Persistent organic pollutants

Persistent organic pollutants (POPs) are found in trace quantities in all areas of the environment. They are all toxic and accumulate in humans and plants. POPs do not readily break down in the environment with half-lives in soils in the order of years, although they may be transformed both physically and chemically over long periods.

Over recent years there has been a growing interest in these pollutants and in particular their potential chronic toxicity and impacts on human health. This is reflected by the recent international agreement to reduce releases of these chemicals under the UN/ECE Persistent Organic Pollutants Protocol (detailed above) and their consideration for air quality standards by the EPAQS. The detailed methodology for the compilation of these inventories depends on the combination of emission factors gathered from a range of sources and production statistics used elsewhere in the emission inventory or developed for the specific sector concerned.

The UK NAEI does not include emission estimates for some POPs since many have been banned in the UK for a number of years. Table 6.2 below indicates the years in which particular POPs were banned or use severely restricted, and whether the listed POPs are included in the NAEI.

¹Hexachlorobenzene and pentachlorophenol are also emitted from other sources as well as being or having been active ingredients in pesticides.

² Use of pentachlorophenol is severely restricted rather than banned absolutely.

³NA indicates that a year of ban is not applicable as the compound was never approved for use in the UK as a pesticide.

Polycyclic aromatic hydrocarbons (PAHs)

Polycyclic aromatic hydrocarbons are a large group of chemical compounds with a similar structure comprising two or more joined aromatic carbon rings. Different PAHs vary both in their chemical characteristics and in their environmental sources and they are found in the environment both as gases and associated with particulate material. They may be altered after absorption into the body into substances that are able to damage the genetic material in cells and initiate the development of cancer, although individual PAHs differ in their capacity to damage cells in this way.

The speciated PAH inventory was first compiled for the 1996 emissions inventory (see "Speciated PAH Inventory for the UK" Wenborn MJ 1999) and has allowed a more detailed understanding of the PAH emissions in the UK.

There have been several pollutant classifications relating to PAHs. Although there are a vast number of PAHs, the NAEI inventory focuses on sixteen. These 16 PAHs have been designated by the United States Environmental Protection Agency (USEPA) as compounds of interest under a suggested procedure for reporting test measurement results (USEPA 1988). The estimated emissions for individual compounds are given in Appendix 5. A subset of this includes six of the PAHs identified by the International Agency for Research on Cancer (IARC) as probable or possible human carcinogens (IARC 1987). In addition, the Borneff 6 PAHs have been used in some EC emission inventory compilations. A further subset of PAHs are those to be used as indicators for the purposes of emissions inventories under the UN/ECE’s Persistent Organic Pollutants Protocol. These classifications are given in the following table.

The main environmental impact of PAHs relate to their health effects, focusing on their carcinogenic properties. The most potent carcinogens have been shown to be benzo[a]anthracene, benzo[a]pyrene and dibenz[ah]anthracene (APARG 1996). The semi-volatile property of PAHs makes them highly mobile throughout the environment via deposition and re-volatilisation between air, soil and water bodies. It is possible that a proportion of PAHs released in the UK are deposited in the oceans and/or subject to long range transport making them a widespread environmental problem.

EPAQS published in 1999 a recommendation for an air quality standard for PAHs based on the use of benzo[a]pyrene as an indicator of the overall carcinogenicity of the PAHs present in the atmosphere. Emissions of benzo[a]pyrene (BaP) and the total of the 16 PAH’s are summarised in Table 6.4. Aluminium production and anode baking (carried out for the aluminium industry) is the largest source of PAH emissions in the UK, contributing 63 % of the total emissions of the 16 PAHs in 1995. Emissions from anode baking then fell considerably, comprising only 20% of the 16 PAH emission for 1999. Table 6.4 shows a reduction in emissions of benzo[a]pyrene from anode baking from 48% of the national total in 1995 to 13% in 1999. As a consequence of investment in abatement equipment following from the authorisation regime implementing the Environmental Protection Act 1990, one of the anode baking plants has dramatically reduced its emissions and the other will follow shortly.

Anode baking is currently the largest single source of the emissions for eight of the individual PAHs studied. The largest sources of emission for the remaining eight PAHs considered here are: road transport, domestic coal combustion, domestic wood combustion and creosote production. For many of these compounds, the anode baking source sector still accounts for a significant percentage of the total emission.

Other major sources of all the PAHs are industrial and domestic coal combustion and domestic wood combustion. Collectively, vehicles are a significant source of many PAHs, with cars burning leaded petrol being the largest subgroup. This reflects the higher emission factors resulting from not having catalysts.

Wood treatment is a significant source of some of the lighter PAHs such as acenapthene, fluorene and anthracene. Emissions from bitumen production and use have not been estimated due to a lack of emission data. It is possible that bitumen use is a significant source of benzo[a]pyrene and other PAHs. Increased measurement of PAHs by both industry and regulators, particularly in the aluminium sector, has allowed improvements in the precision of the emission estimates.

Emissions of PAH and BaP from domestic combustion have increased since 1997. This reflects the increased consumption of coal in the domestic sector. Similarly the emissions from "Other Industrial Combustion" increase from 1998 to 1999. This is also due to the higher consumption of coal in 1999.

The uncertainties associated with the emissions estimates of PAHs are considered in Section 6.4.

1. The PAHs selected are listed above in Table 6.3
2. Benzo[a]pyrene

Dioxins and Furans (PCDD/F)

The term "dioxin" is used to refer to the polychlorinated dibenzo-p-dioxins (PCDD) and "furan" is used for polychlorinated dibenzofurans (PCDF). Although there are 210 PCDD/F compounds in total, the emissions of importance are those of the 17 congeners (7 PCDDs and 10 PCDFs) as defined by the NATO/CCMS (Committee on the Challenges of Modern Society 1988) international toxic equivalent (I-TEQ) scheme. TEQ schemes weight the toxicity of the less toxic congeners as fractions of the toxicity of 2,3,7,8-TCDD, the most toxic congener. The inventory is in terms of the sum of the weighted emissions expressed as ‘I-TEQs’ which are widely used in UK and European legislation. However, more recently the World Health Organisation (WHO) has suggested a modification to the values used to calculate the toxic equivalents for some of the PCDDs and PCDFs. They have also suggested that there is value in using a similar approach for the PCBs which have dioxin-like toxicity and combining the PCDD/F and PCB TEQs together. The International and the WHO toxic equivalence factors (TEFs) for PCDD/Fs are shown in Table 6.5

¹ NATO/CCMS (1988)

² WHO (1998)

PCDD/Fs have been shown to possess a number of toxicological properties. The major concern is centred on their possible role in immunological and reproductive effects. The main sources of PCDD/Fs are thermal processes, but they can also be released to the environment from some chemical processes.

PCDD/Fs can arise from any thermal process where chlorine, is present in any form. For example, coal and other solid fuels contain trace amounts of chlorine compounds which can under certain combustion conditions result in PCDD/F formation. In addition PCDD/Fs can themselves be present in the feed stock material, or chlorinated impurities may be introduced into the feed stock of some thermal processes. The amount of chlorine required for PCDD/F formation may be small and consequently many processes have the potential to emit these pollutants. PCDD/Fs can also be emitted from the chemical production and use of polychlorinated aromatic pesticides and herbicides, many of which are now controlled. However, some chlorinated organic chemicals such as the wood preservative pentachlorophenol are still used in the UK and these have the potential to be sources of PCDD/Fs e.g. from the combustion of treated wood.

The PCDD/F emission estimates for 1990-1995 are derived from emission factors which have been revised to reflect changes in the degree of implementation of abatement and of industry structure as a result of measures taken by industry.

The estimated PCDD/F emissions for 1990-1999 are summarised in Table 6.6 below.

Previously the largest sources of PCDD/F emission was waste incineration. However, emissions have fallen rapidly from 1993 to 1999. Emissions from waste incineration in 1999 are more than an order of magnitude lower than those in 1990. This significant trend has been driven by the introduction of control measures. MSW incinerators not meeting the new standards closed in the period leading up to December 1996. New designs of MSW incinerator result in significantly lower levels of PCDD/F emissions.

The relatively low emissions from chemical incinerators reflects the use of rotary kilns and the incorporation of a secondary combustion chamber in the process to destroy organic contaminants together with the relatively low waste throughput and advanced pollution abatement equipment. However, clinical waste incineration remains a significant source. This is due to the fact that emissions from clinical waste incinerators (although showing significant reductions) have not been reducing as rapidly as the total PCDD/F total.

Emissions from power stations are fairly low because the combustion is efficient and the post-combustion fly ash temperatures are rapidly reduced. The emission factors associated with industrial and domestic coal combustion are significantly higher and sum to give a similar contribution, even though the coal consumption is less. However, emissions from all three sectors have decreased with the reduction in the quantity of coal burned.

Emissions from accidental fires and open agricultural burning are included in the Nature and Agricultural sector. The latter has greatly decreased since the cessation of most agricultural burning. Accidental fires are currently treated as a source of constant magnitude, and consequently, the percentage contribution from this sector to the total PCDD/F emission has risen as emissions from other significant sectors have decreased.

There are significant emissions from sinter plants owing more to the large gas volumes emitted than to high concentrations. Emissions from iron and steel plant are probably underestimated since only electric arc furnaces are considered. Scrap used in electric arc furnaces and secondary non-ferrous metal production will contain chlorinated impurities such as plastics and cutting oil which contribute to PCDD/F formation.

It is generally accepted that the source of PCDD/F emissions from road transport are the 1,2-dichloroethane scavengers added to leaded petrol. Over recent years both the consumption of leaded petrol, and the lead content of leaded petrol has decreased. Consequently the emissions of PCDD/F from this sector have decreased. Unleaded petrol and diesel is likely to contain only trace quantities of chlorinated impurities. For 1999, the contribution to the PCDD/F emission total from road transport was 4%.

Polychlorinated biphenyls (PCBs)

PCBs are synthetic organic compounds that have mainly been used in electrical equipment as dielectric insulating media.

PCBs have been linked with subtle sub-chronic effects such as reduced male fertility and long-term behavioural and learning impairment- they are classified as probably carcinogenic to humans. Certain PCBs have been assessed as having dioxin-like effects. PCBs are extremely persistent in the environment and possess the ability to accumulate in the food chain. These compounds are highly insoluble in water but accumulate in body fat. Present human exposure is probably dominated by the accumulation through the food chain of the PCBs present in environmental reservoirs such as soils and sediments as a result of previous releases to the environment.

PCBs have not been manufactured and used in the UK for many years, but old PCB-containing equipment still exist. It is estimated that 81% of primary PCB emissions to the atmosphere are associated with such appliances. These emissions primarily arise from in-service appliances; however emissions during disposal are also considered to be significant. Large quantities of PCBs are thought to have been disposed of to landfill in the past, mainly in the form of electrical components or fragmentiser residues, but now such equipment containing PCBs are disposed of by chemical incineration. PCBs are also emitted from the soil having previously been deposited there from the air.

PCB speciation has been incorporated into the emission estimates since the 1998 inventory. A summary of the total PCB emission estimates for 1990 to 1999 is given below in Table 6.7 (detailed emission estimates are give in Appendix 8). In addition TEQs for PCBs are included in Appendix 8 for the first time.

Sales of PCBs in the UK were stopped in 1986, though it is thought that they are still manufactured in some countries. The total PCB emission in 1990 was dominated by leaks from capacitors (89% of total emission), and this is the case for 1999 (82% contribution). However, not all electrical equipment containing PCBs is readily identifiable. Emissions from electrical equipment will probably continue, and will only start to fall significantly as the relevant electrical equipment is either destroyed or reaches the end of its working life.

In 1997 an Action Plan was published by DETR (now DEFRA) which laid out how the commitments made by the UK at the Third International North Sea Conference at the Hague in 1991 and in accordance with the requirements of Directive 96/59/EC. Regulations now require all PCB holders in the UK to report their stocks to the relevant regulatory bodies. These stocks (except for certain exemptions) should have been destroyed by the end of December 2000.

PCBs can be formed in trace amounts from chlorinated precursors in thermal processes such as scrap metal recycling. As a result, there are significant emissions from the iron and steel industrial sector, as with PCDD/Fs.

PCBs occur in sewage sludge due to their persistent nature. Not all the PCBs spread on land will volatilise but the potential for emissions to air is greater than that of landfill. The emission estimate comprises only 1% of the total and is highly uncertain. Emissions arise from waste incineration and refuse derived fuel production result from the PCB content of the waste.

Pesticide Emissions

There is little available information to enable accurate estimates of pesticide emissions to air. The emissions estimates presented here follow from significant improvements to the earlier emission estimates first made in 1996.

Despite these improvements, the confidence in the accuracy of these estimates is low. Relevant data is currently scarce with the majority of emission factors coming from the USA or Europe. The emissions factors used here will have been derived for a particular method of pesticide application and during atmospheric conditions which may not be representative of the situation in the UK. Until further data becomes available it is difficult to reduce the uncertainty associated with these estimates.

Pesticide emissions to the air occur predominately through three pathways: during manufacture, during application and volatilisation after application. Tables 6.8, 6.9 and 6.10 show the estimated emissions of lindane (g-HCH), pentachlorophenol (PCP) and hexachlorobenzene (HCB) respectively.

Lindane (g HCH)

Lindane is applied as an insecticide and fungicide in agriculture and is used for wood preservation and in domestic and veterinary formulations. Until 1990 lindane was also used as a remedial wood treatment i.e. in a curative role rather than a preservative/preventative. However, data on quantities used for a remedial wood treatment prior to 1990 are not available.

HCH exists in several isomers, however as a result of regulation in the UK, g-HCH accounts for more than 99% of the total HCH use. Consequently only the g isomer has been considered in any detail here. The emission estimates presented in Table 6.8a were made assuming that emissions arise from: the application of g-HCH, treated wood and agricultural and domestic use. g-HCH emissions are dominated by emissions from treated wood and wood preserving sources, contributing 66% and 14% to the 1999 total emission respectively. Emissions from wood preserving are expected to fall.

Emissions from agricultural activities are also significant, accounting for around 18% of total 1999 g-HCH emissions. These emissions are based on statistics giving the use of pesticides containing lindane, obtained from the Pesticide Usage Survey Group (MAFF, 1991a,b,c; 1992a,b,c,d) The emission factors used are taken from van der Most et al (1989).

Emissions of g-HCH arising from domestic applications are thought to be comparatively small. However, usage statistics are scarce and were only available for 1988 ( DOE, 1989). Emission factors are taken from van der Most et al (1989).

For completeness, the total emissions of HCH are also included here (see Table 6.8b below), although the differences are obscured due to rounding. These total HCH emissions estimates assume the worst case scenario of 1% contribution from non g isomers to the HCH total.

Pentachlorophenol (PCP)

Pentachlorophenol is used as a biocide, and is effective in destroying insect eggs. It is used in the timber and textile industries. The emission estimates given here also include emissions of sodium pentachlorophenoxide (NaPCP) and pentachlorophenyl laureate (PCPL) as well as PCP since these are also included in the proprietary formulations.

The estimated PCP emissions for 1990 to 1999 are given in Table 6.9. The largest percentage contribution to the total 1999 PCP emission arises from wood that has been treated within the last 15 years. This accounts for some 89% of the 1999 total PCP emission.

Once again it is very difficult to be certain of these estimates due to the lack of research into emission rates and limited knowledge of quantities used both in the year of the estimate and in previous years. An emission factor of 3% of the wood content per year was used- the same method used for lindane.

PCP emissions from the textile industry primarily arise from volatilisation during application as a cotton preservative. Emission factors used were based on a study of PCP emissions in the UK (Wild, 1992) who report that approximately 30% of the applied PCP is lost through volatilisation. Emissions from this sector are comparatively small.

PCP is used in the agricultural sector as the active ingredient in disinfecting wooden trays used in mushroom farming. Usage statistics are reliable coming from the Pesticide Usage Survey Group (MAFF, 1991a,b,c; 1992a,b,c,d). The emission factor assumes 30% loss due to volatilisation (Wild, 1992). Emissions from this sector are comparatively small.

The emission inventory for PCP is very uncertain as limited emission factors are available on the release of PCP during agricultural activities and statistics are not actively collected on the extent of its usage. There is some data on release of PCP from combustion processes, but the available studies are not consistent with each other suggesting that the uncertainty may be considerable. However combustion processes are not significant sources.

Hexachlorobenzene (HCB)

Studies in the USA have identified two main industrial sources of HCB (Mumma et al, 1975) (Jacoff et al, 1986). These are the manufacture of chlorinated solvents (e.g. trichloroethylene, tetrachloroethylene and carbon tetrachloride) and the manufacture of specific pesticides where HCB remains as an impurity. HCB emissions can also result from the use of hexachloroethane tablets as a degassing agent in secondary aluminium melting (van der Most et al, 1992). HCB emissions may also arise from combustion sources, but other than waste incineration these could not be estimated though they are believed to be small.

Statistics for chlorinated solvent production in the UK are commercially confidential, hence estimates were made based on UK solvent usage data from the Solvent Industries Association and import and export statistics.

Although there is no UK manufacture of pesticides that results in the production of HCB, pesticides with HCB as an impurity are still imported and used in the UK for agricultural pest control. Statistics for the use of these pesticides is provided by the Pesticide Usage Survey Group (MAFF, 1991a,b,c; 1992a,b,c,d).

HCB emissions in secondary aluminium melting result from the use of hexachloroethane (HCE) tablets as a degassing agent. Regulations now control the use of HCE and so very little secondary aluminium is now melted using HCE. Estimates of the quantity of degassing agent supplied and industrial expert estimates of the quantity of HCE used per tonne of aluminium melted were used to estimate the total aluminium melted using HCE.

Emission factors for HCB from solvent production, pesticide manufacture and aluminium smelting are taken from van der Most et al (1989).

Emissions from chlorinated solvent production and pesticide application are the most significant sources in the UK (Table 6.10) and in 1999 were estimated to account for 29% and 70%, respectively, of the total HCB emissions. This represents a significant change in the relative contributions to the total for 1990 where the same sectors contributed 46% and 43% respectively. This change is a direct result of the reduced emissions from the production of chlorinated solvents, but only very small changes are noted between more recent years.

Short Chained Chlorinated Paraffins (SCCP)

Introduction

Short chain chlorinated paraffins (SCCPs) are a range of commercially available chlorinated paraffins with 10-13 carbon atoms. The commercial products are usually mixtures of different carbon chain paraffins with a range of different degrees of chlorination. SCCPs are considered persistent organic pollutants- they do not occur naturally and due to their bioaccumulative and toxicological properties they are of concern to the environment.

Production and Emissions to Air

SCCPs are currently manufactured in the EU and are marketed under a variety of trade names with an average chlorine content of 40-74%. Current production in the EU is thought to be in the region of 15,000 tonnes per year.

The main uses of SCCPs are in the metal working, rubber manufacture, paint, sealant, leather and textile industries. However, it has been reported that there are negligible emissions to air of SCCP from production sources, and releases from the majority of industrial consumption results in emissions primarily to water (with very low emissions to air). Emissions from waste water to the atmosphere are unlikely to be large due to the physical properties of SCCPs.

The most important source of emission of SCCPs in the EU is considered to be the leather industry. There is some confusion concerning the leather finishing industry. The confusion concerns whether finishing agents are prepared by sulphonation of SCCPs or if they are prepared as mixtures of SCCPs and sulphonated compounds. It has been reported that it is more likely that the finishing agents are mixtures of sulphonated compounds and SCCPs. Assuming that this is correct the emissions are most likely to come from use of the SCCP and sulphonated material mixtures and from the formulation process.

Emission Estimates

It has been reported that the use of SCCP in the leather industry in the UK is between 1 and 2 tonnes per year. By assuming the emissions of SCCP are proportional to use of SCCP in the leather industry and using the estimated release from leather industry in the EU it is possible to make an estimate of the release to air in the UK. The estimated SCCP emission to air for the UK is 1.5 kg/year.

It should be appreciated that there is considerable uncertainty associated with this estimate. An alternative estimation method gives a UK emissions of 62 kg/year. Until more data is available on the emissions from the individual industrial sectors it is not possible to determine an emission estimate with any confidence.

Improvements that can be made to the UK release inventory for SCCP are shown below:

• Undertake a more thorough literature search.
• Obtain any relevant emissions testing reports from the trade bodies concerned with the leather, textiles and paint industries.
• Further investigate the emissions from treated leather and textiles during use.

These areas will be investigated for future reports.

Polychlorinated Napthalenes (PCN)

Introduction

Polychlorinated Napthalenes (PCNs) are a group of 75 theoretically possible chlorinated naphthalenes containing between one and eight chlorine atoms. Their chemical structure is similar to that of PCBs. PCNs are widely considered be associated with cancer and chronic liver disease.

PCNs have been used in a variety of industries. The most important uses are Cable insulation, wood preservation, engine oil additives, electroplating masking compounds, feedstock for dye production, dye carriers, capacitors and refractive testing oils.

PCNs have been produced in a number of countries including the UK, USA and France, their synonyms and trade names include Halowax, Nibren waxes, Seekay Waxes, Cerifal Materials and N-Oil. The majority of production generates a standard mixture of the different PCN congeners.

Production and Consumption

A number of assumptions give an estimate of the world-wide PCN production as 150,000 tonnes. Similar assumptions can be made to estimate the UK production as 6,650 tonnes.

Emission Estimates

There is very little information concerning the production of PCNs for commercial purposes.

Commercially produced PCNs are thought to be the most important source of PCNs in the atmosphere with the other source sectors being thermal sources, other industrial processes and contamination in PCB industrially produced mixtures.

In recent years production of PCNs has stopped (1960’s or 70s) so the major releases that were present during their extensive use have decreased. The potential sources at present are expected to be dominated by the disposal routes of capacitors and engine oil in the past (this is where the majority of the PCNs produced are thought to have been used). Another potential source of PCNs may be the incineration industry, PCNs have been found in fly ash and flue gas in waste incinerators. Similarly landfill is expected to be a source of PCN emissions.

PCNs have been found in emissions from incinerators and are thought to be produced from the combustion of PAHs. Therefore PCNs could in theory be produced from other high temperature combustion processes. A full review of emission measurements from such processes would be required prior to ascertaining the scale of the emissions of PCNs from such a potentially large array of sources.

As the information regarding the emission of PCNs in the UK is relatively sparse, it is not currently realistic to quote an emission estimate for PCNs.

Polybrominated Diphenyl Ethers (PBDEs)

Introduction

There are 209 possible congeners of polybrominated diphenyl ethers (PBDEs). Concern about potential risks to human health and the environment has centred on the potential toxicity, persistence and the tendency for bioaccumulation of some brominated diphenyls.

Since the 1960s, PBDEs have been added as flame-retardants. They are used in a variety of materials (Strandman et al. 2000), including thermoplastics (e.g. high-impact polystyrene) that are used in electrical equipment, computer circuit boards, casings, upholstery, furnishings; interiors in cars, buses, trucks and aeroplanes, rugs, drapery and building materials.

Production and Releases to Air

The annual EU production of polybrominated diphenyl ethers has been estimated to be 11,000 tonnes per year. It has been reported (EU 2000) that the UK used up to 2,000 tonnes of polybrominated biphenyl in 1994. Production of the three commercial mixtures (penta-, octa- and deca-dibrominated diphenyl) has virtually ceased in the EU.

The possible routes of release of PBDEs vary from production to the disposal of the materials for which they are used. There is limited information concerning the releases and it is difficult to attempt to estimate an emission inventory without any measurements of releases from sources or potential sources. Attempts have been made to gather UK usage information. However, information is not easily accessible, particularly as PBDEs are a material used in such a wide variety of industries.

Emission Estimate

It has not been possible to obtain UK specific emission data for PBDEs, but an estimate of the UK emission of PBDEs has been made using the total EU estimate. This is done by scaling with population. Without further assessment of the potential emissions from materials such as plastic and upholstery during production use and disposal it is not possible to make a more accurate estimate. The resulting unspeciated UK emission estimate for PBDE’s is 13.8 tonnes per year.

There are a number of improvements that can be made to the UK emission estimate. Resources should be focussed on the following aspects of production and use of secondary products that contain PBDEs.

• Emission from manufacturing sites
• Releases from materials during use
• Release from materials during and following disposal

These areas will be investigated to inform future reports.