Incineration is one option for final disposal of PVC at end of life or for residues from recycling. Concerns have been raised about potential emission of dioxins from PVC incineration, particularly from municipal waste but also from PVC production plants.
Background on dioxins
When an organic substance is incinerated in the presence of chlorinated compounds, dioxins can generated unintentionally due to incomplete combustion, whatever the incinerated substance may be. For example, dioxins are generated from natural phenomena such as the volcanic activities and forest fires.
PCDD/Fs (polycholrinates dibenzo-P-dioxins/furans) were found in samples of archived surface soils, collected from different locations around the world in the early 1880s, in contemporary surface soils from around the world, in archived sub-surface soils collected at Rothamsted Experimental Station (UK) in the 1870/80s, and in sections of peat core deposited from 5000 years ago up to the present.
Incineration and control measures
Through complete combustion, PVC can be broken down into water, carbon dioxide and hydrogen chloride (HCl). However, complete combustion is rarely feasible in reality, and dioxins can be unintentionally generated as by-products according to incineration conditions.
The European Union Commission published a Green Paper in July 2000 on the Environmental Issues of PVC. The Commission states that: “It has been suggested that the reduction of the chlorine content in the waste can contribute to the reduction of dioxin formation, even though the actual mechanism is not fully understood. The influence on the reduction is also expected to be a second or third order relationship. It is most likely that the main incineration parameters, such as the temperature and the oxygen concentration, have a major influence on the dioxin formation. The Green Paper states further that “at the current levels of chlorine in municipal waste, there does not seem to be a direct quantitative relationship between chlorine content and dioxin formation”. These views are based on many in-depth studies carried out in various parts of the world.
J. Vehlow (Forschungszentrum Karlsruhe Technik und Umwelt Institut für Technische Chemie) investigated the behavior of a large range of chlorinated products in the feed of municipal solid waste incinerators. His conclusion was: “The increased Cl and Br levels (in the feed) caused no significant increase of the concentration of PCDDs or PCDFs in the raw gas”. These findings are in line with many studies concerning the possible impact of PVC materials in the feed of municipal waste incinerators.
The most extensive study was performed in the United States, where the impact of the waste feed chlorine content on PCDDs and PCDFs emissions was analysed on 155 facilities19. The conclusion was: “The hypothesis that the amount or type of chlorine in the waste feed to combustion units is directly related to PCDDs/PCDFs concentrations measured at the combustion outlet is not supported by the preponderance of the data examined during this study”.
A study included chlorine feed concentrations from less than 0.1% to 80%20 (1900 test results, 169 facilities, MSWI, HWI, Hazardous Waste Incinerators, Hazardous Waste Fired Boilers, Cement Kilns, Biomass Combustors, Laboratory, Bench-, Pilot-Scale Combustors). The study showed no statistically significant relationship between chlorine input and PCDD/F stack concentration.
A study later performed at the University of Umeå showed that the chlorine source and level are unimportant for formation of chlorinated organic pollutants.
EU regulations are spread over several health and environmental Directives. However on 24 October 2001 the European Commission adopted a Communication on a Community Strategy for dioxins, furans and PCBs, aiming to reduce the presence of dioxins and PCBs in the environment and a as well as to reduce the presence of dioxins and PCBs in feed and food. The conclusions were adopted on 12 December 2001 by the Environment Council.
The main regulations in place in the EU includes:
- Council Directive 96/61/EC concerning integrated pollution prevention and control (IPPC) provides that EU wide emission limit values for dioxins should be established if the need is identified.
- Directive 2000/76/EC “on the incineration of waste” sets a 0.1 ng/m3 TEQ limit on dioxin + furan emissions in the exhaust gas from all incineration and co-incineration plants, except those treating only vegetable waste but including cement kilns co-incinerating waste. The maximum concentration of dioxins and furans in waste water is 0.3 ng/l.
- Decision 2000/479/EC “on the implementation of a European Pollutant Emission Register (EPER) requires the public reporting of dioxin emissions to air and water from all major industrial sites.
- Council Regulation (EC) 2375/2001 sets maximum levels for dioxin contaminants in foodstuffs.
- Recommendation 2002/201/EC sets action limits and target levels in various foodstuffs and animal feed.
The EU Scientific Committee for Food (SCF) has established a tolerable weekly intake (TWI) of 14 picogram toxic equivalents (TEQ) per kilogram body weight for dioxins and dioxin-like PCBs. This TWI is in line with the provisional Tolerable Monthly Intake (PTMI) of 70 pg/kg bodyweight/month established by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) at its fifty-seventh meeting (Rome, 5-14 June 2001) and concurs with the lower end of the range Tolerable Daily Intake (TDI) of 1-4 pg WHO-TEQ/kg body weight, established by the World Health Organisation (WHO) Consultation in 1998. According to the report “Releases of Dioxins and Furans to Land and Water in Europe” produced for Landesumweltamt Nordrhein-Westfalen, Germany on behalf of the European Commission in September 1999, waste treatment and disposal activities contribute 30% of the 38,230 g I-TEQ released yearly to land in the EU plus Norway and Switzerland. Industrial processes contribute 36% (34% from pesticide production), and fires contribute 21%.
Dioxin levels in the environment
Data for the Dioxin Inventory reports (Stage I 1997 and stage II 2001) were published by the North Rhine-Westphalia State Environment. The studies were carried out on behalf of the European Commission.They reflect the emission situation of the period 1993 to 1995. Stage I estimated that an annual PCDD/F air emission of 6500 g I-TEQ per year is released to air by all known sources in the 17 countries considered. Much less is known about PCDD/F emissions through waste water and process residues/wastes. Some of the reviewed national documents contain emission estimates which amount to a total of 3500 g I-TEQ per year for residues and about 20 g I-TEQ per year for waste water.
Stage II came up with a revised total emission to air of 3715 – 6415 g/year for 1995, of which 2823 – 4110 g/year from industrial sources (including waste incineration)
Quaß et al (2000) attempted to provide estimates of PCDD/F emissions to air, land and water for the reference period 1993- 1995 in the 15 EU member states, Norway and Switzerland. Estimated emissions to air were 5,728 g I-TEQ/year with municipal solid waste incinerators (MSWI) the predominant source at 1,437 g I-TEQ/yr, followed by sintering plants at 1,010g I-TEQ/yr.
In Japan, total dioxin emissions to air and water decreased from about 8 kg TEQ in 1997 to about 1 kg in 2002 and about 300 g in 2007 (Dioxins (Government of Japan, 2009),.
The toxicity of dioxins
Dioxins are said to be “the deadliest poison of all”, since the median lethal dose (LD50 ) of 2,3,7,8-TCDD for guinea pigs was determined to be 1 μg (one thousandth of a mg)/kg body weight (Fig.2-7), which is far less than that for sarin or potassium cyanide. However, the LD50 value varies largely among animal species. The most noted health effect in people exposed to large amounts of 2,3,7,8-TCDD is chloracne. Chloracne is a severe skin disease with acne-like lesions that occur mainly on the face and upper body. Other skin effects noted in people exposed to high doses of 2,3,7,8-TCDD include skin rashes, discoloration, and excessive body hair. Changes in blood and urine that may indicate liver damage also are seen in people.
Exposure to high concentrations of TCDDs may induce longterm alterations in glucose metabolism and subtle changes in hormonal levels. The regular levels of daily intake are very unlikely to lead to acute toxicity, such as would happen in the case of accidental ingestion.
Although dioxins are speculated to be carcinogenic to humans, the International Agency for Research on Cancer (IARC), which is an affiliate organization of the World Health Organization(WHO), has classified 2,3,7,8-TCDD under Group 1: “carcinogenic to humans “, based on the results of animal experiments.
On the other hand, there are other PCDDs such as 1,2,3,7,8- PeCDD, which are classified under Group 3: “not classifiable as to its carcinogenicity to humans”. However, the epidemiological study literature from which IARC drew the above conclusion states that the relative risks for people exposed to 20 years or more in high concentrations of 2,3,7,8-TCDD – up to 100~1,000 times the value for the general public - would be 1.2~1.64) . Incidentally, the risk for lung cancer for a cigarette smoker consuming one packet a day is reported to be 4~5 times higher than that of a nonsmoker. Furthermore, it is said that 2,3,7,8-TCDD does not have direct carcinogenic effects on genes, but enhances the effects of other carcinogens (promotional effects), and has a threshold value.
Tolerable daily intake (TDI)
In 1998, the WHO European Centre for Environment and Health (WHO-ECEH) and the International Programme on Chemical Safety (IPCS) performed a health risk assessment of dioxin-like compounds. The assessment was carried out by a panel of international experts and was based on the most recent knowledge regarding critical effects, dose-response relationships and quantitative risk extrapolation. A Tolerable Daily Intake (TDI) of 1-4 pg WHO-TEQ/kg body weight was recommended and, in contrast to the earlier assessments included the dioxin-like PCBs (WHO, 1998). This figure is based on the lowest exposures at which adverse effects were observed in experimental animals.
It includes an overall uncertainty factor of 10, in order to account for possible differences in susceptibility between humans and experimental animals and in between people. The upper limit of 4 pg WHOTEQ/ kg body weight per day is provisional: the ultimate goal is to reduce human intake levels below 1 pg WHO-TEQ/kg body weight per day.
In most industrialized countries, concentrations of dioxins in environmental samples, foods, human tissues and breast milk have decreased during the 1990s, mainly due to enforced environmental regulations.
In industrialized countries, the daily intake of dioxins (PCDDs and PCDFs) is in the order of 1 to 3 pg I-TEQ per kg body weight per day.
Dioxin emissions VCM manufacturing facilities
The ethylene dichloride (EDC) purification section is one of the emission sources, to which standards for the quality of discharged water are applicable under the OSPAR Decision 98/4. This Decision sets a limit of 1 μg TEQ per tonne oxychlorination capacity in waste water, after final treatment, for all EDC/VCM plants, from January 1st 2006.
During the oxychlorination step in EDC/VCM production processes, it has been known that at 50~300°C, besides carbon, hydrogen, oxygen and chlorine, catalytic effects of metals such as copper chloride can generate trace amounts of dioxins through side reactions. In Europe, until the introduction of the EPER reporting there was no official survey of dioxin emissions from EDC/VCM plants. In all previous surveys, these plants were part of a broader category (e.g. chemical industry). The results of the 2001 EPER reporting of emissions to air show that no site hosting an ECVM plant reported dioxin and furan emissions to air above the 1 g/year threshold.
Information about dioxin emissions can be extracted from the (publicly available) eco-profiles of VCM. The latest figures were collected in 2005, based on the average 2004 performance of all Western European plants. These figures are “cradle to gate” and hence include also dioxins generated during chlorine production. Nevertheless, the figures are low, i.e. < 0.0416 ng TEQ/kg VCM produced emitted to air, and < 0.2375 ng TEQ/kg VCM produced emitted to water. Based on a VCM production of 5 million t, the yearly total emission related to VCM production (including its chlorine supply) was therefore below 1.40 g/year TEQ in 2004.