Download summary of peer technical review comments on the

SUMMARY OF PEER TECHNICAL REVIEW COMMENTS ON THE
HEXACHLOROBUTADIENE DOSSIER SUBMITTED UNDER THE UNECELRTAP POPS PROTOCOL
Introduction: Hexachlorobutadiene (HCBD) is a halogenated aliphatic compound,
mainly formed as a by-product in the manufacture of chlorinated aliphatic compounds
(most likely tri- and tetrachloroethene and tetrachloromethane). It has also been
manufactured and used as an agricultural fumigant. HCBD has other applications in the
manufacture of rubber, as an additive in lubricants and transformer oils, and as a heat
dissipating liquid. The majority of manufacture appears to have been dramatically
reduced since the mid-1980s, and HCBD is no longer subject to large-scale manufacture
or use. In 2005, The Netherlands proposed HCBD for listing as a persistent organic
pollutant (POP) under the UNECE-LRTAP POPs Protocol. The LRTAP nomination
process includes the submission of a risk profile by the proponent Party, which, if
considered acceptable by the LRTAP Executive Body, then undergoes one or more
technical reviews. The technical review process has been separated into Track A (POPs
characteristics) and Track B (management options). This report is an abbreviated
summary of four independent technical reviewers of the risk profile undertaken under
Track A of this process. The original technical reviews are appended and should be
referred to should clarification be needed.
Methods: The technical reviews were conducted in a similar manner to those routinely
undertaken for peer-reviewed journal articles or government document preparation.
Reviewers were instructed to be transparent, and to include critical evaluation of such
aspects as, inter alia, availability, reliability, completeness and relevance of the
information and references. Only information contained in the dossiers was to be
addressed, and reviewers were to refrain from any elaboration of their content or
comments that could be considered to reflect policy. Thus, the statements and
conclusions made in the technical reviews address the sufficiency and veracity of the risk
profile in making the case that a substance is a POP under the LRTAP POPs Protocol.
Reviewers were at liberty to suggest additional citations and information, as routinely
performed in peer reviews, based on the reviewer’s knowledge of the subject and
contemporary literature. Following an introductory teleconference to discuss the peer
review charge, the reviewers acted independently and were instructed not to seek to
obtain consensus on issues, although conversations between reviewers were permitted.
Individual, independent, peer review reports were submitted by each reviewer. These
reports are summarized here with the understanding that the purpose of this summary is
to compile the independent findings, not to seek consensus on decisions or to provide any
further interpretation. For brevity, the terms “concluded” or “agreed” are used in this
following summary to refer to independent evaluations of whether the risk profile
provides sufficient information to draw its stated conclusions, rather than a concurrence
among reviewers or a de novo assessment of POPs characteristics.
POP characteristics in terms of the guidance and indicative numerical values
provided in Executive Body Decision 98/2 for:
Potential for long-range atmospheric transport: All four technical reviewers agreed
that the risk profile provides sufficient information that HCBD has the potential for longrange transboundary atmospheric transport.
Reviewers agreed that HCBD has a vapor pressure well below 1000 Pascals and
an atmospheric half-life greatly in excess of two days. Two reviewers noted that
evidence of the potential for long-range transport has been shown in a recent
study, which found low concentrations of HCBD in biota from Greenland; one of
these reviewers also mentioned that air monitoring in Sweden has detected HCBD
in areas of no known release.
Toxicity and ecotoxicity: All four reviewers agreed that the risk profile provides
sufficient information that HCBD has the potential to adversely affect human health
and/or the environment.
Three reviewers noted the acute toxicity of HCBD to aquatic organisms.
One reviewer noted that HCBD is classified in the European Union as harmful
according to several criteria relating to contact with skin, eyes, and the respiratory
system, as well as to toxicity and adverse effects in the aquatic environment.
Three reviewers noted that nephrotoxicity has been observed in rat studies.
Two reviewers noted that HCBD is regarded as genotoxic; one of these reviewers
also noted apparent mutagenicity and carcinogenicity, while the other reviewer
considered that the carcinogenic risk was unclear and provided additional
contemporary citations.
Persistence: Three reviewers agreed that the risk profile provides sufficient information
that HCBD meets the criteria for persistence. The fourth reviewer found that there was
insufficient reliable data to draw a conclusion on whether HCBD is persistent.
All four reviewers noted that there was conflicting or insufficient information on
the persistence of HCBD in water, soil, and sediment.
Three reviewers noted that, although the results are contradictory, they indicated
that HCBD is recalcitrant or persistent under aerobic conditions in water,
sediment, and soil. One of these reviewers noted two additional studies, not in the
dossier, which support the recalcitrant properties of HCBD in the environment.
Two reviewers noted that reductive dechlorination of HCBD may occur under
anaerobic conditions.
Bioaccumulation: All four reviewers agreed that the risk profile provides sufficient
information that HCBD meets the criteria for bioaccumulation.
All four reviewers noted that the log Kow values reported for HCBD are very near
to 5.
Three reviewers noted the conflicting data in relation to the BCF values.
One of these reviewers noted that the dossier does not explain why studies with
much lower BCF values observed in several aquatic organisms should be rejected.
This reviewer considered that the BCF values presented in the dossier did not
provide sufficient weight of evidence for meeting the criteria but subsequently
found reliable data, not in the dossier, indicating that a BCF higher than 5000 can
be expected for HCBD in carp.
Monitoring or equivalent scientific information suggesting long-range
transboundary atmospheric transport: All four reviewers agreed that the risk profile
provides sufficient information that HCBD has the potential for long-range transboundary
atmospheric transport.
Reviewers noted that there were very limited monitoring data on HCBD from
remote areas. Reviewers agreed that the presence of HCBD in biota from remote
areas, particularly Greenland, suggested long-range atmospheric transport as the
source of this contamination.
Sufficiency of the information to suggest that the substance is likely to have
significant adverse human and/or environmental effects resulting from its longrange transboundary atmospheric transport: Executive Body Decision 1998/2(2)
stipulates a technical evaluation of the sufficiency of the information that the substance is
likely to have significant adverse effects resulting from its LRAT. The conclusions of the
technical reviewers on this issue are carefully worded and best conveyed verbatim. Please
refer to the attached original documents for additional information and clarification.
Reviewer A: Available data does not allow to directly and adequately characterize
adverse human and/or environmental effects resulting from long-range
transboundary atmospheric transport. Nevertheless, monitoring data showing
HCBD presence in remote regions, and characteristics as environmental
persistence, potential for bioaccumulation, and toxicity to aquatic and mammalian
species suggest that potential damage could result from environmental pollution
determined by long-range transport. The information produced in the dossier is
considered sufficient to support the candidature of HCBD as a global POP.
Reviewer B: The dossier does not provide much information on the likelihood of
HCBD having significant adverse human and/or environmental effects resulting
from its long-range transboundary atmospheric transport. However, based on both
models used in the EMEP report, sufficient evidence was presented on the
likelihood of HCBD to have a long-range transboundary atmospheric transport.
… Adverse environmental effects could result from HCBD present in remote
regions. … Although data available does not allow to directly and adequately
characterize a human health risk, reasons for concern are related to the
toxicological endpoints identified in animal models.…
Reviewer C: Detection of HCBD in remote regions and in biota does not
necessarily, of itself, indicate an adverse effect. The levels detected are very low,
well below any known toxic effect level. There is no evidence in the dossier of
any time trend. There is only very limited evidence of non-threshold effects such
as might lead to adverse effects even at the very low concentrations measured.
There is some evidence of potential genotoxicity and some evidence of
carcinogenicity which could lead to non-threshold effects, but this evidence is not
presented in the dossier. It is not possible to conclude therefore from the available
data, that significant harm will arise from the transboundary transport.
Reviewer D: There was no supporting information in the dossier or any
supporting information dealing with the adverse effect of HCBD on humans. The
toxicity data for multiple mammal species suggests that HCBD is fairly toxic with
a NOAEL set at 0.2 mg/kg in rats due to renal toxicity. There are other toxicity
data that suggest via other routes of exposure (inhalation, dermal contact,
intraperitoneal) that HCBD exhibits some toxicity as a mutagen, teratogen or
carcinogen. That alone is cause for concern that toxicity is exhibited in multispecies via multi-exposures. Coupled with the fact that HCBD has shown
dramatic toxicity of aquatic organisms at fairly low concentrations (LC50 at the
μg/L level). It is thus conceivable to draw the conclusion that HCBD may have
adverse human effects if extrapolation is made from test species to humans.
Clearly HCBD has adverse environmental effects based on ecotoxicity data.
Though production is dramatically reduced, some nations continue to produce
HCBD (at least the 9 who admit to production) and HCBD will continue to be
emitted and thus exposure to humans and the environment will occur. Criteria met
for suggestion that HCBD has adverse human and/or environmental effects. …
The weight of evidence in the dossier suggests that HCBD meets the criteria for
inclusion as a LRTAP-POP due to POP characteristics, potential for long range
transport, toxicity and ecotoxicity, persistence, bioaccumulation, and monitoring
data. In addition, data appears to suggest ecotoxicity and multi-species, multipathway, multi-endpoint toxicity in non-human species. … However, based on
my technical review of the above data, it is my recommendation that HCBD be
included as a LRTAP-POP.
Conclusions on the technical content of the dossier: Reviewers considered the dossier
to be well-written and the literature used up-to-date, although one reviewer provided
additional references to the literature and another reviewer provided a web link to
additional data on bioaccumulation. One reviewer considered that the information
provided within the dossier was not sufficient to characterize HCBD as meeting the
indicative criteria of Executive Decision 98/2 for consideration as a POP; in particular,
the evidence on the persistence in various environmental media was considered
conflicting and inconclusive.
Disclaimer: The views expressed in this technical review are solely those of the
reviewers and do not necessarily represent the views of any organization and/or
government to which the reviewers are affiliated. Mention of trade names or commercial
products does not constitute endorsement or recommendation for use.