Question

1. Chemicals are more readily absorbed through the skin or GI tract if they are

A. polar compounds

B. ionic compounds

C. lipid soluble

D. non-ionic, neutral compounds

E. both (C) and (D)

2. Which of the following processes or interactions would interfere with the delivery of the ultimate toxicant to its target site (intracellular molecule) where it produces the toxic effect?
A. increased porosity of capillaries

B. reabsorption

C. specialized membrane transporters

D. activation of the toxicant (toxication)

E. excretion

3. Which of the following would enhance the absorption of a toxicant through the various skin layers?
A. hydrophilicity

B. lipophilicity

C. active transport mechanisms

D. hydration of the skin

E. Both (B) and (D)

4. Which of the following are common endpoints:

A. death

B. No Observable Effect Level

C. No Observable Adverse Effect Level

D. Lowest Observable Adverse Effect Level

E. All of the above

5. Lead is known to undergo biomagnification and accumulates in the bones. What do you think is the fate of lead taken up by a whale that has died of natural causes? Assume the whale occupies the highest trophic level of its ecosystem.

A. The lead will be eliminated from the food chain because no species prey upon the whale.

B. The lead will re-enter the food chain via decomposers breaking down the whale's bone tissue.

C. The lead will be broken down to a non-toxic form by decomposers.

D. The lead will re-enter the food chain via evaporation and precipitation.

Answer 1

1. Answer is E (Both C and D)

Chemicals are more readily through the skin or GI tract if they are lipid soluble , non-ionic and neutral compound.

The skin and GI tract id primarily composed of lipophillic cholesterol, cholesterol esters and ceramides. So lipid soluble chemicals make it through the layer and into the circulation faster.The structure of the lipid bilayer allows small, uncharged substances such as oxygen and carbon dioxide, and hydrophobic molecules such as lipids to pass through the cell membrane.

Small uncharged polar molecules, such as H2O also can diffuse through membrane. Charged or ionic molecule are unable to diffuse through a phospholipid bilayer regardless of size. Even H+ ions cannot cross a lipid bilayer by free diffusion.

2. Answer is E -excretion

Mechanism of toxicity:

step 1: Delivery from the site of exposure to the target

step 2: Reaction of the ultimate toxicant with the target molecule

step 3: Cellular dysfunction and resultant toxicities

step 4: repair or Dysrepair

Delivery is the movement of the toxicant from the site of exposure to the site of its action.

Ultimate toxicant is the chemical that reacts with the endogenous target molecule (e.g. receptor, enzymes, DNA, protein, lipid) or critically alters the biological environment, initiating structural or functional alteration that result is toxicity.

Factors which affect the delivery or increase the absorption or transfer of a chemical from the exposure site into the systemic circulation are-

1. Reabsorption,

2. increased porosity of capillaries

3. Specialized membrane transport

4. activation of the toxicant

So the excretion is the process which interfare with the delivery of the ultimate toxicant to its target site where it produces the toxic effect.

3. Answer is E(both B and D)

Toxicant move across the stratum corneum by passive diffusion. There are no active transport mechanism within the epidermis. Polar and nonpolar toxicant diffuse through the stratum corneum by different mechanism:

Polar compounds, which are water soluble, diffuse through the outer surface of the hydrated keratinized layer. so option D is correct (Hydration of the skin)

Nonpolar compounds, which are lipid soluble, dissolve in and diffuse through the lipid material so option B is also correct (lipophilicity).

4. Answer is E (all of the above)

Common endpoints are death, no observable effect level,  No Observable Adverse Effect Level or Lowest Observable Adverse Effect Level