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By labeling HS 1500 with a radioactive 14C, it was proven that after oral application and under certain circumstances, low amounts of low molecular humic acids are for a short time absorbed from the gastrointestinal tract. But the biological availability of the substance is very low (less than 0.1% of the applied high doses). The plasma concentration curve assumes a first order kinetic for invasion and excretion. After oral application of 500 mg/kg b.w. HS 1500 the half life period was 1.5 hours and maximum plasma concentration was 3 micrograms/ml. The result obtained indicate that HS 1500 is toxicological riskless after oral administration. Taking into account the pharmacokinetic data, residues of the substance in animal tissues can be ruled out with high significance.

Influences of the low molecular humic substance HS 1500 on parameters of organs (testis weight, epididymis weight), FSH-, and LH-levels in plasma as well as on the spermatogenesis of male rats were studied. After a daily oral application of 1000 mg/kg b.w. and 2000 mg/kg b.w., respectively over a period of 60 days (40th to 100th day of life) only 2 animals of the high dose group were observed with bilateral testicular atrophy. Despite of the two animals with testicular atrophy no significant differences between treated and control rats were observed with respect to testis morphology and spermatogenesis. There is no evidence whether the differences between the hormone levels and the testicular atrophy revealed is regarded to a HS 1500-effect or not. But otherwise a direct influence of HS 1500 can be ruled out with high certainty. Possibly because of the thin covering layer on the gastrointestinal mucous membrane formed by HS 1500, the absorption of nutritive substances is inhibited. Therefore the growth of sensitive organs like testis and epididymis, in the development period, can be decreased. Nevertheless, even after long time application the spermatogenesis is not influenced.

The influence of a low molecular synthetic humic substance (HS 1500) on pre- and postnatal development of rats was investigated. After oral application of 1000 mg/kg and 2000 mg/kg b. w. HS 1500 during the period of organogenesis (6th to 15th day p. c.) and from 16th day p. c. up to weaning neither adverse effects in the mothers nor in the fetuses were reported. The occurrence of a single malformation (gastroschisis) after application of 1000 mg/kg b. w. from day 6 to 15 of pregnancy, few ossifications of phalanges and differences in swimming behaviour are not regarded as the effect of the substance. In conclusion, the oral use of HS 1500 in the treatment of gastrointestinal diseases in animals during pregnancy is regarded to be riskless.

Using the synthetic humic acid product HS 1500 and the native product Sodium-Humate, the suitability of the HET-CAM-test to evaluate irritating effects was tested. Neither sensitizing nor irritating properties were detectable in concentrations of up to 10% in either humic acid solution. This leads us to the conclusion that both products are very mildly acting substances on mucous membranes and skin, causing no irritative effects. In order to improve the certainty of these results, it is still currently recommended to carry out the Draize-test in addition to the HET-CAM procedure (SPIELMANN, 1992). We are convinced that the HET-CAM-test can be a very useful first step in distinguishing between irritative and non irritative substances and in protecting animals from pain, even in the event that the results of both tests do not clearly correspond to each other. Taking into account the results of our experiments, a modified HET-CAM-test also seems to be useful to predict the antiphlogistic effects of chemical substances.

This paper describes results of ecotoxicological investigations concerning the effects of industrial pollutants on farm animals. By means of simultaneous experiments using dusts from lignite-filters and sedimentation-filters as well as sulfur dioxide (SO2) as stress models and by using studies on farm animals in pollutant-burden regions of eastern Germany it could be shown, that pollutants can lead to disorders of health, efficiency and behaviour, like o. g. heavy metals, and to contamination of food of animal origin. Dusts, resulting from combustion of lignite and SO2 initiate non specific effects in the organism and it is only difficult to determine their part on the decrease of productivity and metabolic disorder of farm animals in pollutant regions.

Investigations were performed to determine the hexobarbital sleeping time (HST) of a strain of Wistar rats (WIST/Lppt). Another aim of the studies was to demonstrate possibilities to use the HST as a method to get additional informations during pharmacological and toxicological experiments. The age--and sex--dependent changes in the hexobarbital sleeping time of the investigated strain of rats are in coincidence with results of other authors, using different rat strains. Additionally, the HST more or less depends on circadian and circannual rhythm. It was stated that the HST as a prescreening-method before starting investigations in detail is of great importance.

The influence of the pesticide Sodium-2,2-dichlorpropionate (Na-DCP; Dalapon) was investigated on dairy cows concerning of its effect on ability and health condition. The investigations were carried out in practice using several parameters (feeding, efficiency, haematological and clinicochemical parameters, tests of the slaughtered organisms including their patho-histological examination). The arising of residues was controlled in milk, organs and tissue as well. The pesticide was daily applied orally with the feedstuff in 3 different dosages (2.5, 10, 30 mg/kg b. w./d). Feedstuff consumption, results of milk production and milk quality were not influenced by Na-DCP. The presented results can not verify with safety the insignificant alterations of some clinicochemical parameters (Creatinine, Bilirubin). Direct after the deposit of Dalapon in all samples of milk, organs and tissue residues of this pesticide could be observed. The maximum tolerable residue levels for animal in the ex-GDR were exceeded under these conditions.

Bioavailability of iron (II) bounded as a chelate to macromolecular humic acids was investigated in two different concentrations using retention rates of 59Fe in piglets (age: 24 h). Investigations period was from 3 hrs. to 21 days following application. 21 days after a single oral application of the humic-acid-iron-complexes, 25% of the total Fe was detected in the animal, distributed in the erythrocytes (80%), muscles and bones (8% respectively) and liver (4%). For the first time in veterinary medicine these results enable a combined therapy of enteric and iron-deficiency syndrome by using only one drug. Recommendation for dosing is provided.

Humic acids derive from a class of natural substances in humic substances. The chemical properties of certain defined humic acid products enable their application in diseases of the digestive system of mammals when combined with metabolic disorders, especially in rearing age. The simple administration (via feed), their exceptional safety and the absence of side effects (e. g. allergy, resistance) as well as no residue formation in animal derived products allow a broad application of these substances in veterinary medicine, even when regarding ecotoxicological aspects.