Influence of exposure regimen on nitrogen dioxide-induced morphological changes in the rat lung.

Experiments were performed to study the influence of concentration, exposure pattern, and length of exposure on the degree and extent of morphological alterations in the NO2-exposed rat lung. Four weeks of continuous exposure to 20 mg NO2/m3 consecutively revealed damage and loss of cilia, replacement of desquamated type I pneumocytes by type II pneumocytes resulting in a cuboidal epithelial lining, an influx of alveolar macrophages, and hypertrophy and hyperplasia of the bronchiolar epithelium. The animals recovered almost completely from the induced lesions within 8 days. Continuous exposure to 1, 2.5, or 5 mg/m3 displayed minimal alterations in the 5 mg/m3 group. The effects increased with exposure time. Intermittent or continuous exposure to 20 mg NO2/m3 resulted in minor differences after 4 weeks. The onset of the lesions was delayed and the massive influx of alveolar macrophages in the continuously exposed animals failed to appear in the intermittently exposed animals. This work demonstrates that in subacute experiments: Concentration plays a more important role in inducing pulmonary lesions than exposure time when the product of concentration and time is kept constant. This effect is stronger during intermittent exposure than during continuous exposure. Continuous exposure seems to be a more important factor with regard to a macrophage response than intermittent exposure. The rat lung has a large capacity to repair almost completely from damage caused by short-term NO2 exposure.

Toxicology of tert-butylhydroquinone (TBHQ).

This paper traces the history of the EEC Scientific Committee for Food's examination of available toxicological data on tert-butylhydroquinone (TBHQ). Studies of mutagenicity, metabolism, enzyme activities, reproduction and long-term toxicity and carcinogenicity are reviewed. The author concludes that dose level is an important factor in the induction of forestomach tumours. Further long-term toxicity testing of TBHQ is needed to evaluate its genotoxicity. However, since information is not available, an attempt is made to calculate the 'safety' margin between actual intake by man and the conventional no-effect level in dogs and rats.

Carcinogenicity study in rats with a mixture of eleven volatile halogenated hydrocarbon drinking water contaminants.

A lifetime carcinogenicity study was carried out in Wistar rats, with a mixture of the following halogenated hydrocarbons: trichloromethane, tetrachloromethane, monobromodichloromethane, trichloroethylene, tetrachloroethylene, 1,2-dichlorobenzene, 1,3,-dichlorobenzene, 1,4,-dichlorobenzene, 1,2,3,-trichlorobenzene, 1,2,4,-trichlorobenzene, 1,3,5-trichlorobenzene. From this mixture 0.22, 2.2, or 22 mg was added per liter drinking water representing concentrations being three orders of magnitude higher than found in several water wells. Most of the changes found in body weight, hematology and pathology correlated with intercurrent diseases or were in accordance with background pathology. With respect to incidence and time of occurrence of tumors, no significant differences were found between the control and the high dose group when lifespan correction was applied. Thus it is concluded that in the present study no significant toxic or carcinogenic effects are induced by lifetime exposure of rats to a mixture of volatile halogenated hydrocarbons in the drinking water.

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.

Maleic hydrazide, carcinogenicity study in rats.

The carcinogenicity of maleic hydrazide is discussed by several national and international organizations because of contradictory results of a number of carcinogenicity studies carried out in the past. Because maleic hydrazide is used in agriculture on edible crops, an oral carcinogenicity study with rats was carried out for 28 months at dietary levels of 0, 1.0 and 2.0% maleic hydrazide which contained less than 1.5 mg hydrazine/kg product as impurity. In this study as well as in an experiment with mice carried out with the same batch of maleic hydrazide at the International Agency for Research on Cancer (IARC) in Lyon, France, treatment did not affect tumor incidence and it was concluded that maleic hydrazide itself is not a carcinogen. Most likely the presence of relatively high levels of hydrazine as an impurity was responsible for the contradictory results in studies as reported previously. Furthermore the results of this study showed that 1.0 and 2.0% maleic hydrazide in the diet caused proteinuria and increased protein/creatinine ratio's in the urine in both sexes without detectable histopathological changes in kidney or urinary tract. From this study, based on the effects of kidney function the "no-toxic" effect level is considered to be lower than 1.0% maleic hydrazide in the diet of rats.

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.

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.

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.

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.

Toxicity of methylmercury chloride in rats. II. Reproduction study.

A reproduction study over 3 generations of rats was carried out in which groups of 20 female and 10 male rats received in the diet 0, 0.1, 0.5 and 2.5 ppm MeHgCl. The parameters studied included growth, food intake, haematology, serum and urinalysis, organ weights and reproductive performance, No effect was exerted on fertility index, lactation index or on the 21-day body weights of pups but the viability index was impaired at 2.5 ppm in the F1 and F2 generations. Weight gain reductions observed at 12 weeks for the 2.5 ppm level were not accompanied by reductions in food intake. At 6 months, Fla females on 2.5 ppm showed a reduced leucocyte count whilst P males on 0.5 and 2.5 ppm showed an increase in neutrophils and a decrease in lymphocytes. The relative weights of the kidneys, heart, spleen brain and thyroid were increased at 2.5 ppm and in some cases the increases of kidney weights were inconsistently seen at the 0.1 and 0.5 ppm levels. No significant histological changes were seen at any level. In a special 7-week study involving the F3a generation, weanling rats obtained from the four different F2a groups, each comprising 20 females and 10 males, were all transferred to diets containing 25 ppm MeHgCl. Toxicity signs were evident at 7 weeks. No evidence was obtained of increased susceptibility to the toxicity of MeHgCl in successive generations.

The short-term toxicity of some feed additives to different freshwater organisms.

The short-term toxicity (EC50 respectively LC50 after 2 or 4 days) of 13 feed additives was determined to 4 freshwater organisms of different trophical levels: Chlorella pyrenoidosa, Daphnia magna, Lebistes reticulatus and Salmo gairdneri. The most toxic (LC(EC)50 less than 1 mg/1) were robenidine (to all tested organisms) and stenorol (to Daphnia); moderately toxic (1 less than LC(EC)50 less than 10 mg/1) was pyrimethamine. Amprolium, ethopabate, furazolidone and zoalene proved to be little toxic (LC(EC)50 greater than 10 mg/1); whereas buquinolate, carbadox, clopidol, decoquinate, grofas and sulfaquinoxaline were under the experimental conditions not toxic for the tested organisms.

Short-term toxicity of 1-naphthaleneacetic acid in rats.

In a 90-day feeding study, 4 groups of 10 male and 10 female rats received in the diet 0,200, 1000 and 5000 ppm 1-naphthaleneacetic acid (1-NAA). Growth and food intake was reduced significantly only in males on 5000 ppm. Haematological examination yielded essentially negative results except for a non-significant reduction at the 1000 and 5000 ppn levels in the leucocyte count, mainly due to a reduction in neutrophils. No significant effects were observed in the renal concentration test, urinalysis, renal histochemistry or histology of a wide range of organs at any level of 1-NAA tested. Increased relative weights of thyroid, testes, brain and liver were confined to the 5000 ppm level. The increase in relative liver weight was not accompanied by histological liver damage and was associated with elevated liver microsomal enzyme activity. The loss of glucose 6-phosphatase (G6Pase) and increase in glucose 6-phosphate dehydrogenase (G6PDH) seen histochemically in the centrilobular region of the liver in males on 5000 ppm, accompanied by glycogen depletion in the liver, could however be indicative of liver damage. On the basis of conventional criteria, a no-effect level of 1000 ppm would have been indicated by this study but in view of liver glycogen depletion at all levels tested a no-effect level was not established.

Long-term toxicity and reproduction studies with metaldehyde in rats.

Rats received 0, 200, 1000 and 5000 ppm metaldehyde in the diet for 2 years. Reproduction studies over three generations using the same dietary levels were carried out. In the third litter of each generation attention was paid to possible embryotoxic or teratogenic effects. The parameters studied included growth, food intake, behaviour and survival, haematology, clinical biochemistry, organ weight, histopathology, reproductive performance and teratogenicity. At 5000 ppm the relative liver weight was increased and this was accompanied by an increase in liver microsomal enzyme activity. The most striking observation was a dose-related development of posterior paralysis in females due to a transverse lesion of the spinal cord. The latency period was more than 550 days. Three rats with posterior paralysis showed a transverse lesion of the spinal cord. No significant histological damage to other organs was seen. The tumour incidence was not increased in any of the metaldehyde dosage groups. The reproduction study confirmed the findings of the long-term test. Posterior paralysis appeared in at least 50% of the females on 5000 ppm metaldehyde in all 3 generations. Some were affected at 1000 ppm but none at 200 ppm. Histologically, a fracture or distortion of thoracic vertebrae and subsequent compression of the spinal cord was found. The onset of paralysis was related to the time of delivery. The reproductive performance was susceptibility in this respect to metaldehyde. Apart from one male rat on 200 ppm with clinical posterior paralysis without transverse lesions in the spinal cord, this level was without toxic effects both in the long-term and 3-generation reproduction study.