L5: Bioconcentration, Bioaccumulation, Biomagnification in Food Webs

Question 1

Bioconcentration

Answer 1

net accumulation in organism from water only

Question 2

Bioconcentration factor (BCF)

• definition
• BCF<1 vs >1
• trends (Kow, WS)

Answer 2

ratio of chemical conc in the organism to that in the surrounding water
- Contaminants in organism on lipid weight basis

BCF of 1 or <1 means little/no accumulation from water
BCF>1 means contaminant taken up from water (there is bioconcentration)

BCF higher for higher Kow (lipophilicity) compounds
- Above log 6 tends to decrease b/c molecule becomes too large to cross membrane
BCF lower for higher WS compounds

Question 3

In food, Kow mainly determines bioavailability

Answer 3

Bioavailability from food typically greatest at log Kow of 6

Uptake tends to be lower for larger, higher Kow b/c steric hindrance

Question 4

In soils/sediments, bioavailability generally decreases as:

Answer 4

Carbon content of soils/sediments increases (binds contaminants more tightly)
Log Kow increases above 6, b/c binds to soils/sediments rather than organism

Question 5

Biomagnification

Answer 5

when contaminant biomagnifies, it increases in concentration from 1 trophic level to next

Question 6

Biomagnification factor (BMF)

Answer 6

Divide contaminant conc at trophic level C by next lowest trophic level

For organic compounds that are not metabolized, biomag. predicted by log Kow
o More Cl=more Kow=higher BMF
BMFs typically >1 for log Kow above 4 and below 8

Question 7

Inorganics Biomagnification in Aquatic Ecosystems

Answer 7

Metal/metalloids: rarely biomagnify, except organic forms of mercury and selenium that bind to some aa in proteins

Question 8

Organics Biomagnification in Aquatic Ecosystems

Answer 8

In general, predicted by Kow (if no metabolism)
Log Kow 4-6 strong potential for biomag
Log Kow >7-8 lower assimilation due to larger sizes of molecules, reduced uptake across membranes

Question 9

Bioaccumulation

Answer 9

net accumulation of contaminant, result of uptake from all sources and processes within individual (uptake, storage, biotransformation, elimination)

Question 10

Bioaccumulation factor (BAF)

Answer 10

If BAF>BCF, then important uptake from food

Bioaccumulation tend to be higher for lower log Kow, decrease in those values above log 8

Question 11

Factors influencing Contaminant Bioaccumulation (4)

Answer 11

Temperature: affects physiology, feeding, growth, metabolism, egestion, respiration rates
- Generally, higher temp leads to higher bioaccumulation

Size: larger animals have diff metabolic rates than smaller

Sex: maternal transfer in females (breastmilk, placenta)
Species: lipid contents, lifespan, feeding habits

Question 12

Larger organisms…

Larger, older fish…

Answer 12

slower excretion rates

higher contaminants than smaller, younger fish (lower excretion rates)

Question 13

Using ratios of stable isotopes of N to assign trophic level

Answer 13

15N (heavier) has 1 more neutron than 14N (lighter), same # of protons
Measured in tissues, represents longer-term diet of animal

Animals excrete more 14N, retain more 15N from proteins in diet
Animal tissues have more 15N than diet
Measure δ15N –higher values indicate higher trophic level (Increase up trophic levels)

Question 14

Trophic magnification factor (TMF)

Answer 14

antilog of slope, avg biomagnification per trophic level thru entire food web

Slope represents avg trophic transfer of contaminant thru food web

Question 15

Advantages of TMF over BAF or BMF

Answer 15

Don’t have analytical challenges of measuring contaminants in water (BAF)
TMFs account for ecological complexity in food webs
TMFs measure biomagnification across entire food web, rather than individual species (BMFs)