Histological change in the hepatopancreas of terrestrial isopods as potential biomarker of cadmium and zinc exposure

[摘要] ENGLISH ABSTRACT: Metals occur naturally in the environment but since the industrial revolution the amountsofbioavailable metals in the environment have increased significantly. There are variousanthropogenic sources of metals in the environment. In recent years there has been anincreasing interest in the use of biomarkers in terrestrial invertebrates for the assessmentof the potential adverse effects of chemicals in soil ecosystems. Terrestrial isopods areone of the groups that play an important role in the decomposition process as fragmentorsof dead plant material in soil ecosystems. They are also known to accumulatecontaminants in their bodies, especially in the hepatopancreas. Cadmium has no knownbiological function and is deposited in the environment through a variety of sources.Zinc on the other hand is one of the essential metals and play an important role in thenormal metabolism of animals. Zinc too, is deposited in the environment through avariety of anthropogenic sources. The aim of this study was to undertake anexperimental and field evaluation of the role cellular change in the hepatopancreas ofterrestrial isopods can play in conjunction with other sublethal responses to contribute tothe assessment of the impact of cadmium and zinc in terrestrial ecosystems.Porcel/io laevis was used as test species in the laboratory experiments in thisstudy, to conduct sublethal toxicity tests. Cadmium- and zinc sulphate were used as thecontaminants, applied separately and as mixtures. The isopods were weighed before thebeginning of the exposures and every week throughout the exposure period of six weeks.At the end of the exposure period they were dissected to remove the hepatopancreas. Thezinc and cadmium content of the hepatopancreases and rest of the bodies of the isopods were determined by atomic absorption spectrophotometry. Hepatopancreas samples werealso prepared for histological analysis, and measurements of the Percentage Cellular Area(PCA) were made using image analysis. Specimens of Porcellionides pruinosus werecollected from contaminated- and uncontaminated field sites. Hepatopancreas- and restof the body samples of P. pruinosus were also analysed for cadmium and zinc.Histological sections of the hepatopancreas were similarly prepared and analysed, as inthe laboratory experiments.Exposure to cadmium- and zinc sulphate affected the mass of P. laevis negativelyin the single metal exposures. However, these two metals neutralised each other'seffects in the mixture toxicity exposures, pointing towards an antagonistic interaction.Administered cadmium- and zinc sulphate resulted in the accumulation of cadmium andzinc in the isopods, especially in the hepatopancreas. In the mixture toxicity experimentscadmium and zinc influenced the accumulation of each other. Cadmium- and zincsulphate, whether administered separately or as mixtures, changed the structure of thehepatopancreas and this was quantitatively shown through PCA measurements. PCA ofthe hepatopancreas of terrestrial isopods was shown to be a good general biomarker ofexposure and effects for cadmium as well as for zinc. It is suggested that PCA couldserve as a general biomarker to predict possible impairment of growth or mass change ofisopods exposed to cadmium and zinc mixtures. The findings of the field survey alsosuggest that PCA may be suitable to be used as a general biomarker to measure metalinduced stress in woodlice from contaminated field sites.

[发布机构] Stellenbosch University