VPT 421: Veterinary Toxicology (2+0)

EXCRETION OF XENOBIOTICS

• Xenobiotics are excreted via faeces, urine, sweat, breath or milk.
• The rate at which a foreign compound is eliminated from the body will depend upon its chemical or physical form, the route and carrier medium in which it was presented, the simultaneous presence of materials affecting its solubility in the diet, whether or not it has an affinity for a particular tissue or organ and the species, age, general health and the functional capacity of the liver and kidney in the exposed individual.
• The excretion rate may be of primary concern because some toxicants can cause violative residues in food-producing animals.
• When the absorption rate exceeds the excretion rate a foreign compound will accumulate in the body.
• Organochlorine compounds, arsenic trioxide, metallic copper, lead and its salts are poorly absorbed from the gut as they are relatively insoluble. They are consequently excreted in faeces.
• Many compounds are excreted via kidneys.
• Excretion of toxicants in sweat is importance for detecting agents used for doping.
• The lungs excrete some agents like coniine, paraffin and ketone bodies.
• Agents of toxicological importance like aflatoxins are excreted in milk.
• Bioaccumulation is said to occur when an organism absorbs a toxic substance at a rate greater than that at which the substance is excreted.
• As people spend so much time, for so long periods, in toxic environments in work place, even very low levels of toxicants can be lethal over time.
• Naturally produced toxins can also bioaccumulate.
• Bioaccumulation occurs within a trophic level and it is the increase in concentration of a substance in an individual’s tissues due to uptake from food and sediments in an aquatic milleu. Bioaccumulation also takes place in mammals.
• Biomagnification, also known as bioamplification or biological magnification, is the increase in concentration of a substance such as the pesticides that occurs in the food chain.
• Bioconcentration is defined as occurring when uptake from the water is greater than excretion.
• This bioconcentration and bioaccumulation occur within an organism and biomagnification occurs across trophic (food chain) levels.