medaka, sex is determined chromosomally. Normal males are XY while
females are XX. Edmunds et al. examined the chromosomal sex
and the morphological/functional sex of individuals at the age of
10 weeks, after injection. They found that at a DDT dose of 227
nanograms per egg (less than one half of the lethal dose, 511 ng/egg)
86% of the genetic males were sex-reversed. Genetic females showed
no effects of treatment. None of the control group were sex reversed.
They also exposed another treatment group to 2 ng/egg of 17ß-estradiol
and found that 1 in 5 genetic males were sex reversed.
et al. also tested whether treated, sex reversed males were
fertile. They paired sex-reversed males with normal males and found
that 50% (3 of 6 pairs) were fertile.
doses needed to induce complete sex reversal (227 ng/egg or 227
ppm) were high relative to concentrations reported for background
field levels. On the other hand, the lethal dose they observed was
substantially higher than that reported for wild lake trout (10
ppm). The reasons for this discrepancy are unknown. They may involve
species differences or differences in the toxicity of the form of
DDT used, or differences in the impact of delivery via microinjection
vs. maternal transfer.