Effect Of Deltamethrin On Gills And Livers In Danio Rerio

In recent years, pyrethroid pesticides have been widely used in agriculture, forestry, health,warehousing and other industries according to its characteristics of high efficiency, low residueand light stability. However, the extensive use of these pesticides, coupled with lax management,caused an increasing number of pesticides and their residues into the water through a variety ofways, which may broke the balance of the water ecosystem. Pyrethroids pesticides arefat-soluble which can easily enter the body of fish and produce a strong toxic effect through theblood to various tissues and organs. Gills and liver are the target organ of many kind ofchemicals, and the tissue lesions of them can be used as an indicator of water pollution.Danio rerio belong to vertebrates, with characteristics of small size, flexible operation, easyfeeding, high survival rate, short growth cycle and sensitive to poisons. What’s more, it has ahigh degree of similarity to human tissues and organs, nervous system and cardiovascular system.Therefore, it has been used as a model organism of developmental biology, genetics, toxicologyand other studies.This paper selected the pyrethroid pesticide deltamethrin as test chemical to adult Daniorerio. According to the50%Lethal Concentration(48h-LC50) to Danio rerio of the deltamethrin,five concentration groups,0.1TU,0.5TU,1TU and2TU with control were setting. Frozensections of gills and livers in Danio rerio exposed to different concentrations of deltamethrinwere observed and the histological changes were analyzed in order to explore the intrinsicresponse mechanism to deltamethrin in Danio rerio. The results showed that:1.48h acute toxicity test indicated that: the48h-LC50of deltamethrin on Danio rerio was5.2μg/L meaning that deltamethrin are highly toxic poisons to Danio rerio. Danio rerio mortalityrate was positively correlated to the concentration of deltamethrin, which had a high correlationcoefficient, and this correlation has obvious dose-effect relationship. Danio rerio can exhibit significant behavioral changes by different poisons, which is related to the adaptation of Daniorerio in toxic condition.2. After exposed to four concentrations (0.1TU,0.5TU,1TU and2TU) of deltamethrin for48h, a strong toxic effect on gill tissues of Danio rerio were found. The structure of gill tissueswas severely damaged with gill lamellae epithelial cell swelling, hyperplasia, and swollen in top.These caused thickening of gill lamellae, distribution disorder of column cell and increase inchloride cells and mucus cells. After exposed to deltamethrin for48h, the thickness of gilllamellae increased significantly, which increased by a factor of1.6times even in the lowestconcentration of deltamethrin (0.1TU). When treated with2TU deltamethrin, the thickness of gilllamellae increased by a factor of2.5times. The damage enhanced with the extension of exposuretime. Furthermore, the damage more was more obvious in higher concentration of deltamethrin.During the experiment, there was a stable period which may caused by the adaptation of Daniorerio to deltamethrin.3. After exposed to four concentrations (0.1TU,0.5TU,1TU and2TU) of deltamethrin for48h, a strong toxic effect on liver of Danio rerio were found. While, the performance of thedamage required for a longer time compared with the gill tissues, which may be associated withthe circulation processes in Danio rerio. Deltamethrin caused edema, vacuolization, fatdeposition and karyopyknosis in liver cells, along with the dilatation and congestion of hepaticsinusoid. After exposed to deltamethrin for48h, the number of liver cells per unit area wassignificantly decreased, which decreased by22%even in the lowest concentration ofdeltamethrin (0.1TU). When treated with2TU deltamethrin decreased by56%compared withthe control group. The damage enhanced with the extension of exposure time. Furthermore, thedamage more was more obvious in higher concentration of deltamethrin. There was a stableperiod as same as in the gill tissues which may caused by the ability to adapt to the environmentand self-regeneration of liver cells.4. The Change of the damage level of liver and gill tissues in Danio rerio over time has acertain similarity with stepwise stress model. Most of the exposed group had a stable periodsimilar to the model adaptation phase.In conclusion, deltamethrins were highly toxic poisons to liver and gill tissues of Danio rerio.While, the toxic effect on gill tissues was more severely, which may be related to the function of gills and the mechanism of deltamethrin. Overall, the level of damage in gill and liver tissues ofDanio rerio were positively correlated to the concentration of deltamethrin and the exposuretime. Part-time existence of damage mitigation phenomenon, and Danio rerio environmentaladaptability drugs have a certain relationship. The stable period may caused by the adaptation ofDanio rerio to environment.