Making Acute Tests More Ecologically Relevant: Cadmium Bioaccumulation and Toxicity in an Estuarine Clam under Various Salinities Modeled in a Toxicokinetic–Toxicodynamic Framework

Abstract

Salinity has considerable effects on the toxicity of metals in estuarine waters. The effects of salinity are manifold, making it difficult to summarize for risk assessments. In this study, we separated and quantified the multiple effects of salinity on cadmium (Cd) in a toxicokinetic–toxicodynamic framework. The estuarine clam, Potamocorbula laevis, was used as a model organism. Cd bioaccumulation was measured using a stable-isotope-tracer technique; in parallel, toxicity tests were conducted. With the increase of salinity from 5 to 30, Cd uptake decreased monotonically. In contrast, the intrinsic sensitivity of organisms, measured by the toxicodynamic parameters, reached its minimum at intermediate salinities (i.e., 10 to 20). The overall salinity effects were dominated by the effects on Cd bioaccumulation; therefore, Cd toxicity decreased monotonically with the increases of salinity. The model developed in this study could provide predictions of no-effect concentration (1.7 to 34.9 μg L–1, end point mortality) and the median lethal concentration (LC50) of Cd at different salinities. In conclusion, we developed a framework for quantifying the multiple effects of salinity and a method for estimating no-effect concentration from acute toxicity tests, which can be used for better assessments of metal risks in estuarine waters.

Role of Toxicokinetic and Toxicodynamic Parameters in Explaining the Sensitivity of Zebrafish Larvae to Four Metals

“…The TD parameter C IT explained up to 70% of the variation in toxicity to the four metals (Figure A), suggesting that C IT was the major TD parameter in determining the survival rate. The parameter C IT reflects the toxicity of bioavailable metal: higher C IT values indicate a higher toxicity threshold concentration . Aquatic species with smaller body sizes are always associated with a lower C IT and are more sensitive to toxicants, , which further indicates the relationship between C IT and metal toxicity.…”

“…The parameter C IT reflects the toxicity of bioavailable metal: higher C IT values indicate a higher toxicity threshold concentration. 33 Aquatic species with smaller body sizes are always associated with a lower C IT and are more sensitive to toxicants, 14,66 which further indicates the relationship between C IT and metal toxicity. However, the parameter C IT can explain well the toxicity of Cd, Pb, and Zn, but it cannot explain why the toxicity of Cu is higher than those of Cd and Pd (Figure 4A).…”

“…The processes that lead to toxicity at the organismal level can be described by TK and TD models . The general unified threshold model of survival (GUTS) is an often-used mechanistic TK-TD model that can successfully simulate the bioaccumulation of pollutants and its correlation to survival over time for aquatic organisms. , The GUTS model was separated into two parts, which included the TK and TD processes, to estimate the specific parameters describing the TK process (including uptake and elimination) and the TD process with survival as end point. Since metal toxicity may be more closely linked with the metal subcellular distribution pools rather than overall metal bioaccumulation, the link between metal bioaccumulation in different subcellular pools and metal toxicity may be more realistic in the TK modeling.…”

Copper Adsorption to Microplastics and Natural Particles in Seawater: A Comparison of Kinetics, Isotherms, and Bioavailability

“…63 Cu and 65 Cu were measured using an ICP-MS (Agilent 7900) with germanium ( 72 Ge) used as an internal standard to correct sample matrix effects and instrument drift. The increase of 65 Cu ([ 65 Cu]’) in a sample was calculated as follows where [ 65 Cu] and [ 63 Cu] are the total concentrations of Cu measured by ICP-MS, and 65 F (0.3085) is the isotopic abundance of 65 Cu in the calibration standard. , The increase of 65 Cu in the control sample was due to the adsorption of newly added 65 Cu, while that in the filtrate sample resulted from the gut juice extraction.…”

“…where [ 65 Cu] and [ 63 Cu] are the total concentrations of Cu measured by ICP-MS, and 65 F (0.3085) is the isotopic abundance of 65 Cu in the calibration standard. 37,38 The increase of 65 Cu in the control sample was due to the adsorption of newly added 65 Cu, while that in the filtrate sample resulted from the gut juice extraction. Data Analysis.…”