Detection of various organic contaminants in the aquatic environment at low concentrations, has raised concerns for animal and human health. Structural similarities of these compounds to estrogens and ecdysones suggests that organic pollutants may interfere with hormonal system of aquatic organisms. Techniques of traditional toxicity tests that are based on observable physiological defects may fail to identify sub-lethal / subobservable effects. Under these techniques the mode of action of pollutants cannot be investigated. Thus, there is a need for more sensitive techniques that are capable to evaluate effects at molecular level and provide an early warning to environmental pollution. Toxicogenomic is proposed to be a useful tool to meet this goal. However, there is a limited data that compare toxicogenomic and traditional toxicity test approaches. The aim of this thesis is to evaluate the utility of qRT-PCR based toxicogenomic analysis in risk assessment. To achieve this goal, we first analyzed toxicogenomic and physiological responses of Daphnia manga exposed to three class of widely detected organic pollutant sphthalates, perfluorinated alkylated substances and brominated flame retardant in Paper I-III. Investigated endpoints included effects on hatching, acute toxicity, survival, developmental abnormalities, reproduction success, swimming and feeding behavior, fat metabolism, and life span. Result of these studies demonstrated a high degree of correlation between transcriptional data and the traditional physiological data. Besides, toxicogenomic approach was able to identify effects of sublethal concentrations. Thus, in Paper IV we analyzed environmental sample from Akaki river in Ethiopia using transcriptional approach and showed toxicogenomic tools utility in environmental risk assessment. Overall, the finding of these studies showed that the use of toxicogenomic can improve traditional physiological based toxicity assay to determine environmental risk assessment. Furthermore, toxicogenomic analysis can be performed with relatively short time and limited volume of samples.
Phthalates are used as plasticizers to increase durability, resistivity and flexibility of plastic materials. The commonly used phthalate, diethylhexyl phthalate (DEHP) is used in different plastic materials like food packaging, toys and medical devices. DEHP has been linked to different toxicities in humans as well as in animals, and as a consequence other phthalates, including dibutyl phthalate (DBP) and diethyl phthalate (DEP) are being introduced. The increased use of phthalates has resulted in contamination of aquatic ecosystem and it directly threatens the aquatic life. In this study, we analyzed the effects of three phthalates DEHP, DEP and DBP using freshwater organism Daphnia magna. Although, exposure of the three phthalates at 1 and 10 μM did not result any lethality and hatching delay, the chronic exposure for 14 days resulted in reduction of body length. There was enhanced fat accumulation on exposure to all the phthalates, as indicated by oil red O staining. qRT-PCR analysis of genes involved in fat metabolism suggests that the increase in fat content could be due to inhibition of absorption and catabolism of fatty acids. Reproduction analysis showed that DBP and DEP did not alter fecundity but surprisingly, DEHP at 1 μM increased reproduction by 1.5 fold compared to control group. Phthalates also showed negative effect on lifespan as DEP at 10 μM and DBP at both 1 and 10 μM significantly reduced the lifespan. Our data indicates that along with the banned phthalate DEHP, the other substitute phthalates DEP and DBP could also have detrimental effect on aquatic organisms.
Funding Agency:
Örebro University
Per- and polyfluorinated alkyl substances (PFASs) are synthetic organofluorine compounds with unique stability accompanied with hydrophobic and lipophobic properties. Perfluorooctane sulfonate (PFOS) and Perfluorooctanoic acid (PFOA) are of high concern due to their wide application in consumer and industrial products, extreme persistence, abundant occurrence in the environment and their toxic effect to humans and animals. However, knowledge on the molecular mechanisms of toxicity and the effects on reproduction output remain scarce. In this study, we analyzed the effects of PFOS and PFOA on Daphnia magna. Acute toxicity, development, reproduction, lipid metabolism (lipid-accumulation) and lifespan was investigated, as well as the expression of genes related to these endpoints. Exposure of PFOS and PFOA at 1, 10 and 25 μM did not cause acute lethality. Hatching was reduced following exposure to both compounds, and lifespan was decreased following exposure to 25 μM PFOS. Body length of Daphnia magna was reduced significantly by 25 μM PFOS following 7 days exposure. Lipid staining revealed that all PFAS exposures increased lipid accumulation. qRT-PCR analysis of genes involved in lipid metabolism suggests that the increase in lipid content could be due to inhibition of genes involved on absorption and catabolism of fatty acids. Exposure to both PFOA and PFOS reduced the fecundity significantly. Downregulation of genes involved in development and reproductive process, including vtg2, vasa, EcRA, EcRB, usp, jhe, HR3, ftz-F1, E74 and E75 were observed. The alterations in developmental and reproductive genes as well as the disturbed lipid metabolism provides mechanistic insight into the possible causes for decreased fecundity and lifespan observed following exposure to both PFOS and PFOA.