No. Those "chemtrails" are just water vapor that is in the jet fuel. All (liquid)fuel has some water in it. When you run a car, you will see alittle of this vapor condencing into water droppletts. In jets, when this fuel is burned, the vapor becomes trapped in the thick atmosphere. It then condences into a cloud. No need to be alarmed.
Although it would be possable to put substences into the fuel that could be harmfull, that doesn't mean they will. Just think; Just because you CAN kill a person, doesn't mean you WILL kill someone.