity model → endogenous lifecycle model → spatially explicit population model). Models are compared in a pairwise fashion according to increasing realism and evaluated as to whether conservatism increases or decreases with each step. The principle of efficiency is shown to be a challenging ideal, though some cause for optimism is identified. Strategies are suggested for studying efficiency in tiered ecological model deployment.

Birds feeding on tebuconazole treated seeds have reduced breeding output

Drilled seeds are an important food resource for many farmland birds but may pose a serious risk when treated with pesticides. Most compounds currently used as seed treatment in the EU have low acute toxicity but may still affect birds in a sub-chronic or chronic way, especially considering that the sowing season lasts several weeks or months, resulting in a long exposure period for birds. Tebuconazole is a triazole fungicide widely used in agriculture but its toxicity to birds remains largely unknown. Our aim was to test if a realistic scenario of exposure to tebuconazole treated seeds affected the survival and subsequent reproduction of the red-legged partridge (Alectoris rufa). We fed captive partridges with wheat seeds treated with 0%, 20% or 100% of tebuconazole application rate during 25 days in late winter (i.e. tebuconazole dietary doses were approximately 0.2 and 1.1 mg/kg bw/day). We studied treatment effects on the physiology (i.e. body weight, biochemistry, immunology, oxidative stress, coloration) and reproduction of partridges. Exposed birds did not reduce food consumption but presented reduced plasmatic concentrations of lipids (triglycerides at both exposure doses, cholesterol at high dose) and proteins (high dose). The coloration of the eye ring was also reduced in the low dose group. Exposure ended 60 days before the first egg was laid, but still affected reproductive output: hatching rate was reduced by 23% and brood size was 1.5 times smaller in the high dose group compared with controls. No significant reproductive effects were found in the low dose group. Our results point to the need to study the potential endocrine disruption mechanism of this fungicide with lagged effects on reproduction. Risk assessments for tebuconazole use as seed treatment should be revised in light of these reported effects on bird reproduction.

Estimating the potential effects of pesticide seed treatments on the reproductive success of arable birds

In temperate zones, seeds of spring-sown crops may be an attractive food source for breeding farmland birds. We modelled the effects of pesticide seed treatments on the reproductive success of 4 UK arable bird species (Rook, Linnet, Skylark, Yellowhammer) exposed to treated seeds of 3 spring-sown crops (beans, barley and linseed). We ran three types of model, 1) a "broods-at-risk" model looking at the temporal overlap between nesting and seed-sowing dates, and estimating the proportion of those nests that suffered toxicity-exposure ratios < 5; 2) a "seasonal success" Markov chain model estimating the number of chicks successfully raised in the course of a breeding season.; and 3) the potential effects of pesticides on population growth rates. Based on physiology, Rooks, should be less at risk from treated seeds than smaller species because bigger birds eat less as a proportion of their bodyweights. However, in nearly all our scenarios, Rooks were more vulnerable, followed by Skylark and Linnet, with Yellowhammer being least affected. A principal cause is that Rooks are more likely to be breeding at a time when treated seeds are being sown. Furthermore, whereas the other species may make several breeding attempts and early failures from pesticide exposure may be compensated by later successes, Rooks breed only once in a season. The results are also supported by historical evidence of Rook population declines following pesticide seed treatments.

Reflections on bird and mammal risk assessment for plant protection products in the European Union: Past, present, and future

The use of plant protection products on agricultural crops can result in exposure of birds and mammals to toxic chemicals. In the European Union, the risks from such exposures are assessed under the current (2009) guidance document from the European Food Safety Authority (EFSA), designed to increase the realism of the theoretical risk assessments in comparison to its predecessor (SANCO/4145/2000). Since its adoption over 7 yr ago, many plant protection products have been evaluated successfully using the 2009 EFSA guidance document. However, there are still significant areas of improvement recommended for future revisions of this guidance. The present Focus article discusses experiences to date with the current scheme, including levels of conservatism in input parameters and interpretation by regulatory authorities together with proposals for how the guidance document could be improved when it is revised in the not too distant future. Several areas for which further guidance is recommended have been identified, such as the derivation of ecologically relevant bird and mammal reproductive endpoints and the use of modeling approaches to contextualize risk assessments. Areas where existing databases could be improved were also highlighted, including the collation of relevant focal species across Europe and expansion of the residue database for food items. To produce a realistic and useable guidance document in the future, it is strongly recommended that there is open and constructive communication between industry, regulatory authorities, and the EFSA. Such collaboration would also encourage harmonization between member states, thus reducing workloads for both industry and regulatory authorities. Environ Toxicol Chem 2017;36:565-575. © 2017 SETAC.

Quantification of potential exposure of gray partridge (Perdix perdix) to pesticide active substances in farmlands

Estimating exposure of wild birds to plant protection products is of key importance in the risk assessment process evaluating their harmful potential. In this paper, we propose an ecologically-relevant methodology to estimate potential exposure to active substances (ASs) of a farmland focal bird, the gray partridge Perdix perdix. It is based on bird habitat use of fields at the time of pesticide applications. It accounts for spatio-temporal heterogeneity at population and landscape scales. We identify and quantify the potential exposure to 179 ASs of 140 clutches during pre-laying, laying, and incubation phases, and of 75 coveys. The data come from a large scale field study combining radiotelemetry and a farmer survey. They were collected in 12 different representative sites. The proportion of clutches potentially exposed to a given chemical was ≥5% for 32 ASs; prothioconazole and epoxiconazole ranking first. 71% of clutches were potentially exposed to ≥1 AS and 67% to ≥2 ASs. Mixtures involved 2 to 22 ASs. They emerged from commercial formulations, tank mixtures, bird habitat use, and combinations. ASs were fungicides (53%), herbicides (25%), and insecticides (16%) used on a variety of crops in April-June, when ground-nesting birds are breeding. The European Food Safety Authority conclusions report a long-term first-tier toxicity-to-exposure ratio (TERlt) <5 for 11 out of 19 documented ASs, and higher-tier TERlt <5 for 5 out of 10 ASs. This suggests a potential risk for bird reproduction in farmlands. Globally 13% of coveys were potentially exposed to 18 ASs during the first month (1-4 coveys per AS). The use of our field data in future research and risk assessment is discussed.

Detection and drivers of exposure and effects of pharmaceuticals in higher vertebrates

Pharmaceuticals are highly bioactive compounds now known to be widespread environmental contaminants. However, research regarding exposure and possible effects in non-target higher vertebrate wildlife remains scarce. The fate and behaviour of most pharmaceuticals entering our environment via numerous pathways remain poorly characterized, and hence our conception and understanding of the risks posed to wild animals is equally constrained. The recent decimation of Asian vulture populations owing to a pharmaceutical (diclofenac) offers a notable example, because the exposure route (livestock carcasses) and the acute toxicity observed were completely unexpected. This case not only highlights the need for further research, but also the wider requirement for more considered and comprehensive 'ecopharmacovigilance'. We discuss known and potential high risk sources and pathways in terrestrial and freshwater ecosystems where pharmaceutical exposure in higher vertebrate wildlife, principally birds and mammals, may occur. We examine whether approaches taken within existing surveillance schemes (that commonly target established classes of persistent or bioaccumulative contaminants) and the risk assessment approaches currently used for pesticides are relevant to pharmaceuticals, and we highlight where new approaches may be required to assess pharmaceutical-related risk.

Quantifying the effects of pesticide exposure on annual reproductive success of birds

The Markov chain nest productivity model (MCnest) was developed for quantifying the effects of specific pesticide-use scenarios on the annual reproductive success of simulated populations of birds. Each nesting attempt is divided into a series of discrete phases (e.g., egg laying, incubation, nestling rearing), and results from avian toxicity tests are used to represent the types of effects possible in the field during each breeding phase. The expected exposure dose each day throughout the breeding season can be compared to the toxicity thresholds assigned to each breeding phase to determine whether the nest attempt is at risk. The primary output of the model is an estimate of the number of successful nest attempts per female per year, which is multiplied by the number of fledglings per successful nest to estimate the number of fledglings per female per breeding season (i.e., annual reproductive success). In this article, we present a series of MCnest simulations to demonstrate the extent to which the magnitude of change in annual reproductive success can be affected by considering life history attributes and the timing of pesticide applications relative to a species' typical breeding phenology. For a given pesticide-use scenario, MCnest can identify which species are at greatest risk. By allowing multiple species to be run under a single scenario, it can also help to identify the life-history traits that contribute to a species' vulnerability to a given pesticide-use scenario. It also can determine which application dates have the greatest impact and demonstrate the extent to which pesticide characteristics (e.g., residue half-life, mode of action) affect productivity. MCnest goes beyond the current qualitative screening-level assessments of risks to avian reproduction to provide an approach for quantifying the reduction in annual reproductive success by integrating species life history and timing of pesticide exposures, despite limitations in existing information on species life history and toxicity responses from existing laboratory tests.

Selecting surrogate endpoints for estimating pesticide effects on avian reproductive success

A Markov chain nest productivity model (MCnest) has been developed for projecting the effects of a specific pesticide-use scenario on the annual reproductive success of avian species of concern. A critical element in MCnest is the use of surrogate endpoints, defined as measured endpoints from avian toxicity tests that represent specific types of effects possible in field populations at specific phases of a nesting attempt. In this article, we discuss the attributes of surrogate endpoints and provide guidance for selecting surrogates from existing avian laboratory tests as well as other possible sources. We also discuss some of the assumptions and uncertainties related to using surrogate endpoints to represent field effects. The process of explicitly considering how toxicity test results can be used to assess effects in the field helps identify uncertainties and data gaps that could be targeted in higher-tier risk assessments.

Population-level impacts of pesticide-induced chronic effects on individuals depend more on ecology than toxicology

The current method for assessing long-term risk of pesticides to mammals in the EU is based on the individual rather than the population-level and lacks ecological realism. Hence there is little possibility for regulatory authorities to increase ecological realism and understanding of risks at the population-level. Here we demonstrate how, using ABM modelling, assessments at the population-level can be obtained even for a pesticide with complex long-term effects such as epigenetic transmission of reproductive depression. By objectively fitting nonlinear models to the simulation outputs it was possible to compare population depression and recovery rates for a range of scenarios in which toxicity and exposure factors were varied. The system was differentially sensitive to the various factors, but vole ecology and behaviour were at least as important predictors of population-level effects as toxicology. This emphasises the need for greater focus on animal ecology in risk assessments.

Influence of avian reproduction ecotoxicological endpoints in the assessment of plant protection products

The aim of this paper is to examine the statistical relevance of bird species on the endpoints of avian long-term toxicity studies (eggs laid, eggs set, eggs hatching, embryo survivor, 14-day old survivors and eggshell thickness). Data from 561 animals of three different species (Colinus virginianus, Anas platyrynchos and Coturnix coturnix japonica) tested with five different pesticides were analyzed in this study. The substances considered were: Thiamethoxam (EZ-3-(2-chloro-1,3-thiazol-5-ylmethyl)-5-methyl-1,3,5-oxadiazinan-4-ylidene(nitro)amine), Thiacloprid ((Z)-3-(6-chloro-3-pyridylmethyl)-1,3-thiazolidin-2-ylidenecyanamide), Acetamiprid ((E)-N(1)-[(6-chloro-3-pyridyl)methyl]-N(2)-cyano-N(1)-methylacetamidine), Phosmet (O,O-dimethyl S-phthalimidomethyl phosphorodithioate) and Dicofol (2,2,2-trichloro-1,1-bis(4-chlorophenyl)ethanol). Several general lineal mixed models were conducted to evaluate the factors affecting variables used in long-term reproductive toxicity tests. Test significance was p < 0.01 in all models tested. Model R(2) value was high (0.80) for all variables except for eggs laid (R(2) = 0.42) for the three species studied. Tukey studentized range test showed significant differences among species and pesticides. For pre-hatching period the differences were significant for eggs laid and eggs set among species. C. japonica showed statistical differences for egg hatching. With respect to embryo survivor and 14 days old survival, significant different were found for C.virginianus and A. platyrynchos, respectively. These results indicate that the selected species have an influence in the endpoints to be used for risk assessment.

Case Study Part 1: How to calculate appropriate deterministic long-term toxicity to exposure ratios (TERs) for birds and mammals

In the European Union, first-tier assessment of the long-term risk to birds and mammals from pesticides is based on calculation of a deterministic long-term toxicity/exposure ratio (TER(lt)). The ratio is developed from generic herbivores and insectivores and applied to all species. This paper describes two case studies that implement proposed improvements to the way long-term risk is assessed. These refined methods require calculation of a TER for each of five identified phases of reproduction (phase-specific TERs) and use of adjusted No Observed Effect Levels (NOELs) to incorporate variation in species sensitivity to pesticides. They also involve progressive refinement of the exposure estimate so that it applies to particular species, rather than generic indicators, and relates spraying date to onset of reproduction. The effect of using these new methods on the assessment of risk is described. Each refinement did not necessarily alter the calculated TER value in a way that was either predictable or consistent across both case studies. However, use of adjusted NOELs always reduced TERs, and relating spraying date to onset of reproduction increased most phase-specific TERs. The case studies suggested that the current first-tier TER(lt )assessment may underestimate risk in some circumstances and that phase-specific assessments can help identify appropriate risk-reduction measures. The way in which deterministic phase-specific assessments can currently be implemented to enhance first-tier assessment is outlined.

A review and analysis of study endpoints relevant to the assessment of "long term" pesticide toxicity in avian and mammalian wildlife

The ecological assessment of long term or reproductive effects from pesticide exposure in birds and mammals is currently seen to be problematic. In birds especially, the current test results are difficult to extrapolate to a field situation. For example, whereas a majority of laboratory studies report clutch size reductions in response to graded pesticide doses, this effect is rarely, if ever, seen in the wild in response to exposure to toxicants. Also, current laboratory tests in birds provide a very truncated measure of reproductive performance. At the opposite end of the spectrum, the ecological assessment of long-term impacts to wild mammal populations suffers from an overabundance of very detailed information generated on a few rodent and non-rodent test species. It becomes critical here to identify which of the multitude of assessment endpoints should form the basis of an ecological assessment. Whether bird or mammal, I suggest that it is essential to separate parental from developmental endpoints and to apply the different effect levels to agent-based models of population growth and performance. Only then can we hope to gain a real understanding of the true long-term consequences of pesticide or other chemical exposure.

Case Study Part 2: Probabilistic modelling of long-term effects of pesticides on individual breeding success in birds and mammals

Long term exposure of skylarks to a fictitious insecticide and of wood mice to a fictitious fungicide were modelled probabilistically in a Monte Carlo simulation. Within the same simulation the consequences of exposure to pesticides on reproductive success were modelled using the toxicity-exposure-linking rules developed by R.S. Bennet et al. (2005) and the interspecies extrapolation factors suggested by R. Luttik et al. (2005). We built models to reflect a range of scenarios and as a result were able to show how exposure to pesticide might alter the number of individuals engaged in any given phase of the breeding cycle at any given time and predict the numbers of new adults at the season's end.

Risk assessment of UK skylark populations using life-history and individual-based landscape models

Following a workshop exercise, two models, an individual-based landscape model (IBLM) and a non-spatial life-history model were used to assess the impact of a fictitious insecticide on populations of skylarks in the UK. The chosen population endpoints were abundance, population growth rate, and the chances of population persistence. Both models used the same life-history descriptors and toxicity profiles as the basis for their parameter inputs. The models differed in that exposure was a pre-determined parameter in the life-history model, but an emergent property of the IBLM, and the IBLM required a landscape structure as an input. The model outputs were qualitatively similar between the two models. Under conditions dominated by winter wheat, both models predicted a population decline that was worsened by the use of the insecticide. Under broader habitat conditions, population declines were only predicted for the scenarios where the insecticide was added. Inputs to the models are very different, with the IBLM requiring a large volume of data in order to achieve the flexibility of being able to integrate a range of environmental and behavioural factors. The life-history model has very few explicit data inputs, but some of these relied on extensive prior modelling needing additional data as described in Roelofs et al. (2005, this volume). Both models have strengths and weaknesses; hence the ideal approach is that of combining the use of both simple and comprehensive modeling tools.

Estimating the exposure of birds and mammals to pesticides in long-term risk assessments

This paper reviews current EU pesticide risk assessment guidance [European Commission (2002) Guidance document on risk assessment for birds and mammals under council directive 91/414/EEC, SANCO/4145/2000EC 2002], and examines some of its assumptions and problems arising from them. Issues associated with obtaining data that adequately describes exposure over the appropriate time-scale are common to both acute and long-term risk assessments but are probably less problematic for long-term exposure. Improvements in problem formulation and ways in which temporal and spatial factors might be incorporated into long-term risk assessments are suggested. The most important temporal issue for long-term risk is how best to model the degree to which wildlife habits are predictable from day to day. In relation to spatial factors, it is suggested that long-term risk assessments could make better use of pesticide usage data that sample usage patterns throughout the UK. The usefulness of detailed simulated farming landscapes populated by wildlife represented as agent-based models, should be explored.