24 Questions
What is the result of gamma-hexa chlorocyclohexane (γ-HCH) binding to GABA receptors?
Inhibition of GABA-dependent Cl- flux into the neuron
What is a characteristic of organochlorine insecticides that contributes to their persistence in the environment?
High lipid solubility
What is the consequence of slow biotransformation of organochlorine insecticides?
Environmental persistence and accumulation
What is the result of bioaccumulation and biomagnification in food chains?
An increase in the concentration of contaminants in higher trophic levels
Why have organochlorine insecticides been banned in many countries?
Due to their toxicity and environmental persistence
What is a common source of lead poisoning in cattle?
Grazing in contaminated areas
What is the characteristic of organochlorine insecticides that contributes to their ability to accumulate in living tissue?
High lipid solubility
What is the definition of a pesticide?
Any substance or mixture of substances used to prevent, destroy, repel, or mitigate any undesirable plant or animal pest
What is the veterinary importance of pesticides?
To control vector-borne diseases, promote agricultural production, and control domestic pests
What is the fate of most ingested lead?
It is eliminated in the faeces
What is the effect of the complex aromatic ring structure of organochlorine insecticides on their biotransformation?
It slows down their biotransformation
How can individuals be exposed to pesticides?
Occupationally, environmentally, and at their residence
Which enzyme is inhibited by lead?
Haeme synthetase
What is the consequence of the sequestration of organochlorine insecticides in body tissue having a high lipid content?
Accumulation of the insecticides in the body
What is the primary route of elimination for mercury?
Urine
How are pesticides grouped based on their target of action?
Based on their target of action
What is the effect of selenium and vitamin E on mercury toxicity?
They protect against toxicity
What is the mechanism of action of insecticides?
They target the nervous system of insects
What determines the intensity of biological effect of insecticides?
The dosage and duration of exposure
Which form of mercury is highly toxic when inhaled?
Elemental mercury
What is a characteristic of chemical insecticides?
They are non-selective and can affect non-target species
What is the primary organ where mercury is stored?
Liver and kidneys
What is the mode of action of lead toxicity?
Inhibition of haeme synthetase
What is an example of how pesticides can be used to control vector-borne diseases?
By controlling vectors that transmit diseases like malaria and Tryps
Study Notes
Lead Toxicity
- Lead is a ubiquitous environmental contaminant
- Cattle, horses, and dogs are more susceptible to lead toxicity, while chickens, goats, pigs, and cats are more resistant
- Only 1-2% of lead is absorbed from the gastrointestinal tract, and about 98% is eliminated in the feces
- After absorption, lead is carried to erythrocyte membranes and then to the liver, where it is excreted in bile and reabsorbed through the enterohepatic biliary cycle
- Lead toxicity arises from the inhibition of haeme synthetase, a thiol-containing enzyme required for incorporating iron into the haeme molecule
Mercury Toxicity
- Mercury is a liquid at room temperature and exists in various organic and inorganic forms
- Young ruminants are more susceptible to mercury toxicity than horses and pigs
- Elemental mercury is non-toxic orally but highly toxic through inhalation, while inorganic mercury is less toxic and organic mercury is more toxic
- Selenium and vitamin E can protect against mercury toxicity
- Sources of mercury poisoning include organic and inorganic forms, such as fungicides, seed dressing agents, and mercuric salts
Toxico-kinetics of Mercury
- Mercury is distributed throughout the body and stored mainly in the liver and kidneys after absorption
- Mercury is eliminated slowly, primarily in the urine
Pesticides
- Definition: any substance or mixture of substances used to prevent, destroy, repel, or mitigate any undesirable plant or animal pest
- Veterinary importance: control of vector-borne diseases, promotion of agricultural production, and control of domestic pests
- Individuals may be exposed to pesticides through occupational, environmental, or residential means
Classification of Pesticides
- Insecticides: destroy, repel, or prevent harmful insects
- Herbicides: control weeds
- Rodenticides: control rodents
- Fungicides: control fungi
Insecticides
- All chemical insecticides poison the nervous systems of target organisms
- Mechanism of action may be similar in all species, with only the dosage dictating the intensity of biological effect
- Examples: γ-HCH (lindane) and DDT
Kinetics of Organochlorine Insecticides
- Properties: persistence in the environment, accumulation in living tissue, bio-concentration, and bio-magnification in food chains
- Biologically active body burdens at higher levels due to low volatility, chemical stability, high lipid solubility, and slow rates of degradation
- Slow biotransformation due to complex aromatic ring structure and number of chlorine substituents
- Environmental persistence and accumulation lead to sequestration in body tissue with high lipid content
Bioconcentration and Biomagnification
- Bioaccumulation: intake of a long-lasting contaminant exceeds the ability to metabolize or excrete, leading to accumulation within the tissue of the organism
- Biomagnification: concentration of a contaminant is magnified hundreds or thousands of times as it passes up the food chain
This quiz covers the sources of lead toxicity in animals, including vegetation grown in contaminated areas, grazing in contaminated areas, and use of certain drugs. It also discusses the susceptibility of different animal species to lead toxicity.
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