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 are 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. PCDD/Fs were detected in most of the samples.
The study provides further evidence for the widespread occurrence of PCDD/Fs in the environment prior to 1900, and for a complex array of sources (including natural) and environmental transformation processes17 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. The next most important sources of emissions - residential wood combustion, clinical waste incineration and wood preservation - were difficult to estimate and therefore subject to high uncertainty. As emissions from industrial sources decreased, non-industrial sources (wood combustion, accidental fires, PCP-treated wood) may have become more important in relative terms.
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. For example, trace amounts of dioxins are generated through incineration of newspapers or paraffin that is composed only of carbon and hydrogen. These materials generate the same level of dioxins as with PVC when common salt is added as chlorine source (Makino, K. Tsubota et al., Chemosphere 46(2000) 1003~1007)
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.
The chlorine source and level are unimportant for formation of chlorinated organic pollutants
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.
More recently, a study performed at the University of Umeå21 showed that the chlorine source and level are unimportant for formation of chlorinated organic pollutants.
Dioxin regulations
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
A study undertaken by AEA Technology (UK) entitled Compilation of EU Dioxin exposure and health data co-funded by theEnvironment Directorate-General, was presented to the Commission task force on dioxins in October 1999. The main conclusion of the report was that, for some parts of the population, the daily intake of dioxins and dioxin-like compounds is still above the levels recommended by the World Health Organisation (WHO), despite the fact that dioxin levels have been decreasing in the recent years in all countries for which data for the last 10 to 15 years are available. On average, exposure fell by 10% per year between the mid-eighties and the mid-nineties.
Japanese data illustrate decreasing exposure of populations in developed countries. Fig.5-27 shows the transition of average dioxin concentrations in the environment for 1997~2001, studied by the national and municipal governments. According to the results of research in 2001, average dioxin concentrations in the environment were: 0.13 pg-TEQ/m3 in air, 0.25pg-TEQ/L in water (public water bodies), 8.5pg-TEQ/g in sediment (public water bodies) and 6.2pg-TEQ/g in the soil. This proved that the environmental quality standards established by the government have been met at most monitoring points.
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 levels22 .The regular levels of daily intake are very unlikely to lead to acute toxicity, such as would happen in the case of accidental ingestion.
Carcinogenicity
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 006.
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 001 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.
Reporting of emissions to water is not yet mandatory. Results assembled by Det Norske Veritas during the second verification of the ECVM Charter in 00 yielded a total emission to water below g/year I TEQ. This is consistent with figures from Japan: Fig.5- 9 shows the results of surveys on dioxins emission from VCM production facilities during 1997~ 001. During the period of this survey, total dioxins emission from VCM facilities was less than 1g per year, which is equivalent to about 0.4% of total emissions from all industries ( 05.8g-TEQ) and about 0.05% of total emissions including emissions from waste incinerators.
