Ecotoxicology Toxicology Uptake and distribution of xenobiotics.

Ecotoxicology

ToxicologyUptake and distribution

of xenobiotics

pH = 6.4[conc. 4]

Ca++

+ + + + + +

- - - - - - - -

pH=7.4[conc. 2]

Functions of the biological membrane

Maintain homeostasisSelective uptake and excretion

Excitability

The biological membrane

The lipophilic route

Phospholipid

Passage of chemicals through the membrane depends on:

SizeFat solubility

Resemblance with endogenous molecules

The passage takes place through:

Passive diffusion through the phospholipidsThrough water and ion channels

Active transport through channelsEndocytosis

Passive diffusion most important toxicologically

The diffusion rate increases with the water-octanol distribution coefficient (Kow)

n-octanol

Water

Kow<1 1 >1 >>1

1:5 1:1 5:1 21:1

][

octanol][

conc

concKow

water

1 10 102

103

104

105

106

107

108

109

Solubility in water (nM)

10

102

103

104

105

106

107

n-octanol:waterDistribution coefficient

2,2',4,4',5,5'-PCB

DDT2,2',4,5,5'-PCB

DDE4,4'-PCB

ParathionNaphtalen

Benzen

Toluen

Chloroform

p-dichlorbenzen

Chlorbenzen

Benzoic acid

KowD

iffu

sio

n r

ate

O and N increase hydrophilic characteristics

Alkyl groups increase lipophilic characteristics

mnemonic rule: compound lipophilic if

4>+ONC

Ionization

AH A- + H+

BOH B+ + OH-

+- +

-

pH dependentWater

+-

+-

+-

+-

+-

+-

+-

The diffusion follows the concentration gradient given by Fick’s law

CAPdtdn

P = Permeability constant (mol/cm2)

A = Area

ΔC = Concentration difference

COO-

NH3+

COO-

NH3+

COOH

NH2

COOH

NH2

+ H+ + H+

H++ + H+

1

1

1

1

100

1000

2512

251

Stomach pH 2

COO-

NH3+

COO-

NH3+

COOH

NH2

COOH

NH2

+ H+ + H+

H++ + H+

1 1

11

100

10

2512

251

Intestine pH 6 Plasma pH 7.4

Plasma pH 7.4

Uptake of Benzoic acid og Aniline

The hydrophilic route

Channel for divalent cation

2+

2+2+

2+

2+2+

2+

Pyrethroides’ effect on excitable membranes

Cadmium passes the Ca++ channel

Cd++ [0,97 Å] Ca++ [0,99 Å]

Endocytosis

H +

H + lysosome

receptor

coated vesikel

iron - transferrin complex

Endocytosis of iron

Uptake, distribution and excretionof xenobiotics

Alimentary canal Respiratory surfaces Skin

Faeces

Bile

Secretory structures

Secretions

Lungs/gills

Alveoli

Air/water

Liver

Blood and

lymph

Kidney

Bladder

Urine

Extra-cellular fluid

Organs

Soft

tissue

Hard

tissue

Fat

Enterohepatic circulation

1 2 3 4 5Day no

2.5

2.0

1.5

1.0

0.5

Pp

m H

g (

Hg

++

)

1 2 3 4 5 6 7 8Day no

90

60

30

Pp

m H

g (

MeH

g)

1 2 3 4 5 6 7 8Day no

120

60

40

Wei

gh

t (m

g)

1 2 3 4 5 6 7 8Day no

120

60

40

Wei

gh

t (m

g)

Mercury uptake in maggots

10 ppm

1.0 ppm

0.1 ppm

Air route

Alimentary channel

Blood / haemolymphe

Bronchioler / T

racheoles

Bronchi / T

rachea

Nose and pharynx

HydrofileLipofile

The skin

Wet skin: Increases penetration by a factor 3Soap and other detergents: Increased penetration of hydrophilic compoundsOrganic solvents: Irreversible degradation of corneum

Xenobiotics are distributed in tissue fluids

Plasma: 4% of body weightExtracell. fluid: 13% -Intracell. fluid: 41% -

Intracellularfluid

Extracellularfluid

Pla

sm

a Lipophilic compoundsHydrophilic compounds

Plasma - protein linkage

K1

K2

The organism’sothercompartments

ondissociati2

1 KK

K

High Kdiss loosely boundLow Kdiss tightly bound

Low affinity and high capacity toxicological most important

DoseBlood sample

Compartment of distribution

(mg/l)ionconcentrat Plasma

(mg)DoseVD

”Apparent compartment of distribution” VD

VD low: high depositing in organs

VD high: low depositing in organs

Depositing to organs

Co

nc

.

Time

1. order

Co

nc

.

Time

0. order

Brodie-Gillette’s box model

Bound

Free

Bound

Free

Bound

Free

Metabolites

Excretion

Absorption

Target site

Depot

Metabolism

Excretory organs

Nephridia in earthworm

Vertebrate kidney

Nephridium of an invertebrate

Excretion

CK

on

c.

Tid

1. order

Co

nc

.

Tid

0. order

Ckdt

dCe

0 10 20 30 40 50

Time (days)

30

50

100

% dioxin remainingIn body

T½ = 30,5 days

eee

t0

k

0,693

k

ln2

k

lnClnCT½