Assessing abalone growth inhibition risk to cadmium and silver by linking toxicokinetics/toxicodynamics and subcellular partitioning

Bioavailability and toxicity of silver nanoparticles: Determination based on toxicokinetic-toxicodynamic processes

Determining the bioavailability and toxicity mechanism of silver nanoparticles (AgNPs) is challenging as Ag⁺ is continuously released by external or internal AgNP dissolution in the actual exposure system (regardless of the laboratory or the natural environment). Here a novel pulsed-gradient Ag⁺ (AgNO₃) exposure was conducted with zebrafish (Danio rerio) larvae to simulate dissolved gradient concentrations of Ag⁺ from polyvinylpyrrolidone (PVP)-coated AgNPs. The accumulation and toxicity of the pulsed-gradient Ag⁺ (AgNO₃) and, in the meantime, the released Ag⁺ from PVP-AgNPs were predicted using a toxicokinetic-toxicodynamic (TK-TD) model with obtained Ag⁺ parameters. In order to further understand the possible mechanism of PVP-AgNP releasing Ag⁺ in the body, subcellular fractions (S9) of zebrafish were also used to incubate with AgNPs in vitro to mimic the realistic in vivo scenarios. In the TK process, in vivo analysis showed that AgNPs released around twice as many Ag⁺ into the body than were detected with a single Ag⁺ pulse-exposure system; this was supported by evidence that subcellular S9 fractions might cause the PVP-AgNPs to lose the capping agent and favor Ag⁺ release. In the TD process, toxicity (survival rate) was predicted by the total bodily Ag(I) concentration, suggesting that AgNP toxicity in larvae was mainly due to gradually released Ag⁺ rather than AgNPs themselves. This study helps clarify the role of Ag⁺ in AgNP toxicity and offers a novel framework by which to investigate the toxicity of metal nanoparticles and corresponding metal ions in biological systems.

Applications of dynamic models in predicting the bioaccumulation, transport and toxicity of trace metals in aquatic organisms

This review evaluates the three dynamic models (biokinetic model: BK, physiologically based pharmacokinetic model: PBPK, and toxicokinetic-toxicodynamic model: TKTD) in our understanding of the key questions in metal ecotoxicology in aquatic systems, i.e., bioaccumulation, transport and toxicity. All the models rely on the first-order kinetics principle of metal uptake and elimination. The BK model basically treats organisms as a single compartment, and is both physiologically and geochemically based. With a good understanding of each kinetic parameter, bioaccumulation of metals in any aquatic organisms can be studied holistically and mechanistically. Modeling efforts are not merely restrained from the prediction of metal accumulation in the tissues, but instead provide the direction of the key processes that need to be addressed. PBPK is more physiologically based since it mainly addresses the transportation, transformation and distribution of metals in the organisms. It can be treated conceptually as a multi-compartmental kinetic model, whereas the physiology is driving the development of any good PBPK model which is no generic for aquatic animals and contaminants. There are now increasingly applications of the PBPK modeling specifically in metal studies, which reveal many important processes that are impossible to be teased out by direct experimental measurements without adequate modeling. TKTD models further focus on metal toxicity in addition to metal bioaccumulation. The TK part links exposure and bioaccumulation, while the TD part links bioaccumulation and toxic effects. The separation of TK and TD makes it possible to model processes, e.g., toxicity modification by environmental factors, interaction between different metals, at both the toxicokinetic and toxicodynamic levels. TKTD models provide a framework for making full use of metal toxicity data, and thus provide more information for environmental risk assessments. Overall, the three models reviewed here will continue to provide guiding principles in our further studies of metal bioaccumulation and toxicity in aquatic organisms.

Prediction of acute toxicity of cadmium and lead to zebrafish larvae by using a refined toxicokinetic-toxicodynamic model

The biotic ligand model (BLM) and the toxicokinetic-toxicodynamic (TK-TD) model are essential in predicting the acute toxicity of metals in various species and exposure conditions; however, these models are usually separately utilized. In this study, a mechanistic TK-TD model was developed to predict the acute toxicity of 10(-6)M Cd and 10(-6)M Pb to zebrafish (Danio rerio) larvae. The novel approach links the BLM with relevant TK processes to simulate the bioaccumulation processes of Cd or Pb as a function of the maximum uptake rate of each metal, the affinity constants, and the concentrations of free metal ions and H(+) in test solutions. Results showed that the refined TK-TD model can accurately predict the accumulation and acute toxicity of Cd and Pb to zebrafish larvae at pH 5.5, 6.5, and 7.0.

Exposure to heavy metals and polycyclic aromatic hydrocarbons and DNA damage in taiwanese traffic conductors

BACKGROUND

Exposure to traffic-related air pollutants, including polycyclic aromatic hydrocarbons (PAH) and heavy metals, has been associated with the etiology and prognosis of many illnesses. However, the specific causal agents and underlying mechanisms for different health outcomes remain unclear. The aims of this study were to assess the relations between urinary biomarkers of exposure to PAHs (1-hydroxypyrene-glucuronide, 1-OHPG) and heavy metals (cadmium, Cd; nickel, Ni; arsenic, As; lead, Pb; and copper, Cu) and the effect of their interaction on DNA damage (8-oxo-7,8-dihydro-guanine, 8-oxodG).

METHODS

We recruited 91 traffic conductors and 53 indoor office workers between May 2009 and June 2011 in Taipei, Taiwan. Postshift urine samples from 2 consecutive days were analyzed for 1-OHPG, Cd, Ni, As, Pb, Cu, and 8-oxodG. To estimate the effects from PAHs and metals on DNA damage, we constructed a linear mixed model adjusted for confounding variables.

RESULTS

We found that urinary 1-OHPG and Cd levels were independent predictors of urinary 8-oxodG levels (β = 0.112; P = 0.015 for 1-OHPG; β = 0.138; P = 0.031 for urinary Cd). The joint effect of urinary 1-OHPG and Cd levels was associated with urinary 8-oxodG levels (P = 0.001).

CONCLUSIONS

Co-exposure to environmental PAHs and Cd could cause oxidative DNA damage.

IMPACT

These findings suggest that the additive interaction between exposure to environmental PAHs and Cd could enhance the burden of oxidative stress.