Oestrogens Found in the Environment Have Raised Concerns About Effects

Oestrogens found in the environment have raised concerns about effects on reproductive health of animals. Researchers studied the effects that oestrogens 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-oestradiol (5, 25, and 100 nanograms/litre) 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-oestradiol 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-oestradiol 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-oestradiol, 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.)
-What is the significance of using the concentrations of 5, 25, and 100 ng/l of 17β-oestradiol 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.