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

Odendaal, James Philander (2002-12)

Thesis (PhD)--Stellenbosch University, 2002.

Thesis

ENGLISH ABSTRACT: Metals occur naturally in the environment but since the industrial revolution the amounts ofbioavailable metals in the environment have increased significantly. There are various anthropogenic sources of metals in the environment. In recent years there has been an increasing interest in the use of biomarkers in terrestrial invertebrates for the assessment of the potential adverse effects of chemicals in soil ecosystems. Terrestrial isopods are one of the groups that play an important role in the decomposition process as fragmentors of dead plant material in soil ecosystems. They are also known to accumulate contaminants in their bodies, especially in the hepatopancreas. Cadmium has no known biological 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 the normal metabolism of animals. Zinc too, is deposited in the environment through a variety of anthropogenic sources. The aim of this study was to undertake an experimental and field evaluation of the role cellular change in the hepatopancreas of terrestrial isopods can play in conjunction with other sublethal responses to contribute to the assessment of the impact of cadmium and zinc in terrestrial ecosystems. Porcel/io laevis was used as test species in the laboratory experiments in this study, to conduct sublethal toxicity tests. Cadmium- and zinc sulphate were used as the contaminants, applied separately and as mixtures. The isopods were weighed before the beginning 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. The zinc and cadmium content of the hepatopancreases and rest of the bodies of the isopods were determined by atomic absorption spectrophotometry. Hepatopancreas samples were also prepared for histological analysis, and measurements of the Percentage Cellular Area (PCA) were made using image analysis. Specimens of Porcellionides pruinosus were collected from contaminated- and uncontaminated field sites. Hepatopancreas- and rest of the body samples of P. pruinosus were also analysed for cadmium and zinc. Histological sections of the hepatopancreas were similarly prepared and analysed, as in the laboratory experiments. Exposure to cadmium- and zinc sulphate affected the mass of P. laevis negatively in the single metal exposures. However, these two metals "neutralised" each other's effects in the mixture toxicity exposures, pointing towards an antagonistic interaction. Administered cadmium- and zinc sulphate resulted in the accumulation of cadmium and zinc in the isopods, especially in the hepatopancreas. In the mixture toxicity experiments cadmium and zinc influenced the accumulation of each other. Cadmium- and zinc sulphate, whether administered separately or as mixtures, changed the structure of the hepatopancreas and this was quantitatively shown through PCA measurements. PCA of the hepatopancreas of terrestrial isopods was shown to be a good general biomarker of exposure and effects for cadmium as well as for zinc. It is suggested that PCA could serve as a general biomarker to predict possible impairment of growth or mass change of isopods exposed to cadmium and zinc mixtures. The findings of the field survey also suggest that PCA may be suitable to be used as a general biomarker to measure metal induced stress in woodlice from contaminated field sites.

AFRIKAANSE OPSOMMING: Metale kom natuurlik voor in die omgewing, maar sedert die industriële revolusie het die hoeveelheid bio-beskikbare metale in die omgewing betekenisvol toegeneem. Daar is verskeie antropogeniese bronne van metale in die omgewing. Die afgelope paar jaar was daar toenemende belangstelling in die gebruik van biomerkers by terrestriële invertebrate vir die assessering van potensiële negatiewe effekte van chemiese stowwe in grondekosisteme. Terrestriële Isopoda is een van die groepe wat 'n belangrike rol speel III die ontbindingsproses as fragmenteerders van dooie plantmateriaal III grondekosisteme. Hulle akkumuleer ook kontaminante in hul liggame, veral in die hepatopankreas. Kadmium het geen biologiese funksie nie, en word vrygestel in die omgewing deur verskeie bronne. Sink, aan die ander kant, is een van die essensiële metale en speel 'n belangrike rol in die metabolisme van diere. Sink word ook in die omgewing vrygestel deur 'n verskeidenheid antropogeniese bronne. Die doel van die studie was om deur eksperimentele en veldondersoek die rol van sellulêre veranderinge in die hepatopankreas van terrestriële Isopoda in samehang met ander subietale response te evalueer om by te dra tot die assessering van die impak van kadmium en sink op terrestriële ekosisteme. Porcellio laevis is as toets-spesie in die laboratorium eksperimente gebruik om subietale toksisiteitstoetse mee uit te voer. Kadmium- en sinksulfaat is as kontaminante gebruik, en is apart en gemeng toegedien. Die houtluise is geweeg voor die begin van die blootstellings en elke week deur die loop van die blootstellingsperiode van ses weke. Aan die einde van die blootstellingsperiode is hulle gedissekteer om die hepatopankreas te verwyder. Die sink en kadmium inhoude van die hepatopankreas en res van die liggame van die houtluise is bepaal met behulp van atoomabsorpsiespektrofotometrie. Monsters van die hepatopankreas is ook voorberei vir histologiese analise, en metings van die Persentasie Sellulêre Oppervlak (PSO) is gedoen met behulp van beeldanalise. Eksemplare van Porcellionides pruinosus is versamel van 'n gekontamineerde- en 'n ongekontamineerde gebied. Monster van die hepatopankreas en res van die liggaam van P. pruinosus is ook geanaliseer vir kadmium en sink. Histologiese sneë van die hepatopankreas was ook voorberei en geanaliseer, soos in die laboratorium eksperimente. Blootstelling aan kadmium- en sinksulfaat het die massa van P. laevis negatief beïnvloed in die enkelmetaal-eksperimente. Hierdie twee metale het egter mekaar se effekte in die mengseltoksisiteitstoetse "geneutraliseer". Dit dui op 'n antagonistiese interaksie. Toegediende kadmium- en sinksulfaat het gelei tot die akkumulasie van kadmium en sink in the houtluise, veral in die hepatopankreas. In die mengseltoksisiteitstoetse het kadmium en sink mekaar se akkumulasie beïnvloed. Kadmium- en sinksulfaat, apart of as mengsels toegedien, het die struktuur van die hepatopankreas verander, en dit is kwantitatief aangetoon deur die PSO metings. PSO van die hepatopankreas van houtluise is 'n bruikbare algemene biomerker van blootstelling en effek vir kadmium en sink. Dit word voorgestel dat PSO kan dien as 'n algemene biomerker om negatiewe effekte op die groei of massaverandering van houtluise te voorspel wat aan kadmium en sink mengsels blootgestel word. Die bevindinge van die veldondersoek dui daarop dat PSO gepas mag wees om gebruik te word as 'n algemene biomerker om metaal-geïnduseerde stres by houtluise vanaf 'n gekontamineerde gebied te meet.

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