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Appendix 3: Chemicals Listed in Annex C: Definition, Risks, Toxicity

[Adapted from: UNEP Chemicals (unpublished draft circulated December 2004). (Advance Draft) Guidelines on Best Available Techniques and Provisional Guidance on Best Environmental Practices Relevant to Article 5 and Annex C of the Stockholm Convention on Persistent Organic Pollutants, prepared by the BAT/BEP Expert Group established by INC-6, December 2004.]

1 What are the chemicals listed in Annex C?

1.1 Definition

The chemicals listed in Annex C of the Stockholm Convention comprise: polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs) and hexachlorobenzene (HCB).

1.2 Characteristics

The chemicals listed in Annex C, in addition to their documented toxicity, are persistent, bioaccumulative and undergo long-range transport.  Persistent chemicals do not easily degrade in the environment.  Bioaccumulative chemicals are usually fat soluble and build up in higher trophic levels, including in humans.  The chemicals listed in Annex C, as semi-volatile compounds, undergo a series of evaporations and condensations in the environment, making them mobile.

1.3 Uses

PCDD and PCDF have never been used as commercial products nor were they intentionally manufactured for any reason other than for laboratory purposes.

PCBs have been used as coolants and lubricants in transformers, capacitors and other electrical equipment because they do not burn easily and are good insulators.  Among other things, products that may contain PCB include old fluorescent lighting fixtures and electrical devices containing PCB capacitors.

HCB has been widely used as a pesticide to protect the seeds of onions and sorghum, wheat and other grains against fungus.  It has also been used to make fireworks, ammunition and synthetic rubber, and as a solvent in the production of pesticide.  [Note: in New Zealand, HCB was only ever used in small quantities experimentally between 1970 and 1972 as a seed-dressing fungicide for cereal grain.]

The following guidelines and guidance, however, do not apply to the commercial production of PCB and HCB, but rather to those processes that inadvertently lead to their formation and release.

2 What are the risks to humans of chemicals listed in Annex C?

2.1 Exposure

Because these chemicals exist throughout the environment, almost all living creatures, including humans, have been exposed to the chemicals listed in Annex C.  Human exposure to Annex C chemicals arises mainly via the dietary consumption of animal fats, including breast milk, but can also arise from accidental or occupational situations.  The health effects that have been associated with these exposures depend on a variety of factors, including the level of exposure, and the duration and frequency of exposure.

2.2 PCDD and PCDF

Much of the information on the toxicity of these chemicals is based on extensive studies of the most toxic member of the family, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in experimental animals.  TCDD and related compounds can produce a wide variety of effects in animals and might produce many of the same effects in humans.  Chloracne is a skin condition indicative of dioxin poisoning in humans.

The International Agency for Research on Cancer (IARC), under the World Health Organisation (WHO), identified 2,3,7,8-TCDD as the most toxic of all dioxin compounds, and as carcinogenic to humans, based mainly on studies of cases involving occupational heavy exposure.  Animal studies have also shown an increased risk of cancer from long term exposure to PCDD/PCDF.

TCDD exposure results in a wide variety of reproductive and developmental effects in a number of species of experimental animals, including reduced viability, structural alterations, growth retardation and functional alterations.  There is also evidence of neurobehavioral effects and effects on immune and various endocrine functions, including those of the thyroid.  Because of this evidence in animals, particularly at high doses but in some cases at doses close to those with relevance for human beings, scientists are concerned about the potential for these same effects to occur in humans, especially the effects of prenatal exposure on developing children.

2.3  PCB

The most commonly observed health effects in people exposed to large amounts of PCB are skin conditions.  IARC has also determined that PCBs are probably carcinogenic to humans.  A few studies of workers indicate that PCBs were associated with certain kinds of cancer in humans, such as cancer of the liver and biliary tract.  Rats that ate food containing high levels of PCB for two years developed liver cancer.

Studies in exposed workers have shown changes in blood and urine that may indicate liver damage.  In the Yusho and Yucheng incidents, each involving about 2000 cases, Japanese and Taiwanese people were exposed to high concentrations of PCB and PCDF through consumption of contaminated rice oil.  Liver disease mortality was two to three times more frequent than national rates in both cohorts (IARC).

PCB exposures in the general population are not likely to result in skin and liver effects.  Most of the studies of the health effects of PCB in the general population examined children of mothers who were exposed to PCB, which showed that PCBs may be associated with developmental or endocrine effects.  Women who were exposed to relatively high levels of PCB in the workplace or ate large amounts of fish contaminated with PCBs had babies that weighed slightly less than the babies of women who did not have these exposures.  Babies born to women who ate PCB-contaminated fish also showed abnormal responses in tests of infant behaviour.  Some of these behaviours, such as problems with motor skills and a decrease in short-term memory, lasted for several years.

2.4 HCB

The United States Department of Health and Human Services has determined that HCB may reasonably be expected to be a carcinogen.  Studies in animals show that long term ingestion of large amounts of HCB can damage the liver, thyroid, nervous system, bones, kidneys, blood, and immune and endocrine systems.

3 How is the toxicity of chemicals listed in Annex C measured?

3.1 Toxic equivalency

For PCDD/PCDF the most toxic compounds have chlorines in the 2, 3, 7 and 8 positions.  For PCB, the highest toxicity is with compounds where the molecule can assume a planar conformation, analogous to that of PCDD/PCDF.  The toxicity of mixtures of these materials is evaluated as a single number called the toxic equivalent (TEQ).

To determine the TEQ of a mixture, the amount of each of the toxic members of the family is multiplied by a weighting factor relative to the most toxic chemical, 2,3,7,8-TCDD.  This weighting factor is called a toxic equivalency factor (TEF).  The first scheme, derived by the Committee on Challenges of Modern Society of the North Atlantic Treaty Organisation in 1988 and called TEFs, covered 17 PCDDs/PCDFs.  Twenty-nine of the 419 individual PCDDs, PCDFs and PCBs were TEFs assigned by WHO in 1997.  This list was recently updated after a reassessment in 2005 (see Table A.3 below).  HCB does not have a toxic equivalency factor.

3.2 Tolerable intakes

The tolerable daily intake (TDI) is the amount of intake per kg of body weight per day of a chemical substance judged not to give rise to manifestations of health effects if such an amount is taken every day for an entire lifetime.  The TDI established by WHO in 1998 for chemicals contributing to TEQ was set at 1.4 pg TEQ/kg body weight/day.  In 2001, the Joint FAO/WHO Expert Committee on Food Additives set a provisional tolerable monthly intake (PTMI) of 70 pg TEQ/kg body weight/month, which approximates to 2.3 pg/kg body weight/day.  New Zealand has an interim maximum monthly intake (IMMI) of 30 pg TEQ/kg body weight/ month.[Establishment of a maximum intake for dioxin, Public Health Perspectives 2002, 5(4): 6.]

Table A.3:   Toxic equivalency factors for PCDDs, PCDFs and dioxin-like PCBs for humans and mammals

PCDD/PCDF congener

TEF value

 

PCB congener

TEF value

2,3,7,8-TCDD

1

 

Non-ortho PCBs

 

1,2,3,7,8-PeCDD

1

 

PCB #81

0.0003

1,2,3,4,7,8-HxCDD

0.1

 

PCB #77

0.0001

1,2,3,6,7,8-HxCDD

0.1

 

PCB #126

0.1

1,2,3,7,8,9-HxCDD

0.1

 

PCB #169

0.03

1,2,3,4,6,7,8-HpCDD

0.01

 

 

 

OCDD

0.0003

 

Mono-ortho PCBs

 

 

 

 

PCB #105

0.00003

2,3,7,8-TCDF

0.1

 

PCB #114

0.00003

1,2,3,7,8-PeCDF

0.03

 

PCB #118

0.00003

2,3,4,7,8-PeCDF

0.3

 

PCB #123

0.00003

1,2,3,4,7,8-HxCDF

0.1

 

PCB #156

0.00003

1,2,3,6,7,8-HxCDF

0.1

 

PCB #157

0.00003

2,3,4,6,7,8-HxCDF

0.1

 

PCB #167

0.00003

1,2,3,7,8,9-HxCDF

0.1

 

PCB #189

0.00003

1,2,3,4,6,7,8-HpCDF

0.01

 

 

 

1,2,3,4,7,8,9-HpCDF

0.01

 

 

 

OCDF

0.0003

 

 

 

Source: Van den Berg et al, 1998 and 2006.

For further information

  • Government of Japan 2003.  Information Brochure Dioxins.  Government of Japan, Ministry of the Environment: Tokyo. www.env.go.jp/en/chemi/dioxins/brochure2003.pdf
  • International Agency for Research on Cancer (IARC) monographs: http://monographs.iarc.fr/
  • Joint FAO/WHO Expert Committee on Food Additives (JECFA), Fifty-seventh meeting, Rome, 5–14 June 2001, Summary and Conclusions.  www.fao.org/es/esn/jecfa/ index_en.stm
  • United States Centers for Disease Control.  TOXFAQs for Hexachlorobenzene.  Agency for Toxic Substances and Disease Registry.  www.atsdr.cdc.gov/tfacts90.html
  • United States Centers for Disease Control.  TOXFAQs for Polychlorinated Biphenyls.  Agency for Toxic Substances and Disease Registry.  www.atsdr.cdc.gov/tfacts17.html
  • WHO (World Health Organization).  Dioxins and Their Effect on Human Health.  WHO: Geneva.  www.who.int/mediacentre/factsheets/fs225/en/

 

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