Effect assessment of synthetic glucocorticoids to the selected freshwater invertebrate and vertebrate species
Creators: name: Bal, Navdeep
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 300599
subject: Fisheries sciences not elsewhere classified
classificationCode: 410102
subject: Ecological impacts of climate change and ecological adaptation
classificationCode: 419999
subject: Other environmental sciences not elsewhere classified

description: Anthropogenic activities in the aquatic environment have resulted in an unmanaged disposal of pharmaceuticals and personal care products (PPCPs), which is a cause for concern. An emerging class of aquatic contaminants that scientists are becoming aware of are glucocorticoids (GCs) from the category of steroid hormones. GCs in their natural form as cortisol controls metabolic, reproductive, immunity and stress related responses in mammals and teleosts. However, highly potent synthetic GC drugs like dexamethasone (DEX), prednisolone (PDS) were developed for human medication in order to treat severe inflammatory diseases and to minimize the side effects of GCs since there were problems with the high doses and clinical GC resistance. <br><br>Recently GC activity (based on reporter gene assays) have been detected in effluents from hospitals and sewage treatment plants (STPs) in Australia. Since these treated STP effluents are released into rivers, lakes or creeks, the biological effects of GCs on aquatic organisms are of concern, yet information on their effects is very limited. The present study aimed at effect assessment of synthetic GCs to selected freshwater invertebrate and vertebrate species such as crustaceans (Ceriodaphnia dubia), gastropod (Physa acuta), and early life stage (ELS) of fish species, Maccullochella peelii and Macquaria ambigua. <br><br>Multigenerational (F0-F3) PDS and DEX exposures were conducted to determine the effects on the life-history traits and at population level of C. dubia. There was a positive trend of increased toxicity followed by reduced life history traits such as fecundity, brood size, time to first brood and intrinsic rate of population increase and body growth (length and area) of C. dubia in the case of both studied chemicals. Exposed species exhibited more sensitivity to DEX than PDS chemical and calculated EC50 (95% CI) values in F3 generation were 18.2 µg/L (CI: 15.6-21.1) for DEX and 303.5 µg/L (CI: 256-356) for PDS. <br><br>The preliminary investigation of 42 d PDS exposure to P. acuta showed premature and delayed embryonic hatching at ≥31.25 µg/L and ≥125 µg/L PDS respectively. Lower calcium (Ca) concentrations and impairment of shell development in juveniles at ≥62.5 µg/L, resulted in shell thinning. Further to this, the multigenerational PDS exposure (126 d) presented a deep insight into the developmental malformations, in particular, shell structure and ontogenesis suppression in almost all predominant life-cycle stages (egg, juvenile and adult) of P. acuta snails. LOEC (lowest observed effect concentration) for multigenerational PDS exposure was at 4 µg/L as measured from biological, molecular, biochemical and morphological indices in exposed F0-F2 generations. Long-lasting anomalies in epigenetic phenomena resulted in transmission of toxic effects into the produced progeny. <br><br>In addition to multigenerational invertebrate studies, the present research has provided a great insight into GC toxicity to ELS of two Australian native freshwater fish species, Murray cod and golden perch. The three studied GC drugs (PDS, DEX and hydrocortisone-HC) were found to have toxic effects of varied magnitude on the exposed larvae as evident from measured biological, cellular, histological, morphological and behavioural (swimming and feeding) endpoints during 14 d exposure period. Golden perch larvae were observed to be more sensitive than the Murray cod larvae when exposed to the same drug concentration in identical exposure conditions. Survival EC20 (95% CI) values for DEX, PDS and HC were 0.03 µg/L (0.01-0.06), PDS: 103 µg/L (80.5-130), HC: 281 µg/L (232.4-334.6) respectively for 7 dph (days post hatching) golden perch larvae and 0.22 µg/L (0.12-0.4), PDS: 164 µg/L (124-212), HC: 421.7 µg/L (335.3-517.7) respectively for Murray cod.<br><br>Further to preliminary GC investigation to fish ELS, two independent ELS exposure bioassays were conducted to determine the effects of chronic PDS exposures on different developmental stages of Murray cod using newly hatched and unexposed 14 dph larvae. Glucocorticoid induced-osteoporosis (GIOP) like symptoms were observed in PDS exposed 35 dph larvae. Histopathological analysis of the morphogenesis of eye structure exhibited cataract-like phenotypes in PDS treated larvae. Ca and phosphorous (P) concentrations were significantly reduced at 31.25 and 15.6 µg/L respectively. Larvae dependent on external food exhibited the greatest sensitivity towards PDS toxicant and their sensitivity was greater than that of early yolk-sac larvae. This finding was evident in the multiple physiological, morphological and behavioural parameters studied. <br><br>The present study has further investigated the influence of temperature and synthetic GCs on the organogenesis of golden perch larvae. Survival and yolk-sac depletion rate of exposed 7 dph larvae at the extreme higher and lower test temperatures (30oC and 15oC) and GC (PDS and DEX) exposures were significantly different to those exposed to GCs at the other two test temperatures (20 and 25oC). In addition to short term exposure, chronic 21 d PDS exposure at 21oC significantly affected the biological, craniofacial development and behavioural activities (feeding activity and touch-evoke response) of the exposed golden perch. Cell death (apoptosis) in the 96 hph PDS exposed larvae was found to be increasing with an increased drug dose. Short term exposure of fish ELS to higher or lower temperatures in combination with additional chemical stressors like synthetic GCs; or chronic exposure to GCs at median temperatures, could potentially imbalance the population and ecosystem and limit the capacity of fish populations to respond effectively to changing conditions. <br><br>The present study has highlighted the importance of multigenerational and chronic ELS exposure studies of invertebrates and vertebrates in identifying the responses of stressed non-target aquatic organisms under long-term exposure of GC compounds. Furthermore, worst case screening level risk assessment through calculation of HQs showed PDS and DEX as high risk contaminants and revealed that there is a potential ecological risk associated with release of these GC chemicals into the aquatic ecosystems. Both Murray cod and golden perch fall under a category of endangered or threatened Australian freshwater fish species. Results of the present study cumulatively provide a reference point to utilize freshwater Australian native species to monitor GC pollution. The continual and uncontrolled exposure of anthropogenic GC chemicals in an aquatic ecosystem may result in reduction in local biodiversity by reducing total number of species which become sensitive to a chemical stressor over a period of subsequent generations and thereby affecting them at their population level.