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REM 610 Exercise 6. March 17, 2010. Questions – 24DP. Can 24DP be expected to “bioaccumulate” in the food-chain? YES - There is a general increasing trend in concentrations with increasing trophic level. Does 24DP biomagnify in the food-chain?

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rem 610 exercise 6

REM 610Exercise 6

March 17, 2010

questions 24dp
Questions – 24DP

Can 24DP be expected to “bioaccumulate” in the food-chain?

YES - There is a general increasing trend in concentrations with increasing trophic level.

Does 24DP biomagnify in the food-chain?

NO – The lipid normalized concentration does not show a general increase with increasing trophic level

What is the main reason for differences in concentrations among organisms?

  • An increase in lipid levels in higher trophic species
  • There is also a difference between benthic and pelagic species.
questions 24dp1
Questions – 24DP

In this situation, the concentration in the sediments was higher than in the water (i.e. they were not in equilibrium); thus the benthic species have a high lipid normalized concentration as well because they are assumed to be in equilibrium with the sediments.

What is the main route of 24DP uptake – relative importance of water and food?

  • The main route of uptake is water from the gills
  • With increasing Kow, uptake from food becomes more important
questions 24dp2
Questions – 24DP
  • 24DP + H2O  24DP- + H3O+
  • pKd = 6.8, pH = 6.8
  • Kd = [H3O+]*[24DP-]/[24DP]
  • Kd/[H3O+] = [24DP-]/[24DP]
  • 10-6.8/10-6.8 = [24DP-]/[24DP] = 1/1 ratio
questions 24dp3
Questions – 24DP
  • Therefore, the reaction is in equilibrium at pH 6.8 and 50% of the chemical will be in 24DP form.
  • Chemical dissociates into an ionized form which is not available for uptake
  • Acidification increases the H3O+ concentration and shifts the reaction to the left (i.e. more 24DP will be present) thus, the bioavailability goes up, and the concentrations in organisms go up
questions 24dp4
Questions – 24DP

How is 24DP eliminated by the fish?

  • Through the gills
questions 24dp5
Questions – 24DP

Summarize your findings regarding the potential of 24DP to bioaccumulate in the food-chain

  • 24DP is a chemical that bioconcentrates in organisms with BCFs ranging between 50 and 100.
  • This bioconcentration is mainly due to partitioning of the chemical between the water and the lipids of the biota in the food-chain (for pelagic species) WHICH reflects the chemical’s Kow.
  • Concentrations in the benthic species reflect sediment-biota(lipid) partitioning
  • Differences in lipid content result in differences in the BCF
  • Biomagnification does not take place
part ii pcb
Part II - PCB

Does PCB “bioaccumulate” in the food chain? Is this due to biomagnification or differences in lipid levels of the organisms?

Yes – a combination of both differences in lipid levels and biomagnification

What is the bioavailability of PCB in Lake water? What is the effect of eutrophication?

See next slide

questions pcb
Questions -PCB
  • Bioavailability of PCB = 0.999
    • Still close to 1.0 due to small organic carbon content of water
  • Eutrophication reduces the bioavailability of the chemical (effects uptake from water)
    • 2x OC content in water bioavailability = 0.998
    • 1000x OC content in water bioavailability = 0.475
    • however, concentrations in the organisms remain similar because main route of uptake is dietary
questions tcdf
Questions - TCDF
  • Use bioaccumulation model to investigate the effects of metabolic transformation of TCDF on bioaccumulation in the food chain
  • RESULTS – TCDF does not bioaccumulate because it is metabolized by the organisms (concentrations drop as trophic level increases); the overall rate of elimination increases
part iii wqc
Part III - WQC

Summarize the limitations and merits of WQC = LOAEC x Safety Factor (2-10) Approach to WQC development.

Limitations

  • extrapolating from the lab to the field does not take into account potential biomagnification and different exposure/environmental conditions
  • Assumes equilibrium between the water and the organisms (if using tissue residue guidelines you don’t make that assumption)
  • Related to above pt. – there may be disequilibrium between water and sediments (e.g. sediments at a higher fugacity – resulting in higher f in benthic species and may “drive up” fugacity in the food chain)
  • Safety factors are fairly low considering they are supposed to take into account numerous sources of variability and protect all species and all life stages
  • Also does not take into account the presence of multiple stressors (environmental, biological and chemical) that are present in environment but not in the lab.
slide12
Lab Tox Test

Field

Kow = 1,000,000

Lipid content = 0.05 kg/kg

BCF = 50,000 L/kg

Cwater = 1 pmol/m3

Zwater = 1 pmol/Pa. m3

fwater = 1 Pa

Cfish = 50,000 pmol/m3

Zfish = 50,000 pmol/Pa.m3

ffish = 1 Pa

Kow = 1,000,000

Lipid content = 0.20 kg/kg

BAF = 20,000,000 L/kg

Cwater = 1 pmol/m3

Zwater = 1 pmol/Pa. m3

fwater = 1 Pa

Cfish = 20,000,000 pmol/m3

Zfish = 200,000 pmol/Pa.m3

ffish = 100 Pa

slide13
Lab Tox Test

Field

Kow = 1,000,000

Lipid content = 0.20 kg/kg

BAF = 20,000,000 L/kg

Ctoxic effect = 0.001 mol/m3

Cwater = 0.001/20,000,000 = 0.05 nmol/m3

Kow = 1,000,000

Lipid content = 0.05 kg/kg

BCF = 50,000 L/kg

Ctoxic effect = 0.001 mol/m3

Cwater = 0.001/50,000 = 20 nmol/m3

Safety Factor = 100

WQG = 0.2 nmol/m3

part iii wqc1
Part III - WQC

Merits

  • It is simple to develop guidelines
  • There is a lot of data on LC50s or EC50s etc. – all based on water concentrations so it is fairly universally applied and consistent (though not necessarily the best approach)
  • Others…

Suggest an alternative approach for developing EQC?

  • Use internal concentrations or tissue residue guidelines
  • Others…
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