and Environmental Hazards (Wales) /
Hanson Cement, Padeswood, Flintshire
Review of Dioxins
(Emissions Data)
Authors: CRCE(Wales)
Date:6th July 2011 / Version:FINAL
Publication/ Distribution:
- Hanson Cement Environmental Risk Assessment Group
- Hanson Cement Project Board
Review Date: It is not intended to provide further revisions to this document
Purpose and Summary of Document:
- To provide information on emission of dioxins to atmosphere from Hanson Cement
- To provide emission limits and regulatory history regarding dioxin emissions from Hanson Cement
- To provide toxicological information on dioxins
- To place information in the context of national and regional emissions
- To complement information provided by the Food Standards Agency
Copyright Statement
Raw data contained in this report remains the property of supplier, Interpreted data remains property of the Health Protection Agency
Maps reproduced by permission of Ordnance Survey on behalf of Her Majesty’s Stationary Office. © Crown copyright and database right 2011. All rights reserved
Health Protection Agency / Hanson Cement: Review of Dioxins
(Emissions Data )
Executive Summary
Background to report
This report has been prepared at the request of the Public Health Wales- led Hanson Cement Investigation by the Centre for Radiation, Chemicals and Environmental Hazards (CRCE)(Wales), part of the Health Protection Agency. This analysis forms part of the wider investigation into the potential public health impacts of Hanson Cement, Padeswood plant being carried out at the request of the Welsh Assembly Government Minister for Health and Social Services and co-ordinated by Public Health Wales.
Dioxins are the common name given two classes of chemicals known as polychlorinated dibenzo-p-dioxins polychlorinated dibenzofurans (PCDFs). These chemicals are predominantly formed from the incomplete combustion of organic materials in the presence of chlorine. As such they are a by-product of both natural combustion processes and human activity. Exposure to sufficient concentrations of dioxins over a prolonged period may increase the risk of cancer and causeeffects on the immune and reproductive systems and effects on development of the foetus.
This report has been prepared to complement a separate review of levels of dioxins in food and soil being carried out by the Food Standards Agency.
Key Findings and Recommendations
Key Findings
- Emissions of dioxins from the cement works at Padeswood have fallen markedly during the study period. This is due to the replacement of older kilns 1-3 with a new kiln 4 in 2005. Kiln 4 is required to be Waste Incineration Directive (WID) compliant due to its use of waste as a fuel.
- Emission limits used at the plant are derived based on technical achievabilityand not human health. It is technically achievable for such plant to emit dioxins at much lower levels than those recommended for health and as such it is unlikely that occasional breaches of the emission standards would lead to ill health in the surrounding communities.
- Significantly elevated concentrations of dioxins were emitted from the plant during 2004. However, the modelled exposure at that time indicated that the most hypothetically exposed individual would receive a dose which did not significantly exceed the tolerable daily intake (TDI).
Recommendations
- The report makes no specific recommendations.
1.Introduction
This report has been prepared at the request of the Public Health Wales-led Hanson Cement Investigation by the Centre for Radiation, Chemicals and Environmental Hazards (CRCE)(Wales), part of the Health Protection Agency. The Health Protection Agency in Wales works closely with Public Health Wales as part of a functionally-integrated model to reduce the dangers to environmental hazards. This analysis forms part of the wider investigation into public health impacts of Hanson Cement, Padeswood plant being carried out at the request of the Welsh Assembly Government Minister for Health and Social Services and co-ordinated by Public Health Wales.
The principal potential pollutants from the manufacture of cement in a cement kiln are products of combustion including particulate matter, oxides of nitrogen and oxides of sulphur, acid gases and dioxins) and heavy metals. There are also possible fugitive emissions of dust from the crushing and grinding of raw ingredients and finished clinker. This report collates and examines the available information relating to stack emissions of dioxins. This information has been used to examine emissionsof dioxins from Hanson Cement and place them in context.
1.1Introduction to Dioxins
Dioxins are the common name given two classes of chemicals. This group consists of 75 different compounds known aspolychlorinated dibenzo-p-dioxins (PCDDs) (ATSDR 1998, HPA, 2008), and a further 135 polychlorinated dibenzofurans (PCDFs) (HPA, 2008, ATSDR 1998). These chemicals are predominantly formed from the incomplete combustion of organic materials in the presence of chlorine. As such they are a by-product of natural combustion processes (e.g. Forest Fires) and human(anthropogenic) activity, such as waste combustion, bonfires and agricultural waste combustion and oil refining (HPA, 2008, ATSDR 1998).
Dioxins are high molecular weight compounds with low water solubility and low vapour pressure. These parameters control much of their behaviour in the environment. Generally, due to the low vapour pressures of dioxins, the amount present as a vapour is considered negligible, meaning that most is associated with particulate matter and is therefore generally associated in combustion processes with small particles such as ash (ATDSR, 1998). Dioxins are also not very soluble in water, which means that they are not generally transported in water droplets. Deposition is primarily by physical processes such as gravitational (dry) settling (larger particles will settle close to the site while smaller particles take longer to settle and may travel further), and through wet deposition (scavenging of particles by rain). As a result of this inhalation of dioxins is not considered to be a major route of exposure. The majority of dioxins emitted into the atmosphere will either deposit on water bodies, where it becomes part of the sediment, on hard surfaces, where it becomes part of urban run-off, or on the surface of vegetation where there is potential to enter the food chain(ATSDR, 1998).
Dioxins vary in terms of chemical structure and in toxicity. The most toxic and most widely studied of these is 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) (Figure 1). However there are 16 other compounds of concern which are all structurally similar to TCDD in that they have chlorine in the same 2,3,7 and 8 positions(HPA, 2008, ATSDR, 1998). In order to assess the risk from complex mixtures of dioxins, an internationally-agreed approach has been adopted that assigns a relative potency factor to each of the other 16 compounds, based on a comparison with the potency of TCDD. These relative potency factors are called Toxic Equivalency Factors (TEF). The total toxic equivalency (TEQ) of a mixture is the sum of the ‘TEF x concentration’ for each dioxin in the mixture. The toxicity of the mixture is then equal to the toxicity of an equivalent amount of the TCDD. There are a number of different weighting systems for estimating the TEQ. The International Toxic Equivalents system (I-TEQ) is used in the permitting and monitoring of Hanson Cement, while others such as the current WHO-TEQ system, which also includes TEFs for dioxin-like polychlorinated biphenyls (PCBs), are also widely accepted.
Figure 1: Structure of TCDDAt high exposures, such as have been seen in the past in people exposed occupationally or following industrial accidents, the most frequent effect is a severe form of acne called chloracne (HPA, 2008). This may be present for many yearsas dioxinsare not rapidly metabalisedin the body. Liver damage has also been observed in some individuals(HPA, 2008). Children exposed to dioxins would be expected to display similar effects, although appear to be more sensitive than adults(HPA, 2008).
Studies in individuals who had high exposures also provide evidence that dioxins are associated with an increased risk of cancer and, possibly, ofcardiovascular disease. The International Agency for Research on Cancer has classified TCDD as causing cancer in humans(HPA, 2008). A wide range of toxic effects has been observed in animal studies, including cancer, effects on the immune and reproductive systems and effects on development of the foetus(HPA, 2008 van LeeuwenYounes, 2000, COT, 2001).
In conclusion, food is the main route (>90%) of human background exposure to dioxins (WHO). Contamination of the food chain is primarily caused by deposition of emissions on farmland and waterbodies and subsequent bio-accumulation.
1.2Air Quality Standards and Health Effect Guidelines
There is no air quality objective for dioxins. The Waste Incineration Directive (WID) states that UK point source emissions should be reduced to 10% of their 1985 value by 2005 (EU, 2000). The WID also determines that emissions of dioxins from waste combustion processes must comply with the European Convention on Long Range Trans-boundary Air Pollution. This convention sets an emission limit for dioxins from stationary sources at 0.1ng m3 (1 ng = 10-9 g) as this level was capable of being met by current abatement technologies (UNECE, 1979).
The UK’s Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (COT) has reviewed current data and set a tolerable daily intake (TDI) at 2 picograms per kilogram body weight per day (pgKg bw-1 day-1) (COT, 2001). ATDI is defined as the amount of a substance that can be taken in each day that over a lifetime will not present a significant risk to health. A study in which female rats were exposed to TCDD throughout pregnancy was used as the basis of the TDI. The lowest level at which an adverse effect was seen, the Lowest Observed Adverse Effect Level (LOAEL), was used to calculate the rat maternal body burden (because of the long-term accumulation of dioxins in the body, the effects were related to the total body burden rather than to a daily dose). This was converted to an equivalent human maternal body burden by dividing by a numerical factor to take account of uncertainties in extrapolating from rats to humans, and in using a LOAEL rather than a No Observed Adverse Effect Level. This body burden was estimated to result from a lifelong daily intake of about 2 pg TCDD/kg bw/ day (COT, 2001).
The Committee considered that a TDI based on these reproductive effects would also protect against any risk of carcinogenicity from dioxins and dioxin-like PCBs since a significant increase in incidence of tumours was only found at doses that were higher than the LOAEL (COT, 2001).
An earlier review by World Health Organisation (WHO) established a TDI in the range 1-4 pg/Kg bw day-1 (van LeeuwenYounes, 2000). In its analysis of the health data the WHO emphasise that the TDI is a measure of lifetime exposure, and occasional short term exposures above the TDI would have no health consequences, provided that the average intake over long periods is not exceeded(van LeeuwenYounes, 2000). Furthermore, COT have also stated that occasionally consuming more than the TDI would not be expected to result in harmful effects, providing that the average intake over a prolonged period is within the TDI (COT, 2001).
The relationship between stack emissions and any likely human exposure to those emissions requires modelling of intake based upon local factors, such likely impact on soil and herbage concentrations and consideration of amount and type of impacted food consumed.
2.Background to Dioxin Emissions
2.1UK Emissions
The National Atmospheric Emission Inventory provides details on the UK emissions of a number of chemicals including dioxins. Over the last 20 years there has been a significant reduction in the total amount of dioxins emitted into the atmosphere (Figure 2.1.1).
Figure 2.1.1: Total UK dioxin emissions to atmosphere between 1990 and 2009When these data are examined for the Combustion in Manufacturing Industries and Construction sector (which includes cement manufacture), it is apparent that emissions have been falling in line with UK trends (Figure 2.1.2), at least in part as result of a more stringent regulation of such processes.
Figure 2.1.2: Total UK dioxin emissions to atmosphere from combustion in manufacturing industries and construction sector.
By 2008 the main emissions of dioxins were associated with urban areas (Figure 2.1.3). It is clear that dioxin emissions are expected to be substantially higher in urban areas.
/ 0 – 0.01 mg km20.01 – 0.1 mg km2
0.1 – 0.3 mg km2
0.3 – 1 mg km2
1– 10.0 mg km2
10.0 – 100.0 mg km2
100-1000 mg km2
> 1000 mg km2
Figure 2.1.3: UK total emissions of dioxins on a 1km grid square basis in 2008(NAEI, 2011)
2.2Regional Emissions
When total emissions are examined at a regional level it is clear that dioxin emissions are primarily linked to the more populated NorthEastern side of the County of Flintshire (Figure 2.2.1), with particularly high emission expected on immediately adjacent to the coastline and in more populated areas such as Mold and Buckley.
/ 0 – 0.01 mg km20.01 – 0.1 mg km2
0.1 – 0.3 mg km2
0.3 – 1 mg km2
1– 10.0 mg km2
10.0 – 100.0 mg km2
100-1000 mg km2
1000 mg km2
Hanson Cement Site
Figure 2.2.1: Total modelled emissions of dioxins in 2008 on 1km grid square basis (NAEI, 2011)
It is also possible to obtain point source emission data for 2008 from the National Atmospheric Emissions Inventory. This allows the location of the principal individual emitters of pollutants (Figure 2.2.2). Hanson Cement is identified as the largest point source emitter of Dioxins in Flintshire in 2008 and is the 6th largest point source emitter in Wales. However, in order to put that into context, it should be noted that emissions from Hanson Cement accounted for only 1% of the total combined emissions from the highest ten point source emitters in Wales that year. Furthermore, on a regional basis there are significantly greater emissions from an industrial plant immediately adjacent to the county boundary. When plants within 15mile radius of Padeswood are considered then Hanson Cement emissions only represents 11% of industrial point source emissions in that area.
/ 0.0001 g per annum (pa)0.0001 – 0.0005 g pa
0.0005 – 0.001 g pa
0.001 – 0.005 g pa
0.005 – 0.01 g pa
0.01 – 0.05 g pa
0.05-0.1 g pa
0.1 – 0.5 g pa
0.5 – 1 g pa
>1 g pa
Hanson Cement
Figure 2.2.2: Point source emitters of dioxins in Flintshire in 2008(NAEI, 2011)
3.Emissions Limits and Stack Monitoring
There are two aspects when considering the impact of emissions at source. The first is to examine the prescribed limits for emissions i.e. those contained as conditions in the permit. The second aspect is to examine the data recorded for actual dioxin emissions from the point sources. The concentration of dioxins in emissions are measured as an equivalent concentration of TCDD using the I-TEQ system.
The history of the limits (Table 3.1) applied to point source emissions at the site shows that prior to 2002, there were no emission limits for dioxins at the Cement works in Padeswood. Prior to commissioning of the new kiln 4 in 2005,the permit also required the operator to conduct a baseline soil and moss bag survey of dioxins/furans and dioxin-like PCBs. The current emission limits are in line with the Waste Incineration Directive (WID) which covers burning of wastes in incinerators and as fuels in other manufacturing processes (e.g. Cement Kilns).
Table 3.1: History of dioxin emission limits contained in environmental permitsEmission Point / Authorisation BH3738
November 1999 / Authorisation BR8611
March 20021 / Permit BL1096
20042
A1 (Kiln 1&2 stack) / Limit to be set following period of monitoring / 0.1 ngm-3 / 0.1 ngm-3
A2 (Kiln 3 stack) / Limit to be set following period of monitoring / 1.0 ngm-3 / 1.0 ngm-3
A8 (Kiln 4 stack) / ----- / 0.1 ngm-3
1 Limit applied as of 1st July 2002
2In addition to the limit, decommissioning of Kiln 3 was required prior commissioning of Kiln 4 and Kilns 1&2 were not permitted to be operated at the same time as Kiln 4 without written permission.
Although there were no specific limits, emissions of dioxins have been monitored at Padeswood Cement works since 2000. Estimates of total site emissions (Figure 3.1) show a general reduction in point source emissions that mirrors national trends.
The notable exception to this trend is 2004, where total emissions for the site are recorded as 25 times higher than for the previous 12 months. This peak in dioxin emissions is also captured in the national data for the sector (Figure 2.1.2), where it is evident that the emissions from the Cement works at Padeswood represented approximately 50% of total emissions frompoint sources resulting from combustion bythe UK manufacturing industries and construction sector.
Comparison of the emissions recorded at each monitoring point available against emission limits (Figure 3.2) indicate that despite limits being in place, Kilns 1&2 were rarely recorded as emitting in accordance with the permit conditions and that Kiln 3 also emitted significantly more than permitted levels. However, it is important to emphasise that Castle Cement Ltd were prosecuted for these breaches and the potential exposure to dioxins were investigated at the time (see Section 4). Since commissioning of Kiln 4 the majority of samples taken have been below emission limits. The exception is an exceedance that occurred in 2008 during a trial of Solid Recovered Fuel (SRF) use in the kiln. Analysis of the cause pinpointed issues with the waste feed system and the trial was terminated until the feed system was redesigned. Subsequent measurements returned to normal.
Figure 3.1: Total emissions of dioxins to atmosphere from cement works at Padeswood (EA 2011)Figure 3.2: Total recorded emissions compared to emission limits for cement works at Padeswood
It must be stressed that the standard is based upon technical achievability and that exceedance does not automatically imply a risk to health.