| In order to clarify organoarsenical effects on ecological environment and toxic mechanism, and further to evaluate the safety of organoarsenical used as additives, the experiments were designed to study their toxic effects on soil microorganisms, Chinese Cabbage and Carassias auratus (Cara), and also the residue and elimination of roxarsone in fish. 1. Studies on ecotoxicity of organoarsenical additives50mg/kg arsanilic acid (calculated with As content, the same below ) could stimulate soil respiration and respiration intensity increased 8.4%~39.7%. 100mg/kg and 200 mg/kg of roxarsone also enhanced soil respiration initially, and then turned to inhibit it and respiration intensity reduced 14.5%~19.3%. Arsanilic acid at the dose of 50 mg/kg could decrease soil ammonification 17.3%~29.1%, but the 200 mg/kg of arsanilic acid promoted significantly soil ammonification. The effects of roxarsone was contrary to the arsanilic acid. Roxarsone at the dose of 200 mg/kg inhibited the ammonification. Arsanilic acid could inhibit soil nitrification, the effects stronger with increasing of doses. Roxarsone only at dose of 200 mg/kg showed inhibition. At later stage the two additives both stimulated soil nitrification. The results showed organoarsenical additives could enhance soil respiration, but had different effects on soil ammonification and nitrification.Chinese Cabbage were cultivated in nutrient solution in stead of soil. The effects of organoarsenical additives on the fresh weight and dry weight, the overground and underground parts, and root system were investigated. When the two additives at the dose of 100 mg/kg were added, Chinese Cabbage initiallylost water and withered, and gradually recovered later. The effects were positively correlated with doses and time. Chinese Cabbage grew slowly in all treated groups, became short and small, with the root developed poorly. The results showed that organoarsenical additives inhibited the growth of Chinese Cabbage strikingly, and the toxicity of roxarsone to Chinese Cabbage was more serious than that of arsanilic acid.Roxarsone showed the low toxicity to Cara, but the margin of safety was narrow. When fishes were exposed to the water containing roxarsone, the LC50 were as follows: 24h LC50181.69mg/L, 48h and 96h LC50176.57mg/L, the relationship between toxicity and duration was not significant. In the acute (5d) and subchronic exposed experiments the Cara brain, liver and gill were collected to determine the activities of lactate dehydrogenase (LDH), superoxide dismutase (SOD), glutathione S-transferase (GSH-ST) and the contents of malondialdehyde (MDA). The activities of LDH in brain and liver at dose of 30 and 45 mg/L (calculated with As content, the same below ) were inhibited significantly and showed dose-effect relationship, but that of LDH in gill was motivated at the 5th day. The contents of MDA in brain and liver increased significantly in all treated groups.Initially the activities of SOD in brain, liver and gill were enhanced significantly and then inhibited markably when dose increased. These results suggested that Cara might develop a kind of compensational protection effect in order to eliminate reactive oxygen metabolites. In acute exposed experiment the activities of GSH-ST in brain were inhibited strikingly. The gill and liver GSH-ST activites showed a significant compensational increase at the second day, and then turned to be inhibited at 5th day. These results showed roxarsone could inhibit enzyme with sulfhydryl group and the ability of antioxidation. The oxidative damage to brain and liver in Cara were remarkable and showed dose-effect relationship.Cara were exposed to water containing roxarsone (lOmg/L, calculated with As content) for 15 days and then transfered to fresh water without roxarsone for the eliminating test. Roxarsone showed a rapid absorbtion and distribution in Cara. The As concentration in gill,muscle,serum and guts reached the highest steady state level quickly. Total As level in muscle was only 0.3~0.4mg/kg, less than the Maxium residue limit (MRL, aquatic product, ^0.5 mg/kg). Theresidue of As in gut reached to 30.25 mg/kg. Roxarsone in muscle,serum andinternal organs were eliminated rapidly with first-order rate kinetic process. Thehalf time of elimination(ti/2) were 2.5~2.8h. With initial 2h the As in gilldecreased r apidly from 3.42mg/kg to 0.30 m g/kg, and then eliminated s lowlyand the Un was 9.45h.2. Studies on the toxicity and the mechanism of neurotoxicity of roxarsone inratsThe onset of roxarsone toxicosis in rats was acute and the oral LD50 was 149.6mg/kg. The rats manifested a nervous syndrome as muscle tremors, paraparesis and paraplegia.The roxarsone were given in rats by the diet at the doses of 1 0, 20 and 50mg/kg.b.w, respectively. The nitric oxide (NO) in treated groups increased significantly as the dose increased at the first and third week and showed a dose-effect relationship, then recoverd to the level similar to that of control group. The change of nitric oxide synthase (NOS) in rat brain coincided with those of NO. The NO contents in liver decreased at the first and third week, but increased significantly in high dose group. After rapidly decreased to low level initially, the activities of Na+K+-ATPase and Mg++-ATPase in rat brain increased. The Ca++-ATPase in all groups decreased at initial stage, and dropped markably in high dose group at fifth week. The activities of r-GT in brain decreased significantly with the increasing doses at the first week, but there were not different among all the groups at the later stage.The MDA content in brain and liver of rats in treated groups increased significantly at the first and third week and recovered to the nomal level of control group at fifth week. The SOD in brain showed a compensational increase initially in treated groups, but at the fifth week the activities of SOD were inhibited. The results showed that roxarsone could induce lipid peroxidation and then lead to a compensational recovery.The studies on LDH and its isoenzyme in rats showed that the LDH activities in brain increased initially and decreased significantly in the later experiment. The activities of LDH in liver were inhibited at the first week, and recovered gradually in low and middle doses but in high dose group still decreased markably. The LDH isoenzymes in brain were separated bypolyacrylamide gel electropheresis and measured by soft scanning densitometer. The spectrum of LDH5 in brain was not significant or disappeared. The activities of LDHi component in high dose initially decreased but then increased, whereas that of LDH4 showed a contrary change. The activities of LDHi component in low and middle dose kept up a steady increase,but that of LDH4 decreased.In the acute(single doses of 62.5 and 125mg/kg) and subchronic (10,20 and 50mg/kg by feeding for 5 weeks) toxicity tests roxarsone could induce an serious nervous syndrome. Histopathologic examinations revealed the lesions as follows: neural cell degeneration in brain, myelin and axonal degeneration in the spinal cord. The lesion of cervical spinal cord were more serious than those of thoracic and lumbar spinal cord. The lesions lightened during the recovery period of toxicosis in the acute toxicity test. In the subchronic toxicity the lesions became serious with the increasing dose and duration and showed dose-effect-duration relationship. In the acute toxicity test hematoxylin and eosin staining (HE) and the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) methods were used for morphological studies. At the fifth day a large number of neuron and neurogliocyte in the brain and cervical,thoracic and lumbar spinal cord appeared apoptosis, but at the tenth day the apoptosis decreased.These results suggested that roxarsone could induce lipid peroxidation and damage the membrane of neural cell, inhibited the activities of ATPase and then caused the ion imbalance, which enhanced the NOS activity and increased the content of NO in brain, the excessive NO induced neurotoxicity. |
PDF Full Text Request