An Assessment of the Potential Hazards of Anticoagulant Rodenticides to Plethodontid Salamanders

We assessed the hazards of the anticoagulants diphacinone and brodifacoum to salamanders of the family Plethodontidae or lungless salamanders. We completed this research in anticipation of an attempt to eradicate the invasive house mouse (Mus musculus) from the Farallon Islands National Wildlife Refuge, California, USA, where the endemic subspecies Farallon arboreal salamander (Aneides lugubris farallonensis) occurs. We exposed live-captured salamanders of 3 species (Aneides lugubris, Ensatina eschscholzii xanthoptica, and Batrachoseps attenuatus) to anticoagulant rodenticides by both oral and dermal exposure routes in laboratories at the U.S. Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Services, National Wildlife Research Center, Fort Collins, Colorado, USA. The amount of exposure was high, simulating a worst-case scenario. There were some deaths (9 of 37 treated salamanders; 24.3% mortality). We did not observe the sublethal effects of weight loss or reduced food (cricket) consumption that has been observed in studies of other taxa (mammals and birds). Skin sloughing and sores on the undersides of certain salamanders exposed to rodenticides as well as some controls left it unclear whether this effect was caused by the anticoagulant. Following trial completion, we analyzed whole bodies of salamanders for rodenticide residues. Residue concentrations were very low (million) when compared with results from some other studies. We concluded that while anticoagulant rodenticide posed some hazards (both lethal and sublethal) to salamanders, the level appears to be relatively low, especially given the very high exposure rates applied in this study compared to the exposure they would encounter in an aerial broadcast of rodenticide baits in an invasive rodent eradication project

Determination of residue levels of the avicide 3-chloro-4-methylaniline hydrochloride in red-winged blackbirds (\u3ci\u3eAgelaius phoeniceus\u3c/i\u3e) by gas chromatography-tandem mass spectrometry

The avicide 3‑chloro‑4‑methylanaline hydrochloride (chloro‑p‑toluidine hydrochloride, CPTH, DRC-1339) is used to control pest bird species that damage agricultural crops. A specific and sensitive gas chromatographytandem mass spectrometry method was developed and validated for the determination of CPTH in avian breast muscle, GI tract, kidney, and liver. Tissue samples were extracted with a solution of acidified water and acetonitrile. The sample was made basic and cleaned up with a combination of liquid-liquid partitioning and solid phase extraction. Separation was achieved using a HP-5 ultra-inert GC column (15 M, 0.25 μm film) with detection on a triple quadrupole mass spectrometer in multiple reaction monitoring (MRM) mode. The monitored transition for CPTH was m/z 140.9→106.2 for quantitation and 139.9→105.2 and 139.9→77.2 for confirmation. The linear range was 5 to 5000 ng/mL. The precision for the determination of CPTH in all tissues averaged 7.2% and the accuracy averaged 6.7%. The recovery of CPTH fortified at 5 different levels averaged 101% in liver, 98.8% in GI tract, 92.9% in breast muscle, and 87.9% in kidney. The established method was successfully used to determine CPTH residue levels in red-winged blackbirds exposed to three different doses of CPTH

Brodifacoum residues in fish three years after an island-wide rat eradication attempt in the tropical Pacific

Invasive rats are known to threaten natural resources and human health and safety. Island-wide rat eradication attempts have been increasing in number and scale during the past several decades, as has the frequency of eradication success. The most common method to remove all rats from an island is to broadcast anticoagulant rodenticide bait into every rat’s home range on the island. Broadcast of toxicants can put humans and other nontarget species in marine and terrestrial environments at risk of exposure. The persistence of anticoagulant residues is somewhat unknown, particularly in marine environments. Three years after ~ 18,000 kg of 25 mg/kg brodifacoum bait was broadcast across Wake Atoll to eliminate rats, we collected whole-body fish samples from six near-shore sites and one intermittently land- locked pond to test for brodifacoum residues. Of the 69 samples tested using high- performance liquid chromatography with fluorescence detection, 20 were suspected of brodifacoum contamination and therefore subject to more selective liquid chromatography-mass spectrometry analysis. Of those 20 fish, brodifacoum was detected in two individuals of blacktail snapper (Lutjanus fulvus), although at levels too low to be accurately quantified. Both fish containing detectable brodifacoum residues were caught within an intermittently land-locked pond in an area of the island that received heavy brodifacoum baiting, and not truly in the “marine environment”. Brodifacoum was not detected in any of the samples collected within the lagoon of the atoll or within near-shore waters outside the lagoon. These results demonstrate that under some circumstances very low levels of brodifacoum can occur in a low proportion of fish tissues for as long as three years after the application of the rodenticide to an environment. Such information is valuable in assessing the relative environmental risks associated with rodenticide use in rodent eradications for protection of threatened species and restoration of island ecosystems. The overall result is one of declining incidence and magnitude of residue concentrations over time and within limited environmental circumstances

Making predictions in a changing world: The benefits of individual-based ecology

Ecologists urgently need a better ability to predict how environmental change affects biodiversity. We examine individual-based ecology (IBE), a research paradigm that promises better a predictive ability by using individual-based models (IBMs) to represent ecological dynamics as arising from how individuals interact with their environment and with each other. A key advantage of IBMs is that the basis for predictions-fitness maximization by individual organisms-is more general and reliable than the empirical relationships that other models depend on. Case studies illustrate the usefulness and predictive success of long-term IBE programs. The pioneering programs had three phases: conceptualization, implementation, and diversification. Continued validation of models runs throughout these phases. The breakthroughs that make IBE more productive include standards for describing and validating IBMs, improved and standardized theory for individual traits and behavior, software tools, and generalized instead of system-specific IBMs. We provide guidelines for pursuing IBE and a vision for future IBE research

Is Sensitivity to Anticoagulant Rodenticides Affected by Repeated Exposure in Hawks?

A seminal question in wildlife toxicology is whether exposure to an environmental contaminant, in particular a secondgeneration anticoagulant rodenticide, can evoke subtle long lasting effects on body condition, physiological function and survival. Many reports indicate that non-target predators often carry residues of several rodenticides, which is indicative of multiple exposures. An often-cited study in laboratory rats demonstrated that exposure to the second-generation anticoagulant rodenticide brodifacoum prolongs blood clotting time for a few days, but weeks later when rats were re-exposed to the first-generation anticoagulant rodenticide warfarin, coagulopathy was more pronounced in brodifacoum-treated rats than naïve rats exposed to warfarin. To further investigate this phenomenon, American kestrels were fed environmentally realistic doses of chlorophacinone or brodifacoum for a week, and following a week-long recovery period, birds were then challenged with a low-level dietary dose of chlorophacinone. In the present study, neither hematocrit nor clotting time (prothrombin time, Russell’s viper venom time) were differentially affected in sequentially exposed kestrels compared to naïve birds fed low-level dietary dose of chlorophacinone. While the present findings do not reveal lasting effects of anticoagulant exposure on blood clotting ability, findings in laboratory rats and other species have demonstrated such effects on blood clotting, and even other molecular pathways associated with immune function and xenobiotic metabolism. Additional studies using an environmentally realistic route of exposure and dose are underway to further test this hypothesis

Development of Dietary-Based Toxicity Reference Values to Assess the Risk of Chlorophacinone to Non-Target Raptorial Birds

Regulatory changes in the use of some second-generation anticoagulant rodenticides in parts of North America may result in expanded use of first-generation anticoagulant rodenticides (FGARs). Recent toxicological studies with captive raptors have demonstrated that these species are considerably more sensitive to the FGAR diphacinone than traditional avian wildlife test species (mallard, bobwhite). We have now examined the toxicity of the FGAR chlorophacinone (CPN) to American kestrels fed rat tissue mechanically amended with CPN, or rat tissue containing biologically-incorporated CPN, for 7 days. Nominal CPN concentrations in these diets were 0.15, 0.75, and 1.5 μg/g food wet weight, and actual CPN concentration in diets were analytically verified as being close to target values. Food intake was consistent among groups, body weight fluctuated by less than 6%, exposure and adverse effects were generally dose-dependent, and there were no dramatic differences in toxicity between mechanically-amended and biologically-incorporated CPN diets. Using benchmark dose statistical methods, toxicity reference values at which clotting times were prolonged in 50% of the kestrels was estimated to be about 80 μg CPN consumed/kg body weight-day for prothrombin time and 40 μg CPN/kg body weight-day for Russell’s viper venom time. Based upon carcass CPN residues reported in rodents from field baiting studies, empirical measures of food consumption in kestrels, and dietary-based toxicity reference values derived from the 7-day exposure scenario, some free-ranging raptors consuming CPN-exposed prey might exhibit coagulopathy and hemorrhage. These sublethal responses associated with exposure to environmentally realistic concentrations of CPN could compromise survival of exposed birds

The physics of Lyman α escape from high-redshift galaxies

Lyman α (Lyα) photons from ionizing sources and cooling radiation undergo a complex resonant scattering process that generates unique spectral signatures in high-redshift galaxies. We present a detailed Lyα radiative transfer study of a cosmological zoom-in simulation from the Feedback In Realistic Environments (FIRE) project. We focus on the time, spatial, and angular properties of the Lyα emission over a redshift range of z = 5–7, after escaping the galaxy and being transmitted through the intergalactic medium (IGM). Over this epoch, our target galaxy has an average stellar mass of M⋆ ≈ 5×10^8M⊙ .We find that many of the interesting features of the Lyα line can be understood in terms of the galaxy’s star formation history. The time variability, spatial morphology, and anisotropy of Lyα properties are consistent with current observations. For example, the rest-frame equivalent width has an EW_(Lyα,0) > 20˚A duty cycle of 62 per cent with a non-negligible number of sightlines with >100˚A⁠, associated with outflowing regions of a starburst with greater coincident UV continuum absorption, as these conditions generate redder, narrower (or single-peaked) line profiles. The lowest equivalent widths correspond to cosmological filaments, which have little impact on UV continuum photons but efficiently trap Lyα and produce bluer, broader lines with less transmission through the IGM. We also show that in dense self-shielding, low-metallicity filaments and satellites, Lyα radiation pressure can be dynamically important. Finally, despite a significant reduction in surface brightness with increasing redshift, Lyα detections and spectroscopy of high-z galaxies with the upcoming James Webb Space Telescope is feasible

Ageing-induced shrinkage of intervessel pit membranes in xylem of Clematis vitalba modifies its mechanical properties as revealed by atomic force microscopy

Bordered pit membranes of angiosperm xylem are anisotropic, mesoporous media between neighbouring conduits, with a key role in long distance water transport. Yet, their mechanical properties are poorly understood. Here, we aim to quantify the stiffness of intervessel pit membranes over various growing seasons. By applying an AFM-based indentation technique “Quantitative Imaging” we measured the effective elastic modulus (Eeffective) of intervessel pit membranes of Clematis vitalba in dependence of size, age, and hydration state. The indentation-deformation behaviour was analysed with a non-linear membrane model, and paired with magnetic resonance imaging to visualise sap-filled and embolised vessels, while geometrical data of bordered pits were obtained using electron microscopy. Eeffective was transformed to the geometrically independent apparent elastic modulus Eapparent and to aspiration pressure Pb. The material stiffness (Eapparent) of fresh pit membranes was with 57 MPa considerably lower than previously suggested. The estimated pressure for pit membrane aspiration was 2.20+28 MPa. Pit membranes from older growth rings were shrunken, had a higher material stiffness and a lower aspiration pressure than current year ones, suggesting an irreversible, mechanical ageing process. This study provides an experimental-stiffness analysis of hydrated intervessel pit membranes in their native state. The estimated aspiration pressure suggests that membranes are not deflected under normal field conditions. Although absolute values should be interpreted carefully, our data suggest that pit membrane shrinkage implies increasing material stiffness, and highlight the dynamic changes of pit membrane mechanics and their complex, functional behaviour for fluid transport

Toxicity reference values for chlorophacinone and their application for assessing anticoagulant rodenticide risk to raptors

Despite widespread use and benefit, there are growing concerns regarding hazards of second-generation anticoagulant rodenticides to non-target wildlife which may result in expanded use of first-generation compounds, including chlorophacinone (CPN). The toxicity of CPN over a 7-day exposure period was investigated in American kestrels (Falco sparverius) fed either rat tissue mechanically- amended with CPN, tissue from rats fed Rozol bait (biologically-incorporated CPN), or control diets (tissue from untreated rats or commercial bird of prey diet) ad libitum. Nominal CPN concentrations in the formulated diets were 0.15, 0.75 and 1.5 µg/g food wet weight, and measured concentrations averaged 94 % of target values. Kestrel food consumption was similar among groups and body weight varied by less than 6 %. Overt signs of intoxication, liver CPN residues, and changes in prothrombin time (PT), Russell’s viper venom time (RVVT) and hematocrit, were generally dose-dependent. Histological evidence of hemorrhage was present at all CPN dose levels, and most frequently observed in pectoral muscle and heart. There were no apparent differences in toxicity between mechanically-amended and biologically-incorporated CPN diet formulations. Dietary-based toxicity reference values at which clotting times were prolonged in 50 % of the kestrels were 79.2 µg CPN consumed/kg body weight-day for PT and 39.1 µg/kg body weight-day for RVVT. Based upon daily food consumption of kestrels and previously reported CPN concentrations found in small mammals following field baiting trials, these toxicity reference values might be exceeded by free-ranging raptors consuming such exposed prey. Tissue-based toxicity reference values for coagulopathy in 50 % of exposed birds were 0.107 µg CPN/g liver wet weight for PT and 0.076 µg/g liver for RVVT, and are below the range of residue levels reported in raptor mortality incidents attributed to CPN exposure. Sublethal responses associated with exposure to environmentally realistic concentrations of CPN could compromise survival of free-ranging raptors, and should be considered in weighing the costs and benefits of anticoagulant rodenticide use in pest control and eradication programs