Use the following information to answer the question(s) below.
Estrogens found in the environment have raised concerns about effects on reproductive health of
animals. Researchers studied the effects that estrogens in the water have on sexual differentiation
in zebrafish. They exposed embryo-larval (0-21 days post-hatching), juvenile (21-42 days post–
hatching), and adult (over 200 days post-hatching) fish to three concentrations of 17β-estradiol
(5, 25, and 100 nanograms/liter) that are within the range of concentrations found in water
leaving sewage treatment plants in different countries. They then examined the proportion of
males and females when the fish exposed at embryo-larval and juvenile stages reached
adulthood. Embryo-larval stage fish that had been exposed to 100 ng/l 17β-estradiol resulted in
adult populations that had substantially more females than males compared to control groups.
Embryo-larval fish that had been exposed to 5 and 25 ng/l of 17β-estradiol did not show a
statistically significant shift in the proportion of females. (Brion, F., C. R. Tyler, X. Palazzi, B.
Laillet, J. M. Porcher, J. Garric, and P. Flammarion. 2004. Impacts of 17β-estradiol, including
environmentally relevant concentrations, on reproduction after exposure during embryo-larval-,
juvenile-, and adult-life stages in zebrafish (Danio rerio). Aquatic Toxicology 68:193-217.)
58) Refer to the paragraph on the effects of estrogens in the environment. What is the
significance of using the concentrations of 5, 25, and 100 ng/l of 17β-estradiol for the dose in
this experiment?
A) These concentrations are similar to those found in many animals.
B) These concentrations are found in the environment.
C) These concentrations are effective, yet not lethal to the fish.
D) These concentrations are standard in toxicology assays.
59) Refer to the paragraph on the effects of estrogens in the environment. You are assigned to
write the report to the Environmental Protection Agency, which needs to decide what level of
17β-estradiol to permit in sewage output. You do not want to make the level any lower than
necessary, because it requires substantial additional money for the extra treatment of sewage.
Given the data presented above, what level of 17β-estradiol would you suggest is safe to prevent
feminization of fish?
A) 2.5 ng/l
B) 12.5 ng/l
C) 25 ng/l
D) 100 ng/l