January 16, 2006

Leukemia risk from chlorination seen mixed

NEW YORK (Reuters Health) - Long-term exposure to the
by-products of chlorination in drinking water appears to raise
the risk of one type of leukemia -- chronic myeloid leukemia
(CML) -- but decrease the risk of chronic lymphoid leukemia
(CLL) and other types, new research shows.

The findings, which appear in the American Journal of
Epidemiology, are based on a population-based study comparing
686 leukemia cases and 3420 similar but unaffected "controls"
for whom water quality information was available for 30 years
or longer. The subjects were Canadian residents between 20 and
74 years of age.

Long-term exposure to the chlorination by-product
triahalomethane at levels greater than 40 micrograms per liter
raised the risk of CML by 72 percent, Dr. Patrick Levallois,
from Institut National de Sante Publique in Sainte-Foy, Canada,
and colleagues note.

By contrast, such long-term exposure cut the risk of CLL by
40 percent, the team found.

Further analysis showed a decreased risk of several
leukemia subtypes as the duration of chlorination by-product
exposure increased, the report indicates.

"Total trihalomethanes and bromodichloromethane may be
particularly important in the etiology of CML, but the possible
protective effect of chlorination disinfection by-products on
CLL remains unclear," the authors conclude. "Random error or
selection bias could explain these results," they say.

SOURCE: American Journal of Epidemiology, January 15, 2006.