Hydrogen sulphide (H2S) is notorious for its odor of rotten eggs. New research indicates that the chemical could have a more insidious side, however. Results of a study published in the July issue of the Journal of Experimental Biology suggest that the gas can inhibit an organism's ability to form memories.

In humans, exposure to high levels of H2S is known to cause headaches, dizziness, lack of coordination and difficulty remembering, among other symptoms. But the effects of low-level concentrations of the pollutant, which is produced by industries such as pulp and paper processing, are less well studied. Ken Lukowiak of the University of Calgary and his colleagues set out to study how H2S affects the learning and memory in a very simple animal, the pond snail Lymnaea stagnalis. The creature is useful for studying neuronal function and how memories form because it learns just one task: when to open its breathing apparatus, the pneumostome. While training the snails to breathe in response to certain stimuli, the researchers exposed them to different concentrations of H2S at various points of the regime and then tested their memories 24 hours later.

The team found that snails exposed to the highest environmental concentrations of H2S were unable to learn or retain memories. Those subjected to lower concentrations could learn, but did poorly compared to control snails that lived in water free of H2S. Indeed, when the authors graded the creatures' abilities, they found that as the concentration of H2S increased, there was an increase in the frequency of snails that received a failing grade. Going forward, the team hopes to be able to show how H2S alters learning and memory ability at the single neuron level. Such research may eventually shed light on anecdotal reports of impaired learning in schoolchildren living downwind of H2S-tainted gas wells.