Sampling and Analysis of Dioxins in the ... - IDS-Environment

Sampling and Analysis of Dioxins in the Environment
Ian Barnabas
Analytical and Environmental Services, Northumberland Dock Road, Wallsend, Tyne
and Wear, UK, NE28 0QD.
Introduction
Dioxin is a collective term for over 200 compounds from the group of
polychlorodibenzo-p-dioxins (PCDDs) and polychlorodibenzofurans (PCDFs), which
belong to the chlorinated hydrocarbons class of compounds. However, it is the 17
dioxins and furans (or congeners) that have chlorine substitution at the 2,3,7,8-
positions which are classed as the most toxic and have therefore generated the most
interest. 2,3,7,8-TCDD (the Seveso poison), is counted among the most dangerous
environmental pollutants. In addition, dioxins are not easily degradable and have a
tendency to bio-accumulate in lipid tissue of mammals and this combined with their
ubiquitous presence in the environment has led to great concern over the potential
human health effects.
Sources of dioxin
Dioxins are generally produced as unwanted by-products during thermal processes
involving the burning of organic material or following chemical manufacture from
some industrial processes. Dioxins are produced as traces in unwanted side-reactions
during the manufacture of certain chemical products containing chlorine (e.g. the
disinfectant hexachlorophane, the pesticide trichlorophenyloxyacetic acid, the wood
preservative pentachlorophenol (PCP) and special substances such as polychlorinated
biphenyl, PCB), as well as during the incineration of chlorinated hydrocarbons (e.g.
the plastic PVC). Alongside the chlorinated dioxin compounds, other halogenated
dioxins, for example brominated or mixed brominated/chlorinated dioxins (with
bromine) can also be formed. During waste incineration traces of dioxins have also be
found and it is for this reason that they find themselves as compounds to be monitored
within the Hazardous Waste Incineration Directive. However, due to tighter control of
these point sources it has been estimated that uncontrolled burning of residential
waste and accidental fires at landfill sites may now account for the greatest overall
environmental burden.
Background Levels
A recent study of EU background concentrations of dioxins in various matrices is
summarised below (1) .
Matrix Measured Typical Max Concentration Units
Range
Contaminate Sites
Soil

Human Exposure and Health Effects
Humans can be exposed to dioxins through a number of routes including inhalation of
air, dermal absorption, ingestion of soil, and consumption of drinking water and food.
However, is has been quoted in literature many times that greater than 95% of the
daily dioxin intake is from food and in particular foodstuffs rich in fat are important
due to the lipophilic nature of dioxins. It is for this reason that the world health
organisation (WHO) has recently set tolerable daily intakes of dioxins at between 1-4
pg/kg bw/day.
Short-term human exposure to high levels of dioxins may result in skin lesions, such
as chloracne and patchy darkening of the skin, and altered liver function. Long-term
exposure is linked to impairment of the immune system, the developing nervous
system, the endocrine system and reproductive functions. Chronic exposure of
animals to dioxins has resulted in several types of cancer. 2,3,7,8-TCDD was
evaluated by International Agency for Research on Cancer (IARC) and was
categorised as a known human carcinogen. However, 2,3,7,8-TCDD does not affect
genetic material and there is a level of exposure below which cancer risk would be
negligible.
Sampling Methodology
Sampling protocols are obviously dependent on the matrix being sampled. The more
common environmental sample types are summarised below.
Ambient Air
Protocols for sampling ambient air generally follow US Environment Protection
Agency (EPA) methodology (2) and utilise high volume samplers, typically sampling
between 300 and 400 m 3 in a 24 hour period. The dioxins in particulate are trapped
first on a filter paper with vapour phase samples being trapped on polyurethane foam
plugs (PUF). A range of 13 C 12 labelled dioxins and furans are added to the PUF plug
prior to sampling. These compounds behave in an identical manner to the native
dioxins and are subsequently analysed to determine whether there has been losses
during the sampling procedure.
Stack Emissions
Two main methods are widely used throughout Europe for monitoring dioxin
emissions from stacks and are based on EPA (3) and CEN (4) standards. The
methodology is similar and is based on a heated sample probe which is inserted into
the stack and is used to obtain a representative sample under isokinetic conditions (the
sample is removed from the stack at the same flow rate as the stack gas flow). In a
manner similar to ambient air sampling, the dioxins are then trapped first on a heated
filter paper and then on a polymeric resin (XAD) to sample those dioxins in the
vapour phase (alternative systems do exist but are not discussed here). Any
condensate obtained from the stack gas may also be taken for analysis. Finally, the
entire front section of the sampling train is rinsed with solvent to ensure any
particulate present in the system is included. Again, 13 C 12 labelled dioxins and furans
are added to both the filter and resin to ascertain whether there has been any
breakthrough during sampling.
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A typical sample submitted to the laboratory for analysis is shown in Figure 1, where
the filter(i), resin trap(ii), condensate(iii) and solvent rinses(iv) are depicted.
iii
iv
ii
i
Figure 1. A typical stack emission sample submitted for analysis.
Soils, Sediments and Liquids
Soil, sediment and liquid samples are taken in accordance with standard sampling
procedures for organic samples, with special attention paid to the cleaning procedures
of the glass containers.
Analytical Methodology
Procedures for analysing dioxins have similar sources to those for sampling. Both
EPA (5),(6) and CEN (7) methodologies are used and again, are similar to each other. In
all cases, 13 C 12 labelled dioxins and furans (different to those added prior to sampling)
are spiked into the sample before extraction. The relative concentration of the
compound is then used to compensate for any losses during the analytical procedure.
Quality control procedures are extensively used throughout the whole process and it is
estimated that most reference methods have over 20 individual pass/fail criteria built
into the method. The analytical process is broken down into each of the key stages.
Sample Extraction
The methodology used to prepare the sample for analysis is dependent of the matrix
type but generally involves traditional Soxhlet extraction with an organic solvent
(often toluene). Soils and related samples are air dried prior to the extraction stage.
Liquid samples are filtered to remove particulate matter prior to separation using a
water immiscible solvent. The filter is then Soxhlet extracted and subsequently
combined with the solvent from the water extraction. In the case of air samples, the
entire sample (filter, resin/PUF, solvent rinses and condensate) are combined and
Soxhlet extracted together. Typical extraction times, regardless of matrix type, are in
excess of 24 hours and produce 200-300 ml of solvent.
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Sample Clean-up
Clean-up procedures are of particular importance for dioxin analysis in order to
remove gross contamination from the resulting sample extract. In addition, specific
clean-ups are employed to remove potential interferences (e.g. PCBs and
polychlorinated diphenyl ethers) which are often present at much larger
concentrations than the dioxins being measured and which can cause problems with
the final analysis stage. The type and number of clean-up procedures used for any
given sample is obviously dependent on the amount of contamination present in the
sample but are often based on column chromatography using various polarity
adsorbents. Silica (neutral, acidic and basic) is useful in removing polar interferences,
also carbon, florisil and alumina are often successfully employed. Many other
procedures may be used as multiple clean-ups are often required and the choice is left
largely to the analyst.
Analysis
The final analytical determination of dioxin concentration is carried out using high
resolution gas chromatography-high resolution mass spectrometry (HRGC-HRMS).
Low resolution GC-MS may be employed but generally only as a screening technique
for samples containing high concentrations of dioxin. HRMS is a specialist technique
and requires a skilled analyst but is necessary to ensure low limits of detection are
achievable and chromatographic interferences are minimised. Concentrations are
calculated for each of the 17 individual 2,3,7,8-substitued toxic congeners and ‘total’
values for each chlorine substitution level (i.e. tetra, penta chlorinated) are also given.
Analysis is carried out on a primary non-polar capillary column, although a second
polar column may also be used to ensure all of the 17 toxic congeners can be uniquely
separated from all other ‘non-toxic’ dioxins. Typical detection limits achievable with
the technique are in the order of 25-250 fg on-column, depending on the specific
congener.
Reporting
Concentrations of each of the 17 individual 2,3,7,8-substituted congeners are reported
and international toxic equivalency factors (TEF) are used to determine the overall
relative toxicity of the sample in international toxic equivalents (I-TEQ) (8) . This is a
recognised system where all of the 17 toxic congeners have their toxicity expressed
relative to the most toxic compounds, 2,3,7,8-TCDD (given an arbitrary TEF of
1.000). Multiplication of the concentration with the corresponding TEF gives the
concentration in I-TEQ. Several schemes exist although the NATO/CCMS scheme is
often used for environmental samples and is shown in table 2.
In addition to reporting the toxic congeners, group totals are also generally given for
each of the five chlorination level (tetra to octa). This can give valuable information
regarding the nature of the dioxin. A profile from a stack emission sample containing
high levels of dioxin is shown in figure 2 where the filter (particulate phase) and resin
(vapour phase) have been analysed separately. As expected, the more volatile dioxins
are present in the vapour phase whereas the less volatile dioxins are retained in the
particulate phase.
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COMPOUND
I-TEF
2,3,7,8-TCDF 0.100
2,3,7,8-TCDD 1.000
1,2,3,7,8-PeCDF 0.050
2,3,4,7,8-PeCDF 0.500
1,2,3,7,8-PeCDD 0.500
1,2,3,4,7,8-HxCDF 0.100
1,2,3,6,7,8-HxCDF 0.100
2,3,4,6,7,8-HxCDF 0.100
1,2,3,7,8,9-HxCDF 0.100
1,2,3,4,7,8-HxCDD 0.100
1,2,3,6,7,8-HxCDD 0.100
1,2,3,7,8,9-HxCDD 0.100
1,2,3,4,6,7,8-HpCDF 0.010
1,2,3,4,7,8,9-HpCDF 0.010
1,2,3,4,6,7,8-HpCDD 0.010
OCDF 0.001
OCDD 0.001
Table 2. NATO/CCMS Scheme of Toxic Equivalents.
16000
14000
pg in sample
12000
10000
8000
6000
4000
2000
XAD-2 Resin
Filter
0
TCDF's PeCDF's HxCDF's HpCDF's OCDF
Homologue group
Figure 2. Dioxin profile from a contaminated stack emission.
Conclusions
Dioxins are ubiquitous pollutants in the environment that may have adverse effects on
both animal and human health. Their accurate and timely quantitation and
identification of their sources is therefore of great importance. The sampling and
analysis procedures employed for environmental samples are specialised and require
dedicated facilities and equipment. Overall emission levels are diminishing across
Europe due to increased awareness of the problem, more stringent legislation and
improved monitoring.
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References
1. Compilation of EU dioxin exposure and health data, Task 2 Environmental
Levels. Report produced for European Commission DG Environment, UK
DETR:1999.
2. US Environmental Protection Agency Compendium Method TO-9A
Determination of polychlorinated, polybrominated and brominated/chlorinated
dibenzo-p-dioxins and dibenzofurans in ambient air. January 1999.
3. United States Environmental Protection Agency, Emission Measurement
Branch, Technical Support Division, OAQPS Method 5 Determination of particulate
emissions from stationary sources.
4. BS EN 1948-1:1996 Stationary source emissions – Determination of the mass
concentration of PCDDs/PCDFs Part 1. Sampling.
5. United States Environmental Protection Agency, Emission Measurement
Branch, Technical Support Division, OAQPS Method 23 The determination of
Polychlorinated Dibenzo-p-dioxins and Polychlorinated Dibenzofurans From
Municiple Waste Combustors.
6. United States Environmental Protection Agency Office of Water Regulations
and Standards Industrial Technology Division July 1989 Method 1613 Tetra- through
Octa- Chlorinated Dioxins and Furans by Isotope Dilution.
7a. EN 1948-2:1996 Stationary source emissions – Determination of the mass
concentration of PCDDs/PCDFs Part 2. Extraction and Clean-up.
7b. EN 1948-3:1996 Stationary source emissions – Determination of the mass
concentration of PCDDs/PCDFs Part 3. Identification and quantification.
8. International toxicity equivalence factor (ITEF) by Kurtz FW, Barnes DG,
Bottimore DP, Greim H. The international toxicity equivalency factor (I-TEF) method
for estimating risks associated with exposure to complex mixtures of dioxins and
related compound. Toxicol Environ Chem 1990:26:99-109
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