Ukrainian Occupational Medicine Scientific Research Institute, Kryvyi Rih, Ukraine

Abstract. Objective. Analysis and generalisation of literature data and own studies on the toxicological characteristics of diisodecyl phthalate, plasticiser — high molecular weight phthalate.
Materials and methods. Study of toxicity parameters of diisodecylphthalate, plasticiser. The analytical review of scientific publications has been made using the abstract database of scientific libraries and text database of PubMed publications.
Results. The paper provides a scientific analysis of literature and own studies on the parameters of acute, subchronic, chronic toxicity, and long-term effects of diisodecyl phthalate with various routes of entry into the body of experimental animals.
Conclusions. Diisodecyl phthalate is characterised by low values in terms of acute toxicity on the body of experimental animals. Longterm administration of diisodecyl phthalate is associated with hepatotoxic effects. Embryotoxic and teratogenic effects are manifested in high concentrations, which is not a limiting criterion in the systematic assessment of the plasticiser safety. Mutagenic and carcinogenic effects have not been established.
Key words: plasticiser, diisodecyl phthalate, toxicity, reproductive toxicity, mutagenicity, carcinogenic action.

Introduction. The use of plasticisers (diisodecyl adipate, vinyl trimethoxysilane) in the production of a wide range of polymeric materials and plas-tic masses, which are used in various industries, requires the development of hygienic standards in the working zone air and preventive measures aimed at reducing their harmful effects on the body of workers [1, 2]. High molecular weight phthalate esters, including di-isodecyl phthalate (DIDP), are used as plasticisers in the production of elastic polyvinyl chloride (PVC), used in construction, engineering, medicine, everyday life, etc. The main advantages of DIDP are the ability to provide ready-made products with plasticity, elasticity, flexibility, extending the life of their service.

In the production conditions, a substance may enter the body by inhalation and through the skin, much less — through the gastrointestinal tract.

Di-isodecyl phthalate DIDP is a mixture of branched C-10 isomers of phthalates. CAS No.: 26761-40-0 and 68515-49-1), empirical formula: C28H46O4, the structural formula:

CAS № 68515-49-1

CAS № 26761-40-0

The above structures represent only a few of the many possible DIDP isomers.

DIDP molecular weight is 446.74, oily viscous transparent liquid with a weak aromatic smell; boiling point is 250–257 °C (4 mmHg); melting point is minus 50 °С; density is 0.97 g/cm3 (20 °С); log Kow is 10.36 (25 °С); saturated vapour pressure 15.93 hPa (25 °C); subjected to hydrolysis in acid and basic media. DIDP dissolves in most organic solvents but does not dissolve in glycerol, glycols and some amines.

Materials and methods of the study. Toxicity is assessed based on the results of own research and analysis of literary sources on the study of toxicological properties at the different duration of action and various ways of entering the body of experimental animals and experiments on the study of long-term effects of the action.

The irritating effect of DIDP on the skin and mucous membranes in the experi-ment was studied in accordance with the guidelines [3] following international rules and standards of bioethics [4].

Results of the study and their discussion. A study of DIDP local effects on the skin of animals showed that the plasticizer produces an irritating effect at the level of 1–2 points, the reaction was reversible with the effect of skin peeling. Data from literary sources also indicate DIDP irritating effect of 1–2 points [5].

Introduction of DIDP into the conjunctival sac of the rabbit eye led to the mucosal hyperaemia of 2 points in all animals after 1 h of observation, the reaction disappeared within 48–72 h.; sex sensitivity was not detected. The results are consistent with the literature data, which indicate the irritating effect of DIDP on the mucous membranes of animal eyes; the substance does not damage the eye cornea [5, 6].

It has been established that DIDP is characterised by a moderate skin-resorptive action: Applications at a dose of 3,160 mg/kg for 24 hours on the skin of rabbits caused anorexia, moderate depression in all experimental animals; after the termina-tion of the substance action, the state of the animals normalised, the autopsy showed no significant pathological changes in the skin of animals [5].

The results of the sensitising effect of DIDP on guinea pigs were ambiguous: The modified Buehler test has established the sensitising effect of the substance [7]; Buehler and GPMT tests have found the allergic properties of DIDP [5]. The authors explain this fact by the presence of impurities in trademarks of the plasticiser, as well as by a complex scheme of conducting the modified test Buehler.

Parameters of acute toxic effects of DIDP on the body of experimental animals are characterised by low values upon inhalation, oral, skin effect (Table 1) [5, 8, 9–10]. Administration of DIDP by inhalation to rats, the symptoms of intoxication developed next day and manifested by a decrease in body weight, development of signs of excitation of animals, uncertain gait; the autopsy detected foci of inflammation in the lungs [5].

Table 1. Parameters of DIDP acute toxicity

The information search shows that the toxic properties of DIDP have been studied in subacute, subchronic and chronic studies, with different ways of admin-istration.

Following inhalation of DIDP multiple doses (2 weeks) to rats, NOAEL is determined at 500 mg/m³; the histological examination revealed in the lungs a moderate increase in the width of alveolar septa on the background of a minor inflammatory reaction, an increase in the number of alveolar macrophages and type II pneumocytes; spleen and kidneys were without significant histological changes [11].

Following oral administration of DIDP, NOAEL is established at 304 mg/kg for males and 264 mg/kg for females for 21 days. The toxic effect was manifested by an increase in the absolute and relative weight of the liver, kidneys and absolute weight of testicles; a probable decrease in the level of triglycerides and cholesterol was observed in the blood serum of males [5, 12].

DIDP toxicity rates in subchronic, chronic studies and in the study of long-term effects of an action are presented in Table 2.

In the subchronic experiment (41 days), when DIDP was administered with food to rats, NOAEL was substantiated at 264 mg/kg for females in the blood serum according to biochemical hepatotoxicity, NOAEL for males was not established, since increased liver mass and changes in liver hydroxylation processes were observed at levels of all doses. Blood serum in males showed a decrease in triglycerides and cholesterol levels; in males and females — changes in the activity of enzymes of lipid metabolism. Electron microscopic examination of the liver in high dose rats showed a marked increase in the size and number of peroxisomes in hepatocytes, more pronounced in males [11].

According to the subchronic study (90 days), a dose-dependent increase in the absolute weight of the liver in rats was established. According to this parameter, NOAEL was determined for males at the level of 200 mg/kg, for females — 60 mg/kg; pathological changes in the testicles, ovaries, liver and kidneys were not observed [5, 6, 11].

Table 2. Parameters of subchronic and chronic toxicity, remote effects of DIDP action

The results of the subchronic experiment (13 weeks) conducted on dogs con-firmed the hepatotoxic effect of the substance: NOAEL is established on the level of 15 mg/kg based on the incidence of vacuolated hepatocytes [11].

Thus, according to the results of the subacute and subchronic action of DIDP, it is established that the intake of the substance with food leads to a hepatotoxic effect, as indicated by an increase in the absolute and relative weight of the liver, an increase in the number of peroxisomes, and an increase in the catalytic activity of enzymes in hepatocytes in experimental animals [13]. Since rat hepatocytes are characterised by high peroxisis and increased activity of catalytic enzymes, authors suggest using NOAEL at 15 mg/kg to characterise the subchronic toxicity of DIDP [5].

The reproductive toxicity of DIDP was studied on Sprague-Dawley rats, which received the substance on corn oil via a gastric tube at doses of 100; 500 and 1,000 mg/kg from Days 6 to 15 of gestation. In females receiving a dose of 1,000 mg/kg, a significant reduction in body weight gain and feed intake was ob-served. A dose-dependent increase in the number of small skeletal anomalies was detected in 21-day-old foetuses: Appearance of cervical and lumbar foetal ribs is statistically confirmed following exposure to high doses. According to the parameter of weight loss in pregnant females, NOAEL for a maternal body is established at the level of 1,000 mg/kg; NOAEL for foetuses is 500 mg/kg based on the incidence of small skeletal anomalies [14, 15].

A study of the effect of DIDP on the reproductive function of Sprague Dawley rats was conducted using a two-generation test. In females at high doses (0.4 % and 0.8 %), a significant decrease in body weight gain and feed intake, an increase in the absolute weight of the liver and kidneys were observed; histological examination showed hepatocellular hypertrophy [16].

In rats F₁ at a dose level of 0.2 %, there was an increase in the relative weight of the kidneys and liver. In rats F₂, a significant reduction in survival rates, a decrease in body weight were observed at doses of 0.2 and 0.4 %. It was shown that the effect of DIDP did not adversely affect fertility rates of rats F₁ and F₂, no changes were observed in the histological examination of reproductive organs of rats of both generations. NOAEL: was 0.4 % (253 mg/kg) for rats F₁ and F₂, based on weight loss; 0.06 % (≈ 33 mg/kg) for F₂ rats based on the survival rates. The results of the studies indicate that DIDP may be excreted into breast milk [156].

It has been established that DIDP has no antiandrogenic effect, no oestrogenic activity in vitro and in vivo [17, 18].

According to DIDP assessment on the potential negative effects on reproduc-tive health of a person, conducted within the National Toxicology Program (NTP) by the Centre for the Evaluation of Risks to Human Reproduction (CERHR), it has been determined that there is no direct evidence of the adverse effects of the substance on human reproductive parameters. The authors emphasise that with potential human exposure to DIDP high doses, there is a minimal risk for the development of long-term effects [11].

In vitro studies have found that DIDP does not induce mutagenic effects in bacterial cultures, in lymphoma culture of mice and Balb/c-3T3 cells without and with metabolic activation [19–22]. A negative result was found in in vivo studies using a mouse bone marrow micronucleus test [23].

The level of DIDP skin absorption is very low: The maximum absorption rate is set at 4 % of the dose within 7 days, DIDP excretion from the body is very slow. In humans, the level of skin absorption of the substance is expected to be lower than that of rats [11, 24].

DIDP absorption through the digestive tract decreases with increasing a dose: 56 % at 0.1 mg/kg, 46 % at 11.2 mg/kg and 17 % at a high dose of 1,000 mg/kg [25].

Following oral and inhaled administration, DIDP is rapidly excreted and does not accumulate in tissues; when the radioactive label is used, less than 1 % of radio-activity is detected after 72 hours; elimination ways are urine and faeces [25]. DIDP metabolic-waste products are monoisodecyl phthalate and an alcohol fragment, monoisodecyl phthalate is oxidised or hydrolysed to phthalic acid; metabolic prod-ucts are detected in the liver and kidneys [8].

Literature sources provide information on DIDP effects on the human body. Application of 0.2 ml of DIDP to the skin with an occlusive bandage for 24 hours (15 volunteers) does not irritate the skin [26]. In another study, application of 5 % DIDP on the basis of vaseline oil showed signs of irritation in 2 volunteers of 144 [27], application of 5 % DIDP for two days with the occlusive bandage resulted in skin irritation in 2 volunteers of 310 [28]. After applying DIDP to the skin (24-hour exposure, 3 times a week), no clinical signs of sensitisation and skin irritation was observed in 104 volunteers within 3 weeks [29]. Literature sources contain only one case of a possible sensitising action in a worker upon contact with DIDP. Since sensitising properties are not established for phthalate esters, in particular for diethylhexylphthalate (DEHP) and dibutyl phthalate (DBP), it can be assumed that the risk of sensitisation of workers exposed to DIDP is minimal.

Conclusions

1. The substance has an irritating effect on the skin at the level of 1–2 points at dif-ferent exposures (from 5 minutes to 24 hours.), the effect is reversible with peel-ing of the skin. The irritating effect of DIDP on the eye mucosa is mild and lim-ited by conjunctiva. Sensitising properties of the substance on the body of ani-mals and human are not established. DIDP is characterised by a mild skin-resorptive action.

2. According to the results of subacute and subchronic DIDP action following oral administration, the liver was found to be the target of toxic effects, as evidenced by an increase in the liver mass, lipid metabolism disorders in the absence of liver pathology, an increase in paroxysmal activity of enzymes in rodents.

3. Embryotoxic and teratogenic effects are manifested in high concentrations, which is not a limiting criterion in the systematic assessment of DIDР. Mutagenic and carcinogenic effects have not been established.

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