1Lecture 23Biotic Phase TransfersBioconcentration, Bioaccumulation,Biomagnification, BioavailabilityES/RP 531Fundamentals of Environmental ToxicologyInstructor: Allan [email protected] 2005Bioconcentration• Originally referred to the amount ofchemical residue accumulated by anorganism by adsorption (I.e., throughthe integument) or other routes of entry(including food ingestion)• Results in increased concentration ofpesticide relative to environmentalmatrix (includes food, water, & air)A Negative Context• Bioconcentration is commonly thoughtof as being adverse• Bear in mind that all nutrients andsecondary metabolites are‘bioconcentrated’Modern Usage• Bioconcentration strictly should be used onlywhen referring to accumulation of residues intissues by uptake from an environmentalphase through surface sorption or absorption• Does not include dietary exposure• Commonly used to refer to aquaticorganisms, but also includes terrestrialorganisms, especially if soil dwelling andplantsBioaccumulation• Uptake of contaminants viabioconcentration as well as by foodingestion• Most appropriately used if cannotdistinguish between the twomechanisms of uptakeExpression of Bioconcentration &Bioaccumulation Potential• Ratio of concentration of contaminant inthe tissue (or whole body orbiochemical compartment, like lipids)relative to the concentration ofcontaminant in environmental phase (ormatrix)BCForBAF[C]organism[C]phase=2Equilibrium Partitioning Theory• BCF & BAF can largely be explained byinvoking the same thermodynamic “rules”used to explain physicochemical propertiesand other phase transfers• Thus, uptake of contaminants by aquaticorganisms from water and sediment is oftenexplained by invoking the phrase “equilibriumpartitioning theory”Think About It• Given chemical x & y, x has a lowerfugacity than y in water– Is the BCF in the common testinvertebrate, Daphnia, higher for x or lowerthan for yIn fact, this question cannot be definitivelyanswered until an important piece of thepuzzle is placed on the board!Measuring the BCF• BCF (or BAF) should only bedetermined when the ‘system’ is atequilibrium (or for field measurements,at least in an empirical steady state)flowing waterclean waterconcentration in fishwater concentrationDaysPesticide (ppm)BCF measured hereMust Consider Rate of Depuration• In other words, chemicals aremetabolized at different rates, which willaffect their actual BCF or BAF– DDT• Log Kow ~ 5.7 - 7; Log BCF(water) ~ log 5– Permethrin• Log Kow ~3 - 6; Log BCF (water) ~ log 2! dCAdt= k1•Cw " k2 •CACAS =k1k2•Cw = BCF •CwWhere,CA = concentration in the animal;CAS = concentration in animal at steady state;Cw = concentration in water;k1 = rate constant for uptake from water (day-1);k2 = rate constant for elimination from animal (day-1))3Water Solubility (µg/L)BCF(Fish)Kanazawa (1981)carbaryldiazinonlindanetrifluralindieldrinInverse Correlation Between BCF and Water SolubilityKowBCF(Fish)Kanazawa (1981)Positive Correlation Between BCF and KowcarbaryldiazinonlindanetrifluralindieldrinMechanistic Considerations• Waxy layers on invertebrate cuticle &plant leaves• Mucilaginous layers on plant roots• Lipid bilayer of cell membranes• Possible movement along junctionsbetween cells into interstitial spaces• Gastrointestinal physiology of animalsWax on Arthropod cuticle enhances phase transferCutin & Mucilaginous Film Covers RootsCauses more intimate contact with soilaggregates; enhances phase transferWaxes on leaf surface enhances phase transfer4Dazed & Confused• Probably as a result of early work with DDT,the term biomagnification seems commonlythought to be a major mechanism thatexplains comparatively higher concentrationsof contaminants in organisms from highertrophic levels than in lower levels• However, biomagnification should be usedonly when contaminants havebioaccumulated and experiments haveproven increasingly higher concentrations intissues as trophic level increases– i.e., food chain magnificationHerring gull3,530,000 ppbCatfish11,580 ppbWater0.05 ppbSediments150 ppmPlankton1,880 ppbGull Eggs142,000 ppbHumans2,300 ppbHuman milk1,200 ppbBiomagnification of PCBs inthe Lake Ontario EcosystemPlankton Invertebrates Fish Fish-eating birds0.010.1110100DDT mg/kg, wet weightLeBlanc (1995) ES&T 29:154Evidence for BiomagnificationLeBlanc’s Analysis of Woodwell et al. 1967(Whole Body Residues)Note the “consistent” increase in DDT residues from onetrophic level to the nextWoodwell’s Hypothesis• DDT and PCBs efficiently ingested andabsored in association with food• However, contaminants depurated at a rateslower than the consumption of biomassneeded for energy requirements• Thus, the contaminants are stored in lipophilictissues at much higher concentrations thanoccur in the foodSeminal observations for the hypothesis reported inWoodwell et al. (1967) “DDT residues in an East Coast estuary: Acase of biological concentration of a persistent insecticide.” Science156:821-824.Effect of Trophic Level and Depuration Rate onBiomagnification of a Hypothetical Contaminant0.070.140.290.58-1087.881.137.58.711501.10.361.10.00170.0552.20.723.00.0240.1044.31.44.20.170.2038.72.92.90.580.042--111.001150505010Daily food Intakeas Proportion ofBody WeightTrophicLevelSteady-stateConcentrationfor T1/2 (days) of:ConcentrationFactors for T1/2(days) of:Kelly et al. 2004 ETAC 23:2342BMFmax (biomagnification factors)Note the magnitude differencesbetween the terrestrial organisms ormarine mammals and the aquaticorganismsBirds & MarineMammalsTerrestrialMammalsFishAquaticInvertebrates5LeBlanc (1995) ES&T 29:154BCF X 1000Bioconcentration or Biomagnification?Biomagnification De-Mythified?• LeBlanc (1995) argues that lab experiments show fewsubstances actually biomagnify• Differences in lipophilic contaminant concentrationbetween trophic levels can be explained by lipid contentdifferences from one trophic level to the next• Larger organisms (fish) have slower depuration rates thansmaller organisms (phytoplankton, invertebrates)• The so-called food chain effect has a low probability ofoccurrence relative to passive diffusion from theenvironment– Differences in lipid content and depuration amongorganisms at different trophic levels can account fordifferences in BCF or BAFDDT2,3,7,8-TCDDEndrinPentachlorbenzeneLeptophosTrichlorobenzeneOctachlorodibenzodioxin0.01 0.1 1 10 100 1000 10000