et al. link dioxin exposure of fathers to alterations in
human sex ratio: fewer boys are born to fathers with high dioxin
levels than expected. This is the most recent in a series of papers
showing similar effects by dioxin and dioxin-like compounds, for
example, following dioxin
exposure in Seveso or PCB/dioxin/furan
exposure in Taiwan.
did they do? The city of Ufa sits just west of the Ural
Mountains at the eastern edge of Europe, in the Bashkortostan Republic
of Russia. An agrochemical production plant has operated in Ufa
since the early 1940s. Products manufactured at the plant have included
2,4,5-trichlorophenol (TrCP), hexachlorophene and 2,4,5-trichlorophenoxy
acetic acid (2,4,5-T). Production of the latter ended in 1967.
previous work, Ryan and Schecter (2002)
had demonstrated that a sample of men, women and children associated
with the chemical plant in Ufa carried high levels of dioxin (TCDD)
and another, equally toxic dioxin like compound (PnCDD). Dioxin
toxicity (TEQ) levels in this cohort were more 30 times higher than
in the general population in Bashkortostan.
this paper, Ryan and coworkers combine data from that previous study
with samples from additional chemical factory workers, who were
also found to have high contamination levels. They then examine
birth records for men and women within the sample to calculate the
sex ratio of the exposed sample, and compare that sex ratio to that
of the general population in Ufa and to the Republic of Bashkortostan.
did they find? For the entire cohort of workers, the sex
ratio of offspring was 0.40. This differs significantly from Ufa's
and Bashkortostan's sex ratio (0.512) and from expectations based
on world averages (also 0.512).
additional pattern emerged when they considered the sex ratio of
male vs. female workers. For offspring born to exposed
female workers (but whose father was not a worker), the sex ratio
(0.51) was not different from world averages. But for the
offspring of exposed fathers, the observed sex ratio was significantly
depressed, , to 0.38. And when they examined the a subset
of workers who had produced TrCP, the sex ratio was even lower,
0.23. The median dioxin toxic equivalent value (TEQ) for this subset
of male workers was 715 ppt, compared to the overall median in the
workers of 243.
does it mean?
factors limit Ryan et al.'s ability to link altered sex
ratios specifically to dioxin and dioxin-like compounds.
were undoubtedly exposed to a mixture of chemicals, not dioxin
and dioxin-like compounds alone.
sex ratio and dioxin TEQ levels used in the control group were
from regional averages instead of from a specific sample of people
for whom both parameters were measured.
levels were characterized long after exposures, and to a varying
degree, long after the offspring included in the sex-ratio calculations
were born. Hence the TEQ measurements are at best an estimate
of exposures involved in altering the sex ratio.
when Ryan et al.'s findings are viewed in light of research
with other dioxin-exposed cohorts a clear picture is emerging: High
levels of a father's exposure to dioxin and dioxin-like compounds
is associated with a lower sex ratio, that is, a lower chance
of having a male child.