Subcellular Partitioning Links Toxicokinetic/toxicodynamic Models to Assess the Susceptibility Risk in Farmed Fish Exposed to Metal Stressors
Date Issued
2012
Date
2012
Author(s)
Ju, Yun-Ru
Abstract
Recently, subcellular metal partitioning has been used for assessing metal toxicity in aquatic organisms. In reality, the environmental metal concentration is tended to be fluctuation and pulse as a result of the site-specific water chemistry conditions. But little researches have been studied by using the subcellular partitioning for aquatic organisms exposed to pulsed metals in the field of ecotoxicology. Hence, the purposes of this dissertation were: (i) to develop an integrated toxicological model by linking subcellular partitioning and toxicokinetic/toxicodynamic (TK/TD) models with the experimental data of pulsed copper (Cu)-tilapia (Oreochromis mossambicus) system and published data of cadmium (Cd)-rainbow trout (Oncorhynchus mykiss) system, (ii) to investigate the trade-offs among ecophysiological parameters related to metals bioaccumulation, subcellular partitioning, and susceptibility in farmed fish of tilapia and rainbow trout, and (iii) to provide a probabilistic risk approach to assess susceptibility risks for farmed fish exposed to metals stressors.
A 28-day pulsed Cu exposure experiment was conducted to provide the information on the subcellular partitioning of Cu in tilapia. The Cu bioaccumulation and the distributions of Cu in metabolically active (MAP) and detoxified pools (MDP) can be obtained from the pulsed Cu exposure experiment. The published data of rainbow trout exposed to waterborne and dietborne Cd were adopted to reanalyze and estimate susceptibility and detoxified capacity. This study estimated bioavailability, bioaccumulation, and internal damage of tilapia and rainbow trout in response to pulsed Cu and Cd, respectively. Toxicokinetic parameters of uptake rate (k1), elimination rate (k2), and detoxification rate constants (kd) were derived for tissues in tilapia (gill and muscle) and rainbow trout (gill, liver, and gut). The damage assessment model (DAM) was used to fit to data of time-varying percentage of metal in MAP to estimate killing rate constant (kk), recovery rate constant (kr), and susceptibility. A physiological-based TK model was used to predict tissue burdens for rainbow trout exposed to environmentally relevant Cd concentrations and tissue-specific susceptibility risks can be estimated. A probabilistic risk assessment model was presented to assess the metal exposure risks for tilapia and rainbow trout.
The experimental results indicated that the percentage of Cu in MAP increased with time from 23% to 57% for gill, whereas for muscle, the percentage of Cu in MAP slightly decreased with time from 35% to 28% for tilapia in response to pulsed Cu exposure. Results showed that toxicokinetic parameters of k1s, k2s, and kds were 8.38 and 0.408 mL g-1 d-1, 0.244 and 0.031 d-1, and 0.178 and 0.033 d-1, respectively, for gill and muscle of tilapia exposed to pulsed waterborne Cu. Results showed that k2, kd, and kr ranged from 0.32 – 0.46 d-1, 0.45 – 1.72 d-1, and 1.08 – 1.45 d-1, respectively, for gill of rainbow trout exposed to waterborne Cd (5 – 50 ug L-1), whereas 0.07 – 0.19 d-1, 2.24 – 87.75 d-1, and 1.02×10-6 – 1.37×10-2 d-1, respectively, for gut exposed to dietborne Cd (0.6 – 30.3 ug g-1). This study implicated no significant susceptibility risk for tilapia exposed to waterborne Cu concentrations. The probability that 50% or more of the susceptibility risk in response to Cu exposure for tilapia was only 33.2% Cu in MAP. For rainbow trout exposed to Cd, a most likely probability of % Cd in MAP of gill and liver exceeding 47 – 49%. In contrast with gill and liver, gut had a relative lower Cd susceptibility risk (15 – 17% Cd in MAP). The trade-offs between elimination and detoxification in rainbow trout exposed to Cd, Cu, and zinc (Zn) based on recently published data were also examined. Results indicated that the relationships between k2 and kd were negative for rainbow trout. However, the relationships between kd and % metal in MDP were found to be positive. Results also indicated that rainbow trout had the higher accumulation (~ 60 – 90 %) in MAP when exposed to essential metals of Cu and Zn and had only 10 – 50 % accumulation in response to non-essential metal of Cd.
This study found that metal accumulations of tissues varied with the patterns of exposure metal concentration in farmed fish. An integrated model to assess the susceptibility for farmed fish exposed to metal stressors was provided in this study. The trade-offs between elimination and detoxification were also quantified for providing the valuable insights into the ecotoxicology of farmed species. In conclusion, this study used exposed laboratory data of Cu and Cd to investigate the bioaccumulation, bioavailability, and metal distribution of subcellular partitioning for understanding of the susceptibility risks in framed fish of tilapia and rainbow trout. Hence, the probabilistic risk assessment framework linking with the proposed integrated ecotoxicological model can provide an advice for helping government based bioassessment and biomonitoring programs to protect the farmed fish from metal exposures.
Subjects
Rainbow trout
Tilapia
Cadmium
Copper
Subcellular partitioning
Susceptibility
Toxicokinetics/Toxicodynamics
Detoxification
Risk assessment
Type
thesis
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