Ecotoxicology Toxicology Uptake and distribution of xenobiotics
Functions of the biological membrane Maintain homeostasis Selective uptake and excretion Excitability Ca ++ ph=7.4 [conc. 2] + + + + + + ph = 6.4 [conc. 4] --------
The biological membrane
The lipophilic route
Phospholipid
Passage of chemicals through the membrane depends on: Size Fat solubility Resemblance with endogenous molecules The passage takes place through: Passive diffusion through the phospholipids Through water and ion channels Active transport through channels Endocytosis Passive diffusion most important toxicologically
The diffusion rate increases with the water-octanol distribution coefficient (Kow) K ow <1 1 >1 >>1 n-octanol Water Kow = [ conc]octanol [ conc] water 1:5 1:1 5:1 21:1
n-octanol:water Distribution coefficient 10 7 2,2',4,4',5,5'-PCB 10 6 10 5 DDT 2,2',4,5,5'-PCB DDE 4,4'-PCB 10 4 10 3 Parathion Naphtalen p-dichlorbenzen Chlorbenzen Toluen 10 2 Benzen Chloroform Benzoic acid 10 1 10 10 2 10 3 10 4 10 5 10 6 10 7 10 8 10 9 Solubility in water (nm)
Diffusion rate Kow O and N increase hydrophilic characteristics Alkyl groups increase lipophilic characteristics mnemonic rule: compound lipophilic if C N +O > 4
Ionization AH A - + H + BOH B + + OH - ph dependent Water - + + - + - + + - + - + - + - - + -
The diffusion follows the concentration gradient given by Fick s law dn dt = P A C P = Permeability constant (mol/cm 2 ) A = Area C = Concentration difference
COO - Uptake of Benzoic acid og Aniline Stomach ph 2 COOH COOH Plasma ph 7.4 COO - + H + 1 100 1 2512 + H + NH 3 + NH 2 NH 2 NH 3 + 1000 H + + 1 251 + H + 1 COO - Intestine ph 6 Plasma ph 7.4 COOH COOH COO - 100 + H + 1 2512 + H + 1 NH 3 + NH 2 NH 2 NH 3 + 1 H + + 10 251 + H + 1
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
Endocytosis of iron iron - transferrin complex receptor coated vesikel H + H + lysosome
Uptake, distribution and excretion of xenobiotics Alimentary canal Respiratory surfaces Skin Liver Bile Blood and lymph Extra-cellular fluid Organs Fat Kidney Lungs/gills Secretory structures Soft Hard Bladder Alveoli tissue tissue Faeces Urine Air/water Secretions
Enterohepatic circulation
Ppm Hg (Hg++) 2.5 2.0 1.5 1.0 0.5 Mercury uptake in maggots 10 ppm 1.0 ppm 0.1 ppm Weight (mg) 120 60 40 1 2 3 4 5 Day no 1 2 3 4 5 6 7 8 Day no 90 120 Ppm Hg (MeHg) 60 Weight (mg) 60 30 40 1 2 3 4 5 6 7 8 Day no 1 2 3 4 5 6 7 8 Day no
Air route Blood / haemolymphe Nose and pharynx Bronchi / Trachea Alimentary channel Bronchioler / Tracheoles
The skin Hydrofile Lipofile Wet skin: Increases penetration by a factor 3 Soap and other detergents: Increased penetration of hydrophilic compounds Organic solvents: Irreversible degradation of corneum
Xenobiotics are distributed in tissue fluids Extracellular fluid Plasma Intracellular fluid Lipophilic compounds Hydrophilic compounds Plasma: 4% of body weight Extracell. fluid: 13% - Intracell. fluid: 41% -
Plasma - protein linkage K 1 K 2 The organism s other compartments K = K 1 K dissociation 2 High K diss Low K diss loosely bound tightly bound Low affinity and high capacity toxicological most important
Compartment of distribution Dose Blood sample Apparent compartment of distribution V D V D = Dose(mg) Plasma concentration (mg/l) V D low: high depositing in organs V D high: low depositing in organs
Depositing to organs Conc. 1. order Time 0. order Conc. Time
Brodie-Gillette s box model Target site Bound Absorption Free Bound Free Bound Free Metabolites Metabolism Depot Excretion
Excretory organs Vertebrate kidney Nephridia in earthworm
Nephridium of an invertebrate
Excretion CKonc. 1. order Tid 0. order Conc. Tid
% dioxin remaining In body 100 dc dt = k e C 50 T ½ = 30,5 days 30 0 10 20 30 40 50 Time (days) lnc0 lnct ln2 T½ = = = ke ke 0,693 ke