1、BioavailabilityFree for uptake (fraction).Free for uptake but also cause an effect at the site of action.bioavailablef = 0-1Why this is important?C is highC is lowless reactivemore reactiveThe concerned: total conc. bioavaiFactors affecting bioavailabilityPhysico-ChemicalT, S, TSS, DOCBiologyFeeding

2、Size/ageLipid contentDetoxificationGeochemistryTotal concSpeciationComplexationMetal interactionBioavailabilitysalinityDissolved organic carbonsWaterSpecies ABCCarnivoresSedimentABDeposit feederSedimentWaterPhyto Species ABCHerbivoresSpecies ABCSignificance of speciation(e.g. Polychaete)What are the

3、 bioavailable species in each compartment?-surface-headdownMetals in waterFree ion species.Free ion + inorganic complex ion + organic complex ion.Free ion is the most important species bioavailable (Free Ion Activity ModelFIAM).(do not bind with metals)(inorganic)Ions and speciation in seawater Anio

4、nic: Cl, HCO3, CO3, F, PO4, NH3, SO4, SiO4, OH. Cationic: H, K, Na, Ca, Mg. Metals:Cd: CdCl2Ag: AgCl2-Zn: Zn2+, ZnOH+, ZnCO3, ZnCl+(consider Ksp)(waterchem: substance 0.2m poresize considered dissolved)in unit of psu (part per 1k)Cd in fresh water system is more dangerous because it is in free ion f

5、ormAlgaeDifferent algae have dfrt uptake to dfrt ions, so bioavai is dfrtMusselIdea of FIAM model(Chelating Agent)E - (Ligand)higher reacti(humate acidbase)MLMLLL + M2+L + M2+LKinetic trapPassive diffusion(rare)LLL increasing binding ability(membrane transporter)(ligand)Biotic ligand modelFIAMmodelC

6、onsidered fish gill and GI are biotic ligand (uptake)Dissolved Organic Matter(outside envi only)(gill, kidney)(Fish)H-DOCH+, M2+ compete for DOCParticle phase: phytoplanktonCytoplasm hypothesis: assimilation is related to the metal distribution in algal cytoplasm.divided into cellwall & cytoplasmcel

7、lwall do not considered in bioavai(To quantify)GIFoodDigestionFecesAbsorption Assimilation ExcretionGut A general digestion processInside the body(elimination is not considered here) MetalDesorption Extracellular digestionAbsorptionDiatomsFeces Marine copepods(Cytoplasm 100% bioavai, which contains

8、metal )In 1:1 relationship, bioavai of copepods depends on algea, not the physiology of copepods. (similar to FIAM)Copepods (Reinfelder & Fisher 1991)(a phytoplankton)Use physical methods like freezing or ultrasonic to break coconut shell (cell wall)(cell wall)1:1 relationship 100% assimilationDesor

9、ptionExtracellular digestionAbsorptionDiatomsIntracellular digestionMetalDigestive glandFecesBivalve digestion(double shell)(not 100% assimilation)(endocytosis)MusselsNot 1:1 but significant relationshipSubcellular partitioningMetals can be partitioned in different subcellular fractions: Metal-rich

10、granules; Cellular debris; Organelles;Heat denatured protein; Heat stable protein (MTLP);(-SH)(functional bodies)5 fraction of metalTrophically Available Fraction(enzyme)(cysteine)- detoxi( more bioavai )(assimilation efficiency)FishPredicted vs. actualA more complicated picturepHIntracellular diges

11、tion (endocytosis)Mn+(desorption)Oxic sedimentPartial extraction (1 N HCl).Sequential extraction (Tessier et al. 1979).Different geochemical phases (easily exchangeable, Fe oxide).(sink/reservoir, or link)organisms in sedimentoxicsuboxicanoxicsedimentSO42- S2- odor problem(simulate gut envi)most bio

12、avaisediment - anoxic tube - oxic (bioturbation)porewater - oxicAnoxic sediments Theory of AVS (acid volatile sulfide): Cd2+ + FeS Fe2+ CdS Definition of AVS: sulfide conc. extractable by HCl.S2-may not work in reality for detoxic,due to bioturbation / bioirrigationIf O2 penetrate, MOx will appeared

13、AVS/SEMSEM (simultaneously extractable metal).If AVS/SEM1, metal binding as sulfide, no toxicity.(Acid Volatile Sulfide)PolychaeteComing back to basic biologyNereisbioturbation/bioirrigationOrganic contaminantsKow directly affects accumulation in aquatic organisms. (Kow is the most important factor)QSAR-quantitative structural activity relationship.BCF: bioconcentration factorbut Mn+ need to consider species/physiology(elimination)Kow is too high then some matter may not be bioavai (e.g. pass membrane)Biological quantityAllometric relationship: Y = a WbWeight specifi