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Other effects of PCBs in animals include changes in the immune system, behavioral alterations, and impaired reproduction. [55] PCBs that have dioxin-like activity are known to cause a variety of teratogenic effects in animals. Exposure to PCBs causes hearing loss and symptoms similar to hypothyroidism in rats. [70]
A mixture of PCBs such as Aroclor may contain PCB compounds which are known estrogen agonists but are not classified as dioxin-like in terms of toxicity. Mutagenic effects have been established for some lower chlorinated chemicals such as 3-chlorodibenzofuran, which is neither persistent nor an AH receptor agonist. [23]
Ortho-PCBs may alter hormone regulation through disruption of the thyroid hormone transport by binding to transthyretin. [8] Coplanar PCBs are similar to dioxins and furans, both bind to the aryl hydrocarbon receptor (AhR) in organisms and may exert dioxin-like effects, in addition to the effects shared with non-coplanar PCBs.
Exposure to the coplanar stereoisomer 3,3',4,4',5,5'-hexabromobiphenyl (but not the non-coplanar stereoisomer) in genetically susceptible mice is known to cause immunotoxicity and disorders related to the central nervous system, and even at doses as low as 2.5 mg/kg, excess neonatal fatalities are observed (LD 50 is from 5–10 mg/kg). [1]
The AH receptor is phylogenetically highly conserved, with a history of at least 600 million years, and is found in all vertebrates. Its ancient analogs are important regulatory proteins even in more primitive species. [8] In fact, knock-out animals with no AH receptor are prone to illness and developmental problems. [8]
Today, concentrations of dioxins are found in all humans, with higher levels commonly found in persons living in more industrialized countries. The most toxic dioxin, 2,3,7,8-tetrachlorodibenzodioxin (TCDD), became well known as a contaminant of Agent Orange , a herbicide used in the Malayan Emergency and the Vietnam War . [ 11 ]
New tests done by the Environmental Working Group have found 21 oat-based cereals and snack bars popular amongst children to have "troubling levels of glyphosate." The chemical, which is the ...
Before they can be registered for sale in most countries, xenobiotic pesticides must undergo extensive evaluation for risk factors, such as toxicity to humans, ecotoxicity, or persistence in the environment. For example, during the registration process, the herbicide, cloransulam-methyl was found to degrade relatively quickly in soil. [10]