Embryo environmental effects

One of the pollutants known to interfere with cardiovascular development is 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD). TCDD is a persistent, bioaccumulative environmental contaminant, as well as a potent developmental toxicant and human carcinogen [30]. Piscine, avian, and mammalian cardiovascular systems are sensitive to TCDD toxicity, with effects including cardiac enlargement, edema, and several dysfunctions. In zebrafish embryos, these effects include areduction in cardiomyocyte number at 48 hpf, decreased heart size, altered vascular remodeling, pericardial edema, and decreased ventricular contraction culminating in ventricular standstill [31-34]. 

There is no evidence to argue that the other half result from prenatal environmental effects. But it s reasonable to assume that the prenatal environment in its various forms can be an important factor, and that countless possibilities exist for both lethal and nonlethal effects due to that factor. The simple fact that so many embryos are apparently lost means embryos are particularly vulnerable to damage. 

Toxic equivalency factors (TEFs) are estimated relative to 2,3,7,8-TCDD, which is assigned a value of 1. They are measures of the toxicity of individual compounds relative to that of 2,3,7,8-TCDD. A variety of toxic indices, measured in vivo or in vitro, have been used to estimate TEFs, including reproductive effects (e.g., embryo toxicity in birds), immunotoxicity, and effects on organ weights. The degree of induction of P450 lAl is another measure from which estimations of TEF values have been made. The usual approach is to compare a dose-response curve for a test compound with that of the reference compound, 2,3,7,8-TCDD, and thereby establish the concentrations (or doses) that are required to elicit a standard response. The ratio of concentration of 2,3,7,8-TCDD to concentration of test chemical when both compounds produce the same degree of response is the TEF. Once determined, a TEF can be used to convert a concentration of a dioxin-like chemical found in an environmental sample to a toxic equivalent (TEQ). 

Allran, J.W. and Karasov, W.H. (2001). Effects of atrazine on embryos, larvae, and adults of auurau amphibiaus. Environmental Toxicology and Chemistry 20, 769-775. 

Verhallen, E.Y., van den Berg, M., and Bosveld, A.T.C. (1997). Interactive effects of the EROD—inducing potency of PHAHs in the chicken embryo hepatocyte assay. Environmental Toxicology and Chemistry 16, 277-282. 

Immunotoxic Effects of Environmental Chemicals on Amphibian Embryos... 

Green VA. 1970. Effects of pesticides on rat and chick embryo. In Hemphill D, ed. Trace substance environmental health 3, Proc 3 Ann Conf, University of Missouri, 183-209. 

There is evidence that the chorion may reduce exposure of zebrafish embryos to some compounds (31), and the environmental conditions in which embryos are grown may affect chorion permeability (32). However, the degree to which the chorion serves as a barrier to chemical exposure is controversial and poorly understood. Some have concluded that the effects are too small to justify the efforts of dechorionation (5). Dechorionation removes the possibility of decreased exposure to chemicals in the embryo medium, but damage to the embryos can sometimes result. It is, therefore, important to ensure that removal is done with as much care as possible. 

Landauer, W. 1953a. Genetic and environmental factors in the teratogenic effects of boric acid on chicken embryos. Genetics 38 216-228. 

A 1963 report of embryotoxic and teratogenic effects of Aroclor 1242 anticipated the later findings of PCBs as environmental pollutants by five years. When McLaughlin et al. injected the Aroclor into the yolk sacs of 20 fertilized eggs prior to incubation, only one chick hatched--and it died within two days (ref. 140). Embryos examined showed beak deformities, edema and a retarded growth pattern. 

M.F. Cavieres, J. Jaeger and W. Porter, Developmental Toxicity of a Commercial Herbicide Mixture in Mice I, Effects on embryo implantation and litter size, Environmental Health Perspecitves, 2002, 110, 1081. 

Elute To remove a sorbed chemical substance from a sorbent by means of a fluid Embryotoxlc The adverse health effects on the growing embryo Embryotoxlclty and fetotoxlclty Any toxic effect on the conceptus as a result of prenatal exposure to a chemical the distinguishing feature between the two terms is the stage of development during which the insult occurred EMIC Environmental Mutagenesis Information Center... 

For the purposes of this chapter, the term reproduction will be used primarily in reference to vertebrate species of animals (especially mammals) and will be inclusive of development (Figure 36.1), which is sometimes treated as a separate topic in toxicology texts. This particular chapter emphasizes what is currently known about the adverse effects of known chemical warfare agents and selected environmental contaminants on male and female reproductive function, as well as xenobiotic-induced effects on the growth, maturation, and sexual differentiation of the embryo and fetus. Endocrine disruption is an extremely common mechanism of action for xenobiotics associated with impaired reproductive function and will be discussed along... 

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