Understanding The Effects Of Water Chemistry On The Toxicity Of Copper In An Estuarine Clam Potamocorbula Laevis Using The Toxicokinetic-Toxicodynanic Model

Water chemistry of estuarine ecosystems is complex and dynamic.Among the many factors that affecting the toxicity of metals,salinity and dissolved organic matter(DOM)are the two key factors.Salinity and DOM not only affect the bioavailability and bioaccumulation of metals,but also affect the physiology and intrinsic sensitivity of aquatic organisms.In the study,we investigated the effects of estuarine water chemistry on the bioaccumulation and toxicity of copper(Cu)in a model organism Potamocorbula laevis under the framework of the toxicokinetic-toxicodynamic model using the stable isotope tracer technique and toxicity tests.Below are the major results of this study:(1)The effects of salinity on the bioaccumulation and toxicity of Cu in the clam P.laevis:At low Cu concentrations(i.e.,6-9 μg/L),Cu uptake rate constant[ku,L/(g·h)]decreases significantly with salinity(5-30)and can be quantitatively described with the empirical equation:ku= 1/(1.35+0.116·Salinity).At high Cu concentrations(i.e.,300-500 μg/L),the inhibitive effects of salinity against the bioaccumulation of Cu are not significant;Cu toxicity increases with the elevation of salinity.The median lethal concentrations are 269 μg/L,224 μg/L,and 192 μg/L at salinity 5,15,and 30,respectively.The increases of Cu toxicity can be explained by the increased killing rate of Cu from 0.44 mg/(μg·h)to 2.08 mg/(μg·h).The probable underlying physiological mechanism is the deviation from the optimal salinity of the calm.(2)The effects of salinity fluctuation on the bioaccumulation and toxicity of Cu in the clam P.laevis.At low Cu concentrations(6-9μg/L),the uptake rate constant(ku)were 0.877、0.554 and 0.410 μg/L at fixed salinity 5,15 and 30,respectively.The 1:1 regression line between measured and modeled data,r2=0.915;At high Cu concentrations(422-500 μg/L),the 1:1 regression line between measured and modeled data,r2=0.969.TK-TD model provides good prediction in this study.(3)The effects of DOC on the bioaccumulation and toxicity of Cu in the clam P.laevis.At low DOC concentrations(<2.50 mg/L),DOC lowered the uptake rate constant(ku)of Cu by reducing the concentration of bioavailable Cu species.These effects of DOC were more obvious at low Cu concentrations.At high DOC concentrations(>2.50 mg/L),effects of DOC on Cu bioaccumulation was unexpected.DOC increased the bioaccumulation of Cu.We speculated that it was due to the flocculation of DOC,which acted as a carrier of Cu and was ingested by the filter-feeding clams.The increased Cu bioaccumulation was not translated into higher toxic effects,presumably due to the lower toxicity of intestinal Cu,which can be egested rapidly.Overall,DOC showed protective effects against the toxicity of Cu.In conclusion,this study use toxicokinetic-toxicodynamic model to predict and quality the effects of salinity and DOM on the bioaccumulation and toxicity of copper(Cu)in a model organism Potamocorbula laevis.This model could be used to different metals or different biological species,providing a framework for organizing future studies in this area,and facilitate the better management of metal risks in estuarine systems.