Hello Ingrid, The Wiki - in most cases, quotes sources; If you scroll
down to the bottom of that page you'll find them. I won't debate Wiki
reliability since that may be construed as being off-topic.

My post was meant to show both sides of the coin, and get the original
poster to check the Wiki ( in case he hadn't ); After all I did post
specific instances where it was used ( from the Wiki ). My post wasn't
meant to lessen the value of your own personal experience with
Malathion, however the poster must be warned about the risks involved
in handling chemicals.

In this particular case:
1. Enclosed areas with poor ventilation - like a gardening shed.
2. Reaction between Malathion and Chlorine ( tap water is chlorinated
).
3. Impurities that may cause harm.
4. Malathion getting in-to drinking water.