G.J. Van Esch

No-effect levels organochlorine pesticides based on induction of microsomal liver enzymes in short-term toxicity experiments

Abstract A number of organochlorine pesticides were given in the diet of rats during 2 weeks. The induction of microsomal liver enzymes by different dose levels of these compounds was studied. In this way a no-effect level was established for each pesticide. This was then compared with no-effect levels from the literature, based on histopathological abnormalities in the liver in long-term experiments. In general, good agreement was found, except for some compounds, such as chlorfenson, kelthane and chlordane, for which a much lower no-effect level was found in this study. The capacity for inducing enzymes decreased in the order: heptachlor, DDT, chlorfenson, dieldrin, dicofol, chlordane, tetrasul, V110, hexachlorobenzene (HCB), lindane, endosulfan. Polychlorinated biphenyl (PCB) was also studied. This substance had a very high enzyme-inducing capacity for aniline hydroxylase (AH), but only a medium one for aminopyrine demethylase (APDM) and hexobarbital oxidase (HexOx). Methoxychlor and dichlobenil did not show any enzyme induction at the dose levels tested.

Semichronic toxicity study of sodium bromide in rats.

Abstract A 90-day toxicity study was carried out in rats on diets containing 0, 75, 300, 1200, 4800 and 19200 ppm sodium bromide. The animals on the highest level did not groom themselves sufficiently and exhibited signs of motor incoordination. The male animals in this group showed significant growth retardation. Plasma bromide levels increased within 3 weeks to a plateau. In all groups, except in the highest dosage group, these plateaus were directly proportional to the bromide concentrations in the diets, as were the bromide concentrations in brain and kidneys after 13 weeks. Total molar halogen concentration in plasma, however, remained constant throughout the investigation. No striking effects on hematological and biochemical parameters were seen except for a doubling of the percentage of neutrophil granulocytes in the highest dosage group. In female animals on 1200, 4800 and 19200 ppm and in male animals on 19200 ppm bromide an increase of relative thyroid weight was found. In male rats an increase of the relative weight of the adrenals was found in the 19200 ppm group and a decrease of relative prostate weight was seen in the two highest dosage groups. Histopathologically a dose-related disturbance of the endocrine system and some of its target organs was found.

Hexachlorobenzene toxicity in pigs

Hexachlorobenzene Toxicity in Pigs. den Tonkelaar, E. M., Verschuuren, H. G., Bankovska, J., de Vries, T., Kroes, R., and van Esch, G. J. (1978). Toxicol. Appl. Pharmacol. 43 , 137–145. A 90-day toxicity study was carried out in which pigs received 0.05, 0.5, 5.0, and 50 mg/kg/day of hexachlorobenzene (HCB). Special attention was given to the induction of porphyria and microsomal liver enzymes and the concentration of HCB in blood and tissues. Animals given the highest dose (50 mg/kg) showed clinical signs associated with porphyria and died during the experiment. At lower dosages these signs were not observed. An increased excretion of coproporphyrin was found in the 5.0- and 0.5-mg/kg groups, as well as induction of microsomal liver enzymes accompanied by increased liver weight (at 5.0 mg/kg) and characteristic histopathological changes in the liver. The concentration of HCB in blood and tissues was elevated at all dosages. Concentrations in fat were approximately 500 times greater than those in blood, while the concentration in liver was higher than in the kidneys and brain. Under the conditions of this experiment, a no-effect level was judged to be 0.05 mg/kg/day of HCB.

Study on the carcinogenicity of lead arsenate and sodium arsenate and on the possible synergistic effect of diethylnitrosamine

Abstract In a lifetime (29-month) carcinogenicity study, rats were treated with lead arsenate (PbHAsO 4 ) or sodium arsenate (Na 2 HAsO 4 ·7H 2 O) and the possibility that diethylnitrosamine (DENA) may exert a synergistic or additive action on the effects of these compounds was studied. Lead arsenate was fed in the diet at levels of 1850 or 463 ppm, while sodium arsenate was fed at a level of 416 ppm. Additional groups of rats were fed 463 ppm lead arsenate or 416 ppm sodium arsenate in combination with DENA given in an intubated dose of 5 μg/day on 5 days/wk. The rats receiving these diets were weaned by mothers receiving the same diet during lactation. Food intake levels (for the first 12 wk) and body weights were recorded, haematological studies were carried out after 12 months and complete gross and microscopic examinations were conducted at autopsy. At level of 1850 ppm, lead arsenate was toxic and caused intra- and extrahepatic bile-duct lesions. Intranuclear inclusions due to the ingested lead were present in the kidneys and liver, but only for the first 12 months. Other histopathological changes, commonly found in these rats, were equally divided between the groups. No differences were apparent either in the tumour incidence of the different groups or in the times at which tumours were detected. An adenoma in the renal cortex and a bile-duct carcinoma, both found in the group fed 1850 ppm lead arsenate, may have been indicative of a very weak carcinogenic action of this compound, but no definite conclusion used in this study. No additive or synergistic effect could be attributed to DENA, which also failed to induce tumours at the low dose level used, suggesting the possible existence of a no-effect level for this carcinogen.

Toxicity of methylmercury chloride in rats III. Long-term toxicity study

Four groups, each of 25 male and 25 female weanling rats, were given dietary levels of 0, 0.1, 0.5 and 2.5 ppm MeHgCl for 2 years. Observations were made on behaviour, growth, food intake, haematology, serum enzymes, urinalysis, microsomal liver enzymes, organ weights and histology with special reference to the nervous system, histochemistry of the kidneys and cerebellum and on tissue Hg concentrations. Significant findings included a slight growth reduction in females at 2.5 ppm, increased relative kidney weight at 2.5 ppm and histochemical changes in kidney enzymes at 2.5 ppm. No effect was seen on the nature or incidence of pathological lesions or tumours at any level. From the results obtained in the short-term, reproduction and long-term studies, the no-toxic effect level for rats appears to be between 0.1 and 0.5 ppm MeHgCl in the diet. Exposure of the Dutch population does not appear to present a health hazard at the moment because the mean intake of total Hg is still far below the intake deemed to be safe.

Carcinogenicity study with epichlorohydrin (CEP) by gavage in rats

Weanling Wistar rats of both sexes were given epichlorohydrin by gastric intubation for 2 years, 5 times a week at dosages of 0, 2, and 10 mg/kg body weight. Mortality and body weight gain were recorded and histopathological examination for tumours was carried out; after 1 year also haematology was performed. Towards the end of the study a slight dose-related increase in mortality was observed in males, along with a decrease in mean body weight in the survivors. At pathological examination a high incidence (100% for females, 81% for males) of squamous cell carcinomas of low-grade malignancy was observed in the forestomach of animals at risk (greater than 18 months) from the 10 mg/kg group. In the 2 mg/kg group forestomach tumours were found at a lower incidence (7% for females, 14% for males), whereas this tumour was not found in control animals. Other tumours diagnosed in this study occurred at background level and were not influenced by treatment.

Toxicity of methylmercury chloride in rats I. Short-term study.

In the range-finding test, 6 groups of 4 male and 4 female weanling rats were given dietary levels of 0, 0.1,0.5, 2.5, 12.5 and 250 ppm methylmercury chloride (MeHgCl) for 2 weeks. Signs of central nervous system toxicity, weight loss and high mortality appeared at 250 ppm but not at lower levels. No haematological changes were observed at 0.1-12.5 ppm. The relative weights of the liver in females on 2.5 and 12.5 ppm and of the kidneys in females on 12.5 ppm were significantly increased; the effects in males were less marked. Total mercury concentration in the kidneys increased proportionally with increasing dietary levels of MeHgCl. In the short-term test, 5 groups of 15 male and 10 female weanling rats were given dietary levels of 0, 0.1, 0.5, 2.5 and 25 ppm MeHgCl for 12 weeks. Toxic signs, weight loss and restricted food intake were observed at 25 ppm starting from week 9 onwards. Haematological, serum enzyme and urinalysis changes were seen at 25 ppm. Liver microsomal enzyme activity was increased non-significantly and liver glycogen was depressed at 25 ppm. Organ weight changes were evident at 25 ppm and histological changes seen in the spleen, kidneys, brain, spinal cord and peripheral nerves were confined to the 25 ppm level. Histochemical changes in kidney enzymes occured at 2.5 and 25 ppm. Hg concentrations in blood, hair, kidneys, liver and brain were higher at 12 weeks than 6 weeks and generally increased with increasing MeHgCl level in the diet.

Long-term toxicity studies of chlorpropham and propham in mice and hamsters

Abstract Isopropyl N -phenylcarbamate (propham; IPC) and isopropyl N -(3-chlorophenyl)-carbamate (chlorpropham; CIPC) were tested for carcinogenic properties in hamsters and mice. The hamsters were given 0·2% IPC or CIPC in the diet, while mice were given 0·1% CIPC by the same route, using 0·1% urethane as a positive control. Other mice were given sc injections of CIPC. All experiments included the necessary negative controls. Neither IPC nor CIPC caused any increase in tumour incidence in hamsters. In the mouse, urethane induced multiple lung tumours in nearly all the animals, whereas the tumour incidence in the CIPC group was of the same order as that of the controls. In both of the latter groups, only solitary lung tumours were induced. Similarly, no increase in tumour rate followed sc application of CIPC. These results, showing no tumorigenic effect with either IPC or CIPC, are discussed in the light of data on the metabolism of these compounds.

Short-term toxicity of strontium chloride in rats

A range-finding experiment with strontium chloride hexahydrate (0, 3, 30, 300 and 3000 ppm in the diet) and subsequently a 90-day test with the same compound at dose levels of 0, 75, 300, 1200 and 4800 ppm in a semipurified diet was carried out with SPF-derived Wistar-rats. The diet contained adequate levels of Ca, Mg, P and Vit.D3. Growth, food intake, behaviour and mortality were measured, extensive haematology and clinical biochemistry carried out, organ weights determined, X-ray photographs of the bones taken and complete histopathological examination was performed. In addition Sr-content of blood, bone and muscles was determined. Thyroid weights were significantly increased in the males of the 1200 and 4800 ppm group. Histological evidence for increased thyroid activity was noticed in the males of the 4800 ppm group. Pituitary weights were significantly decreased in the females of the 300 ppm and 4800 ppm group, but not of the 1200 ppm group. A histologically confirmed glycogen depletion of the liver was noted biochemically in the highest dose group (4800 ppm). Sr-content in bone was increased at all dose levels having a constant level from 4 weeks onwards, thus indicating that a no effect level cannot be established. If the increased Sr-concentration in the bone can be considered a non-toxic effect, the non-toxic effect level appears to be 309 ppm.

Effect of food deprivation on low level hexachlorobenzene exposure in rats

The purpose of the present study was to determine if food deprivation could modify the biological activity of hexachlorobenzene (HCB) in the rat. Male and female Wistar rats were divided into 6 groups containing 6 animals. Groups 1, 3 and 5 were fed standard control diet ad libitum for 2 weeks. For the next 4 weeks their respective diets contained 0, 20 and 100 ppm HCB. Groups 2, 4 and 6 were also fed a standard control diet for 2 weeks but at an intake of approximately 50% of those groups fed ad libitum. For the following 4 weeks food deprivation was continued but the control diets were replaced with diets containing 0, 40 or 200 ppm HCB. The parameters measured were food, body weight changes, changes in tissue weights, microsomal enzyme activity and histopathology of liver, kidneys, adrenals and pancreas. Tissue residue profiles were established for plasma, liver, brain and adrenals. Food deprivation augmented the induction of microsomal enzyme activity by HCB in both males and females at both dose levels. Liver hypertrophy was observed in both males and females fed 200 ppm HCB and subjected to food libitum. Food deprivation resulted in a higher plasma, liver, brain and adrenal accumulation of HCB in both males and females.