by Louisa Dalton
Ice can be more dangerous than water when it comes to the toxicity
of environmental contaminants. Reactions in ice can result in
more toxic photoproducts.
Chemists at Masaryk University in the Czech Republic compared
the fate of 2-chlorophenol and 4-chlorophenolâ€”widespread
contaminants from the paper and pesticide industriesâ€”when
exposed to ultraviolet light both in ice and in water [Environ.
Sci. Technol., published online April 15, http://dx.doi.org/10.1021/es035076k].
The water reaction proceeded far faster; within 30 minutes, all
chlorophenols (CPs) had converted to dihydroxybenzenes, which
are themselves not stable in sunlight.
In ice, on the other hand, the CPs lasted for up to 10 hours
and the major products were more stable dimers: 5-chlorobiphenyl-2,4'-diol,
for example. In addition, the ice products, after prolonged irradiation,
were more toxic to marine bacteria and rat liver cells than both
the water photoproducts and the parent contaminants.
â€œArctic ecosystems are a sink of anthropogenic
pollutants,â€ says Jana KlÃ¡novÃ¡,
a coauthor and chemist at Masaryk. Pollutants evaporate in warm
climates, travel, and condense at the cold poles, where the photochemistry
can be different and more damaging. The Masaryk group believes
that ice may catalyze unique reactions because of the distribution
and motion of organic pollutants in frozen water. They are now
testing photoproducts of other pollutants in ice: polychlorinated
biphenyls, polycyclic aromatic hydrocarbons, and DDT.