The information below is adapted from: Dearden, J. C., Proof of Evidence submitted on behalf of Residents Against Incineration (RAIN) regarding proposals at Ince Marshes, Ellesmere Port, Cheshire (2008)
Dioxins are a family of 75 polychlorinated dibenzo-p-dioxins (PCDDs). This compound is one of the most toxic chemicals known, and is a known human carcinogen and endocrine disruptor. Similar chemicals are polychlorinated dibenzofurans (PCDFs), of which there are 135. Other related compounds are polychlorinated biphenyls (PCBs), of which there are 209, many of which are known [Mukerjee 1998] to be endocrine disrupters. Yet others are polybrominated diphenyl ethers (PBDEs), of which there are 209, and polybrominated biphenyls (PBBs) of which there are also 209. PBDEs and PBBs are used as flame-retardants for electrical goods, clothing and furniture. They are known to be endocrine disruptors and to cause developmental neurobehavioural defects [Mikula & Svobodová 2006, Eriksson et al 2006]. The principal cause of their presence in the environment is widely accepted to be incineration [D’Silva et al 2004].
All these compounds are hydrophobic (lipophilic) and therefore tend to accumulate in adipose tissue in the body. They are also chemically very stable and are therefore resistant to metabolic attack, and therefore to excretion, since chemicals need to be reasonably soluble in water in order to be readily excreted.
PCBs, PBBs and PBDEs can be present in waste materials. Dioxins (PCDDs and PCDFs) are not normally present in waste, but are formed when chlorine-containing organic substances (e.g. PVC) are burned. If combustion takes place at temperatures of about 850ºC, any dioxins already formed are destroyed, but can re-form again post-combustion. Cunliffe and Williams [2007] found that “formation of PCDD/PCDF on flyash deposits in the post-combustion plant of incinerators can result in the release of significant amounts of PCDD/PCDF to the flue gas stream”. Littarru [2006] has shown that about 57% of emitted dioxins (in terms of TCDD equivalents) are in the flue gases, with about 43% sorbed on the fly-ash.
As recently as 1997 Douben [1997] of H.M. Inspectorate of Pollution stated that “MSW incinerators are the dominant source of PCDD/F emissions to atmosphere and are responsible for up to 80% of the inventory”. It is now acknowledged that dioxin emissions from incinerators have fallen considerably in recent years. However, there remain a number of areas of concern.
Dioxin emission levels from incinerators are measured once or twice a year by external assessors who have to give prior notice of their visits. It is thus likely that operators ensure that a plant is running under optimal conditions for a visit. If much more frequent or continuous measurements are made, the total dioxin emissions are found to be very much higher than those calculated from biannual measurements. De Fré and Wevers [1998] found that emissions measured using the European standard method EN 1948 over a 6-hour period were 30 to 50 times lower than the average over a two-week continuous period. Reinmann et al [2006] showed that use of continuous dioxin sampling enabled operators to reduce dioxin emissions by a factor of 10, through careful control of operating conditions. True dioxin emissions from the proposed Ince incinerator, which would be subjected only to biannual checks, are thus likely to be very much higher than claimed.
Incinerators do not, for various reasons, run under optimal conditions all the time. Grosso et al [2007] found that even under steady-state conditions total dioxin release varied between 1.5 and 45 g TEQ per tonne of waste burned, depending on whether activated carbon was used and how fly-ash was collected.Sam-Cwan et al [2007] investigated the post-combustion re-synthesis of dioxins, and found that levels at waste heat boiler outlets were 10.8 – 13.6 times higher than at the furnace outlets, whilst water spray cooling was very effective at removing dioxins. Peel’s Environmental Statement [2007] states: “Each energy recovery boiler includes an economiser to cool the flue gas to temperatures suitable for the air emission control equipment”. It thus appears that the Peel process would significantly increase dioxin levels in the flue gases prior to treatment, and consequently would make reduction of dioxin levels more difficult.
Incinerators have to be shut down on occasion, both for routine maintenance and because of operating problems. It has been observed that during shutdown and startup, the levels of dioxins and other pollutants can be much higher than under optimal operation. Tejima et al [2007] tested the dioxin stack emissions of an MSW incinerator under conditions of startup, steady state and shutdown. They found concentrations of WHO-TEQ dioxin of 36 – 709 g.m-3 during startup, 2.3 g.m-3 during steady state operation, and 2.5 – 49 g.m-3 during shutdown. They estimated that 41% of the total annual emissions could be attributed to the startup period, assuming three startups per year. L.-C. Wang et al [2007] found that a single startup could contribute about 60% of the PCDD/F emissions for one whole year of normal operations; hence, assuming three startups per year, 64% of total annual emissions could come from startup. H.C. Wang et al [2007] found that during startup the PCDD/F removal efficiency was only 42% with selective catalytic reduction, compared with > 99% during normal operation.
It is clear from the above that levels of pollutants emitted from incinerators can vary greatly, and can exceed the statutory limits placed upon their emission. (It must be noted here that those limits are generally based on what is achievable and measurable, rather than what is safe [House of Commons 2001]). In 2001 Greenpeace carried out a review of the performance of municipal waste incinerators in the U.K. [Greenpeace 2001]. They found that for the ten incinerators that they reviewed, there were 546 self-reported limit exceedances in the two years 1999 and 2000, covering HCl, SO2, NOx, CO and particulates. It is noted that there were no reported exceedances of limits for dioxins or other substances that are not continuously measured. The Greenpeace report says that “it is difficult to accept that this is truly the case. High levels of pollutants in the gases often indicate a malfunction in the system or poor combustion of waste. For example, high levels of carbon monoxide would indicate poor combustion conditions under which increased production of dioxins, particles of incomplete combustion and other pollutants might be expected. Similarly, high levels of hydrogen chloride may be the result of large amounts of chlorine in the system, which again would provide improved conditions for dioxin formation. These peaks in production of dioxins and other hazardous substances are unlikely to be recorded by sampling undertaken only for a few hours, twice a year”. A Defra report [2004] stated that “there were 56 incidents of emissions outside permitted limits at the 14 incinerators accepting MSW in the UK in 2003…Three quarters of the incidents related to increased emissions of carbon monoxide and hydrogen chloride, which would not be expected to result in any significant environmental impacts (but see Greenpeace comments above). There were four incidents of dioxins and furans above permitted levels, and one incident of cadmium emissions above permitted levels”.
Another reason for variable levels of pollutant emissions is lack of adequate control by the plant operators. The Greenpeace report states that “no incinerator currently operating in England is able to meet the legal requirements of its license (sic)”, and points out that despite the 546 exceedances, only one prosecution (of Sheffield City Council in 1999) was brought by the Environment Agency in the period 1999-2000.
Incineration produces two forms of solid residue – fly-ash, which is fine particulate matter carried with flue gases, and bottom ash, which falls from the fire-grate. They constitute, between them, about one quarter to one third of the total pre-combustion weight of waste.
Fly-ash is known to sorb chemicals from the flue gases. As pointed out earlier, around half of emitted dioxins are sorbed on fly-ash [Littarru 2006]. Fly-ash is also responsible for the so-called dioxin memory effect [Cunliffe & Williams 2007], whereby slow de novo synthesis of dioxins occurs on the surface of the fly-ash; the dioxins then slowly desorb into the flue gases [Weber et al 2002] for prolonged periods after the implementation of beneficial changes to the incineration process. There is recent evidence [Jiang et al 2007] that fly-ash from larger incinerators (which Ince would be) has higher content of volatile components and higher leaching toxicity. Fly-ash is classed as hazardous waste, and has to be disposed of to landfill. There is concern that, because of its dust-like nature, less than extremely stringent handling could disperse dioxins and other pollutants such as metals sorbed on the fly-ash into the atmosphere around the RRP. Recent figures for the metal content of fly-ash from the Eastcroft (Nottingham) incinerator are: zinc 0.3%, lead 0.1%, copper 0.05%, manganese 0.05%, 0.01% chromium, 0.01% cadmium, 0.01% vanadium. For an estimated fly-ash production of 49,000 tonnes per annum (tpa), this means 147 tpa of zinc, 49 tpa of lead, 24.5 tpa of copper and of manganese, and 4.9 tpa of chromium, cadmium and vanadium. We are concerned that in the main body of Peel’s Environmental Statement there is an indication that some fly-ash could be used in construction. This is in our view irresponsible.
Bottom ash contains similar proportions of heavy metals (except cadmium, which is lower than in fly-ash). Under the List of Wastes (England) Regulations 2005, incinerator bottom ash is classed as non-hazardous. However, the Environment Agency recently confirmed, in a letter to Mr. Alan Watson [Watson 2008], that 12 out of 96 bottom ash samples that they tested met the criteria for hazardous waste, and the EA website [Environment Agency 2006] now states that zinc oxide has been given an ecotoxic classification (H14 by R50/53, very toxic to aquatic organisms and may cause long-term effects in the aquatic environment). This probably means that all of Peel’s bottom ash (estimated in their Environmental Statement to be 36,000 tonnes per annum) would have to be disposed of as hazardous waste, and should not be used for block-making or indeed for any other purpose. If the testing of Peel’s bottom ash showed the presence of chemicals meant that it was classified as hazardous waste, this would impact significantly on the economics of the operation. It should be noted that The Netherlands will soon require a higher immobilisation efficiency of bottom ash treatment [Xiao et al 2008].
It should also be noted that there are high levels of dioxins on Frodsham Marshes, arising, it is believed, from the former I.C.I. chemical plant (now IneosChlor) at Runcorn [Vale Royal 2002].
