PVC

According to Wikipedia, Polyvinyl chloride, commonly abbreviated PVC, is the third most widely produced plastic, after polyethylene and polypropylene.

PVC can be made softer and more flexible by the addition of plasticizers, the most widely used being phthalates. In this form, it is used in clothing and upholstery, and to make flexible hoses and tubing, flooring, to roofing membranes, and electrical cable insulation. It is also commonly used in figurines and in inflatable products such as waterbeds, pool toys, and inflatable structures.

PVC is the most toxic plastic for our health and environment. No other plastic contains or releases as many dangerous chemicals. These include dioxins, phthalates, vinyl chloride, ethylene dichloride, lead, cadmium, and organotins. There’s no safe way to manufacture, use or dispose of PVC products."

So let's look at a few of these chemicals. First, Phthalates. "Phthalates are chemicals used to soften or plasticize PVC products such as flooring, which can be released from PVC into the air. The phthalates cling to dust and can then be breathed in. Over 90% of all phthalates are used in PVC products. Some phthalates, such as DEHP, have been linked to reproductive problems including shorter pregnancy duration and premature breast development in girl, and sperm damage and impaired reproductive development in boys. Some studies have also found a correlation between phthalates and obesity, a growing problem for children across the country. Furthermore, a number of studies have linked phthalates and PVC in building materials with asthma in children and adults."

"PVC’s lifecycle is uniquely responsible for the release of Dioxins, some of the most toxic chemicals ever studied by the EPA. Dioxins are a class of chemicals unintentionally created from the manufacture and disposal of PVC products, such as vinyl flooring. Dioxin is a potent cancer-causing agent and is considered to be a “known human carcinogen” by the World Health Organization’s International Agency for Research on Cancer and the U.S. Department of Health and Human Services’ National Toxicology Program. According to the US EPA, the levels of dioxin-like compounds found in the general population may cause a lifetime cancer risk as high as one in 1,000. This is 1,000 times higher than the generally “acceptable” risk level of one
in a million. Dioxin also causes a wide range of non-cancer effects including reproductive, developmental, immunological, and endocrine effects in both animals and humans."

Furthermore, the State of California is currently considering a bill that would ban the use of PVC in consumer packaging due to the threats it poses to human and environmental health and its effect on the recycling stream. Specifically, the language of the bill analysis stipulates that EPA has listed vinyl chloride, a "constituent element" of PVC, as a carcinogen. It also further cites that there are concerns about the leaching of phthalates and lead from the PVC packaging.

I could go on and address the other chemicals, but I think the fact that it has been linked to asthma, cancer, reproductive, developmental, and immunological issues is enough of a reason to search for alternatives.