Addendum for PCP
Prepared by:
BiPRO GmbH
Mai 2010
Table of Content
1Introduction
2Short risk profile of PCA
3Transformation of PCP to PCA
4Potential sources of PCA in remote regions
4.1PCP
4.2HCB and HCH (α-HCH and γ-HCH)
5Impurities of dioxins and furans during the production of PCP
6Link between PCP and the occurrence of dioxins and furans in the environment
7References
1Introduction
This report is an addendum to the report “Pentachlorophenol, Dossier prepared in support of a proposal of pentachlorophenol to be considered as a candidate for inclusion in the Annex I to the Protocol to the 1979 Convention on Long-Range Transboundary Air Pollution on Persistent Organic Pollutants (LRTAP Protocol on POPs)”[LRAT dossier, 2008].
The original report for pentachlorophenol (PCP) was finalized by Poland in May 2008. Based on the information provided in the report it was concluded that PCP fulfils the indicative values for long range transport and toxicity. The fulfilment of the indicate value for bioaccumulation was considered to be doubtful and the indicative value for persistence not to be met. In this respect, it was stated that PCP does not meet the indicative value for persistence for water, sediment and soil. The authors mentioned that the metabolites (e.g. pentachloroanisole (PCA)) should be considered as well to provide a complete picture of the risks of PCP and that consideration of the impurities in technical PCP (e.g. dioxins (PCDDs), furans (PCDFs) and hexachlorobenzene (HCB)) may lead to another conclusion in meeting the indicative values.
Within the subsequent “Lead Reviewer’s Track A Summary of Expert Reviews of PCP”, the reviewers concluded that the POPs characteristics of PCA have been described in the PCP dossier (May 2008) but not really evaluated against the criteria[Summary of reviews, 2009]. All reviewers had concerns about PCA. PCA was considered one of the major metabolites in the environment and in biological systems. Based on available and scientific information, all reviewers concluded that PCA may fulfil some and/or all of the POPs indicative numerical values in Executive Body Decision 1998/2. The POPs indicative numerical values for the biological and environmental degradation products of PCP are not clearly addressed in the PCP dossier (May 2008). Therefore, based on available information, there were some different opinions about the fate and biological effects resulting from PCP long-range transboundary atmospheric transport between the reviewers. As a consequence, it has to be clarified whether PCA fulfils the POP criteria. Furthermore, manufacturers of PCP expressed doubts whether PCA detected in remote areas results from PCP metabolism or other precursors like HCB and hexachlorohexanes (HCH) [Letter PCP task force, 2009]. Therefore, there exists an information need regarding the conditions and the rates of transformation of PCP to PCA.
Except from one reviewer, who stated that dioxins and furans are outside the scope of the review, the other reviewers were quite unanimous in their judgement that the use of PCP is inseparably coupled to the emission of dioxins and furans, due to the impurities as a result of all known production processes, due to burning of treated wood and due to degradation in the environment.In chapter 4 of this addendum information regarding the PCDD and PCDF impurities in PCP products resulting from the production processes is provided. The purpose of chapter 5 is to answer the question whether a causal connection between the use of PCP products and the occurrence of PCDDsand PCDFs in the environment canbe established.
To ensure that the POP dossier on PCP contains the latest relevant information on the POP characteristics of its metabolite PCA, this addendum with an update on the available literature and an assessment of PCA including an evaluation against the criteria in Executive Body Decision 1998/2, has been elaborated. A database literature research as well as online information was used to gather new information on toxicological and ecotoxicological data of PCA, transformation of PCP to PCA and connections between PCDD/F content of PCP products and occurring of PCDDsand PCDFs in the environment.
2Short risk profile of PCA
Identity
Chemical structure:
Formula:C7H3Cl5O
CAS registry number:1825-21-4
CAS chemical name:Pentachloroanisole
IUPAC name:1,2,3,4,5-Pentachloro-6-methoxybenzene
SMILES notation: COC1=C(C(=C(C(=C1Cl)Cl)Cl)Cl)Cl
Synonyms:1,2,3,4,5-Pentachloro-6-methoxy-benzene; 2,3,4,5,6-pentachloro-anisol; Benzene, pentachloromethoxy-; ether,methylpentachlorophenyl; Methyl pentachlorophenate; Methyl pentachlorophenyl ester; Methyl pentachlorophenyl ether, PCA
Molecular weight:280.362 g/mol
Vapour pressure (25 °C):0.0459 Pa at 25 °C (Calculation (MPBWIN v1.42) according to modified grain method) [LRAT dossier 2008].
0.0458 Pa (Modeled via EPIWIN) [Summary of reviews, 2009]
0.0933 Pa [Dobbs and Grant, 1980]
Log Kow: 5.30 (KOWWIN v1.67) [LRAT dossier 2008]
5.45 Experimentally by [Opperhuizen and Voors, 1987]
Henry’s law constant:1.94x 10-3 atm-m3/mole (1/H = 12.7 Estimated using HENRYWIN v 3.10) [LRAT dossier 2008]
Toxicity and Ecotoxicity
As a result of the literature review which was carried out to gather information on the POP characteristics of PCA, it must be noted that literature data concerning the toxicity of PCA is limited to this date. The metabolism of PCA has been taken into consideration when assessing the toxicological and ecotoxicological potential of PCA.
Metabolism of PCA:
Male Sprague-Dawley rats and New Zealand White rabbits were administered 14C-labelled PCAin corn oil by gavages as single doses of 25 mg/kg and were then placed in individual metabolism cages for as long as 4 days. Peak blood level of radioactivity occurred 6 hr after administration of the dose to rats and between 3 and 4 hr in rabbits; the blood elimination half-life ranged from 8 to 15 hr in rats and averaged 6 hr in rabbits. Rats excreted an average of 54.2% of the administered radiolabel in the urine and 32.4% in the faeces during the 96 hr following the dose; rabbits excreted an average of 84.2 and 13.1% of the radiolabel in the urine and faeces, respectively, during this time. Examination of the metabolites in the rat showed that 60% of the urinary radioactivity was attributable to tetrachlorohydroquinone (TCH), 3% to free PCP and 29% to conjugated PCP. Faecal metabolites were PCP (85.7%), TCH (4.3%) and polar metabolite(s) (10%). In the rabbit, 58% of the urinary radioactivity was attributable to TCH, 8% to free PCP and 34% to conjugated PCP. Faecal metabolites consisted of PCP and conjugated material [Ikeda et al., 1994].
Yuan J.H. et al. (1993) presented results from a “Toxicology and Carcinogenesis Study of PCA in F344 Rats and B6C3F Mice” within the US National Toxicology Program [U.S. Department of Health and Human Services, 1993].They studied toxicokinetics of PCA in F344 rat and B6C3F1 mouse of both sexes by gavages at doses of 10, 20 and 40 mg/kg and by i.v. at 10 mg/kg. PCA was rapidly demethylated to PCP in both rat and mouse and the resulting PCP plasma concentrations were much higher than that of parent PCA due to the much smaller apparent volume of distribution of PCP. Peak plasma concentrations of PCA and PCP increased with dose in both rat and mouse. Bioavailability of PCA was low in both rat and mouse and was sex independent. The high plasma concentrations and relatively long biological half-life of PCP in both species after both i.v. and oral dosing with PCA indicate possible bioaccumulation of PCP upon multiple oral administrations of PCA[Yuan et al., 1993].
PCP and PCA were rapidly taken up by rainbow trout exposed to these compounds at 0.025 mg/l in water. After exposure of trout to PCP for 24 hr, the liver, blood, fat, and muscle contained 16, 6.5, 6.0, and 1.0 μg/g, respectively. The concentrations of PCA in the same tissues after an exposure to [14C]PCA were of the same order of magnitude as was found with PCP except that fat contained as much as 80 μg/g. Elimination rates for 14C from the blood, muscle, fat, and liver after a similar exposure were different for PCA and PCP. The half-lives for PCP residues in the blood, liver, fat, and muscle were 6.2, 9.8, 23 and 6.9 hr, respectively, while PCA was more persistent having half-lives in these same tissues of 6.3, 6.9, 23, and 6.3 days. Thin-layer chromatographic and GC-MS analyses of the tissues of the PCP-exposed trout indicated that there was no methylation of PCP in any of the tissues studied. Bile from PCP-exposed trout contained high concentrations (250 μg/g) of PCP, mostly as the glucuronide conjugate, but no other metabolites were detected. However, bile from PCA-exposed trout contained PCP glucuronide (10 μg/g) as well as PCA, indicating demethylation of this compound in vivo by rainbow trout [Glickman et al., 1977].
Toxicity of PCA
PCP and PCA were investigated for their acute toxicity in male (m) and female (f) mice. The substances were administered orally and intraperitoneally, respectively. The oral LD50 values were: 129±9 (m) and 134±9 (f) mg/kg for PCP, 318±22 (m) and 331±22 (f) mg/kg for PCA. The intraperitoneal LD50 values were: 59±4 (m) and 61±4 (f) mg/kg for PCP, 281 ±20 (m) and 293±20 (f) mg/kg for PCA [Renner et al., 1986].Oral toxicity GHS categories are determined by Oral LD50 per mg/kg bodyweight. GHS Category 4 Acute-Toxicity Oral is fulfilled for LD50 values between 300 and 2000 mg/kg, category 3 for LD50 values >50 - <300 mg/kg. According to the data of Renner et al. (1986) PCP would be classified as toxic cat.3 and PCA as cat. 4.
The relative toxicity of PCP and 25 of its identified intermediates of microbial transformation have been evaluated in the static Tetrahymena pyriformis population growth assayby Bryant et al. (1994).It was observed that methylation of the hydroxy group modestly increased hydrophobicity. Since there was a decrease in reactivity, methylation of chlorophenols resulted in a decrease in toxicity. Toxicity of anisole and its chloro-derivatives was correlated with hydrophobicity. The reduction in toxicity of these aromatic ethers in comparison to phenols is a reflection of the change in molecular reactivity and mechanism of toxic action. It was noted that for most chemicals, toxicity is a combination of hydrophobicity and reactivity. While phenols act as weak acid respiratory uncouplers or polar narcotics, ethers act as nonpolar narcotics[Bryant et al., 1994]. Cserjesi et al. (1972) also reported that PCA was less toxic than PCP to Trichoderma viirgatum, Cephaloascus frgrans and Penicillium sp, as well as to fish in laboratory toxicity tests[Cserjesi et al., 1972]. However, even if PCA might not be as toxic as PCP the increased hydrophobicity resulting in longer body half-lives and higher potential to bioaccumulate should be considered when evaluating potential risks to environmental and human health.
PCA was evaluated for its mutagenic potential in the L5178Y TK+/TK- mouse lymphoma forward mutation assay using established procedures[McGregor et al., 1987]. Six experiments were conducted: two without metabolic activation and four with metabolic activation. The dose levels tested in these experiments ranged from 0-500 ug/ml. The two experiments without metabolic activation were discarded because no clear mutagenic response was obtained at dose levels where PCA did not precipitate. Significant mutagenic responses were obtained in the remaining four experiments. Thus, PCA was positive in these tests and the lowest effective dose tested was 31.25 ug/ml. It was concluded that there was sufficient evidence to suggest that pentachloroanisole can induce increases in mutant fraction in the presence of S9 mix. It is further reported that in the Salmonella test, positive responses were obtained with PCAby Mortelmans et al.(1986). It was also reported that according to NTP data PCA was positive in the SCE test, but negative in the chromosomal aberrations test[NTP 1989]. Based on the results of the study and the cited further evidence in other test systems it can be concluded that PCA has to be considered as having mutagenic properties.
Toxicology and Carcinogenesis Studies of PCA in F344 Rats and B6C3F Mice (Feed Studies) were performed in the scope of the National Toxicology Program. Under the conditions of these 2 year gavage studies there was some evidenceof carcinogenic activity of PCA in male F344/Nrats based on increased incidences of benign pheochromocytomas of the adrenal medulla. There was equivocal evidenceofcarcinogenic activity of PCA in female F344/N rats based on marginally increased incidences of benign pheochromocytomas of the adrenal medulla. There was some evidenceof carcinogenic activity of PCA in male B6C3F1 mice based on increased incidences of benign pheochromocytomas of the adrenal medulla and hemangiosarcomas of the liver. There was no evidence of carcinogenic activity of PCA in female B6C3F1 mice given doses of 20 or 40 mg/kg. PCA administration was associated with increased incidences of adrenal medulla hyperplasia in female rats and increased incidences of pigmentation in the renal tubule epithelium, olfactory epithelium, and hepatocytes of male and female rats. In addition, decreased incidences of pancreatic adenomas and focal hyperplasia in male rats and decreased incidences of mammary gland fibroadenomas and uterine stromal polyps and sarcomas (combined) in female rats were observed. Hyperthermia-related lesions in male rats receiving 20 or 40 mg/kg were considered indirectly related to PCA administration.PCA administration was associated with increased incidences of adrenal medulla hyperplasia and hypertrophy and hepatocellular mixed cell foci in male mice. In male and female mice, non neoplastic liver lesions associated with PCA administration included hepatocellular cytologicalteration, Kupffer cell pigmentation, biliary tract hyperplasia, and subacuteinflammation [U.S. Department of Health and Human Services, 1993].The results show that PCA should be considered as a potential carcinogen. However, the present knowledge is not sufficient for a definite assessment. Nevertheless, it can be concluded that there is some evidence that PCA possesses carcinogenic properties.
Male and female Sprague-Dawley (Spartan) rats were exposed to dietary levels of 60, 200 or 600 ppm PCA for 181 days, through mating and pregnancy. The daily intakes of PCA were 0, 4, 12 or 41 mg/kg body weight. An intake of 41 mg PCA/kg/day was associated with a decrease in the number of corpora lutea and increase in embryolethality. PCA exposure also resulted in reductions in fetal body weight and crown-rump lengths of males at 4 and 41 mg/kg/day. Female fetuses were unaffected [Welsh et al., 1987].The results presented by Welsh et al. (1987) indicate that PCP might be toxic to reproduction.
The toxicity of water from three rivers in the Santee-Cooper drainage of South Carolina was evaluated in a series of on-site studies with larval striped bass Morone saxatilis. Mortality and swimming behaviour were assessed daily for larvae exposed to serial dilutions of water collected from the Santee, Congaree, and Wateree rivers. After 96 h, cumulative mortality was 90% in the Wateree River, and a dose-response pattern was evident in serial dilutions of the water. Larvae exposed to water from the Santee and Congaree rivers swam lethargically, but no appreciable mortality was observed. Acutely toxic concentrations of inorganic contaminants were not detected in the rivers; however, PCA was twice as high in the Wateree River as it was in the other two rivers. Phenolic compounds may have contributed to larval mortality in the Wateree River and to lethargic activity of larvae in the Santee and Congaree rivers [Finger et al., 1988].
An overview on the results of different further studies presenting data on acute toxicity of PCA to animals is provided inTable 1These results also support the findings of the above mentioned studies and show that PCA can induce adverse effects in the environment.
Table 1:Toxicity values of PCA. MAC = Minimum affective concentration.
Species Scientific Name / Species Common Name / Endpoint / Exposure Duration / Concentration / ReferenceDaphnia magna / Water flea / EC50 / 2 (days) / 27.2 (ug/L) / Brooke, L.T., 1991
Cladocera / Water flea / LC50 / n.a. / 27 (µg/L) / Sanchez-Bayo, 2006
Pimephales promelas / Fathead minnow / LC50 / 4 (days) / 650 (ug/L) / Brooke, L.T., 1991
Pimephales promelas / Fathead minnow / LC50 / 4 (days) / > 1190 (ug/L) / Brooke, L.T., 1991
Hydra attenuate / MAC / 96 (hours) / 10 (µg/ml) / Mayura et al., 1991
Mice / EC50 / n.a. / 318 (m) (mg/kg)
331 (f) (mg/kg) / Renner et al., 1986
Human exposure to PCA:
The general population is exposed to PCA in food, especially oils and fats, and in ambient air. Dietary exposure may occur by eating contaminated fish and fish products such as fish liver oil. Occupational expose, as well as general population exposure, may occur via dermal contact with soil or wood products that had been treated with PCP. Proposed daily intake rates are 0.56 ng regarding air intake (assume mean conc. 28 pg/m3 [Hoff et al., 1992]) and 0.07 µg (adults), 0.018 µg (infants) and 0.040 µg (toddlers) [Gartrellet al.,1986 b] for food intake (assume conc. of 0.001 µg/kg [Gartrell et al.,1986 a], 70 kg for adults; 0.002 µg/kg (Gartrell et al.,1986 b], 9.2 kg for infants; and 0.003 µg/kg [Gartrell et al.,1986 b], 13.4 kg for toddlers).
Conclusion
The criterion from Executive Body Decision 1998/2 for information on Toxicity and Ecotoxicity to be submitted for the procedure for adding substances to annexes I, II or III to the Protocol on Persistent Organic Pollutants are as follows:
Potential to adversely affect human health and/or the environment
PCA is not industrially produced. Thus, there is only limited data available dealing with its toxicity. Nevertheless, the existing studies and information lead to the conclusion that PCA can be regarded as causing adverse effects on human and environmental health. It seems that PCA has the potential to fulfil the three CMR criteria. The existing data is not sufficient to allow a final assessment of CMR properties. In addition there is some evidence that PCA has the potential to adversely affect the environment.Furthermore, a substance with BCF values as high as PCA can be expected to cause toxicity in aquatic organisms at very low concentrations, only on the basis of narcotic effects [Summary of reviews, 2009]. When assessing the toxicological potential of PCA it also has to be considered that PCA may be rapidly and effective degraded to PCP in living organisms. PCA is demethylated back to PCP. If demethylation within the organism occurs, this may lead to effects equivalent to those of PCP, but at lower external concentrations, because of the higher bioaccumulation potential of PCA. Therefore PCP can be regarded as the effective metabolite of PCA. It has been shown that PCP is highly toxic for human when ingested by humans, moderate to highly toxic to many species of fish, non mutagenic or weakly mutagenic and possibly carcinogenic to humans.
Therefore, PCA on its own and due to the toxicity of its main metabolite (PCP) should be considered to fulfil the criterion from Executive Body Decision 1998/2 for Toxicity and Ecotoxicity.
Persistence
All the relevantavailable information on persistence of PCA is included in the Risk Profile UNECE May 2008[LRAT dossier 2008].
PCA can be photo-oxidized in the atmosphere through reactions with hydroxyl (OH) radicals. The calculated half-life for PCA based on this reaction is 9.8 days, with an atmospheric (OH) concentration of 1.5E6 OH/cm3 (AopWin v1.92).