A significant challenge in ecotoxicology and risk assessment lies in placing observed contaminant effects in a meaningful ecological context. Polychlorinated biphenyls (PCBs) have been shown to ...affect juvenile snapping turtle survival and growth but the ecological significance of these effects is difficult to discern without a formal, population-level assessment. We used a demographic matrix model to explore the potential population-level effects of PCBs on turtles. Our model showed that effects of PCBs on juvenile survival, growth and size at hatching could translate to negative effects at the population level despite the fact that these life cycle components do not typically contribute strongly to population level processes. This research points to the utility of using integrative demographic modeling approaches to better understand contaminant effects in wildlife. The results indicate that population-level effects are only evident after several years, suggesting that for long-lived species, detecting adverse contaminant effects could prove challenging.
•Previous studies have shown the PCBs can impact juvenile snapping turtles.•We used a demographic model of turtles to evaluate population-level PCB effects.•PCB effects on turtles may translate to negative population responses.•Long-term monitoring is needed to detect contaminant effects on natural turtle populations.•Demographic models can improve our understanding contaminant ecotoxicity.
A demographic model was used to show that PCB induced effects on young snapping turtles can result in adverse effects at the population level.
In the United States, new regulatory restrictions have been placed on the use of some second-generation anticoagulant rodenticides. This action may be offset by expanded use of first-generation ...compounds (e.g., diphacinone; DPN). Single-day acute oral exposure of adult Eastern screech-owls (
Megascops asio
) to DPN evoked overt signs of intoxication, coagulopathy, histopathological lesions (e.g., hemorrhage, hepatocellular vacuolation), and/or lethality at doses as low as 130 mg/kg body weight, although there was no dose–response relation. However, this single-day exposure protocol does not mimic the multiple-day field exposures required to cause mortality in rodent pest species and non-target birds and mammals. In 7-day feeding trials, similar toxic effects were observed in owls fed diets containing 2.15, 9.55 or 22.6 ppm DPN, but at a small fraction (<5%) of the acute oral dose. In the dietary trial, the average lowest-observed-adverse-effect-level for prolonged clotting time was 1.68 mg DPN/kg owl/week (0.24 mg/kg owl/day; 0.049 mg/owl/day) and the lowest lethal dose was 5.75 mg DPN/kg owl/week (0.82 mg/kg owl/day). In this feeding trial, DPN concentration in liver ranged from 0.473 to 2.21 μg/g wet weight, and was directly related to the daily and cumulative dose consumed by each owl. A probabilistic risk assessment indicated that daily exposure to as little as 3–5 g of liver from DPN-poisoned rodents for 7 days could result in prolonged clotting time in the endangered Hawaiian short-eared owl (
Asio flammeus sandwichensis
) and Hawaiian hawk (
Buteo solitarius
), and daily exposure to greater quantities (9–13 g of liver) could result in low-level mortality. These findings can assist natural resource managers in weighing the costs and benefits of anticoagulant rodenticide use in pest control and eradication programs.
We conducted a factorial experiment to compare sublethal and lethal responses of juvenile snapping turtles exposed maternally and/or through the diet to polychlorinated biphenyls (PCBs) over 14 ...months posthatching. Maternal exposure did not affect embryonic development or hatching success. Thyrosomatic indices were not influenced by treatments, although hepatosomatic indices were lower in animals having been exposed to PCBs maternally relative to those having been exposed both maternally and via the diet. Dietary PCB exposure reduced metabolic rates of juveniles in two of three assays conducted. Approximately eight months after hatching, high rates of mortality began to emerge in individuals having been exposed maternally to PCBs, and mortality rate correlated with PCBtotal in eggs. Prior to death, individuals that died experienced lower growth rates than those that survived, suggesting chronic effects prior to death. By 14 months posthatching, only 40% of juveniles derived from females in the contaminated area had survived, compared to 90% from the reference area. Such latent effects of maternally derived contaminants suggest that assessments of environmental impacts based upon shorter-term studies may provide very conservative estimates of the severity of effects, as they cannot capture responses that may emerge later in the life cycle.
We conducted field studies over three years to assess body burdens and maternal transfer of polychlorinated biphenyls (PCBs) as well as indices of sexual dimorphism in snapping turtles (Chelydra ...serpentina) of the upper Hudson River (NY, USA.) We collected adult turtles in areas known to be contaminated with PCBs and in nearby reference areas for measurement of body size, precloacal length, and penis size. We analyzed PCB concentrations in eggs collected over three years and in whole blood from adults in one year. Total PCB concentrations (mean ± standard error) in eggs were 2,800 ± 520 and 59 ± 5 ng/g wet weight in the contaminated area and the reference area, respectively. Eggs from the contaminated area were significantly enriched in tri‐, penta‐, and hepta‐PCBs relative to the reference area. Blood from adults in the contaminated area averaged 475 ± 200 and 125 ± 34 ng/g wet weight for males and females, respectively. In the reference area, blood PCB concentrations were 7 ± 3 and 4 ± 1 ng/g wet weight for males and females, respectively. Significant positive relationships were found between carapace length and blood PCB concentration for both sexes in the contaminated area; however, only a marginal relationship was found between female carapace length and concentration of PCBs in their eggs. Our results suggest that PCB contamination of the upper Hudson River presents risks of establishing high body burdens and of maternal transfer of PCBs to eggs, although our measures of gross morphology revealed no discernable expression of abnormal sexual development or reproduction.
Perchlorate is a surface and groundwater contaminant found in areas associated with munitions and rocket manufacturing and use. It is a thyroid-inhibiting compound, preventing uptake of iodide by the ...thyroid gland, ultimately reducing thyroid hormone production. As thyroid hormones influence metabolism, growth, and development, perchlorate exposure during the embryonic period may impact embryonic traits that ultimately influence hatchling performance. We topically exposed eggs of red-eared sliders (Trachemys scripta) and snapping turtles (Chelydra serpentina) to 200 and 177μg/g of perchlorate (as NaClO4), respectively, to determine impacts on glandular thyroxine concentrations, embryonic growth and development, and metabolic rates of hatchlings for a period of 2months post-hatching. In red-eared sliders, in ovo perchlorate exposure delayed hatching, increased external yolk size at hatching, increased hatchling mortality, and reduced total glandular thyroxine concentrations in hatchlings. In snapping turtles, hatching success and standard metabolic rates were reduced, liver and thyroid sizes were increased, and total glandular thyroxine concentrations in hatchlings were reduced after exposure to perchlorate. While both species were negatively affected by exposure, impacts on red-eared sliders were most severe, suggesting that the slider may be a more sensitive sentinel species for studying effects of perchlorate exposure to turtles.
PDF
