Comparative Lethality of In ovo Exposure to PCB 126, PCB 77, and 2 Environmentally Relevant PCB Mixtures in Japanese Quail (Coturnix japonica).

The Japanese quail (Coturnix japonica) egg bioassay was used to directly compare the toxicity of 3,3',4,4',5-pentachlorobiphenyl (PCB 126), 3,3',4,4'-tetrachlorobiphenyl (PCB 77), and 2 environmentally relevant polychlorinated biphenyl (PCB) mixtures over specified dose ranges relative to vehicle and uninjected controls. Measures included lethality and deformities. Results showed clear dose-response relationships for PCB 126 and the 2 PCB mixtures by logistic analysis of covariance using a varying threshold model because there was a low but significant slope for mortality of vehicle controls over incubation. No dose-dependent increase in mortality was observed with PCB 77 treatment. Mortality increased above baseline for PCB 126 and the 2 mixtures after embryonic day 7 (ED07) to a stable slope from ED10. Median lethal doses and thresholds for response differed for PCB 126 and the 2 PCB mixtures, with the mixtures having lower initial toxicity and all showing progressively greater toxicity over the course of development. Further, the lethality of the PCB mixtures appeared to involve both aryl hydrocarbon receptor (AhR) and non-AhR mechanisms. Incidence of deformities was unrelated to treatments. In summary, complex mixtures of PCBs were lethal in a dose-related manner, with sublethal effects from exposure to PCB 77. Environ Toxicol Chem 2019;38:2637-2650. © 2019 SETAC.

Effects of in ovo exposure to 3,3',4,4'-tetrachlorobiphenyl (PCB 77) on heart development in tree swallow (Tachycineta bicolor).

Tree swallow (Tachycineta bicolor) eggs from 2 uncontaminated sites, the Patuxent Research Refuge (Laurel, MD, USA) and the Cobleskill Reservoir (Cobleskill, NY, USA) were dosed with polychlorinated biphenyl (PCB) 77 to evaluate effects on the developing cardiovascular system. To ensure embryonic viability, treatments were administered into the air cell at embryonic day 2.5 including: untreated (control), vehicle (filtered sterilized fatty acid mixture), 100 ng/g and 1000 ng/g egg. Eggs were dosed in the field with 0.2 µL/egg, returned to the nest, collected at embryonic day 13, hatched in the laboratory, and necropsied. The PCB 77-treated hatchlings were compared with uninjected, vehicle-injected, and environmentally exposed hatchlings collected from a PCB-contaminated Upper Hudson River (NY, USA) site. The PCB 77-treated embryos showed no effects on hatching success or hatchling mortality, heart index, or morphological measures of 4 distinct heart layers (heart width, length, septal thickness, total and ventricular cavity area) compared with controls. Hatchlings that had received PCB 77 exhibited increased incidence of a cardiomyopathy and absence of the ventricular heart wall compact layer (Chi square test; p < 0.001); environmentally exposed embryos showed no apparent effects. The compact layer is essential in development and overall heart function for ventricular cardiomyocyte proliferation and normal heart contraction. The finding that in ovo exposure to PCB 77 resulted in distinct cardiomyopathy has implications for long-term individual fitness. Environ Toxicol Chem 2018;37:116-125. © 2017 SETAC.

Assessing effects of environmental chemicals on neuroendocrine systems: potential mechanisms and functional outcomes.

Environmental pollutants encompass a vast array of compounds. Most studies in birds have focused on toxicological effects, with little attention to non-lethal effects. Consequently, it has proven difficult to assess potential risk associated with exposure to endocrine disrupting chemicals (EDCs). Assessing potential adverse effects due to exposure is further complicated by the great variation that occurs across avian species. These include variations in reproductive strategies, life span, sexual differentiation, and migration. Differences in reproductive strategies, particularly in the developmental patterns and mechanisms for precocial and altricial chicks, predispose birds to wide variations in response to steroids and steroid-like EDCs. We have investigated the effects of EDCs in precocial birds including Japanese quail (Coturnix japonica) and mallard ducks (Anas platyrhynchos) as well as in wild altricial songbirds. Studies in Japanese quail characterized endogenous steroid hormone changes during development and have demonstrated that the developing embryo uses the yolk as a 'steroid hormone depot'. It appears that actual embryonic exposure is quantitatively lower than indicated by the treatment in egg injections and that the true amount of compound necessary for bioactivity may be quite low relative to the actual dosage delivered. Additionally, embryonic exposure to specific EDCs adversely affected sexual differentiation in quail, especially impacting male sexual behavior as well as neural systems, immune response, and thyroid hormones. Many of these studies considered single compounds; however, wild birds are exposed to complex mixtures and multiple compounds. We tested complex mixtures of polychlorinated biphenyls (PCBs) at concentrations that bracketed those found in eggs in contaminated regions. Results indicated that the predictive value of the toxic equivalency (TEQ), based on comparative activation of the aryl hydrocarbon receptor (AhR) relative to dioxin was not as accurate as expected. We discuss the potential of developing an endocrine disruption index (EDI) to bridge the inconsistencies observed between responses predicted by the TEQ and those observed in vivo following exposure to EDCs. Further, we will discuss how an EDI would complement the adverse outcome pathways analyses to consider the range of effects of endocrine disruptors in birds.

The effects of an environmentally relevant 58-congener polychlorinated biphenyl (PCB) mixture on cardiac development in the chick embryo.

Chicken (Gallus domesticus) embryonic exposure in ovo to a 58-congener polychlorinated biphenyl (PCB) mixture resulted in teratogenic heart defects in chick embryos at critical heart developmental stages Hamburger-Hamilton (HH) stages 10, 16, and 20. The 58-congener mixture contained relative proportions of primary congeners measured in belted sandpiper (Megaceryle alcyon) and spotted sandpiper (Actitis macularia) eggs collected along the upper Hudson River, New York, USA, and chicken doses were well below observed environmental exposure levels. Embryos were injected with 0.08 µg PCBs/g egg weight and 0.50 µg PCBs/g egg weight (0.01 and 0.064 ng toxic equivalent/g, respectively) at embryonic day 0, prior to incubation. Mortality of exposed embryos was increased at all developmental stages, with a marked rise in cardiomyopathies at HH16 and HH20 (p < 0.05). Heart abnormalities occurred across all treatments, including abnormal elongation and expansion of the heart tube at HH10, improper looping and orientation, indentations in the emerging ventricular wall (HH16 and HH20), and irregularities in overall heart shape (HH10, HH16, and HH20). Histology was conducted on 2 cardiac proteins critical to embryonic heart development, ventricular myosin heavy chain and titin, to investigate potential mechanistic effects of PCBs on heart development, but no difference was observed in spatiotemporal expression. Similarly, cellular apoptosis in the developing heart was not affected by exposure to the PCB mixture. Conversely, cardiomyocyte proliferation rates dramatically declined (p < 0.01) at HH16 and HH20 as PCB exposure concentrations increased. Early embryonic cardiomyocyte proliferation contributes to proper formation of the morphology and overall thickness of the ventricular wall. Therefore, in ovo exposure to this 58-congener PCB mixture at critical stages adversely affects embryonic heart development.

Effects of an environmentally relevant polychlorinated biphenyl (PCB) mixture on embryonic survival and cardiac development in the domestic chicken.

A 58-congener polychlorinated biphenyl (PCB) mixture based on contaminant analysis of spotted sandpiper eggs collected along the upper Hudson River, New York, USA, in 2004 was used to study in ovo PCB effects on cardiac development in the domestic chicken. Fertile eggs were injected prior to incubation with the following doses of the PCB mixture: untreated, sham, 0, 0.03, 0.08, 0.3, 0.5, 0.7, and 2.06 µg PCBs/g egg weight (toxic equivalent quotient [TEQ] range of 0.004-0.266 ng/g). In addition, there were untreated and sham-control groups. Embryonic development was monitored throughout incubation and chicks were necropsied at hatch. Hatchability followed a dose-dependent curve with significant (p < 0.05) mortality above the 0.5 µg PCBs/g egg weight treatment compared with controls. The median lethal dose (LD50) of this PCB mixture in hatchling chicks was estimated as 0.4 µg/g egg weight (0.052 ng TEQ/g egg wt) based on the lethality curve. Cardiac arrhythmia was observed at embryonic day 14 of development in embryos treated at concentrations of 0.5 µg/g egg weight and above. Histological analysis was utilized to characterize any cardiac abnormalities. Cardiomyopathies increased across treatments in a dose-dependent manner compared with control groups. Identified abnormalities included the absence of the trabeculated layer of the ventricular wall, ventricular dilation, thinning of the ventricular walls, malformation of the septal wall, and most commonly, absence of the compact layer of the ventricular wall. Chick heart width, depth, total area, compact layer depth, septal width, chamber area, and ventricular wall dimensions did not differ across treatments. The present study supports prior reports of adverse developmental effects of PCBs on cardiovascular systems in birds. Although the eggs hatched, measured cardiomyopathies suggest potential deleterious long-term impacts on individual health and fitness.