Environmental and Safety Issues on PVC

Over the years, two major controversial issues have been associated with large-volume use of PVC plastics. The first has to do with the fate and health impacts of

Dewatering and drying of product

Figure 2.8. Flow diagram for suspension or emulsion polymerization of vinyl chloride.

Dewatering and drying of product

Figure 2.8. Flow diagram for suspension or emulsion polymerization of vinyl chloride.

additives used in vinyl products, particularly the phthalates used as plasticizers and the heavy metal compounds used as thermal stabilizers. Potential toxicity and the environmental consequences of phthalate released from plasticized PVC products have been debated for decades. The second concern is the potential production of dioxins and furans on the incineration of PVC in mixed municipal solid waste streams. These issues have been controversial, with numerous studies that seem to both refute and support these claims being published in the literature.

a) Plasticizers Phthalates, such as the commonly used di-2-ethylhexyl phthalate (DEPH) and diisononyl phthalate (DINP), are used at a 10-50 wt % in soft flexible PVC compositions used in products such as flexible roofing membranes or vinyl sheets. These plasticizers tend to migrate slowly to the surface of the product and can therefore enter the environment or come into human contact. Common plasticizers are indeed found in low levels dispersed in the environ-ment11 in most parts of the world [16] and generally believed to be even ingested routinely along with food. The low acute and chronic toxicity of these common plasticizers is well established [17, 18]. Based on pronounced biological effects caused by large doses of the plasticizer in animals, various human diseases have been attributed to this low-level intake of plasticizers [19]. The European Commission in 1999 banned the use of DEPH in soft toys used by young (under 3 years) children, encouraging voluntary restrictions on the use of the plasticizer by the manufacturers [20].

The research literature on the topic shows phthalates are not genotoxic. The observation that they cause liver cancer in laboratory rats, however, is well established, but this particular carcinogenic mechanism is not expected to be operative in humans. Authorities such as the World Health Organization's International Agency on Research on Cancer and the expert panel on American Council on Science and Health in the United States [21] both found no evidence of DEHP causing cancer in human populations. PVC is used in medical devices such as blood bags, infusion systems, and in hemodialysis equipment, and it is likely that those using these devices do receive relatively higher doses of the dissolved plas-ticizer into their bodies. Therefore, the issue of toxicity of common plasticizers is an important one with practical health implications. The prevailing expert opinion in the United States, however, is that the use of plasticized PVC in medical, toy, and other applications are quite safe [19]. Another more recent health concern is endocrine disruption12 by chemicals, and plasticizers are included in the class of relevant chemical agents. (Also included in the category of endocrine disrupters are compounds that occur in nature, specially the phytoestrogens in plant species.) The contributing effect of the PVC plasticizers to the bioavailable environmental

11 Phthalates do undergo breakdown in the environment via biodegradation (both by aerobic and anaerobic pathways), hydrolysis, and photodegradation.

12 As the name suggests, these chemicals cause changes in the endocrine system of humans and animals. The specific human effects include low sperm counts, incidence of undescended testicles, and increased susceptibility to testicular and prostrate cancer.

pool of endocrine disruptors is unknown and its relevance to human health has not been established at this time [17, 22].

b) Stabilizer Depending on the region of the world, commonly used photothermal stabilizers in PVC include compounds of lead, tin, barium, zinc and cadmium. Toxicity of all lead compounds causing neurological effects in children, kidney damage, sterility, and even cancer is well known. Cadmium compounds and organotin compounds are also toxic, affecting the nervous system and the kidney.

These metal compounds leaching out of PVC into the environment in landfill situations is a serious potential concern. However, in landfills (as well as in the potable water systems that use PVC pipes), these compounds are for the most part locked in the rigid plastic matrix. Unlike in plasticized systems, no significant rates of migration of these chemicals is unlikely. Consequently, release of heavy metals in any significant quantities into landfill leachate, sewer environments, or water distribution networks is not anticipated [23].

The same is not true, however, for fires that involve PVC materials [24] or for uncontrolled incineration of PVC waste. While the plastic is not particularly flammable in a fire due to its high halogen content (among common polymers, PVC ranks among the best in terms of time to ignition), considerable amounts of the metal compounds can be released [24] into the atmosphere. Research aimed at replacing these metal-based stabilizers with alternatives that are safer in fires is valuable in responding to this real problem associated with plastic fires.

c) Dioxins Dioxins and furans [polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF)] are a class of compounds where some of the members are highly toxic environmental pollutants.13 They are suspected human carcinogens and may alter endocrine and immune functions. Dioxin was the primary toxic component of Agent Orange (and was also released at Love Canal in Niagara Falls, New York, and at Seveso, Italy.). Some of these compounds occur in nature while others are anthropogenic, most commonly produced during the combustion of materials. However, improvements in incineration processes and reductions in emissions have resulted in a steady decrease of PCDD/PCDF levels in the environment as well as in human milk [25]. Most dioxins enter the human system via food (particularly the meat and dairy products). However, the extent to which these compounds are toxic to human beings (as opposed to animal models for which most data is available) is not entirely clear. Different mammalian test species show widely different susceptibility to dioxins. Studies by Ames et al. [26] concluded that despite the potent toxicity dioxins posed to rodents it was unlikely to be a significant human carcinogen at the levels to which the population is typically exposed.

13 Of the 210 compounds that comprise the class PCDDs and PCDFs, 75 PCDDs and 135 PCDFs are found in the environment as a result of combustion and natural processes. The most toxic of these, based on animal studies, is 2,3,7,8-tetrachlorodibenzo-p-dioxin.

The principle source of these toxic emissions is the incineration of mixed waste (including waste containing plastics) [27], but it is not entirely clear if changing the amount of PVC waste in a waste stream would result in a corresponding change in the dioxin emissions [28]. It is generally believed that incineration at a high enough temperature in adequately designed incinerators would minimize dioxin emissions, if any, from the process. Incineration with energy recovery can be an effective means of waste management for mixed waste streams. As waste streams typically include a PVC fraction, it is important to reliably quantify and establish unambiguously the role of PVC in dioxin generation under large-scale incineration.

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