Certain chlorinated propanols occur as contaminants in hydrolysed vegetable proteins. Processing of defatted vegetable proteins by traditional hydrochloric acid hydrolysis leads to the formation of 3-chloro-1,2-propanediol and 1,3-dichloro-2-propanol. These two compounds were evaluated by the Committee at its forty-first meeting (Annex 1, reference 107), when it concluded that 1,3-dichloro-2-propanol is an undesirable contaminant in food and considered that its concentration in hydrolysed proteins should be reduced to the lowest level technically achievable. Since that time, new data have become available, and the Codex Committee on Food Additives and Contaminants asked the Expert Committee to re-evaluate 1,3-dichloro-2-propanol.

2.1.1 Biotransformation

The metabolites identified in the urine of rats treated orally with 1,3-dichloro-2-propanol at a dose of 50 mg/kg bw per day for 5 days were beta-chlorolactate (approximately 5% of the dose), N,N’-bis-acetyl-S,S’-(1,3-bis-cysteinyl)propan-2-ol (1%), and N-acetyl-S-(2,3-dihydroxypropyl)cysteine. The authors proposed that epoxy-chloropropane (epi-chlorohydrin) is formed as an intermediate, and may either undergo conjugation with glutathione to form mercapturic acid or be hydrolysed to 3-chloro-1,2-propanediol. The latter undergoes oxidation to beta-chlorolactate, which is further oxidized to oxalic acid. Formation of other epoxides was postulated, but epoxides are formed from alpha-chlorohydrins only at high pH, and this is unlikely to occur under physiological conditions (Jones & Fakhouri, 1979).

Ethylacetate-extractable metabolites were found in the 24-h urine of male Wistar rats given a single subcutaneous injection of about 62 mg/kg bw of 1,3-dichloro-2-propanol. The parent compound accounted for 2.4% of the dose, 3-chloro-1,2-propanediol for 0.35%, and 1,2-propanediol for 0.43%. 2,3-Dichloro-1-propanol was also found (0.16% of the dose), but the authors attributed this to its presence as an impurity (1.7%) in the preparation of 1,3-dichloro-2-propanol administered to the rats. Metab olites that were not extractable in ethylacetate were not analysed (Koga et al., 1992).

Alcohol dehydrogenase might be able to oxidize 1,3-dichloro-2-propanol to dichloroacetone, a metabolite that can also be formed by rearrangement of the epichlorohydrin intermediate (Eder & Dornbusch, 1988; Weber & Sipes, 1992).

The Committee noted that only small percentages of the doses were accounted for as identified metabolites, probably because of selective extraction procedures and limited attempts to identify metabolites.

2.1.2 Effects on enzymes and other biochemical parameters

1,3-Dichloro-2-propanol has been reported to deplete glutathione both in vitro and in vivo (Hammond et al., 1996; Garle et al., 1997; Fry et al., 1999; Garle et al., 1999; Hammond & Fry, 1999) and to induce and/or be metabolized by the cytochrome P450 enzyme isoform CYP 2E1 (Garle et al., 1997; Hammond & Fry, 1997; Fry et al., 1999). Oxidation of 1,3-dichloro-2-propanol probably produces intermediates that react rapidly with and deplete cellular glutathione stores in the liver.

2.2.1 Acute toxicity

The LD₅₀ of 1,3-dichloro-2-propanol given orally was reported to be 120 mg/kg bw in rats, and that by intraperitoneal application was 110 mg/kg bw (Pallade et al., 1963). In another study, the LD₅₀ in rats treated orally was 140 mg/kg bw (Smyth et al., 1962). In rabbits, the LD₅₀ after dermal application was 800 mg/kg bw (Smyth et al., 1962). In mice, the LC₅₀ over 1–15 days was 1.7–3.2 mg/L of air (Pallade et al., 1963); in rats, an LC₅₀ value of 0.66 mg/L of air after exposure for 4 h was reported (Smyth et al., 1962). When tested on rabbit eyes, 1,3-dichloro-2-propanol caused irritation and moderately severe damage (Smyth et al., 1962; Grant, 1974). It was slightly irritating to rabbit skin (Smyth et al., 1962).

Groups of male Wistar rats were given 1,3-dichloro-2-propanol by intraperitoneal injection at a dose of 18, 36, 73, 140, or 290 mg/kg bw (17–275% of the LD₅₀) in 20% ethanol; controls received 20% ethanol alone. Rats given the two lowest doses showed no histological abnormalities or any alterations in clinical chemical parameters. At 73 mg/kg bw, irregular zonal hepatocellular necrosis was reported, and at 140 or 290 mg/kg bw diffuse massive hepatocellular necrosis and a marked elevation in serum alanine aminotransferase activity were seen. These high doses also caused degeneration of the tubular epithelium of the kidneys and erosion of the gastrointestinal tract mucosa (Katoh et al., 1998).

Three groups of eight male Wistar rats were given 1,3-dichloro-2-propanol as a single subcutaneous injection at a dose of 50 mg/kg bw and killed 6, 24, or 72 h after injection, when blood was collected for haematological and clinical chemical analyses. At 6 and 24 h after dosing, the platelet counts were decreased and the activity of serum aspartate aminotransferase increased. The activity of serum alanine aminotransferase was also increased, but only at the 6-h sacrifice time. At 72 h, no significant changes in haematological or serum chemical end-points were observed (Fujishiro et al., 1994).

A single intraperitoneal injection of 1,3-dichloro-2-propanol at a dose of 50 mg/kg bw to male Wistar rats produced histological evidence of liver injury. Serum alanine aminotransferase activity was increased after treatment, with a peak 24 h after dosing; the values had returned to baseline by the end of 1 week. Histological examination revealed zonal necrosis of the centrilobular space, with a peak 24–48 h after injection. By 48 h after dosing, the centrilobular spaces had collapsed and there was active phagocytosis by macrophages. Evidence of perisinusoidal cell proliferation and accumulation of collagen fibrils was also found. By 72 h after treatment, numerous regenerating sinusoidal structures and hepatocytes were present. One week after treatment, healing with slight perivascular fibrosis was observed, with scattered granulomas (Haratake et al., 1994).

2.2.2 Short-term studies of toxicity

The study summarized below was reported only in an abstract, and the findings could not be evaluated critically. 1,3-Dichloro-2-propanol was given to groups of 10 male and 10 female Sprague-Dawley rats at a dose of 0, 0.1, 1, 10, or 100 mg/kg bw per day by gavage in distilled water on 5 days/week for 13 weeks. Decreases in body-weight gain and feed consumption, altered haematological parameters, increased liver and kidney weights, alterations in serum chemistry and urinary parameters, gross pathological changes in the stomach and histopathological changes in the stomach, kidney, liver, and nasal tissue were observed in males and females at the highest dose. The changes in serum chemistry were considered secondary to the renal and hepatic changes. At 10 mg/kg bw per day, increased liver weights were found in males and females and histopathological changes in the stomach, kidneys, and liver of males. The treatment related-effects observed at this dose were less frequent and/or less severe than those observed at the highest dose. No effects were observed at 0.1 or 1 mg/kg bw per day (Jersey et al., 1991).

2.2.3 Long-term studies of toxicity and carcinogenicity

Groups of 80 male and 80 female Wistar KFM/Han rats, 4 weeks of age were acclimatized for 10 days and then received 1,3-dichloro-2-propanol (purity, 99%; stability confirmed at 6-month intervals) in their drinking-water at a concentration of 0, 27, 80, or 240 mg/L, corresponding to intakes of 0, 2.1, 6.3, and 19 mg/kg bw per day for males and 0, 3.4, 9.6, and 30 mg/kg bw per day for females, for up to 104 weeks. The drinking-water was prepared daily, and the stability, concentration, and homogeneity of 1,3-dichloro-2-propanol were determined regularly. The animals were given a pelleted diet, which was tested regularly for contaminants and found to contain low, biologically insignificant levels of aflatoxin, estrogen, pesticides, and heavy metals, and provided ad libitum. Ten rats of each sex per group were killed after 26, 52, and 78 weeks of treatment.

The treatment-related pathological, hyperplastic, and neoplastic findings are shown in Table 1 for all animals, including those killed ad interim. The mortality rates of the groups of 50 animals that were exposed throughout the study were higher for males (32/50) and females (27/50) at the high dose than for controls (males, 18/50; females, 13/50) (statistics not reported). The rates were 11/50 males and 9/50 females at the low dose and 16/50 males and 14/50 females at the intermediate dose.

There were no treatment-related signs of toxicity or changes in food and water consumption; however, statistically significant (p < 0.05) reductions in mean body weight were observed for males at the high dose after 74 weeks and for females at this dose after 78 weeks. Dose-related increases in relative weights were observed for a number of organs, in particular the liver and kidney. Thus, increases were seen after 26 weeks for the liver in all treated males and females (p < 0.05), and for the kidney in males at the intermediate and high doses (p < 0.05) and in females at the high dose (p < 0.05); after 52 weeks for the livers of males and females at the intermediate and high doses (p < 0.05) and for the kidney in females at the high dose (p < 0.05); after 78 weeks for the liver and kidney in males and females at the high dose (p < 0.01); and after 104 weeks for the liver, kidney, and brain in males and females at the high dose (p < 0.01).

At the end of the study (104 weeks), the following non-neoplastic, treatment-related hepatic lesions were found: an increased incidence of fatty changes in males at the intermediate and high doses, a dose-dependent incidence of sinusoidal peliosis in all treated groups, eosinophilic foci in animals at the intermediate and high doses, and glycogen-free foci in animals at the highest dose. After 52 weeks of treatment, peliosis and fatty changes were present in all treated groups. After 78 weeks of treatment, the incidence of peliosis was greater than that observed after 52 weeks, and the frequency of lipidosis was greater in groups at the intermediate and high doses than that after 52 weeks of treatment. Eosinophilic foci occurred in males at the high dose. In addition, at the end of the study, follicular hyperplasia was evident in the thyroid glands of males at the high dose.

Female rats at the high dose in particular showed statistically significantly (p < 0.05) decreased haemoglobin concentration and erythrocyte volume fraction at 26 and 104 weeks and red blood cell count at 104 weeks. Clinical biochemical and urine analyses suggested hepatotoxicity, primarily in females at the high dose, and statistically significantly (p < 0.05) increased activities of aspartate and alanine aminotransferases (at 78 and 104 weeks), alkaline phosphatase (at 104 weeks), and gamma-glutamyltransferase (at 104 weeks) in female rats. Statistically significant (p < 0.05) increases in urinary concentrations of protein and amylase were seen in females at the high dose after 52, 78, and 104 weeks of treatment, suggesting nephrotoxicity.

Histopathological examination revealed several tumours in various organs, including dose-related neoplastic lesions in male and female rats at the two higher doses. Statistically significant positive trends were found (see Table 1) for hepatocellular adenoma in females, hepatocellular carcinoma in males and females, renal tubule adenoma in males, lingual papilloma and carcinoma in males and females, thyroid follicular adenoma in males, and thyroid follicular carcinoma in females. These neoplastic lesions occurred in the treated animals after 26 weeks (hepatocellular adenoma), 52 weeks (hepatocellular adenoma and carcinoma, lingual papilloma and carcinoma), and 78 weeks (hepatocellular carcinoma, renal tubule adenoma, lingual papilloma and carcinoma, thyroid follicular adenoma). In addition, one stomach papilloma was found in a female at the high dose after 78 weeks; and one stomach carcinoma was found in a female at the low dose and carcinomas in the oral cavity were found in one female at the intermediate dose and two males at the high dose at terminal sacrifice. The neoplastic lesions found in control rats were two hepatocellular adenomas (in a male and a female) and one thyroid follicular adenoma (in a female).

The results strongly suggest a carcinogenic effect of 1,3-dichloro-2-propanol on the liver, kidney, oral epitheliium and tongue, and thyroid gland in rats at the intermediate and high doses. The significance of the sinusoidal peliosis observed in all treated groups was not clear, but peliosis has been suggested to represent a pre-neoplastic stage of vascular hepatic neoplasia (Wayss et al., 1979). The increased incidences of hepatic fatty change and haemosiderin-storing Kupffer cells in the liver in animals at the intermediate and high doses were suggested to reflect metabolic disturbance of the liver by 1,3-dichloro-2-propanol (Research & Consulting Co. AG, 1986).

2.2.4 Genotoxicity

The results of studies on the genotoxicity of 1,3-dichloro-2-propanol are summarized in Table 2. Only one study in vivo, a test for induction of wing spots in Drosophila melanogaster, was available. Investigations on the mechanisms of genotoxicity of 1,3-dichloro-2-propanol (Hahn et al., 1991) indicated that it depends on the chemical formation of epichlorohydrin, which has mutagenic activity (Rossi et al., 1983).

2.2.5 Reproductive toxicity

In a study reported only in an abstract cited in the Hazardous Substances Data Base, which could not be evaluated critically, groups of 20, 10, and 10 male Wistar rats were given either water (controls) or 1,3-dichloro-2-propanol at 15 or 60 mg/kg bw per day by gavage for 14 days, respectively. The treated rats showed spermatocoele or sperm granuloma formation in the epididymides (Tunstall Laboratories, 1979).

Groups of eight or nine male Wistar rats were given 1,3-dichloro-1,2-propanol at a single intraperitoneal injection of 44 mg/kg bw and then observed for 6 weeks. The animals were then killed and the left and right testes and epididymes were weighed and examined histologically. Sperm from the right epididymis was removed, counted, and analysed morphologically. No statistically significant effects of treatment were found on body-weight gain, the weights of the testes or epididymis, or the results of the histological evaluations. A significant decrease in the number of sperm in the body and tail (combined) of the epididymis was reported (Omura et al., 1995).

Severe irritation of the throat and stomach has been reported after ingestion of 1,3-dichloro-2-propanol (Gosselin, 1976).

Twelve workers involved in the cleaning of a saponification tank used in the manufacture of 1,3-dichloro-2-propanol were exposed by inhalation to the compound at an unknown concentration. No data were available on potential exposure to other chemicals that may have been present. Of the 12 workers, five developed acute hepatitis, and two of them died. Autopsy of one of the cases revealed sub-massive hepatocellular necrosis. In this subject, serum alanine and aspartate amino-transferase activities, total bilirubin concentration, plasma ammonia concentration, and lactate dehydrogenase activity were markedly increased, and prothrombin time was sharply decreased before death. The plasma concentration of 1,3-dichloro-2-propanol was reported to be 200 ng/ml about 48 h after exposure (Shiozaki et al., 1994). In another worker exposed to lower concentrations, the only evidence of hepatic injury was increased activity of serum aspartate aminotransferase (Haratake et al., 1993; Iwasa et al., 1993; Shiozaki et al., 1994).

In its pure state, 1,3-dichloro-2-propanol is a liquid with a boiling-point of 174 °C. It is soluble in 10 parts of water and miscible with solvents such as ethanol and ether (Windholz, 1976).

During the 1980s, 1,3-dichloro-2-propanol was quantified in acid-hydrolysed vegetable protein by gas chromatographic techniques that were typically capable of quantifying concentrations > 1 mg/kg. The analytical approach involves extraction and concentration, followed by chemical derivatization with a reagent such as heptafluorobutyrylimidazole to provide a derivative that is suitably volatile and can be readily detected. The application of mass spectrometric detection has increased the sensitivity of the analysis, so that limits of quantification of 0.025 mg/kg (Food & Drug Administration, 2000) and < 0.005 mg/kg (Crews et al., 2000) have been reported more recently.

Less work has been published on 1,3-dichloro-2-propanol than on 3-chloro-1,2-propanediol in recent years. The method developed for measurement of the latter compound in foods and food ingredients (Brereton et al., 2000) cannot automatically be used, as 1,3-dichloro-2-propanol is considerably more volatile than 3-chloro-1,2-propanediol and significant amounts are lost during concentration. However, a modification of the method has been successfully used to quantify 1,3-dichloro-2-propanol at concentrations > 0.025 mg/kg in soya sauce (Food & Drug Administration, 2000), which involves partitioning the ether:hexane extract with acetonitrile, which can then be concentrated without losing the extracted 1,3-dichloro-2-propanol. The compound is derivatized with heptafluorobutyrylimidazole before gas chromato-graphy and mass spectrometric detection.

An alternative method has been reported that is capable of detecting 1,3-dichloro-2-propanol in soya sauce at concentrations < 0.005 mg/kg (Crews et al., 2000). This methods involves headspace gas chromatography with mass spectrometric detection and a deuterated internal standard. Full details of the method and its validation are reported to be in preparation.

In a recent survey of soya sauces in the USA, 1,3-dichloro-2-propanol was detected (at > 0.025 mg/kg) in six of 21 samples at concentrations between 0.07 and 1.9 mg/kg. All the samples also contained 3-chloro-1,2-propanediol at concentrations > 1 mg/kg (Food & Drug Administration, 2000).

Few data were available from recent surveys. The survey of soya sauces in the USA showed a direct relationship between the concentrations of 1,3-dichloro-2-propanol and 3-chloro-1,2-propanediol, the latter being approximately 50 times higher. However, this observation was based on a relatively small number of samples.

In another report of the results of analyses of soya sauces, 1,3-dichloro-2-propanol was found only in samples with high concentrations of 3-chloro-1,2-propanediol (Crews et al., 2000). In this study, 1,3-dichloro-2-propanol was detected in five of the 14 samples tested at concentrations between 0.01 and 4.3 mg/kg. These five samples also had the highest concentrations of 3-chloro-1,2-propanediol, ranging from 15 to 100 mg/kg. When one sample containing 0.01 mg/kg of 1,3-dichloro-2-propanol was eliminated, the ratio of 3-chloro-1,2-propanediol to 1,3-dichloro-2-propanol varied between 16:1 and 78:1.

1,3-Dichloro-2-propanol and 3-chloro-1,2-propanediol are formed when chloride ions react with triglycerides in foods under a variety of conditions, including food processing, cooking, and storage. These compounds have been found in various foods and food ingredients, most notably in hydrolysed protein products and soya sauces. The mechanisms of formation have not been completely elucidated. It has been shown, however, that 3-chloro-1,2-propanediol is a precursor of 1,3-dichloro-2-propanol in protein hydrolysates (Collier et al., 1991). Their formation can be minimized by use of good manufacturing practices. When both compounds are found in a food or a food ingredient, the concentration of 1,3-dichloro-2-propanol is far lower than that of 3-chloro-1,2-propanediol.

Information on the concentrations of 1,3-dichloro-2-propanol in food ingredients was submitted by the United Kingdom, the USA, and the International Hydrolyzed Protein Council. A submission from the Czech Republic contained information on the reactions of chlorinated propanols and other chlorinated compounds but did not include information useful for preparing this assessment. Information on the consumption of soya sauce was received from Australia, Japan, and the USA.

5.2.1 Relevant period of intake

1,3-Dichloro-2-propanol would not show acute toxic effects at any level of intake that might reasonably be expected. This analysis therefore addresses only the probable long-term consumption of the compound owing to its presence in foods.

5.2.2 Soya sauce consumption in Australia, Japan, and the USA

The mean consumption of soya sauce by Australian consumers was approximately 11 g/person per day, and the consumption by consumers at the 95th percentile was approximately 35 g/person per day. In Japan, the per-capita consumption of soya sauce was approximately 30 g/person per day. In the absence of information on the residual concentration of 3-chloro-1,2-propanediol, and thus 1,3-dichloro-2-propanol, in soya sauces in Australia and Japan, the Committee was unable to estimate the intake of 1,3-dichloro-2-propanol in those countries. However, the residual concentrations can reasonably be assumed to be similar to those used in the estimate from the USA, below, as the data used were for soya sauces produced domestically in Canada and the USA as well as for soya sauces imported from Asia. The Australian intake of 1,3-dichloro-2-propanol would be 10 µg/person per day at the mean and 30 µg/person per day at the 95th percentile of consumption. The Japanese intake would be approximately 27 µg/person per day at the mean and 55 µg/person per day at the 90th percentile, assuming that consumption of soya sauce is twice the mean.

The report from the USA contained information on the relationship between concentrations of 1,3-dichloro-2-propanol and 3-chloro-1,2-propanediol. Additional information available in the literature was combined with this information and analysed graphically. A linear relationship was found, with a ratio of at least 20:1. This ratio was used with the available data on the concentrations of 3-chloro-1,2-propandiol from the evaluation of the Committee contained in this volume to estimate the intake 1,3-dichloro-2-propanol from its presence in soya sauces.

The mean consumption of soya sauce in the USA was 8 g/person per day, and that at the 90th percentile was estimated to be 16 g/person per day. The mean concentration of 1,3-dichloro-2-propanol, based on the 20:1 ratio of 3-chloro-1,2-propanediol to 1,3-dichloro-2-propanol and a mean concentration of 3-chloro-1,2-propanediol of 18 mg/kg found in a survey of commercially available soya sauces in the USA, was 0.9 mg/kg. Combination of the consumption of soya sauce with the mean residual concentration yielded a mean intake of 1,3-dichloro-2-propanol of 7 µg/person per day and intake at the 90th percentile of 14 µg/person per day.

5.2.3 International estimates of intake

The descriptions of the GEMS/Food regional diets contain limited information on consumption of soya sauce: the Far Eastern diet includes soya sauce, at a level of 11 g/person per day and the Middle Eastern diet at 0.1 g/person per day; none is reported in the other regional diets, representing consumption of < 0.1 g/person per day. The background intake of 1,3-dichloro-2-propanol can be estimated roughly from the data submitted by the United Kingdom on residual concentrations of 3-chloro-1,2-propanediol in savoury foods and the 20:1 ratio of this compound with 1,3-dichloro-2-propanol. If it is assumed that approximately one-eighth of the diet, 180 g, consists of savoury foods that might contain 1,3-dichloro-2-propanol (out of 1500 g/day solid food, used as the default level in the USA) and that those foods contain a mean residual concentration of 0.0006 mg/kg 1,3-dichloro-2-propanol, the background intake is approximately 0.1 µg/person per day.

No information was available on studies specifically of the control of the formation of 1,3-dichloro-2-propanol in foods or food ingredients. However, it seems likely that any steps taken to prevent or minimize contamination of acid-treated foods with 3-chloro-1,2-propanediol will also result in reductions in the concentration of 1,3-dichloro-2-propanol.

7.1.1 Biotransformation

The metabolism of 1,3-dichloro-2-propanol has been studied in mammalian systems (Jones & Fakhouri, 1979; Koga et al., 1992) but not in humans or human preparations that would allow assessment of risk or determination of safety to humans. Likewise, no evidence was available to evaluate the degree or extent of any differences in metabolism between mammals and the bacteria used in assays of genotoxicity. Hence, the relevance of the results of the in-vitro assays for predicting the potential interaction of 1,3-dichloro-2-propanol with genetic material in humans is largely predicated on their reputation for predicting the outcomes of studies of carcinogenicity in mammals. The reliability of such predictions is good, particularly when the test systems are combined with mammalian metabolizing preparations. Therefore, keeping in mind the limitations of such extrapolations, the results of in-vitro tests for genotoxicity can be used to assess the genotoxicity of 1,3-dichloro-2-propanol to humans.

7.1.2 Toxicological studies

The most appropriate study for assessing the carcinogenic risk of 1,3-dichloro-2-propanol to humans was performed by the Research & Consulting Co. AG (1986), Itingen, Switzerland. In this study, male Wistar (KMF/Han) rats given 1,3-dichloro-2-propanol for 2 years showed increased incidences of benign and malignant neoplasms of the kidney, liver, and tongue, and female rats had increased incidences of benign and malignant neoplasms of the liver and tongue. An increase in the incidence of thyroid follicular cell neoplasms in treated rats of each sex was probably not reliable enough to be included in a risk assessment or safety evaluation. As reported for the renal tumours induced by 3-chloro-1,2-propanediol in a different strain of rats, Fischer 344 (see monograph, this volume), the tumours appeared concurrently with chronic progressive nephritis, which is commonly observed in aging rats. However, the incidence of renal tubule hyperplasia, considered to be a precursor of neoplasia and not generally associated with chronic progressive nephritis, was also associated with treatment, supporting the conclusion that these tumours were compound-induced and not toxic manifestations of chronic progressive nephritis.

No studies in humans or studies with biomarkers that are relevant for evaluating dose–response relation ships or risk were available.

The studies of genotoxicity performed with 1,3-dichloro-2-propanol are reviewed above and in Table 2. The compound caused point mutations in bacteria and mammalian cells in culture in standard test systems, but there were no studies to evaluate its genotoxicity in intact mammalian organisms or in humans. The results of the in-vitro studies were nevertheless sufficiently robust to conclude that 1,3-dichloro-2-propanol can readily interact with chromosomal material in cells and can be expected to do so in target tissues in vivo.

7.2.1 Measurement of response

The doses administered and the incidences of renal neoplasia and hyperplasia, liver neoplasia, and neoplasia of the tongue in male and female Wistar rats are presented in Table 1.

7.2.2 Selection of model for extrapolation

The strength of the data from the study of Research & Consulting Co. AG (1986), showing induction by 1,3-dichloro-2-propanol of neoplasia at multiple sites, and the relatively unequivocal findings of genotoxicity in vitro suggest use of an extrapolation technique in which no practical biological threshold is assumed. Another approach would be to express the estimated human dose as a fraction of the dose that was consumed by the animals in the study, to provide a clear notion of the degree of safety provided by current levels of exposure. It would also allow for a judgement of whether the risk associated with such an exposure is significant.

One extrapolation approach that is transparent, accommodates the requirement for no practical threshold and does not require computer programs is the model proposed by Gaylor & Kodell (1980). With this model, a dose–response curve can be established from the data in the observable region of the dose–response relationship with any model. Graphical techniques may often suffice. A decision is then made about the point at which the study data can no longer be considered to be reliable for predicting the dose–response curve. A default linear extrapolation is subsequently made from that region to zero, and the risk corresponding to a given dose can be determined. This value is described as a plausible upper bound on risk, not an actuarial risk, even for the test species. This approach is similar to the familiar no-effect-level approach for biological thresholds. One superior feature is that the data describing the observable dose–response relationship can be incorporated into the assessment.

No suitable epidemiological studies or studies incorporating biomarkers were available to assess potency in humans.

The assessment of risk with no practical threshold was based on the findings of the study by Research & Consulting Co. AG (1986). The response, renal tubule neoplasia in male rats, was essentially linear with dose in the observable region of the curve, rendering trivial any decision about where to convert to linearity at low doses. Hence, a simple linear proportion derived from the lowest dose at which there was a response (6.2 mg/kg bw per day; three renal tumour-bearing rats out of 50 rats in the group) and the response in the control group (no renal tumour-bearing animals out of 50) provides the slope of a linear line that defines the potency of the response, as follows:

(3/50 – 0/50) ÷ 6.2 mg/kg bw per day = 0.009 (mg/kg bw per day)exp^–1.

Extrapolating from other points on the dose–response curves in this simple fashion gives a value for the potency, or unit risk, of about 0.01 per mg/kg bw per day. The upper bound on the risk provided by this procedure can be estimated by multiplying this potency, or unit risk, by the estimated daily exposure expressed in mg/kg bw.

An alternative way of expressing the margin of safety—a procedure for deciding whether the risk associated with a given exposure is significant or not—is to compare the estimated dose that produced tumours in experimental animals by estimated human consumption. The corresponding dose to rats in the relevant study was 19 mg/kg bw per day, which can be compared with the intake of consumers of soya sauce at a high percentile of < 1 µg/kg bw per day, providing a margin of safety of about 20 000. The Committee concluded that this expression of the margin of safety was the preferred way of judging the safety of this compound.

Absorption, distribution, metabolism, and excretion

Approximately 5% of an oral dose of 1,3-dichloro-2-propanol was excreted in the urine of rats as beta-chlorolactate, and about 1% of the dose was excreted as 2-propanol-1,3-dimercapturic acid. In another experiment, the urine of rats contained the parent compound (2.4% of the dose), 3-chloro-1,2-propanediol (0.35% of the dose), and 1,2-propanediol (0.43% of the dose). Epoxy-chloropropane (epichlorohydrin) was postulated to be an intermediate; it may either undergo conjugation with glutathione to form mercapturic acid or be hydrolysed to 3-chloro-1,2-propanediol. The latter undergoes oxidation to beta-chlorolactate, which is further oxidized to oxalic acid.

Toxicological studies

The oral LD₅₀ of 1,3-dichloro-2-propanol in rats is 120–140 mg/kg bw.

In several short-term studies in rats, 1,3-dichloro-2-propanol at doses > 10 mg/kg bw per day and higher caused significant hepatic effects. These were associated with oxidative metabolism, which yielded intermediates that reacted with and depleted glutathione.

In a 13-week study in rats, overt hepatotoxicity, including increased liver weights, histological changes, and/or increased activity of serum alanine and aspartate transaminases, was seen after oral administration of 1,3-dichloro-2-propanol at doses > 10 mg/kg bw per day. These doses also caused histopathological changes in the kidney, increased kidney weights, and alterations in urinary parameters. The NOEL was 1 mg/kg bw per day.

The results of the one long-term study of toxicity and carcinogenicity in rats confirmed the hepatotoxicity and the nephrotoxicity seen in the 13-week study. Furthermore, it demonstrated a clear carcinogenic effect of 1,3-dichloro-2-propanol at the highest dose tested, 19 mg/kg bw per day. The tumours (adenomas and carcinomas) occurred in liver, kidney, the oral epithelium and tongue, and the thyroid gland. No increase in tumour incidence was seen at the lowest dose tested, 2.1 mg/kg bw per day. Treatment-related non-neoplastic lesions of the liver were observed, sinusoidal peliosis being found in all treated groups.

1,3-Dichloro-2-propanol has been reported to be hepatotoxic in humans exposed occupationally.

1,3-Dichloro-2-propanol was clearly mutagenic and genotoxic in various bacterial and mammalian test systems in vitro. The only available study in vivo showed no effect in a wing spot test in Drosophila melanogaster.

Occurrence

Information on the concentrations of 1,3-dichloro-2-propanol in soya sauce was submitted by the USA. Additional information was derived from a published report on the concomitant occurrence of 3-chloro-1,2-propanediol and 1,3-dichloro-2-propanol in soya sauces, which showed that 1,3-dichloro-2-propanol may be present in samples of hydrolysed vegetable protein and soya sauce that contain 3-chloro-1,2-propanediol at concentrations >1 mg/kg. In those products in which 1,3-dichloro-2-propanol was quantifiable, the ratio of the concentrations of 3-chloro-1,2-propanediol to 1,3-dichloro-2-propanol was at least 20.

Estimates of dietary intake

A report from the USA was used by the Committee to estimate the intake of 1,3-dichloro-2-propanol from its presence in soya sauces. Information about the consumption of soya sauce was received from Australia, Japan, and the USA.

At any level of intake that might reasonably be expected, 1,3-dichloro-2-propanol would not have acute effects. The analysis therefore addressed only long-term intake of the compound from its presence in foods.

The intake of 1,3-dichloro-2-propanol from food other than soya sauce can be estimated roughly from data on residual concentrations of 3-chloro-1,2-propanediol in savoury foods and the upper-bound 20:1 ratio of 3-chloro-1,2-propanediol:1,3-dichloro-2-propanol. If it is assumed that about one-eighth of the diet, 180 g (on the basis of 1500 g/day of solid food), consists of savoury foods that might contain 1,3-dichloro-2-propanol and that the mean residual concentration of the compound in those foods is 0.0006 mg/kg, the background intake is approximately 0.1 µg/person per day.

The upper-bound 20:1 ratio of 3-chloro-1,2-propanediol:1,3-dichloro-2-propanol was used by the Committee to estimate the intake of 1,3-dichloro-2-propanol from consumption of soya sauce. The average concentration of 3-chloro-1,2-propanediol in a survey of 90 commercially obtained soya sauce samples was 18 mg/kg; the residual concentration of 1,3-dichloro-2-propanol was therefore assumed to be 0.9 mg/kg.

The mean and 90th percentile consumption of soya sauce in the USA (consumers only) were reported to be 8 and 16 g/person per day, respectively. The resulting estimate of the intake of 1,3-dichloro-2-propanol would be 7 µg/person per day at the mean level of consumption and 14 µg/person per day at the 90th percentile of consumption. The values for the mean and 95th percentile consumption of soya sauces in Australia are 11 and 35 g/person per day, respectively, resulting in estimates of intake of 10 and 30 µg/person per day for consumers, respectively. Per-capita intake of soya sauce in Japan (approximating the intake of consumers only) was reported to be 30 g/person per day, resulting in an estimate of the intake of 1,3-dichloro-2-propanol of 27 µg/person per day. An upper percentile intake of 55 µg/person per day was estimated by assuming consumption of soya sauce of two times the mean.

Although only a few studies of kinetics and metabolism and few short- and long-term studies of toxicity and of reproductive toxicity were available for evaluation, they clearly indicated that 1,3-dichloro-2-propanol was hepatotoxic, induced a variety of tumours in various organs in rats, and was genotoxic in vitro. The Committee concluded that it would be inappropriate to estimate a tolerable intake because of the nature of the toxicity. Thus:

• The results of the long-term study of toxicity and carcinogenicity showed significant increases in the incidences of both benign and malignant neoplasms in at least three independent tissues.
• It has been shown unequivocally that this contaminant can interact with chromosomes and/or DNA; however, the tests were confined to bacterial and mammalian test systems in vitro, and there were no data on intact mammalian organisms or humans.

The Committee noted that the dose that caused tumours in rats (19 mg/kg bw per day) was about 20 000 times the highest estimated intake of 1,3-dichloro-2-propanol by consumers of soya sauce (1 µg/kg bw per day).

The available evidence suggests that 1,3-dichloro-2-propanol is associated with high concentrations of 3-chloro-1,2-propandiol in food. Regulatory control of the latter would therefore obviate the need for specific controls on 1,3-dichloro-2-propanol.

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    See Also:
       Toxicological Abbreviations
       1,3-dichloro-2-propanol (ICSC)
       1,3-DICHLORO-2-PROPANOL (JECFA Evaluation)