Seasonal diet-based resistance to anticoagulant rodenticides in the fossorial water vole (Arvicola amphibius).

Anticoagulant rodenticides (AR) resistance has been defined as "a major loss of efficacy due to the presence of a strain of rodent with a heritable and commensurately reduced sensitivity to the anticoagulant". The mechanism that supports this resistance has been identified as based on mutations in the Vkorc1 gene leading to severe resistance in rats and mice. This study evaluates the validity of this definition in the fossorial water vole and explores the possibility of a non-genetic diet-based resistance in a strict herbivorous rodent species. Genetic support was explored by sequencing the Vkorc1 gene and the diet-based resistance was explored by the dosing of vitamins K in liver of voles according to seasons. From a sample of 300 voles, only 2 coding mutations, G71R and S149I, were detected in the Vkorc1 gene in the heterozygous state with low allele frequencies (0.5-1%). These mutations did not modify the sensitivity to AR, suggesting an absence of genetic Vkorc1-based resistance in the water vole. On the contrary, vitamin K1 was shown to be 5 times more abundant in the liver of the water vole compared to rats. This liver concentration was shown to seasonally vary, with a trough in late winter and a peak in late spring/early summer related to the growth profile of grass. This increase in concentration might be responsible for the increased resistance of water voles to AR. This study highlights a non-genetic, diet-related resistance mechanism in rodents to AR. This diet-based resistance might explain the different evolution of the Vkorc1 gene in the fossorial water vole compared to rats and mice.

Impact of ageing and soil contaminants on telomere length in the land snail.

Telomeres (TLs) are non-coding DNA sequences that are usually shortened with ageing and/or chemical exposure. Bioindicators such as the land snail can be used to assess the environmental risk of contaminated soils. As for most invertebrates, the evolution of TLs with ageing or exposure to contaminants is unknown in this mollusc. The aims of this study were to explore the relationships between ageing, contaminant exposure, sublethal effects and TL length in the terrestrial gastropod Cantareus aspersus. TL length was investigated in haemocytes from five age classes of C. aspersus. The impact of contaminants on sub-adult snails exposed to Cd, Hg or a mixture of polycyclic aromatic hydrocarbons (PAHs) in soils for one or two months was studied. Bioaccumulation, growth, sexual maturity and TLs were measured. TL attrition was significant for the juvenile and sub-adult stages, but not later. Exposure to Cd increased the mortality (around 30%). Exposure to polluted soils inhibited growth (19-40%) and sexual maturity (6-100%). Although the health of the snails exposed to Cd, Hg and PAHs was altered, TL length in haemocytes was not disturbed, suggesting a high capacity of this snail species to maintain its TLs in haemocytes under chemical stress. These results first address TL length in snails and reveal that the relationship commonly proposed for vertebrates between TL shortening and ageing or exposure to contaminants cannot be generalized.

Unintentional wildlife poisoning and proposals for sustainable management of rodents.

In Europe, bromadiolone, an anticoagulant rodenticide authorized for plant protection, may be applied intensively in fields to control rodents. The high level of poisoning of wildlife that follows such treatments over large areas has been frequently reported. In France, bromadiolone has been used to control water voles (Arvicola terrestris) since the 1980s. Both regulation and practices of rodent control have evolved during the last 15 years to restrict the quantity of poisoned bait used by farmers. This has led to a drastic reduction of the number of cases of poisoned wildlife reported by the French surveillance network SAGIR. During the autumn and winter 2011, favorable weather conditions and high vole densities led to the staging of several hundreds of Red Kites (Milvus milvus) in the Puy-de-Dôme department (central France). At the same time, intensive treatments with bromadiolone were performed in this area. Although no misuse has been mentioned by the authorities following controls, 28 Red Kites and 16 Common Buzzards (Buteo buteo) were found dead during surveys in November and December 2011. For all these birds, poisoning by bromadiolone as the main cause of death was either confirmed or highly suspected. Other observations suggest a possible impact of bromadiolone on the breeding population of Red Kites in this area during the spring 2011. French regulation of vole control for plant protection is currently under revision, and we believe this event calls for more sustainable management of rodent outbreaks. Based on large-scale experiments undertaken in eastern France, we propose that direct control of voles at low density (with trapping or limited chemical treatments) and mechanical destruction of vole tunnels, mole control, landscape management, and predator fostering be included in future regulation because such practices could help resolve conservation and agricultural issues.

Scavenging of rodent carcasses following simulated mortality due to field applications of anticoagulant rodenticide.

Worldwide, agricultural uses of anticoagulant rodenticides (ARs) cause poisonings of non-target wildlife as observed in France where bromadiolone is used to control water vole outbreaks. Following bromadiolone field application, a part of the vole population may die aboveground of the treated plots and thus, can represent an important risk of secondary poisoning for scavengers. In this study, water voles were trapped in a non-treated area and their carcasses were placed aboveground in plots located in an area where a vole outbreak occurred. Then, the environmental persistence, the diurnal and nocturnal scavenging rates of water vole carcasses were assessed in autumn 2011 and in spring 2012. The diurnal scavenger species were also identified. The environmental persistence of the carcasses to reach at least a scavenging rate of 87.5 % was 0.5-1.5 day. The average rates of diurnal and nocturnal scavenging ranged from 67 to 100 % and 5 to 100 %, respectively. They depended on the composition of the scavenger community present near the monitored plots; diurnal scavenging rates being higher with corvids than with raptors. In autumn, the red kite and the common buzzard were the main scavengers in one of the plots, what suggests a high risk of poisoning for these raptors during post-nuptial migration. So, the collection of vole carcasses after treatments and the limitations of bromadiolone applications when high densities of predators/scavengers are observed could be implemented to mitigate the risks of secondary poisoning.

Wildlife ecotoxicology of plant protection products: knowns and unknowns about the impacts of currently used pesticides on terrestrial vertebrate biodiversity.

Agricultural practices are a major cause of the current loss of biodiversity. Among postwar agricultural intensification practices, the use of plant protection products (PPPs) might be one of the prominent drivers of the loss of wildlife diversity in agroecosystems. A collective scientific assessment was performed upon the request of the French Ministries responsible for the Environment, for Agriculture and for Research to review the impacts of PPPs on biodiversity and ecosystem services based on the scientific literature. While the effects of legacy banned PPPs on ecosystems and the underlying mechanisms are well documented, the impacts of current use pesticides (CUPs) on biodiversity have rarely been reviewed. Here, we provide an overview of the available knowledge related to the impacts of PPPs, including biopesticides, on terrestrial vertebrates (i.e. herptiles, birds including raptors, bats and small and large mammals). We focused essentially on CUPs and on endpoints at the subindividual, individual, population and community levels, which ultimately linked with effects on biodiversity. We address both direct toxic effects and indirect effects related to ecological processes and review the existing knowledge about wildlife exposure to PPPs. The effects of PPPs on ecological functions and ecosystem services are discussed, as are the aggravating or mitigating factors. Finally, a synthesis of knowns and unknowns is provided, and we identify priorities to fill gaps in knowledge and perspectives for research and wildlife conservation.

Effects of chronic exposure to toxic metals on haematological parameters in free-ranging small mammals.

Blood circulates through the vascular system to carry oxygen, nutrients and metabolites to and away from tissues, and as such is a key-component of animal physiology. The impacts of metal pollution on blood, however, are poorly documented in free-ranging vertebrates. While the counteracting effect of selenium on mercury toxicity is well known in marine mammals, its potential role against the toxicity of other metals is less studied, especially on terrestrial wildlife. We explored the consequences of chronic exposure to two non-essential metals (cadmium and lead) along a pollution gradient in Northern France, on eleven haematological parameters in two free ranging small mammals, the wood mouse Apodemus sylvaticus and the bank vole Myodes glareolus. We hypothesized that haematology was related to metal concentrations in tissues, and that selenium might exert modulating effects. Concentrations of cadmium and lead in the tissues indicated an increased chronic exposure to and accumulation of metals along the gradient. Some haematological parameters were not explained by any measured variables while some others varied only with gender or age. Red blood cells, red blood cells distribution width, and blood iron concentration, however, decreased with increasing cadmium in the tissues in wood mice. Red blood cells and haemoglobin decreased with increasing renal lead and hepatic cadmium, respectively, in bank voles. Red blood cells distribution width in wood mice increased with cadmium concentrations in the liver but this was counteracted by high selenium levels in the same organ. An interaction of selenium and lead on red blood cells was also observed in bank voles. Further, selenium concentrations were associated with an increase of monocytes in wood mice. The present results show that toxic metals were related to haematology changes, particularly erythrocyte indicators, and that some essential elements like selenium should be measured as well since they may counteract toxic effects.

Metals in the Réunion harrier: tissue concentrations and meaning for conservation.

The Réunion harrier is an endemic raptor on Réunion Island. Several threats endanger its population, poisoning by rodenticides being considered as the main one currently. No information is available on its exposure to other chemicals notably trace metal elements such as lead (Pb), mercury (Hg), and cadmium (Cd). The Réunion harrier is still a victim of poaching nowadays. When shooting is not lethal, animals may carry embedded shot in their body and thus be exposed to toxic level of Pb as demonstrated for other raptors. Moreover, recent monitoring suggests a decrease of its breeding success over time. It is known that Hg and Cd could impair reproduction and disturb embryo development in birds. The aim is to measure metal concentrations in the tissues of 30 carcasses of harrier collected from 2016 to 2021. Lead was analyzed in the liver and humerus, while Hg and Cd were measured in livers. Concentrations were compared to toxicological reference values. Overall, the Réunion harrier was not exposed to toxic levels of Pb or Cd. For Hg, 53% of the individuals have residues higher than the threshold compatible with oxidative stress, and 13% have liver concentrations above those compatible with reproduction impairment. A positive correlation was found between the proportion of urban habitat in a 55 km2 area centered on the location where the harrier was found and the concentration of Hg in the liver. We conclude that Hg exposure could be a threat for the Réunion harrier population and recommend monitoring the exposure of the most sensitive stages, i.e., embryos and nestlings, to this metal with non-invasive methods.

Impacts of neonicotinoids on biodiversity: a critical review.

Neonicotinoids are the most widely used class of insecticides in the world, but they have raised numerous concerns regarding their effects on biodiversity. Thus, the objective of this work was to do a critical review of the contamination of the environment (soil, water, air, biota) by neonicotinoids (acetamiprid, clothianidin, imidacloprid, thiacloprid, thiamethoxam) and of their impacts on terrestrial and aquatic biodiversity. Neonicotinoids are very frequently detected in soils and in freshwater, and they are also found in the air. They have only been recently monitored in coastal and marine environments, but some studies already reported the presence of imidacloprid and thiamethoxam in transitional or semi-enclosed ecosystems (lagoons, bays, and estuaries). The contamination of the environment leads to the exposure and to the contamination of non-target organisms and to negative effects on biodiversity. Direct impacts of neonicotinoids are mainly reported on terrestrial invertebrates (e.g., pollinators, natural enemies, earthworms) and vertebrates (e.g., birds) and on aquatic invertebrates (e.g., arthropods). Impacts on aquatic vertebrate populations and communities, as well as on microorganisms, are less documented. In addition to their toxicity to directly exposed organisms, neonicotinoid induce indirect effects via trophic cascades as demonstrated in several species (terrestrial and aquatic invertebrates). However, more data are needed to reach firmer conclusions and to get a clearer picture of such indirect effects. Finally, we identified specific knowledge gaps that need to be filled to better understand the effects of neonicotinoids on terrestrial, freshwater, and marine organisms, as well as on ecosystem services associated with these biotas.

Main conclusions and perspectives from the collective scientific assessment of the effects of plant protection products on biodiversity and ecosystem services along the land-sea continuum in France and French overseas territories.

Preservation of biodiversity and ecosystem services is critical for sustainable development and human well-being. However, an unprecedented erosion of biodiversity is observed and the use of plant protection products (PPP) has been identified as one of its main causes. In this context, at the request of the French Ministries responsible for the Environment, for Agriculture and for Research, a panel of 46 scientific experts ran a nearly 2-year-long (2020-2022) collective scientific assessment (CSA) of international scientific knowledge relating to the impacts of PPP on biodiversity and ecosystem services. The scope of this CSA covered the terrestrial, atmospheric, freshwater, and marine environments (with the exception of groundwater) in their continuity from the site of PPP application to the ocean, in France and French overseas territories, based on international knowledge produced on or transposable to this type of context (climate, PPP used, biodiversity present, etc.). Here, we provide a brief summary of the CSA's main conclusions, which were drawn from about 4500 international publications. Our analysis finds that PPP contaminate all environmental matrices, including biota, and cause direct and indirect ecotoxicological effects that unequivocally contribute to the decline of certain biological groups and alter certain ecosystem functions and services. Levers for action to limit PPP-driven pollution and effects on environmental compartments include local measures from plot to landscape scales and regulatory improvements. However, there are still significant gaps in knowledge regarding environmental contamination by PPPs and its effect on biodiversity and ecosystem functions and services. Perspectives and research needs are proposed to address these gaps.

Field mixtures of currently used pesticides in agricultural soil pose a risk to soil invertebrates.

Massive use of pesticides in conventional agriculture leads to accumulation in soil of complex mixtures, triggering questions about their potential ecotoxicological risk. This study assessed cropland soils containing pesticide mixtures sampled from conventional and organic farming systems at La Cage and Mons, France. The conventional agricultural field soils contained more pesticide residues (11 and 17 versus 3 and 11, respectively) and at higher concentrations than soils from organic fields (mean 6.6 and 10.5 versus 0.2 and 0.6 µg kg-1, respectively), including systemic insecticides belonging to neonicotinoids, carbamate herbicides and broad-spectrum fungicides mostly from the azole family. A risk quotient (RQi) approach evaluated the toxicity of the pesticide mixtures in soil, assuming concentration addition. Based on measured concentrations, both conventional agricultural soils posed high risks to soil invertebrates, especially due to the presence of epoxiconazole and imidacloprid, whereas soils under organic farming showed negligible to medium risk. To confirm the outcome of the risk assessment, toxicity of the soils was determined in bioassays following standardized test guidelines with seven representative non-target invertebrates: earthworms (Eisenia andrei, Lumbricus rubellus, Aporrectodea caliginosa), enchytraeids (Enchytraeus crypticus), Collembola (Folsomia candida), oribatid mites (Oppia nitens), and snails (Cantareus aspersus). Collembola and enchytraeid survival and reproduction and land snail growth were significantly lower in soils from conventional compared to organic agriculture. The earthworms displayed different responses: L. rubellus showed higher mortality on soils from conventional agriculture and large body mass loss in all field soils, E. andrei showed considerable mass loss and strongly reduced reproduction, and A. caliginosa showed significantly reduced acetylcholinesterase activity in soils from conventional agriculture. The oribatid mites did not show consistent differences between organic and conventional farming soils. These results highlight that conventional agricultural practices pose a high risk for soil invertebrates and may threaten soil functionality, likely due to additive or synergistic "cocktail effects".

Pervasive exposure of wild small mammals to legacy and currently used pesticide mixtures in arable landscapes.

Knowledge gaps regarding the potential role of pesticides in the loss of agricultural biodiversity worldwide and mixture-related issues hamper proper risk assessment of unintentional impacts of pesticides, rendering essential the monitoring of wildlife exposure to these compounds. Free-ranging mammal exposure to legacy (Banned and Restricted: BRPs) and currently used (CUPs) pesticides was investigated, testing the hypotheses of: (1) a background bioaccumulation for BRPs whereas a "hot-spot" pattern for CUPs, (2) different contamination profiles between carnivores and granivores/omnivores, and (3) the role of non-treated areas as refuges towards exposure to CUPs. Apodemus mice (omnivore) and Crocidura shrews (insectivore) were sampled over two French agricultural landscapes (n = 93). The concentrations of 140 parent chemicals and metabolites were screened in hair samples. A total of 112 compounds were detected, showing small mammal exposure to fungicides, herbicides and insecticides with 32 to 65 residues detected per individual (13-26 BRPs and 18-41 CUPs). Detection frequencies exceeded 75% of individuals for 13 BRPs and 25 CUPs. Concentrations above 10 ng/g were quantified for 7 BRPs and 29 CUPs (in 46% and 72% of individuals, respectively), and above 100 ng/g for 10 CUPs (in 22% of individuals). Contamination (number of compounds or concentrations) was overall higher in shrews than rodents and higher in animals captured in hedgerows and cereal crops than in grasslands, but did not differ significantly between conventional and organic farming. A general, ubiquitous contamination by legacy and current pesticides was shown, raising issues about exposure pathways and impacts on ecosystems. We propose a concept referred to as "biowidening", depicting an increase of compound diversity at higher trophic levels. This work suggests that wildlife exposure to pesticide mixtures is a rule rather than an exception, highlighting the need for consideration of the exposome concept and questioning appropriateness of current risk assessment and mitigation processes.

Investigations of responses to metal pollution in land snail populations (Cantareus aspersus and Cepaea nemoralis) from a smelter-impacted area.

A cross-transplantation field experiment was performed to investigate about possible adaptation/acclimatization to metal pollution in common garden snail Cantareus aspersus (ex-Helix aspersa) and brown-lipped grove snail Cepaea nemoralis populations. Adults were collected from an area surrounding a former smelter (ME), highly polluted by trace metals (TMs) for decades, and from an unpolluted site (BE). Subadults of first generation (F1) were exposed in microcosms in a 28-day kinetic study. Four exposure sites were chosen around the smelter along a soil pollution gradient (vegetation and soil otherwise comparable). Bioaccumulation in snail soft tissues globally increased with soil contamination, with Cd, Pb and Zn concentrations reaching 271, 187, 5527 µg g(-1), respectively. Accumulation kinetic patterns were similar between snail species but C. nemoralis showed greater TM levels than C. aspersus. Some inter-population differences were revealed in TM accumulation (bioaccumulation factors, accumulation kinetics) but did not suggest consistent adaptive responses. We did not detect negative effects of TM exposure on snail condition (body weight, shell size, shell weight). ME C. aspersus snails produced heavier shells than BE snails under exposure to TMs at the highest level, suggesting an adaptive response. The protocol used in this study, however, did not allow unambiguously distinguishing whether this response was due to genetic adaptation or to maternal effects. Abnormal but reversible shell development of adult ME C. nemoralis suggested physiological acclimatization. Differences in responses to TMs between populations are observed for conchological parameters, not for bioaccumulation, with different strategies according to the species (acclimatization or adaptation/maternal effects).

Numerical response of predators to large variations of grassland vole abundance and long-term community changes.

Voles can reach high densities with multiannual population fluctuations of large amplitude, and they are at the base of predator communities in Northern Eurasia and Northern America. This status places them at the heart of management conflicts wherein crop protection and health concerns are often raised against conservation issues. Here, a 20-year survey describes the effects of large variations in grassland vole populations on the densities and the daily theoretical food intakes (TFI) of vole predators based on roadside counts. Our results show how the predator community responded to prey variations of large amplitude and how it reorganized with the increase in a dominant predator, here the red fox, which likely negatively impacted hare, European wildcat, and domestic cat populations. This population increase did not lead to an increase in the average number of predators present in the study area, suggesting compensations among resident species due to intraguild predation or competition. Large variations in vole predator number could be clearly attributed to the temporary increase in the populations of mobile birds of prey in response to grassland vole outbreaks. Our study provides empirical support for more timely and better focused actions in wildlife management and vole population control, and it supports an evidence-based and constructive dialogue about management targets and options between all stakeholders of such socio-ecosystems.

Modelling and spatial discrimination of small mammal assemblages: an example from western Sichuan (China).

We investigate the relationship between landscape heterogeneity and the spatial distribution of small mammals in two areas of Western Sichuan, China. Given a large diversity of species trapped within a large number of habitats, we first classified small mammal assemblages and then modelled the habitat of each in the space of quantitative environmental descriptors. Our original two step "classify then model" procedure is appropriate for the frequently encountered study scenario: trapping data collected in remote areas with sampling guided by expert field knowledge.In the classification step, we defined assemblages by grouping sites of similar species composition and relative densities using an expert-class-merging procedure which reduced redundancy in the habitat factor used within a multinomial logistic regression predicting species trapping probabilities. Assemblages were thus defined as mixtures of small mammal frequency distributions in discrete groups of sampled sites.In the modelling step, assemblages' habitats and environments of the two sampled areas were discriminated in the space of remotely sensed environmental descriptors. First, we compared the discrimination of assemblage/study areas by linear and non-linear forms of Discriminant Analysis (Linear Discriminant Analysis versus Mixture Discriminant Analysis) and of Multiple Regression (Generalized Linear Models versus Multiple Adaptive Regression Splines). The "best" predictive modelling technique was then used to quantify the contribution of each environmental variable in discriminations of assemblages and areas.Mixtures of Gaussians provided a more efficient model of assemblage coverage in environmental space than a single Gaussian cluster model. However, non-linearity in assemblage response to environmental gradients was consistently predicted with lower deviance and misclassification error by Multiple Adaptive Regression Splines. The two study areas were mainly discriminated along vegetation indices. However, although the Normalized Difference Vegetation Index (NDVI) could discriminate forested from non-forested habitats, its power to discriminate assemblages in Maerkang, where a greater diversity of forest habitat was observed, was seen to be limited, and in this case NDVI was outperformed by the Enhanced Vegetation Index (EVI). Our analyses highlight previously unobserved differences between the environments and small mammal communities of two fringe areas of the Tibetan plateau and suggests that a biogeograph-ical approach is required to elucidate ecological processes in small mammal communities and to reduce extrapolation uncertainty in distribution mapping.

Telomere dynamic in humans and animals: Review and perspectives in environmental toxicology.

Telomeres (TLs) play major roles in stabilizing the genome and are usually shortened with ageing. The maintenance of TLs is ensured by two mechanisms involving telomerase (TA) enzyme and alternative lengthening telomeres (ALT). TL shortening and/or TA inhibition have been related to health effects on organisms (leading to reduced reproductive lifespan and survival), suggesting that they could be key processes in toxicity mechanisms (at molecular and cellular levels) and relevant as an early warning of exposure and effect of chemicals on human health and animal population dynamics. Consequently, a critical analysis of knowledge about relationships between TL dynamic and environmental pollution is essential to highlight the relevance of TL measurement in environmental toxicology. The first objective of this review is to provide a survey on the basic knowledge about TL structure, roles, maintenance mechanisms and causes of shortening in both vertebrates (including humans) and invertebrates. Overall, TL length decreases with ageing but some unexpected exceptions are reported (e.g., in species with different lifespans, such as the nematode Caenorhabditis elegans or the crustacean Homarus americanus). Inconsistent results reported in various biological groups or even between species of the same genus (e.g., the microcrustacean Daphnia sp.) indicate that the relation usually proposed between TL shortening and a decrease in TA activity cannot be generalized and depends on the species, stage of development or lifespan. Although the scientific literature provides evidence of the effect of ageing on TL shortening, much less information on the relationships between shortening, maintenance of TLs, influence of other endogenous and environmental drivers, including exposure to chemical pollutants, is available, especially in invertebrates. The second objective of this review is to connect knowledge on TL dynamic and exposure to contaminants. Most of the studies published on humans rely on correlative epidemiological approaches and few in vitro experiments. They have shown TL attrition when exposed to contaminants, such as polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), pesticides and metallic elements (ME). In other vertebrates, the studies we found deals mainly with birds and, overall, report a disturbance of TL dynamic consecutively to exposure to chemicals, including metals and organic compounds. In invertebrates, no data are available and the potential of TL dynamic in environmental risk assessment remains to be explored. On the basis of the main gaps identified some research perspectives (e.g., impact of endogenous and environmental drivers, dose response effects, link between TL length, TA activity, longevity and ageing) are proposed to better understand the potential of TL and TA measurements in humans and animals in environmental toxicology.

Do bromadiolone treatments to control grassland water voles (Arvicola scherman) affect small mustelid abundance?

BACKGROUND: The use of pesticides can affect non-target species by causing population declines through indirect intoxication. Small mustelids (SMs; weasels, Mustela nivalis L.; stoats, Mustela erminea L.) consume water voles (WVs, Arvicola scherman S.) and can be exposed to bromadiolone, an anticoagulant rodenticide used in some countries to reduce WV damage to grasslands. Here, we investigated whether bromadiolone affected SM abundance. RESULTS: We monitored SM abundance using footprint tracking tunnels in spring and autumn at ten sites. Among these sites, four were treated with bromadiolone, while six were not treated. We found reduced SM abundance at these four sites from spring to autumn (treated sites, mean ± SE SM abundance change = -1.68 ± 0.42; untreated sites, 0.29 ± 0.25). Using a linear model, we observed that SM abundance decreased as a function of the quantity of bromadiolone applied during the 3 months before the autumn estimate. We found that WV abundance increased at treated sites (linear model, treated sites, mean ± SE WV abundance change = 1.4 ± 0.4; untreated sites, 0.33 ± 0.25). Thus, at treated sites, SM abundance declined despite increased food availability. By analyzing residues in vole livers and SM scats we showed that SMs may be exposed to bromadiolone at the sites where this compound was used. CONCLUSION: This study is the first to document the relationship between SM abundance and bromadiolone usage for small mammal control. Declines in SM abundance were observed at treated sites, where bromadiolone residue was found in SM scats. This correlative approach suggests that bromadiolone treatment may lead to seasonal SM declines and associated WV increases. © 2018 Society of Chemical Industry.

Kinetics of bromadiolone in rodent populations and implications for predators after field control of the water vole, Arvicola terrestris.

We document the kinetics of bromadiolone in two rodent populations after a field control of water voles, and their implications for predator exposure. Water voles and common voles were trapped aboveground and underground from 1 to 135 days after bromadiolone treatment in the field. Livers, digestive tracts, and rests of the body were analyzed separately. Our results indicate that 99.6% of the water voles trapped underground and 41% of the common voles trapped aboveground contain bromadiolone residues. Concentrations were maximal between 3.3 and 6.5 days after treatment, according to the tissues examined and the model applied for water voles, and after 1.3 to 3.7 days for common voles. Water voles appeared available almost exclusively for foraging predators. Common voles, found less likely to be poisoned and exhibiting weaker concentrations, were mainly sampled aboveground. The liver, primarily eaten by some predators and scavengers, contains a larger bromadiolone quantity (59% of the total amount found in water voles). The rejection of the digestive tract by those species may lead to a subsequent consumption of voles with higher bromadiolone concentrations (from +3.8 to +5.8% of concentration) and provide a moderate risk increase. After 135 days, eight of the ten water voles and one of the two common voles exhibited detectable residues. Additionally, one specimen presented higher concentrations than the others, and similar to those measured in Voles trapped between the first 15-20 days. This may have consequences on predator intoxications several months after treatment. These results integrate individual differences for the two main rodent species present in treated areas. Implications for predator exposure were investigated at the end of the study and suggest that, if the risk of secondary poisoning is maximal during the first 15-20 days when the rodent densities remain high, exposure conditions are maintained for at least 135 days.

Kinetic and dynamic aspects of soil-plant-snail transfer of cadmium in the field.

The proper use of bioaccumulation in the assessment of environmental quality involves accounting for chemical fluxes in organisms. Cadmium (Cd) accumulation kinetics in a soil-plant-snail food chain were therefore investigated in the field under different soil contamination (from 0 to 40 mg kg(-1)), soil pH (6 and 7) and season. Allowing for an accurate and sensitive assessment of Cd transfer to snails, toxicokinetics appears an interesting tool in the improvement of risk assessment procedures and a way to quantify metal bioavailability for a defined target. On the basis of uptake fluxes, snails proved to be sensitive enough to distinguish moderate soil contaminations. The soil pH did not appear, in the range studied, as a modulating parameter of the Cd transfer from soil to snail whereas the season, by influencing the snail mass, may modify the internal concentrations. The present data specifying a time integrated assessment of environmental factors on metal bioavailability and transfer to terrestrial snails should ensure their rational use in environmental biomonitoring.

Biotic interactions modify the transfer of cesium-137 in a soil-earthworm-plant-snail food web.

The present study investigated the possible influence of the earthworm Aporrectodea tuberculata on the transfer of cesium-137 ((137)Cs) from a contaminated (130 Bq/kg) deciduous forest soil to the lettuce Lactuca sativa and to the snail Cantareus aspersus (formerly Helix aspersa) in two laboratory experiments. In the first experiment, the International Organization for Standardization 15952 test was used to expose snails for five weeks to contaminated soil with or without earthworms. In these conditions, the presence of earthworms caused a two- to threefold increase in (137)Cs concentrations in snails. Transfer was low in earthworms as well as in snails, with transfer factors (TFs) lower than 3.7 x 10(-2). Activity concentrations were higher in earthworms (2.8- 4.8 Bq/kg dry mass) than in snails (<1.5 Bq/kg). In the second experiment, microcosms were used to determine the contribution of soil and lettuce in the accumulation of (137)Cs in snails. Results suggest that the contribution of lettuce and soil is 80 and 20%, respectively. Microcosms also were used to study the influence of earthworms on (137)Cs accumulation in snail tissues in the most ecologically relevant treatment (soil-earthworm-plant-snail food web). In this case, soil-to-plant transfer was high, with a TF of 0.8, and was not significantly modified by earthworms. Conversely, soil-to-snail transfer was lower (TF, approximately 0.1) but was significantly increased in presence of earthworms. Dose rates were determined in the microcosm study with the EDEN (elementary dose evaluation for natural environment) model. Dose rates were lower than 5.5 x 10(-4) mGy/d, far from values considered to have effects on terrestrial organisms (1 mGy/d).

How subcellular partitioning can help to understand heavy metal accumulation and elimination kinetics in snails.

To understand bioaccumulation kinetics of metals within biota inhabiting industrially contaminated soils, toxicokinetic dynamics and subcellular fractionation were carried out with the terrestrial snail Helix aspersa in a long-term (six-month) laboratory experiment. Accumulation and elimination kinetics were determined for Cd, Pb, and Zn in both viscera and foot of snails and were described accurately by one-compartment models. The subcellular fractions were obtained by sequential centrifugations and were analyzed by isolating metal-rich granules, tissue fragments, and cytosolic fractions. Different fractions showed metal-specific binding capacities that might be useful in identifying the biological significance of accumulated metal levels in snails. Cadmium was retrieved mainly from the cytosolic fraction, where it was stored in the long term and not excreted, thus explaining the linear accumulation patterns. Most of the accumulated Pb was found in the granular fraction, and snails appeared able to excrete these concretions, leading to achievement of a steady state in internal Pb body burdens. Significant levels of Pb, however, were retrieved at the end of the depuration phase and retained in the cell debris fraction. Zinc showed affinities for both cytosolic and granular fractions, leading to intermediate uptake and excretion patterns. The dynamics of the different sequestration forms at the subcellular level support the observed kinetics of metal body burdens and, in association with the determination of uptake fluxes, allow precise assessment of metal accumulation in snails.