11. Alternatives to Persistent Organic Pollutants
by Dr. Bo Wahlström
In preparation for the IFCS Expert Meeting on Persistent Organic Pollutants in Manila, The Philippines, in June 1996, the Swedish National Chemicals Inspectorate (KemI) established a project, in co-operation with the Swedish Environmental Protection Agency, to investigate alternatives to the POPs listed in UNEP Governing Council Decision 18/32.
The project included activities such as identification of alternatives for existing uses and toxicological and ecotoxicological hazard assessments, as well as cost estimates, for some important alternatives. Socio-economic factors were not considered, but some simpler comparisons of costs for products and new technologies were performed.
The following is a summary of the report from the project, published as KemI Report 4/96 "Alternatives to Persistent Organic Pollutants" which was presented at the meeting in The Philippines last year. Single copies of the report may be obtained from the Swedish National Chemicals Inspectorate upon request.
2. The Twelve POP's in the UNEP GC Decision
In principle the concept of persistent organic pollutants is an openended entity until it is further defined by applying specific criteria or establishing substance lists. The UNEP Governing Council Decision 18/32 on Persistent Organic Pollutants from 1995 follows the latter approach. It identifies twelve substances or groups of substances that should be initially considered. The Swedish Chemicals Policy Committee proposes the criteria approach and gives cut-off values to be applied in selecting substances that should be restricted or phased out. This will also be discussed in another presentation at this meeting.
The twelve substances and groups of substances listed in the UNEP 18/32 decision are the following: aldrin, dieldrin, endrin, chlordane, heptachlor, DDT, mirex, toxaphene and hexachlorobenzene (HCB), which are all pesticides, polychlorinated biphenyls (PCB) and HCB which are industrial chemicals, and polychlorinated dioxins and furans (PCDD/F) which are by-products of various industrial and other processes.
Within the UNECE Convention on Long Range Transboundary Air Pollution (LRTAP) negotiations for a protocol on POPs are ongoing. In the negotiations six more chemicals have been added to the twelve UNEP chemicals, namely hexabromo biphenyl, pentachlorophenol (PCP), short-chain chlorinated paraffins, chlordecone, lindane and polyaromatic hydrocarbons (PAHs). This will be discussed in another presentation at this meeting.
3. The precautionary and substitution principles
In Sweden, the precautionary principle is an approach to chemicals which implies that anyone handling chemicals must in advance take such precautions as are needed to prevent damage to man and the environment, instead of taking measures when damage has occurred. This principle is also expressed in the Chemical Products Act, and in the proposed Environmental Code.
The diffuse use of chemicals in products and materials means that whole populations and the entire environment is exposed to many substances at low levels. Many research methods are presently not suited to this situation. We are of the opinion that measures against chemicals must in the future to a higher degree be based on suspected rather than proven effects.
Substitution as a basic principle is written into Swedish chemicals legislation. It is also a tool that is used daily by purchasers and customers in their relations with manufacturers and suppliers. It includes a lot more than just substituting one chemical by another. When properly applied it involves all parts of the lifecycle of a product, and possible ways and means, including other techniques altogether, to achieve the same final objective. In many cases the application of the substitution principle may result in no chemical being used, or a completely different method being used. As an example, if the ultimate target is to keep a metal surface clean, substituting one organic solvent by another is only one way to reach the target. In the agricultural field the concept of Integrated Pest Management (IPM) often leads to substitution, not only of chemicals, but also of techniques and equipment.
In the following the term alternatives is used in this broader sense, involving both chemical and non-chemical alternatives to the listed POPs, be they pesticides or industrial chemicals. For obvious reasons this does not apply in the same sense for the by-products, although substitution of materials at the source should not be disregarded.
For practical reasons the POP's are subdivided into pesticides, industrial chemicals and by-products.
4.1. Alternatives for the Control of Arthropods of Medical and Veterinary Importance
DDT seems to be the only one of the twelve listed POPs which is still being used on a large scale for control of arthropods of medical or veterinary importance. The present main uses of DDT are against malaria and leishmaniasis vectors as residual sprays indoors. At a more limited scale DDT is used in plague control programmes. In a few tropical countries aldrin/dieldrin, heptachlor and toxaphene may possibly still be used for control of tsetse flies and ectoparasites on cattle.
Chemical as well as non-chemical means exist, which are more appropriate than the use of DDT and other POPs, for control of arthropods of medical and veterinary importance. There seems to be no justification (apart from economical reasons) for the continued use of DDT, aldrin/dieldrin, heptachlor and toxaphene in vector control. Alternatives to DDT and other POPs for control of arthropods of medical or veterinary importance are summarised below. In the full report the most important names of medically important arthropods and arthropod-borne diseases are listed.
Malaria (Anopheles mosquitoes)
Environmental management including elimination or reduction of larval breeding sites, better house designs, improved housing conditions including screening with mosquito netting, case detection, and drug treatment are some of the more optimal methods for control of human malaria. Pyrethroid-impregnated bednets and curtains may be the methods of choice where the vectors are biting indoors. Less specific methods include the use of indoor spraying with residual pyrethroids (permethrin, deltamethrin, lambda-cyhalothrin), etofenprox, bendiocarb, fenitrothion, malathion, pirimiphos-methyl, propoxur or other pesticides. In vector populations exhibiting broad-spectrum resistance to organophosphate compounds and carbamates following bendiocarb spraying, pirimiphos-methyl may be effective because it is not affected by the changed acetylcholinesterase metabolism selected for in the resistant population.
Several malaria-endemic countries are still using DDT, as indoor residual sprays, in attempts to control malaria. DDT and several other POPs are known to be associated with harmful effects on a number of different organisms at nearly all trophic levels. The cost of low volume spraying of bendiocarb, cyfluthrin or deltamethrin is comparable with that of conventional DDT spraying. It is recommended that the use of DDT for vector control and any other pest control purposes be generally prohibited throughout the world. It is emphasised that this recommendation encompasses the use of DDT in malaria and all other disease and pest control programmes.
Larvicides used, but not recommended here, against Anopheles include arsenicals (e.g., Paris Green), DDT, dieldrin, chlorpyrifos, malathion, methyl- and ethyl parathion, pirimiphos methyl and temephos. Because of their potentially harmful effects on the non-target fauna larviciding with these chemicals should, in general, not be carried out where populations of non-target organisms may be adversely affected. The use of Bacillus thuringiensis israelensis (B.t.i.) and other organisms, in particular fish, and environmental management to reduce mosquito breeding are usually more appropriate options. In many ethnic communities, different plant species are traditionally used for their mosquito repellent or larvicidal properties. In view of the rapidly declining diversity of plants and other organisms on the Earth, there is an urgent need to scientifically investigate the properties of various plants, particularly concerning their potentially arthropod-repellent, pharmacological and other potentially beneficial properties.
Mosquito-borne arboviruses: yellow fever, dengue
(Aedes aegypti, Ae. albopictus)
Environmental management including source reduction, i.e., the elimination of larval breeding sites, is the main method of choice. B. thuringiensis and/or B. sphaericus can be complementary options against the larval populations. According to WHO there is no alternative to temephos for use as a larvicide in potable water. However, increased source reduction, and improved water storage and water distribution facilities should eventually make the use of temephos and other potentially harmful chemicals in potable water an obsolete method of mosquito control. Biocontrol based on Toxorhynchites may become a cost-effective method in certain areas. Support for scientific research on these and other biocontrol agents for control of container-breeding disease vectors should be increased (as well as research on biocontrol of vectors breeding in more permanent aquatic habitats).
Mosquito-borne filariasis (Culex quinquefasciatus, Cx. pipiens)
Filariasis caused by the nematode Wuchereria bancrofti, and transmitted by Culex quinquefasciatus (and other mosquitoes) is an important medical problem in many tropical and subtropical, urban and suburban low-income areas of the world. Environmental management, particularly reduction or elimination of larval habitats by proper construction of sewage systems, latrines etc. are recommendable measures for control of Culex-transmitted filariasis. A complementary method to be considered is the application of the AbiopesticideA Bacillus sphaericus and/or polystyrene beads may be used for control of Culex larval populations, which are often breeding in waters polluted with organic wastes. Other complementary measures which should be encouraged include improved sanitation and house design, the screening of houses with netting, and the use of mosquito bednets. Pyrethroid-treated bednets provide excellent protection against both filariasis and malaria. Because they are non-specific, potentially hazardous to other organisms, and do not provide permanent control, methods based on pesticides, e.g., malathion, fenitrothion, fenthion, chlorpyrifos and propoxur, and synthetic insect growth regulators (IGRs) - although often recommended by others - are considered to be among the less suitable alternatives.
African trypanosomiases (tsetse flies, Glossina)
In foci of sleeping sickness, i.e. African human trypanosomiasis, which is transmitted by tsetse flies (Glossina), the integration of community participation and the use of traps or pyrethroid-treated screens can reduce the number of infected flies to insignificant levels. The use of traps or screens may also be used in tsetse-infested areas where cattle or livestock are being kept. However, the utilisation of trypanotolerant cattle varieties and/or increased production and more use of plant proteins for human consumption, are ecologically more appropriate and cost-effective, and should become the main options rather than the production of meat from trypanosomiasis-susceptible cattle. Thus, if it is still considered necessary to control tsetse flies and African trypanosomiases, in areas where sleeping sickness is absent, there are indeed methods available, which are relatively appropriate from the environmental, public health, veterinary and economic points of view. The use of DDT, dieldrin, endosulfan or any other environmentally detrimental chemical or method cannot be justified.
Flies in urban and suburban areas
Many synanthropic flies breed in organic waste material, including animal and human faeces, and are potential vectors of a number of human enteric infections caused by viruses, bacteria, protozoa and helminths. Environmental management methods including the reduction or elimination of potential fly larval breeding habitats are the main options for control. This includes the proper handling and destruction of human and animal excreta and organic wastes, fly-proofing of latrines and the construction of proper sewage systems. Improved housing conditions and house designs are complementary measures. There are a large number of environmental and other appropriate methods for the control of nuisance flies in livestock and poultry production facilities. The use of chemical insecticides will, in general, only provide temporary solutions and often rapidly induces the development of resistance in the fly (and other vector) populations to the class(es) of chemicals used.
DDT is one of the compounds which is usually used for controlling epizootics and epidemics of plague. This serious, but presently relatively rare, disease is caused by a bacterium which naturally occurs in certain populations of rodents inhabiting areas where, in general, human cases of plague rarely occur. However, from these natural plague foci the infection may spread. Surveillance of the infection in the natural plague foci should therefore be carried out on a permanent, routine basis. Epidemics of plague can occur in any area of the world where the sanitary and environmental conditions favour the breeding of rats and their fleas in close association with man. To avoid human cases of plague in urban and suburban areas surveillance and control of fleas and rodents are the main measures to rely on. The monitoring of resistance against chemical insecticides and rodenticides among flea and rodent populations, respectively, should, therefore, be carried out routinely, particularly in countries or regions where plague is enzootic. Environmental methods including the reduction of potential food sources for rodents, rodent trapping by baited traps, and poisonous baits to kill rodents are among the main methods recommended for control of domestic and peridomestic rodent populations. A moderately effective vaccine against plague is available for use by persons potentially becoming exposed to the infection, e.g., people living within or near plague enzootic foci. Valuable information relevant for the control of plague, fleas and rodents has been provided by PAHO and WHO. In view of the detrimental effects caused by DDT in non-target organisms, the occurrence of high levels of resistance to DDT in a number of populations of plague vectors, and the availability of relatively cheap and apparently less harmful, alternative chemicals, e.g. deltamethrin, it is considered inappropriate to use any of the persistent organochlorine compounds in attempts to control flea vectors of plague.
Ticks and tick-borne infections
Pasture-spelling and pasture rotation may be used to control tick species attacking and transmitting diseases to farm animals. Pasture spelling is widely used in Australia. Certain breeds, races or species of livestock are more tolerant than others to ticks and tick-borne infections. Such livestock should be used for traction, and meat and milk production rather than less disease-resistant breeds. There are vaccines available against some important tick-borne diseases. Anti-tick vaccines may become available for veterinary use in the near future. For personal protection in tick-infested areas the use of appropriate clothing, possibly with the additional use of a chemical tick-repellent, and prompt removal of attached ticks are measured that can be recommended. A number of plants are traditionally used for their tick-repelling properties. There is an urgent need to investigate the pharmaceutical and arthropod-repellent potentials of many of these plant species.
4.2 Protection of Plants and Building Constructions
This chapter suggests alternatives to the listed POP pesticides, used in plant protection or in protection of building constructions. It has been found that the use of POP pesticides has decreased drastically during the last decades. There is today very limited use against pests on plants and plant parts (e.g. wood in building constructions). It is however surmised that the following use may still be occurring:
1. Chlordane and heptachlor: mainly against termites damaging plants and constructions. This use is being phased out in country after country (most recently Australia), but several countries are still using them. Both substances are produced in and exported from the US.
2. Mirex: limited use against leafcutter ants and other ants in certain Central and South American countries. Production may possibly still be occurring in some of these countries.
3. Several POP pesticides: against different pests, mainly in developing countries. This use can largely be characterised as AresidualA, since it essentially involves old stocks of pesticides which are no longer produced (e.g. toxaphene in Nicaragua). POP pesticides which are still in production may also be used for illegal purposes (e.g. DDT against agricultural pests).
Effective alternative pesticides are available for the identified current uses, although some of these alternatives may require more frequent treatments, making them costlier. This is for example the case with termite protection of buildings.
Termite protection of buildings
A number of alternative termiticides have been extensively tested for long-term efficiency, both in temperate and tropical areas. Although not providing as long protection as the POPs, chlorpyriphos, isophenphos, permethrin, fenvalerate and cypermethrin were all effective.
In Australia, chlorpyriphos is the main chemical recommended as replacement to chlordane and heptachlor, but stress is also put on building techniques and barriers made of steel mesh or minerals. In Ohio chlorpyriphos, bendiocarb, permethrin, fenvalerate and cypermethrin are recommended, as well as using pressure-treated wood impregnated with chromated copper arsenate.
Termite protection of crops, nurseries and forest plantations
About 200 termite species are known to attack trees and crops. Of tree and shrub crops, cocoa and tea are most seriously affected, but other cultures suffer as well. Control is here best achieved by tree or bush hygiene, as chemical treatment will in any case be expensive. Seedlings and young plants can be protected by soil treatment with insecticides, and carbofuran, carbosulfan, chlorpyriphos and cypermethrin may here give as good control as POP pesticides, such as chlordane and heptachlor.
Of food and cash crops, sugarcane is the most susceptible and damaged. Maize is also seriously damaged by termites, maybe particularly in Africa. Possible non-POP pesticides include carbofuran, chlorpyriphos and carbaryl.
It is generally accepted that newer pesticides are more expensive than older ones, particularly when the newer ones are still protected by patents. Many of the encountered APOP alternativesA are however by now also rather old, why development costs will already have been recovered. In certain applications, such as termite protection, POP pesticides will nevertheless have a cost advantage through their long residual effect.
It has not been possible to make any direct calculations of the total cost of replacing remaining POP pesticide use with other pesticides, as sufficient information is lacking. A few examples of cost differences are given in the full report, but to be able to make such estimates, one must have precise information on product costs, required treatment frequencies and total areas requiring control. This kind of data is generally not available, or is at least very difficult to collect, particularly in developing countries. Studies on replacement costs must be made in the countries concerned.
Remaining POP pesticide users today are largely resource-poor farmers in developing countries. It is therefore emphasised, that alternative pest control methods must focus on non-chemical techniques, since these often are more affordable. An additional disadvantage of possible alternative synthetic pesticides is that these are, in some cases, more toxic than the POP pesticides. It is also suggested that more research is directed towards the development of botanical pesticides for local production.
Further activities which will contribute to the elimination of remaining POP pesticide use are intensified awareness-raising education efforts on pesticide use, and the destruction of old pesticide stocks.
4.3 Assessment of Hazardous Properties of Alternatives to POP Pesticides
It is difficult to define in an exact manner the possible alternatives to the various POPs used as pesticides. New products are continuously entering the market, old products are withdrawn, new uses for old products are developed, agricultural techniques, e.g crop rotation, application methods are changing etc. The chemical alternatives selected are therefore only given as examples. For any specific use the possible alternatives must also be assessed with regard to risk, since risk is always specific to the situation.
The main conclusion from the project, however, is that a wide range of chemical and non-chemical alternatives to the listed nine POP pesticides are already available. Secondly, the use of the nine listed POP pesticides has decreased drastically during the last decades and many of them are no longer reported to be produced. The major remaining use areas identified are DDT for vector control, chlordane and heptachlor against termites and mirex against ants. The information on current production and use of HCB is contradictory. It is uncertain if production of HCB for fungicide purposes is taking place. If HCB is still used as a fungicide it is easily replaced with other compounds and methods. In addition to these identified uses it is well known that there are substantial stocks of old pesticides including POP pesticides in many countries. Therefore, it is probable that there still is a certain use of POP pesticides for other purposes than the above mentioned.
For some of the chemical alternatives toxicological and ecotoxicological profiles have been compiled. The substances have been selected from the examples identified as alternatives to the POPs utilised in the major remaining use areas. The reason for selecting them is not that they in any way are the best available chemical alternatives from health and environmental viewpoints, they only serve as examples.
The proposed chemical alternatives are in most cases preferable from an environmental point of view, compared to the listed nine POP pesticides. This is not always the case from the health point of view. Since many of the chemical alternatives are highly acute toxic the health aspects must be considered case by case, taking the risk-benefit analysis into special account. For a specified use, appropriate protective equipment and safety instructions can limit the health risks.
5. INDUSTRIAL CHEMICALS
5.1 Replacement of PCB's in Sweden
The total import to Sweden of PCB between 1957-1980 has been estimated to 8,000-10,000 metric tonnes. A substantial part of the import, probably more than 50% was re-exported in goods. The use of PCB in Sweden has been restricted since 1972, and in 1978 it was decided that no new permits to use PCB in new products should be issued. Remaining part in the power sector of the industry has also been removed. Transformers or capacitors containing PCB and with a higher rating than two kilovoltamperes (reactive) may not be used after the 31st of December 1994.
The estimated net use of PCB for different purposes was in 1970 about 210 metric tonnes. PCB was replaced swiftly and efficiently in Sweden. All use except in closed vessels ceased in the early 1970s. The remaining transformers and capacitors with PCB in the power sector were replaced over a time-period lasting until the end of 1994.
PCB containing transformers were never manufactured in Sweden. The problem with PCB filled transformers and contaminated transformer oils has therefore been less severe, compared to many other industrialised countries. The main chemical alternative to PCB in transformers is mineral oil with different additives.
The transfer to new chemical products and technical solutions was accomplished without too many obstacles in most sectors of the industry. In the power sector the costs for replacing PCB can be estimated to around 100 MSEK, provided that energy savings and increased technical life-time is taken into account. Destruction costs for PCB has been a main cost factor.
PCB was used in the manufacture of capacitors in Sweden before 1978. The use for this purpose accounted for about 80% of the import of PCB. Chemical alternatives for PCB as capacitor fluid include a multitude of chemical compounds. The capacitor fluid most frequently used today in Sweden is a mixture of methyl(phenylmethyl)benzene and methylbis(phenylmethyl)benzene.
PCB was used in different building materials as a plasticiser. Chemical alternatives include chlorinated paraffins and phthalates. Chlorinated paraffins are however replaced due to environmental concerns, and the use of phthalates will be restricted with a rapid phase-out regarding those substances which are the most harmful to the environment. Substantial amounts of PCB, an estimated 190-650 metric tonnes, still remains in buildings. It is obvious that measures to deal with these problems may cost many times more than the replacement already accomplished.
Destruction capability and capacity are keys to a successful and final solution to the PCB problem. The destruction cost is also the major cost factor in the replacement. 17,667 metric tonnes of PCB containing waste was received by SAKAB, the Swedish hazardous waste treatment plant, between 1987-1995. This gives an idea of how much PCB wastes that have to be handled.
The Swedish definition of PCB contamination in waste is stringent. If other countries can and should use a similar limit depends on both contamination pattern and economic resources. Substantial amounts of PCB is now stored in many countries around the globe. Destruction capability and capacity are therefore the keys to a successful and final solution to the PCB problem.
The chemical and technical properties of PCB are to some extent unique, but chemical or technical alternatives were in most cases already available when the Swedish phase-out began in the early 1970s. The replacement of PCB as dielectric fluid in capacitors is an exception, and in this case the replacement was more complicated and time consuming. Today competing chemical and technical products without PCB are commercially available in all areas of application, including the power sector. Lack of alternatives is therefore not a limiting factor anymore and can not be an argument against replacement. The choice between alternatives can instead focus on the technical and environmental qualities of the products in question. The replacement products will of course represent the same spectrum of possibilities and risks as other commercially available and used chemicals.
Comments on the Swedish phase-out of heavy electric PCB equipment
The administrative application of the restrictions imposed on the use of PCBs in the 1971 PCB Law made new use possible, after a period of transition, only in power capacitors rated higher than 2 kVA reactive power. Electric power producers and distributors, often publicly owned, and high voltage customers in the industry were the major users. A new risk with the use of PCBs was revealed by a number of accidents and fires involving PCBs. The reason was the formation of PCDD/Fs in the fire. Internationally best known is the Binghampton case in 1981, New York, USA, and in Sweden Surahammar in 1982, where costly decontamination operations had to be carried through. These risks were not considered acceptable. Regulation of the use in working area was introduced by the National Board of Occupational Safety and Health in 1985. Awaiting the gradual exchange of the capacitors as their technical life time expired was not seen as a good solution, because the risks would increase with time to an unacceptable level and mixed capacitor batteries would not be possible for fire protection reasons. Superior technical substitutes as regards electrical properties were available in 1978. The phase-out was planned in discussions with the industry and the waste incinerator company, with a time schedule which would not create a need for storage of PCB waste. As long as the equipment is to be kept operative it will be supervised and taken care of, but if it is stored as waste, the control of leakage and fire protection would be more difficult to maintain. The amendment of the Ordinance on PCBs came into force in 1989 and at that time the exchange of PCB power capacitors was already going on because of the occupational rules and because of the superior technical properties of the new types of capacitors with lower losses and less specific volume.
After 31 December 1994 PCB power capacitors and transformers may not be used. The major problem in the waste management has been the large capacitors and transformers. They can not be charged into the incinerator and they are so few that investments in decontamination facilities will make the treatment cost very high. Some transformers were earlier exported to the UK, which has an incinerator which can accomodate whole transformers. The ramaining transformers, about 100 are emptied and the PCB fluid is incinerated, but one or two per cent of the PCB content is still left in the transformer carcass and they are stored. The capacitors can not be emptied of the fluid as the PCBs are vacuum impregnated into the windings and absorbed in paper or plastic. They will have to be shredded or charged into an incinerator which can accommodate them.
5.2. Destruction of PCB's
Good practices in storage, handling and destruction of PCBs are critical. Measures should be taken to avoid emissions of PCBs to water, soil and air and to prevent accidents. As regards destruction methods high temperature incineration in special plants for hazardous waste is still the primary option. Cement kilns, if properly controlled and operated, also can provide the necessary conditions for the destruction of PCBs. Dehalogenation and hydrogenation still have some limitations to their applicability. The scrupulous decontamination of PCB transformers is essential, both for re-use, retrofilling, and for metal recovery. There is concern over the fate of PCBs in landfills. The conclusion is that landfilling is not a good method for disposal. It might, however, be used for temporary storage of contaminated soil or sediments if the PCB concentration is very low if no other options are available. It is preferable to separate PCB containing components in waste intended for landfills.
5.3. Assessing the Hazardous Properties of PCB Substitutes
A brief evaluation of the potential health and environmental hazards associated with PCB substitutes in two major use areas - dielectric media and heat transfer fluids - shows that for such uses technically acceptable substitutes are currently available on the market. Many of these replacements constitute a distinct improvement as compared to PCBs from the toxicological and ecotoxicological viewpoint. Since an adequate database is available, in particular, this conclusion is warranted for products based on linear polydimethylsiloxanes (silicone oils) as well as for biphenyl. Based on chemical structure as well as on scarce information found in the open literature, this seems also to be true for a number of other compounds represented by non-halogenated alkylated aromatics. Access to unpublished studies conducted by industry would, no doubt, have permitted a more satisfactory assessment.
The main drawback with compounds like biphenyl and ditolylether, is a relatively high toxicity to aquatic organisms. They are, on the other hand used in closed systems and furthermore are readily biodegradable. It should be realized, however, that the main option in avoiding PCBs and similar products is not necessarily more acceptable chemical substitutes, but the introduction of alternative engineering designs. Thus, instead e.g. of PCB-containing (askarels) transformers, resin (glass, nomex, high temperature potting compounds) encapsulated transformers equipped with air cooling can be used.
Although suitable from the technical point of view, the toxicological and ecotoxicological properties of certain chemical substitutes are such as to render them highly unsuitable as substitutes in this context, mainly because they are very similar to PCBs in many crucial respects. Examples of such compounds are polychlorinated terphenyls (PCTs), alkylsubstituted chlorodiphenyls, as well as polychlorinated naphthalenes (PCNs).
5.4. Replacement of HCB in Sweden
Minor amounts of HCB (hexachlorobenzene) has been used in some parts of the Swedish industry. HCB has not been manufactured in Sweden and previous use has been replaced. Estimates of the international production are contradictory. It therefore seems premature to neglect HCB as an organic micro-pollutant of environmental concern.
HCB has been used as a pesticide, in the manufacture of military pyrotechnics, as a fluxing agent in aluminium smelting, as a porosity control in the manufacture of graphite electrodes and as a peptising agent in the rubber industry and intermediate in dye manufacture and organic synthesis. Among these applications HCB has been used in aluminium smelting and in the manufacture of graphite electrodes in Sweden.
HCB has been replaced by chlorine gas in aluminium smelting. In the manufacture of graphite electrodes the use does not seem to be necessary.
PCDD/F's, Sources, Emissions and Measures
Sources and emissions of polychlorinated dioxins and furans (PCDD/Fs) and abatement strategies to combat the formation and release have been compiled from recently published and presented material.
Municipal waste incineration may at present still be the main source of PCDD/Fs emissions into the atmosphere. Introduction of improved technologies is expected to reduce the emissions by one or two orders of magnitude. Combustion processes like cable smouldering, but also traditional hospital waste incineration, show very high specific emissions, which locally can be high. Domestic heating appliances, specially those fired with coal or wood, give emission levels, which are not extremely high, but the total amount of fuel burned this way and the location of the sources may cause this category not to be negligible. Emissions from road traffic are expected to decrease further because of the reduced use of halogenated scavenger containing leaded petrol.
A number of categories might be characterised as relatively less important sources, because the emission levels is low, and/or the scale of these processes is small. This generally applies to fossil fired powerplants, use of landfill gas, incineration of sewage sludge and most high temperature industrial processes. Processes related to the metal industry are relatively important, this specially concerns sintering processes, and the secondary metal industry.
There are several possibilities for the control or prevention of PCDD/Fs release emissions. Measures for the reduction of PCDD/Fs release emission reduction focus on the substitution of relevant raw and starting materials, process modifications and on the retrofitting of the existing plants.