以系統層級動態研析吳郭魚暴露於擾動金屬濃度之生態生理反應

Abstract

Fluctuation exposure of contaminant is ubiquitous in aquatic environments. Traditional standard laboratory toxicity tests were performed at constant exposure scenarios typically did not elucidate the short-term pulsed exposure toxicity to aquatic organisms. Little is known about copper (Cu) and arsenic (As) toxic effects with pulsed and fluctuation exposures on aquatic organisms. The purpose of this dissertation was to develop a quantitative systems-level approach utilizing toxicokinetics, toxicodynamics, bioavailability, and bioenergetics mechanisms to elucidate the ecophysiological response of tilapia (Oreochromis mossambicus) to fluctuating or sequential pulse Cu and As stresses. This study investigated the relationship among bioavailable metal, accumulative concentration and critical damage level induced growth toxicity for tilapia based on biotic ligand model (BLM), threshold damage model (TDM), and ontogenetic growth-based dynamic energy budgets in toxicology (DEBtox) model. This study conducted the sequential pulsed Cu exposure bioassays on tilapia population to provide Cu acute/chronic toxicokinetics information. The 10-day and 28-day sequential pulsed Cu exposure experiments were conducted to obtain the bioconcentration factor (BCF) for tilapia population. This study linked bioavailability and bioaccumulation mechanisms to estimate the time and water chemistry dependent BCF. This also study analyzed the As exposure experimental data and pulsed Cu exposure bioassays of tilapia with growth inhibition response by using the proposed systems-level mechanistic model with periodic pulses and fluctuating exposures to simulate and compare the outputs. The ontogenetic growth-based DEBtox model was used to estimate growth coefficient (A0) based on chronic growth bioassay, for assessing Cu and As chronic growth toxicities to tilapia. The experimental results indicated that larvae had the highest BCF of 1116.10 mL g-1 that was greater than those of juveniles 225.50 mL g-1 and adults 94.00 mL g-1 in acute pulsed Cu exposure, whereas juveniles had the highest BCF 154.54 mL g-1 than that of adults 23.10 mL g-1 in chronic pulsed Cu exposure. Besides, tilapia had a higher Cu accumulation capacity than that of As (BCF=2.89 mL g-1). Results also showed that BCF value depended significantly on water chemistry conditions and ions concentration. Moreover, BCF value decreased with the increasing of exposure duration. This study also found that tilapia in response to low-frequency Cu/As pulsed exposure had longer 50% safe probability time (ST50) than that of high-frequency pulsed exposure, whereas the longer ST50 was found in high frequency for Cu/As fluctuating exposure. The results indicated that the regulations were triggered between the pulsed intervals. The accumulation of the second Cu pulsed exposure was positively influenced by first Cu pulsed exposure that was consistent with the results of model simulation. The growth coefficients were estimated to be 0.029± 0.0015 g1/4 d-1 (Mean±SE) for control and 0.019±0.0017 g1/4 d-1 for pulsed Cu exposures in tilapia. The results indicated that growth coefficient depends positively on the exposure concentrations, revealing that Cu concentration inhibited growth energy and affected the growth of tilapia. The estimated dimensionless mass ratio revealed that sequential and fluctuating Cu exposure could increase tilapia energy acquisition than that of sequential and fluctuating As exposure for overcoming externally fluctuation-driven environments. This study showed that the dynamics of physiological responses were dependent on the pulsed and fluctuating concentrations, duration, frequency, and different chemical exposure characters in tilapia. Moreover, the time and ions-dependent BCF provided a tool to assess the relationship between accumulation and toxic effect in the field situation. We anticipated that this study could provide a completed quantitative systems-level dynamic approach for understating the ecophysiological response of aquatic organisms in response to metal stresses in the field situations. We also hoped that the proposed dynamics of ecophysiological response mechanistic model could successfully assess the long-term metal exposure risk for tilapia population in the field situation of metal exposure impact.