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WSU ESRP 531 - Fundamentals of Environmental Toxicology

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ES/RP 531 Fundamentals of Environmental Toxicology Fall 2003ESRP531 Lect 21 Biocon.doc Page 1 of 23November 19, 2003Lecture 21 Biotic Phase Transfer (Bioconcentration, Bioaccumulation, Bioavailability)I. Bioconcentration: A term coined sometime in the 1970s to refer to “the amount of achemical residue accumulated by an organism by adsorption, and by absorption via oral orother route of entry, which results in an increased concentration of the pesticide by theorganism or specific tissues” (Kenaga 1973)A. Residues of compounds accumulate on the external surfaces of organisms as well asinternally.1. By the original definition of bioconcentration, the accumulation (or uptake) was viasurface (i.e., organism’s “skin” or integument) and food exposure.2. Although bioconcentration and other terms associated with uptake, i.e.,bioaccumulation and biomagnification, have very negative connotations, allorganisms “naturally” bioconcentrate nutrients and other chemicals (for ex., anysecondary plant metabolites, many of which are biologically active in otherorganisms)B. Today’s usage of bioconcentration refers to non-food routes of uptake of a chemicalinto tissue from soil, water, or air.1. In the 1980’s, the term bioconcentration was distinguished from biomagnification(Ernst 1985), wherea. Bioconcentration was the direct uptake of a substance by an organism fromwater without consideration of the ingestion of contaminated materials.Similarly, for terrestrial organisms, bioconcentration is the direct uptake throughthe “skin”, which is most relevant for invertebrates in soil. However,bioconcentration should also be considered for plants—either through directexposure of leaf surfaces or roots in soil.C. Bioconcentration factor (BCF) is defined as the ratio of the measured residue in anorganism compared to the residue of the pesticide in the ambient air, water, or soilenvironment of an organism.1. The result of such a process (i.e., the uptake of the chemical from an environmentalphase) is reported as the bioconcentration factor, BCF, or the ratio of theconcentration in the organism and the ambient medium.a. BCF = Corg/Cphase ; where phase is generally considered soil or water2. BCF may be expressed on a whole body weight basis (fresh or dry) or on fatcontent basis.3. BCFs are experimentally determined but only valid when measured after the bodyand environmental media burdens of residues have reached a steady state.4. Note that equilibrium will not really be reached because the concentrations in thebody (as well as the environment) are constantly changing, shifting the processaway from true equilibrium.D. Bioaccumulation refers to the uptake of pollutants via food and water1. As for the BCF, a bioaccumulation factor (BAF) can be determined.a. Indeed, the BAF is most appropriate when uptake through the integumentcannot be distinguished from uptake via ingestion of contaminated food.E. Biomagnification1. Bioconcentration/Bioaccumulation and Biomagnification may often be confused.ES/RP 531 Fundamentals of Environmental Toxicology Fall 2003ESRP531 Lect 21 Biocon.doc Page 2 of 232. Biomagnification is considered to result from the direct uptake of a substance byan organism via food and the accumulation of a contaminant at increasingly higherlevels in higher trophic levels, i.e., the so-called food chain effect.Figure 1. Increase in PCB concentrations among successive trophic levels in Great Lakes basin(Safe, S. 1980, in Halogenated Biphenyls, Terphenyls, Naphthalenes, Dibenzodioxinsand Related Products, R. K. Kimbrough, ed., Elsevier, citing the Int’l. JointCommission Report)3. Biomagnification is the result of bioconcentration and bioaccumulation, but it isdistinguishable from these chemodynamic processes.a. Biomagnification is characterized by body burdens of a contaminant in highertrophic level organisms (as indicated by tissue concentration) that are higherthan in lower trophic organisms that the higher trophic levels are consuming.4. Food Chain Effects (biomagnification along trophic levels)a. One of the early issues in ecotoxicology (before the term was coined) waswhether contaminants could be transferred from one trophic level to another,and whether the chemical could accumulate at the highest trophic levels tolethally toxic effects.1. This notion of biomagnification was popularized in Rachel Carson’s SilentSpring.b. One early study involved an examination of the transfer of DDT to robins afterspraying elm trees; some time after the first year’s application in 1950, dyingrobins were observed, especially after rainfall.ES/RP 531 Fundamentals of Environmental Toxicology Fall 2003ESRP531 Lect 21 Biocon.doc Page 3 of 231. Concentrations of DDT in soil after spraying in the top two inches rangedfrom 6 to 18 ppm.2. Concentrations of DDT on leaves ranged from 15 - 263 ppm (includes 1 daybefore the second spray and 1 day after)3. Earthworms contained from 33-164 ppb DDT4. Barker (1958) suggested that earthworms tended to come to the soil surface,especially after heavy rains; the earthworms had concentrated DDT byselective feeding on sprayed leaf mulch (concentrations of DDT were ~25ppb in autumn); robins fed on the earthwormsc. The Barker (1958) study led to the hypothesis that successive predators willinevitably acquire higher residues than their prey contain, but this principle isnot well founded because it ignores1. The variable degree of assimilation; i.e., the amountof pollutant within thepredator decreases as the percentage assimilation decreases.2. Growth dilution; growth of the predator increases both food consumptionand the mass of tissue within which the pollutant is distributed.3. Depuration rate may alter with exposure route4. Different tissues and organs within an organism may have differentconcentration of pollutant, and approach steady states at different rates.5. Pollutant concentration will be higher than in the prey only when the rate offood consumption as a proportion of the predator’s body weight exceeds therate constant for excretion plus metabolism.5. Food Web Concept; organisms do not necessarily feed at one trophic level only;therefore, food source or relationships between prey and predator should beconsidered more of a food web rather than a food chain.a. Furthermore, the type of food eaten will vary by season and year6. The steady-state concentration of a pollutant will vary among trophic


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WSU ESRP 531 - Fundamentals of Environmental Toxicology

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