Track A review : PeCB
PEER REVIEWS OF THE DRAFT DOSSIER
Pentachlorobenzene
REVIEWER: Ingrid Hauzenberger
Summary:
Introduction
Pentachlorobenzene (PeCB) belongs to the group of chlorinated benzenes.
Due to their risk profile PeCB is severely restricted or banned in many
countries. Thus levels in the environment have decreased during the past
years. However releases still occur from various sources (e.g. barrel burning of
households, pesticide use). Monitoring data show that PeCB is present in all
environmental media including humans and in remote areas.
Method
The review evaluates critically the technical content of the proposal like in
governmental documents and risk assessments.
The risk profile was compared against the indicative numerical values given in
EB 1998/2. In addition the submitted data in the proposal were assessed for
their quality and completeness. The factors that had been taken into account
for the conclusions on para. 2 a-b of EB 1998/2 were also recorded.
POP characteristics-Summary of dossier in terms of the guidance and
indicative numerical values provided in Executive Body Decision 98/2 for:
Potential for long-range atmospheric transport:
Based on the submitted data (vapour pressure, half-life, model
calculation and monitoring data) it can be assumed, that PeCB is
subject to LRAT. The indicative numerical values given in EB 1998/2
regarding vapour pressure and atmospheric half-life are fully met.
Toxicity and ecotoxicity:
There is sufficient evidence that PeCB has a high (eco)toxic potential
and can adversely effect human health and the environment. The
requirement of EB 1998/2 with regard to toxicity is met.
Persistence:
Based on the provided information PeCB exhibits a half-life in water >
two months. Also in sediment PeCB is resistant to biodegradation.
Under certain conditions PeCB might be degraded in soil. However all
reported half-lives except one exceed the indicative numerical value
given in EB 1998/2. It can be concluded that PeCB is persistent in the
environment.
Bioaccumulation:
The submitted data show that PeCB has a high bioaccumulation
potential, which is substantiated by log Kow of around 5 and BCFs up to
260 000. Tests under suggested steady-state conditions and a field
study gained BCF values on wet weight basis above the indicative
numerical values of EB 1998/2. One BAF value determined in a
Track A review : PeCB
terrestrial model species suggests an extremely high bioaccumulation
potential.
Monitoring or equivalent scientific information suggesting long-range
transboundary atmospheric transport
Based on submitted monitoring data from remote regions it can be concluded
that PeCB is susceptible to LRAT. Though environmental concentrations are
declining PeCB can still be detected in sensitive areas such as the Arctic and
in biota.
Sufficiency of the information to suggest that the substance is likely to
have significant adverse human and/or environmental effects resulting
from its long-range transboundary atmospheric transport –
Human and wildlife are exposed to a cocktail of different contaminants in the
environment including remote regions. Therefore it will be difficult to relate or
predict effects to one single compound, especially if they have high hazard
potentials. In this respect the PEC/PNEC approach is not a suitable tool to
protect ecosystems in sensitive areas. PeCB exhibit persistent, bio accumulative and toxic properties. Due to the widespread distribution of PeCB
in the environment including remote regions, the occurrence in arctic top
predators and the hazard potential, adverse effects on human health and the
environment cannot be excluded.
ConclusionsThe dossier is well prepared, updated and fulfils the requirements of EB decision
1998/2. However, data on human health could be more comprehensive.
Introduction
A proposal on pentachlorobenzene (PeCB) prepared by the Netherlands was
submitted on behalf of the European Commission to the UN ECE secretariat for
consideration as a potential POP amending Annex I of the POP Protocol. According
to the EB decision 1998/2 the proposal includes a risk profile, which addresses risks
to human health and the environment associated with the uses and releases and a
summary report on e.g. monitoring and degradation data. It further states that if the
risk profile is deemed acceptable a technical review of the proposal shall be
prepared. This technical review serves this purpose concerning the Track A review,
which is limited to the evaluation of the proposal against the indicative numerical
values according para 1. a-d and para 2. a-b of EB 1998/2.
The review evaluates critically the technical content of the proposal like in
governmental documents and risk assessments. The review evaluates critically the
technical content of the proposal like in governmental documents and risk
assessments. The review is based on the information contained in the dossier, an
addendum to the dossier and the response to the comments to the dossier. As
agreed additional information e.g. from open literature was only considered in critical
cases or if more recent relevant information was available.
The risk profile was compared against the indicative numerical values given in EB
1998/2. In addition the submitted data in the proposal were assessed for their quality
and completeness. The factors that had been taken into account for the conclusions
on para. 2 a-b of EB 1998/2 were also recorded.
Track A review : PeCB
POP characteristics
a) Potential for long-range atmospheric transport (LRAT)
EB 1998/2 considers for LRT the evidence that the substance has a vapour pressure
below 1 000 Pa and an atmospheric half-life greater than two days. Or alternatively,
monitoring data showing that the substance is found in remote regions.
Based on the vapour pressure of around 2 Pa PeCB can be considered as semivolatile. The Henry’s Law Constant confirms that volatilisation from surface water and
moist soil can take place (HSDB, 2003). In the atmosphere PeCB might remain as a
vapour and is susceptible to photooxidation at a very slow rate. The calculated
atmospheric half-life is 45 to 467 days, but no further information explaining this wide
range is given in the proposal. Monitoring data indicate that the wide distribution of
PeCN in the northern hemispheric atmosphere is a result of the long atmospheric
residence time. Monitoring and model data by EMEP also show the ability of PeCB
(i.e. high calculated transport distance) to undergo LRAT.
Conclusion: Based on the submitted data (vapour pressure, half-life, model
calculation, monitoring data) it can be assumed, that PeCB is subject to LRAT. The
indicative numerical values given in EB 1998/2 regarding vapour pressure and
atmospheric half-life are fully met.
b) Persistence
The indicative numerical values for persistence according EB 1998/2 are half-life in
water greater than two months, or half-life in soils or sediments greater than six
months. Alternatively, evidence that the substance is otherwise sufficiently persistent
to be of concern within the scope of the protocol.
Abiotic degradation of PeCB was observed in a laboratory photolysis study using an
organic solvent/water solution 1:9. However, based on the hydrophobic characteristic
of the substance adsorption to suspended matter in the water column and transport
to the sediment can be expected. Thus under field conditions susceptibility to
photodegradation is likely to be limited. The proposal reported estimated half-lives for
photodegradation of > six month.
The degradation rate in sediment is low despite the occurrence of anaerobic
conditions, which can favour reductive dechlorination. The dossier also pointed out,
that occurrence of PeCB from metabolism of HCB is possible. The reported half-lives
in soil under anaerobic conditions were several years.
Laboratory soil studies indicate half-lives greater than six months. Information on
HCB, which can also be of relevance, shows that under water saturation high rates of
dechlorination are observed (Brahushi et al., 2004).
In an agricultural field study the decrease of PeCB was partly attributed to
volatilisation. Reported half-lives are 103 and 219 days.
Conclusion: Based on the provided information PeCB exhibits a half-life in water >
two months. Also in the sediment PeCB is resistant to biodegradation. In soil certain
conditions may occur which favour PeCB degradation resulting in half-lives less than
six months. However these applies only to one reported value in the proposal. All
other reported half-lives in soil exceed the indicative numerical value given in EB
1998/2.
Track A review : PeCB
c) Bio-accumulation
Indicators for bio-accumulation according EB 1998/2 are (i) a BCF or BAF greater
than 5 000 or a log Kow greater than 5; or alternatively, if the bio-accumulation
potential is significantly lower than (i) other factors, such as high toxicity of the
substance, that make it of concern within the scope of the protocol.
The proposal gives a good overview on the range of reported BCFs (from 1 800 to
260 000), which reflects different test designs and conditions as well as differences in
expression of BCFs. Though the BCF related to lipid content enables good
comparison of test results, regulatory bodies (e.g. EU, EPA) use trigger values based
on BCF wet weight basis.
Taking the comments from industry into consideration data and explanations for
BCFs and log Kow have improved. However, detailed test conditions (e.g. lipid
content of test species), if available at all, were not reported und could have
contributed to a better interpretation of the reported values.
The submitted data (including a field study) show that uptake of PeCB in aquatic
species can result in very high BCF values. Furthermore an elimination half-live
greater than 300 days for eels was found (WHO, 2004), which also flags the
accumulation potential of this substance. US EPA (1998) used a BCF value of 8 314
to characterise the bioaccumulation potential of PeCB. A BAF of 401 000 was
determined in a terrestrial species (E. andrei) (Government of Canada, 2003).
The log Kow is around 5 (4.8 to 5.2, whereas 5 out of 7 measurements were slightly
above 5) and indicates further the high potential for bioaccumulation.
Conclusion: The submitted data show that PeCB has a high bioaccumulation
potential, which is substantiated by a log Kow of around 5 and a range of BCF values
from 1 800 up to 260 000. The high variation of BCF values is probably based on
different expression of BCFs and test conditions. However, tests under suggested
steady-state conditions and a field study reveal BCF values on wet weight basis
above the indicative numerical values of EB 1998/2. One BAF value determined in a
terrestrial model species suggests an extremely high bioaccumulation potential.
d) Toxicity and ecotoxicity
EB 1998/2 describes toxicity as adverse effects to human health and/or the
environment.
Ecotoxicity: The toxicity of chlorobenzenes to aquatic organisms increases with
increasing chlorination partly due to increased uptake and bioaccumulation of higher
chlorinated compounds (WHO, 2004). The proposal compiles acute and subchronic
toxicity data for aquatic organism (algae, crustaceans and fish) from regulatory
bodies and IPCS/WHO. Based on a LC50 of 250 µg/l in fish and a NOEC of 10 µg/l in
crustaceans PeCB can be regarded as very toxic to aquatic organisms. PeCB is also
toxic to algae (Sicko-Goad et al., 1989).
No data were available on sediment dwelling organisms or other terrestrial species
and wildlife.
Human Health: The dossier recapitulates data from animal experiments with PeCB.
The lowest LD50 value for acute toxicity (oral exposure, rats) was found to be 250
mg/kg bw. In a subchronic study a NOEC of 12,5 mg/kg was established. Negative
results were obtained in Ames test, other mutagenicity tests with mammalian cells
which were found to be negative (IRIS, Toxnet) were not mentioned in the proposal.
The dossier points out that PeCB has been classified concerning carcinogenicity in
Track A review : PeCB
Group V (inadequate data for evaluation). Data from rat and monkey metabolism
studies, Engst et al. (1976) and Rozman et al. (1979) where pentachlorophenol
(classified as B2, probable human carcinogen) was found to be one major metabolite
of pentachlorobenzene are missing in the proposal. Pentachlorophenol has also
been identified in the urine of rabbits administered pentachlorobenzene (Kohli et al.,
1976).
In the adapted dossier another toxicity study from NTP with rats and mice was
included. NOELs for histological lesions in the liver in rats were found to be 33 ppm
for male rats and 330 ppm for female rats, whereas the NOEL for histological lesions
in female mice was 100 ppm and no NOEL could be determined for male mice. Blood
abnormalities were reported as well. From the reviewers point of view several
important findings were not mentioned in the proposal. The organs most affected by
exposure with PeCB were beside the liver the kidneys in rats, with male rats being
more sensitive. Thyroid gland effects also occurred in rats, though they were
observed in the 1000 and 2000 ppm dose group only.
From the ethical point of view the term “epidemiologic studies” should be used
instead of the term “human studies” in the proposal.
Conclusion: There is sufficient evidence that PeCB has a high (eco)toxic potential
and can adversely effect human health and the environment. The requirement of EB
1998/2 with regard to toxicity is met.
Release to the environment
a) Environmental levels
The proposal reported monitoring data in different media: air (including precipitation),
sediment, soil and biota (mosses, mussel, blubber, fish, bird and bear) focusing on
remote regions. Data on PeCB levels in seawater were obtained by Strachan et al.
(2001) who investigated PeCB concentrations in the Bering and Chukchi Sea.
Industry provided additional information on herring gull eggs, sediment and
suspended matter from the Great Lakes and Niagara river. Data demonstrated that
PeCB concentrations declined steadily in this region. A trend which is confirmed by
other monitoring data, mainly obtained from industrial regions (HSDB, 2003).
Recently more data has become available for remote areas. According to
Government of Canada (2003) peak chlorobenzenes (PeCB and HCB)
concentrations in northern lake sediments also dated back to the late 1970s and
1980s. Nevertheless PeCB still occur in environmental media and biota in remote
regions. Monitoring data could not show a declining trend for Σchlorobenzenes in
polar bears (Verreault et al., 2005). However, only the sum of chlorobenzenes
including PeCB was reported. Concentrations of PeCB were elevated in bottom
sediments from harbours of northern Norway and the Kola Peninsula compared to
previous reports for background areas at offshore locations (de March et al., 1998 in
AMAP, 2004). However these concentrations could also originate from arctic local
sources.
b) Levels in humans and biota compared to effect levels
PeCB is detected in environmental media as well as in biota. PeCB has also been
detected in human adipose tissue and human milk (e.g. Smeds and Saukko, 2001).
Currently there is no adequate scientific tool available to estimate risks arising from
substances, which show persistent, bioaccumulative and toxic properties. In this
respect the PEC/PNEC approach is not a suitable tool to protect sensitive areas such
as the Arctic. Ecotoxicity data were also limited for such a comparison (no effect data
for sediment-dwelling or soil-born organisms, birds or wildlife are available).
Track A review : PeCB
Compared to the high aquatic toxicity, levels in some arctic species were also relative
high. However, due to the fact that contamination of human and environment is not
restricted to PeCB it is difficult to relate effects to this special compound. As it is
shown in polar bears (Verrault et al., 2005) exposure occurs through a suite of
chlorinated hydrocarbons, including organochlorine pesticides and by products,
polychlorinated biphenyls and metabolites of these compounds. Several classes of
compounds like heavy metals, PBDE, PFOS which were not investigated in this study
also contribute to the body burden of polar bears and other species of remote
regions, including marine mammals as it is shown in other publications. Such
compounds can alter biological functions and behaviour in several ways and can
contribute to a reduced fitness and/or more severe effects. Therefore any effort
should be taken to reduce body burden and environmental concentrations to
chlorinated hydrocarbon contaminants. Taking into consideration the arguments
above this is in contradiction to the statement of industry, which claimed that
insufficient evidence for significant exposure to biota in remote regions exsists.
Conclusion
PeCB can be characterised as persistent, toxic and bioaccumulative. Though
emissions from PeCB have been effectively reduced this compound can still be found
in environmental media and biota including humans. PeCB has recently been
detected in a variety of arctic species including top predators. Organisms and
humans are exposed to a cocktail of different contaminants. Ecotoxicity effect data
are limited and synergistic effects are difficult to predict. Therefore any effort should
be taken to reduce body burden and environmental concentrations of these
contaminants.
According to the risk profile of PeCB adverse effects to humans and the environment
including remote areas cannot be excluded.
The dossier is well prepared, updated and fulfils the requirements of EB decision
1998/2. However, data on human health could be more comprehensive.
Acknowledgment
Special thanks to Dr. Maria Uhl for her cooperation and review of the human health
part.
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